CHEMICAL MANIPULATION, 
 
 INSTRUCTIONS 
 
 STUDENTS IN CHEMISTRY, 
 
 METHODS OF PERFORMING 
 
 EXPERIMENTS OF DEMONSTRATION OR OF RESEARCH, 
 WITH ACCURACY AND SUCCESS. 
 
 BY 
 
 MICHAEL FARADAY, 
 
 F.R.S., M.R.I. 
 
 #c. fyc. <?. 
 
 NEW EDITION. 
 
 LONDON: 
 JOHN MURRAY, ALBEMARLE-STREET. 
 
 MDCCCXXX. 
 

 LONDON : 
 
 Printed by WILLIAM CLOWES, 
 Stamford-street. 
 
HIS GRACE THE DUKE OF SOMERSET, 
 
 PRESIDENT, 
 
 THE VICE-PRESIDENTS, 
 
 MANAGERS, 
 VISITORS, AND MEMBERS 
 
 OF THE 
 
 3t\ogal Sfngtitution of (great asrttaut, 
 
 THIS CONTRIBUTION TO THE SCIENCE, 
 
 WHICH HAS BEEN SO EMINENTLY PURSUED IN THEIR LABORATORY 
 AND THEATRE, 
 
 IS RESPECTFULLY INSCRIBED, 
 
 BY THEIR FAITHFUL SERVANT, 
 
 THE AUTHOR. 
 
PREFACE TO THE SECOND EDITION. 
 
 MY reason for venturing to add a new work on 
 Chemistry to the many excellent productions which 
 previously existed, was because there seemed to be a 
 deficiency in the particular kind of instruction which 
 it was my intention to convey. In the execution of 
 my task I endeavoured to make every other point sub- 
 ordinate to the one of embodying a mass of useful in- 
 formation on the practice of Experimental Chemistry. 
 Being intended especially as a book of instruction, 
 no attempts were made to render it pleasing, other- 
 wise than by rendering it effectual ; for I concluded 
 that, if the work taught clearly what it was intended 
 to inculcate, the high interest always belonging to a 
 well made or successful experiment would be abun- 
 dantly sufficient to give it all the requisite charms, 
 and more than enough to make it valuable in the 
 eyes of those for whom it was designed. 
 
 It may well be supposed that the confirmation of 
 my opinion by the necessity of a second Edition of 
 the work affords me no slight pleasure, and I feel, 
 even more than I did at first, the propriety of the 
 view which I had taken of the character of the in- 
 struction required. 
 
 In the present edition I have made many correc- 
 
 b 2 
 
Vlll PREFACE TO THE SECOND EDITION. 
 
 tions and alterations, without enlarging the book ; 
 for although I have always felt that much valuable 
 instruction in Manipulation had been omitted, yet 
 deeming the utility of the work to depend greatly 
 on its limitation to a moderate size, I found it im- 
 possible to introduce any additional matter without 
 displacing that which was more important ; nor do I 
 anticipate that I shall incur blame by withholding that 
 which has not been tried, and, in my own judgment, 
 is of less moment than that which experience has 
 proved to be useful and desirable. 
 
 M. FARADAY. 
 
TABLE OF CONTENTS. 
 
 Page 
 
 INTRODUCTION ..... 1 
 
 SECT. I. The Laboratory . f . . . 1 1 
 
 II. Balance; weighing . . . .24 
 
 III. Measures; measuring .... 66 
 
 IV. Sources and management of heat . . .83 
 
 1. Furnaces .... 83 
 
 2. Lamps . . . . .101 
 
 3. Blow-pipes . . . . 107 
 
 4. Thermometers . . . .132 
 
 V. Comminution: Trituration, Mortars, Granulation 144 
 
 VI. Solution, Infusion, Digestion . . .163 
 
 VII. Distillation; sublimation . . . 191 
 
 VIII. Precipitation . . . . .223 
 
 IX. Filtration, Decantation, Washing . . 230 
 
 X. Crystallization . . . . .246 
 
 XI. Evaporation; Desiccation . . . 255 
 
 XII. Coloured tests; Neutralization . . .260 
 
 XIII. Crucible operations ; Fusion; Reduction . 277 
 
 XIV. Furnace tube operations . . . .296 
 
CHEMICAL MANIPULATION, 
 
 INTRODUCTION. 
 
 CHEMISTRY is necessarily an experimental science; its conclu- 
 sions are drawn from data, and its principles supported by 
 evidence derived from facts. A constant appeal to facts, there- 
 fore, is necessary ; and yet so small, comparatively, is the num- 
 ber of these presented to us spontaneously by Nature, that were 
 we to bound our knowledge by them, it would extend but to 
 a very small distance, and in that limited state be exceed- 
 ingly uncertain in its nature. To supply the deficiency, new- 
 facts have been created by experiment, the contrivance and 
 hand of the philosopher having been employed in their produc- 
 tion and variation. In reference to the varieties of inert 
 matter, their possible forms, states, and properties, and the 
 powers which influence them. Chemistry, if occupied only in 
 the observation of such phenomena as are presented by Nature, 
 would do little more than record the quiescent state of things, 
 which has followed the active exertion of the inherent powers 
 of matter ; and the chemist would have but little opportunity 
 of observing substances in their energetic state, or of witnessing 
 the exertion of the powers inherent in them. Even when such 
 appearances might naturally be presented, either their vast- 
 ness, their complication, or their rarity, would in many cases 
 prevent the deduction of correct conclusions. 
 
 If it were our object to learn as much as possible of the 
 nature of a substance taken at random from the surface of the 
 earth, how slight would be the amount of information derived 
 from a consideration of it in its natural state ; we should be 
 
 B 
 
2 INTRODUCTION. 
 
 able to decide, perhaps, that the air did not affect it ; that light 
 did not sensibly injure it ; that the rain or dews did not dis- 
 solve it ; that the difference between summer and winter did 
 not apparently alter it ; that the ground beneath was not 
 affected by it ; and perhaps some other points respecting its 
 nature might be ascertained : but what are these compared to 
 the knowledge gained by submitting it to a high temperature, 
 either alone or in contact with different substances ; by sub- 
 jecting it to the action of other bodies as solvents under pecu- 
 liar circumstances, and operating upon it in the numberless 
 ways which art and experience may dictate to us ? Unaltered 
 as it appeared before, it may now change its form, yield new 
 substances and enter into new combinations, and, instead of 
 being an inert lump, may prove an active and powerful agent 
 in many of the purposes of civilized life. Hence the im- 
 portance of multiplying facts by every possible means, whilst 
 engaged in these pursuits ; and hence Chemistry is necessarily 
 an experimental science. 
 
 Great, therefore, are the advantages which result from ex- 
 periment ; nor is the case at all exaggerated, for in Chemistry it 
 may safely be stated that more than nine-tenths of the facts 
 upon which the science is founded are evolved by artificial 
 means. Without, indeed, the great body of truth thus fur- 
 nished, the science could not have existed : for though not 
 exclusively, it is pre-eminently experimental; being in this 
 respect strikingly distinguished from Astronomy, Botany, 
 Zoology, and other sciences, which have regard to appear- 
 ances and phenomena presented by Nature. From this cir- 
 cumstance it derives many of its peculiar charms. 
 
 These considerations are abundantly sufficient to show the 
 intrinsic importance of experiments; and when to .them are 
 added those which arise from the great extent and dominion of 
 the science itself over the powers and properties of all matter, 
 and its influence in administering to the wants, comforts, and 
 pleasures of life, little need be urged in extenuation of an 
 attempt to facilitate, to students in Chemistry, the acquirement 
 of the art of making experiments. 
 
 Experiment has two principal objects the proof or demon- 
 stration, and the extension of our present knowledge ; in both 
 
INTRODUCTION. 3 
 
 of which it is essentially necessary to the progress of chemical 
 discovery. When an experiment has been devised, its general 
 nature and principles arranged in the mind, and the causes to 
 be brought into action, with the effect to be expected, properly 
 considered, then it has to be performed. The ultimate objects 
 of an experiment, and also the particular contrivance or mode 
 by which the results are to be produced, being mental, there 
 remains the mere performance of it, which may properly 
 enough be expressed by the term manipulation. 
 
 Notwithstanding this subordinate character of manipulation, 
 it is yet of high importance in an experimental science, and 
 particularly in Chemistry. The person who could devise 
 only, without knowing how to perform, would not be able to 
 extend his knowledge far, or make it useful ; and where every 
 doubt or question that arises in the mind is best answered by 
 the result of an experiment, whatever enables the philosopher 
 to perform the experiment in the simplest, quickest, and most 
 correct manner, cannot but be esteemed by him as of the 
 utmost value. It is, indeed, to him like the external senses to 
 the mind a channel of information by which things before 
 unperceived are made known, and like them it has its con- 
 tinual use. 
 
 There are many experiments, and even whole trains of 
 research, which are essentially dependent for success on mere 
 manipulation; such, for instance, are various analytical pro- 
 cesses, in which the principles of the process and the modes 
 of detecting and separating the substances being well known, 
 the accuracy with which they are successively separated, and 
 their quantities correctly ascertained, depends entirely upon 
 manipulation. Such is the case in most of the analyses of 
 ordinary siliceous, calcareous, or aluminous stones: such is 
 also the case in the analysis of organic substances by any of 
 the processes recommended in chemical works: it is the 
 same with the manufacture of many chemical preparations; 
 and the separation of four or five gases, a problem of frequent 
 occurrence, is to the chemist who has made but moderate 
 progress even in his studies, a matter entirely of manipulation. 
 
 By accurate and ready manipulation, therefore, an advan- 
 tage is gained independent of that belonging to the knowledge 
 
 B 2 
 
4 INTRODUCTION. 
 
 of the principles of the science ; and this is so considerable, 
 that of two persons having otherwise equal talents and infor- 
 mation, the one who manipulates best will very soon be in 
 advance of the other ; for the one may obtain satisfactory con- 
 clusions from his experimental inquiries, while the other is left 
 in doubt or led astray by his imperfect and incorrect results. 
 This advantage may be illustrated by the use of the tinder 
 syringe, a small instrument consisting of a cylinder about half 
 an inch in diameter, and three or four inches in length, closed 
 at one end and fitted with a piston, to the extremity of which 
 a piece of amadou is fastened : by forcing the piston down 
 and compressing the air suddenly, so much heat is evolved 
 as to fire the tinder. Some persons cannot perform this 
 simple experiment, whatever may be the strength or alert- 
 ness which they endeavour to bring into action ; whilst others, 
 with a very slight force and the mere approach of their hands 
 towards each other in the air, will in every instance obtain 
 the effect desired, and produce the required ignition. Were 
 this a new experiment to the persons making it, the object 
 being to prove whether air when highly compressed gives out 
 much heat or not, the first person would either come to a 
 wrong conclusion, or, if he doubted the success of his experi- 
 ment, would arrive at none at all, whilst the second would be 
 enabled to form a correct and affirmative decision, and thus 
 would have added an important fact to his previous knowledge. 
 In other cases where the appearances may be such that we 
 have no method of anticipating, or, when produced, of cor- 
 recting them, as in the habitudes of an unknown substance 
 or its action upon other bodies, then careful manipulation is 
 of the utmost importance : without it the appearances pro- 
 duced may arise or be modified by extraneous substances 
 present, or by other causes overlooked; and the conclusions 
 may be erroneous at the time when it is most important they 
 should be correct, because the subject is new, and because 
 from its novelty but a small proportion of previous knowledge 
 will bear upon the point and help to correct the error. Nor 
 is the tyro alone thus liable to be misguided ; for it would not 
 be difficult to point out instances where the most acute minds 
 have in this way been led to false conclusions. 
 
INTRODUCTION. O 
 
 Another consequence of skilful manipulation is, that by its 
 means a train of research may frequently be carried much 
 farther than its original object; and that in two ways. In 
 the first place, the occurrence of clear and distinct phenomena, 
 besides proving satisfactorily the direct object of inquiry, fre- 
 quently suggests to the mind collateral views which, pursued 
 and extended, terminate in additional chains of information 
 and discovery ; whereas, if the experiments be less clear, though 
 sufficient may be distinguished to satisfy the mind on the sub- 
 ject in question, nothing more is done, and no new object or 
 view arises. In the second place the operations may be per- 
 formed on comparatively very minute quantities ; and that 
 which in the hands of one person had hardly sufficed to supply 
 very general information of its nature, may in those of another 
 be made to yield matter for a full and minute investigation, 
 terminating in the development of its nature and habits, with 
 a perfection equal to that obtained with the largest masses. 
 Frequent illustrations of the importance of manipulation in 
 thus effecting all that can be desired with small quantities, is 
 afforded in the occasions that arise juridically in testing for 
 arsenic ; for the fractions of a single grain will in the hands 
 of some persons afford the most striking and convincing proofs, 
 whilst many grains will with others present no satisfactory 
 conclusion. 
 
 When the substance under examination is rare (and that is 
 frequently the case both in natural and artificial productions), 
 the facility of working with small quantities is of the highest 
 importance, as otherwise the opportunity of gaining informa- 
 tion may be entirely lost, or if preserved is retained only at a 
 great expense. There existed in the British Museum a small 
 fragment of a black stone, the source and history of which 
 were unknown ; it was unique, no other specimen being in the 
 Museum or known to be in existence; yet as it presented 
 some peculiar characters, Mr. Hatchett was induced to examine 
 it, and, working with a portion of the stone weighing not 
 more than 200 grains, he was enabled to discover in it a new 
 metal, which he distinguished by its various characters from 
 all those previously known, and which he named Columbium. 
 
6 
 
 INTRODUCTION. 
 
 Ekeberg afterwards discovered a metal which he named Tan- 
 talium, conceiving it to have been observed and distinguished 
 for the first time by himself; but Dr. Wollaston, who examined 
 it and compared it with Columbium, was able to identify it 
 with that metal, although he had not more than five grains of 
 the stone from the British Museum upon which to make his 
 experiments. 
 
 Finally, habits of correct and delicate manipulation very 
 much facilitate experimental inquiries at all times. It is not 
 in difficult researches only that it is desirable, but even in such 
 common operations as testing for lime, or iron, or sulphuric 
 acid, its advantages become manifest; for either time is 
 shortened, or the apparatus considered as necessary is dimi- 
 nished, or effectual substitution is made for those that may be 
 wanting ; and thus the experiment becomes easy, where other- 
 wise it would be considered impossible. Besides facilitating 
 such inquiries, it also diminishes the expense both in materials 
 and apparatus, and it produces beneficial habits in the mind 
 by exercising it both in invention and perception, even in this 
 subordinate part of its operations. " Nothing," as Dr. John- 
 son observes, " is to be considered as a trifle by which the 
 mind is inured to caution, foresight, and circumspection. The 
 same skill, and often the same degree of skill, is exerted in 
 great and little things." 
 
 The importance of instruction in manipulation has long 
 been felt by the author during his experience in the Royal 
 Institution of Great Britain ; and the deficiency in the means 
 of teaching it induced him to think he might perform an 
 acceptable service by putting together such information on 
 the subject as there was reason to suppose would be generally 
 useful to the student. No book contains those minute direc- 
 tions which are necessary in the present extensively cultivated 
 state of the science ; nor can verbal instruction teach that per- 
 fection of manipulation which is only to be gained by constant 
 operation. But there is so much that can be taught, so much 
 that can be suggested by such instruction, that it seems extra- 
 ordinary not one of the many treatises upon Chemistry has 
 been aevoted to this subject, especially when it is considered 
 
J INTRODUCTION, 7 
 
 that, of the great numbers who now desire, or are assumed, to 
 have some knowledge of Chemistry, very few have access to 
 competent practical sources. 
 
 Such are the considerations which have given rise to the 
 present work, and under their influence it has been composed. 
 The object of the volume is to facilitate to the young chemist 
 the acquirement of manipulation, and, by consequence, his 
 progress in the science itself. It does not attempt to inculcate 
 the principles of the science, but the practice ; neither does it 
 claim to teach a habit of reasoning, but has solely in view the 
 art of experimenting ; and though sometimes it may be neces- 
 sary to speak of the properties of bodies, or to draw conclusions, 
 it will always be done in subordination to the main object. 
 The volume, indeed, is not intended to supply the place, or 
 imitate in its nature any one of the numerous and useful works 
 on Chemistry now extant, but to be rather an accompaniment 
 to all of them, supplying that portion of knowledge which, 
 however essential to the pupil, was not of a nature to consort 
 with their more scientific contents. 
 
 In the pursuit of this object it is intended to describe 
 
 The conveniences and requisites of a Laboratory. 
 
 General Chemical Apparatus and its uses. 
 
 The methods of performing Chemical Operations. 
 
 The facilities acquired by Practice ; and 
 
 The causes which make Experiments fail or succeed. 
 
 Although a laboratory will be described in a complete state, 
 well appointed, and with all the conveniences that tne author 
 is acquainted with, yet it is intended that the directions shall 
 be such as to enable the experimenter to perform the opera- 
 tions, when desirable, with the smallest numoer of requisites; 
 for though many may wish to be made acquainted with all 
 that is useful, yet to a much larger number of persons a know- 
 ledge of the few essentials is of the greatest consequence. To 
 omit the description of a complete laboratory, in a work devoted 
 to chemical experiment, would of course be improper ; but it 
 would certainly be a much greater error to omit showing, 
 
8 INTRODUCTION. 
 
 as far as the author's knowledge will serve him, how many 
 things may be dispensed with in cases of necessity, and how 
 few are the absolute requisites for the greater number of opera- 
 tions. The general principles upon which apparatus is formed 
 will be inculcated, for the purpose of leading the student to 
 the ready substitution of one thing for another, and to that 
 contrivance by which the wants of the operator may be ob- 
 viated ; and therefore small, temporary, and generally useful 
 apparatus will be pointed out as often as possible. 
 
 It is not intended to describe processes particularly, such as 
 the preparation of each of the acids, or of the alkalies, or of 
 other important substances ; or such as are numerous in the 
 chemical arts, though reference to them will probably be 
 frequent. The work is intended principally to assist in ob- 
 taining a knowledge of the chemistry of research, and not the 
 chemistry of the arts, or rather, not of the ultimate and refined 
 processes of chemical preparations ; otherwise than as, the 
 principles being the same, the instruction which is advan- 
 tageous in the one case will be useful in the other. The book 
 is principally for beginners; but this will not induce the author 
 to reject as improper any information he may have to give 
 relative to the facilities of making experiments, though they 
 may relate to the production of refined and abstruse results. 
 Lastly, it may be remarked, that it is intended for a country 
 where most of the requisites are supplied in trade. 
 
 Professedly disclaiming a scientific character, the arrange- 
 ment of the volume is one of mere convenience, but it has not 
 been adopted without considerable thought. As the work was 
 not intended to teach the principles of Chemistry, but to be 
 a useful laboratory companion, that arrangement was consi- 
 dered as best, which, though not scientific, seems most con- 
 venient for including the different parts of manipulation, 
 without any great violence to the relation of the whole subject. 
 It has therefore been divided into sections, or principal divi- 
 sions : but the professed object of each has not always been 
 strictly adhered to, since it has often been found convenient and 
 useful to include information on other points, which nevertheless 
 have always some degree of connexion with the subject under 
 consideration. Those who may read the work for instruction 
 
INTRODUCTION. 
 
 will probably not find many difficulties in the arrangement, 
 particularly as they will be aided by a copious index. 
 
 Such are the objects of the present book, and the means by 
 which their attainment has been attempted. That it is faulty, 
 the author has no doubt; indeed, he is thoroughly convinced 
 it cannot be otherwise. It contains little more than a selection 
 from the experimental practices and methods of one person ; 
 and though in the more ordinary operations of Chemistry the 
 author's may resemble those of most other chemists, and there- 
 fore be well adapted for general adoption, yet in those peculiar 
 facilities that others may by practice have attained, it must 
 necessarily be imperfect. Acquisitions of this kind made by 
 any chemist must be in relation to his particular trains of 
 research ; and as there are but few who possess the power of 
 ranging through the whole of this extensive science, it cannot 
 be expected that many should have perfect knowledge of 
 the facilities belonging to all departments of experimental 
 Chemistry. The author has been anxious that omissions of 
 importance should be as few as possible. 
 
 Finally, he has to observe, with reference to the pupil's 
 expectations in consulting this book, that even supposing it 
 were perfect, it could only point out the methods for him to 
 practise ; and therefore, though aided by the principles of the 
 science detailed in other works, and the experimental directions 
 in the present volume, he must still perfect his knowledge by 
 study and the labours of his own hands. 
 

 
 
SECTION I. 
 THE LABORATORY. 
 
 1. As the Laboratory is a spot where every chemist will pass 
 a great portion of his time, it is natural that its arrangement 
 and furniture should at first claim much of his attention ; for, 
 being the place peculiarly fitted up for the performance of 
 chemical experiments, fitness for that purpose must have ma- 
 terial influence over the facilities required for those practical 
 exercises, which by their results are so important in the for- 
 mation and correction of his opinions. 
 
 It is, however, very curious, and at the same time instructive, 
 to remark the different views taken by chemists as to the 
 essentials and requisites of a laboratory. Some will not think 
 it approaches to perfection unless it consists of a large room on 
 the ground floor, well stocked with tables, cupboards, furnaces, 
 and various other et caeteras ; and having in connexion with it 
 a second room, dry, comfortable, and fit for the reception of 
 the balance, air-pump, and similar apparatus; and a third 
 apartment, which however may be a kitchen or even a cellar, 
 intended to contain moveable furnaces, bricks, tiles, sand, and 
 the numerous rough materials which are now and then re- 
 quired: whilst others will be satisfied with a small cupboard, 
 and think that sufficient to contain all that is required for their 
 operations. Much of this variety of opinion depends upon 
 the difference in the pursuits of the persons. He who studies 
 chemistry by microscopical experiments, testing the qualities 
 rather than ascertaining the quantities of matter, may find a 
 cupboard abundantly sufficient for his operations, or may even 
 pack all his requisites on a tray; whilst the person who is 
 engaged in metallurgical processes, in extensive experiments 
 on gaseous matter, or in the applications of chemistry to the 
 arts, will find a laboratory essential to his progress. Part of 
 the difference in opinion is founded, however, on mere matter 
 
12 THE LABORATORY ITS SITUATION SIZE. [Sect. I. 
 
 of taste and inclination ; and those who love the science, and are 
 in circumstances to pursue it liberally, will probably never 
 think a damp kitchen or a small attic sufficient for their purpose. 
 It was in a spirit of this kind that the late Dr. Marcet, when 
 he purchased a house on the banks of the lake of Geneva, 
 which unfortunately he did not live long to occupy, appropri- 
 ated one of the best rooms in it to the purposes of a laboratory, 
 not knowing, as he himself said, why he should not do what 
 he could to make that a pleasant place where he found so much 
 pleasure. 
 
 2. When the laboratory is attached to a public institution, 
 where it is devoted to the progress and teaching of the science, 
 and where it is intended to facilitate the researches of two or 
 three persons at the same time, it must necessarily be of large 
 size, possessing the accompaniments of an apparatus and a 
 store-room, and all the facilities which have been found useful 
 in variety of research, and in extensive operations. 
 
 3. Hence it may be observed, that in various circumstances, 
 the place may be either large, of a moderate size, or small, and 
 yet not in the first case exceed, or in the last fall short of what 
 is required. In a volume like the present it will be proper 
 that a good and convenient laboratory should be described, 
 with all its requisites and accompaniments, the whole being 
 adapted according to the convenience of the person who may 
 for the first time be forming his chemical establishment. 
 
 4. If equally convenient, it is generally better that the room 
 to be converted into or built for a laboratory should be on 
 the ground or basement floor, as water is then easily laid on, 
 the foul water from the sink can be readily conveyed away, 
 and coal, carboys, and other dusty and heavy articles more 
 conveniently carried into it. The size, as has been before 
 intimated, may vary very much ; but a room of from 20 to 24 
 feet by 16 or 18 feet, will well answer the purpose. Where, 
 however, it is otherwise unimportant, the size of a laboratory 
 intended to be actively used should be as large as possible, 
 otherwise, when chemical apparatus accumulates, and several 
 sets of experiments are in progress at once, it may be found 
 that confusion and error arise solely from the want of room. 
 
 5. If the place is to be built for the purpose, then no diffi- 
 
Sect. I.] 
 
 THE LABORATORY FLUES. 13 
 
 culty will arise in the construction and arrangement of the 
 flues and lights; which, though of great importance, cannot 
 usually be introduced or altered easily in a room already 
 finished. Where the opportunity occurs, the place should be 
 furnished with several flues, and an advantage is gained if their 
 terminations in the room are separated a little distance from 
 each other. Sometimes it is easy to spread these over one side 
 or wall of the room, the stack in which they unite being carried 
 up immediately in their neighbourhood. One flue is essentially 
 necessary for the draught of that furnace which will be lighted 
 daily for ordinary operations, and the ventilation and warming 
 of the place. Another is in many cases essentially requisite 
 for the construction of a wind furnace ; another or two are 
 desirable to serve as vents for the conveyance of fumes, or 
 occasionally to be connected with moveable furnaces. The 
 lower extremity of each is generally best terminated by a stone 
 in the wall having a round aperture : when out of use, this is to 
 be closed by a stopper ; when in service, the stopper is to be 
 withdrawn, and the flue continued by a piece of funnel-pipe 
 fitted loosely into the hole ; the pipe being continued to the 
 furnace in operation, or otherwise terminated, according to the 
 use to which the flue is to be put. All of them should have 
 dampers, that perfect government of the draught may be 
 obtained. If but one flue can be had, it must be turned to 
 account in the best way possible, either by making it divide 
 and terminate below in two or three places, using brickwork 
 or funnel-pipe for this purpose, as may be convenient ; or by 
 supplying the place of furnaces and apparatus requiring flues, 
 by such substitutes as will allow of their being dispensed with, 
 in the manner hereafter to be described. When necessary, a 
 brick flue may be altogether omitted, and its place supplied 
 by funnel-pipe, but this arrangement is almost always uncom- 
 fortable and inconvenient. 
 
 6. It is generally a matter of indifference, or at least of taste, 
 whether a laboratory have skylights or windows, but it is 
 always an advantage to have it well lighted. Skylights throw 
 the light very agreeably over sand-baths and furnaces, and 
 are exceedingly convenient in crucible operations, in conse- 
 quence of the manner in. which the light falls into the vessels. 
 
14 THE LABORATORY WINDOWS ^VENTILATION. [Sect. I. 
 
 One side-light should, however, in all cases be provided, for the 
 purpose of observing most advantageously the action of re- 
 agents. Where, upon the addition of test solutions, only faint 
 opalescence or colour is produced, considerable management 
 is at times required for its observation in the most advantageous 
 way ; and in these cases, and generally indeed in testing, a side 
 or window- light is by far the best. There is another point 
 relative to the admission of light to a laboratory, which in the 
 present state of chemical science is worthy of consideration. 
 The solar rays have been found highly influential in causing 
 chemical change : they effect combinations and decompositions 
 in a manner unattainable by any other agent, and are now 
 frequently resorted to, not merely in the preparation of pecu- 
 liar substances, as chloro-carbonic acid, chloride of carbon, &c., 
 but also in the processes of analysis, where chlorine is an agent 
 used, and likewise in new experimental researches. It would 
 be well, therefore, in the construction of a laboratory, to pro- 
 vide, if possible, for the direct admission of solar light ; and 
 this is the more desirable, inasmuch as, were it always attainable, 
 chemists would more frequently try the chemical powers of 
 this peculiar agent, at present but little known, and would 
 probably add rapidly to the comparatively small stock of know- 
 ledge we possess concerning it. 
 
 7. The mode of lighting a laboratory is to a considerable 
 extent connected with its ventilation, and the necessity of 
 rapidly changing the air of the place, when required, should 
 be kept in view ; for though much may be effected by means 
 of hoods and flues, yet it is impossible at all times to prevent 
 the contamination of the atmosphere by the general diffusion 
 of deleterious vapours or gases through it to such an extent as 
 to render an immediate change of the whole very necessary. 
 
 8. There are several large articles of great utility in a labo- 
 ratory, which may be almost considered as fixtures, and which 
 require consideration in the first place, on account of the com- 
 parative permanency of their arrangement. Of this kind are 
 the general furnace, the tables, the sink, the cupboard, the 
 shelves, &c. The first of these, or a general working furnace, 
 is in my opinion very important, from the extreme facility 
 which, when conveniently constructed or arranged, it gives to 
 
Sect. I.] THE LABORATORY WORKING FURNACE. 15 
 
 every ordinary operation. Its use is partly domestic, partly 
 chemical ; for it has to warm and air the place, occasionally to 
 heat water, as well as to supply the means of raising a crucible 
 to ignition, or of affording a high temperature to flasks through 
 the agency of a sand-bath. These objects are best obtained 
 by those furnaces which are built with a table top (169). The 
 fire-place itself is constructed of brickwork with iron front and 
 fittings, and the flue, being conveyed horizontally for three or 
 four feet, is afterwards carried off to and connected with the 
 main flue existing in the wall. The fire-place and horizontal 
 flue are covered with a large plate of cast-iron, of from two to 
 three feet in width ; this is formed in the middle, over the 
 heated part, into sand-baths, a round moveable one over the 
 fire itself, and a long fixed one over the flue. The sand- 
 baths supply every gradation of heat, from dull redness if 
 required down to a temperature of 100 or lower ; whilst on 
 each side of them exists a level surface, which answers every 
 purpose of an ordinary table, and supplies extraordinary faci- 
 lities to experiments going on in the sand-bath or furnace. 
 Nor are these advantages gained by any serious sacrifice of 
 heating power in the furnace itself, for it is easy so to construct 
 it as to make its ordinary combustion not more rapid than 
 that of a common fire, and yet by closing the fire-door and 
 opening the ash-pit to obtain a heat that will readily melt 
 gold, silver, or cast iron. 
 
 9. A furnace like this is best placed in the middle or towards 
 one end of the laboratory, independent of the wall, for then it 
 most effectually warms the air of the place, and there is work- 
 ing room all round it ; the flue may either descend and be 
 carried off for a short distance under ground, or it may be 
 connected by funnel-pipe with the upright chimney (5). But 
 if more convenient, either as occupying less of the room of a 
 small laboratory or for other reasons, it may be placed with 
 advantage against one side ; and where the laboratory is made 
 out of a room previously built, the best situation is generally 
 against the fire-place, and the flue of the furnace is then easily 
 connected with the chimney previously existing. 
 
 10. When a furnace of this kind stands against the wall, it 
 is frequently advantageous to construct a wooden hood over 
 
16 THE LABORATORY FILTERING STANDS. [Sect. I. 
 
 the sand-bath, to receive and conduct away the fumes evolved 
 during the digestions and solutions made upon it. An exten- 
 sive hood, however, requires a separate flue, or it will injure 
 the draught of the fire ; and if the furnace be in the middle of 
 the laboratory, a fixed hood of any kind interferes with its 
 convenient use. It is generally better in these cases to adopt 
 the temporary hood and contrivances which will be described 
 hereafter (392). A particular description of the construction 
 of the furnace itself will also be given under the head of 
 furnaces (169). 
 
 11. The tables are most important parts of laboratory fur- 
 niture ; they should be as extensive as the room will admit of, 
 and be so placed as to allow of ready access ; hence a large 
 one, or two placed towards the middle of the room, and in 
 such a situation as to be well lighted, are very useful. They 
 should be made strong, and be furnished with drawers, unless 
 indeed one be closed in by doors, so as to form cupboards 
 having shelves within to hold rough articles ; and if such a 
 one could have a situation given it near the sink, as a kind of 
 cleansing and washing table, its advantage would soon be 
 experienced. The table appropriated to testing operations and 
 experiments with corrosive fluids, as acids and alkalies, is 
 sometimes covered with lead, or even with earthenware, glazed 
 tiles being very convenient for the latter purpose, but a hard 
 or heavy substance endangers the safety of thin glass vessels 
 when laid down upon it. 
 
 12. There are some things which necessarily have their 
 appropriate and constant place on the tables. The filtering 
 stands (528) are of this kind, and are thus raised to a conve- 
 nient height for operations : they should have a situation 
 chosen for them, which, though convenient for use and close to 
 that part of the table to be kept clear for general purposes, 
 should not be in the way of the operations constantly going on 
 there. A drawer or other dry place in the immediate neigh- 
 bourhood of these stands, should be appropriated to filtering 
 paper. The mercurial trough (736) is another apparatus 
 which should have its assigned place upon the tables ; and the 
 particular table upon which it stands, or upon which mercurial 
 operations are generally performed (144) ; should have a groove 
 
Sect. I.] THE LABORATORY SINK CUPBOARDS. 17 
 
 cut round it near to the edge, with a hole in one place for the 
 facility of collecting the scattered mercury. Any of the metal 
 which may be spilled is swept or wiped into the groove, and 
 thence into a hole, and thus collected and preserved. 
 
 13. A sink, with an abundant supply of water, is very im- 
 portant ; and although it is just possible that a jug, with a large 
 leaden funnel and a pan beneath, may suffice, yet so advan- 
 tageous is the unlimited use of water and a regular sink with 
 its drain, that much should be done to secure them. The 
 water should be laid on from a cistern that contains a never- 
 failing supply, and the sink should be made of strong wood- 
 work lined with lead ; for though that metal is liable to the 
 action of mercury and some metallic solutions, yet on the 
 whole it is less subject to chemical action than any other sub- 
 stance ordinarily placed in a similar situation. The sink should 
 be made as large as convenient, not exceeding 30 inches by 
 42, and should have a drain which will freely carry off all the 
 slops and water that are likely to be thrown down. An iron 
 stink-trap should be placed at the commencement of the drain, 
 not merely for the purpose of preventing unpleasant smells, 
 but for the retention of the mercury gradually washed down, 
 which in an active laboratory of research amounts to no 
 small quantity in two or three years. A sink is useful not 
 only for washing bottles, glasses, jars, &c., but for many che- 
 mical operations, such as filling airholders, washing minerals, 
 preparing gluten, distillation, Sec., and should be made con- 
 venient for all these purposes. It will of course be placed in a 
 corner, and as much out of the way as is consistent with its 
 free use ; a place in the immediate neighbourhood being appro- 
 priated to its cleansing accompaniments, pails, pans, brushes, 
 brooms, &c. 
 
 14. Cupboards are so useful, that one, or, if possible, more, 
 with shelves inside, ought to be provided. In these are to be 
 kept clean test-glasses, jars, measures, retorts, flasks, receivers, 
 &c., for here they are preserved from the dust and dirt which 
 are constantly moving and settling in the laboratory itself. The 
 shelves should be placed at different intervals, so as to receive 
 glasses of various sizes ; and one or two of them should have 
 a number of round holes cut out, from an inch to four inches 
 
 c 
 
18 THE LABORATORY SHELVES RETORTS. [Sect. I. 
 
 in diameter, to receive the necks of retorts, flasks, and receivers. 
 Between the shelves should be fixed various hooks and nails to 
 hold and retain tube apparatus, such as siphons, detonating 
 tubes, tubes of safety, &c. One cupboard-shelf should be 
 particularly appropriated to receive products of experiments in 
 progress which have to be preserved for a few days (1302) ; 
 or things which, being valuable, are but rarely required, as 
 potassium, &c. 
 
 15. All parts of the walls of the laboratory within reach, 
 conveniently situated, and not otherwise occupied, should be 
 fitted up with shelves in a firm manner, to receive bottles and 
 jars. These must vary in strength, size, and interval, accord- 
 ing to their intended uses ; such as are to hold the bottles con- 
 taining the usually extensive and continually accumulating 
 series of chemicals, need seldom be of greater height or depth 
 than to receive a six or eight ounce phial standing close against 
 the wall. Those intended for the jars of the pneumatic trough 
 must be wider and at greater intervals ; and those, again, which 
 are intended to hold the stock-bottles must be considerably 
 stronger, in consequence of the weight to be borne by them. 
 In arranging the shelves, it will be proper to pay attention to 
 their situation; the first series, for instance, containing the 
 chemicals and tests in constant use, should be near the table 
 upon which operations are most generally carried on, whilst 
 the stock-bottles may be put upon shelves considerably out of 
 the way. A shelf near the sink, with holes in it, upon which 
 apparatus which has been washed and rinsed may be placed 
 to drain, is very useful; and two or three others in the same 
 neighbourhood, or somewhere out of the way, supply places 
 for chemical lamps, oil-cans, and other dirty articles that can- 
 not but exist in a laboratory. 
 
 16, Retorts are very conveniently preserved by being hung 
 on wire rings from an inch to an inch and a half or two inches 
 in diameter. These are easily made out of copper wire, and 
 being screwed or fastened in a row into a wooden partition, 
 receive the necks of the retorts, and hold them in a very safe, 
 compact, and convenient manner. The advantage is obtained, 
 also, of seeing the whole stock of retorts at once, and instantly 
 choosing that best fitted for any required purpose. 
 
Sect. I.] THE LABORATORY PLACES OF BLOCKS, ETC. 19 
 
 17. Analogous in its office to the shelves, is the tube-rack; 
 it is intended to hold pieces of glass tube from one to four 
 feet long, and generally consists of a shelf about three feet 
 long and from six to eight inches wide, having a piece fast- 
 ened on the front so as to form a raised edge about an inch 
 high : or it might be made with some advantage by driving 
 three or four long pins or holdfasts into the wall in a line, the 
 end of each being turned up. No wooden bottom is in this case 
 used, and the piece of glass tube required is more readily 
 selected from among the rest, than when upon a rack of the 
 former kind ; the smaller pieces are, however, apt to fall 
 through. 
 
 18. A part of the wall should be selected to be furnished 
 with long spikes, either by driving them into the brickwork, 
 or fastening up a board to which they are attached. These 
 serve to hold retort and flask rings, and large bent tubes, such 
 as siphons, curved pieces, &c. ; smaller spikes will answer a 
 similar purpose for the numerous coils and pieces of wire that 
 are continually required. 
 
 19. One or two large wooden blocks will be found useful in 
 a laboratory ; they may serve as bases on which to place heavy 
 mortars, and one of them will form a good 'support for a spike 
 or anvil. They should have their appointed situations on the 
 floor. 
 
 20. A set of ten or twelve small blocks of wood, about four 
 inches square and of different thicknesses from half an inch to 
 three inches, are also of great service in supporting parts of 
 apparatus at different heights. 
 
 21. Some consideration must be given in appointing the 
 places of the various pieces of apparatus and furniture in most 
 common use ; and their relation to the tables, the bottles, and 
 each other, must be taken into account. The pneumatic 
 trough (729) is in constant service, and must not therefore be 
 situated in a dark place, or far from the centre of activity : 
 access to it should be ready, and communication from other 
 parts open and free. The jar shelves (15) should, if possible, be 
 placed near. The mercurial trough already mentioned as 
 standing upon the table (12) should be similarly circum- 
 stanced. The table blow-pipe (242) is a very essential article, 
 
 C 2 
 
20 THE LABORATORY COAL-BOX TOOLS. [Sect. I. 
 
 and in continual use : it should have a place against the wall 
 near to its appendage, the tube-rack. The dirty, but useful 
 coal-box, should have a convenient, but low and unobtrusive 
 situation given to it, that it may fully perform its part without 
 interfering with the uses or advantageous situation of other 
 things. It can hardly be imagined without experience how 
 much is gained by an attention to these details ; for though an 
 operation may, either from its desultory nature or its subordi- 
 nate character, be of little consequence when considered sepa- 
 rately, yet when it has to be repeated again and again, and 
 from its recurrence is continually entering into the business 
 of the day, it attains a degree of importance which makes its 
 ready and accurate performance of the greatest consequence. 
 
 %%. The necessity of such things in the laboratory as flasks, 
 retorts, receivers, bottles, phials, mortars, &c., will be evident^ 
 but any information respecting them will be most advanta- 
 geously given hereafter. They are better supplied as they 
 are wanted, rather than by a previous order ; and in that way 
 the accumulation of what is unnecessary, is to a great extent 
 avoided. 
 
 23. But there are other things, properly denominated tools, 
 which, being always useful, should be immediately procured. 
 Amongst these, an anvil or spike, with its foot-block, should 
 stand on the ground, and a vice should be fixed against one of 
 the tables. Two or three hammers, including one intended 
 for mineralogical purposes, some cold chisels, a screw-driver, 
 a saw, cutting chisels, gimlets, brad-awls ; half-round, flat, 
 and small three-square files; half-round, flat, and rat-tail 
 rasps ; pincers, pliers, forceps, a trowel, a soldering-iron with its 
 appendages, are the tools which, with a glue- pot, and a collec- 
 tion of nails and screws, will be found necessary : and to these 
 may be added a saw-knife for cutting soft brick ; coarse spa- 
 tulas, either of wood or bone, or made from iron hoop ; and a 
 cork-screw. 
 
 24. There are several articles which may be considered as 
 materials in a laboratory. Bricks are often wanted to build 
 up temporary furnaces, or to form supports : mortar is con- 
 sequently useful ; river-sand is required for sand-baths and 
 other purposes, and is readily obtained from the bricklayer. 
 
Sect. I.] THE LABORATORY MATERIALS DRAWERS. 21 
 
 Corks are useful in a thousand ways (1331), and should be 
 provided of good quality, and of all sizes from a large bung 
 downwards: old cards are extremely convenient. Matches, 
 string, and bladder, are necessary. 
 
 25. Many of these useful articles are best preserved in 
 drawers, and hence the necessity of a number of these recep- 
 tacles in a laboratory. If the tables do not supply enough of 
 them, it will be desirable to have a strong rough set exclu- 
 sively for these purposes. The appropriation of drawers 
 requires some method : one should be appointed to receive 
 fragments of glass tubes too small to remain in the tube-rack ; 
 another should be kept exclusively for the reception of those 
 useful laboratory vessels, glass tubes of various sizes closed at 
 one end (910) ; another, from containing corks, will be the cork- 
 drawer ; another, the tool-drawer ; the files and rasps, however, 
 being, from their quantity and general use, worthy of a drawer 
 to themselves; the round glass plates, stirrers, and tapers, 
 used in the laboratory, will also occupy a drawer ; string, with 
 bladder and sand-paper, another ; and tow, with dusters, 
 another ; drawers being the most convenient places for these 
 things. One drawer should be divided within into various 
 compartments intended for different small apparatus, as blow- 
 pipes, forceps, a scratching diamond, platina foil and wire, 
 fee. 
 
 Besides drawers, a few small strong wooden boxes are con- 
 venient in a laboratory, for containing lime, lute, manganese, 
 sand, Sec. 5 and a few wooden trays, with low rims, are exceed- 
 ingly serviceable for removing apparatus. 
 
 26. Distilled water must be included among the chemist's 
 requisites ; and so much advantage is gained by its abundant 
 supply, that any accessible source should be eagerly sought. 
 Distilled water in large quantities is by no means uncommon 
 in towns, for in consequence of the numerous applications of 
 steam, the opportunities of collecting it are frequent. Where- 
 ever steam is used for the conveyance of heat through pipes, 
 the condensed water may, with a very little contrivance, be 
 collected in abundance, by placing a clean cask or vessel under 
 the place where it issues forth. Such water must of course be 
 tested to prove its purity ; that being rejected for laboratory 
 
22 THE LABORATORY DISTILLED WATER. [g ec t. I 
 
 use, which from any derangement in the pipes or other circum- 
 stance is found to be impure. Where the laboratory cannot 
 be supplied in this way, the water must either be bought or 
 distilled (424) ; the furnace before described (8.177) is ex- 
 tremely well adapted for the application of a still for this 
 purpose. Distilled water is best preserved for table use in a 
 bottle holding about a quart, or three pints, which should be 
 quite distinct in its form or appearance from any other bottle 
 in the laboratory, so that no mistake respecting it may at any 
 time arise. 
 
 27. A flint and steel, with matches, or, what is far better, an 
 eupyrion, should always be conveniently placed in the labora- 
 tory, and near to it a candle and candlestick. The little appa- 
 ratus called Hertner's Eupyrion is now so well known in most 
 towns, that no difficulty will exist in obtaining it. To those 
 who do not know the instrument, it may be as well to observe, 
 that it consists of a very small bottle half filled with asbestus, 
 rather closely pressed, and moistened with very concentrated 
 sulphuric acid, the quantity being such, that though it 
 thoroughly wets the asbestus, it cannot flow amongst it or upon 
 the sides of the bottle ; the bottle is closed by a good tight 
 cork, and should never be opened except when a match is to 
 be introduced, and immediately the latter is withdrawn, it 
 should be closed again. The matches are small slips of wood 
 tipped with sulphur in the usual way, but they are then again 
 tipped over the sulphur by being dipped for the eighth of an 
 inch into a mixture of three parts, by weight, of chlorate of 
 potash, and two parts of starch or sugar, mixed with a little 
 vermilion to give it colour, and water enough to make it into 
 a thin paste : this is allowed to dry thoroughly. One of these 
 matches suddenly dipped into the bottle, so as to touch the 
 sulphuric acid, and snatched out again, will immediately 
 inflame. For the eupyrion may be substituted the phos- 
 phorus bottle, made by stirring a piece of phosphorus about 
 in a dry bottle with a hot wire ; the phosphorus undergoes 
 partial combustion, and forms a highly combustible coat over 
 the interior : a common sulphur match rubbed against the 
 inside of the bottle and drawn out into the air, immediately 
 inflames ; or if it should not do so, a second stir with the hot 
 
Sect. I.] THE LABORATORY APPARATUS- ROOM, ETC. 23 
 
 wire, or two or three days' rest, will generally render the bottle 
 a good one. It should be closed by a glass stopper so as to 
 prevent access of air, except at the short momentary intervals 
 when it is in use. Both this and the eupyrion are to be pre- 
 ferred to flint and steel. 
 
 28. There remains little besides to perfect the preliminary 
 furniture of a laboratory. A blank writing-paper book should 
 be upon the table, with pen and ink, to enter immediately 
 the notes of experiments (1290). A chair may be admitted, 
 and one will be found quite sufficient for all necessary purposes, 
 for a laboratory is no place for persons who are not engaged 
 in the operations going on there. 
 
 29. Having thus described the laboratory, it will easily be 
 understood, that great advantages would arise from the asso- 
 ciation of another room or two with it, which, nevertheless, 
 may be dispensed with. A good balance is a very delicate 
 piece of apparatus, and is soon injured and deranged if ex- 
 posed to the attacks of the damp and corrosive vapours that 
 are continually floating about in the laboratory, in which it 
 should therefore be allowed to remain as little as possible, and 
 yet from its constant use should not be far removed. If there 
 be a small dry room at hand, it will be very convenient gene- 
 rally to keep the balance in it ; and there the air-pump and its 
 receivers, the electrical machine, Leyden jar, and a quantity 
 of delicate apparatus, will usually be its companions. 
 
 30. On the other hand, such things as lute, sand, charcoal, 
 coke, bricks, crucibles, voltaic troughs, carboys, Sec,, do not 
 require a dry place, and would even cause inj ury if retained in 
 the same room with the balance ; yet it is advantageous, if 
 otherwise convenient, to remove them from the laboratory 
 into a separate place, that the former may be left unembar- 
 rassed and clear for operations. These, therefore, would go 
 very properly into a dry cellar or covered shed, or any place 
 that would suit as a rough lumber-room. Still it may be ob- 
 served, that these places are not essential; and where the 
 laboratory establishment is but small, all the delicate apparatus 
 may be put into a dry cupboard, and the other things find their 
 situation in the laboratory itself. 
 
 31. It was once intended to annex a plan of a convenient 
 
24 THE LABORATORY, ETC. [Sect. I. 
 
 and complete moderate-sized laboratory, but the idea was 
 resigned, in consequence of the difficulty of exhibiting the 
 important parts in more than one case out of ten. There will 
 scarcely be two of these chemical workshops which may not 
 advantageously differ in the arrangement of some of their 
 essentials, as well as in the extent of their different parts; 
 some being extensive in one department, others in another. 
 A notion of the most necessary furniture of a small laboratory, 
 or of one to be comprised in cases of necessity on the surface, 
 and within the drawers of a single table, may easily be gathered 
 from the manipulatory parts of the present work. If the want 
 of time, or if other circumstances, should necessarily limit the 
 chemical pursuits, the author would advise a person so situ- 
 ated to begin by providing a spirit-lamp, a blow-pipe, a 
 pair of pliers, some platina foil and wire, a platina capsule, a 
 few Florence flasks, a chemical lamp, a few evaporating basins, 
 a few pieces of quill glass tube, and two or three dozen bottles ; 
 with some of the most useful chemicals, as the acids and alka- 
 lies, and six or eight of the most important tests ; and to pur- 
 chase all other things as the necessity for them may arise. 
 
 SECTION II. 
 BALANCE, WEIGHING, &c. 
 
 32. ON entering upon a part of this work which relates more 
 directly to manipulation than the matter of the preceding 
 pages, it may be proper to state very distinctly, that the object 
 is not to give information relative to the nature or construction 
 of chemical apparatus in general, but to teach its simplest, 
 most effectual^ and accurate use. It will be the endeavour of 
 the author to keep all in strict subordination to this object ; 
 and when he enters into the construction and principles of an 
 instrument, it will be solely with a view to the clear compre- 
 hension of the manner of using it. Hence a reason for the 
 apparent disproportion which will now and then appear in the 
 
Sect. II.] DELICATE AND COMMON BALANCES. 25 
 
 details of this subordinate and descriptive part : for whatever 
 the pupil or chemist can himself do towards the correction or 
 construction of an instrument, will be fully described, whilst 
 that which must, of necessity, be done by the workman, will 
 be passed over in silence. To teach a person how to make a 
 balance, or to inform him how it is made, is not the object of 
 the writer ; whilst, on the contrary, its use is the very point 
 in view : whatever, therefore, facilitates the latter, or whatever 
 can be done to correct slight derangement, by one who is not 
 a workman, ought now to claim our attention. 
 
 33. A chemist cannot do without a delicate balance ; it is 
 absolutely necessary to his repetition of the most important 
 experiments of others, or to his own independent progress. 
 If he be an active operator, he will require two or three ba- 
 lances ; for the weights with which it is necessary to work are 
 almost without limit, and cannot be estimated by the same 
 instrument. Large quantities, if weighed in balances com- 
 petent to show minute differences in small weights, would, by 
 flexure of the beam or change in the points of support, infallibly 
 injure or even destroy them ; and small weights cannot be 
 appreciated in instruments intended for great quantities, 
 because of the strength it is necessary the latter should have, 
 and the consequent weight and comparative roughness of the 
 parts. One pair of scales should therefore be provided that will 
 weigh from one ounce up to three or four pounds, or even 
 more, and be so constructed as to turn with two or three grains, 
 when loaded with their greatest weight. They can, when re- 
 quired^ be made very delicate and correct, but, except in parti- 
 cular cases, that is not necessary. Another pair of scales, 
 calculated to weigh from half a grain to two or three -ounces, 
 with considerable accuracy, and turning with about one half or 
 one third of a grain when fully loaded, should be kept for 
 laboratory purposes. These are intended for common use ; and 
 as it is a great object to save the superior instrument from the 
 injury occasioned by too frequent use, and to preserve it from 
 exposure to the vapours which are constantly escaping in the 
 progress of operations, or from the bottles, should be substi- 
 tuted as often as possible for the latter, especially in cases which 
 require the balance in the laboratory. The choice instrument 
 
26 COMMON BALANCES WEIGHTS. [Sect. II. 
 
 should be sufficiently delicate to weigh from 600 to 1000 grains 
 and downwards, indicating distinctly and certainly differences 
 equal to the ^-^ or ^^ocr P art f tne weight in the scale. 
 
 34. The materials and construction of balances vary so much, 
 as also do the circumstances which influence their purchase, 
 that no general directions on this point can be well given. 
 Whether large or small, they are best on fixed supports, and 
 not suspended loosely, although very good ones of the latter con- 
 struction are made. They should be preserved from all damp 
 and vapours ; and the beam of the large one, if its construction 
 will admit of it, and even of the next pair, frequently oiled 
 and wiped. The more delicate instruments should be cleaned 
 by the maker : much harm is sometimes produced by rough 
 and hasty cleansing ; and if, when about to be used, it is seen 
 that a spot arising from rust, or corrosion, or any other cause, 
 exists on the beam or pan of a delicate balance, it is better to 
 compensate for the difference of weight it occasions, by adding 
 a temporary counterpoise to the pans, than to try to remove it 
 previous to the operation. If the balances are so constructed 
 as to pack into boxes or cases, they should be kept in such 
 cases when not in use. Delicate instruments are always in- 
 closed in cases, and are so fixed in them as to require and admit 
 of their use without removal. When not in use, the cases 
 should always be closed. A loose green baize or linen bag to 
 throw over the balances when in the laboratory, and not in 
 use, is serviceable, and whenever of necessity the delicate 
 balance is brought into the laboratory, it should be returned 
 to its proper situation immediately that it is done with. The 
 instrument itself is so expensive, so soon suffers injury, and 
 then has its value and use so rapidly diminished, that every 
 care should be taken to preserve it in efficient order. 
 
 35. The weights for these balances are as various as the in- 
 struments themselves. They will be wanted from 3 Ibs. down 
 to the hundredths of a grain, and will form at least two sets, 
 the one consisting of avoirdupois pounds, ounces, and drachms, 
 and the other of grains, from 1000 down to the minutest 
 fractions. It is usual to construct these weights in sets, 
 containing as few as possible in each. Thus 4 weights of 1, 2, 
 3, and 4 grains are sufficient to weigh from 1 to 10 grains, and 
 
Sect. II.] WEIGHTS REQUISITE THE MOST ADVANTAGEOUS. 27 
 
 with similar weights of 10, 20, 30, 40, 100, 200, 300, and 400, 
 will weigh up to 1100 grains. The weights might be still 
 further diminished in number by using such as are expressed 
 by the following series, 1, 3, 9, 27, 81, 243, and a series of 
 twelve so constructed would weigh any number from 1 to 
 265,720. But this is not at all desirable in practice, and 
 several of each particular weight, or several sets of weights, 
 should be in use at once. This will not be necessary with the 
 pounds, ounces, and drachms, because they are comparatively 
 but seldom used in the laboratory, but with the grain weights 
 it is required : for it is desirable, in all possible cases, to refer 
 to the same kind of weights for simplicity of calculation and 
 comparison, and grain weights being those generally and con- 
 veniently referred to, it follows necessarily that such are in 
 constant use ; this being the case, all delay or difficulty arising 
 from a deficiency of weights should be avoided by an abundant 
 supply. It frequently happens, that in the estimation of a loss 
 or gain of weight, or in taking specific gravities, two or more 
 weights of the same value are wanted ; and this, together with 
 occasional losses, will render it evident that there should be a 
 liberal extra quantity. For this reason a small box, divided 
 into compartments, containing a variety of grain weights, from 
 a tenth up to 1000 grains, and intended to accompany the 
 balance ordinarily in use, is exceedingly convenient. It is well 
 to have a perfect set, from 500 downwards to the hundredths 
 of a grain, to be always kept with the best balance, there being 
 two or three sets of the fractions of a grain. Repetitions of 
 those above a grain are in this case not required, but may be 
 supplied, when wanted, from the laboratory-box. 
 
 36. These weights are sometimes made of brass ; the smaller 
 ones, however, are commonly of platina. The fractions of a 
 grain should always be of platina, and it would be much better 
 if that metal were constantly used for weights not surpassing 
 10 grains. Perhaps its expense for heavier weights would 
 sometimes be objectionable, but this is fully compensated by 
 the unchangeableness of the weights either from oxidation or 
 corrosion, and the facility with which they are cleaned from 
 ordinary dirt, either by slight wiping or momentary exposure 
 
28 WEIGHT-BOX ITS ACCOMPANIMENTS. [Sect. II 
 
 to the flame of a spirit-lamp. Where expense is no object, all 
 the weights should be of platina ; their permanent correctness 
 compensating abundantly for the increased cost. 
 
 37. If platina be not used, there is probably no common 
 metal better than brass, of which to construct weights; the 
 larger grain weights, and also the pound series and its divi- 
 sions, may be made of this alloy. It is liable to be affected 
 very materially by the laboratory fumes, and in consequence 
 small weights constructed of it are often rendered useless in a 
 very short period. Keeping them in a close box retards this 
 kind of injury. The pound and ounce weights are frequently 
 constructed in sets, each weight being hollo w, having the form 
 of a truncated cone, and fitting into the others, so as when 
 arranged together to form a solid mass. Such weights are 
 very convenient in arranging counterpoises, the cup form 
 enabling the largest weight used to receive all the additional 
 matter required to make the counterpoise accurate, as will be 
 seen in the practice to be described hereafter (64) . 
 
 38. The laboratory-box of grain weights should include a 
 pair of small brass pincers or forceps, for the divisions of a 
 grain (54). The latter are too minute to be moved expe- 
 ditiously and safely by the hand ; and unless the weights be 
 comparatively large^ the handling of any of them is liable to 
 communicate extraneous matter, and thus render them more 
 or less inaccurate. 
 
 39- Associated with the weights should be some convenient 
 substances for the purpose of counterpoising crucibles, capsules, 
 tubes, &c. (64). A little box of clean shot of different sizes 
 mixed together, answers this purpose in part very well ; and 
 its contents may be completed by a few pieces of thin sheet 
 lead or tin foil. 
 
 40. The balance and weights should be carefully examined 
 at intervals, to ascertain their accuracy, for if they involve 
 unnoticed errors, the experiments made with them may be 
 worse than useless. Some curious conclusions, tending to 
 subvert most important chemical truths, might be quoted as 
 having arisen solely in this way. 
 
 41. The theory of the balance is so simple, that the tests 
 
Sect. II.] ACCURACY OF A BALANCE EXAMINED. 29 
 
 of its accuracy will be easily understood, and as easily prac- 
 tised *. It may be considered as an uniform inflexible lever, 
 supported horizontally at the centre of gravity, and support- 
 ing weights at equal distances from the centre, by points in 
 the same horizontal line with the centre of gravity. If the 
 weights be equal, the one will counterpoise the other ; if not, 
 the heavier will preponderate. In the balance, as usually 
 constructed, there are certain departures from the theory as 
 above expressed some from the impossibility of execution, 
 and others in consequence of their practical utility ; and a good 
 balance may be said to consist essentially of a beam made as 
 light as is consistent with that inflexibility which it ought to 
 possess, divided into two arms of equal weight and length, by 
 a line of support or axis, and also terminated at the end of 
 each arm by a line of support or axis intended to sustain the 
 pans. These three lines of support should be exactly parallel 
 to each other, in the same horizontal plane, and correctly per- 
 pendicular to the length of the beam 5 and the plane in which 
 they lie should be raised more or less above the centre of 
 gravity of the beam, so that the latter should be exactly under 
 the middle line of suspension. It will be unnecessary in this 
 place to speak of the coarse faults which occur in the ordinary 
 scales these will easily be understood ; and from what has to 
 be stated of the examination of the most delicate instrument, 
 the impossibility of avoiding them without incurring an 
 expense inconsistent with their ordinary use, will be as readily 
 comprehended. 
 
 42. It will be easily understood that a beam constructed 
 with knife edges resembles the one before mentioned ; and 
 being supported on horizontal planes by the central line of 
 suspension, as is generally the case, will take a horizontal 
 position, in consequence of the situation of the centre of gra- 
 vity. The addition of the pans causes no change in this ulti- 
 mate position of the beam, because they are of equal weights. 
 The delicacy of a balance depends very materially upon the 
 relative situations of the centre of gravity, and the lines of sup- 
 port, i. e. the middle and the extreme lines of suspension. If 
 
 * See Nicholson's or Ure's 'Dictionary of Chemistry, article Balance. 
 
30 CIRCUMSTANCES INFLUENCING THE INDICATIONS. [Sect. II. 
 
 the centre of gravity be considerably depressed below the 
 fulcrum, then, upon trying the oscillations of the balance by 
 giving it a little motion, they will be found to be quick, and 
 the beam will soon take its ultimate state of rest ; and if 
 weights be added to one side, so as to make it vibrate, or turn 
 as the expression is, or else to bring it to a certain permanent 
 state of inclination, the quantity required will be found to be 
 comparatively considerable. As the centre of gravity is raised, 
 the oscillations are slower, but producible by a much smaller 
 impulse, the beam is longer before it attains a state of rest, 
 and it turns with a smaller quantity. When its situation 
 coincides with the fulcrum or centre of oscillation, that also 
 being in the plane joining the two extreme lines of suspension, 
 then the smallest possible weight will turn the beam (sup- 
 posing the knife edge and suspending plane perfect), the oscil- 
 lations no longer exist, but one side or the other preponderates 
 with the slightest force ; and the valuable indication which is 
 furnished by the extent and velocity of the vibrations is lost. 
 The case where the centre of gravity is above the fulcrum 
 rarely if ever occurs ; such a balance, when equally weighted, 
 would set on the one side or the other, that side which was in 
 the slightest degree lowest tending to descend still lower, until 
 obstructed by interposing obstacles ; unless, indeed, the fulcrum 
 was placed considerably above the line joining the extreme 
 points of suspension, in which case the weights in the pans 
 might counteract the effect dependent upon the elevation of 
 the centre of gravity. In balances intended to carry large 
 quantities, it is necessary to place the centre of gravity lower 
 than in those for minute quantities, that they may vibrate 
 regularly and readily, and hence one cause why they are infe- 
 rior in delicacy, for, as a consequence of the arrangement, they 
 will not turn (or indicate), except with a larger weight. 
 
 43. The vibrations of a balance vary with the quantity of 
 matter with which it is loaded ; and the more the weight in the 
 pans, the slower their occurrence. These should be observed, 
 and the appearances retained in the mind, in consequence of 
 the useful indications they afford in operations of weighing. 
 A certain extent and velocity of vibration would, in some de- 
 gree, indicate to the person used to the instrument nearly the 
 
Sect. II.] EXAMINATION OF A BALANCE. 31 
 
 weight required to produce equilibrium ; but the same extent 
 and velocity, with a weight much larger or smaller, would not 
 be occasioned by an equal deficiency or redundancy of weight, 
 as in the former case. The weight required also to effect a 
 certain inclination of the beam, or to turn it, should be known, 
 both when it is slightly and when heavily loaded. If the in- 
 strument turns with T ^ of a grain when 600 grains are in each 
 scale, or with -QQ^QQ of the weight to be estimated, it may be 
 considered as very good. 
 
 44. Balances are sometimes liable to set, as it is called, when 
 overloaded. The effect consists in a permanent depression of 
 that side which is lowest : thus, if a balance be equally weighted 
 in each pan, but overloaded, it will, if placed exactly horizontal, 
 remain so ; but the slightest impulse or depression on one side 
 destroys the equilibrium, the lower side continues to descend 
 with an accelerated force, and ultimately remains down, being, 
 to all appearance, heavier than the other. Generally speaking, 
 the more delicate a balance, the sooner this effect takes place, 
 and hence one limit to the weight which it can properly carry. 
 This setting of the balance, and the general diminution of deli- 
 cacy by increase of weight, should be carefully kept in mind. 
 The setting is considered as dependent upon the position of 
 the fulcrum, below the line which joins the extreme points of 
 suspension of the beam ; the effect which would thus be pro- 
 duced being masked for a time by the centre of gravity in the 
 beam falling below the fulcrum. 
 
 45. When the beam, freed from the pans, but supported on 
 its stand, has been found to oscillate regularly and equably, 
 and gradually to attain a horizontal position of rest, it should 
 be reversed, that is, taken up and turned half-way round, so as 
 to make that arm which before pointed to the right, now point 
 to the left. The beam should then again be made to oscillate ; 
 and if it performs regularly, as before, finally resting in a hori- 
 zontal position, it has stood a severe test, and promises well. 
 The faults which are likely to be disclosed in this way, depend 
 upon imperfections in the work of the middle knife edge and 
 the planes upon which it rests'. The edge is made either of 
 agate or steel, and should be formed out of one piece of matter, 
 and finished at once ; every part of the edge being ground upon 
 
32 EXAMINATION OF A BALANCE. [Sect. II. 
 
 the same flat surface at the same time. In this way the existence 
 of the two extreme or bearing parts of the edge in one line is 
 insured ; but when the two parts which bear upon the planes 
 are formed separately upon the different ends of a piece of agate 
 or steel, or, what is worse, when they are formed on separate 
 pieces, and then fixed one on each side the beam, it is scarcely 
 possible they should be in the same line, and, if not^ the beam 
 cannot be correct. These knife edges usually rest upon planes, 
 or else in curves. The planes should be perfectly flat and 
 horizontal, and exactly at the same height ; the curves should 
 be of equal height, and their axis in the same line. If they 
 are so, and the knife edge is perfect, then the suspension will 
 be accurately on the line of the edge, and reversing the beam 
 will produce no change. 
 
 46. When the pans are hung upon the beam, the balance 
 should of course still remain horizontal. The lines of sus- 
 pension for the pans are not so difficult to obtain correctly as 
 that before spoken of; but they should be tried by changing 
 the pans, then by reversing the beam, and afterwards by chang- 
 ing the pans again. The irregularities which may in this way 
 be discovered in a balance can be corrected only by the work- 
 man, and are always difficult points in the final adjustment. 
 Faults may exist in a slight degree in a very excellent instru- 
 ment, and the inaccuracies which might result from ignorance 
 of them may be avoided when they are known, by attention to 
 directions. 
 
 47. The arms should in length and weight be equal to each 
 other : the length of each is accurately the distance from the 
 middle to the distant knife edge, all the edges being considered 
 parallel to each other, and in the same plane. The two arms 
 should accord perfectly in this respect ; but the weight is by 
 no means necessarily subject to equality, though it is better 
 that it should be so. One arm, with its pan, may be consi- 
 derably heavier than the other, but from the disposition of the 
 weight in the lighter arm towards the extremity, or in the 
 heavier towards the middle of the beam, the equilibrium may 
 be perfect ; and, therefore, no inaccuracy be caused thereby in 
 the use of the balance. Instruments are usually sent home in 
 equilibrium, and require no further examination as to this parti- 
 
Sect. II.] 
 
 EXAMINATION OF THE WEIGHTS. 33 
 
 cular point than to ascertain that they really are in adjust- 
 ment ; and that, after vibrating freely, they take a horizontal 
 position. If they should not do so, the fault is easily corrected 
 for the time by a small counterpoise. 
 
 48. Equality in the length of the arms is much more im- 
 portant, and may be ascertained in two or three ways. Sup- 
 pose the balance with its pans to vibrate freely and rest in a 
 horizontal position, and that after changing the pans from one 
 end to the other, the balance again takes its horizontal state of 
 rest. In such a case an almost certain proof is obtained of 
 equality in the length of the arms. They may, however, be 
 equal, and yet this change of the pans from end to end may 
 occasion a disturbance of equilibrium, because of the unequal 
 distribution of weight in the beam and pans ; but, to insure an 
 accurate test, restore the pans, and consequently the equili- 
 brium, to the first state; put equal, or at least counterpoising 
 weights, into the pans, loading the balance moderately, and 
 then change the weights from one pan to another, and again 
 observe whether the equilibrium is retained ; if so, the lengths 
 of the arms are equal. 
 
 Tests of this kind are quite sufficient for the purpose of the 
 chemist; who, having ascertained that his balance, whether 
 slightly or fully laden, vibrates freely, turns delicately, has 
 not its indications altered by reversing the beam or changing 
 counterpoising weights, may be perfectly satisfied with it, and 
 leave the fuller consideration of the difficult points and cor- 
 rections to the instrument maker. 
 
 49. The weights should undergo an examination as well as 
 the balance, and it is necessary to make this with reference to 
 their accuracy when new, and also to their change by wear or 
 corrosion. It is essential in the first place to set out with a 
 good standard, and though this point is of necessity generally 
 left to the workman, yet, when possible, it is very desirable 
 that the 1, 10, 100, and 1000 grain weight should be compared 
 with others of good authority. The most ready method of 
 detecting errors in the subdivisions, is to make up equal quan- 
 tities from different weights, and compare them together in the 
 balance, a large one being tried against eight or ten smaller, as 
 the 100 grain weight against those of 40, 30, 10, 8, 5, 4, 2, 
 
 D 
 
34 PROCESS OF WEIGHING. [Sect. II. 
 
 and 1 ; and then again, from a quantity made up of several, to 
 remove some and replace them by others, as for instance, for 
 the 30 grain weight above, to substitute a 10 and four 5 grain 
 weights. The fractions of the grain should be examined in 
 the same manner, and if any material error exists, it will thus 
 readily be discovered. Should the balance in use be one 
 which, from accident or other circumstances, is affected in its 
 indications by changing the weights in the pans, then, in these 
 trials, all the changes should be made in one pan only, the 
 weight in the other being considered as a mere counterpoise, 
 and left undisturbed from first to last. The trials with those 
 weights which accompany the best balance, and are intended 
 exclusively for very delicate experiments, should be made with 
 extreme care. 
 
 50. The examinations which are to take place at different 
 periods to ascertain the continued correctness of the weights, 
 are to be conducted in a similar manner, except indeed when 
 there is reason to suspect the alteration of a particular weight, 
 which will then of course be tried against one admitted to be 
 correct. These trials should be more or less frequent, accord- 
 ing to the exposure of the weights ; those, which from being 
 continually in the laboratory rapidly change their colour and 
 appearance, will often require examination; but platinum 
 weights are in this respect unalterable, and are liable to very 
 little derangement of any kind from ordinary use. 
 
 51. The operation of weighing is very simple, and it is only 
 because in the hands of the chemist it becomes one of extreme 
 delicacy and frequency, that the facilities for its performance 
 require to be mentioned. It should in the first place be ascer- 
 tained before every operation, that the balance is in order, as 
 far as relates to its perfect equilibrium, and to the freedom of 
 vibration ; and also that no currents of air are passing through 
 the case, so as to affect its state of motion or rest ; a situation 
 being chosen where such influences may be avoided. If from 
 any accidental cause it be not in equilibrium, it should be 
 balanced by a fragment of paper, or a slip of tin or lead foil. 
 If its vibrations are imperfect and impeded, the cause, what- 
 ever it be, must be discovered and removed, or a delicate 
 weighing cannot be performed. 
 
Sect. II.] ADJUSTMENT OF THE WEIGHTS. 35 
 
 52. When the substance to be weighed consists of one or 
 a few pieces only, it is merely necessary to put it into one 
 pan, and to add weights to the other, until the two are in 
 equilibrium. A delicate balance is always furnished with 
 means of supporting the pans, independently of the beam ; 
 and the beam itself is also supported when required, by other 
 bearings than its knife edges ; and in such a manner as to 
 admit of the rapid removal of these extra supports, that the 
 instrument may be left free for vibration. This is done that 
 the delicate edges of suspension may not be injured, by being 
 constantly subjected to the weight of the beam and pans, and 
 that they may suffer no sudden injury, from undue violence 
 or force impressed upon any part of the balance. When, 
 therefore, a large weight of any kind is put into, or removed 
 from the pans, it should never be done without previously 
 supporting them by these contrivances : for the weight, if 
 dropped in, descends with a force highly injurious to the sup- 
 porting edges ; or if a large weight be taken out without first 
 bringing the pans to rest, it cannot be done without producing 
 a similarly bad effect. No weight heavier than a grain should 
 be introduced without this precaution, which, besides being 
 requisite for the reason described, is otherwise advantageous. 
 
 53. When a weight is put in which is assumed to be nearly 
 equal to the substance to be weighed, the balance should be 
 brought to a horizontal state of rest, this being usually done 
 by the same means as those appointed to support the pans ; 
 it should then be liberated gradually, so as to leave the pans 
 wholly supported by the beam. The whole being upon its 
 true centres of suspension, it will be observed whether the 
 weight is sufficient or not, and the rapidity of ascent or descent 
 in the pan containing it, will enable a judgment to be formed 
 of the quantity still to be added or removed (43). Bringing 
 the balance to a state of rest as before, such quantity should 
 be added, and trial again made ; and it is better to repeat this, 
 for every required alteration of weight, however small it may 
 be, than to endeavour to adjust the weight, whilst the whole 
 is suspended from the knife edges, and the pans are swinging 
 in the air. 
 
 54. As the weight approaches to equality with the substance 
 
 D 2 
 
36 SMALL WEIGHTS ESTIMATION OF WEIGHTS. [Sect. II. 
 
 to be weighed, the oscillations become slow, and the beam 
 ultimately rests in a line more or less inclined, being the same 
 with that above and below which the oscillations are made. 
 The positions of this line may be judged of, therefore, whether 
 the balance be at rest or in 'motion, and is a material indica- 
 tion of the weight to be added or taken away ; a person who 
 from observation of the oscillations of a balance and the posi- 
 tion of this line, is able to take advantage of the indication it 
 affords, will effect the required equilibrium in three or four 
 trials, when another person, unobservant of these points, will 
 not do it in less than ten or twelve. The small weights should 
 always be removed by a little pair of pincers (38), for when 
 the fingers are used, there is frequent risk that they may leave 
 something adhering to the larger weights in the pan, or may 
 brush out the smaller. The weights are safer too in pincers 
 than in the fingers. 
 
 55. It sometimes happens that the balance appears to vibrate 
 with difficulty, or to stick, though no sufficient cause can be 
 discovered. On these occasions a slight tremor given to the 
 instrument, by tapping on the case, or by a vibratory motion, 
 will frequently assist the balance, and confer sufficient delicacy 
 to allow of the operation being completed. The weight should 
 always be estimated when the instrument is at rest, but it 
 should be carefully ascertained by the freedom of vibration, 
 that this rest is the consequence of perfect equilibrium, and 
 not due to the want of delicacy in the instrument or to acci- 
 dental obstruction. 
 
 56. When the balance has ultimately been brought into a 
 state of equipoise, the weight is next to be estimated. The 
 operator generally takes an account of the additions and sub- 
 tractions as he proceeds, but the resulting quantity should be 
 confirmed by inspection. Remove the weights, therefore, from 
 the balance, and if there be niany, and especially small ones, 
 this is best done by slipping them all out of the pan together 
 into a small basin, or upon a sheet of paper, and then, by 
 laying them out, their amount may be ascertained. To detect 
 any error that may have arisen, either in calculation or other- 
 wise, make up the quantity in other weights, the fewer the 
 better, introduce these into the pan in place of the former, 
 and see if they also accurately counterbalance the substance 
 
Sect. II.] 
 
 APPROPRIATION OF BALANCE PANS. 37 
 
 weighed : if they do, the accuracy of the weight is insured ; if 
 not, the cause of the discrepancy must be sought for, dis- 
 covered and corrected. 
 
 57. When the operation of weighing has to be repeated 
 frequently, as happens in certain parts of analytical processes, 
 it economises time to have the smaller weights arranged in 
 order before the balance ; the hundredths together on the right 
 hand, then the tenths, then the grains below ten, and ulti- 
 mately the large weights. 
 
 58. In weighing substances that are hot, great attention 
 should be paid to any effect produced by the ascending current 
 of air, in elevating the pan containing the hot material, and 
 thus giving erroneous results : a silver capsule, weighing 600 
 grains when cold, appeared to weigh less by seven-tenths of a 
 grain when heated by a spirit lamp, and again placed in the 
 scale. If it had previously contained ten grains of a sub- 
 stance, to be subjected to such a temperature, a loss of about 
 0.7 of a grain would have appeared to take place, when actu- 
 ally none might have occurred. Besides this probable fallacy, 
 the introduction of a hot substance or vessel into the pan is 
 liable to affect the arm of the beam above, if delicately con- 
 structed, and cause derangement for the time merely by its 
 expansion. 
 
 59. Although, when the balance is in perfect order, it is 
 indifferent which pan receives the substance and which the 
 weights, it is advantageous always to use the same pan for the 
 same purpose. Attention to this custom is a correction to a 
 certain extent for inequality in the length of the arms ; for 
 though in the latter case a difference must exist between the 
 weight and its counterpoise to produce equilibrium, yet this 
 difference is constant, and quantities increased or diminished 
 in equal proportions will equally balance each other, so long 
 as the contents of the pans are not changed. If then the 
 weights are always put into one pan, the quantities weighed 
 in the other will be in the same proportion as the weights, 
 though not exactly equal to them ; and the products of an 
 analysis estimated thus would be as accurately known as if 
 the balance had been perfect. But if, on the contrary, the 
 products were put first into one pan and then into the other. 
 
38 WEIGHING OF POWDERS ON GLASS OR PAPER. [Sect. II. 
 
 they would sometimes be over-rated, and sometimes under- 
 rated, and the differences would very soon, by accumulation, 
 be irreferable either to the weights or each other. 
 
 60. Attention will be required in practising this rule in cases 
 where frequent alterations in weight are taking place. Suppose 
 carbonate of lime, in a crucible, had been weighed in the 
 substance pan by weights in the weight pan ; if it were heated 
 violently it would become quick-lime, and lose in weight, but 
 this loss could not be ascertained correctly by returning the 
 crucible and lime into the same pan it was in before, and then 
 adding weights to make up the deficiency, but must be done 
 by removing weights from the weight pan ; and if a second 
 alteration were effected in the weight, as by converting the 
 lime into a hydrate or sulphate, that must also be estimated by 
 weights added to the weight pan, no weights ever being mingled 
 in the same pan with the substance, but every change in the 
 weight of the substance being estimated in the one pan by a 
 corresponding change of weight in the other. 
 
 61. When weighing powders, or moderately divided matter, 
 it is better not to lay them at once on the pan, but upon some 
 interposed substance. For this purpose, two slips or pieces 
 of glass, or two watch glasses, of equal weight, should be used, 
 one in the weight scale, and one in the substance scale. They 
 are easily preserved clean, and possess the advantage of gene- 
 rally resisting chemical action, and permitting the substance 
 to be washed off them without injury. Or, in place of two 
 pieces of glass, one piece, or a little Wedgewood's basin 
 counterpoised, will answer the purpose. But two pieces of 
 paper are generally more convenient, and there are few sub- 
 stances which may not be weighed upon them. Hot-pressed 
 wove paper is the best ; its smooth surface preventing adhesion 
 even of the finest powders. It should not be torn, but cut, 
 for the fragmented edge would retain a portion of the powder 
 when passing over it; its form is given and its adjustment 
 easily made by a pair of scissors. Its flexibility is very con- 
 venient in assisting to convey powders into a flask, or other 
 narrow-mouthed or small vessel. All these advantages are 
 obtained by the use of a material, which has, in addition, those 
 of being very cheap and clean, and the few cases in which it 
 
Sect. II.] USE OF SPATULAS IN WEIGHING. 39 
 
 is objectionable, as where the substance to be weighed is moist 
 or deliquescent, are easily distinguished, and its insufficiency 
 may then be supplied by the use of glass or metal. 
 
 62. In transferring small quantities of powder from place 
 to place, as for example into and out of the balance, and 
 adjusting them, spatulas are very useful, and one of platina, 
 for this and other purposes, is requisite in every laboratory. 
 It may be about half an inch wide, at least three inches long, 
 and so thick as to resist considerable force without bending ; 
 otherwise it will not be the generally serviceable instrument it 
 ought to prove. For those who are inclined to indulge in the 
 luxuries of chemistry, a pocket knife, with a platinum blade, 
 is a very excellent tool, answering many of the purposes of the 
 spatula above described. With reference to the removal of 
 powders, ivory and bone spatulas answer the purpose well; 
 but in case of the absence of all these, their place at the balance 
 may be supplied by a slip of the same hot-pressed wove writing- 
 paper before mentioned, cut from the sheet with scissors. In 
 effecting the ultimate adjustment of the quantity, the smallest 
 portions may be taken by it from the heap in the scale, and by 
 a slight lateral shake, the smallest quantity may be dropped 
 from it into the pan : copper and platinum foil do not make 
 good temporary spatulas, unless bent down the middle, for 
 they are apt to give way between the fingers, and by their 
 elasticity to scatter the substance. 
 
 63. It is not necessary in weighing out given quantities of 
 powder, 100 grains for instance, to bring the balance to rest 
 every time a little of the substance is added or removed, in- 
 asmuch as by a short practice both may be done without com- 
 municating any other impulse to the instrument than that 
 resulting from the alteration of weight, 
 
 64. In using the balance, the operation very often consists 
 merely in counterpoising, no estimate of the quantity being 
 required, but simply an accurate and temporary weight cor- 
 responding to that of the substance or vessel. Platina cru- 
 cibles, capsules, glass tubes, &c., either alone or with their 
 contents, very frequently require to have their weights thus 
 compensated ; for counterpoises should be considered as weights, 
 and go into the weight scale. If but a small one be required, 
 
40 COUNTERPOISING WEIGHTS USEFUL. [Sect. II. 
 
 a slip of tin foil, leaf lead, or even of paper or card, will answer 
 the purpose very well, the piece being trimmed down by scis- 
 sors till it balances the object in the other pan. If a larger 
 one is wanted, a piece of plumbers 1 sheet lead is convenient, 
 and may be accurately adjusted by a pocket knife. Besides 
 sheet lead, shot of different sizes (39), are often used for this 
 purpose, being poured into the weight pan until there is nearly 
 sufficient to balance the contents of the opposite scale, and the 
 final adjustment made by a piece of lead, or tin foil, or paper. 
 When shot are not at hand, the counterpoise may be nearly 
 made up by large weights, and adjusted as before by metal 
 foil. Where the whole consists of many parts, it is desirable 
 that they should be preserved compactly together, lest any 
 portion be dispersed, and inaccuracy introduced. The hollow 
 weights (37) are for this reason very useful in counterpoising ; 
 the largest weight that is not too heavy should be taken, and 
 the requisite addition placed within it. If such a convenience 
 be not present, then perhaps the best plan is to put a piece of 
 clean smooth paper (writing paper if ready) of a few inches 
 square, into the pan, in the first place, and add weights to 
 complete the counterpoise; the ultimate adjustment can be 
 made as before, or even upon the edge of the piece of paper ; 
 when that is done, enclose the loose portions of the counterpoise 
 in the piece of paper, wrapping all up safely together, again 
 see that it is accurate, and then set it aside in the drawer of 
 the balance, or in the place appointed for such things, until it 
 is required. In consequence of the change in weight of paper, 
 either by desiccation in a dry place, or the absorption of 
 moisture in a damp one, a counterpoise so wrapped up should 
 be kept in a place similar in dryness to that from whence the 
 paper came, and the chances of change are diminished as the 
 time is less during which it is necessary to be preserved. 
 When the mind is alive to this source of error, it is easily 
 avoided, by keeping paper for the purpose in the place where 
 counterpoises are kept, or by drying the paper and keeping 
 the counterpoises also in a dry state. 
 
 65. Sometimes vessels or substances are to be weighed which 
 will not conveniently rest in the pans without a little con- 
 trivance : tubes, if long, now and then interfere with the case 
 
Sect. II.] SUSPENSION FROM THE PANS. 41 
 
 containing the balance, and flasks are liable to roll over, 
 the loss of their contents. Tubes of moderate 
 length, such for instance as are used in the pro- 
 cesses of organic analysis, can often in these cases 
 be weighed by the use of a small loose loop or ring 
 of twine, which, being slipped over the suspending 
 wires of the balance pan, is to be raised nearly to 
 the top, and then by passing the tube through it, 
 the upper part will be supported, whilst the lower 
 end rests in the pan, the whole being in a position 
 approaching to the vertical. In this case it is ne- 
 cessary that the loop and tube be arranged so that 
 the latter does not touch the beam, or in any way 
 interfere with the free suspension of the pan supporting it. 
 
 Such a loop is also very convenient in supporting flasks in 
 the balance, for being allowed to descend upon the suspending 
 wires of the pan, it prevents the neck of the flask from passing 
 between them, and retains it in a position sufficiently vertical 
 to avoid the loss of any of its contents. 
 
 66. Many balances, in order to facilitate their various uses, 
 have a hook at the bottom of each pan : to this a thread or 
 wire is readily attached, and being terminated beneath in one 
 or more loops, is easily made to sustain a tube or other article 
 to be weighed, which from its inconvenient shape will not lie 
 safely in the pan itself. 
 
 67. When it is required to weigh liquids, they must of 
 course be retained in some convenient vessel, the weight of the 
 vessel being either known, or counterpoised, in the first place, 
 or ascertained by an after operation. Glasses, flasks, capsules, 
 and small tubes, are all useful in turn to retain fluids. The 
 glasses and capsules will stand readily in the pan, and the flask 
 may be supported as before mentioned (65) by the loop of 
 twine, or by being placed upon a small wooden ring about two 
 inches in diameter, and an inch wide, covered with list, which 
 serves as a temporary foot (68). The tubes will more fre- 
 quently be required to contain scarce fluids, or perhaps such 
 as have actually been formed in them during an experiment, 
 and will often require supporting. It is for this and for many 
 purposes of adjustment at the balance, convenient to have two 
 
42 SUPPORTING RINGS ADJUSTMENT OF FLUIDS. [Sect. II. 
 
 rings of good cork, about three quarters of an inch high, kept 
 with it, fitting loosely into each other, and having for the 
 internal diameter of the smaller, half an inch, and for the 
 external diameter of the larger, two inches. These will sup- 
 port most tubes in a more or less inclined position ; 
 and in any case where they will not answer the 
 purpose, a temporary stand is easily made out of a 
 cork, by piercing a hole through it with a rat-tail 
 rasp, of the proper size to receive the tube. 
 
 68. The listed rings referred to (67) are exceedingly 
 useful in the laboratory for the support of retorts, flasks, 
 globes, receivers, and all vessels of a circular form. They are 
 easily made out of a slip of thin pliant wood, or a piece of 
 sheet copper, the rough ring being covered by rolling list 
 round it. A number of them should be provided for labo- 
 ratory purposes, from two to six inches in diameter, and of 
 different heights. 
 
 69. Where a certain weight of fluid is wanted, its final ad- 
 justment is easily effected by several methods. If it be water 
 or alcohol, or a substance that does not act upon paper, it is 
 best to add a little over weight, and then to remove the excess 
 by bibulous paper. If a piece of filtering paper be folded up 
 several times in the same direction it will form a loose rod, 
 the end of which being dipped into the fluid, rapidly imbibes 
 a quantity by its porosity and capillary attraction : when it 
 has arisen about an inch in the paper, which it will do instantly, 
 if the moist piece be pulled off and the fresh end again im- 
 mersed, a second portion will be taken. Upon pulling off the 
 moist end, especially if done by a hard pinch extending slightly 
 over the dry part above, a ragged extremity is left, which by 
 a little management in dipping the paper into the fluid ob- 
 liquely, may have a pointed form given to it. This may be 
 used in removing either large or small quantities, and is very 
 convenient for the final adjustment of the weight : by allowing 
 only a few of the filaments which remain to enter the fluid, the 
 latter passes up slowly, and its quantity may be judged of by 
 the gradual progress of the moisture above ; so that with very 
 little trial the precise quantity required may be removed. 
 Such at least is the case with water and most aqueous solutions. 
 
Sect. II.] ADJUSTMENT OF FLUIDS BY ROD BY TUBE. 43 
 
 With alcohol, fixed and volatile oils, it is not so, because the 
 imbibed part does not separate with particular facility from 
 the dry portion, or leave the useful filamentous edge spoken 
 of. The final adjustment is here, however, easily made by a 
 slip of paper folded once or twice, or by other means to be 
 described. 
 
 70. There is no difficulty in the rough adjustment of any 
 fluid ; for even when corrosive, the larger portions may be 
 removed by dipping into it a small capsule, or a spatula : in 
 these cases the final adjustment may be completed by taking 
 up the small remaining excess by means of a glass rod. Upon 
 dipping a rod into a fluid and withdrawing it rapidly, as much 
 as would be contained in three or four drops may be readily 
 and neatly removed ; the rod being cleaned, more may be 
 taken away by the same process : as the quantity removed is 
 proportionate in some measure to the moistened surface of the 
 rod, it is evident that by using one which is conical at the end, 
 the smallest desired quantity may be taken up at once, and the 
 adjustment accurately effected. 
 
 71. One other mode of adjustment it may be well to men- 
 tion, leaving the many varieties which may be conveniently 
 devised as occasion may offer, for spontaneous suggestion. It 
 is sometimes necessary to weigh out a certain portion of a fluid, 
 which, from being a new product or the result of a peculiar 
 experiment, and small in quantity, will not admit of the 
 slightest waste. A tube about the eighth or tenth of an inch 
 in diameter, drawn out to a capillary termination, is then very 
 convenient. If its fine extremity be immersed in the fluid, 
 
 which we will consider as in excess in the balance, capil- 
 lary attraction causes a portion of it to enter the tube ; if 
 enough be not removed, by inclining the tube, more will 
 enter in consequence of the diminished perpendicular 
 height of that within ; if too much be removed by the 
 second insertion, an elevation of the tube into a position 
 more perpendicular will cause the passage of a portion 
 from it into the vessel ; and in this way more or less 
 may be taken away and accurate adjustment obtained. 
 Should the fluid be tardy in its motion within, from the 
 dry ness of the interior or smallness of the lower aperture, it 
 
44 WEIGHING SUBSTANCES WHICH CHANGE IN AIR. [Sect. II. 
 
 may be helped while passing in or out, by applying the mouth 
 of the operator to the upper orifice ; but this should be avoided 
 generally, lest any portion of moisture be introduced. When 
 it is necessary to lay the tube down, it may be placed in a 
 position nearly horizontal across a glass or ring (68) , or any 
 ready support, the lower small extremity being out of contact 
 with any other substance. When the operation is finished, 
 the quantity which ultimately remains upon the tip of the tube, 
 the only part that has at any time been immersed, is so small 
 as to be no object, and this is the whole of the waste incurred. 
 The portion remaining within the capillary tube is to be re- 
 stored to what is left of the original quantity. 
 
 72. Peculiar management is required in estimating the 
 weight of certain substances which rapidly undergo change, 
 and are hence liable to alterations in weight during the time 
 occupied in the performance of the operation. Suppose, for 
 instance, it were necessary to weigh some hydrate of chlorine 
 obtained by compressing the moist crystals produced at tem- 
 peratures below 40, within folds of cold bibulous paper ; or 
 that the weight of hydrated chloride of calcium in crystals, 
 and dried in the same manner, by compression, were required ; 
 the first would evaporate in the air, and not only injure the 
 balance and neighbouring bodies, but also lose weight; and 
 the latter, by deliquescing, would gain weight ; both with such 
 rapidity as entirely to prevent the attainment of accuracy. 
 These effects will be completely avoided by transferring them, 
 not to the pan of the balance, but to a portion of water of 
 known weight, and ascertaining the increase of weight so occa- 
 sioned. In such a case, therefore, weigh or counterpoise a 
 portion of water in a test glass or basin, and then, the crystals 
 being prepared and dried by compression, transfer them 
 rapidly to the water, and ascertain their quantity by the in- 
 crease of weight; then proceed with the analysis or experi- 
 ment, using the solution in place of the crystals. It is evident 
 that an expedient of this kind has its limits, consisting in the 
 nature of the experiment to be made, and the action of the 
 water on the substances ; but it is often very valuable, and 
 now and then removes a difficulty which could not otherwise 
 be surmounted. The choice of the substance which is to re- 
 
Sect. II.] WEIGHING INDETERMINATE QUANTITIES. 45 
 
 ceive the changeable body must depend upon circumstances, 
 and sometimes alcohol, sometimes water, and sometimes an acid, 
 alkaline, or neutral solution, is to be preferred. 
 
 73. It may here be observed, that as in many experiments 
 one quantity is equally convenient with another, so that it be 
 accurately known, we have the advantage in such cases of 
 avoiding any trouble dependant upon adjusting accurately the 
 quantity of matter, and obtain the same end by adjusting the 
 weights, the matter itself being left undisturbed. Thus if it 
 were wished to know how much chloride of silver would be 
 furnished by a given weight of crystalline hydrated chloride of 
 calcium, 76.43, or any other number of grains, would answer 
 the purpose as well as an accurate hundred, and the facility of 
 immersing the body in water as above described is obtained. 
 The particular cases where an opportunity of this kind, de- 
 pendant upon the adjustment of the substance or the weight 
 at pleasure, can be taken advantage of, must depend upon the 
 judgment of the experimenter. 
 
 74. Similarly changeable products, the weights of which 
 are required, are frequently produced in vessels, and especially 
 in tube operations. In such cases the method will be to coun- 
 terpoise or weigh the vessel and its contents, then to remove 
 the substance, and, cleaning the vessel, to ascertain the loss of 
 weight ; that being the weight of the substance. Wherever 
 such a course is necessary, the use of vessels that may be 
 cleaned without injury or change is evidently needful : hence 
 a great advantage of tubes and vessels of glass, or platinum 
 crucibles and capsules. 
 
 75. Substances which fume, and which may in consequence 
 cause injury to the balance, should be weighed in close vessels. 
 Of such kind are some of the acids, ammonia, and numerous 
 mixtures. 
 
 76. Small capillary tubes, made by drawing out a piece of 
 thin quill glass tube at the blowpipe, as hereafter to be de- 
 scribed (Sect, xx), are exceedingly convenient for the esti- 
 mation of minute quantities of valuable liquid products, or 
 
 moderately but not excessively volatile 
 substances, such as ether, &c. : the tube 
 may be of the general form of that depicted in the woodcut, and 
 
46 MODE OF WEIGHING VOLATILE FLUIDS. [Sect. II. 
 
 of the same size or larger, as may be convenient ; having been 
 counterpoised, it is to be charged with the fluid to be weighed, 
 by dipping into it the smaller extremity, and inclining the 
 tube. When a sufficient quantity has entered by capillary 
 attraction, the tube is to be withdrawn, the small portion of 
 external moistened surface wiped, and the whole weighed, 
 care being taken that the end does not touch any substance, 
 for then the fluid may be drawn out. In this way the quantity 
 can be accurately ascertained, and then, that the experiment 
 may include all weighed, it will be found of advantage if the 
 tube, being of no consequence to the result, may be thrown 
 with its contents into the solvent, or added directly to the sub- 
 stance upon which the action is to take place : the tube itself 
 being broken up and disregarded. 
 
 77. Sometimes it is desirable hermetically to close one end or 
 even both ends of the tube charged as above ; this is easily 
 
 done by having it of the annexed form, 
 the capillary termination being rather 
 wider than the part a little above it. In this case, when the 
 tube is filled as far as is desirable, by inclining or inverting it, 
 the surface in the narrow part will leave the extremity, and 
 this being introduced for a moment into the flame of a spirit 
 lamp, will be effectually sealed ; this done, the fluid is to a 
 great degree secured and rendered stationary in the tube, and, 
 if required, it is easy, by approaching the other end to a spirit 
 lamp, to soften the glass, draw it out, and seal it, in the man- 
 ner to be shewn hereafter. 
 
 78. Where in place of any particular weight, merely an 
 equal, double, or triple quantity of one substance is wanted to 
 be added to another, a convenient quantity of the one most 
 worthy of consideration may be put into one pan, and counter- 
 balanced once, twice, or thrice, by the other. In mixing dry 
 substances, or in making analyses with reference to the kind 
 rather than the weight of bodies present, this comparative 
 mode of estimation is frequently useful. 
 
 79. In most processes of weighing, the buoyancy of the air 
 is overlooked, and though, in consequence of the very superior 
 density of solid and fluid matter generally, as compared to the 
 atmosphere around us, errors thus introduced are usually 
 
Sect. II.] SPECIFIC GRAVITY OF A SOLID. 47 
 
 unimportant, yet the chemist should be aware of its influence, 
 and alive to its possible interference. From the mariner in 
 which gases are usually weighed, the error does not then exist, 
 but it is sometimes more considerable than would be expected 
 in experiments made with substances, at one time in the gase- 
 ous state, and at another in the liquid or solid form. The 
 production of water, for instance, from the combination of 
 oxygen and hydrogen, is an important experiment, and has 
 been often repeated ; the weight of the water should accurately 
 correspond with the weights of the gases combined. The 
 weights of the gases are in the usual method correctly ascer- 
 tained, but the weight of the water estimated in the usual 
 way is diminished by the buoyancy of the air, which in this 
 case amounting to about -g^th part, would introduce an error 
 to that extent, were this effect not to be taken into account. 
 
 80. The determination of specific gravity is of constant 
 occurrence with the chemist, and though it resembles the 
 general operation of weighing, there are peculiarities connected 
 with it which require attention. It is not intended here to go 
 into a consideration of the general process, but, leaving that to 
 be obtained from elementary works, only to notice those 
 things which occasionally give rise to errors, or are necessary 
 to correct results. If the substance be a solid, the well-known 
 process of weighing it first in air and then in water, and 
 dividing the first weight by the loss in the second, is to be 
 followed; and though here again minute errors are intro- 
 duced in consequence of the buoyancy of the air in the first 
 weighing, they are not of a nature to require attention in this 
 place. 
 
 81. Balances are expressly furnished with contrivances to 
 facilitate the immersion of the body in water, when required, 
 so that its weight may be ascertained in that position. The 
 substance which passes the surface of the water, supporting 
 the immersed body and connecting it with the scale beam, is 
 generally a horse hair, and for common purposes, it is perhaps 
 the best. When, however, a hydrostatic balance is not at 
 hand, and an ordinary balance is to be used for the purpose, 
 the suspending link has frequently to be selected from several 
 substitutes which present themselves in the laboratory. It 
 
48 SPECIFIC GRAVITY SUSPENDING LINE. [Sect, II. 
 
 should not be penetrable or alterable by the water ; it should 
 not be thick ; it should not be weak. If it be the first, as a 
 piece of thread for instance, the quantity of water in it under- 
 goes continual variation in consequence of the difference of 
 immersion as the balance vibrates, and thus a change of weight 
 is occasioned in that which ought to be constant. If it be the 
 second, as a piece of string, it introduces errors of two kinds, 
 one dependent on the buoyant power of the water over the 
 part which is sometimes immersed and sometimes not, and 
 which if the same point were not always brought to the sur- 
 face of the water would act upon it, as it would upon the stem 
 of the hydrometer (103) ; the other dependant upon the 
 capillary attraction of the water, which, within certain limits, 
 would cause a larger elevation of the fluid round the string 
 when thick, than if it were small, and add a proportionate 
 weight to it. If it were the third, it would present an obstacle 
 to the correction of the faults last mentioned, inasmuch as it 
 would not admit of being made thin for want of strength. 
 
 82. These errors become serious when they affect a small 
 body, a gem for instance, and in such cases, or wherever the 
 weight will admit of its application, a filament of unspun silk 
 is probably the best substance that can be used. It is unaf- 
 fected by the water ; has scarcely any weight, or any buoy- 
 ancy given to it by immersion in the fluid, so minute is its 
 bulk ; it does not cause any sensible elevation of fluid round it 
 where it cuts the surface of the liquid, and retains no air- 
 bubbles. It has but little strength in consequence of excessive 
 tenuity, and therefore must not be pulled hastily or subjected 
 to sudden snatches. 
 
 83. When a silk fibre will not answer the purpose, or can- 
 not be obtained, a fine wire will very conveniently supply its 
 place ; and it is only in cases of necessity that recourse should 
 be had to thread, fine twine, or any substance made up of 
 numerous fibres. But if some of the latter must answer the 
 purpose, then silk thread is better than any other, because of 
 its strength ; and what is called thrown silk, which consists of 
 a few fibres .only, twisted together, is, when strong enough, 
 almost unobjectionable. In all these cases of substitution, 
 take that substance which, being of sufficient strength, is the 
 
Sect, II.] SPECIFIC GRAVITY IMMERSION IN WATER. 49 
 
 thinnest and most compact, and in all cases it is desirable that 
 the mass of which the specific gravity is to be taken should be 
 as large as the line will safely support ; for if a coarse sus- 
 pending thread be used in taking that of a small fragment, the 
 errors relating to the thread, which are several in number, 
 affect the result much more importantly than if the operation 
 had been performed upon a large piece. 
 
 84. There are several points relative to the immersion of 
 the body in the water, which require attention. The water 
 must be distilled for delicate experiments; but on ordinary 
 occasions, when that cannot be obtained, the lightest rain- 
 water may be substituted, or in common cases even well or 
 spring water of ascertained purity. Several wells are known, 
 amongst which are the deep ones of London, which supply 
 water as pure or purer than town rain-water. The temperature 
 of the water and the substance to be examined should be the 
 same, or otherwise currents will be produced, which to a slight 
 degree affect the results : indeed, all delicate experiments must 
 be made at one particular temperature, and 60 Fahrenheit is 
 very convenient for the purpose. A considerable difference of 
 temperature at different times prevents the results from being 
 comparable with each other. 
 
 85. The body, as well as the various contrivances for its 
 suspension, constructed by the instrument makers, such as 
 pincers, forceps, &c.. must of course be fully immersed in the 
 water. It should have at least half an inch of the fluid around 
 it in every direction, that perfect freedom of motion in the 
 balance may be obtained. All bubbles of air adhering to 
 it should be removed by a hair pencil. Water taken from 
 the bottom of any deep portion which has been exposed 
 to contact with the air for a length of time, will frequently 
 evolve bubbles, either spontaneously or upon the immersion of 
 a rough substance, in consequence of its relief from the pre- 
 viously superincumbent pressure. Spring- water drawn from 
 the bottom of a well will illustrate this effect, which is very 
 inconvenient when it happens with such water as is used for 
 taking specific gravities from the succession of bubbles pro- 
 duced. Exposure to the air for an hour or two, or pouring it 
 
 E 
 
50 OSCILLATION OF THE BALANCE. [Sect. II. 
 
 to and fro in a broken stream several times in the air, is a 
 remedy for the evil. 
 
 86. The oscillations of the balance, though much slower 
 than those which occur when the body is weighed in air, 
 should be quite free. Supposing the balance to be in good 
 order, and the body suspended with perfect liberty in the 
 water, neither touching any part of the vessel nor approaching 
 the surface, still serious obstructions may exist, especially when 
 the substance is small, the balance delicate, and the suspending 
 link thick. Suppose a horse-hair to be used for suspension, 
 which, from the manner in which it is wetted by the water, 
 causes a small depression on the surface of the fluid around it 
 as it descends, and a little elevation as it ascends. Such is a 
 very common effect, and is produced not only on the first 
 immersion and emersion of the hair, but is repeated at every 
 ascent and descent, within certain limits. It is evident that 
 this will very seriously retard the oscillations of a delicate 
 balance, and prevent its motion either one way or the other by 
 a force equal to the weight of the little elevation of water. 
 This may be partly corrected by tapping the vessel containing 
 the water, or the case of the balance, so as to occasion a slight 
 tremor. Whenever it happens, the equilibrium should not 
 be considered as obtained, unless the water have a plane surface 
 at the part where it surrounds the hair. 
 
 87. The substance used as a support always becomes wetted 
 by immersion in the water ; and in consequence of the extent 
 of oscillation, a portion of the wetted part is constantly out of 
 the water when the balance is poised. This affects the result 
 in two ways : first by the quantity of water which adheres to it, 
 and which varies in proportion as it has been immersed to a 
 greater or smaller depth, or as it is impervious to water like a 
 hair, or more or less porous like thread ; secondly, by the little 
 elevation of water which then exists round the line by capillary 
 attraction, and which is the same whether more or less of the 
 part above has been wetted. The weight of the water thus 
 raised above the surface is counterbalanced by an equal weight 
 in the opposite pan; thus an error to that extent is intro- 
 duced, which, though generally small, may, from ignorance, 
 
Sect. II.] SPECIFIC GRAVITY SUSPENDING LINE. 51 
 
 inattention, or the minute size of the piece operated with, at 
 times become important. 
 
 88. Although the suspending line may have been very accu- 
 rately compensated in the air, before the body to be immersed 
 in water was attached to it, yet when partly immersed during 
 the progress of the experiment, the counterpoise is no longer 
 its equivalent, the part immersed being buoyed up by a force 
 equal to the weight of the water which it displaces ; and this, 
 with a large horse-hair, or a still coarser line of suspension, 
 would be important. It may be estimated, as well also as the 
 effect of the little elevation of water before spoken of, after the 
 weighing has been finished, by removing the body, again 
 immersing the hair to the same depth as before, allowing it to 
 be wetted to the same degree, and seeing how much it differs 
 from its weight when freely suspended in a dry state in the 
 air. Balances which are fitted up with apparatus for hydro- 
 statical experiments have counterpoises for the suspending 
 parts, both when in and out of the water ; which might be 
 made perfectly accurate were the surface of the water always 
 brought to the same place upon the suspending line. 
 
 All these errors are lessened by diminution in the size of the 
 suspension line ; and when that is a silk filament, they almost 
 disappear. Hence the great use of this substance in delicate 
 experiments, as those made with small gems, minute globules 
 of metal, or other rare substances. 
 
 89. When the substance of which the specific gravity is to 
 be taken is soluble in water, some other fluid of known specific 
 gravity must be used, which does not dissolve it. There 
 are very few cases which may not be met by alcohol, oil of 
 turpentine, or olive oil. 
 
 90. Not unusually, the body to be examined is porous like 
 coke, or divided, as in sand or powders, into numerous parts. 
 In these cases, a beautiful instrument in principle has been 
 devised by M. Say*, in which soluble as well as insoluble 
 substances may be tried, provided they do not give off vapour ; 
 and the only precautions necessary are to prevent the existence 
 
 * Annales de Chimie, xxiii., p. 1 ; or Nicholson's Quart. Journ., vol. i., 
 p. 325. 
 
 2 
 
52 
 
 SAY'S INSTRUMENT FOtt POWDERS, ETC. [Sect. II. 
 
 of cavities unconnected with the air, and to destroy such 
 minute cellular structures as, like that of charcoal, have the 
 power of absorbing gases or vapours. It is proper, therefore, 
 to reduce the substance to solid fragments, by breaking it down 
 coarsely, or pulverizing it more or less in a mortar. 
 
 91. Mr. Leslie, who at a much later period thought he had 
 invented the instrument, published an account from which 
 the following description is taken. It consists of a glass tube, 
 a e, about three feet long, and open at both ends. The wide 
 part, a 6, is about 4-10ths of an inch in dia- 
 meter ; the part b e, 2-10ths. The two parts 
 communicate at 6 by an extremely fine slit, 
 
 which suffers air to 
 
 pass, 
 
 but retains sand or 
 
 powder. The mouth at a is ground smooth, 
 and can be shut so as to be air-tight, by a small 
 glass plate, f. The substance whose specific 
 gravity we wish to find (suppose it to be sand) 
 is put into the wide part of the tube, a 6, which 
 may either be filled to the top or not. The 
 tube being then held in a vertical position, has 
 the narrow part immersed in mercury, contained 
 in an open vessel, till the metal rises within to 
 the gorge 6. The lid is then fitted on air-tight, at a. In this 
 state it is evident there is no air in the tube, except that mixed 
 with the sand in the cavity a b. Suppose the barometer at the 
 time to stand at 30 inches, and that the tube is lifted perpen- 
 dicularly till the mercury stands in the inside of b e, at a point 
 c, 15 inches (or one half 30) above its surface in the open 
 vessel, it is evident then that the air in the inside of the tube 
 is subjected to a pressure of exactly half an atmosphere, and 
 of course it dilates, and fills precisely twice the space it origi- 
 nally occupied. It follows, too, that since the air is dilated to 
 twice its bulk, the cavity a b contains just half of what it did 
 at first ; and the cavity b c, now containing the other half, the 
 quantity of air in each of these parts of the tube is equal : 
 in other words, the quantity of air in b c is exactly equal to 
 what is mixed with the sand in a b, and occupies precisely the 
 same space which the whole occupied before its dilation. Let 
 us now suppose the sand to be taken out, and the same expert 
 
Sect. II.] 
 
 SPECIFIC 'GRAVITY OF FLUIDS. 53 
 
 ment repeated but with this difference, that the cavity a b is 
 filled with air only. It is obvious that the quantity being 
 greater, it will, when dilated to double the bulk under a pres- 
 sure of 15 inches, occupy a larger space, and the mercury will 
 rise, let us suppose only, to d. But the attenuated air in the 
 narrow tube always occupies exactly the space which the whole 
 occupied at ordinary atmospheric pressure ; and this space, 
 therefore, is in the one case b e, and in the other b d. Hence 
 it follows, that the cavity c d, which is the difference between 
 these, is equal to the bulk of the solid matter in the sand. 
 Now, by marking the number of grains of water held by the 
 narrow tube b e on a graduated scale attached to it, we can 
 find at once what is the weight of a quantity of water equal 
 in bulk to the solid matter in the sand, and by comparing 
 this with the weight of the sand, we have its true specific 
 gravity. 
 
 When this apparatus is not at hand, and the substance is in 
 small pieces, it must be supported in the usual way by a cup, 
 which is of course to be counterpoised first in air and then 
 in water, exactly as was described with the line or retaining 
 forceps before mentioned. 
 
 92. The specific gravity of fluids is ascertained by weighing 
 equal bulks of them at the balance, or by the immersion of 
 hydrometers or bulbs bodies which, by their floating or 
 sinking, indicate the comparative weights of the substances 
 into which they are introduced. Bottles are usually provided 
 by the instrument maker as measures of the bulk of fluid to be 
 weighed ; these are arranged to hold a given quantity of dis- 
 tilled water expressible by weight, in round numbers, as 1000, 
 800, 500, 280 grains, &c., and are closed by a ground stopper. 
 The ultimate adjustment is effected by removing portions 
 from the lower surface of the stopper, so that when the bottle 
 is filled with water, and the stopper put into its place, the 
 quantity which remains in, and entirely fills the bottle, is of 
 the bulk required. The stoppers, instead of being solid, are 
 sometimes made of a piece of thick thermometer tube of fine 
 bore, the intention being to afford a free passage for the excess 
 of fluid when the stopper is forced into its place. This answers 
 the purpose very well with water and less volatile fluids, though 
 
54 SPECIFIC GRAVITY BOTTLES. [Sect. II. 
 
 it is not necessary ; but with very volatile fluids, as alcohol, 
 ether, &c., it occasions an evil. It does not merely afford a 
 small surface for evaporation, but, in consequence of the 
 impossibility of grinding a stopper so accurately that when in 
 its place it shall not let a little of these limpid fluids pass, 
 actually accelerates the evaporation ; for the ether, for instance, 
 passing by capillary attraction between the stopper and the 
 bottle, evaporates round the edge, whilst the air enters in a 
 constant succession of bubbles by the centre passage, and thus 
 a rapid diminution in the bulk of the fluid takes place; 
 whereas if the bottle had been closed by a solid stopper, 
 although the minute ring of fluid round the top would evapo- 
 rate, no more would be able to rise, because air could not 
 enter to supply its place, and the bulk would be compara- 
 tively unchanged. 
 
 93. Specific gravity bottles are constructed of various sizes, 
 and are each accompanied by a weight, which counterpoises 
 the bottle full of distilled water, the quantity of water required 
 for the purpose having been ascertained and marked upon it. 
 All that is required in estimating the specific gravity of any 
 other fluid is, to fill the bottle with it, to ascertain its weight 
 by observing how much heavier or lighter it is than the weight 
 furnished with the instrument, and adding and subtracting 
 accordingly; the result, divided by the weight of water, 
 will be the specific gravity. It is necessary, in these experi- 
 ments, that the temperature be observed, or rather, indeed, 
 when convenient, that they be made at the same temperature, 
 or it will not be possible to compare them unless previously 
 corrected by calculation, which would in many cases be diffi- 
 cult. For the same reason it is requisite that the bottle should 
 not be handled by uncovered hands, lest heat be communicated 
 to it, and its bulk and the volume of the fluid within be 
 affected : but upon introducing the stopper, the overflow of 
 liquid should be wiped off with a clean cloth, which may be 
 used at the same time to prevent contact with the hands ; and 
 in transferring it to the balance, the fingers should be defended 
 in a similar way : or if this be difficult, from any particular 
 circumstance, they must not on any occasion touch more than 
 the thick rim of glass round the stopper. 
 
Sect. II.] VERIFICATION OF SPECIFIC GRAVITY BOTTLES. 55 
 
 94. It is further necessary that the bottle contain nothing 
 but the particular substance to be weighed. To insure this 
 point, it is requisite that it be washed out after every experi- 
 ment, the last two or three rinsings being made with distilled 
 water ; if it be then dried, nothing more remains to be done, 
 upon the performance of a new experiment, than to put in the 
 liquid and to weigh. But as it is inconvenient and unnecessary 
 at all times to dry the bottle, as when the specific gravity of 
 several solutions are to be taken in succession, it may, on such 
 occasions, be left moist within ; and then, at the next experi- 
 ment, if the substance to be operated with is abundant, and 
 one that mixes with water, as a mineral water, alcohol, or an 
 aqueous solution, all that is necessary is, that the bottle should 
 be rinsed with it two or three times before it be filled for 
 weighing. If it be a substance that is scarce, or oily, or that 
 will not mix with water, the bottle must be washed and dried. 
 
 95. Instruments procured from the maker should be verified 
 by the purchaser before they are used. For this purpose the 
 bottle and stopper should be well cleaned and dried, and, being 
 brought to the temperature of 62 Fahrenheit, should be coun- 
 terpoised. The bottle must next be carefully filled with pure 
 water at 62, and the increase of weight ascertained ; this is 
 the weight of the water, and should correspond with that 
 marked on the weight or the stopper : finally, the counterpoise 
 and water, weighed together, should exactly balance the weight 
 sent with the bottle. If the maker graduates the bottles at 
 any other temperature than 62, it is useless to expect an exact 
 accordance with estimates made at 6, but he should always 
 do it at a known and constant temperature, with which the 
 purchaser should be acquainted ; and that of 62 Fahrenheit 
 is for several reasons better than any other. 
 
 96. The directions given for the verification of a bottle 
 made purposely for the estimation of specific gravities of 
 liquids, will easily enable a person to supply its want. He has 
 but to select a small well- stoppered phial of convenient capacity, 
 to clean, dry, and weigh it, and then to ascertain, as before, 
 how much water it will hold ; the weight of this water will be 
 a divisor, and the weight of any other fluid filling it, a 
 dividend ; the quotient will be the specific gravity of the latter 
 fluid. 
 
SPECIFIC GRAVITY BULBS. [Sect. II. 
 
 97. Small bulbs blown out of glass 
 tube, or even small thermometer bulbs, 
 like those figured in the margin, are often 
 useful in estimating the specific gravity 
 of rare fluid products. The little bulb 
 represented in the tube is easily made, as 
 is hereafter to be shown (1198) ; and 
 having been counterpoised and furnished 
 with a temporary handle, by coiling a 
 piece of platina wire round it, may be 
 warmed by a spirit lamp, and then dipped 
 into the fluid in the tube ; as it cools, a portion will enter; upon 
 removing, rewarming, and reimmersing it, a second portion 
 may be introduced by the same mode of proceeding ; a small 
 bubble of air will ultimately remain within, but this may be 
 expelled by warming the fluid in the tube with the bulb im- 
 mersed in the state in which it is represented in the engraving ; 
 the liquid will expand by the heat, and force out a part, of the 
 air ; then by immersing the bottom of the tube in water to 
 lower the temperature as contraction takes place, the fluid will 
 enter the bulb. A second or third performance of the heating 
 and cooling process will effectually fill the vessel with liquid. 
 
 98. The filling of bulbs in this manner is very often required 
 in certain trains of research, and amongst others in organic 
 analysis. Hence it is necessary to point out one or two cir- 
 cumstances requiring attention in the operation. When the 
 bulb is about four-fifths full, and the attempt is made to fill 
 it by applying heat whilst it is immersed in the liquid, it will 
 perhaps be found that the bubble of air expands and contracts 
 as its temperature changes, but does not go out of the vessel ; 
 the fluid which enters remaining, by capillary attraction, in the 
 narrower part of the top, and consequently passing out 
 again upon the re-elevation of temperature. But in 
 such a case it is necessary, before the heat is applied, 
 to make this portion of the fluid and the air change 
 places, which is easily done : for this purpose the tube, 
 with its contents, should be held by the upper part, 
 and suffered to hang as it were below the hand ; a 
 swing of a foot or two in extent should then be given to it, so 
 
Sec 1 . II.] BULBS FILLED FLUIDS HEATED IN TUBES. 57 
 
 as to produce centrifugal force; all the fluid will descend 
 except that which is contained in the narrowest part of the 
 neck, and the air will take its place ; the tube and bulb should 
 then be heated to expel more air, and fresh fluid suffered to 
 enter, which is to be treated in the same way if required. If 
 anything renders it inexpedient to subject the whole tube to 
 this motion, the bulb can be withdrawn, and being held by the 
 wire or in the hand, can then be shaken in the same way and 
 with the same effect. 
 
 99- In the next place the fluid may be 
 volatile, and subject to waste by repeated 
 elevations of temperature in an open tube ; 
 but in such circumstances it is easy to close 
 the tube effectually by the fore finger of the 
 left hand, whilst the thumb and second finger 
 are occupied in holding it (919) : the heating 
 and cooling are then to be performed without 
 allowing the end to be unclosed, and no 
 waste is occasioned. 
 
 100. This point of manipulation will require a little prac- 
 tice to allow of all the advantage being derived from it which 
 it is capable of affording in other operations ; but when required, 
 a volatile fluid, ether for example, may be heated until its 
 vapour has a force of two or even three atmospheres, if the 
 tube be strong enough, and be retained there for a quarter of 
 an hour, or more, without any loss. The portion of common 
 air in the tube is to be allowed to escape or not, according to 
 circumstances (919), and may be made use of at times, as will 
 be found by practice, to prevent the accession of heat to the 
 fingers. 
 
 101. Returning to the fluid with which the bulb has been 
 filled : upon removing the latter when cold, allow its exterior 
 to drain as much as possible ; the wire must then be taken off, 
 the surface wiped, and the bulb put upon a cork stand (67), 
 and weighed. As the vessel will then be required full of water, 
 it must be emptied of the fluid. Replace the wire handle, 
 invert the bulb, holding its aperture within the mouth of the 
 tube to which its contents are to be restored, and apply a 
 little heat ; a part of the liquid will be forced out, or indeed 
 
58 SPECIFIC GRAVITY BULBS DRIED. [Sect. II. 
 
 the whole if it be volatile ; if not, on cooling, a bubble of air 
 will enter, and a second and third application of heat will dis- 
 place the whole of the contents. On introducing a portion of 
 water and displacing it, and repeating this two or three times, 
 the bulb will be sufficiently cleansed, may then be filled en- 
 tirely with water, and weighed when cold as before. The 
 weights of equal bulks of the fluid and water are now known, 
 and the specific gravity readily obtained by calculation. 
 
 10S. Although the process has been described in this order, 
 it is generally better, after weighing the bulb, to introduce the 
 water and obtain its weight first, and then that of the peculiar 
 fluid ; for if an accident happens in the water experiment, and 
 the bulb is destroyed, it does not involve a repetition of the 
 process with the valuable liquid. Further, it is easy at all 
 times to free the bulb from the water of the first part of the 
 process, but not always so to dissipate the remains of peculiar 
 substances which may be decomposable by heat or not soluble 
 in water. The bulb may be emptied of water by first throw- 
 ing out the larger part as already described, then heating it 
 over the flame of a spirit lamp, or in hot air, to convert the 
 rest of the moisture into vapour, and either retaining it there 
 some time, or, if that be inconvenient, allowing it to cool, that 
 the vapour may condense and the air enter. A second appli- 
 cation of heat, at the same time that it converts the remaining 
 water into steam, throws out a portion with the expelled air ; 
 being cooled and again heated a few times, the bulb is soon 
 effectually dried. The process may be expedited by cooling 
 a part near the mouth first, which is easily done by touching 
 it with a cold substance (1356), and causing the principal con- 
 densation of moisture there, and then also heating the same 
 part first ; in this way the air carries out the water in fewer 
 operations, but these facilities are only to be learned and 
 appreciated by practice. In all exposures of the bulb to heat, 
 in experiments relating to specific gravity, especial care must 
 be taken that the heat is not such as to soften the glass 
 after one of the fluids has been weighed, for in that case 
 the form and size of the vessel will be altered, the process 
 must be recommenced, and the previous trouble will be utterly 
 useless. 
 
Sect. II.] HYDROMETER CIRCUMSTANCES AFFECTING IT. 59 
 
 103. The specific gravity of fluids is frequently 
 ascertained by the hydrometer, a well-known instru- 
 ment, which is of great service where hasty estimates 
 of only moderate accuracy are required ; but it will 
 not give correct or even uniformly incorrect results 
 without attention. The stem being the part which 
 cuts the surface of the liquid, resembles in that respect 
 the suspending link used in taking the specific gravity 
 of solids (87, Sec.), and is liable to be affected in a 
 similar way, but in many cases to a much greater 
 extent, because of its necessary thickness* If its sur- 
 face does not moisten freely with the fluid in which it 
 floats, it will be found easy, upon trial, to make the hydrometer 
 stand two or three degrees, or more, higher or lower in the 
 same liquid ; and when the hydrometer does readily become 
 wetted, and has even had the stem purposely moistened, the 
 same effect may be produced, and that not in fluids particularly 
 viscid, but in water and aqueous solutions : hence a source 
 of irregularity in the indications of the instrument, which must 
 be avoided as much as possible. For this purpose, keep the 
 hydrometer perfectly clean, and free from any unctuous or 
 greasy matter which might be the consequence of handling it. 
 When put into the fluid it should be allowed to sink gradually 
 till at rest, and then be depressed about an inch lower, which 
 will give it an ascending power, and moisten a certain portion 
 of the stem; the jar containing the fluid is to be tapped to 
 cause vibration, and the instrument allowed again to take a 
 state of rest, when its position should be observed. The instru- 
 ment should then be raised about half an inch out of the fluid, 
 and, tapping the jar as before, suffered to sink slowly, and 
 observed whether it takes the same position it occupied at first ; 
 if it does, the observation is as correct in this respect as it 
 can be. 
 
 104. If the fluid be viscid, the liability of inaccuracy in this 
 instrument is increased, both by the difficulty with which it 
 sinks or rises to the point to which its mere weight would carry 
 it, and also by the greater quantity which adheres to the part 
 of the stem that, having been immersed, is afterwards raised 
 above the surface. If the fluid be turbid, it is not the gravity 
 
60 HYDROMETER ITS INDICATIONS. [Sect. II. 
 
 of the suspending fluid itself that is obtained,, but of the liquid 
 so laden with other matter. . Some precipitates will be days, 
 and even weeks, before they will settle from the fluid in which 
 they are formed, and yet are so heavy as very materially to 
 increase the specific gravity of the whole ; and M. P. S. Girard 
 has stated*, that a peculiar molecular attraction exists between 
 such particles in the fluid as to buoy up the hydrometer by a 
 force, not merely equal to the increased weight, but considerably 
 surpassing it. Brewers and other persons frequently require 
 the specific gravity of a mixture of solid and fluid matter 
 their object being, by the buoyance of the hydrometer, to esti- 
 mate the former as well as the latter ; but if the effect here 
 noticed exists, a source of error is introduced of which 
 they take no account, unless, indeed, their instruments be 
 graduated by experiment with fluids similar to those they 
 wish afterwards to examine. It is probably, however, so 
 small, as to be of no importance in their comparatively rough 
 estimates. 
 
 105. In all experiments made with the hydrometer, an ascent 
 of the fluid will take place round the stem, producing the 
 elevation before mentioned (87). This occasions a curve in 
 the surface, and some persons read off the graduation on the 
 stem, where it coincides with the middle of this curve others 
 at the top, and others again at the bottom. It is necessary, 
 for the sake of consistent observations, always to read off from 
 the same part of the curve ; and if the instrument has been 
 graduated by experiment, the divisions being made with re- 
 ference to the part of the curve from which they are afterwards 
 to be read, it will so far be correct. As the force which causes 
 the elevation tends to depress the instrument in the fluid, 
 observations made at the bottom of the curve will be nearer 
 to the truth than those made at the top. But the curve itself 
 varies, not merely in size, because of differences in the weight 
 or specific gravity of the fluid, but in weight also, because of 
 differences in the cohesive attraction of different fluids. 
 
 106. Amongst other points relative to the state of the fluid, 
 temperature should not be forgotten ; constancy in this respect 
 
 . * On Liquid Atmospheres and their Influence on the Solid Particles they en- 
 velop. Memoires de I'Acaclemie Royale, iv., 1819, 1820. 
 
Sect. II.] HYDROMETER OBSERVED VERIFIED. 61 
 
 being as important as in experiments made with the bottle. 
 (9395.) 
 
 107. The hydrometer, when first procured, should be veri- 
 fied by trial in solutions of which the specific gravity has been 
 ascertained by the bottle. It is not necessary to make many 
 trials of this kind, its verification being more readily effected 
 in the following manner. First, ascertain with two fluids of 
 different specific gravities, that one indication towards each 
 end of the scale is correct. Then, suspending the hydrometer 
 from the pan on one side of a balance, let it descend into a 
 solution as light, or lighter than any to be measured on the 
 scale, but buoying it up by weights in the other pan, so that 
 the surface of the fluids shall cut the scale at the lower part. 
 Make equal additions of weight in succession to the pan from 
 which the hydrometer is suspended, and observe the descent 
 each time: if they are equal, as read off on the scale, then the 
 divisions are equal in bulk, and the graduation is correct ; if 
 unequal, the graduation is incorrect, and would not correspond 
 with the results obtained by the specific gravity bottle. The 
 more numerous the points thus observed, that is, the smaller 
 the weight added each time, the more accurate and close is 
 the trial*. 
 
 108. A solid glass ball, or bulbs of glass, are frequently used 
 for ascertaining the specific gravity of fluids. If a ball of 
 glass suspended from the balance be wholly immersed in a 
 liquid, it will be buoyed up by a force equal to the weight of 
 the liquid it displaces, and seem to lose weight to that amount. 
 By being immersed, therefore, in succession into different 
 liquids, the weights of equal volumes are thus obtained, for 
 the ball measures out the volume each time, and the specific 
 gravities are then known. The precautions here required are 
 the same as those belonging to the experiments on the specific 
 gravity of solid bodies. (8188.) 
 
 109. Sometimes several hollow bulbs of different specific 
 gravities are used ; those which are too heavy sinking, and 
 those which are too light floating. The proper strength _of 
 some solutions evaporated in the large way is thus estimated. 
 
 * See Moore on the Graduation of the Hydrometer ; Dublin Philosophical 
 Journal. 
 
62 SPECIFIC GRAVITY BULBS. [Sect. II. 
 
 Sea- water, for instance, in salt-works, is concentrated by expo- 
 sure to air, until it has such a specific gravity, that, of two 
 previously-arranged glass bulbs, one will sink and the other 
 swim. Their use in chemical research is rare ; but an excellent 
 instance of the delicacy with which the principle may in some 
 cases be applied, as also a specimen of useful manipulation, 
 may be found in Mr. Crichton's paper on the maximum den- 
 sity of water *. 
 
 110. Another instance of the application of similar bulbs to 
 the determination of specific gravity, when no other means 
 were available, occurs with respect to the liquids produced by 
 the condensation of gases f. The bulbs used were very small, 
 and made as hereafter to be described (1199). Their specific 
 gravities were ascertained by putting them into different solu- 
 tions of known specific gravity, and the bulbs thus prepared 
 were introduced into the vessels in which the gases were to 
 be liberated or condensed. When surrounded by the fluid, 
 its density was in some degree judged of by the sinking or 
 swimming of the included bulb, and then by successive trials 
 with heavier or lighter bulbs, more accurately ascertained. 
 
 111. Substitutes for a balance, though not often required, 
 are, in particular situations, very valuable, and there are few 
 philosophic travellers who have not felt this want. Mr. Bevan 
 recommends for this purpose a strung bow J, which, if not at 
 hand, may generally be made out of a piece of whalebone, a 
 stick, or other substance, and which, being suspended by the 
 middle of the bow, is to have the body to be weighed attached 
 to the middle of the string. The flexure occasioned by it is 
 to be observed, which will best be done by marking the point 
 to which that part of the string from which the body hangs, 
 descends : then removing the substance and replacing it by 
 weights, sufficient are to be used to cause the same flexure, 
 and thus the weight of the substance will be obtained. An 
 elastic beam, stick, or other body, firmly fixed at one end, 
 and loaded at the other with the substance and the weights in 
 succession, will answer the same purpose ; and the means of 
 
 * Annals of Philosophy, New Series, v. 40 1 . 
 
 f Philosophical Transactions, 1823, p. 191. 
 
 I Technical Repository, vi, 196. 
 
Sect. II.] BLACK'S DELICATE BALANCE. 63 
 
 making a temporary scale-pan, to receive the substance and 
 the weights, and a graduation to measure its descent, are so 
 simple and evident as not to require description. 
 
 112. The following account of a very delicate and easily 
 constructed balance is from a letter written by Dr. Black to 
 Mr. Smithson *, and is a valuable piece of information to those 
 who, having occasion for, are deprived of the use of, a good 
 balance. ' The apparatus I use for weighing small globules 
 of metal, or the like, is as follows: a thin piece of fir- wood, 
 not thicker than a shilling, and a foot long, 0.3 of an inch 
 broad in the middle, and 0.15 of an inch at each end, is 
 divided by transverse lines into 20 parts, that is, 10 parts on 
 each side of the middle. These are the principal divisions, 
 and each of them is subdivided into halves and quarters. 
 Across the middle is fixed one of the smallest needles I could 
 procure, to serve as an axis, and it is fitted in its place by 
 means of a little sealing-wax. The numeration of the divi- 
 sions is from the middle to each end of the beam. The ful- 
 crum is a bit of brass plate, the middle of which lies flat on 
 my table when I use the balance, and the two ends are bent up 
 to a right angle so as to stand upright. These two ends are 
 ground at the same time on a flat hone, that the extreme sur- 
 faces of them may be in the same plane ; and their distance is 
 such that the needle, when laid across them, rests on them at a 
 small distance from the sides of the beam. They rise above 
 the surface of the table only 1J or 2-lOths of an inch, so that 
 
 the beam is very limited in its play. The weights I use are 
 one globule of gold which weighs one grain, and two or three 
 others which weigh one-tenth of a grain each; and also a 
 number of small rings of fine brass wire, made in the manner 
 first mentioned by Mr. Lewis, by appending a weight to the 
 wire, and coiling it with the tension of that weight round a 
 thicker brass wire in a close spiral, after which the extremity 
 of the spiral being tied hard with waxed thread, I put the 
 covered wire in a vice, and applying a sharp knife, which is 
 
 * Annals of Pnilosophy, New Series, x, 52. 
 
64 RITCHIE'S BALANCE. [Sect. II. 
 
 struck with a hammer, I cut through a great number of the 
 coils at one stroke, and find them as exactly equal to one 
 another as can be desired. Those I use happen to be the 
 one- thirtieth part of a grain each, or 300 of them weigh 10 
 grains, but I have others much lighter. 
 
 6 You will perceive that, by means of these weights placed 
 on different parts of the beam, I can learn the weight of any 
 little mass, from one grain or a little more to the T ^ 7 of a 
 grain. For if the thing to be weighed weighs one grain, it 
 will, when placed on one extremity of the beam, counterpoise 
 the large gold weight at the other extremity ; if it weigh half 
 a grain, it will counterpoise the heavy gold weight placed at 
 5 ; if it weigh 0.6 of a grain, you must place the heavy 
 gold weight at 5, and one of the lighter ones at the extremity 
 to counterpoise it ; and if it weighs only one, or two, or three, 
 or four hundred ths of a grain, it will be counterpoised by one 
 of the small gold weights placed at? the first, or second, or 
 third, or fourth division ; if, on the contrary, it weigh one 
 grain and a fraction, it will be counterpoised by the heavy 
 gold weight at the extremity, and one or more of the lighter 
 ones placed on some other part of the beam. 
 
 e This beam has served me hitherto for every purpose ; but 
 had I occasion for a more delicate one, I could make it easily 
 by taking a much thinner and lighter slip of wood, and grinding 
 the needle to give it an edge. It would also be easy to make 
 it carry small scales of paper for particular purposes;' the 
 fulcrum being then placed on a stool or any other support that 
 is horizontal, raised, and narrow. 
 
 113. Mr. Ritchie has also contrived a very cheap and deli- 
 cate balance. It consists of a slender beam of wood, about 18 
 or 4 inches long, tapering a little from the middle to each 
 end. A fulcrum of tempered steel, resembling the blade of a 
 penknife, is made to pass through the middle of the beam a 
 little above the centre of gravity. Similar steel blades are 
 also made to pass through the ends of the beam for suspending 
 the scales. The fulcrum rests on two small portions of ther- 
 mometer tube, fixed horizontally on an upright wooden sup- 
 port, held firmly by a foot ; the support has a slit passing along 
 the middle, to allow the indicating needle attached to the beam 
 
Sect. II.] WEIGHING WITH INACCURATE BALANCES. 65 
 
 beneath the centre of gravity to play freely between the sides. 
 A small scale made of card, and divided into any number of 
 equal parts, is placed on the support for the purpose of ascer- 
 taining the point at which the needle becomes stationary. 
 This balance, Mr. Ritchie says, possesses extreme delicacy, 
 and may be made even more sensible than that belonging to 
 the Royal Society of London. 
 
 The equality of the two ends is not a necessary consider- 
 ation, according to the method of double weighing referred to 
 before, and invented by Borda. To weigh with the balance, 
 let the body be placed in one of the scales, and bring the indi- 
 cating needle to any point by small shot placed in the other 
 scale, remove the body and replace it by as many known weights 
 as will bring the needle to the former position. These weights 
 give the weight of the body*. 
 
 114. In weighing with these balances, or generally with 
 such as are a little out of order, the weights should be ap- 
 plied and ascertained on the same side with the substance, 
 that irregularities of action may be avoided as much as pos- 
 sible. Thus, the substance to be weighed should be put into 
 one pan, and counterpoised by any convenient thing, as sand, 
 in the other ; after which, removing the substance, its place 
 is to be supplied by weights, until an exactly equal effect is 
 produced, when of course the amount of the weights used 
 will be the weight of the substance. Or if a given quantity be 
 wanted, first counterpoise the weight, and afterwards replace 
 it by the substance to be weighed. Inequality in the arms is 
 thus compensated. 
 
 115. Substitutes for weights, should they ever be required, 
 may be made by means of a balance in one or two ways. 
 Pieces of metal or other convenient substances may be adjusted 
 to have equal, double, triple, or any other proportion of weight, 
 to a standard piece, and, being used as weights at the time, 
 will give proportionate results ; or if results comparable with 
 other weights are required, their value may be estimated by 
 actual comparison at a future convenient opportunity. Such 
 regular weights, of considerable accuracy, are easily obtained, 
 by cutting off equal or given lengths of a copper wire, the 
 
 * Brewster's Journal, v. 118. 
 
 F 
 
66 LABORATORY MEASURES. [Sect. Ill- 
 
 wire being of such thickness that at least half an inch in length 
 may be allowed for the smallest weight : its uniform thickness 
 should be ascertained by trying the first and the last weight 
 cut off against each other. Occasionally the products obtained 
 from experiments may be balanced by pieces of lead, which 
 are to be weighed when an opportunity occurs, and the results 
 numerically estimated. 
 
 116. A method of making small weights has been already 
 described in Dr. Black's letter (112), but Mr. Smithson finds 
 it preferable, first to ascertain the weight of a certain length 
 of wire, and then to take that portion of it which may suffice 
 for the weight wanted. If fine wire is employed, a set of small 
 weights may be thus made with great accuracy and ease. 
 Inconvenience from the length of the wire in the higher 
 weights is obviated by rolling it round a cylindrical body into 
 a ring, and twisting this to a cord*. 
 
 117. The following relative table of different weights will be 
 frequently used in the laboratory. 
 
 Grains. 
 
 Pound avoirdupoise 7000 
 
 Ounce avoirdupoise 437.5 
 
 Pound troy 5760 
 
 Ounce troy 480 
 
 Gramme 15.4063 
 
 Decigramme 1.5406 
 
 Centigramme 0.1540 
 
 Milligramme 0.0154 
 
 SECTION III. 
 MEASURES MEASURING. 
 
 118. ORDINARY laboratory service requires no other measures 
 than such as are fitted to ascertain the bulk of liquids or gases. 
 Hence two integers are abundantly sufficient, the pint and the 
 cubic inch. The pint measures may be such as are furnished 
 in commerce, either conical, cylindrical, or of any other form, 
 * Annals of Philosophy, New Series, x, 53. 
 
Sect. III.] MEASURES GRADUATIONS. 67 
 
 and of glass, and graduated : but they should always be verified 
 before they are permitted to pass into use. Where the same 
 measure is used for large as well as small quantities, those which 
 are conical have an advantage in the smaller divisions over 
 such as are cylindrical, the surfaces of small quantities being 
 less, and consequently the bulks more accurately determined ; 
 but it is better to have two or three measures of different sizes, 
 varying in diameter, for different quantities. The wine pint 
 measure has been usually divided into sixteen parts, each being 
 called a fluid ounce, and liquids were frequently measured by 
 these ounce volumes, which in such bulk weighed more or less 
 than an ounce. The standard or imperial pint now to be used is 
 larger than the wine pint, in the ratio of 6 : 5 (154) . It is to be 
 divided into twenty parts, to be called fluid ounces ; these will 
 not be the same exactly with the former fluid ounces, but will 
 have the great advantage, when estimated with distilled water, 
 of weighing an exact ounce avoirdupoise. The measure should 
 be graduated in two places on opposite sides, that when the 
 volume of a fluid is to be determined, its surface may, 
 for greater accuracy, be observed by both graduations. 
 A pint, a half pint, and a quarter pint measure, of 
 the form and relative dimensions as to height and 
 diameter of the one figured in the wood-cut, should be 
 
 in the laboratory. It is also useful to have a gradu- 
 
 ation on the vessels in cubic inches, this being done on 
 both sides at equal distances from the former gradu- 
 ations. 
 
 119. These measures should be graduated according to the 
 late parliamentary standard, by which the pint is ascertained 
 to consist of 8750 grains of water at 62 Fahrenheit, barometer 
 at 30 inches ; and the cubic inch of 252.458 grains of water, 
 at the same temperature and pressure. They are verified by 
 being counterpoised (64), and having these quantities of water, 
 or their multiples, or divisions, weighed into them, and the 
 coincidence of the surface of the liquid and its corresponding 
 mark noted. If they do not agree, a slight scratch should be 
 made with a diamond or file, at the place where the mark 
 ought to be (132). 
 
 120. Preparatory to the use of these vessels, one particular 
 
 F2 
 
63 ESTIMATION OF BULK GLOBULAR MEASURES. [Sect. III. 
 
 place upon a table or shelf should be selected, which is fiat, 
 firm, and should generally be kept clear of other things for 
 this purpose alone. The measure, when placed upon it, should 
 stand steady and perfectly upright. In the verification, it 
 will be necessary to observe, that when the measure containing 
 the weighed quantity of water is placed in this situation, the 
 surface of the fluid should coincide both with the graduation 
 on the near, and also on the farther side : this is best seen by 
 bringing the eye to a level with the surface ; and still further 
 security is gained as to the right position of the measure, if 
 the water stand at equal heights on the lateral graduations of 
 the denomination not immediately in use. In measuring at 
 any future time, similar precautions should be observed, and 
 these will require attention the more imperatively, if from any 
 circumstance one particular spot is not selected, as above ad- 
 vised, but, on the contrary, any part of the table used. 
 
 121. With liquids which moisten the glass, an elevation of 
 the fluid round its surface in contact with the vessel will take 
 place. The measurement, except in minute vessels, will be 
 most accurately made, if taken from the general surface of the 
 fluid, and not from the middle or top of the elevation (769) ; 
 but it is essentially necessary that it be always made in the 
 same way as that adopted in the verification of the measures. 
 With mercury there will be a depression round the glass instead 
 of an elevation, except in particular circumstances. It is here 
 again most correct to make the estimate from the general 
 surface of the fluid. 
 
 122. When very accurate measurement is desirable, as in 
 the analysis of a mineral water, it is better to perform it in a 
 
 globular vessel having a glass neck, and of such ca- 
 pacity as to be filled partly up the neck by a weighed 
 pint or half pint of water at 62 ; the exact place 
 being then marked with a diamond or file. So little 
 surface is left at the place where the bulk is estimated, 
 that scarcely any variation can occur in that respect ; 
 and if the measurements be made at a constant temperature, 
 they are very accurate. Two such measures, a pint and a 
 half-pint, will be sufficient. Small quantities are generally 
 more accurately determined by weight than by measure. 
 
Sect. III.] CUBIC INCH MEASURES THEIR VARIETY. 
 
 69 
 
 123. Three jugs, of half a pint, a pint, and a quart, \vill be 
 found of great service for ordinary use. 
 
 124. The cubic inch, with its divisions and multiples, is 
 used both for liquids and gases. For exclusive liquid use, 
 the cubic inch graduation on the vessels already mentioned, 
 will suffice ; those to be described, will serve generally for both 
 forms of matter. 
 
 125. Bottles are sold by the instrument makers, which con- 
 
 tain an exact cubic inch when the stopper is 
 put into its place. Tubes also of similar capa- 
 city, and supplied with a ground stopper, are 
 manufactured with a graduation on the side, 
 by which the subdivision is carried to tenths 
 and twentieths, and even farther if necessary. 
 Whether these are in the laboratory or not, 
 there should be, at all events, a few jars and 
 tubes accurately graduated into cubic inches, 
 tenths, and hundredths; one jar may be about 
 
 two inches in diameter and six inches hio-h : 
 
 & * 
 
 another about an inch in diameter, and of the 
 same height; a third, which will be almost a 
 tube, half an inch in diameter, and eight or 
 nine inches long ; and a fourth of the same 
 length, but still smaller. These should be 
 moderately thick, so as, when filled with mercury, to bear the 
 weight of that metal, and sustain laboratory use, without great 
 risk of breaking : they should be ground at the ends, so as to 
 be closed accurately by a flat piece of glass (1348). It will be 
 sufficient that the smaller vessels be graduated on one side only, 
 but it is better that, when the diameter is an inch and a half or 
 more, they should be graduated upon opposite sides, for the pur- 
 pose of observing more accurately, as before explained (120). 
 
 126. All these measures should be verified by weighing 
 into them successive portions of water or mercury. A cubic 
 inch of water at 62 weighs, as before mentioned, 252.458 grains, 
 and a cubic inch of mercury at the same temperature 3425.35 
 grains*. Water is very convenient for the estimation down 
 
 * This assumes the specific gravity of mercury as 13 .568, which is what I find 
 pure mercury to possess at 62 Fahrenheit. Sir H. Davy makes it heavier. Of 
 
70 GRADUATION OF VESSELS OF TUBES. [Sect. III. 
 
 to the cubic inch, and some divisions below it ; but for the 
 tenths, and especially the hundredths, mercury is far more 
 exact and expeditious. 
 
 127. It is frequently necessary to graduate vessels, and 
 especially tubes, in the laboratory. The general method of 
 doing this will be easily understood from what has been said 
 with regard to the verification of measures bought of the 
 maker ; but there are some facilities in the practice which will 
 require description. Tubes are generally in use for the mea- 
 surement of gas at the mercurial trough, and should be several 
 in number, and of different diameters, to afford opportunity 
 for a graduation more or less minute. The laboratory is but 
 poorly stocked that has not a dozen of them. They should 
 not be less than the one-fifteenth of an inch in thickness when 
 of a diameter smaller than half an inch, and thicker if wider. 
 The closed ends should be of equal thickness with the sides, 
 and should be round, not pointed. 
 
 128. The marks on vessels graduated by the instrument- 
 maker are cut by the glass-grinder's wheel, but in the labora- 
 tory they are made with simpler instruments. A gun-flint is 
 convenient for scratching on the surface of glass. Fragments 
 of diamond are also set in handles for the same purpose ; they 
 are not intended to cut, but merely to abrade or roughen the 
 surface, and are called scratching or writing diamonds (974). 
 Small three-square files, about half an inch wide on each side, 
 are so useful in the laboratory for marking on convex surfaces 
 of glass or for cutting tubes (1152), that they cannot be dis- 
 pensed with. 
 
 129- Having selected the tube, first draw a line upon it 
 from top to bottom. This is easily done by laying the tube 
 upon the table, against the edge of a flat slip of wood or a ruler, 
 and drawing either the flint or scratching diamond down it 
 where it rests against the ruler, bearing as it were into the 
 angle formed by the ruler and the surface of the tube. The 
 line should not be broad and rough, but regular, neat, and 
 straight. The tube is now to be balanced by a counterpoise 
 (64), and is then ready to receive the successive portions of 
 
 course any metal likely to enter as impurity into mercury would render it 
 lighter. 
 
Sect. III.] GRADUATION OF A TUBE BY WEIGHING. 
 
 mercury, by which equal given volumes are to be measured out, 
 and to have them marked off by small lines across the long one 
 first drawn. Suppose the hundredths of a cubical inch are to 
 be marked down, the tube being about 2-10ths of an inch 
 internal diameter : 34.25 grains of mercury, which at 62 
 Fahrenheit are equal in bulk to the one-hundredth of a cubical 
 inch, are to be weighed into it ; the tube is to be marked at 
 the level of the mercury, another 34.25 grains of metal is to be 
 weighed in, and its place marked on the scale, and the opera- 
 tion so carried on until the graduation is finished. 
 
 130. But easy as this is in description, it is otherwise in 
 practice, without the aid of certain facilities. If the mercury 
 be added without care, either too much or too little will be in- 
 troduced; and when the adjustment is nearly complete, scarcely 
 little enough can be given or taken away, owing to the density 
 and cohesion of the metal. Prepare, therefore, a tube like the 
 
 one represented in the drawing (1181), 
 about half an inch in diameter, four 
 inches long, cut level at one end, so as 
 to be closed by the finger if required, and drawn off laterally 
 to a capillary opening at the other. If mercury be poured into 
 such a tube, it will not flow out at the capillary opening whilst 
 the position is such as in the figure, and this is easily given to 
 it on the table by resting it on a list ring (68). But when 
 elevated sufficiently, the pressure of the column of metal will 
 cause it to flow out, and either in a continuous stream or in 
 minute successive drops, according to the degree of inclination : 
 a still greater command over the flow of metal is obtained by 
 applying the finger to the upper extremity, and thus relieving 
 the metal from the pressure of the atmosphere upon its upper 
 surface to a greater or smaller degree, as may be required. It 
 it is easy in this way to supply more or less of the metal at 
 pleasure. 
 
 131. When therefore 34.25 grains of mercury are wanted 
 in the tube, place the latter in one pan, and weight amounting 
 to 34.25 grains in the other ; then, introducing the capillary 
 extremity of the mercury feeding-tube into the mouth of the 
 balanced tube, allow metal to flow in, moderating its addition 
 as the balance approaches equilibrium, ultimately adding it 
 
72 ADJUSTMENT MARKING ON GLASS. [Sect. III. 
 
 only in minute drops. In this way the weight required is 
 nearly attained in a very short time. Have it rather a little 
 over than under weight, and, relinquishing the feeding vessel, 
 proceed to adjust the portion in the tube to be graduated. 
 For this purpose, close its aperture with the fore finger of the 
 right hand, invert the tube and its contents, which will of 
 course cause the mercury to rest partly on the finger, and then, 
 by slightly relaxing the finger, let a little drop squeeze out 
 beneath the edge of the glass into the palm of the left hand, 
 where it is to be preserved. Restore the tube to its right po- 
 sition, and place it in the balance; if too heavy, put the first 
 drop of mercury out of the hand as useless, and take a second 
 drop from the tube as before. In this way it will ultimately 
 be obtained too light, but only by a part of the minute drop in 
 the hand. Break this drop into several spherules by pressing 
 upon it with the finger, and take one, two, three, or more of 
 them into the tube, by pressing the edge of the glass against 
 the palm just beneath the drops, when they will roll in; ob- 
 serving each time whether the mercury in the tube balances 
 the weight. In this way accurate adjustment may be obtained 
 in a portion of time not exceeding a fourth part of that re- 
 quired to read this description. 
 
 132. The next object is to mark the volume occupied by 
 the mercury, that being exactly the one-hundredth of a cubical 
 inch. The mark will be best made with a three-square or flat 
 file ; and it will be found much easier to commence it from 
 the cross line running up and down the tube, than from an 
 unbroken surface. To make a fair mark requires a steady 
 pressure on the file, and then motion to a slight extent. The 
 feel will indicate whether a mark has been made, but the 
 learner should practise first on a piece of waste glass tube, 
 commencing both from an unabraded surface and from a cross 
 line ; and by making a mere spot, or marking a line of half 
 an inch in length. He will in this way learn in half an hour 
 to appreciate, by the feel, the kind and the extent of mark he 
 makes. He should also practise marking upon any desired 
 spot. For this purpose the tube should be held in the left 
 hand, with the thumb close upon the spot to be marked ; then 
 placing the edge of the file upon the particular place, and 
 
Sect. III.] 
 
 MARKING ON THE GLASS AND TUBE. 
 
 73 
 
 supporting the pressure at the same time by the thumb at its 
 side, the slightest possible motion, sufficient to break the sur- 
 face, should be given. If the commencement be exactly in the 
 right place, there is no difficulty in continuing it,, the file, 
 when its motion is renewed, catching the previously roughened 
 part; if the commencement be in the wrong place, another 
 trial must be made: the practice of making the mark where 
 desired will soon be acquired. 
 
 133. This point attained, the next thing to be done is to 
 mark the tube so as to record permanently the volume occu- 
 pied by the mercury. For this purpose it must be placed in 
 a steady upright position ; and though this may be effected 
 sufficiently well with very small tubes by holding them firmly 
 in the hand, yet it is an incorrect method with larger ones. 
 Choose therefore a flat place on the wall, in a convenient situa- 
 tion, and at the height of the eye. From a line level with the 
 eye, and about two or three inches downward, and for a width 
 of five or six inches, blacken the wall, 
 either by pigment or attaching a piece of 
 black paper to it. Then firmly fix a piece 
 of wood planed smooth and true, about 
 the third of an inch thick, an inch wide, 
 and six inches in length, to the wall in an 
 upright position, across the middle of the 
 blackened part, so that half its length 
 shall be on the white part above. Two 
 upright re-entering angles are in this way produced, against 
 which the tubes may be firmly held, and the necessary position 
 thus effectually obtained. The black and white surfaces be- 
 hind will each be found advantageous in turn, for showing the 
 coincidence of the surface of the mercury with any particular 
 part of the glass, according to the light and other circum- 
 stances ; and by shifting the tube a little up or down, the part 
 where the mercury stands may be placed on one or the other 
 at pleasure, and yet the eye be brought to the same horizontal 
 line with it without any difficulty. By this means the position 
 of the tube, of whatever size it may be less than an inch, is 
 securely obtained, use being made of the angle on either side 
 of the lath. An advantage sometimes results from using a 
 
74 FACILITIES IN MARKING THE TUBE. [Sect. III. 
 
 piece of lath planed obliquely, so as to be thicker at one edge 
 than the other ; large tubes being applied to the deep angle on 
 one side, and small tubes to the shallower angle on the other. 
 Sometimes an angle previously existing on the walls of the 
 laboratory, as that formed by a bead, may be used for these 
 purposes. 
 
 134. The tube when held in the angle may easily be marked 
 as before mentioned, by laying the three-square file horizon- 
 tally across it upon the perpendicular line previously drawn, 
 and abrading the surface by a little motion and pressure. 
 The first mark is merely to be a slight extension of the rough 
 surface on the side of the line ; a mere spot, which, if wrong, 
 may be neglected, and another made ; if right, may afterwards 
 be lengthened into a line. There is no necessity for retaining 
 the tube against the wall whilst the division is being fully 
 marked; if the commencement be correct, the tube may be 
 taken down, and the line completed in any other position that 
 may be convenient. 
 
 135. But there is yet another point to be considered before 
 we can proceed thus far. Mercury, when contained in glass 
 vessels, is, in consequence of its cohesive attraction, depressed 
 at that part of its surface where it verges towards the sides of 
 the vessel ; the place of contact with the glass is thus rendered 
 lower than the general surface, and consequently a small space 
 beneath that level remains unfilled by the metal. Hence a 
 mark made to correspond with that surface would include a 
 space in the vessel rather larger than that occupied by the 
 metal; and though in wide vessels or tubes the error thus 
 introduced is minute, it is not so in tubes of small diameter, 
 and frequently amounts to one of the divisions marked upon 
 them. When to this is added the consideration that the con- 
 vexity of the mercury, in graduating a tube, is the reverse of 
 that which occurs when using the same tube over mercury 
 to measure gas (798), it is evident that always reading off 
 from the top or bottom of the curve would but increase the 
 errors in this case ; and that with small quantities of gas, and 
 in delicate experiments, they would become very serious. To 
 these may be added another circumstance, which complicates 
 the errors still further, namely, that when the tubes are used 
 
Sect. III.] SURFACE OF MERCURY OBSERVED. 75 
 
 with or over water, the convexity is the reverse of that with 
 mercury, and the correction required consequently of a con- 
 trary kind. 
 
 136. With reference to the process of graduation, the diffi- 
 culty thus introduced may be avoided by using mercury which 
 is not quite clean, but which, from containing a little of some 
 other metal, as tin, lead, &c., has a film formed upon its sur- 
 face. The mercury of the pneumatic trough, if in much use, 
 is generally of this kind, or a small quantity can be readily 
 made so for the purpose, by adding one grain of lead to four 
 or five thousand grains of the fluid metal, that quantity being 
 quite sufficient. When such mercury is put into a tube, a 
 slight tremor given to it extends the film and allows the 
 metal to flow beneath, so as to acquire a flat surface instead of 
 a round one, and then the volume may be accurately marked 
 off by a line upon the glass coinciding with that surface (138). 
 Care is to be taken that the mercury used be not excessively 
 foul, or so dusty as to throw up a thick coat of film to its 
 surface, since no indication of volume belonging to a given 
 weight of mercury would then be obtained. 
 
 137. No further difficulty will now arise in the way of 
 graduating a tube. The 34.25 grains of mercury are to be 
 weighed in, the tube is to be placed against the wall, slightly 
 shaken to produce a level surface, and then a division is to be 
 marked by the file. Another 34.25 grains of mercury are to 
 be weighed into the tube to the metal already contained in it, 
 and the volume is to be marked as before ; third, fourth, and 
 fifth divisions are to be obtained in the same way, and thus a 
 scale will be gradually produced. 
 
 138. By degrees the tube, if large, will contain so much 
 mercury as to be too heavy for the balance. But it is then 
 easy to use a smaller vessel to weigh the metal in, transferring 
 the mercury from that into the tube each time, and graduating 
 as before. One advantage of thus weighing the measuring 
 portions of metal in a separate vessel is, that water may be 
 introduced into the tube under graduation. This facilitates 
 the production of the level surface required on the mercury, 
 and sometimes assists in marking down the graduations by the 
 particular appearance of the -tube : but as dirty mercury froths 
 
76 ESTIMATION OF LARGE DEGREES. [Sect. III. 
 
 more readily in water than in air, the operator should be aware 
 of any error in bulk that might arise from this cause : and a 
 little time should also be allowed before a mark is made, that 
 the water may pass to the surface from between the glass and 
 the metal, and the mercury attain its level. No quantity of 
 water that is worth consideration will remain adhering to the 
 glass after it has stood a few seconds. 
 
 139- There is another mode of obtaining the successive 
 portions of mercury ; it is by measuring instead of weighing, 
 yet with such accuracy as to be unobjectionable, and is as 
 follows. Procure a piece of glass tube, of such diameter that 
 the division required shall occupy in it from half an inch to an 
 inch in length ; for hundredths it may be one-sixth of an inch 
 internal diameter, and for tenths, about one-third of an inch ; 
 draw out one extremity at the lamp table, so as to 
 give it the form in the figure (1181), the lower end 
 being a capillary continuation, from which mercury 
 will flow out in a small stream, by the pressure of 
 half an inch of metal above. Close the lower ex- 
 tremity by introducing the tip into the flame of a 
 "' V spirit lamp, so that the sealed part may afterwards 
 
 I be cut off without removing more than the one- 
 
 sixteenth or one-eighth of an inch. Counterpoise the tube. 
 Now weigh into it (if for hundredths) 34.25 grains of mer- 
 cury, or if for tenths, 342.53 grains ; and when the weight is 
 accurately adjusted, observe whether the metal be continuous 
 throughout ; if not, make it so. The only thing which will in- 
 terfere with this continuity is the occurrence of a bubble or two 
 of air about b (see the figure). These are easily removed by 
 introducing a horse hair or thin platina wire down between the 
 glass and the mercury, until it reaches the bubble, the air of 
 which will immediately pass up by the hair or wire. The air 
 which is sure to remain in the capillary part may be removed 
 in the same manner as low as a, but it is better that a small 
 but constant portion should remain between the bottom of 
 the mercury and the sealed part. The next thing to be done 
 is to mark the tube at the surface of the mercury, and by 
 weighing in two, three, four, or more portions, each of 34.25 
 grains, and marking off their heights, an accurate graduation 
 
Sect. III.] GRADUATION FACILITIES OF MEASUREMENT. 77 
 
 will be produced. Now by the scratching of a file, and then a 
 little lateral force as directed in glass-blowing (1152), cut off 
 the sealed capillary end about half way below a, and thus open 
 that extremity. 
 
 140. The measure is now complete, and all that is further 
 requisite is the mode of using it. Suppose mercury, equal to 
 one or more divisions, were required; pour some of the metal 
 into the measure above its highest division, at the same time 
 closing its capillary opening by bearing a finger slightly 
 against it ; then shutting the top by the fore finger, allow the 
 mercury to run out at the capillary termination (130), until 
 its upper surface coincides with the uppermost line. Now 
 stop the stream by inclining the measure ; until, having directed 
 the jet into the tube to be graduated, any mercury that after- 
 ward passes out may be received by it. Again relieve the 
 finger above, so that the metal may fall as before, passing 
 through the extremity into the lower tube; and when the level 
 in the measure again coincides with a division, it will be known 
 that the hundredth of a cubic inch has gone from it into the 
 tube to be graduated. Prevent the passage of more mercury 
 by inclining the measure ; mark off the portion already trans- 
 ferred ; then add a second hundredth in the same way, and 
 proceed in this manner to any extent required. When once a 
 measure of this kind is made, it is exceedingly convenient and 
 ready in its use, and, being of sufficient length, will readily 
 serve to estimate tenths as well as hundredths. 
 
 141. One other mode of measuring the mercury in these 
 cases of graduation it will be necessary to mention,, because it 
 is common, and at times has peculiar advantages. It consists 
 in forming a tube which, when closed with the finger, shall 
 hold exactly the quantity of mercury required. The use of 
 such a tube requires a little practice, for when the diameter is 
 more than the third of an inch, variations in the pressure of 
 the finger upon its open end, or the use of the finger or thumb 
 indifferently, cause sensible variations in the quantity con- 
 tained. By practice such uniformity is obtained, however, as 
 not to involve any important error. 
 
 142. These measures are best made in the following man- 
 ner: select a piece of tube sealed at one end, with a rounded 
 
78 MEASURES FOR GRADUATION. 
 
 [Sect. III. 
 
 termination, and which shall be competent to hold about twice 
 the bulk desired ; counterpoise it, and then weigh in the 
 mercury corresponding to the volume required. Mark this 
 volume, and, pouring the mercury into another tube or dish, 
 cut off the measure (1152) as near as may be to the mark ; 
 leaving it, if not exact, rather larger than is required. Draw 
 out a few thick threads of cement (1123, 1125), or make a 
 thin roll of wax, and, having poured the mercury back into the 
 intended measure, put upon it a piece or two of the cement or 
 wax, and, covering it with the finger, depress it into the fluid 
 metal, and observe whether there be sufficient to fill the tube 
 or not } the wax or cement is to be increased or diminished in 
 bulk, until with the mercury it exactly fills the tube when 
 closed by the finger: and this adjustment is to be made over 
 a Wedgewood's basin, that any particles of mercury thrown 
 out during the trial may be readily returned to the tube, and 
 prevent alteration of the original quantity. When this ad- 
 justment of the wax has been obtained, pour out the mercury, 
 drop the wax to the bottom of the tube, warm the latter so as 
 to melt the wax, and then allowing it to cool, the measure is 
 completed ; but for greater security, verify it by ascertaining 
 that it does measure out the right weight of mercury. 
 
 143. It is not necessary in every case to weigh out mercury 
 for each division on the graduation ; for when the divisions 
 are small, as on a comparatively large tube, it can frequently 
 be effected as accurately, or more so by the unassisted eye, as 
 by measurement with mercury. Thus, for instance, if a tube 
 of one- fourth of an inch in diameter were to be graduated into 
 tenths and hundredths of a cubical inch, and by measuring 
 every four hundredths by some of the preceding methods, the 
 resulting divisions were found to be as. nearly as possible equal 
 in length, and consequently the tube uniform ; then the single 
 hundredths may, by very little practice, be marked off by the 
 eye alone more accurately than by any other method usually 
 adopted in the laboratory, and sufficiently so for the most re- 
 fined experiments. The object is of course to divide the space 
 of four hundredths, first into two of two hundredths, and each 
 of these into two of one hundredth. This is best done, not by 
 holding the tube vertically against the wall, but laying it hori- 
 
Sect. III.] GRADUATION PRECAUTIONS. 79 
 
 zontally upon the table on a surface of uniform colour ; and 
 the division should first be made by dots as before mentioned 
 (132), and their uniform and accurate distance acknowledged 
 by the eye before the lines which are to form the scale are 
 marked. Very little experience will show the value and ra- 
 pidity of this method, which, in the hands of a careful person, 
 may be extended to the division of a space into 5, 6, 8, 10, or 
 even more parts. 
 
 144. Where the mercury is measured into the tube to be 
 graduated, every five or ten portions put in should be trans- 
 ferred to the balance and weighed, to ascertain their correct 
 accordance with the quantity marked on the graduation. 
 Thus supposing the measuring tube before described (139) 
 to be in use, when twenty divisions have been transferred from 
 it, the operator should ascertain that the mercury in the tube 
 to be graduated actually amounts to twenty times 34.25 grains, 
 and when forty divisions have been put in, that 1370 grains of 
 mercury are there. 
 
 All these experiments relative to the weighing and mea- 
 suring of mercury should be made on a tray, or over the 
 mercury table (12). 
 
 145. In marking the divisions, every fifth and tenth should 
 be distinguished from the others, for the purpose of ready 
 observation ; the fifths by a little extra length, and the tenths 
 by being marked on both sides the upright line, as indicating 
 larger divisions. 
 
 146. In eudiometrical and other experiments with small 
 quantities of gas, very small divisions are required, and some- 
 times other parts than those of the tenths or hundredths of a 
 cubical inch are, from their size, useful. In these cases it is 
 far better to take other subdivisions of the cubical inch than 
 to have an independent standard, and through it introduce 
 complexity into the laboratory measures. If hundredths are 
 not small enough, divide them into two hundredths, or five 
 hundredths, or thousandths ; or if hundredths are too small, 
 count two of them as one part, which may easily be done upon 
 the tubes graduated as already described ; and indeed every 
 other division may be distinguished by a little additional mark 
 opposite to it on the other side of the perpendicular line. 
 
80 GRADUATION TESTS OF ACCURACY. [Sect. III. 
 
 147. In graduating tubes for eudiometry or any other pur- 
 pose, Dr. Henry has long been in the habit of using a con- 
 trivance which renders the operation greatly quicker, and 
 insures perfect accuracy. It consists of a tube open at both 
 ends, and not more than 0.08 of an inch in diameter. This is 
 carefully divided into equal parts, which may be entirely arbi- 
 trary, but those which he employed are ten grains of mercury, 
 at 60 Fahrenheit, the whole tube containing 100 grains. It is 
 some trouble to divide this tube, but when once prepared any 
 number may by its means be easily graduated. The successive 
 portions of mercury used in dividing wider tubes are measured 
 by this, into which they are drawn, either by plunging it into 
 a jar filled to sufficient height with that fluid, or by the action 
 of the mouth*. 
 
 148. The graduation of jars is to be effected in a manner 
 very similar to that which has been recommended for tubes ; 
 but if performed by weighing, water is a better substance than 
 mercury for all quantities above half a cubic inch, because of 
 the weight of the latter, and the consequent burden it occasions 
 to the balance. A cubic inch of water at 62, it will be re- 
 membered, weighs 252.458 grains. If measures are to be 
 used, the vessels for them should be perfectly clean, so as to 
 become wetted over the interior: they should be well rinsed 
 out with water, and after being left to drain for a few seconds, 
 should, without further drying, be counterbalanced before the 
 given weight of water, which is to form the standard, is intro- 
 duced, and its volume marked (139, 141) ; because on every 
 occasion for their use a similar quantity of moisture will be left 
 in them, after the liquid by which the graduations are to be 
 made has been poured into the jar.^ 
 
 149. In marking the jars it will not be advisable to place 
 them against the wall, as has been directed for tubes, their 
 larger diameter interfering with such an arrangement. They 
 should be put upon a steady, firm place, as the one appointed 
 for measuring (120) ; and the liquid having acquired a state of 
 rest, three points should be marked, upon upright and equi- 
 distant lines, corresponding accurately with the general surface 
 
 * Manchester Memoirs, Second Series, vol. ii. 
 
Sect. III.] INSTRUMENTS TO FACILITATE GRADUATION. 81 
 
 of the water in the jar. These points are best obtained in the 
 first place by the scratching-diamond (128, 974), and may 
 afterwards be extended into short lines by the file (132). 
 
 150. When the jars to be graduated are such as cannot 
 stand steadily upon their own bases, the graduation at three 
 different places becomes still more important. Thus with 
 such as are capped, and, being closed with a stop-cock, require, 
 when graduated, to be supported on other jars, or list rings 
 (68), or over holes, the triple graduation is a security inde- 
 pendent of a correct perpendicular position. For though the 
 jar might perchance shift a little in its situation from the per- 
 pendicular, still if any quantity of water, for instance 20 cubic 
 inches, were then marked off by three lines on different sides 
 of the glass, any quantity which at a future time should coin- 
 cide with those marks, would be known to be accurately 20 
 cubic inches. This might be effected, indeed, by two gra- 
 duations on opposite sides, but it would not be so certain in 
 practice as three. In using three, also, the two first, if mi- 
 nutely incorrect, may be adjusted to perfect accuracy, by very 
 slight motion of the jar before the third mark is made. The 
 necessity of making these graduations at one temperature, that 
 of 62, has been before insisted upon. 
 
 151. Several instruments have been constructed by Dr. 
 Hare*, in which he has introduced a mode of measuring, de- 
 pendent upon the displacement of certain volumes of liquids 
 or gases, by the different parts of a graduated rod. The 
 
 figure represents one of these instru- 
 ments. It consists of a glass tube 
 fixed by one extremity into a cap 
 and collar of leather, and terminated 
 at the other in a capillary opening. 
 A rod graduated into equal parts passes air-tight through the 
 collar of leather, and is moved by a handle at the exterior. If 
 the aperture be immersed in water, and the rod drawn out and 
 thrust in again several times, the air is ejected, water enters, 
 and by inclining the instrument it may be entirely filled with the 
 latter fluid, and left with the greater part of the rod in the air. 
 If it be then removed from the water and dried, it is evident 
 
 * Phil. Mag.lxvii. 21, 
 
82 GRADUATION USEFUL MEASURES. [Sect. III. 
 
 that, by inserting the rod, an equal volume of the water will be 
 expelled from the tube by the capillary aperture, and may be 
 transferred into the vessels to be graduated ; it is also evident 
 that this water may be thrown out in successive minute por- 
 tions, each equal to the other, and to one of the graduations 
 on the rod. When the whole of the rod is thrust in, it is easy, 
 by drawing it out, to replace it by water, as in the filling of the 
 instrument, and then additional equal bulks of water may be 
 measured out. 
 
 152. By terminating the tube as before described (130), 
 and using mercury instead of water, the instrument becomes 
 an excellent measurer of equal portions of mercury, and may 
 then be used in graduating tubes (137). The rod itself is 
 easily graduated to any required dimensions, by observing how 
 much of its length must be inserted to displace a given weight 
 of mercury, as 34.25 grains (137), and then by proceeding to 
 mark off other degrees of equal value. 
 
 153. An instrument of this kind may be made without 
 difficulty, from a tube like that figured at p. 71 ; the rod 
 may be of solid glass, or a glass tube closed at the inner ter- 
 mination ; it should be made to slide through some tow, well 
 impregnated with tallow, which, being wrapped round it, is to 
 form a plug sufficient to close the end of the tube. By tying 
 this over with a piece of cloth, it may be made quite firm and 
 air-tight ; and the rod may then be graduated experimentally. 
 
 154. The following are useful estimates and comparisons 
 of certain measures, both linear and cubic, with the weights of 
 the cubic measures in grains of distilled water added 
 
 Inches. 
 
 Yard 36 
 
 Metre 39.37079 
 
 Decimetre .... 3.93708 
 Centimetre .... 0.39370 
 Millimetre .... 0.03937 
 
 The seconds pendulum vibrating at London, 39^13929. 
 
 Cubic Inches. Grains of distilled Water. 
 
 Imperial gallon . . 277.274 70000 
 
 Imperial pint . . . 34.65925 8750 
 
 Imperial fluid ounce . 1.7329625 .... 437.5 
 
 The old wine pint . . 28 . 8827 .... 7291 . 666 
 
Sect. IV.] SOURCES AND MANAGEMENT OF HEAT. 83 
 
 Cubic Inches. Grains of distilled Water. 
 
 Old fluid ounce 
 Cubic inch 
 Litre 
 
 1.805169 .. 
 1. 
 61.02525 
 
 455.73 
 252.458 
 15406.312 
 
 Decilitre .... 
 Centilitre .... 
 Millilitre . 
 
 6.10252 
 0.61025 
 0.06102 
 
 1540.631 
 154.063 
 15.406 
 
 SECTION IV. 
 SOURCES AND MANAGEMENT OF HEAT. 
 
 155. HEAT is so important, as modifying chemical action, 
 and the chemical and physical properties of bodies, that it must 
 always be of the utmost consequence to the chemist. So great 
 is its influence over his researches, that he has been called the 
 philosopher by fire ; and though the consideration of its 
 peculiar action on matter forms no part of the direct subject 
 of the present volume, yet, as the modes of augmenting and 
 applying it are proportionate in number and extent to the 
 powers of the agent itself, so the sources and management of 
 heat will claim much present attention. It is, however, by no 
 means intended here to dwell upon this subject in its full ex- 
 tent, but rather to limit and compress it as much as possible ; 
 supplying to the student that portion of instruction which re- 
 lates to the simplest and most effectual means of obtaining the 
 temperatures he may require in his experiments, but not ex- 
 tending it to every furnace, lamp, or blowpipe, or even to every 
 one beneficially used in chemical arts and processes. 
 
 1. Furnaces. 
 
 156. There is scarcely any limit to the number of furnaces 
 that have been contrived as particularly adapted either for 
 special or general uses ; all no doubt were good at the time 
 they were devised, and superior for some reason or other 
 to those which had preceded them. But the character of 
 chemical operations has changed so much as to render many 
 of these contrivances useless, or of little importance, and 
 
 G 2 
 
84 CRUCIBLE FURNACE. [Sect. IV. 
 
 each person is now left to select those which are most agree- 
 able to himself, as according best with either his notions or 
 modes of experimenting. For these reasons the author will 
 here describe those which he has been induced to adopt as 
 economical and effectual ; convinced that he ought not to omit 
 them, and that to describe a greater number would be assign- 
 ing to this subject a larger proportion of the present volume 
 than it can fairly claim. 
 
 157. An exceedingly useful furnace, either in a large or 
 small laboratory, may be made out of a black lead or earthen 
 crucible. The proper vessels for this purpose are known by 
 the name of blue pots, and may be had of almost every size, 
 less than the height of 22 inches, and of 12 or 14 inches dia- 
 meter at the top ; they are made of clay and plumbago mixed, 
 and are easily cut by a saw, rasp, or file. The price of one, 
 which will make a very good furnace for small operations, is 
 about six shillings. Anstey's coke crucibles are also service- 
 able for these uses ; they may be cut and worked as readily 
 as the blue pots, retain the heat very well, and are much 
 cheaper : but they crack and fall to pieces by frequent change 
 of temperature, They may be bought at Mr. Foster's, 2, St. 
 John's Square, Clerkenwell ; one 12 inches high, and 7 inches 
 diameter at the top, costing sixteen pence. 
 
 158. One of these vessels, of the height of 12 inches, and 
 7 inches in width at the top within, will make a very useful 
 furnace for the igniting a small crucible, heating a tube, or 
 distilling with large glass retorts at moderate temperatures, or 
 with smaller glass or earthen retorts at higher temperatures. 
 It is in the course of preparation necessary first to have certain 
 round holes pierced in it. These are easily made ; a gimlet, 
 brad-awl, or other small instrument, is to be used, to penetrate 
 
 the sides, and the small apertures thus produced 
 are to be enlarged with a rat's-tail and round 
 rasp, and ultimately finished with a half-round 
 rasp, which will make them of the size required. 
 Four of these holes are to be placed at equal 
 distances from each other, and about two inches 
 from the bottom of the pot ; they may be 1^ or 
 1J inches in diameter ; a second ring of holes, five or six in 
 
Sect. IV.] CRUCIBLE FURNACE BINDING GRATE. 85 
 
 number, is to be made half way between the top and bottom 
 of the pot, and a third row of five or six within two inches of 
 the top ; these holes should be rather smaller than the four 
 lower ones. 
 
 159. The pot should now be bound round with iron or 
 copper wire, -^ of an inch thick, to strengthen and hold it to- 
 gether when it cracks, an effect which is sure to take place 
 after it has been a few times heated. The wire should be 
 carried round in three different places, just above the upper 
 holes between the top and second row, and between the second 
 and lowermost row. A single wire, especially if of iron, is 
 sufficient, and two or three long notches should be made with 
 the edge of a rasp in the line of each ring of wire, just deep 
 enough to receive it and prevent it from slipping down when 
 drawn tight ; the ends should then be twisted together. It is 
 very convenient to have a handle to these furnaces, by which 
 they may be lifted, when hot, with a pair of tongs or a hook. 
 It should be of iron wire one-eighth or more of an inch in 
 thickness ; one piece should be carried under the pot, and 
 lodged in a groove deep enough to receive it, and prevent un- 
 steadiness ; it should rise up on opposite sides of the furnace, 
 until near the top, and there be turned so as to form a hook or 
 ring on each side to receive the handle. This wire should 
 be put on at the same time with that which binds the whole 
 together, and the latter wires should take a turn round the 
 former wherever they cross it, which will add considerably to 
 the strength of the whole. The handle above is easily made 
 of a piece of the same thick wire curved over the top of the 
 furnace, and bent into hooks at the extremities, by which it is 
 to be attached to the former piece. The handle should have 
 such a curve that when not in use it may pass over the edge 
 and lie out of the way against the side of the furnace. 
 
 160. A small round moveable grate of cast iron, like that 
 
 figured in the woodcut, makes this furnace com- 
 plete for many operations. If it be required to 
 heat a crucible, the grate should be of such a size 
 as to drop into the furnace, and rest between the 
 bottom and the second row of holes. The part below then 
 forms the ash-pit, to be supplied with air for the fire by the 
 
86 CRUCIBLE FURNACE FUEL ADDITIONS. [Sect. IV. 
 
 four holes ; and the part above forms the body of the furnace 
 to receive the fire and crucible. If a shallow fire only is 
 wanted, as in process of distillation or the heating of tubes, 
 the grate should be of such a size as, when dropped into the 
 furnace, to descend only a little below the first tier of holes, 
 the ash-pit then having two tier of holes entering it. Half 
 a dozen of these small grates will be required in the laboratory, 
 for the purpose of fitting at different times into different parts 
 of the same furnace, and also for use in different-sized fur- 
 naces, of the kind now described. They are of small price, and 
 may be bought of the philosophical instrument-maker. 
 
 161. When furnaces of this sort are constructed of different 
 sizes, variations in the number and arrangement of the air- 
 holes will of course suggest themselves. A smaller furnace 
 will require only two tiers of holes ; one of three or four for 
 the ash-pit, and another for theSody of the furnace. A larger 
 furnace may require more holes, and may at times have those 
 which communicate with the ash-pit enlarged into other forms, 
 and furnished with stoppers of soft red brick (1354), or pieces 
 of old pots. 
 
 162. The fuel used with these furnaces is charcoal, or in the 
 larger ones charcoal mixed with coke. 
 
 163. The fire is considerably under command, both as to 
 the diminution and increase of its intensity. A box of round 
 stoppers, made of soft brick (1354), or old blue pots, and 
 something like corks in form, should be provided. These 
 serve to close the air-holes which lead either to the ash-pit or 
 directly to the fire, and, by limiting the quantity of air which 
 enters, reduce the combustion in any required degree. When 
 the grate is placed high up in the furnace, as for distillations, 
 these stoppers are frequently required for the lower holes. 
 
 164. On the contrary, to increase temperature, and some- 
 times to increase the body of fuel, additions are made at the 
 
 top of the furnace. A very useful one consists 
 of the upper part of an old crucible, cut off so as 
 to form a ring, which should be bound with wire, 
 as was directed in regard to the furnace (159). 
 Rings of this kind may be from an inch to three inches or 
 more in depth ; and when placed upon the top of the furnace, 
 
Sect. IV.] CRUCIBLE FURNACE TEMPORARY FLUE. 87 
 
 so as to form a continuation of it in height, they considerably 
 increase both the capacity and the draught. They may be 
 made with holes or not, according to their depth. Such holes 
 of course weaken the ring, but when the quantity of fuel in 
 the fire is increased, it is frequently necessary to increase the 
 supply of air also ; and when a crucible stands in the middle 
 of the mass of fuel, these lateral supplies of air, especially in 
 the smaller furnaces, are essential to the vividness of combus- 
 tion, and the high temperature required. 
 
 165. A most useful accompaniment to these small portable 
 
 furnaces is a piece of straight funnel-pipe, about 
 two feet long, four inches in width, and open- 
 ing out below funnel fashion, until it is about 
 eight inches in diameter. This will easily rest 
 upon any furnace not more than eight inches, 
 nor less than four or five inches wide ; is quickly 
 put on or off; stands steadily of itself, and 
 increases the draught powerfully. A wooden 
 handle may be attached to it for convenience ; 
 or without it the tongs will serve to remove it. 
 It may either be taken off when the fire re- 
 quires to be made up, or the pieces of charcoal may be dropped 
 in from above. There is no difficulty in raising a crucible 
 two inches and a half in diameter to a white heat, by a furnace 
 of this kind, and of the dimensions before stated (158) ; and 
 that in any situation which may be convenient upon the tables 
 or the floor, and with all the advantage of arranging or dis- 
 mounting the apparatus with extreme facility. The ignitings 
 and heatings which belong to the analysis of siliceous and other 
 minerals, have long been made in furnaces of this kind at the 
 Royal Institution. 
 
 166. To fit this furnace for the igniting of tubes, it is useful 
 to cut a couple of notches in its upper edge, about an inch 
 deep, in which the tube may be laid when the grate is high 
 in the furnace ; at other times when a smaller heated length 
 only is wanted, it may be passed through two opposite holes 
 lower down in the furnace. When heating a tube in this man- 
 ner, it is not necessary to have a greater space than an inch or 
 an inch and a half between it and the grate. 
 
88 
 
 CRUCIBLE FURNACE ATTACHED TO FLUES. [Sect. IV. 
 
 167. When these furnaces are made out of large pots, the 
 grates being upwards of six inches in diameter, and the fuel 
 chamber six or eight inches high, they become very powerful, 
 and may be used to heat crucibles of considerable size. From 
 the larger dimensions of the grate, it is generally unnecessary 
 to form lateral air-holes through the body of the furnace, but 
 it is then requisite that an abundant supply of air be admitted 
 to the ash-pit, and through the grate to the fire. The fuel 
 used in these larger furnaces should be a mixture of coke and 
 charcoal, or sometimes, when a durable fire is required for long 
 operations, coke alone ; for in such cases the rapidity with 
 which charcoal burns away is inconvenient, and the heat which 
 it produces may be attained with coke by improving the 
 draught. 
 
 168. These furnaces may, wjien the employment of the 
 
 highest heat is desirable, be advantageously 
 connected with the spare laboratory flue (5), 
 and the openings of that flue should be 
 above the level of the furnaces when they 
 stand on the floor. The communication is 
 easily effected by two or three short pieces 
 of funnel-pipe like those in the margin, 
 made to fit into each other ; one having a 
 funnel termination at the bottom, lined with 
 fire-clay, to adapt it to the furnace, and 
 another a bend or joint at right angles. 
 The pipe should be at least four inches in 
 diameter. These furnaces, thus arranged, 
 are very powerful, and, being sometimes 
 wanted for long operations, require to be 
 fed without disturbance of the arrangement ; 
 for which reason it is proper to have an 
 aperture in the funnel-pipe, by which fuel 
 can be introduced, and which may be closed 
 by a stopper, when the fire is in order. 
 Another, and, at times, a more convenient 
 mode of arrangement, is to continue the fur- 
 nace upwards by a deep ring (being the upper part of another 
 pot) in which is an aperture by which the fire can be fed when 
 
Sect. IV.] 
 
 TABLE FURNACE ITS SIZE. 
 
 89 
 
 required, but which can be closed by a stopper when not in use. 
 The funnel-pipe is then to extend from the top of this ring to 
 the hole of the flue in the wall. These large furnaces should 
 be bound with iron hoop. 
 
 For further information relative to these kinds of furnaces, 
 see Lewis's Philosophical Commerce of the Arts, pp. 1 37. 
 
 169- The furnace next requiring description, is that in- 
 tended for general laboratory use, and already referred to (8). 
 Being in constant requisition as a table, it should be about 34 
 or 35 inches in height ; its other dimensions, and even its 
 form, must depend upon the space that can be allotted for it. 
 The one in the laboratory of the Royal Institution, constructed 
 several years since, under the direction of Mr. Brande, has the 
 brick- work 52 inches in length, and 30 inches in width ; the iron 
 plate, including sand-baths, being 57 inches by 42 ; others have 
 been constructed, the plates of which are only 40 inches by 
 27. The principal part of this furnace is necessarily of brick- 
 work, only the top plate, with the 
 baths and the front, being of iron. 
 The front is a curved plate, having 
 two apertures closed by iron doors; 
 one belonging to the fire-place, and 
 the other to the ash-pit. It is 34 
 inches high and 14 inches wide. 
 The ash-hole door moves over the 
 flooring beneath ; the bottom of the fire-place door is 22 inches 
 from the ground, and the door itself is 8^ inches by 7. This 
 front is guarded within at the part which incloses the fire by 
 a strong cast-iron plate, having an opening through it corre- 
 sponding to the door of the fire-place. It has clamps attached 
 to it, which, when the furnace is built up, are inclosed in the 
 brick -work. 
 
 170. In the setting or building of the furnace, two lateral 
 brick walls are raised on each side the front plate, and a back- 
 wall at such a distance from it as to leave space for the ash-hole 
 and fire-place; these walls are lined with Welsh lumps, where 
 they form the fire-chamber : two iron bars arc inserted in the 
 course of the work to support the loose grate bars in the usual 
 manner j the grate being raised 19 inches from the ground. 
 
90 TABLE FURNACE PARTS DIMENSIONS. [Sect. IV. 
 
 The side-walls are continued until of the height of the front, 
 and are carried backward from the front in two parallel 
 lines, so as to afford support for the iron plate which is 
 to cover the whole. The back-wall of the fire-place is not 
 raised so high as the side-walls by six inches and a half, the 
 interval which is left between it and the bottom of the sand- 
 bath being the commencement of the flue or throat of the 
 furnace. In this way the fire-place, which is fourteen inches 
 from back to front, and nine inches wide, is formed, and also 
 the two sides of the portion of horizontal flue which belongs 
 to the furnace, and is intended to heat the larger sand-bath. 
 The bottom of this part of the flue may be made of brick- 
 work, resting upon bearers laid on the two side-walls, or it 
 may be a plate of cast-iron resting upon a ledge of the brick- 
 work on each side, and on the top of the wall, which forms the 
 back of the fire-place. When/such an arrangement is adopted, 
 the plate must not be built into the brick-work, but suffered 
 to lie on the ledges, which are to be made flat and true for the 
 purpose ; for, if attached to the walls, it will, by alternate ex- 
 pansion and contraction, disturb and throw them down. The 
 ends of the side-walls, forming as it were the back of the 
 furnace, may be finished either by being carried to the wall 
 against which the furnace is built, or inclosed by a piece of 
 connecting brick- work, to make the whole square and com- 
 plete, or a warm air cupboard may be formed in the cavity 
 beneath the flue, and the door made to occupy the opening 
 between the walls. Occasionally the flue may be required to 
 descend there, and pass some distance under ground. These 
 points should be arranged and prepared before the plate con- 
 stituting the top of the furnace is put on to the brick-work, so 
 that when the plate with its sand-baths are in their places, 
 they may complete the portion of horizontal flue by forming 
 its upper* side. 
 
 171. The size of this plate is the first thing to be considered, 
 and having been determined upon, from a consideration of the 
 situation to be occupied by the furnace, and the places of the 
 sand-baths having also been arranged, the brick- work must then 
 be carried up, so as to correspond with these determinations, 
 and with the plate itself, which in the mean time is to be cast. 
 
Sect. IV.] TABLE-FURNACE PLATE SAND-BATHS. 
 
 91 
 
 The sand-baths and the plate are to be formed in separate 
 pieces. The bath over the fire is best of a circular form, and 
 of such diameter that, when lifted out of its place, it may leave 
 an aperture in the plate equal in width to the upper part of the 
 fire-place beneath ; so that a still, or cast-iron pot, or a set of 
 rings may be put into its place over the fire. The other sand- 
 bath must be of such a form as to correspond with the shape 
 and size of the flue beneath. These vessels are to be of cast- 
 iron, about three-tenths of an inch thick ; their depth is to be 
 two inches and a half or three inches, and they are to be cast 
 with flanches, so as to rest in the corresponding depressions 
 
 of the plate, that the level of the 
 junctions may be uniform. This 
 will be understood from the ac- 
 companying section of the fur- 
 nace, given through the line AB 
 of the view (169). It is essential 
 that these sand-baths be of such 
 dimensions as to fit very loosely into the apertures in the plate, 
 when cold, a space of the eighth of an inch or more being 
 left all round them, as shown in the section ; otherwise, when 
 heated, they will expand so much as entirely to fill the aper- 
 tures, and even break the plate. The plate itself should be 
 half an inch thick. 
 
 172. When the plate and its sand-baths are prepared, and 
 the brick-work is ready, the furnace is finished by laying the 
 plate on the brick-work, with a bed of mortar intervening. If 
 the walls are thin, or any peculiarity in their arrangement 
 occasions weakness, they should be bound together within 
 by cranks built into the work, and without by iron bands. 
 The alternate changes of temperature from high to low, and 
 low to high, to which the furnace is constantly subject, ren- 
 der it liable to mechanical injury, in a degree much sur- 
 passing that which would occur to a similar piece of brick- 
 work, always retained nearly at one temperature. The square 
 space inclosed by the fire-place and flues may be converted 
 into an excellent drying or warm air chamber if desired (606). 
 
 173. The sand-baths which have been described are liable 
 to an accident, that has induced some chemists to substitute 
 
92 TABLE-FURNACE SAND-BATHS RINGS. [Sect. IV. 
 
 others made of wrought iron. When first heated they fre- 
 quently, indeed generally, crack from the unequal expansion 
 in different parts ; and the plate itself is subject to the same 
 accident. If constructed' of wrought iron, this effect is not 
 produced ; but then after being used for some time they warp 
 into very irregular and inconvenient forms, especially if made 
 of thin metal ; whilst, on the contrary, these of cast-iron, when 
 cracked, are rarely injured for the uses to which they are to 
 be applied, and seldom suffer further change. 
 
 174. These baths should have washed river or sharp sand 
 put into them (24) ; it is heavy, and occasions no dust when 
 moved, whilst, on the contrary, unwashed and bad sand con- 
 tains much dirt, and occasions great injury in experimenting. 
 A piece of straightened iron hoop, about twelve inches in 
 length, should lie on the furnace, as an accompaniment to the 
 baths, being a sort of coarse spatula with which to move about 
 the sand (256381). 
 
 175. These baths are frequently used not for their especial 
 objects, but for the purpose of supplying heat generally to the 
 laboratory ; for the sand being cleared off' the bottom of the 
 bath towards one end, leaves the metal uncovered, which then 
 rapidly communicates heat to the air, and acts with the full 
 and economical effect of a stove. The same arrangement pro- 
 duces a current of hot air upwards, which may frequently be 
 used to warm apparatus, to heat plates for drying filters, &c. 
 
 176. The circular sand-bath is frequently replaced by a set 
 of concentric iron rings, or a cast-iron pot. The rings are 
 
 convenient for leaving an aperture over 
 the fire of larger or smaller dimensions, 
 according as a smaller or larger number 
 are used at once; and being bevelled at 
 the edges, fit accurately into each other, 
 without any risk of becoming fixed by ex- 
 pansion. The external one, like the sand- 
 baths (171), should be made smaller than 
 the depression in the furnace-plate in which it rests. The iron 
 pots are of various sizes, and are adapted to the furnace by 
 means of the rings ; a red heat for sublimation is easily obtained 
 in them. 
 
Sect. IV.] TONGS WIND-FURNACE. 03 
 
 177. Occasionally the sand-bath is replaced by a still, for 
 the production of distilled water (26). The form of the aper- 
 ture and furnace is such as to enable the still to be placed very 
 advantageously as relates to the fire beneath. 
 
 178. Tongs are essential accompaniments to furnaces. 
 There are many forms of these necessary implements ; those 
 which have the rivet in the middle of their length, so as to 
 allow of considerable opening at their extremity, and also have 
 the ends bent downward, are best for common use. They 
 
 should be of different lengths, from a 
 foot to two feet ; and there should be 
 one or two pair having the rivet near 
 the extremity, by which a powerful 
 
 hold is obtained, so as to prevent the slipping of a heavy weight 
 
 from between them. 
 
 179. Mr. Knight, of Foster-lane, has contrived a small 
 furnace, which, at the same time that it is competent for the 
 performance of numerous chemical operations, is generally 
 convenient for its lightness and portability. It is described 
 with several others in many chemical works. The points of 
 manipulation peculiar to each become evident upon inspection. 
 
 180. Wind-furnaces are such as have their combustion 
 urged by a draught of air through them, dependent upon the 
 flue to which they are attached. They are usual amongst 
 refiners, and those who melt metals in pots, as well as in the 
 laboratory ; hence their improvement and perfection are of great 
 importance. The table furnace already described (8 169), 
 and the crucible furnaces, when connected with the laboratory 
 flues, are wind furnaces ; but by proportioning the size of the 
 chimney to that of the furnace, others may be constructed, 
 much surpassing these in the intensity of heat produced. It 
 has been found that the combustion is most vivid when carrried 
 on in a furnace of equal diameter with the flue placed imme- 
 diately over it, the latter being of a height equal to about 
 thirty times its diameter, and free access of air to the grate 
 being permitted. But in practice, many variations are intro- 
 duced, which,, though they diminish the intensity of heat, still 
 pnable the worker of metals to heat a larger mass of matter up 
 
94 WIND-FURNACE BLAST-FURNACE. [Sect. IV. 
 
 to the point he requires, with a diminished consumption of fuel, 
 and consequently at a smaller expense. 
 
 181. In the laboratory of research, the wind-furnace may 
 generally be replaced with advantage by the blast-furnace ; 
 the operations being more manageable and expeditious, the 
 heat greater, and the consumption of fuel smaller. By a 
 little contrivance, one of the crucible furnaces before described 
 (158) is easily converted into a blast-furnace, and a very high 
 temperature for small vessels obtained. This is done by 
 closing the holes of the ash-pit with the stoppers (161), except 
 one, and applying to that the nozzle of a pair of double-hand 
 bellows, from which a blast is to be urged, and the furnace 
 aided at the same time by the piece of upright funnel-pipe 
 (165) ; the fuel is to be charcoal. 
 
 182. Mr. Charles Aikin has devised an arrangement for 
 a blast-furnace on a small scale, which is exceedingly good 
 
 and powerful. The furnace 
 is made out of fragments of 
 \ i broken blue pots, and consists 
 
 of several parts, sections of 
 which are here given, drawn 
 f upon a scale of one inch to 
 
 J% QE JL, ten. The lower piece a is 
 (jf fitted into a tin bottom, con- 
 
 sisting of a circular plate with 
 a rising rim ; the junction 
 being made tight by plaster 
 of Paris. The piece 6, rest- 
 ing upon a, is so formed as to have three circular shoulders 
 running round the inside, one at g, a second at h 9 and a third 
 a little lower, namely, where the grate in section is observed to 
 rest. The grate is circular, and can be removed at pleasure. 
 The piece c is merely a broad rim, which, resting upon the 
 edge of the piece b, increases the capacity of the furnace. The 
 piece d is to be used when, in place of enlarging the fire, it is 
 required to be diminished. It is to be placed within 6, resting 
 at its lower edge on the rim or shoulder h : e is a similar piece, 
 but smaller, it rests also on the shoulder h : it has a notch half 
 
Sect. IV.] AIKIN'S BLAST-FURNACE. 95 
 
 way between the upper and the lower edge, to admit the stem 
 of a tobacco-pipe, or other similarly-formed article. Another 
 part of the furnace is a circular plate of sheet iron, of such a 
 diameter as to fit into the rim g ; this plate is perforated with 
 an aperture three inches and a half in width, into which a very 
 small furnace-body fits, having its lower part pierced with 
 holes instead of a grate ; both these are represented at/. 
 
 183. When the furnace is in use, it is raised on a stand, and 
 the nozzle of a pair of double bellows, twelve inches long and 
 ten inches wide, brought towards the aperture in the lower 
 piece, but not inserted. The fire is lighted by a piece of brown 
 paper and a little small coal, and is sustained either with coke 
 and small coal, or coke alone. The coke is sifted of two sizes, 
 and preserved in boxes, with a ladle to supply it to the fire. 
 When a fire of a moderate size only is wanted, the piece b is 
 used ; if there be occasion to increase it, c is put on. When 
 smaller fires are required, d or e is used. For operations where 
 tobacco-pipes replace ordinary crucibles, the grate is removed, 
 and the piece and plate /placed within b at the shoulder g. 
 
 Mr. Aikin easily melts cast iron at this furnace, and can heat 
 a crucible two inches and a half in diameter, and three inches 
 and a half in height, to bright redness in a very short time. 
 
 184. The following is the description of a most excellent 
 blast-furnace, which has been in use for some years in the 
 laboratory of the Royal Institution. It is sufficiently powerful 
 to melt pure iron in a crucible, in twelve or fifteen minutes, 
 the fire having been previously lighted. It will effect the 
 fusion of rhodium, and even pieces of pure platinum have sunk 
 together into one button in a crucible heated by it. All kinds 
 of crucibles, including the Cornish and the Hessian, soften, 
 fuse, and become frothy in it ; and it is the want of vessels 
 which has hitherto put a limit to its applications. The exte- 
 rior consists of a blue pot eighteen inches in height, and thir- 
 teen inches in external diameter at the top. A small blue pot, 
 of seven inches and a half internal diameter at the top, had the 
 lower part cut off, so as to leave an aperture of five inches. 
 This, when put into the larger pot, rested upon its lower ex- 
 ternal edge, the tops of- the two being level. The interval 
 between them, which gradually increased from the lower to the 
 
96 
 
 POWERFUL BLAST-FURNACE. 
 
 [Sect. IV. 
 
 upper part, was filled with pulverized glass-blower's pots, to 
 which enough water had been added to moisten the powder, 
 which was pressed down by sticks, so as to make the whole a 
 compact mass. A round grate was then dropped into the 
 furnace, of such a size that it rested about 
 an inch above the lower edge of the inner 
 pot : the space beneath it therefore consti- 
 tuted the air-chamber, and the part above 
 the body of the furnace. The former was 
 7 i inches from the grate to the bottom, 
 and the latter 7J inches from the grate 
 to the top. Finally, a horizontal hole, 
 conical in form, and 1 \ inches in diameter 
 on the exterior, was cut through the outer 
 pot, forming an opening into the air-chamber at the lower part, 
 its use being to receive the liozzle of the bellows by which the 
 blast was to be thrown in. The furnace being thus completed, 
 the next object was to dry it gradually, that when used it 
 might not be blown to pieces by confined aqueous vapour ; 
 a charcoal fire was therefore made in it, and left to burn for 
 some hours, being supplied with air only by the draught 
 through the hole into the chamber beneath. When vapours 
 ceased to be formed, the furnace was considered as ready for use. 
 
 185. This furnace has always been used with a pair of large 
 double bellows mounted in an iron frame, the former being 
 raised upon a stool so as to bring the aperture of the air-cham- 
 ber to a level with the nozzle of the bellows. The latter has 
 generally been inserted in the aperture ; for this and similar 
 furnaces are of such depth, compared to their width, that when 
 charged with a crucible and fuel, there is so much resistance 
 to the passage of the air when urged by a blast competent to 
 create and sustain a vivid combustion, that a part returns by 
 the side of the nozzle, if the aperture be left open. The 
 bellows spoken of is far larger than necessary for the furnace 
 described, and is rarely worked to one-third of its power ; for 
 otherwise the heat rises so high as to destroy the crucible, 
 and the results are lost : it is, however, at all times advisable 
 to have an abundant command of air. 
 
 186. The heat produced by this arrangement is such, as at 
 
Sect. IV.] BLAST-FURNACEFUEL SITUATION. 97 
 
 every violent operation, to cause the production of some slag 
 from the melting of the inner surface of the furnace itself, 
 where the combustion has been most vivid. The slag, running 
 down the interior, collects round the edge of the grate, and 
 should be removed with a chisel and hammer, or with an iron 
 rod, after each operation, that the grate may be clear and free 
 from obstruction for the next process. When in the course of 
 time the interior of the furnace is so far injured as to become 
 thin and weak, it must be displaced, and the furnace restored 
 to its original state, by the introduction of a new inside as 
 before (184). 
 
 187. The fuel to be used in this furnace is coke. Its con- 
 sumption is very small, considering the heat that is obtained, 
 in consequence of the short period of each operation. The 
 superiority of the blast-furnace over the wind-furnace in many 
 operations for which high temperatures are required, depends 
 upon the rapidity of its action. It is requisite to employ 
 this furnace in the open air, or under a well arranged vent, for 
 an immense number of sparks, much flame, and a current of 
 hot air are produced during its operation, which might occasion 
 serious mischief in a room, unless the ceiling were at a con^ 
 siderable height, or guarded by a metal screen. 
 
 188. In using a blast furnace, like the one described, some 
 circumstances have to be considered relative to the method of 
 applying the stream of air. If a small pair of bellows be used, 
 the nozzle of which is considerably less than the aperture into 
 which the air is propelled, then a much larger quantity of air 
 is made to enter, if the nozzle be a couple of inches or more 
 from the hole on the outside than if it be actually inserted ; 
 for in the latter case little more than the stream of air from the 
 bellows is thrown through the furnace, whilst in the former a 
 large additional quantity is propelled and drawn by the 
 advancing stream and carried in with it; just, indeed, as hap- 
 pens with the blow-pipe jet of air where the flame and neigh- 
 bouring atmosphere is drawn into the current formed by the 
 propelled central stream. Hence if the bellows be small and 
 the fuel not too compact, advantage may be taken of this cir- 
 cumstance, and the heat more highly raised and sustained than 
 if the effect in question were unattended to. 
 
 H 
 
FUEL COAL COKE. [Sect. IV. 
 
 189. Priestley, and after him Lavoisier, proposed the appli- 
 cation of oxygen to furnaces, to increase the rapidity of com- 
 bustion, and consequently the intensity of heat: but it will 
 evidently be unnecessary to employ it whilst furnaces in which 
 common air is used continue to be more than equal to our 
 means, in consequence of the limit put to their application, by 
 the inadequacy of the vessels we possess to resist higher tem- 
 peratures. 
 
 190. The fuel to be used in furnaces is of three kinds, coal, 
 coke, and charcoal. Coal is the ordinary fuel for the labo- 
 ratory table-furnace (8 169)> or that intended to be in use 
 every-day, and serve for fusions, roastings, and other opera- 
 tions, for which its temperature may be sufficient. It is very 
 desirable that it should be good of its kind, and not that which 
 contains much sulphur, or an abundance of earthy matter; 
 for the first interferes with various fusions and ignitions, and 
 the latter renders the fire dirty and dusty, and when the tem- 
 perature is raised to a high point, causes an abundance of 
 clinkers. On certain occasions, to be hereafter distinguished, 
 especially if the coal be sulphureous and bad, it may be neces- 
 sary to use both coke and charcoal in the table furnace. Coal 
 should never be used in the blast-furnace : for, in consequence 
 of its softening and swelling by heat, it aggregates, closes the 
 small channels by which the air finds a passage through the 
 fuel, and impedes the combustion. 
 
 191. Coke is in constant requisition; it varies in quality 
 with the coal from which it is obtained. Such as is intended 
 for the service of the blast-furnace should be free from sul- 
 phureous, earthy, and metallic matter. Of this kind is the 
 Staffordshire coke, which may be obtained at some of the 
 wharfs on the canals near London. It is frequently so little 
 altered in appearance as to resemble the original coal. It 
 burns away completely in a blast-furnace, leaving scarcely a 
 trace of slag : so that after several successive portions have been 
 introduced, no material quantity of refuse is produced upon 
 the grate, nor anything that will act seriously on the crucible 
 as a flux. 
 
 192. On the contrary, if common gas-coke be used in this 
 furnace, the oxide of iron and earthy matter which it contains 
 
Sect. IV.] FUEL COKE CHARCOAL. 99 
 
 is so abundant that slag is soon produced, which, flowing over 
 the crucible, corrodes and destroys it ; by mixing with the 
 fuel, it tends to prevent the access of air to its surface, and 
 by accumulating upon the grate, at last so far obstructs the 
 entrance of air from beneath, as to prevent the attainment of 
 a high temperature. This .coke is not more than half the 
 price of that from Staffordshire, and is very convenient and 
 serviceable in the laboratory table-furnace, where, when an 
 iron bottle is to be ignited, or a crucible heated only to bright 
 redness, it answers far better as fuel than coal ; and as it does 
 not swell nor aggregate, the passage for air through the fuel 
 remains open, and a general and regular heat is obtained. 
 
 193. The Staffordshire coke when used in the blast-furnace 
 before described (184), should be broken into pieces some- 
 what larger than a walnut, that it may sink down in the fire 
 between the crucible and the furnace, presenting a constantly 
 compact body of fuel (673) ; and it should also be sifted or 
 screened before it is used, to remove the dust and small par- 
 ticles, which otherwise being mixed with it, would interfere 
 with the passage of the air, by stopping up the small vacuities 
 between the different pieces of fuel as they lie in the furnace. 
 
 194. The charcoal intended for laboratory use may be of 
 the ordinary kind, and must not be either too large or too 
 small. If large the pieces should be broken down, or they 
 will be unfit for use in the crucible furnaces, for which it is 
 principally intended. Charcoal is a quick fuel ; but burning 
 with facility, a small quantity of it can be easily retained in a 
 state of regular combustion ; and hence in cases where but 
 little space intervenes between the substance to be heated and 
 the side of the furnace, or when a small temporary fire is 
 required in the air, it is very convenient. Where Staffordshire 
 coke will burn, and by means of a blast or a draught of air 
 will give sufficient intensity of heat, it is very superior to 
 charcoal in duration. Occasionally a mixture of coke and 
 charcoal is convenient, since it affords a combination possessing 
 the qualities of permanency and freedom of combustion. 
 
 A charcoal box is almost as essential to a laboratory as one 
 for coal, and should have its appointed place. 
 
 195, It frequently happens, that instead of a regular fur- 
 
 H 2 
 
100 TEMPORARY FURNACES DEFENCE. [Sect. IV- 
 
 nace fire, a temporary arrangement is much more advantageous ; 
 thus, a fire of pieces of charcoal may be arranged upon a plate 
 of iron or tin, or upon a piece of iron wire- work, and be far 
 more applicable than one in a furnace. Sometimes an iron 
 wire basket, like a common mouse-trap turned upside down, 
 is very useful, and affords great heat because of the access of 
 air to all sides of it, whether urged by draught or bellows. A 
 loose iron grate and a few bricks will often serve to arrange 
 a powerful little furnace ; but these temporary arrangements 
 must be left to be suggested by the wants, and applied by the 
 judgment, of the experimenter. 
 
 196. It must be remembered, that all operations with fur- 
 naces should be carried on in safe situations, care being taken 
 that no danger be incurred by the ascent of sparks, flame, or 
 hot air ; by lateral vicinity to combustible bodies ; or by stand- 
 ing upon an unprotected wooden surface. When from peculiar 
 circumstances a small furnace is necessarily placed in such a 
 situation that danger may be anticipated from the ascending 
 current of air, the latter may frequently be rendered harmless 
 by fixing a plate of tin over the furnace, so as to break the 
 current, and mix the hot air of which it consists with the 
 neighbouring atmosphere. Injury from the vicinity of a 
 heated furnace to wainscoat, a trough, or any thing destructible 
 by heat, may almost always be prevented by interposing a 
 bright sheet of tin-plate ; the heat being then reflected and the 
 neighbouring body kept perfectly cool (1359). 
 
 197. When small furnaces are placed upon tables, stools, 
 or trays, a brick, or a piece of sheet-iron or tin-plate should 
 be interposed, according to the mode by which the heat is 
 likely to be communicated (1357) : a brick or tile should be 
 used in cases of conduction, metal in sheets to catch ashes, and 
 bright tin -plate to prevent the ill effects resulting from radia- 
 tion. When a permanent furnace is erected in a room which, 
 being floored with wood, is to be converted into a laboratory, 
 great care should be taken that the ash-pit and parts adjacent 
 be guarded by a stone flooring laid down for the purpose. 
 The stones should be bedded in a proper manner beneath, that 
 no injury may arise should cracks occur in them, or in case 
 they should not be of sufficient thickness to prevent the trans- 
 mission of heat. 
 
Sect. IV.] LAMPS. 101 
 
 2. Lamps.' 
 
 198. Lamps may be considered as small furnaces, and are 
 very economical and ready sources of heat. Nor are they 
 deficient in temperature ; for the intensity of heat in flame is 
 very high. Since the method of operating on small quan- 
 tities of matter has been practised and improved, not only 
 has the heat of a simple unassisted lamp- flame been taken 
 advantage of, but many contrivances have been practised by 
 which it has been powerfully increased and more beneficially 
 applied. 
 
 199. Of the varieties of lamps used in the laboratory, the 
 most useful is that in which spirit is burned. Spirit lamps 
 may be* bought at the instrument-makers, and are to be 
 trimmed with a cotton wick and supplied with alcohol. When 
 in combustion, the flame though pale produces intense heat, as 
 may be proved by introducing a small platina wire or other 
 piece of filamentous matter into it. The student should in his 
 first practice accustom himself to the introduction of small 
 fragments of minerals, metals, and other substances, into the 
 flame, at the extremity of a thin wire, or a filament of asbestus 
 or cyanite, or upon a narrow slip of platina foil. He will thus 
 habituate himself to various appearances, obtain a knowledge 
 of the heating power, and learn from experience at what part 
 of the flame the highest temperature exists, and where he 
 should intersect it when he wishes to obtain a more moderate 
 but more general heat. 
 
 5200. The flame of alcohol produces no smoke or fuliginous 
 matter, and hence a great and constant advantage possessed 
 by it. If a platina capsule, or a small platina crucible, be held 
 in the flame of a candle, for the purpose of applying heat to its 
 contents, a black sooty film is soon deposited, which from its 
 great radiating power occasions the loss of heat, and prevents 
 that elevation of temperature which the flame otherwise is com- 
 petent to produce. But held in the flame of a spirit lamp, the 
 blackening does not take place, and this circumstance is one great 
 cause why the rise of temperature is to a much higher degree 
 in this than in the former instance. If a candle were used to 
 apply heat to the exterior of a glass flask or retort, the car- 
 bonaceous matter would soon accumulate, so as to obscure the 
 vessel and hide the contents ; but a spirit lamp occasions no 
 
102 SPIRIT-LAMP ALCOHOL FLAME. [Sect. IV. 
 
 such obscuration, and at the* same time that heat is applied, 
 the utmost facility of observing the substances within is 
 afforded. 
 
 201. Where the flame comes in direct contact with the 
 substance under experiment, the advantages are equally on the 
 side of the spirit lamp. For the carbonaceous matter, besides 
 interfering as above described, would frequently have an in- 
 jurious chemical effect; whereas it seldom happens that the 
 water and carbonic acid which result from the combustion of 
 alcohol, produce any change by their contact. 
 
 202. The place of greatest heat in the steady flame of the 
 spirit lamp is just within its summit. The substance to be 
 heated, when it will bear the direct contact of the flame, should 
 be as small as possible, consistently with the power of duly 
 observing its changes. It may be supported by a pair of de- 
 licate platina forceps, or at the end of a piece of fine platina 
 wire or foil ; or when the substance will admit of splintering, 
 may itself be the extreme end of a sharp splinter, and will then 
 require no other support. In all cases the support should be 
 as thin and delicate as possible, that the heat may not be con- 
 ducted by it from the substance to be examined, or the flame 
 itself cooled by contact with it. Occasionally, especially when 
 the support is platina wire, it is advantageous to make that 
 part of it which is next the substance as hot as possible, that its 
 tendency to conduct heat from the body to be ignited may be 
 diminished. This is easily done by holding it so that the wire 
 shall ascend as it were up the side and just within the verge of 
 the flame, still supporting the body to be heated in the hottest 
 part ; or at times it is sufficient to let the support descend from 
 above, the hot air from the flame heating the part next to the 
 substance to a sufficiently high temperature. 
 
 205. When a larger substance is to be heated it is generally 
 best done by putting it lower down in the flame than the hottest 
 point, the flame being made to divide under it, and ascend 
 a little distance on all sides. In this way a small platina cru- 
 cible or capsule may be heated red-hot throughout ; whereas, 
 if put at the summit of the flame, such effect would not be 
 produced because of the partial exposure of the vessel to the 
 surrounding air. 
 
 Platina foil is $ useful accompaniment to the spirit- 
 
Sect. IV.] SPIRIT-LAMP HEAT IN IT ITS POWERS. 103 
 
 lamp. A square inch of its surface may be made at once 
 red hot. It may be readily bent into any convenient form, so 
 as to supply the place of crucibles and capsules for small quan- 
 tities of matter. It suffers scarcely any change by heat, is 
 affected by few bodies except sulphur and the reduced metals, 
 and withal is so bad a conductor of heat that it conveys less 
 from substances lying upon it than any other metal, and does 
 not conduct an inconvenient quantity to the fingers (1353). 
 If pieces of platina foil, about an inch or an inch and a half 
 in diameter or width, be put into a small mortar and pressed 
 upon and moulded with the pestle, they will form excellent 
 capsules for numerous purposes of ignition (371). These may 
 be supported by the wire holders (666). 
 
 205. Spirit-lamps of the usual size will give a flame of any 
 height less than two inches, the wicks being of twisted cotton, 
 usually about a quarter of an inch in diameter ; but a lamp 
 with a larger wick is desirable in the laboratory. One made of 
 copper, with a burner one inch long, by the third of an inch 
 wide, will produce a flame in which a platina crucible nearly 
 two inches in diameter, and small glass retorts, may be heated 
 to redness. 
 
 206. A very powerful and useful spirit-lamp, frequently 
 supplying the place of a furnace, is formed by making an 
 
 aperture of 0,8 or 0.9 of an inch by IA 
 inch, through the body of the lamp, and 
 fixing in it four burners, upon Count 
 Rumford's principle, each of a length 
 equal to the width of the aperture, and 
 the or -fa of an inch wide. These 
 are to be parallel to each other, and at such distances as to 
 have five spaces or air ways, the two outer being half the 
 width of the inner. These burners rise about a quarter of an 
 inch above the lamp, and descend as low as the bottom of the 
 body, being fastened in the aperture by their edges. Each 
 burner is closed beneath, but has a small hole into the lamp as 
 a passage for the alcohol, thus forming as it were a part of the 
 lamp. The lamp is supported upon four balls about half an 
 inch in diameter, to allow of the access of air beneath and up 
 the apertures to the flame. The alcohol is introduced by a 
 hole in the upper surface of the lamp, which is usually closed 
 
104 
 
 [Sect. IV. 
 
 by a screw ; and the burners are trimmed by putting down 
 each a doubled cotton of an Argand lamp until it touches the 
 bottom, and then cutting it off about the eighth of an inch 
 above the top. 
 
 207. Such a lamp is very powerful when applied merely as 
 other spirit-lamps are to the vessels to be heated, but it becomes 
 still more effectual in heating a crucible when assisted by a 
 
 chimney. This may be, as usual, a copper 
 cylinder, resting below upon the flat surface of 
 the lamp, and either level at the top or cut out 
 into three or four large scollops. Two chimnies 
 are useful, of an inch and three quarters in 
 diameter each, one about three and a half, and 
 the other five inches in length. Such a lamp, 
 besides having the power of heating crucibles 
 and retorts, is easily adjusted in any convenient 
 place, soon set to work, and as soon extin- 
 guished; and if convenient, only one or two 
 wicks may be lighted at once, those which are not employed 
 being covered up by the caps which are used to slip over the 
 burners to prevent evaporation when the lamp is not at work. 
 
 208. It would be improper to omit mentioning Mr. Phillips's 
 spirit-lamp *, the advantage of which consists in its ready con- 
 struction in any place and by any person. '* Let a piece of 
 tin plate about an inch long be coiled up into a cylinder of 
 about three-eighths of an inch in diameter, and if the edges be 
 well hammered it is not necessary to use solder. Perforate a 
 cork previously fitted to a phial, and put a cotton wick through 
 the short tin tube, and the tube through the cork ; the lamp 
 is now complete, and will afford a strong flame, taking care of 
 course not to prevent the rise of the spirit by fitting the cork 
 too closely." 
 
 209. All these lamps should have caps for the burners, to 
 prevent the evaporation of the alcohol when they are not in 
 use. Those which are sold in the shops are always furnished 
 with them. The large spirit-lamp above described should 
 have one for each burner, the material being tin plate. Mr. 
 Phillips's lamp may easily have a cover made for it by a little 
 piece of glass tube closed at one extremity. 
 
 * Annals of Philosophy, New Series, VII., 36. 
 
Sect. IV.] PYROLIGNEOUS ETHER OIL-LAMPS. 105 
 
 210. Alcohol is the fuel burned in these lamps, and though 
 it need not be highly rectified, yet the stronger it is the better. 
 The spirits of wine of the distillers, or doubly rectified spirit, 
 is sufficiently good for the purpose, the specific gravity of 
 which is about 0.84 or 0.85. 
 
 11. There is a substance produced in considerable quan- 
 tity, during the destructive distillation of wood, called by 
 Mr. Taylor, Pyroligneous ether. It is more volatile than 
 alcohol, but burns very well in a spirit-lamp. It has a pecu- 
 liar odour, but in consequence of its cheapness has an advan- 
 tage, its price being only sixteen shillings per gallon. It may 
 be obtained either at Apothecaries Hall, or at No. 201, Strand, 
 but is inquired for and sold at both places by the name of 
 Naphtha as often as by its proper name. This confusion of 
 terms is very improper, for Naphtha and Pyroligneous ether 
 are very different substances. 
 
 212. Oil is a fuel so applicable in the service of lamps, and 
 also so economical as compared to alcohol, that oil-lamps must 
 not be omitted in the enumeration of sources of heat. Such as 
 are constructed upon Argand's principle, having circular wicks 
 with a current of air both inside and outside, are most valuable. 
 They are now constantly constructed for laboratory service, 
 the material being copper, and the chimney, in place of glass, 
 being also of that metal. Their principal use is in distillations 
 or evaporations, for they possess the advantages of yielding a 
 nearly uniform heat for several hours together, and allowing 
 its increase or diminution within certain limits at a moments 
 notice, (439, 448, 465). It sometimes happens, that the 
 highest temperature, or greatest quantity of heat of which these 
 lamps are capable, cannot be attained, because, notwithstanding 
 the careful and regular manner in which they have been 
 trimmed, one part of the flame will smoke, if the wick be 
 turned as high as the rest of the flame will bear, without 
 smoking. Upon examination it will generally be found that 
 the part which smokes is that coinciding with the notch by 
 which the arm, connecting the cotton ring with the rack, 
 descends ; in which part the cotton is necessarily more exposed 
 than elsewhere. Should it be so^ the fault is easily corrected 
 for the time, by placing a little slip of copper or tin plate 
 
106 DOUBLE-WICK LAMPS OIL-LAMPS. [Sect. IV. 
 
 against the cotton in that place ; and then the other parts may 
 be raised so high as to give their full combustion without 
 smoke. 
 
 213. Double concentric-wick oil-lamps have been constructed 
 for the purpose of permitting greater combustion and sup- 
 plying more heat. These frequently fail in their applications, 
 and generally because both cottons being attached to one rack, 
 which is necessarily placed considerably on one side, there is 
 great irregularity of action, and too much friction, whence the 
 lamp soon becomes deranged, and is rendered useless. This 
 evil is readily corrected by having two racks, the second being 
 attached to the double cotton ring exactly as the first is, but 
 on the opposite side ; and then with care the lamp may be 
 arranged with accuracy, producing as much heat as may be 
 required for crucible operations (666.) The racks should be 
 raised or lowered regularly and equally, so that both may 
 assist in moving the cotton ; and care should be taken that one 
 be not raised without the other, or the one made to pull against 
 the other. In reference to the wicks also, more care is required 
 with the double than the single lamps, in consequence of the 
 difficulty of trimming the two cottons, so that the flame of one 
 shall not have a greater tendency to smoke than the other. 
 The best method is to cut them as seldom as possible, but 
 instead, to allow them to burn regularly, and when extinguished 
 and cold, to remove the hard crust and leave the singed edge 
 of the cotton that will then be exposed, as undisturbed as pos- 
 sible. A careful attentive experimenter will in this way find 
 no difficulty in keeping a double-wicked lamp in order, and 
 will obtain all the benefit which it is capable of affording; 
 whilst a hasty careless operator will never be able to make the 
 cottons move easily, or burn without smoke, or obtain any 
 advantage from the lamp over an ordinary one. 
 
 214. It is essential in these oil-lamps that an abundant sup- 
 ply of air to the wick be allowed. As generally constructed, 
 there is seldom sufficient air-way, especially in those with 
 double wicks ; and though they may burn moderately well at 
 first, yet the accumulation of oil and dust soon interferes by 
 stopping up the narrow apertures, and thus manifests the defi- 
 ciency. It is advisable to use the best lamp oil ; for the con- 
 
Sect, IV.] GAS-LAMPS BLOW-PIPES. 107 
 
 stancy and steadiness of its flame, and brilliancy of the com- 
 bustion, more than compensate for the higher price of the 
 fuel. 
 
 215. The erection of cjas works for public service is now 
 so general in most large towns and in numerous private esta- 
 blishments, that the chemical gas-lamp, which a few years ago 
 was a mere curiosity, has now become a valuable and econo- 
 mical auxiliary to the establishment of the chemist. The faci- 
 lity of management, and the regularity of flame, are even 
 greater than with the Argand oil-lamp, for by means of jointed 
 or flexible tubes, in conjunction with the smallness of the 
 burner from which the flame proceeds, as compared with the 
 body of an oil-lamp, it can be adjusted with the utmost nicety 
 in any required position. The kind of flame depends upon 
 the form of the burner. A single jet, or a series of jets in a 
 line, or a circular flame, or several concentric flames, may be 
 obtained at pleasure, and thus the applications of the gas-lamp 
 to distillation, the igniting of crucibles, &c,, may be made to 
 surpass in number and effect those of the lamps already 
 described. It is only requisite to have burners of the different 
 forms required, capable of being attached by a ground joint to 
 the gas-pipe, which has been laid down from the works. 
 
 3. Blow-pipes. 
 
 216. The blow-pipe is an instrument which cannot be dis- 
 pensed with in the laboratory ; and, as is usually the case in 
 contrivances for the attainment of any particular object, the 
 most common is the most valuable. The chemist does not 
 possess a more ready, powerful, and generally useful instru- 
 ment, than the mouth blow-pipe, and every student should 
 early accustom himself to its effectual use and application. 
 
 217. The forms which have been given to this instrument, 
 and the materials of which it is constructed, are very various. 
 All that is essential is a tube to conduct the air from the mouth, 
 terminated by a small regular round aperture, by which the 
 air can be thrown out in an undisturbed stream ; and, that 
 facility may be obtained in directing it, the lower end of the 
 instrument is generally turned to one side. 
 
 218. The common blow-pipe is a long conical brass tube ; 
 
108 
 
 BLOW-PIPE COMMON VARIETIES. 
 
 [Sect, IV. 
 
 two or three inches of the narrow end being bent, so that the 
 termination is nearly at right angles to the other part of 
 the instrument. In consequence of the gradual con- 
 densation of moisture from the breath in the tube, when 
 the instrument is much in use, a small portion of aqueous 
 matter is sometimes ejected through the beak into the 
 flame, and upon the substance to be heated. This occa- 
 sions an irregular flame, and sometimes does harm to the 
 heated substance, and the blow-pipe is therefore im- 
 proved, by having a chamber constructed at one part of it 
 for the reception of such moisture ; the accumulated water 
 being removed after the experiments are over. Dr. Black's 
 blow-pipe is a conical vessel, close, except at 
 the summit, to which the mouth is applied, 
 and at a lateral aperture below, from which a 
 small pipe proceeds, terminating in the nozzle 
 or jet. This cone serves not merely to con- 
 dense the moisture, but in a slight degree to 
 regulate the pressure of the air forced through 
 J^ it by the lungs and mouth. Dr. Wollaston's 
 instrument, on the contrary, has no chamber, 
 but consists of two or three pieces of tube, 
 which, when arranged together, form an excellent blow-pipe, 
 and when dismounted, pack into the size of a small pencil-case. 
 219. The essential part of the blow-pipe is the jet or termi- 
 nation by which the air is thrown out. The aperture should 
 be a smooth round hole, not leading suddenly inwardsj to an 
 irregular cavity, but enlarging in an uniform manner, so as to 
 form a small regular conical channel, at least the third of an 
 inch in length, gradually passing into the general air- way of 
 the instrument. The exterior should also be regular in its 
 form, and diminish by degrees to the aperture ; that when a 
 stream of air is forced through the blow-pipe, the external air 
 surrounding the jet may coalesce gradually with the current, 
 and not have the motion communicated to it disturbed 
 by any external irregularities of form. Perhaps the 
 best model for a jet is that obtained by drawing out a 
 piece of cylindrical glass tube (1176), and cutting it off 
 so as to leave an aperture of a proper size ; the nearer 
 
Sect. IV.] BLOW-PIPE JET TEMPORARY. 109 
 
 those which are made of metal approach to this in form, the 
 better they will act. The size of the aperture of a blow-pipe 
 must depend upon the flame to be urged, and the substance to 
 be heated ; for ordinary use it may be one fortieth or one 
 fiftieth of an inch in diameter. 
 
 220. The jets of blow-pipes are constructed of different 
 substances, those being in this respect the best which are made 
 of materials least liable to change. For this reason, and also 
 because of the facility with which differently sized apertures 
 may be used, they are frequently made in separate pieces from 
 the instrument, and arranged to slip on to the extremity at 
 pleasure. From the small quantity of metal required in their 
 construction, they may then be made of platina; and a conical 
 form given to them closely approaching that of the model 
 before mentioned. The single objection to jets with these deli- 
 cate terminations, is the facility with which they are altered in 
 form and injured : but it is only the careless who suffer in this 
 way, for no one acquainted with the value of the instrument 
 will voluntarily subject it to mechanical injury. 
 
 221. When a blow-pipe is not at hand, a very excellent tem- 
 porary one may be made from glass tube. A piece, nine or 
 ten inches in length, and about one-third of an inch in dia- 
 meter, is to be drawn out in the spirit-lamp, so as gradually 
 to diminish in size (1176, 1181), and then to be cut with a 
 file, that its extremity may imitate the jet before figured. It is 
 afterwards to be softened and bent on one side (1154), about 
 two inches above the jet, and thus a perfect instrument for 
 the time will be obtained. It is unfortunately brittle, and the 
 jet is liable to fuse and become closed in the flame when the 
 current of air is suspended ; otherwise it would supersede most 
 of the common blow-pipes. 
 
 222. The first point to be acquired in the use of the blow- 
 pipe, is the practice of the mouth. It is easy by blowing 
 through the tube in the usual manner, to produce a current of 
 air, which if directed upon a lighted candle, will occasionally 
 produce a clear and regular jet of flame. But this operation 
 will soon be found uncertain and fatiguing, and recourse must 
 be had to the action of the mouth and its muscles, not only to 
 regulate, but, at intervals, to perform the whole office of sup- 
 plying air to the instrument. 
 
110 MOUTH BLOW-PIPE USE OF. [Sect. IV. 
 
 223. The practice necessary at first is that of making the 
 mouth replace the lungs for a short time, by using no other air 
 for the blow-pipe than that which it contains. This prac- 
 tice is simple in itself and soon becomes easy, but is difficult 
 to describe. Let the student observe that it is easy, after 
 having closed the lips, to fill the mouth with air, and to retain 
 it so, at the same time that respiration may be freely carried 
 on, the air passing to and from the lungs by the nostrils. 
 The mouth then resembles a close but distended bag, and the 
 means being well observed by which it is thus for a time ren- 
 dered independent of the lungs and nostrils as to air, let a 
 blow-pipe, with a small aperture, be placed between the lips, 
 and then again filling the mouth with air, let it be separated 
 as before from the lungs : let the respiration be carried on as 
 in the former case, but at the same time let the capacity of the 
 moutb be contracted by the Action of the muscles of the cheeks 
 and jaws, and the air which it contained propelled through 
 the blow-pipe. If the aperture be small, this operation will 
 require ten or fifteen seconds, and being repeated a few times, 
 a ready facility of using the blow-pipe, independently of the 
 lungs, will thus soon be acquired. 
 
 224. This step being taken, the next is to combine this 
 process with the ordinary one of propelling air directly from 
 the lungs through the mouth in such a way that, when the 
 action of the lungs is suspended during respiration, the blast 
 may be continued by the action of the mouth itself from the 
 air contained within it. The mouth at this time represents the 
 going fusee of a chronometer, which causes the works to ad- 
 vance during the interval that the direct action of the spring is 
 taken off, by the hand which holds the key when the machine 
 is wound up for the renewal of motive power. The time of 
 fourteen or fifteen seconds, during which the mouth can supply 
 air independently of the lungs, is far more than that requisite 
 for one or even many inspirations ; and all that is required to 
 complete the necessary habit is, the power of opening and 
 closing the communication between the mouth and the lungs, 
 and between the lungs and the air, at pleasure. 
 
 225. The capability of closing the passages to the nostrils 
 is very readily proved ; every one possesses and uses it when 
 
Sect. IV.] BLOW-PIPE PRACTICE HOW ACQUIRED. Ill 
 
 he blows from the mouth ; and that of closing or opening the 
 mouth to the lungs may be acquired with equal readiness. 
 Applying the same blow-pipe to the lips, as before, use the 
 air in the mouth to produce a current, and when it is about 
 half expended, open the lungs to the mouth so as to replace 
 the air which has passed through the blow-pipe ; again cut off 
 the supply as at first, but continue to send a current through 
 the instrument, and when the second mouthful of air is nearly 
 gone, renew it, as before, from the lungs. In this way acquire 
 the power of using the air of one inspiration by mouthfuls, as 
 it may be termed, not at any time letting the air from the 
 lungs press upon that passing through the blow-pipe, except 
 for the short intervals during which it is being renewed in the 
 mouth ; but measuring it out as it were in successive portions, 
 and giving the muscles of the cheeks and jaws the work of 
 propelling it forward. This advance made, then, as the last 
 step necessary, learn to fill the lungs whilst the mouth is in- 
 dependent of them, and occupied in propelling the air ; and 
 this cannot be difficult for many minutes to those who have 
 already done the same thing for ten or fifteen seconds together, 
 as just described. Once effected, let this second inspiration of 
 air be used as the first was, and in the course of three or four 
 inspirations, the student will find no further difficulty in under- 
 standing the succession of actions which are necessary to the 
 production of a continued stream of air, and in performing 
 them either separately or in order, as may be required. 
 
 226. The description of these processes is necessarily tedious, 
 and the performance of them for the first time laborious and 
 tiresome. The pupil should not endeavour in these trials to 
 produce a strong current of air, as that occasions unnecessary 
 fatigue. The smallest stream is as efficient as a larger one. 
 The art once obtained, it will be quite unnecessary in actual 
 practice to repeat the effects in the order they have been de- 
 scribed. The peculiar action of the mouth is not necessary to 
 a continued stream of air, except as connecting the air of one 
 inspiration with that of the next, and continuing the current 
 whilst the experimenter is inhaling ; that effected, the mouth 
 need not be resorted to, except for peculiar purposes, until 
 fresh air is wanted, and inhalation again necessary. 
 
112 BLOW-PIPE ITS USES FUEL FOR ITS LAMP. [Sect. IV. 
 
 ^ ?pfc" ***'" 
 
 227. In fact, however, the mouth, besides continuing, regu- 
 lates and modifies the blast ; and the muscles belonging to it, 
 being more powerful than those which command the lungs, are 
 competent to the production of a much stronger stream of air. 
 This upon occasion is very useful and important. The action 
 of the mouth frequently helps to sustain and regulate the pro- 
 pelling force of the lungs, and frequently, also, when a stream 
 of air for a long period of time is required, the mouth is ad- 
 vantageously used to propel and continue it whilst four or five 
 inspirations are made: the lungs are thus relieved and re- 
 freshed, and this being repeated from time to time, takes from 
 the operation a great portion of its labour. 
 
 228. The powers of the blow-pipe will, in the laboratory, 
 frequently be added to those of the spirit-lamp, especially in 
 the heating of capsules, small platina crucibles, platina foil, 
 glass tubes, (666) &c. But when a very intense heat over a 
 small extent only is required, it would appear that other fuel 
 than alcohol is better for the purpose. A tallow or a wax- 
 candle, or an oil-lamp, with a wick about three-tenths of an 
 inch in diameter, affords a very convenient flame. Sometimes 
 the wicks of lamps are made broad and flat, for the purpose of 
 supplying a greater body of flame when required. 
 
 229. The lamps, if such be used, being trimmed so as to 
 occasion their full ordinary combustion, the jet of the blow- 
 pipe is to be placed in a horizontal position opposite the flame, 
 about the eighth or tenth of an inch above the wick ; and a 
 steady blast of air being thrown from it, it will be found that 
 the flame loses its ordinary form and appearance, and is pro- 
 jected as a luminous pencil along the course of the stream of 
 air. It should be steady, constant, and noiseless, not quiver- 
 ing, uncertain, or roaring. A small proportion at its com- 
 mencement should be brightly luminous, but soon pass into 
 a clear blue conical flame, towards the end of which on the 
 exterior, another should begin to appear of a pale lambent 
 yellow colour, and continue to an inch or more beyond the 
 termination of the blue flame prolonging the cone. The end 
 of the blue flame should be round, well defined, and even 
 sharp in its outline. As the jet is advanced towards, or into, 
 or withdrawn from the flame, so does the latter vary in its size, 
 
Sect. IV.] BLOW-PIPE APPEARANCE OF FLAME. 113 
 
 shape, and steadiness ; and as the power of changing it is 
 useful, the extent to which it may be carried should be ascer- 
 tained and practised. 
 
 230. If a candle be used, it should be snuffed, but not short, 
 the wick inclined a little on one side, and the current of air 
 from the jet sent obliquely upwards. If sent horizontally, the 
 heat soon melts the tallow or wax on the side beneath the 
 flame, and causes it to run down. The candle will frequently 
 require snuffing, and should never be allowed to have any use- 
 less wick. The disadvantage of oil-lamps is, that they also 
 require frequent trimming, and in that respect are not so con- 
 venient as candles. 
 
 281. The lamp or candle should be low, that whilst using 
 the blow-pipe the arms may rest steadily upon the table. The 
 hand should lay hold of the instrument as far from the mouth 
 as convenient, greater freedom of motion and steadiness being 
 thus obtained, and the left or the right hand should be used 
 indifferently. It should be the constant endeavour of the stu- 
 dent when he is using the instrument, to obtain the power of so 
 apportioning his breath, and of retaining the instrument and 
 the flame, that the latter shall appear like a fixture, and neither 
 change in appearance nor direction for several minutes toge- 
 ther ; yet this with such lightness of touch and easy hold, that 
 he may at pleasure send the flame in any direction and upon 
 any place he pleases. 
 
 232. The point of highest temperature in the flame is just 
 at the extremity on the exterior of the blue cone. Here the 
 combustion is complete or nearly so, and has suffered least 
 from cooling agencies ; but there are other parts of the flame 
 which, because of their peculiar qualities, demand a few dis- 
 tinct observations. Without the blue flame combustion is 
 complete ; all the fuel is burnt and the oxygen of the atmos- 
 phere in which the flame is formed begins to appear in excess, 
 and from thence increases outwards. Hence the power of 
 oxygenation to a great degree, in consequence of the elevation 
 of temperature and the free oxygen existing there. On the 
 contrary, within the bjue flame combustion is still going on, 
 consequently combustible matter is present ; there is no free 
 oxygen, and a reducing agency is exerted. Berzelius well 
 
 I 
 
114 BLOW-PIPE FLAME CRUCIBLE HEATED. [Sect. IV. 
 
 recommends that the situation and powers of these parts of 
 the flame should be learned by operating on a globule of tin 
 about the size of a shot placed in a small cavity on charcoal ; 
 the metal will be converted into a white crusty oxide, or be 
 reduced and appear in the metallic state as a brilliant fluid 
 globule, according to the part of the flame directed upon it 
 and the skill of the operator. 
 
 233. When the temperature required is not particularly 
 high, but the substance to be heated is large, a greater flame 
 is to be used (666). It may be obtained from the alcohol 
 lamp, or from an oil lamp with a flat wick, the current of air 
 being directed along the edge of the cotton. A jet with a 
 large aperture may then be employed, and it is occasionally 
 advantageous, by a more powerful or more abundant blast at 
 the same time withdrawing the j^et a little from the flame (229, 
 245), to break down the quiet tranquil flame into a roaring 
 one, the latter having power to heat a greater extent of surface 
 than the former. A crucible or a capsule may be thoroughly 
 ignited by a broken flame ; but the same instrument and lamp 
 with a steady flame, though they will heat one part intensely, 
 would leave another part comparatively cold. In heating a 
 glass tube for the purpose of bending or blowing it out, the 
 same advantage is obtained ; and it is a mistake to suppose the 
 blow-pipe is useful only for the purpose of increasing and con- 
 centrating heat, it being in the laboratory frequently as advan- 
 tageous merely for directing it. When the mouth blow-pipe 
 is used with the large spirit lamp before described (205), a 
 platina crucible one inch and a half in diameter may be heated 
 red hot throughout, and a glass tube of considerable thickness 
 be ignited regularly all round and bent. With a smaller lamp 
 or a candle, the blow-pipe is constantly in use for melting 
 cement or other fusible bodies upon particular parts of appa- 
 ratus, or warming the sides or tops of glass vessels ; and it is 
 for these amongst other purposes that the power of directing 
 the flame upwards or downwards, or in any direction at plea- 
 sure, is required. 
 
 234. The current of air is hot to a great distance beyond 
 the flame, and should have its direction and power well appre- 
 ciated by observation and experiment. It is frequently useful 
 
Sect. IV.] BLOW-PIPE HEAT THEORY. 115 
 
 in warming vessels, and the student will best learn its capa- 
 bilities by holding pieces of paper in its course, at different 
 distances (1142). 
 
 235. The theory of the blow-pipe is simple: its powers 
 depend upon the perfect combustion of the fuel, and the rapid 
 succession of hot gaseous matter against the substance to be 
 heated. The force which propels the stream of air through 
 the instrument is so much greater than the ascending force of 
 the heated gaseous products of the combustion, that the cur- 
 rents are altogether altered : the surrounding atmosphere from 
 the sides and behind the jet of the blow-pipe, including the 
 flame, is drawn in, and made to coincide with the propelled 
 stream of air, so that not merely is the usual form and direction 
 of the flame destroyed and new ones given to it, but with such 
 power that the ordinary and fluctuating motions of the atmos- 
 phere have little or no effect upon it. The heated particles 
 rapidly succeed each other in an invariable direction, and as 
 relates to the position of its parts, a degree of permanency is 
 thus given to the flame. The point at which the particles 
 attain their highest temperature continues the hottest so long 
 as the current is unchanged, and when a body is placed there, 
 it receives the successive action of these particles, and is itself 
 raised to the highest possible temperature. By far the greater 
 portion of the effect is due to the circumstance, that the moment 
 a particle of flame has touched the body and been cooled by 
 communicating heat, it is carried off by the current, and re- 
 placed by other particles of the flame at a maximum tempera- 
 ture. All loss of heat from the body by contact of colder par- 
 ticles is therefore prevented, and the elevation of temperature 
 is limited entirely by the temperature of flame, radiation, and 
 the deteriorating effects due to the conducting power of the 
 supports. 
 
 236. For the attainment of the highest possible temperature 
 in a body subjected to the powers of a flame urged by the blow- 
 pipe, it is necessary to attend to other circumstances besides 
 choosing the hottest place in the flame. It is found in prac- 
 tice, and easily explained by theory, that within certain limits 
 the smaller the particle to be heated the higher will be the 
 temperature acquired. Hence a reason for diminishing the 
 
 I 2 
 
116 BLOW-PIPE SUPPORTS. 
 
 [Sect. IV. 
 
 size of the piece as much as possible. Then the supports 
 should be such as, presenting the smallest quantity of matter 
 by which the heat may be conducted away or otherwise dissi- 
 pated, shall still resist the high temperature necessary to be 
 borne where in contact with the substance, and shall also exert 
 no chemical action upon it, or at least none that can interfere 
 with the properties to be observed. For these reasons platina 
 wire, or a thin slip of platina foil (204, 1353), is frequently 
 used as a support ; and forceps are constructed with delicate 
 terminations of platina for the purpose of holding such solid 
 particles as will not act upon them. These are frequently 
 made with a pair of strong steel nippers at the opposite end, to 
 break or chip off small splinters from minerals or brittle bodies. 
 When a thin splinter can be detached, the fine edge or point 
 is frequently more favourable for high ignition than a whole 
 fragment, however small, supported in. any other way. 
 
 237. Mr. Smithson * uses small plates of day as supports 
 for substances before the blow-pipe. They are formed by 
 extending a white refractory clay by blows with the hammer 
 between the fold of a piece of paper like gold between skins. 
 The clay and paper are then cut together with scissars into 
 pieces about four-tenths of an inch long and two and a half 
 tenths of an inch wide, and hardened in the fire in a tobacco 
 pipe. When cut into small and very acute triangles, they 
 form a substitute for Saussure's sappare. The method of 
 attaching the particle to be heated to the end of these strips, 
 or what is perhaps still better, to the end of a fine platina 
 wire, which has been since adopted by Mr. Smithson, is to 
 mix a very refractory clay with water ; the least quantity of 
 this is to be taken up at the very end of the clay strip or the 
 wire, and the particle chosen touched with it : in a few 
 moments it is dry, and may be introduced into the flame with 
 perfect safety. In this way the smallest observable pieces 
 may be readily experimented with. Sometimes Mr. Smithson 
 makes the powder of the substance into a mixture with water, 
 and uses it instead of the clay for attaching a particle to the 
 end of the wire. 
 
 * Annals of Philosophy, New Series, v. 387. vi. 412. 
 
Sect. IV.] BLOW-PIPE CHARCOAL. 117 
 
 238. Lieut-Colonel Totten* varies these methods by making 
 the pulverized substance into a paste with thick gum-water, 
 and forming it between the fingers into small acute cones, the 
 fourth or fifth of an inch in length. When dry they may 
 easily be held at the end of a wire or in forceps, and the apex 
 being moistened and directed to the particle to be experimented 
 with, adheres to it, and will allow it to be subjected to the 
 highest heat of the blow-pipe without suffering derangement. 
 
 239. In all experiments upon minute particles, or upon 
 splinters, it will be necessary to examine the results with a glass, 
 and not to trust to the naked eye. Appearances of fusion or 
 porosity will frequently escape the unassisted eye, when very 
 evident under a lens. 
 
 240. When charcoal is used as a support for the substance 
 to be heated, whether for the sake of convenience of form, or 
 on account of its chemical relations to the body, that should 
 be chosen which has been made from young succulent wood, 
 has thin bark, and is without cracks or cavities. Alder wood 
 charcoal is by far the best, being soft and generally free from 
 divisions. It may be distinguished by the triangular form of 
 the pith. When used, a little cavity may be made with a 
 knife on its convex surface, or sometimes even at the end of 
 the cylinder where the cross fracture has left a smooth termi- 
 nation, and the substance being placed there, the flame is to be 
 sent obliquely down upon it. Small charcoal, from two-thirds 
 of an inch to an inch in diameter, is most convenient, because 
 of its easy approximation to the lamp or candle. It would be 
 difficult to send the flame perpendicularly into the cavity, nor, 
 if it were easy, would it often be desirable ; for the propelled 
 flame would return upon itself, and causing irregularity in the 
 stream, would fail to produce the usual temperature. The 
 blast should be generally propelled obliquely, that the flame 
 entering over one side of the cavity after having struck upon 
 the matter to be heated, may rebound a little and pass out by 
 the other. 
 
 241. For ample directions in the management and use of 
 the mouth blow-pipe, with all that relates to the characters 
 
 * Annals of Philosophy, New Series, ix. 73. 
 
118 TABLE BLOW-PIPE. [Sect. IV. 
 
 and tests of substances examined by it, the student is referred 
 to Berzelius's Essay * ; which being essential to those who 
 would apply the instrument to its full extent, or beyond what 
 are its ordinary uses in the laboratory, renders any further 
 account of it here unnecessary. 
 
 24<2. The next useful instrument of this kind in the labora- 
 tory, is the table blow-pipe. It consists of a small table, fur- 
 nished beneath with a pair of double bellows worked by the 
 foot. A tube is connected with them, which rising through 
 the table is made adjustable above by sliding or moving joints, 
 and terminates in a jet. This jet is of course larger than that 
 of the mouth blow-pipe, being intended to urge a stronger 
 flame, but still it should be smooth and well formed (219), and 
 its aperture round and symmetrical. It is almost always the 
 work of the instrument-maker, but when a temporary jet is 
 required, it may be obtained excellent of its kind, by drawing 
 out a piece of narrow thick green glass tube in the manner 
 before described (221). The lamp (always sold with the table, 
 though separate from it) should have a burner competent to 
 hold a bundle of twisted cotton half an inch thick and an inch 
 wide, the top of the burner being about two or three inches 
 from the table, that the jet may easily be adjusted to any 
 required position. Tallow or dripping is, perhaps, the most 
 powerful fuel for it ; but in the laboratory, where it is often 
 wanted at a moment's notice, oil is the most convenient. 
 
 243. After having trimmed the lamp, leaving the cotton in 
 a compact wick, rising about one-third or half an inch above 
 the burner, light it, and place it on the table before the jet ; 
 then sitting on a chair with one foot on the treddle, work the 
 bellows slightly, and arrange the jet by moving the joints of 
 the tube, until, being horizontal, or nearly so, its extremity is 
 a little above the cotton, and close upon, or just within, the 
 edge of the flame. The force of the blast should be such as 
 to gather the flame and make it proceed in the same direction 
 with the jet, without any upward inflection of its extremity. 
 If, for want of power in the jet of air, this be not at first at- 
 tained, it should not be effected by working the foot so rapidly 
 
 * Children's translation of BerzeliuSj on the use of the Blow-pipe, 8vo. 
 

 Sect, IV.] TEMPORARY TABLE BLOW-PIPE. 119 
 
 as to fill the bellows and drive the air out by the direct force 
 exerted upon the treddle ; but the upper board of the bellows 
 should have weights placed upon it in such quantity as to cause 
 pressure sufficient upon the air within to make it flow out with 
 the required velocity. From the natural rigidity and tension 
 of the leather, the pressure upon the included air will be 
 greater when the bellows is nearly filled than when almost 
 empty, so that the force of the blast may be varied by keeping 
 the bellows more or less full, without any alteration in the 
 loading weight. When an impulse is required stronger than 
 that which can be produced by the weight and tendency of the 
 bellows to collapse, more or less direct force may be super- 
 added from the foot by means of the treddle. 
 
 244. The pencil need not necessarily include the whole of 
 the flame rising from the wick, but as the remaining part 
 throws off much smoke and fuliginous matter, it is better to 
 conduct these substances away by a small hood and chimney. 
 Such an arrangement has also the advantage of shadin the 
 bright part of the flame from the eyes, in consequence of which 
 the progress of operations carried on in the pale part are much 
 more readily observed. It frequently happens when the flame 
 of the lamp is too large for the jet, that no attempts to force 
 the whole into a clear steady cone will succeed ; but upon ad- 
 vancing the jet a little way into the flame, a part will be 
 thrown forward in the greatest perfection, whilst a portion 
 behind the aperture will rise upright in its usual state, and 
 almost undisturbed. It is even generally advantageous to 
 have this superabundance of flame. The pencil of flame should 
 be conical and steady, not ragged or broken, but ending in a 
 blue point, passing into a pale phosphorescent halo, without 
 any luminous or smoky part at the termination. 
 
 245. Modifications of this flame are required, resembling 
 those described as useful with the mouth blow-pipe (233). 
 When the jet is withdrawn a little way, and the blast impelled 
 with considerable force, the flame is broken, roaring, and some- 
 what diffuse (229) ; it is then bluish, burns without smoke, 
 and is useful in heating a crucible (666), or warming a thick 
 glass tube. 
 
 246. The construction of a temporary blow-pipe to supply, 
 
120 TEMPORARY TABLE BLOW-PIPE. [Sect. IV. 
 
 in cases of necessity, the place of a table instrument, is not 
 difficult (1207). A pipe of glass, pewter, or any other sub- 
 stance will convey the air ; and being tied to a weight or stand, 
 or even a candlestick, may be arranged at the proper height,, 
 for its jet to accord with the lamp to be used. The first rough 
 jet may be made by drawing out a piece of small glass tube 
 in the spirit-lamp, or a candle, and being attached to the 
 apparatus, a second and proper jet may be made by means of 
 it, out of a thicker piece of tube, and substituted for the smaller 
 one (221, 1181). Instead of the bellows a large bladder may 
 be used, or, what is better, a bag made of oiled silk, or some of 
 those fabrics now sufficiently common, in which cloth is ren- 
 dered air-tight by caoutchouc. This may be placed under 
 one end of a board, with weights upon it, or within a portfolio, 
 subject to pressure, and the air may be thrown into it from 
 the lungs by another piece of tube sufficiently long to reach 
 to the mouth. This tube will require a valve to prevent the 
 return of the air; and the simplest that can be constructed for 
 the purpose, in an extemporaneous manner, is perhaps the 
 following. 
 
 247. A piece of any tube of about the diameter of that re- 
 presented in the wood-cut, having a smooth and level end, is to 
 be selected, and also a strip of black oiled silk, of 
 a width rather more than the external diameter of 
 the tube, or, if that be not at hand, a piece of ribbon 
 of the same width, which has been rubbed with 
 wax, so as to have the interstices in it filled up 
 without destroying its flexibility. This is to be 
 adjusted loosely over the end of the tube, and the 
 extremities folded down on opposite sides, and tied 
 with a piece of thread ; the silk itself not being so tight, but 
 that by applying the mouth to the opposite end air may be 
 easily blown through the tube, and out at the extremity be- 
 tween it and the silk ; and yet so near that a pressure being 
 exerted in the opposite direction, the silk will be carried 
 against the end of the tube, and prevent the air from passing 
 out again. The tube by which air is to be thrown into the 
 bag from the mouth, is to have such a valve constructed at 
 its extremity, which is to be introduced through a hole made 
 
Sect. IV.] PNEUMATIC BLOW-PIPE OXYGEN BLOW-PIPE. 121 
 
 in the bag, and tightly tied in it by a few turns of twine. So 
 arranged, the bag is easily filled by air from the lungs, which 
 being gradually expelled at the jet, gives energy to the flame. 
 All the tubes required for this instrument, except the jet, may 
 be made even of paper, in the manner hereafter to be described 
 (1337). 
 
 248. A lamp for such a blow-pipe is soon fitted up; a 
 bundle of cotton threads placed at the side of any small vessel 
 filled with oil will answer the purpose, and none is more con- 
 venient than a little Wedgwood's or evaporating basin. 
 
 249. The pneumatic blow-pipe is an instrument more 
 portable than the table blow-pipe, and is intended to supply 
 its place. There is nothing relative to its manipulation 
 requiring notice, which has not been already mentioned. 
 
 250. Next to 'these ordinary forms of the blow-pipe, in 
 which common air is used to urge the flame and increase tem- 
 perature, come those which employ oxygen or other gases to 
 heighten the effect : and by gradual improvement not only has 
 the temperature, afforded by these instruments, been raised to 
 an extraordinary degree, but at the same time with almost 
 perfect security to the operator. It is only the most simple 
 and effectual of these contrivances which will require attention, 
 and of these merely such points as, from the facility of extem- 
 poraneous application, construction, or correction, may be most 
 immediately instructive and useful to the student. 
 
 251. A very simple and powerful method of increasing tem- 
 perature, the application and advantages of which were first 
 shewn by Dr. Marcet *, consists in urging the flame of an 
 alcohol lamp by a blow-pipe supplied with oxygen gas. The 
 oxygen may be furnished from an air-holder, a gas bag, or any 
 other vessel, in which it has been stored. The flame is much 
 smaller than when common air is used ; it is also brighter, and 
 its different parts have not the same relation : for instance, 
 when the flame is well urged, there is no point in which an 
 excess of combustible matter can be found, or where deoxy- 
 genation can be carried on, as with the common blow-pipe 
 (232), and hence it is never put to such purposes ; or when 
 
 * Thomson's Annals of Philosophy, ix., 21. 
 
122 LEESON'S BLOW-PIPE HARE'S. [Sect. IV. 
 
 * 
 
 applied to them, it only leads to negative or deceitful appear- 
 ances. The hottest part of this flame is very near the mouth 
 of the jet, the distance from it being not more than one third 
 or one fourth that occurring when the same lamp is urged 
 by common air (232). The oxygenating part of the flame 
 (232), is, in the first place, the innermost: then there will 
 usually occur a part where feebly reducing powers reside, and 
 on the outside of that as before an oxygenating atmosphere 
 again, 
 
 252. The arrangement called Leeson's blow-pipe is conve- 
 nient for the application of oxygen gas. It is a bottle of 
 caoutchouc or India rubber, which being distended with 
 oxygen, until it becomes several times its ordinary diameter, is 
 then to be attached to a jet. When the jet is opposite to a 
 flame, and the stop -cock opened, the contraction of the bottle 
 causes a regular stream of gas to flow out for a considerable 
 period, and an intensely hot, but small pencil of flame is 
 obtained. Metallic vessels sufficiently strong to contain several 
 atmospheres of oxygen gas have been used in the same manner, 
 and when made of a globular form, small and air tight, are 
 very pretty and convenient. 
 
 253. The use of hydrogen as fuel, instead of oil, alcohol, 
 &c., has introduced many forms of apparatus (some of which 
 are dangerous to beginners) intended for the special applica- 
 tion of a mixture of it with oxygen gas. Dr. Hare was the 
 first person who used these gases in conjunction, and described 
 the effects produced. He sent them by different channels to 
 the aperture, where they were mixed and burnt at the same 
 instant. There was no danger in this arrangement, and the 
 manner in which it may be repeated, will easily be understood 
 from what has been said, and the directions to be given relative 
 to the manipulation of gases. The heat was very intense. 
 
 254. In consequence of the experiments made by Sir Hum- 
 phry Davy, during the development of the principles of his 
 safety lamp and researches into the nature of flame, in which 
 it was shewn that the flame of explosive gaseous mixtures 
 would not pass back through small apertures or tubes ; blow- 
 pipes were soon constructed, in which the oxygen and hydrogen 
 being mixed in the proportions necessary to form water, were 
 

 Sect. IV.] SAND-BATHS WATER-BATHS. 123 
 
 then compressed in metallic boxes to the extent of many atmos- 
 pheres. Small tubes were afterwards affixed to these boxes, 
 and the mixed gases being allowed to pass out, were inflamed 
 and burnt at the apertures of the tubes. Many circumstances 
 combined to occasion accidents with this apparatus. The tube 
 was at times too large, or it broke, or became heated, or the 
 rapidity of the current in it diminished gradually, and the 
 flame, retrograding under the action of one or more of these 
 circumstances, ignited the mixture in the reservoir and caused 
 explosion : and notwithstanding the numerous contrivances 
 invented to prevent this return of the flame, there is not one I 
 believe, which from some unperceived or uncertain circum- 
 stance, either in the principles of the arrangement, or the acci- 
 dents to which it is liable, has not failed at one time or another. 
 Hence those only can be considered perfectly safe, where the 
 reservoir of gas, as in Dr. Clarke's arrangement, is separated 
 from the operator by a wall or partition, of strength sufficient 
 to give full security : and those are next perhaps, where, as in 
 the arrangement by Mr. Gurney *, the gases are confined in a 
 receptacle so slight (a bladder), that if blown to pieces the 
 fragments can hardly do harm. Then, the only liabilities are, 
 that the explosion itself shall shake and injure the neighbouring 
 apparatus, or throw them about with an injurious violence. 
 
 255. There are still some points in the economy and appli- 
 cation of heat, which require attention before we close this 
 section, as best assimilating with its subject and matter. These 
 principally concern the modes of heating by intermediate 
 agents ; some of which are of considerable general importance 
 in the laboratory, others very valuable in peculiar cases. 
 
 256. All that relates to the general construction and arrange- 
 ment of sand-baths has been already said (369, 176), except 
 what will assimilate with the processes to be performed on them 
 (381). Water-baths resemble sand-baths in offering a medium 
 through which the heat can be applied to the substance to be 
 heated ; but differ from them in limiting the heat to tempera- 
 tures below a certain point, and when required, in retaining it 
 for any length of time near to one fixed degree, that of 
 
 * Transactions of the Society of Arts, \\l, 70. 
 
124 * WATER-BATH ITS USES TEMPORARY. [Sect. IV. 
 
 This temperature is important in the maceration and infusion 
 of many organic substances, for which, though a greater heat 
 would be highly injurious, the one mentioned is desirable and 
 even necessary. Water-baths are generally constructed with 
 and attached to the vessels in which the heating operation 
 is to be performed : thus in the carpenter's glue-pot, the 
 vessel containing the glue is inserted in another containing 
 water, the latter being the one placed in direct contact with 
 the fire. 
 
 257. A water-bath, besides regulating and equalizing the 
 heat when required near to 212, may, from the liquidity of 
 the medium used, have its temperature ascertained by a ther- 
 mometer, and consequently regulated by attention to the 
 source of heat. Hence it offers the facility of raising sub- 
 stances in closed vessels to any given degree, between 212 and 
 ordinary temperatures : thiTs if it were required to know at 
 what point a certain wax or a new resin melted, it would only 
 be necessary to put a piece into a thin tube, and the tube with 
 a thermometer, into a water-bath, of which the temperature was 
 gradually raised, and moving the thermometer about to ascer- 
 tain the temperature of the bath, when just hot enough to 
 retain the substance in a fused state. 
 
 258. In the laboratory, the water-baths are generally of 
 extemporary construction. A tin or copper saucepan, shallow 
 or deep, according to the vessel to be heated, makes a very 
 excellent .one. The immersed vessel should not touch the 
 bottom of the bath ; if it be a flask, or there be two or three 
 to be heated, some hay or straw, or in lieu of them a little tow, 
 should be placed at the bottom of the bath, and the flask or 
 flasks upon it. A board should be placed across the bath 
 with holes in it to receive the necks of the vessels, and retain 
 them upright and steady : or even straw put loosely into the 
 vessel, or between the flasks, will answer the same purpose, 
 and at the same time prevent any bumping or violent ebullition 
 in the water of the bath. When the vessel to be heated 
 touches the bottom of the bath, heat gains access to it by con- 
 duction, the temperature is no longer necessarily the same as 
 the boiling point of the water, and may at times rise so high 
 as to do considerable injury. 
 
Sect. IV.] WATER-BATHS SOLUTION-BATHS. 125 
 
 259. An evaporating basin frequently answers the purpose 
 
 of a water-bath, and the substance to be heated may 
 also be placed in a small basin and floated on the 
 water in the first. A glass tube will often form a 
 water-bath for a tube somewhat smaller (918), and 
 frequently when the aqueous vapour would interfere 
 it is prevented by making the bath-tube the shorter 
 of the two. 
 
 260. It is necessary that attention be paid to the quantity 
 of water in the bath^ that it may not be so far diminished by 
 evaporation as to occasion injury or derangement, either by 
 bringing the floating vessel into contact with the bottom, or 
 leaving parts of the bath itself uncovered. It is often useful 
 for many reasons to put a little oil on the surface of the water 
 in the bath. Suppose, for instance, the source of heat be an 
 Argand lamp (212), or small furnace (158) ; as the tempera- 
 ture rises, evaporation increases so rapidly, that at last the 
 accession of heat is very slow, notwithstanding the rapidity of 
 combustion, and may, at times, even be limited before it has 
 attained the boiling point, the loss in latent heat being equal 
 to the gain in sensible heat. A film of oil upon the surface 
 prevents the evaporation, and, consequently, the loss of heat in 
 this way, and the temperature rises more rapidly, and to a 
 higher degree than when the water is uncovered. If it be 
 required just below 212, it is easily retained there with a 
 much smaller flame or fire than would otherwise suffice, the 
 water is not liable to diminution, nor will it require watching 
 or renewal, and the quantity of steam given off is compara- 
 tively nothing ; a point of some importance at times to the 
 substance in the inner vessel. In all cases when heat is re- 
 quired about a certain point below 212, it is advisable to 
 have a thermometer bulb immersed in the bath. 
 
 261. When temperatures above 212 are required in baths, 
 pure water must be dismissed, and either aqueous solutions or 
 metals used. There are several solutions useful for these 
 purposes, which boiling at different temperatures will, of 
 course, communicate heat up to their boiling points. A satu- 
 rated solution* of 
 
 * Quarterly Journal of Science, xviii. 90. Griffiths. 
 
126 SOLUTION-BATHS METAL-BATHS. [Sect. IV. 
 
 Bitartrate of Potassa, boils at . 214 
 
 Alum & . ,,- : t , ; . 220 
 
 Borax . , , >.','.>.'' 222 
 
 Common Salt *Y 'V ''"' 224 
 
 Tartrate of Potassa . "* 234 
 
 Muriate of Ammonia "-.. . . , 236 
 
 Nitre '. . . . , ... 238 
 
 Rochelle Salt .... 240 
 
 If a particular temperature be required, 234 for instance, 
 it may be obtained in two ways : either by selecting a solu- 
 tion which when saturated boils at that point, as one of tar- 
 trate of potassa, and then the temperature is regulated by the 
 process of ebullition ; or a sufficient quantity of some other salt 
 may be added to the water, so as to form a solution which, 
 though not saturated, will require that or a higher tempera- 
 ture for ebullition, and the exact point may then be regulated 
 by a thermometer. Rochelle salt and nitre are convenient for 
 this purpose, the temperature being carried by them as high 
 as 238 or 240. The use of oil over these solutions is equally 
 advantageous as in the water-baths (260). Such salts should 
 be selected as have no material action^ when in solution, on 
 the vessels used, and are, at the same time, economical and 
 effectual. 
 
 262. Solution-baths will produce temperatures up to 360, 
 but if higher temperatures be desirable, recourse must gene- 
 rally be had to metal-baths. Solution-baths are advantageous 
 for digestions, &c., carried on at temperatures above 212, and 
 while they possess the useful range of 20 or 30 degrees above 
 that point, they may be prepared with economy in sufficiently 
 large quantities. Metal- baths, on the contrary, are, both from 
 the weight and expense of the material, generally on a small 
 scale, and their principal use consists in subjecting substances in 
 tubes or other vessels to a given or an increasing temperature ; 
 or in ascertaining, by the gradual application of heat, which 
 may be measured by a thermometer, at what point any par- 
 ticular effect is produced. For these purposes small baths are 
 as effectual as large ones. 
 
 263. Mercury is the substance which first presents itself for 
 these uses : it may be applied, with care, from very low tem- 
 peratures up to 500 or 600. If the experiments be made 
 
Sect. IV.] METAL-BATHS HIGH TEMPERATURE. 127 
 
 altogether in tubes (259), a temperature of 600 may easily 
 be communicated by means of it ; but if the bath be an open 
 vessel, a dish or crucible, for instance, then temperatures higher 
 than 450 should not be given to it ; for the metal soon after 
 rises in vapour, and the fumes not only occasion waste of 
 mercury, but, at times, produce injury both to the experiment 
 and the health of the operator. 
 
 264. For temperatures from 212 and upwards, fusible 
 metal answers the purpose admirably. It consists of 8 parts 
 of bismuth, 5 of lead, and 3 of tin, fused together. It melts 
 at a heat below 212, and will bear a red or even white heat 
 without evolving fumes; but at dull redness, thick films of 
 oxide form on its surface, which increase with its temperature. 
 Tin or lead are both good metals for temperatures above 
 their fusing points ; the first melts at 441, the other at 609 
 Fahrenheit. 
 
 265. These metallic baths may be used in glass tubes at 
 temperatures beneath that at which glass softens (918), or in 
 evaporating basins up to temperatures of 400 or 500, but 
 only when small. When large, the weight of metal would 
 endanger both the vessel and the experiment. Earthen cru- 
 cibles are convenient for the immersion of tubes and similarly 
 formed apparatus, but when the mass of metal required is 
 great, an iron crucible or pot, or a small cast-iron saucepan, 
 should for safety be resorted to. 
 
 266. A thermometer may be employed to ascertain tem- 
 peratures as high as 650, but it should be open above for 
 degrees higher than 580, as will be stated more fully in the 
 account of that instrument (290). In taking the temperature 
 of the bath the thermometer should be moved in the fluid, for 
 the purposes of equalizing the temperature of the whole by 
 intermixture (286), as much as possible ; and, that the tube 
 or immersed body may also acquire an equal temperature with 
 the bath, it should also be moved about. A little tallow or 
 pitch may be put upon the surface of metallic baths not mer- 
 curial, at temperatures below 700, to prevent the surface from 
 oxidizing ; but, at higher temperatures, the volatilization and 
 decomposition of these bodies would occasion inconvenience. 
 If a bath be hot and covered with a coat of oxide, the latter 
 
128 BATHS TEMPERATURE HOT AIR. [Sect. IV- 
 
 should be moved on one side with a piece of card or stick, at 
 the moment the subject to be heated is introduced, otherwise 
 a coat may intervene, which will tend to prevent the ready 
 transmission of heat. 
 
 267. The operator should always bear in mind when using 
 baths, that the nature of the substance of which the inner 
 vessel, or that containing the body to be heated is composed, 
 has much influence over the transmission of the heat. It is 
 an obstruction through which the heat has to pass, and the 
 obstruction is the greater, as the conducting power of the sub- 
 stance is less. If a substance be put into a glass tube, and 
 that tube immersed in a water-bath at 212, it is some time be- 
 fore the contents of the tube will also acquire 212. If the 
 tube were of metal, its contents would sooner acquire the ulti- 
 mate temperature, because o the superior conducting power 
 of the latter substance over glass (287). 
 
 268. There are occasions, though not of common occur- 
 rence, when a bath is wanted that will not permit a rise of 
 temperature so high as 212. Thus in the preparation of 
 euchlorine from chlorate of potassa and sulphuric acid, it is 
 prudent to heat the tube retort in spirit of wine, or a mixture 
 of alcohol and water ; for the temperature not rising so high as 
 with water alone, there is less probability of any accident with 
 this explosive gas. 
 
 269. Hot air is an excellent heating agent on many occa- 
 sions, in consequence of the facility with which it is obtained 
 and conveyed ; it therefore claims our present attention. If 
 it be convenient to procure it by any slight alteration about 
 the furnace (169), as for instance, by putting a cast-iron pipe 
 in one corner, such a source should not be neglected, and will 
 
 TV be found constantly useful ; but in 
 
 -- 7_\ >j U general it will be more advantageous to 
 
 \^/ obtain it by small fires or lamps, the 
 
 whole of the gaseous produce of the 
 combustion being employed. A shallow 
 charcoal fire in a small crucible fur- 
 nace (158) yields an abundant supply 
 of heated gaseous matter. A piece of 
 funnel pipe (165), supported on a 
 
Sect. IV.] HOT AIR PRODUCED CONDUCTED. 129 
 
 tripod over the fire, serves as a channel for the hot stream which 
 may be conducted upwards or thrown right or left by ad- 
 justing pieces (168), as may be required: and the temperature 
 of the current itself may be regulated within certain limits 
 by placing the funnel pipe at a greater or smaller distance 
 from the furnace, or having different lengths of it, or 
 increasing arid diminishing the fire. Such a current is useful 
 in making slow distillations or rectifications (439) ; in heating 
 flasks or globes ; in warming electrical machines ; and the fire 
 is easily renewed or arranged, and its intensity increased or 
 diminished by opening or closing the holes to the ash-pit with- 
 out disturbing the apparatus above. 
 
 270. Occasionally, an Argand lamp may be substituted 
 for the charcoal fire, when an abundant quantity of hot air 
 may be obtained, by supporting a plate of metal, as a piece of 
 sheet copper a foot square, about an inch above the chimney 
 of the lamp (979). It breaks the current of heated gas and 
 vapours from the chimney, becomes hot itself, and heats the 
 air in contact with it. Such an arrangement is very useful in 
 drying papers placed over it (609) or in warming an electrical 
 machine. Of course every source of combustion for such 
 purposes should yield products free from smoke or fuliginous 
 matter. 
 
 271. Steam is in many situations a very convenient agent 
 for the application of heat up to temperatures not exceeding 
 212 Fahrenheit. If a source of steam, as a neighbouring 
 boiler, be available, nothing more is requisite than to conduct 
 the steam by a small pipe with a stop-cock into a box or vessel 
 containing the substance to be heated. A tin saucepan, for 
 instance, will hold several flasks or two or three retorts, and 
 being closed by a cover, having holes in which to adjust the 
 necks of the vessels, the passage of steam into it, in sufficient 
 abundance, will soon heat them up to 212. 
 
 272. If a steam heat be indispensable for an experiment, 
 and a boiler be not at hand, its place may be readily supplied 
 by a tea-kettle, containing about a pint of water, or even by 
 a tin can; pipes to convey the steam a few feet, if its pressure 
 be not more than that of the atmosphere, may be readily made 
 of oiled cartridge paper (1337). They should be an inch 
 
 K 
 
130 STEAM HEAT READILY OBTAINED. [Sect. IV. 
 
 in diameter, formed of two or three circumvolutions of paper 
 tied round with thread or twine, and placed in an inclined 
 position, that water may not lodge in them. Such pipes should 
 also be surrounded by a loose case, formed by wrapping a 
 sheet of paper round them, so as to make as it were an ex- 
 ternal tube, at least half an inch larger than the internal 
 one. This prevents any great loss of heat, and consequent 
 condensation of the steam within them. 
 
 273. Dr. Ure has contrived a very conve- 
 nient apparatus for the application of heat by 
 steam. It consists of a tin box about eighteen 
 inches long, by twelve broad and six deep. 
 The bottom is hollowed a little by the hammer 
 towards its centre, in which a round hole is 
 cut of five or six inches in diameter. Into 
 this a tin tube three or four 'Inches long is soldered. This 
 tube is made to fit tightly into the mouth of a common tea- 
 kettle, which has a moveable handle. The top of the box 
 has a number of circular holes cut in it of different diameters, 
 into which evaporating capsules of platinum, glass, or porcelain 
 are placed. When the kettle filled with water, and with its 
 nozzle corked, is set on a stove, the vapour playing on the 
 bottom of the capsules, heats them to any required temperature; 
 and being itself continually condensed, it runs back into the 
 kettle to be raised again in ceaseless cohobation. With a 
 shade above to screen the vapour chest from soot, the kettle 
 may be placed over a common fire. The orifices not in use 
 are closed with tin lids. In drying precipitates, the tube of 
 a glass funnel may be corked and placed with its filter directly 
 into the opening of a proper size. For drying red cabbage, 
 violet petals, &c., a tin tray is provided, which fits close to 
 the top of the box within the rim which goes about it. The 
 round orifices are left open when this tray is applied. 
 
 274. A temporary steam bath sometimes readily and ad- 
 vantageously supplies the place of a water bath. Suppose 
 it were required to evaporate a solution at tempera- 
 tures not higher than 212, two evaporating 
 basins should be selected nearly of equal size, 
 and putting water into the smaller, it should be placed on the 
 
Sect. IV.] 
 
 TEMPORARY STEAM-BATHS. 131 
 
 sand bath, or over a lamp or fire, and covered with the larger, 
 into which the solution is to be introduced. The smaller is in this 
 way converted into a chamber containing water at the bottom, 
 and, when heated, steam at the top ; the steam rises, condenses 
 against the bottom of the upper basin, heating it and its con- 
 tents, and the condensed water returns back to that below. 
 The excess of steam, if there be any, passes out at the side 
 where the lip of the basin leaves a little opening, and at such 
 a distance from the interior of the upper basin, as not to in- 
 terfere with the concentration of its contents. 
 
 275. In other cases the water and steam bath may be use- 
 fully combined. The figure represents an arrangement in 
 
 which a saucepan is converted into a tem- 
 porary steam chamber. Three flasks are 
 arranged in it, the necks appearing through 
 holes in a tin plate, which serves as a cover, 
 and which should be dished a little, or de- 
 pressed in the middle. Water to the depth of an inch or two 
 is to be put into the saucepan, and when the vessel is placed 
 over a little charcoal fire, becomes converted into steam, which 
 rising and coming in contact with the flasks, elevates them 
 and all within the vessel to its own temperature. The water 
 condensed on the under surface of the dished cover trickles 
 back to that at the bottom of the vessel, and by management 
 the flasks are retained for any time at <a temperature of 212, 
 with very little escape of steam or evaporation of the water. 
 This arrangement is frequently more convenient than a water- 
 bath made deep enough to receive the whole of the flasks, 
 because of its lightness and the superior steadiness of the 
 flasks, from their not being buoyed up by any quantity of 
 circumambient fluid. A similar arrangement is often useful 
 for distillation or rectification, the body of the retort being 
 introduced into the vessel and heated by the steam which 
 rises from the water beneath. 
 
 276. Upon occasions of refined investigation relative to the 
 force of vapours, or the conversion of liquid bodies into vapours 
 below temperatures of 212, or even as high as 240, it is 
 useful, for the observation of the immersed apparatus, to have 
 baths of water or solutions, in glass jars or other vessels to 
 
 K2 
 
132 STEAM CONDUCTED THERMOMETERS. [Sect. IV. 
 
 which the fire cannot be directly applied, and which yet re- 
 quire to have their temperatures sustained for a certain period 
 of time. In these cases the end is best obtained by throwing 
 steam into the bath itself, through a tube descending to the 
 bottom of the liquid. Such steam must be obtained from a 
 boiler, because of the pressure of fluid it has to overcome; but 
 small experimental boilers from four to six inches in diameter, 
 that may be placed over a lamp, are sufficient. The tubes 
 must be of metal or glass, not of paper. During the experi- 
 ment it is well to cover the bath with oil, to prevent loss of 
 heat by evaporation ; and also to wrap it round with a dry 
 cloth, or a few folds of paper, when it is not necessary to watch 
 the changes within whilst the temperature is rising. In these 
 cases, two or three thermometers should be introduced into 
 the bath to detect any difference of temperature that may 
 occur at different parts ; for where the surface is so large, and 
 the cooling agencies powerful, whilst the source of heat is con- 
 fined to one spot, it is necessary that great care should be 
 taken that all parts of the bath agree in temperature. 
 
 4. Thermometers. 
 
 77. The thermometer being an instrument in constant use 
 for ascertaining temperatures within certain limits, it is essen- 
 tial that the student should be made acquainted with the errors 
 to which it is liable, the means of correcting them, and the 
 general circumstances by which its indications are influenced. 
 It will be unnecessary to describe the method of making these 
 instruments, for in consequence of the general diffusion of 
 chemical science, and the practice of chemical arts, they are 
 constructed and circulated in such quantities in commerce, 
 that it is difficult to imagine a place in which such pursuits 
 are likely to be carried on, where they may not be found. 
 Besides, the construction of a thermometer, though simple in 
 theory, is difficult in practice. It requires great tact and 
 dexterity to produce one of very moderate goodness ; and 
 without steadily watching the process as performed by another, 
 or previously possessing much practical knowledge in glass- 
 blowing, &c., it would be a vain attempt to make one from 
 a written description. Here, therefore, we shall confine our- 
 
Sect. IV.] THERMOMETERS EXAMINED GRADUATION. 133 
 
 selves to the examination and correction of instruments which 
 are made by others ; and this is the more necessary, since 
 ordinary thermometers are frequently inaccurate, sometimes 
 considerably so, and would often lead to gross errors in delicate 
 experiments, though sufficiently correct for common purposes. 
 
 278. The most usual thermometer is that which contains 
 mercury, and is sealed hermetically at the top. It should not 
 include air. To ascertain whether it is perfect in this respect, 
 invert it, and by a short sharp shake or two endeavour to 
 make the column of mercury descend in the tube. If but 
 little mercury be in the tube, nearly the whole being contained 
 in the ball, it may be difficult to effect this; it is then faci- 
 litated by warming the bulb until a longer column is propelled 
 into the tube, when the shake will generally cause it to descend. 
 As the mercury moves in the tube, it will either leave an 
 equivalent void space in the bulb above, or it will part in the 
 tube itself, a portion only of the column passing downwards, 
 In either case the indication with regard to the presence or 
 absence of air in the tube will be the same, for if the metal 
 traverses the whole length freely and descends to the extre- 
 mity or nearly so, no air of any consequence can be present. 
 On the contrary, if it passes but a little way down the tube, 
 air is present. If it will not descend at all by any effort that 
 can safely be made, air may be suspected. When air is pre- 
 sent, it occasions irregularities in the indications of the instru- 
 ment, which can only be accurately ascertained by comparing it 
 experimentally with another thermometer known to be correct. 
 
 79. Supposing no air to be present, the accuracy of the 
 graduation is next to be ascertained. Thermometers are 
 generally graduated by having two points marked upon their 
 stems, corresponding to the melting temperature of ice and 
 the boiling temperature of pure water in a metallic vessel 
 under the pressure of the atmosphere ; and the intervening 
 space is then divided into a certain number of equal parts, 
 each being called a degree. Of these there are 180 in 
 Fahrenheit's scale and 100 in the centigrade scale. If the 
 scale is to be continued above or below these points, it is done 
 by making divisions equal in length to the degrees thus ascer- 
 tained. To try the accuracy of the point marked 32 Fahren- 
 
134 
 
 THERMOMETER GRADUATION EXAMINED. [Sect. IV. 
 
 20. 1 = 50 
 
 heit, mix some pulverized ice or snow with a little water so as 
 to make a thin paste ; introduce the bulb of the thermometer 
 into the mixture, and agitate it there for a few 
 minutes until the mercury is stationary on the 
 graduation. If it accords with the point marked 
 32, it is so far correct. To try the point 212 
 Fahrenheit, put some distilled water into a me- 
 tallic vessel, into which also introduce the bulb 
 of the instrument, holding it near the surface of 
 or in the water ; cover the vessel and make the 
 water boil so as to yield abundance of steam, the 
 barometer being at the same time at 30 inches, 
 or very nearly so ; observe the thermometer after 
 a few minutes, when it has attained its maximum 
 of heat, and if thermetal correspond with 212, 
 that point is also correct. 
 
 280. Finally, to ascertain if the intervening 
 degrees are equal, and in that respect likewise 
 correct, separate a portion of the column of mer- 
 cury in the tube of one, two, or three inches in 
 length from the rest, by inverting and jerking 
 the instrument as before mentioned (278) ; bring 
 it to different parts of the tube, and consequently 
 of the scale, by inclining the instrument more or 
 less in various directions, and by tapping it if 
 there be occasion ; and observe in all these situa- 
 tions whether the portion of mercury so separated 
 occupies the same number of degrees : if it does, 
 the instrument is accurate ; if it does not, the de- 
 grees are of different value in different parts of 
 the scale, and the instrument is incorrect. 
 281. Should it be found impossible thus to separate a small 
 part of the column to serve as a test of the scale between 32 
 and 212, then the instrument must be compared with one 
 known to be correct, either from its having undergone such 
 trial, or from having been formed from a piece of glass tube, 
 previously examined with regard to the equality of its bore, 
 by forcing through it a small cylinder of mercury, and thus 
 measured in different parts (1370). If, on comparison, three 
 
Sect. IV ] THERMOMETERS COMPARED. 135 
 
 or four equidistant points prove to be correct, and the scale is 
 found to have divisions of equal length in all its parts, then 
 it may be considered as good. 
 
 282. The method of ascertaining whether the scale is equally 
 divided, is to lay it by the side of another scale, an inch rule 
 for instance, and observing how many degrees are equal in ex- 
 tent to a given space on the second scale, then to move it up or 
 down, and examine whether in other parts the same number of 
 degrees are also equal to the same space. The student should 
 understand that ascertaining the points of 32 and 212, and 
 also the equality in length of the divisions on the scale, is not 
 sufficient to ensure the accuracy of the instrument ; since, if 
 the tube be conical or otherwise irregular in the bore, a correct 
 graduation would give degrees unequal instead of equal in 
 length (1370). 
 
 283. If neither 32 nor 212 be contained on the scale of 
 the instrument to be examined, then it must be verified by 
 trial with a thermometer known to be correct, and three or 
 four points having been found to accord, the regularity of the 
 divisions must be examined as already described (282). If 
 one of these two important points be included it should be veri- 
 fied as before. 
 
 284?. If the thermometer to be examined contain alcohol 
 instead of mercury, there is no opportunity of separating a 
 small cylinder of fluid to measure the equality of the division ; 
 or of ascertaining the point of 212 in the manner described 
 (279). That of 32, and three or four others, must then be 
 ascertained as already described (281), and the equality of the 
 scale observed by comparison as before (282). 
 
 285. When the scale passes above 212 or below 32, these 
 parts are examined only by observing that the degrees are 
 equal in bulk to those between the two points. This equality 
 is of course measured by the little cylinder of mercury, as 
 before explained (280). 
 
 286. In all experimental comparisons of thermometers, 
 essential care should be taken that time be allowed them to 
 acquire the temperature of the bath in which they are im- 
 mersed ; and they should be constantly moved about in it, 
 and made to change places, or serious differences may exist 
 
136 THERMOMETER VARIATIONS OF. [Sect. IV. 
 
 between them (266, 267). A large and a small bulb, or a 
 mercury and spirit thermometer, will take different periods to 
 heat and cool, and if observed hastily may not only be examined 
 \vhilst of different temperatures, but also whilst both differ 
 from the liquid in which they are immersed : treated in this 
 way good thermometers may seem bad, and more harm than 
 benefit will result from the investigation. 
 
 287. It is for this reason that trials made by putting a good 
 thermometer and the one to be examined into a hot liquor, and 
 observing whether they sink together as the temperature falls, 
 are often fallacious. If the thermometers be dissimilar in bulk 
 or some other circumstance ; if the bath be small, and the time 
 occupied in observing the fall of several degrees be short, the 
 instruments will frequently appear to be a degree or two dif- 
 ferent, when, if properly examined, they would prove to be 
 alike ; and neither of them will indicate, during the process, 
 the temperature of the bath in which they are immersed. It 
 is easy for the student to gain practical proof and experience 
 of the extent of this effect, by taking two thermometers, so far 
 resembling each other, as to indicate alike when immersed in 
 the same bath, and introducing the bulb of one of them into a 
 thin tube with a little mercury in it. Upon immersing that 
 tube in the same bath with the uncovered thermometer, and 
 allowing the heat to gain access to the instrument through the 
 intervening mercury only, he will find on comparing the two 
 instruments how great a difference will be occasioned between 
 their indications, as the temperature of the bath rises or falls. 
 This effect is due to the thin tube and the mercury it con- 
 tains, which obstructing the passage of the heat, retard the 
 changes of temperature in the thermometer itself (267). 
 The effect varies with the thickness of the glass, and the quan- 
 tity of metal, and illustrates sufficiently the differences that 
 may be introduced in hasty experiments, by the variable 
 thickness of the bulb and quantity of mercury in the ther- 
 mometers. 
 
 288. There are some causes which slightly interfere with 
 the permanency of the indications of a thermometer ; but they 
 are of a delicate nature, and need not, except in particular 
 cases, be attended to. It is said that the constant pressure of 
 
Sect, IV.] 
 
 THERMOMETER MERCURIAL. 137 
 
 the atmosphere on the exterior of the bulb, gradually alters its 
 bulk, rendering it smaller, and thus elevating the mercury, and 
 causing it to stand higher in the scale than it ought to do *. 
 It is also said that a thermometer, when cooled or heated con- 
 siderably, and then returned to its former temperature, does 
 not immediately give the same indication that it did before, 
 but is lower than it should be in the first case, and higher in 
 the second, from the tardiness with which the glass regains its 
 orimnal bulk i. These are refinements which it will not be 
 
 O I 
 
 necessary for the student to consider, until he has advanced so 
 far in the science as to be competent to enter into a considera- 
 tion of their presumed effects. All that will be necessary is to 
 try the thermometers, should they be old, to ascertain that the 
 graduation corresponds to the height of the mercury, and that 
 ' they have not suffered a change by time like the first of those 
 referred to. If any opportunity occurs of observing peculiar 
 changes or appearances, it will be proper to note them, for the 
 illustration and explanation of those presumed and delicately 
 influencing causes. 
 
 5289. It will be unnecessary to describe the peculiarities and 
 uses of all the varieties of thermometers. No other liquid than 
 alcohol and mercury is now used. Ordinary alcohol thermo- 
 meters must not be employed for the indication of temperature 
 above 180, for if subjected to higher, they would either yield 
 wrong indications, or burst ; but that fluid having never yet 
 been congealed, they may be applied to the indication of 
 exceedingly low temperatures. Mercurial thermometers may 
 be used for temperatures 20 or 30 below or up to 500 or 
 600. At these high temperatures they are very liable to vary 
 from each other in their graduation, for want of an unexcep- 
 tionable and natural standard point by., which they can be 
 corrected. 
 
 290. A good mercurial thermometer hermetically sealed, 
 will not indicate temperatures higher than 580 (266), for 
 above that point the mercury boils in the bulb ; but when open 
 at the top, and consequently subject to the pressure of the 
 atmosphere, it will indicate temperatures from 60 to 70 higher. 
 
 * Bibliotheque Universelle, xx., 117. 
 f Giornale di Fisica, v. 268. Bib. Universelle, xxi., 25 J, xxii., 2G5. 
 
138 THERMOMETERS LARGE AND SMALL. [Sect. IV. 
 
 If wanted for delicate experiments, these instruments should 
 be small, not merely in the tube, by which the divisions are 
 rendered larger and the indications consequently more minute, 
 but in the bulb also. A thermometer indicates temperature, 
 by taking from or giving to the heat of the body to be 
 examined, until on an equality with it ; hence the body changes 
 in temperature upon the introduction of the instrument, and if 
 it be small, whilst the thermometer is large, the heat which 
 results when they are both alike, may be considerably different 
 from that of the body at first. This would cause an important 
 error, which is only to be avoided or rather diminished, by 
 using a thermometer so small that it shall not occasion a mate- 
 rial change in the temperature of the substance into which it is 
 introduced. A large thermometer is also longer in heating or 
 cooling than a small one, andrmay from the lapse of time neces- 
 sary to allow of its proper change, occasion an alteration of 
 temperature, by allowing the body tried to cool or warm (266). 
 Small thermometers are, therefore, frequently more useful and 
 accurate than larger ones ; and in order to compensate for the 
 diminished mass of mercury whose expansion is actually mea- 
 sured in the instrument, and to prevent the degrees from 
 lessening in length and delicacy with the bulb, the tubes are 
 usually made of a proportionably smaller internal diameter. 
 A great advantage is then gained by using a tube with a flat 
 bore, the capacity being rendered very small, and consequently 
 the degrees comparatively long, whilst the surface to be looked 
 at is large. 
 
 291. When a bulb is thin or large and the column of mer- 
 cury in the tube long, the instrument will occasionally be 
 affected in its indications by the position in which it is held. 
 Suppose a thermometer having a column of mercury of 15 
 inches in the tube, to be held perpendicularly, and afterwards 
 inverted, and the bulb held uppermost : if the column did not 
 descend or part in the latter position, there would be occa- 
 sioned a difference of pressure upon the exterior of the bulb, 
 equal to a whole atmosphere, by this simple change of position ; 
 for the column of mercury of 15 inches first exerting a pres- 
 sure into the bulb, would, in the latter state, be equivalent to 
 an equal pressure added upon its exterior. It is this difference 
 

 Sect. IV.] THERMOMETER OBSERVED. 139 
 
 of pressure which, when sufficient to affect the bulk of the 
 glass bulb, causes an apparent difference in the temperature 
 indicated in the two positions. It will therefore be advisable 
 to try the instrument by change of position, to be aware of 
 any effect of this nature to which it may be subject, and which 
 of course will take place, although in a smaller degree, with 
 any departure from the vertical position. 
 
 292. Another error, occasionally introduced by a long tube, 
 depends upon the variable quantity of mercury submitted to 
 the heat at the time of graduation and the time of use. If a 
 thermometer, with a tube three or four feet long, be graduated 
 by immersion of its bulb, and two or three inches of stem only, 
 into melting ice and boiling water, and then used in situations 
 where the greater part of the stem, as well as the bulb, is ex- 
 posed to heat, the indications may be two or three degrees 
 higher than the temperature to which it is really exposed. A 
 thermometer existed at Whitbread s brewery, some years ago, 
 which, belonging to a deep evaporating vessel, passed through 
 the to]), and descended perhaps three feet before the bulb 
 entered the fluid ; this instrument indicated a heat in the boil- 
 ing wort beneath, some degrees higher than the same wort 
 brought up in a bucket, and tried by another instrument, or 
 even boiled in a smaller vessel, and yet examined in the usual 
 way, it appeared to be correctly graduated : the difference de- 
 pended upon the expansion of the mercury in the stem by the 
 heat of the steam above the liquor, to which it was exposed 
 when in use, which was added to the expansion of that in the 
 ball, the only part heated at the time of graduation. 
 
 293. Some thermometers are formed with a chamber or 
 bulb in the upper part, so that if accidentally raised to the 
 boiling point of the fluid within, the fluid and vapour may 
 pass into this space, and the bursting of the instrument be pre- 
 vented. These are so far advantageous, but they cannot be 
 made free from air, and are in that respect inferior to the 
 others. 
 
 294. Thermometers should not be introduced suddenly into 
 hot or cold substances, for then the glass is liable to crack at 
 the stem, and the instrument consequently be destroyed. 
 
 295. The graduation of these instruments is sometimes 
 
140 AIR THERMOMETER. [Sect. IV. 
 
 made on the glass, and sometimes on a separate scale. When 
 examined, the eye should be brought perpendicularly to that 
 part of the stem where the mercury stands, so as to look 
 directly through and on each side of the tube, that the correct 
 coincidence of the surface with the scale may be observed. If 
 the graduation be looked at obliquely, through or upon the 
 tube, the apparent places of either the mercury or the degrees 
 are not the real ones. 
 
 296. Although accurate graduation has been thus far spoken 
 of, it is with reference only to the mode generally acknowledged 
 and practised, namely, that of ascertaining the freezing and 
 boiling points of water, and dividing the interval into a certain 
 number of equal parts, each of which is called a degree, and 
 used as the model for other degrees, made upwards or downwards 
 on the scale. Whether suchra process is strictly philosophical 
 is not the question ; all divisions must be arbitrary, and that 
 adopted has the essential quality of producing instruments 
 strictly comparable amongst themselves. 
 
 297. Air is a substance, which, though not in general use 
 in the construction of thermometers, is adopted in peculiar 
 trains of experiment ; and the student, when engaged in con- 
 sidering the researches of Mr. Leslie and MM. Petit and 
 Dulong, will have occasion to observe the valuable uses to 
 which these philosophers have put instruments containing it. 
 The simplest air thermometer consists of a thin glass bulb at 
 
 the end of a tube, in which is placed a 
 small cylinder of clean mercury. As 
 the bulb changes in temperature, the air within expands and 
 contracts, and has its changes of bulk indicated by the motion 
 of the metal. 
 
 298. The great expansion of air by small increments of heat, 
 makes these instruments very delicate, but they are liable to 
 actions and accidents which render them quite unfit to replace 
 mercury and alcohol thermometers. In the first place, the 
 bulk of the air is readily affected by pressure, so that altera- 
 tions in the barometer cause movements in the mercury without 
 alteration of temperature. For the same reason difference of 
 position causes different indications as the cylinder of metal 
 presses upon, or draws against the air within ; causing conse- 
 
Sect. IV.] A1R THERMOMETER. 141 
 
 quent changes of volume. In the next place, the mercury is 
 liable to change its situation, and to allow air to pass, if the 
 tube be large ; and, on the contrary, if the tube be small, the 
 mercury has a tendency to adhere, and will not readily give 
 way before the air pressing on one or the other side of it. 
 
 299. When another fluid than mercury is used, the instru- 
 ment not only remains liable to the effects of pressure, but is 
 subject to other inconveniences ; for if the fluid be water, or an 
 evaporable substance, it sends a variable portion of vapour into 
 the globe, according to its temperature, and thus occasions ex- 
 pansion not due to the mere expansion for temperature of the 
 air within ; if it be sulphuric acid, it gradually attracts water, 
 and, becoming diluted, is then liable to the same objection ; 
 and if oil be used, it, together with the other fluids, flows 
 within the glass tube, adheres to it, and does not leave it as 
 the mercury does ; such adhesion is incompatible with accurate 
 measurement. 
 
 300. These instruments can only be used in connection with 
 the barometer. They merely give comparative results, unless 
 indeed their scales be laid down at the time from a mercurial 
 thermometer; and then, from the largeness of the degrees, 
 they serve to indicate very minute changes. When mercury 
 is the substance in the tube, which, by its motion, indicates 
 the change of bulk and consequent alteration of temperature, 
 a few taps given to the instrument will facilitate its change of 
 place. The instrument should always be used in the same 
 position, and if the experiment admits of a horizontal one, it is 
 an advantage, for then the results are not complicated by the 
 pressure of the metal. 
 
 301. The air thermometer has had numerous forms given 
 to it, but it will be unnecessary to consider all of them. Some- 
 
 times it is placed with the bulb upwards, and the lower 
 end immersed in a fluid, which, rising and falling within, 
 indicates the change in the volume of the air: some ob- 
 jections are thus avoided, others are originated. Some- 
 times, in place of dipping into a fluid, the end is turned 
 up, and terminated in a bulb open to the air, and this 
 being partly filled with fluid, a portion of it rises into 
 the tube, and indicates changes in the inclosed air as 
 
142 DIFFERENTIAL THERMOMETER - IGNITION. [Sect. IV. 
 
 before. The scales attached to these instruments are usually 
 of a temporary and arbitrary nature ; for as, from various 
 causes, the latter differ at different times, they will not admit 
 the application of permanent portions of the scales of other 
 thermometers. 
 
 30. The instrument used by Mr. Leslie in his investiga- 
 tions differed in construction from those described, and was by 
 him named the differential thermometer. In this instrument, 
 the aperture, instead of being left open, is attached to a second 
 ball, similar to the first, the tube connecting them being bent 
 Q twice at right angles, as in the figure, and the whole 
 
 closed, so that the indicating fluid within is entirely 
 free from the pressure of the external atmosphere. 
 The fluid used is sulphuric acid, tinged by a Jittlo 
 carmine ; it yields no vapour to the air in the bulb, 
 and should be in quantity sufficient to fill one of 
 
 
 the perpendicular legs and the horizontal part of the tube. 
 When in use, the situation of the fluid is observed whilst both 
 balls are of equal temperature, and then one is subject to the 
 heating or cooling influence, whilst the other is retained un- 
 changed ; the motion of the fluid in the tube indicates whether 
 heat or cold has been occasioned, and, comparatively, to what 
 extent*. The scale is generally arbitrary, but may at any 
 time be compared experimentally with that of a good ther- 
 mometer. 
 
 303. With respect to instruments fitted to measure higher- 
 degrees of heat than those which can be borne by mercurial 
 thermometers, we are yet deficient ; nor does it seem likely 
 that the want will soon be supplied. The student will do 
 well to observe the appearances of a furnace or a substance, as 
 it rises from a dull red heat to the highest possible temperature 
 that can be given to it ; to form in his mind a clear idea of the 
 colour and appearance of the light emitted in succession ; and 
 to select three or four distinct periods of the ignition to serve 
 him, as it were, for degrees. The terms dull red, red, full 
 red, yellow, white, bluish white, or any others he may choose, 
 should not be quite indefinite, but so far understood and appre- 
 
 * Leslie's Experimental Inquiry into the nature and propagation of Heat, p. 9. 
 
Sect. IV.] PYROMETER DANIELI/S. 143 
 
 ciated, and the appearance he intends to express by them so 
 fixed in his mind, that he may be able to say at once whether 
 a fire is above or below any required degree ; or, having 
 registered a particular heat by its appearance in his note book, 
 that he may be able to attain it again with considerable 
 accuracy. 
 
 304. The instrument called Wedgwood's pyrometer, at one 
 time claimed much attention, for the apparent facility of its 
 application, and accuracy of its results. It consisted of pieces 
 of clay which, being heated to a higher or lower degree, con- 
 tracted more or less ; and the contraction being measured, was 
 considered as proportionate to, and therefore a measure of, the 
 temperature to which they had been subjected. Sir James 
 Hall, however, shewed that the indications were fallacious, 
 inasmuch as the same contraction was produced by a long low 
 heat as by a shorter and higher one. Even supposing this 
 could to a certain degree be guarded against by attention to 
 time, the instrument is inapplicable, because the pieces of clay 
 are no longer prepared and sold, in consequence, as it is under- 
 stood, of irregularities in the kinds obtained from different 
 sources. 
 
 305. DanielFs pyrometer, the best instrument of the kind * 
 which has been constructed, claims our attention. Its indica- 
 tions result from a difference in the expansion and contraction 
 of a platina bar, and a tube of black lead ware in which it is 
 contained. These differences are made available by connecting 
 an index with the platina bar, which traverses a circular scale 
 fixed on to the tube. The degrees marked on the scale, though 
 arbitrary, are in each instrument compared experimentally 
 with those of the mercurial scale, and the ratio marked on the 
 instrument ; so that its degrees are readily convertible into 
 those of Fahrenheit. The instrument, after use, will return 
 on cooling to the point from which it set out, and when applied 
 to ascertain a particular temperature, the fusing point of silver, 
 for instance, will give nearly the same indication every time. 
 It is, therefore, much superior to any other that has yet been 
 constructed to measure high temperatures. More recently, 
 
 * Quarterly Journal of Science, xi., 309. 
 
144 COMMINUTION IMPORTANT. [Sect. V. 
 
 Mr. Daniell lias improved this instrument still farther by sepa- 
 rating the scale from the indicating part, so that the latter may 
 be placed wholly in the fire, or even immersed in fuzed metal. 
 Hence, although not so facile in its use as the common ther- 
 mometer, which, indeed, is remarkable for its simplicity, yet it 
 promises to be of extensive use ; and in the numerous situa- 
 tions where circumstances admit of its application, as in glass- 
 houses, potteries, furnaces of all kinds, &c., it far surpasses any 
 other instrument, and furnishes indications of great compara- 
 tive delicacy. 
 
 SECTION V. 
 COMMINUTION. 
 Trituration, Mortars, Granulation, Precipitation. 
 
 306. THE division of matter is often highly advantageous 
 in facilitating chemical action, and various processes have been 
 devised for effecting it in the laboratory ; some suited to the 
 nature of the substance to be divided, others to the particular 
 state of division required. These processes are both mecha- 
 nical and chemical ; for fusion and solution are more fre- 
 quently referred to as means of separating the particles of 
 matter one from another, than for any other purpose (356). 
 The latter processes will not be dwelt upon at present; what 
 relates to them, connected with the object of this book, ar- 
 ranges more conveniently in other sections, and hence, in this, 
 the references to them will be only incidental. The operations 
 more immediately in view, are those which, while they divide 
 a substance, do not alter its physical state. These of course 
 apply to solid bodies only, and the substance, after the ope- 
 ration, is still in the solid form, however minutely the particles 
 may have been divided. No merely mechanical division can 
 bring a solid body into a state, comparable as to physical 
 properties, with the same body when it has had freedom of 
 motion given to its particles by fusion or solution. 
 
Sect. V.] MORTARS PESTLES. 145 
 
 307. Of all the processes adopted in the laboratory for these 
 purposes, none is more extensively useful than that of tritura- 
 tion ; chemical operations cannot proceed well without it ; nor 
 is any vessel more generally convenient for the purpose than 
 the mortar and pestle, and hence, to meet the quantities and 
 qualities of different substances, several of these vessels, of 
 various sizes and materials, should be included in the labora- 
 tory apparatus. 
 
 308. In the first place, a large iron mortar, with its pestle of 
 the same material, and of a proper size and weight, should 
 stand on a block in some corner or convenient place in the 
 laboratory (19). It is useful for breaking large lumps into 
 smaller, and for the pulverization of ores, metals, and heavy, 
 coarse materials. Two or three mortars formed of earthy 
 materials, and of moderate sizes, from a pint to three pints in 
 capacity, should be provided for table use, and a smaller one 
 for rare substances. Those which are intended to effect the 
 pulverization, and at times the solution of various bodies, 
 ought to possess requisites which it is difficult to find com- 
 bined. A vessel is required of a material so hard as to bear 
 the blows and friction of other hard bodies for any length of 
 time, without suffering injury or abrasion of its surface; of an 
 uniform and compact texture ; not brittle ; not permitting 
 the absorption of fluids, or penetratfon by them ; not subject 
 to the action of acids, alkalies, or other solutions ; and of a 
 requisite capacity. 
 
 309. The difficulty of finding these properties united, has 
 caused the introduction of a variety of mortars for various 
 uses. Those for common occasions should admit of the pul- 
 verization of most substances, and the preparation of acid, 
 alkaline, and metallic solutions. These purposes were well 
 answered formerly by mortars of Wedgwood's ware, and 
 there were some excellent ones to be bought with the name of 
 Mist upon them ; but at present no mortars made of porcelain 
 or artificial ware can be procured fit for the laboratory. Both 
 form and material have deteriorated*. A mortar of this kind 
 should scarcely allow of being scratched by the edge of a piece 
 
 * Messrs. Wedgwood are occupied in endeavouring to improve this manufacture. 
 
 L 
 
146 THICKNESS DIMENSIONS. [Sect. V. 
 
 ' ** 7^ *4 ** 
 
 "'* ""'?- . * 
 
 of quartz or flint, and absolutely resist steel, not by any glaze on 
 its surface, but on an accidental fracture, as well as other parts. 
 It should not be stained by having a strong acid solution of 
 sulphate of copper or muriate of iron put into it when dry, 
 and left for twenty-four hours, but should allow the salt to be 
 washed off without any difficulty by cold water. On rubbing 
 down an ounce of sharp river or sea sand to fine powder, the 
 sand should acquire no appreciable increase of weight. It should 
 be sufficiently thick at the bottom to resist the blows to which 
 it will at times be subject, as well as to give weight and steadi- 
 ness. It should not be of brittle material, and 
 therefore fragile or apt to shiver, though, if 
 unavoidable, that fault is more easily borne 
 with than any other of those mentioned. The 
 proportionate thickness of the vessel in different 
 parts relative to its capacity may be represented by the accom- 
 panying woodcut. 
 
 310. The pestles should be of one piece, and of the same 
 material and qualities as the mortar. If in two pieces, as is 
 sometimes the case, the handle being of wood and the bottom 
 only of ware, the cement by which they are fastened occasion- 
 ally falls out, and produces injury to the materials in the 
 mortar ; or by the contraction of the wood, and other causes, a 
 space is formed, which, sometimes receiving and sometimes de- 
 livering dirt, may injure an experiment. The pestle should 
 be strong, and its size such as may be sufficient above to allow 
 of its being grasped firmly in the hand, and below to permit a 
 considerable grinding surface to come in contact with the 
 mortar. Its diameter, in the lower part, may be about one- 
 third, or one-fourth of the upper diameter of the mortar. 
 The curve at the bottom should be of shorter radius than the 
 curve of the mortar, that it may not touch the mortar in more 
 than one part/whilst at the same time the interval 
 around may gradually increase, though not too 
 rapidly towards the upper part of the pestle. A 
 mortar and pestle of the relative convexity figured 
 in the margin, may, by inclining the pestle, or 
 bringing it to different parts of the mortar, allow portions of 
 such different curvature to be placed in juxtaposition, that the 
 
Sect. V.] MORTARS PORPHYRY AGATE. 147 
 
 intervening space shall increase more or less rapidly from the 
 point of contact, in almost any proportion ; a variation which 
 it is of considerable consequence in pulverization to obtain 
 with facility. 
 
 311. Neither pestle nor mortar should be quite smooth at 
 the grinding surfaces, or the materials will slip about between 
 them, and not be retained and pulverized. The roughness of 
 unglazed ware is quite sufficient for this purpose. A rough- 
 ness of this kind is sometimes obtained by use, and is the best 
 that can be produced ; but it indicates that the mortar is 
 abraded by the substances rubbed in it, and, if it happens 
 quickly, shows that the vessel is deficient in hardness. When 
 the mortar is such as to wear but little, and is good in other 
 respects, it is then proper to rub a quantity of sharp sand or 
 emery to powder in it, until the required roughness of surface 
 is produced. The operation will be long and laborious, 
 but a good mortar will repay the pains it requires. Besides 
 these mortars, a couple of small ones of the same materials 
 should be procured. They should all of them be lipped, for 
 the convenience of pouring out fluids or fine powders. 
 
 312. Excellent porphyry mortars are brought to this country 
 from Sweden ; they are very hard, and resist all ordinary 
 chemical action, but they cannot be obtained of large size, 
 and are expensive, from the difficulty of making them out of a 
 solid block. Their forms are variable, being in part dependent 
 upon the pieces out of which they are worked. They should 
 be accompanied with pestles of the same substance. 
 
 313. Small mortars and pestles are also made of agate, and 
 are exceedingly useful for the pulverization and mixture of 
 small portions of matter, which have either been weighed or 
 are scarce. They are generally made more shallow than ordi- 
 nary mortars, and, in consequence of their form, size, hardness, 
 and closeness of surface, allow of the matter being collected 
 with less risk of loss than from mortars of earthenware. Their 
 hardness is such as to enable them to resist abrasion better 
 than any others. They should not be inconsiderately sub- 
 jected to blows, being more brittle than the porphyry or ware 
 mortars, and occasionally having numerous and almost imper- 
 ceptible cracks running through them, which, though so close 
 
 L 2 
 
' 
 
 , 
 
 148 tJSES OF THE MORTAR BREAKING, fSect. V 
 
 as not to interfere with their ordinary use, render them weak. 
 If agate mortars be not left roughened within by the workman, " 
 it takes a long time by ordinary wear to render them so. It 
 is better, therefore, to effect it in such cases by means of the 
 pestle, and a little emery or sharp sand. 
 
 314. Mortars of wood, marble, or iron, are unfit for ordi- 
 nary laboratory service, because of their softness, and the 
 action of different fluids and substances upon them. A 
 wrought-iron mortar of from a pint to a quart in capacity is 
 useful in particular cases, not merely for the pulverization of 
 substances which, not acting upon it, would be too tough or 
 require too many blows for a common mortar, but also as a 
 vessel to contain mercury in its ordinary or in a heated state ; 
 it should have an accompanying pestle of iron. Glass mortars 
 are generally unfit for the laboratory, being too soft and brittle, 
 and yielding both alkali and lead to particular solvents. Their 
 uses are indeed so confined as to render it wise to exclude them 
 altogether. 
 
 315. Let us now consider the operations in which a mortar 
 is available. Most stones may be broken if held lightly in the 
 left hand and struck smartly ^with a hammer ; but when the 
 pieces are reduced beneath a certain size, their inertia does not 
 then afford sufficient resistance. In these and in other cases, the 
 substance, if not too hard, may be broken into smaller pieces 
 very conveniently in a mortar, without loss or dispersion of the 
 fragments. For this purpose it should be placed in the mor- 
 tar, and struck with the pestle in successive sharp firm blows, 
 but not too forcibly. If the body be rather tough, as a piece 
 of sal ammoniac, the pestle should be held firmly in the hand, 
 and impelled, not merely by its descending weight, but the 
 force of the arm should be added and continued, until it is 
 stopped by the substance, something like a thrust being given 
 to it as well as a blow. On the contrary, if the substance be 
 brittle, as glass, or many ores, it is better to hold the pestle 
 lightly in the hand, and, having urged it downwards, to let it 
 fall upon the substance with little more than its own force, using 
 it rather as the head of a hammer, than in the former manner. 
 
 If there be any risk of the fragments being thrown about, the 
 mortar should be covered with a flat piece of pasteboard or 
 
Sect. V.] BREAKING BODIES FRAGMENTS CONFINED. 149 
 
 millboard, having a hole in the middle, through which the 
 pestle may be passed. The fragments broken from the piece 
 pass from under the pestle, and have a general tendency up the 
 sides of the mortar ; hence a cover of this kind is quite suffi- 
 cient to oppose their passage, and retain them within the vessel, 
 notwithstanding the hole in the centre should be considerably 
 too large to be filled by the pestle. For this reason one such 
 cover, in a clean state, will suffice for mortars of different sizes, 
 and should have its assigned place on the walls of the labora- 
 tory. When such a cover is not at hand, a clean cloth with a 
 hole in it for the passage of the pestle may be used, being 
 drawn by one hand tightly over the mouth of the mortar, 
 whilst the other holds the pestle. This is better than to cover 
 both mortar arid pestle with a whole cloth, and to grasp the 
 pestle through it, whilst breaking the body ; for then the cloth 
 hangs in folds, is considerably agitated, and frequently catches, 
 and even scatters portions of the substance. 
 
 316. If the piece to be broken be too hard for the mortar, 
 whilst large, which is now and then the case, or there be 
 reason to fear, injury from it, then it must be either broken in 
 the hand (315), or split or crushed by a hammer on the anvil. 
 When of convenient size, it should, after being laid upon the 
 anvil, be surrounded by the hand, or by the thumb and one, 
 two, or three fingers, according to its size, so that, when struck 
 by the hammer, and split into several pieces, these should not 
 be scattered, but retained together, and afterwards separated 
 by the fingers. The blows should be steady, small at first, 
 and increased in force, until sufficiently powerful. It is not 
 desirable to crush the substance at once, but to break it into 
 large, and afterwards into smaller fragments ; and if the body 
 be one which gives way by degrees, the fracture should be 
 effected by successive blows, and not on a sudden. It is desi- 
 rable that the chemist should, in everything he does, endeavour 
 to obtain a command over the agents he is using, and not apply 
 them with such force, or so carelessly, as to render the results 
 accidental. Even in the breaking of a stone, advantage is 
 gained by a cautious mode of procedure, not merely as con- 
 firming a good habit, but as most effectually preventing waste, 
 and sometimes in preserving peculiar internal appearances. 
 
150 BREAKING ON THE ANVIL DEFENCES. [Sect*. V. 
 
 317. When the substance requires a blow so hard, that it is 
 unpleasant to expose the hand or fingers to the effects which 
 may happen upon its fracture, it may be wrapped up in one 
 or several folds of strong paper or cloth, and then be struck. 
 If the blow break it, the result will be indicated by the sound, 
 and the feel of the hammer in the hand ; if it does not, but at 
 the same time cuts the paper or cloth through, it is not neces- 
 sary for that reason to change the envelope, but the blow must 
 be repeated upon the same place, until the body does separate. 
 In both cases the fragments will be held together by the en- 
 velope, and it is easy to separate them from the wrapper when 
 opened out, by a little motion and friction. 
 
 318. Some substances, and especially some of the metals, 
 as cast iron, copper, alloys of copper, &c., when in mass and 
 cold, can scarcely be broken into\ smaller pieces on the anvil, 
 except by blows so powerful as to endanger neighbouring 
 bodies, and yet will crack and crumble with facility when 
 heated. In these cases, the substances should be made red 
 hot, and struck in that state, until they are sufficiently cracked, 
 and the. separation completed in the vice,, either immediately, 
 or after the temperature has fallen. 
 
 319. Before leaving this subject of the division of large 
 pieces into smaller, it will be proper to observe that many sub- 
 stances may be separated by nippers or a knife. In these 
 cases it is necessary to attend to the grain of the substance, 
 and take advantage of the greater facility of division which 
 exists in one direction than in another. Muriate of ammonia 
 will separate readily with the grain into pieces without much 
 crumbling. If it Js to be pulverized, place it in the mortar 
 with the grain upright, and not horizontal. 
 
 320. It may be remarked that there are many substances, 
 which, though too hard to be broken in the mortar when in 
 large masses, without endangering its fracture, or the abrasion 
 of its surface, still may be readily and properly pulverized 
 when in smaller pieces. 
 
 321. If the object be to reduce the substance into minute 
 fragments only, of the size of a pea, or pin's head, or smaller, 
 but not to powder ; then, having broken it down as before 
 described, the operation is to be continued in the mortar, by a 
 
Sect. V.] BREAKING SMALL PULVERIZATION. 151 
 
 series of blows from the pestle, all grinding action being 
 avoided. The pestle must be held lightly, and allowed to 
 fall sharply on the substance, being directed to those places 
 where the largest pieces are. A slight,, lateral, or shaking 
 motion of the hand holding the mortar, between each blow, 
 will help to return the larger pieces from the edge towards 
 the middle of the mass of fragments, where they ought to be 
 when struck, and no blow should be given towards the edge, 
 if it can be avoided ; it there only tends to reduce those parti- 
 cles smaller which are small enough, and if a large piece be 
 struck there, its fragments are apt to fly up the sides of the 
 mortar ; whereas, if it were' in the middle of the substance, 
 they are caught and retained by the surrounding matter. 
 
 322. It will be found that a process of this kind, in which 
 all grinding action is avoided, will reduce a substance to small 
 fragments or particles, with the least production of fine powder ; 
 and this is highly desirable with some substances which are in 
 a more favourable state for experiment, when crushed or broken 
 into small pieces only, than when more minutely reduced. 
 Flint glass is as convenient a substance as any for the student 
 to practise upon for the acquirement of these methods and 
 illustration of their effects. 
 
 323, In pulverization a very different action of the pestle 
 and hand is required. The object then is to reduce the whole 
 of the substance into fine particles as rapidly as possible. The 
 process of striking or stamping would now be found too slow ; 
 a grinding action is necessary to expedite the operation, and 
 this it will be proper to adopt as soon as possible. Even, 
 therefore, whilst breaking down the larger lumps into smaller, 
 it will be desirable to alter the character of the blow; and 
 instead of holding the pestle lightly in the hand, and letting it 
 almost drop on to the middle of the substance, it should be 
 grasped firmly, and forced down by the muscles of the wrist 
 and arm, pressure being added to the blow ; and it should be 
 made to fall on the substance at the side of the mortar, the 
 pressure being continued till the pestle has reached the middle. 
 The blow is to be oblique in its direction, going down the 
 side of the mortar to the centre. It is best given on the part 
 farthest from the operator, more force being then exerted, as 
 
152 METHOD OF PULVERIZING IN MORTARS. [Sect. V. 
 
 it is continued by a downward pressure to the middle of the 
 mortar. This kind of stroke breaks the larger fragments, 
 grinds both these and the smaller, and mixes and alters the 
 position of the whole ; and, if continued in the same direction 
 whilst the mortar is turned a little way round by the other 
 hand between each stroke, every part of the substance is 
 brought in succession under its comminuting action. 
 
 324. The substance is thus soon reduced to particles so 
 small, that the pressure of the hand is sufficient to continue 
 the division without the force of a blow. After this it is most 
 expeditious to advance the operation by rubbing. For this 
 purpose, the pestle, being grasped firmly, should be moved in 
 larger or smaller circles around the centre of the bottom, at 
 the same time pressing hard and regularly upon it. It is in 
 vain to expect a rapid effect in tjiis operation without pressure, 
 or to give pressure without labour, but certainly much labour 
 is exerted in vain by those who give an unequal and uncertain 
 pressure. The motion of the pestle should be in circles, com- 
 mencing at the centre, and gradually expanding outwards : 
 this, whilst it grinds the substance, gradually displaces it, turns 
 it over, and mixes it. When it has arrived at the exterior of 
 the mass, the circles described should gradually be contracted, 
 until they have again closed in the middle, when they should re- 
 expand, and thus the operation be continued until the powder 
 be sufficiently fine. The process is least fatiguing to the hand 
 when the circles are up the side of the mortar, towards the 
 limits of the substance, and the grinding proceeds most rapidly 
 there. By making a smaller circle now and then, it is easy 
 to urge the fragments outwards in that direction, so as to take 
 advantage of the most favourable circumstances. Occasionally, 
 deviations from this regularity may be convenient, for the pur- 
 pose of moving the substance in different directions ; but it 
 will be found that the more nearly they are adhered to, the 
 more rapid will be the operation. 
 
 325. The pestle may be held in both hands in succession, 
 for the relief of the wrists ; but the hand not occupied by it 
 should take charge of the mortar, and, holding it firmly and 
 steadily, should sometimes turn it a little way round, espe- 
 cially if the force of the hand holding the pestle be unequal 
 
Sect. V.] 
 
 MORTARS. 153 
 
 in different parts of the circle. The motion of the pestle 
 may be either in one direction or the other, and an inver- 
 sion of it is now and then advantageous for the more effec- 
 tual mixture of the particles. During the whole process 
 it should be observed, that every part of the powder is 
 rubbed, and the tendency should be to grind those parts 
 first which appear coarsest, and not to finish one portion 
 before another. 
 
 326. The opportunity already referred to of obtaining dif- 
 ferent inclinations between the surface of the pestle and that 
 of the mortar (310), by either inclining the pestle or carrying 
 it to different parts of the mortar, may now be taken advan- 
 tage of. At the commencement of the grinding, for instance, 
 whilst the particles are coarse, it will be proper to incline the 
 pestle so, that the preceding part may pass over them ; by 
 which they are included between it and the mortar, and are 
 crushed by the following part. Particles are thus instantly 
 broken down, which, if the pestle were held upright, or if 
 inclined in a wrong direction, would merely be pushed for- 
 ward. In the same way, even when the powder is of con- 
 siderable fineness, the pestle may be made to have more of a 
 mixing or a grinding effect, according as it is inclined one way 
 or the other both being peculiarly desirable at times. Many 
 other advantages of this kind are attainable, which are, how- 
 ever, better learnt by practice than from description, which 
 would necessarily be very minute and tedious, and at the same 
 time very imperfect. 
 
 327. The student should be aware also of the peculiar uses 
 of the different parts of the inner surface of the mortar. The 
 powder lies quietly at the bottom of the mortar ; on the sides, 
 a little way from the centre, it also rests with facility, but with 
 a tendency to pass to the middle as the pestle moves over it ; 
 farther outwards it arrives at a part so inclined, that, when 
 forced upwards as the pestle passes, it falls back again when 
 left at liberty ; here consequently a mixing agency may be 
 exerted, whilst the operation of grinding goes on more effec- 
 tually at a part nearer the centre, not merely because the 
 powder rests there and awaits the approach of the pestle, but 
 also because, from its being nearer to a horizontal position, 
 
* 
 
 . 
 
 154 PULVERIZATION - QUANTITY OF SUBSTANCE. [Sect. V. 
 
 * # * 
 
 the hand has more command over the pestle, and power in 
 pressing it down. 
 
 328. The quantity of a substance put into the mortar at 
 once, should bear a proportion to its particular qualities and 
 to the ultimate state of fineness required. If the substance 
 is to be finely pulverized/ only small quantities should be 
 operated on at once, so as to form but a thin layer at the 
 bqttom in those places which the pestle has passed, and to 
 insure the subjection of the whole to trituration. If the layer 
 under the pestle be thick, a grain may be imbedded in it, and 
 remain uncrushed by the pressure. If the substance be in 
 great quantity, a particle may be pushed about from side to 
 side, enveloped in the mass, and without coming under the 
 pestle at all ; and what may happen to one particle may happen 
 to many, and thus the powder^ie a mixture of coarse and fine. 
 For coarse powders larger quantities may be taken. Hence, 
 also, when a lump is to be broken down into a fine powder, 
 it is frequently better to reduce it to a coarse powder, and 
 then, removing it from the mortar, to return it in small portions, 
 each of which is to be brought to the state of fine powder 
 by itself. 
 
 329. A soft or readily pulverizable body may be put into 
 the mortar in larger quantities than a hard one ; thus a larger 
 quantity of chalk may easily be reduced to a fine powder at 
 once, whereas, if as much siliceous sand were operated upon, 
 the attempts to reduce it to a powder as fine would fail, or be 
 interminable. It is easy to understand that any substance 
 whose particles are so hard as to require direct pressure be- 
 tween the mortar and pestle, is in too great a quantity when 
 there is so much present as to prevent the approach, almost 
 to contact, of the two grinding surfaces. 
 
 330. The state of fineness to which a powder has been 
 reduced is judged of principally by the appearance. If the 
 body be coloured, the colour becomes paler as the powder is 
 finer, and generally at last almost disappears. When the 
 powder, in place of flowing freely down the sides of the mortar, 
 begins to adhere and clot as it 'were, it is also a mark of con- 
 siderable division ; and when it is in such a state that, previously 
 dry and granular, it now seems almost moist, and, being moved 
 
-- 
 
 Sect. V.] PULVERIZATION PECULIAR CASE. 155 
 
 about by a spatula, preserves the form given to it even when 
 the lateral surfaces are perpendicular, it is then in an extreme 
 state of division. This indication must, of course, be con- 
 sidered in connection with the hygrometric powers of the body. 
 The student may observe all these appearances by oper- 
 ating upon a few fragments of bottle glass (not flint glass, 
 for then some fallacies are introduced), or a few pieces of 
 calcined flint. 
 
 331. Passing from this general consideration of the process 
 of pulverization, it may be observed that particular bodies 
 require slight variations in the process for particular purposes. 
 If the substance be poisonous, or if it be in exceedingly fine 
 powder, and liable to dispersion from the motion of the air, 
 it may advantageously be moistened with a little water, pro- 
 vided that fluid has no action upon it ; but the trituration 
 is then more laborious, from the greater difficulty of mixture 
 and the adhesion of the substance : it is, however, a precaution 
 continually adopted with substances subjected to the grinding- 
 mill. When the pulverization is finished the substance may 
 be dried, if that be necessary, or, if not, left in the state in 
 which it comes from the mortar. At other times, to confine 
 the powder, the mortar may be closed up by a cover, a mill- 
 board, or a cloth, as described in the directions for breaking 
 down substances (315) ; but the aperture should now be as 
 small as possible, or the finer particles will escape by it. 
 
 332. When the substance to be pulverized is stony and 
 hard, advantage is frequently gained by igniting the mass, 
 and quenching it in water. Flints, many siliceous and other 
 hard stones, are thus rendered more brittle and divisible, and 
 their comminution considerably facilitated. Charcoal is a 
 substance which is found to pulverize with far greater ease 
 and rapidity when hot, or after being recently heated, than 
 when cold ; ignite it, therefore, and in this state introduce it 
 into the mortar, and instantly rub it to powder. Camphor, 
 which has a toughness under the pestle, is easily reduced to 
 powder when moistened with a few drops of alcohol. Gum, 
 when pulverized, should be kept perfectly dry. Zinc may 
 be reduced to powder when hot, in a heated iron mortar, the 
 pestle also being heated. 
 
156 POWDERS MOVED SPATULAS, ETC. [Sect. V. 
 
 333. Shell-lac, some resins, and other substances, when 
 divided for the purpose of facilitating solution, are better in 
 small fragments than in fine powder. Adhesive organic sub- 
 stances which would knead together under the pestle, are 
 frequently rendered capable of division in the mortar, by being 
 mixed with clean sand or glass ; such substances being chosen 
 in these cases as will be inert with respect to the agents to 
 which the bodies are to be subjected. 
 
 334. The transference of materials to and from the mortar, 
 and generally of substances in powder or small grains, is most 
 conveniently effected by the use of spatulas, or similar instru- 
 ments. Common broad bone paper-knives make excellent 
 spatulas for the laboratory, for this and other uses, and may 
 be used to disturb or separate the substance when it adheres 
 together in the mortar, or teethe sides of the vessel ; but the 
 precaution must be taken of not using them in those cases 
 where they may affect or be affected by the substance, or where, 
 from its strong adhesion to the mortar, the removal may cause 
 such abrasion from the spatulas as to communicate so much 
 matter as to be injurious to the experiment. In these cases 
 the platina spatula before referred to in weighing (62) is to be 
 used, and hence a reason for the degree of thickness and 
 strength already recommended. 
 
 335. When the substance to be pulverized is coarse, and 
 Us quantity unimportant, a piece of pasteboard or a card is 
 very useful in supplying the place of the spatula, in clearing 
 the substance from the mortar ; it at times even surpasses it 
 in effect and convenience, from its pliability and consequent 
 adaptation in form to the mortar, and also from the larger 
 quantity which it will lift at once. Some waste cards should 
 always be ready, in one of the laboratory-drawers, for these and 
 similar uses. 
 
 336. Where a hard substance is to be pulverized for the 
 purpose of delicate analysis, it is sometimes necessary to take 
 into account the matter which may be removed from the 
 mortar during the process, and estimate its influence in in- 
 creasing the quantity of products ultimately obtained. In such 
 cases a mortar of known composition should be used, one of 
 agate for instance, where the substance removed may be 
 
Sect. V.] 
 
 PULVERIZATION DIAMOND. 157 
 
 assumed to be silica, and thus the correction made at the 
 proper time, by subtracting so much weight from the silica 
 evolved in the analysis. 
 
 337. It is highly important that the pupil should be aware 
 of the hygrometric power of many substances, which, when 
 they are reduced to powder, is so greatly developed by the 
 enlargement of surface, as very seriously to increase the whole 
 weight of the substance. M. Pajot Descharmes says, that he 
 has had an increase in the weight of rock crystal by mere pul- 
 verization to such an extent, that the original weight was 
 doubled *. 
 
 338. The diamond is most conveniently pulverized in a 
 steel mortar, having a cylindrical chamber ; the pestle is re- 
 placed by a steel cylinder of such size as to pass easily into 
 the cavity. The diamonds are first introduced, and afterwards 
 the cylinder ; and the latter being struck with a hammer, the 
 gems are crushed and reduced to powder of any degree of 
 fineness required, without the risk of dispersion. When first 
 used, a portion of diamond is lost, as it were, by adhesion to 
 the steel surface : this should be left, because it prevents a 
 similar loss at a second or third operation. Such a mortar 
 should be reserved exclusively for the pulverization of these 
 gems ; for, besides avoiding a repetition of the loss already 
 referred to, it would be laborious and difficult to clean the 
 instrument so completely from diamond, that if sapphires, for 
 instance, were afterwards pulverized in it, a portion of diamond 
 should not be mixed with the produce. 
 
 339. In analysis and other operations, a given weight of a 
 substance in powder, as 100 or 200 grains, is often required. 
 This quantity should not be first weighed out, and then pul- 
 verized, because probably a little loss would occur during the 
 operation from adhesion to the mortar, and to the transferring 
 tools ; but more than the weight required should be reduced 
 to powder, and when in a proper state, the exact quantity 
 should be weighed out. 
 
 340. Pulverization is sometimes useful, not for the purpose 
 of accelerating chemical action, but on other accounts. When 
 substances are to be heated which decrepitate in the fire, by 
 
 * Recueil Industrie!, vii. ; 64. Quart. Journ. New Series, iv., 425. 
 
158 SEPARATION OF PARTICLES WASHING. [Sect. V. 
 
 which portions may be dispersed and lost, the effect is pre- 
 vented by previous pulverization. Decrepitation is generally 
 occasioned by the expansion of the outer portions before the 
 interior has had time to heat, and in that respect resembles 
 the breaking of a glass vessel by a sudden increase of temper- 
 ature. By comminuting the substance, this difference in 
 different parts of the same mass is avoided, and the body 
 sustains the heat without disturbance. If the substance be 
 liable to a similar effect from included moisture, pulverization, 
 by opening passages for the vapour, is equally effectual in 
 preventing it. 
 
 341. Pulverization is sometimes effected by grinding the 
 body under a muller, upon a flat stone ; but the process, 
 though useful in some of the arts, especially where the sub- 
 stance is to be mixed with fluid into a paste, is so inferior 
 
 %% to the use of the mortar, in Che laboratory, that it will be un- 
 necessary to describe it here. 
 
 342. It seldom happens, perhaps never, that the operations 
 of pulverization reduce the body into a powder consisting of 
 particles of equal size ; and in by far the greater number of 
 cases, the difference between them is evident. This, though 
 of no consequence on some occasions, renders it necessary on 
 others, to separate the mixture of differently-sized particles 
 
 * into portions containing such as more nearly resemble each 
 other in magnitude. The ordinary and well-known operation 
 of sifting is so simple as to require no notice here, except to 
 point out the use of two or three sieves in the laboratory, 
 which, if used for different substances, should be cleaned after 
 >. every operation, either by a brush, or, which is better, by 
 passing a stream of water through them. 
 
 343. The sieve may also be had recourse to as an excellent 
 means for effecting the mixture of powders, provided the 
 particles are of such size as to pass very freely through it. 
 Two or more such powders, first mingled by the hand or a 
 spatula, and then passed twice or thrice through a sieve, will 
 be very uniformly mixed. 
 
 344. Another mode of separation, in very frequent use, is 
 that of washing ; for as light and minute particles are sus- 
 pended in a fluid, whilst the larger and heavier descend, it 
 
Sect. V.] WASHING OF POWDERS RESULTS. 159 
 
 thus affords a ready mode of separating them. This operation 
 can be applied to few bodies except such as are insoluble in 
 water, that being the fluid almost constantly made use of. It 
 may often be conveniently effected in the mortar in which the 
 pulverization itself is carried on. Suppose a stone were to be 
 reduced to powder, no particle of which should be beneath a 
 certain degree of fineness : the stone should be pulverized in 
 the mortar in the usual manner, and when, from the appear- 
 ance, it is concluded that a considerable quantity of fine pow- 
 der is produced, two-thirds of the mortar should be filled with 
 water, and the powder mixed well up in it ; being now allowed 
 to stand a very short time, until the particles which are con- 
 sidered as too coarse have descended to the bottom, the super- 
 natant mixture should be poured off into a large basin or jar, 
 leaving the heavy powder only in the mortar, with a little 
 water. Then, without adding more water, or endeavouring 
 to remove that which is still present, the pestle is to be used 
 again, until, from the ready mixture of the substance with the 
 water, and the production of a smooth soft paste, it is assumed 
 that much more of it has been reduced to fine powder. Water 
 is to be added to wash this off as before, the finer part being 
 put to the first portion separated ; and the operator is again to 
 proceed with the comminution of the residuum until it has 
 in this manner been entirely removed from the mortar. 
 
 345. If by this process the powder be sufficiently reduced, 
 and a greater regularity as to size amongst its particles be not 
 required, then the mixture of it with water should be left qui- 
 escent until the liquid be clear, and the powder in mass form a 
 stratum beneath. The former should then be poured off, and 
 the latter dried ; and if during desiccation it adheres and pro- 
 duces soft lumps, these are easily broken down in the mortar. 
 
 346. If, on the contrary, more uniformity in the powder be 
 required than is thus obtained by a first set of operations, it 
 may be effected by a second, and this will often be necessary 
 when the substance pulverized is such, that a very short period 
 only can be allowed for the deposition of the larger particles ; 
 for the motion of the water not having subsided, and being 
 unequal in different parts, some large particles will pass over 
 with the finer. In such cases a return of the matter to the 
 

 160 WASHING - IN A MORTAR ITS USES. [Sect. V. 
 
 mortar, and a repetition of the washing, will frequently sepa- 
 rate much of the substance that requires further trituration. 
 This second washing need not be deferred till the whole has 
 settled from the water of the first washing ; but all being stirred 
 together, and allowed to stand for rather a longer period than 
 before, the suspended portion may then be poured off, and the 
 rest operated with as directed (344). 
 
 The longer the period allowed for subsidence, so much the 
 finer will be the particles still remaining in suspension, and 
 .,. hence an easy process for obtaining the substance in powder 
 divided to any degree required. 
 
 347. Another method of washing is to use a small mortar, 
 and, after having powdered the dry substance in the usual 
 way, to place the vessel in a large strong dish, and then, 
 directing a small stream of water into it, to continue trituration 
 in a steady, slow manner. The water, after filling the mor- 
 tar, will flow over into the basin, carrying the smaller par*- 
 ticles with it ; and as the trituration proceeds, the current will 
 continually separate the finer part, until the whole has passed 
 from the mortar into the dish. The fineness of the particles 
 washed over is regulated by the depth of the mortar, the size 
 and force of the current, and the degree of agitation given by 
 the pestle in grinding. To insure a powder of considerable- 
 uniformity, the operation should be repeated as before de- 
 scribed (346). 
 
 348. The same principles and processes may be applied to 
 the separation of insoluble substances of different specific gra- 
 vities. If an ore contain metallic silver diffused through 
 an earthy matrix, the processes of pulverization and washing 
 will almost entirely separate the earths from the metal. Or 
 if platina ore be treated in the same way, a separation of the 
 iridium and osmium, and other substances, from the grains of 
 metal, may in this simple manner be effected to a great extent, 
 and the platina very much cleansed. 
 
 349. It is rarely that any other washing agent than water is 
 had recourse to ; but in peculiar cases, and for small quantities 
 of matter, oil may be used. From its tenacity it requires a 
 longer portion of time before deposition takes place, and the 
 division may consequently , be more accurately effected. It 
 
Sect, V.] DIVISION OF SILICA GRANULATION. 161 
 
 may be burnt off so as to be entirely removed from the powder, 
 provided the latter be of such a nature as not to be affected by 
 the single or joint action of oil and heat. 
 
 350. If silica be required in a state of extreme division, it 
 may be obtained by mixing (343) one part by weight of finely 
 pulverized flint glass, with two parts of pulverized white 
 marble, heating the mixture to bright redness for half an hour, 
 rubbing it in the mortar and again heating it ; then acting 
 upon it in an evaporating dish (369) by muriatic acid added 
 till in slight excess, evaporating to dryness (592), and redis- 
 solving in warm water with a little muriatic acid. The in- 
 soluble portion is to be well washed in abundance of pure 
 water, until free from salts of lime or lead, and being then 
 dried, the silica will be in a state of division far surpassing any 
 which can be obtained merely by mechanical means. The 
 alkalies cannot be used in place of lime or its carbonate, for 
 this purpose, for portions of them remain combined with the 
 silica. 
 
 351. Of the metals, all that are brittle may be pulverized. 
 The division of zinc in this way when hot has been before 
 mentioned (332). Some metals may be obtained in a useful 
 state of division by granulation. This is particularly the case 
 with zinc, copper, tin, and lead. For this purpose, the metal 
 is to be melted in a crucible, and then poured from a height of 
 two, three, or four feet, into a pail or pan, full of water : a 
 considerable depth of water should be allowed, as the slight 
 explosions, which sometimes happen, are then less likely to 
 take place. If the water be hot, the pieces become filmy and 
 blown up as it were into bubbles ; if cold, they have more 
 solidity, are smaller, and approach nearer in their form to shot, 
 differences which are dependent also in part on the temperature 
 of the metal itself. The crucible should be moved during the 
 time the metal is running from it, that the descending stream 
 may continually change its place in the water. 
 
 352. Some metals are brought, by lamination, into a state 
 equally advantageous for chemical action from the extent of 
 surface exposed, as that produced by pulverization ; and the 
 process is applicable in cases when the latter cannot be resorted 
 to. Thus platina, tin, lead, zinc, copper, gold, and silver, are 
 
 M 
 
162 DIVISION OF METALS BY FILING. [Sect. V. 
 
 obtained in the state of foil ; platina, gold, and silver, in the 
 state of leaf ; and are highly advantageous in certain experi- 
 ments, when thus attenuated. The chemical action which 
 takes place between platina and tin is in no way so effectually 
 exerted, or so advantageously shewn, as when pieces of each 
 metal in the state of foil are laid together, folded up into a 
 ball, and heated red hot. They combine in that case with such 
 force as to produce vivid combustion. 
 
 353. The same advantage, dependant upon extension, is 
 obtained to a considerable degree by drawing the ductile and 
 tenacious metals into wire, their state being then for many 
 purposes equivalent to that of actual division. Pure iron, 
 which would resist the processes already described, is success- 
 fully attenuated in this way. 
 
 354. At other times the tough and ductile metals, as well 
 as some others, may be divided by the action of the file. In 
 such cases the files should be very clean. If new, attention 
 should be paid to the oil with which they are in that state gene- 
 rally covered. If they have been used, the absence of dirt, 
 metals, or other substances, from between the teeth, should be 
 ascertained and secured, and the clean state of the surface 
 upon which the filings are to fall, should not be forgotten. 
 Iron and zinc are most generally required in the state of 
 filings. 
 
 355. Occasionally metals may be divided into small particles 
 by being fused, and then poured into a wooden box and well 
 shaken until solid and much cooled. Zinc, lead, tin, anti- 
 mony, &c., may be so pulverized, but usually a part of the 
 charred wood is mixed with the metal, and the surface of the 
 particles is generally oxidized. This method should be used 
 only when no other is applicable or attainable. 
 
 356. Silver, copper, gold, platina, and lead, may be use- 
 fully divided by chemical means silver, by introducing a 
 plate of copper into a solution of acid nitrate of silver, until 
 about one-half or three-fourths are precipitated, the metal not 
 being allowed to accumulate upon the copper, but shaken off 
 from time to time, and at last (removing the copper plate and 
 solution) washed with distilled water until tasteless, and then 
 dried. Copper may be prepared in the same manner by 
 
Sect. VI.] SOLUTION ITS USES. 163 
 
 immersion of a plate of iron in a solution of sulphate of copper 
 with a little sulphuric acid added to it, and should after- 
 wards be washed with dilute sulphuric acid, then with water, 
 and finally dried. Gold may be prepared in very fine 
 powder by adding a solution of proto-sulphate of iron to one 
 of muriate of gold, and then washing with a little muriatic acid 
 and pure water. Platina is procured in a state of extreme 
 division, though the particles adhere slightly together, by 
 heating the ammonio-muriate of platina to dull redness in a 
 crucible, until fumes cease to rise. It has the appearance of 
 a sponge, though perfectly metallic. By heating the tartrate 
 of lead in a close vessel or a tube to dull redness, a mixture of 
 charcoal and lead is obtained, in which the latter is in such an 
 extreme state of division, that on exposure to the air it takes 
 fire. It is the pyrophorus of Dr. Gobel, and seems to owe its 
 property only to the state of division of the metal ; the action 
 of oxygen, which in general is merely sufficient to tarnish the 
 surface of lead, being here, from the comparative absence of 
 all solidity, and the existence of surface to an almost infinite 
 extent, so simultaneously exerted upon every particle as to 
 cause ignition. 
 
 357. Organic substances, which are not sufficiently brittle 
 to admit of pulverization, such as wood, horn, &c., may be 
 cut, or crushed, or rasped, or grated, according to circum- 
 stances ; a division sometimes gross, sometimes minute, being 
 required. 
 
 
 SECTION VI. 
 SOLUTION, INFUSION, DIGESTION, &c. 
 
 358. THERE are two great and general objects to be gained 
 by solution, which render it a process of constant occurrence 
 in the laboratory. The first is that of preparing substances 
 for the exertion of chemical action; and from the perfect 
 manner in which it separates the particles one from another, 
 
 M 2 
 
164 SOLUTION OF TWO KINDS. [g e ct. vi. 
 
 every obstacle dependant upon the attraction of aggregation is 
 removed, at the same time that other advantages are obtained 
 (306) : the second object is that of separating one substance 
 from another; this being continually effected by the use of 
 such fluids as have a solvent power over one or more of the 
 substances present. 
 
 359. These great uses of solution render it proper to shew 
 the means by which to effect and facilitate it ; in what manner 
 to select the vessels and solvents ; and to point out any pecu- 
 liar circumstances or conditions attending it, which may assist 
 the process. But it will be right to premise that the solution here 
 to be considered relates almost always to solid matter, sometimes 
 to liquid matter, but not at all to gaseous substances ; for any 
 processes or directions for the solution of gases in liquids will 
 be more intelligibly and instructively considered in the sec- 
 tion on gaseous manipulation. Indeed the processes requi- 
 site are so different to what are here to be described, as of 
 themselves to suggest the propriety of the separation. The 
 course of this section will be generally from inorganic to 
 organic substances ; for in that way the simplest instances and 
 methods will come first into view. 
 
 360. It may be remarked at the outset, that solution is of 
 two kinds, being effected either by fluids which have no che- 
 mical action upon the substances to be dissolved, or by others 
 which have such an action ; both are of constant use in the 
 laboratory. For where, as very often happens, solvents of the 
 first kind fail, recourse must be had to the latter, and then 
 much care and judgment is required in the selection of those 
 which will best effect the desired end. Attempts have been 
 made to distinguish between these two methods, by the use of 
 the terms Solution and Dissolution, but they have been partial 
 and imperfect, and chemical works now constantly speak of 
 solution of the metals, of earths, &c., and, therefore, virtually 
 reject the distinction. 
 
 361. Water is the great solvent whose aid is first to be called 
 in ; others are to be resorted to only when that is insufficient. 
 So general and important is its use, that in speaking simply of 
 the solubility of a body, water is always understood to be re- 
 ferred to. All aqueous solutions of solid bodies are heavier 
 
Sect. VI.] 
 
 SOLUBILITY INDICATIONS. 165 
 
 than water ; upon this difference is founded a very convenient 
 indication of solubility, frequently useful, always easy. It is 
 to suspend a piece of the substance in a glass of clear un- 
 disturbed water ; if the body be soluble, a descending current 
 will be seen to fall from it, and be visible upon looking through 
 the water horizontally. If it fall rapidly and in dense stria3, it 
 will indicate rapid solubility, and the formation of a dense so- 
 lution ; if it fall in a very narrow stream, it will indicate only 
 moderate or slight solubility ; and by its descending rapidly 
 or in a slow broad stream, or by resting about the substance, 
 a judgment may be made of the comparative density of the 
 solution produced. If no descending current appear, nor any 
 fluid round the substance of a refractive power or colour diffe- 
 rent to that of the water, then the body must be very nearly if 
 not quite insoluble at common temperatures. 
 
 362. Another indication of solubility is gained from the 
 taste. The saliva in the mouth is, as to mere solubility, nearly 
 the same as water, and, generally speaking, those substances 
 which are most sapid are most soluble. The impression of 
 taste in the mouth is, however, frequently a mixed sensation, 
 being dependant in part upon the olfactory nerves ; and con- 
 sequently odorous bodies will frequently appear to be highly 
 sapid, when they are not so upon the tongue*. This is the 
 case with camphor, which, if taken into the mouth after the 
 nostrils have been perfectly closed by the fingers, so that no 
 air can pass through them, will seem to have little or no taste, 
 whereas, the moment the fingers are removed, and the aroma 
 has access to the olfactory nerves, an intense taste, using the 
 word in its ordinary acceptation, is perceived. A similar effect 
 may be observed with a peppermint lozenge or a piece of cho- 
 colate. Still, however, the indication may in many cases be 
 useful, and lias the advantage of requiring no apparatus, and 
 being easy of performance. 
 
 363. If the substance appear to be insoluble, or if it be 
 necessary to know whether it be soluble in alcohol, ether, oils, 
 or any other body, for the purpose of selecting a solvent from 
 among them, a portion should be pulverized finely, and intro- 
 
 * Chevreul, Memoires du Musee, x. 439. 
 
166 SIGNS OF SOLUBILITY PRECAUTIONS. [Sect. VI. 
 
 duced into a small tube,, with a little of the fluid, to be tried, 
 and heated \ if the substance disappear, it is, of course, soluble. 
 But if it be supposed to be a mixed body, and partly soluble, 
 though not altogether so, then the presumed solution should 
 be poured from the tube into an earthenware or platina cap- 
 sule, and evaporated carefully and slowly ; if any substance 
 remain, it of course indicates solubility. Trials by evapora- 
 tion cannot be made with oil unless the body be fixed and will 
 allow the oil to be burned off; nor can trials of very volatile 
 bodies be made in this manner. It is almost needless to add, 
 that cases may occur requiring much chemical skill and judg- 
 ment ; and that it would be impossible to give directions for 
 every possible occasion. 
 
 364. Indications of solution dependant upon chemical ac- 
 tion are obtained from the changed appearance of the substance. 
 A body not soluble in water except by the use of acids or 
 alkalies, is generally, though not always rendered so by 
 chemical action, and has its properties changed. It is rarely 
 that these chemical agents are applied with any other liquid 
 than water. Indications of their power may be obtained in 
 the manner before directed. 
 
 365. With regard to the solution of one liquid in another, 
 no difficulty will occur in ascertaining whether it takes place 
 or not. A small portion of the most valuable should be put 
 into a tube, and then a very little of the other added to it ; 
 agitation, followed by rest, will shew whether the two have 
 permanently mixed, or whether they separate again. If the 
 latter be the case, let further portions of the second liquid be 
 added, agitating and observing as before ; and this should be 
 done until the whole becomes one clear fluid, or until the 
 volume is increased to many times its former bulk. A 
 conclusion, according to the state of things, must then be 
 made. 
 
 366. It may here be proper to warn the student of an 
 appearance which sometimes takes place during mere solution, 
 which has been frequently misconstrued into an indication 
 of chemical action. Common salt, and several other salts, as 
 well as their strong solutions, and also alcohol or spirit added 
 to common or even distilled water, which has been exposed 
 
Sect. VI.] SOLUTION HEAT VESSELS. 167 
 
 to air, frequently causes the evolution of a number of small 
 air bubbles ; these have the appearance of being the direct 
 result of some chemical action, but are occasioned merely by 
 the expulsion of the air dissolved in the water, which being 
 incompatible with the substances added, is separated. Some 
 of those solutions which dissolve air, produce the same ap- 
 pearances when added to the bodies mentioned. 
 
 367. Whenever a dissolving power exists at common tem- 
 peratures, it is generally heightened, and sometimes to a great 
 degree, by an elevation of temperature. There are only two 
 known cases in which heat diminishes the effect ; these occur 
 with lime and magnesia. But there is, I believe, no instance 
 of a body not soluble at common temperatures being rendered 
 so by the mere application of heat : it is the quantity of effect 
 only, and not its existence, that is thus influenced. The 
 change is, nevertheless, very important, as favouring and faci- 
 litating the desired object : and comminution is also of great 
 value preparatory to solution, for the same reason. 
 
 368. The vessels required in the laboratory for the pur- 
 poses of solution are numerous. They should be competent 
 to resist the action of heat, acids, alkalies, all aqueous solu- 
 tions, and, for convenience, should as often as possible be 
 
 transparent. Hence the necessity of a dozen 
 ] \ or two of glasses; they should always be 
 lipped, and ale glasses will answer the pur- 
 pose very well. Glass jars will also be re- 
 quired, and are best of the form depicted in 
 the wood cut (505,) as they then answer other 
 
 purposes, to be referred to in Section VIII. They should be 
 
 from one to two or three pints in capacity. 
 
 369. Lipped earthenware basins, from 1J to 10 inches in 
 diameter, are also necessary. They should be tried by a solu- 
 tion of muriate of iron, or sulphate of copper, both on the 
 glazed and unglazed part, in the manner directed with respect 
 to mortars (309), for which purpose a little of the solution 
 should be put into one basin, a smaller basin dipped into it, 
 and heat applied. A strong solution of sulphate of indigo 
 and an infusion of logwood are also good agents to try them 
 with. The basins should be quite dry when put into them, 
 
168 BASINS CAPSULES FLASKS. [Sect. Vl. 
 
 and after being boiled in the colouring fluid should immedi- 
 ately wash clean in water. Basins which will stand a trial of 
 this kind are in that respect excellent ; and I have recently 
 obtained such from Messrs. Wedgwood's manufactory. 
 
 370. If such as these cannot be obtained, those of more 
 moderate quality must suffice. Of whatever kind they be, 
 they should resist the action of acids and alkalies in solution. 
 They should also be chosen thin rather than stout and thick, 
 though some of both are desirable; but when intended to 
 sustain the application of heat, the thinner they are the better, 
 so that they have sufficient strength to bear safely the utmost 
 weight of fluid they can contain. Chemically considered it 
 is desirable that they should be made very thin at the bottom, 
 and thicker at the sides, they then stand the sudden application 
 of heat much better than if thick at the bottom. Their greater 
 liability to mechanical injury must be guarded against by in- 
 creased care. 
 
 371. A dish or two made of pure silver, and a few platina 
 capsules, are also necessary. They should have a projecting 
 tongue of metal to serve as a handle by which they may be 
 held with a pair of pincers. The silver dishes may be as large 
 as can be permitted up to six inches in diameter. The platina 
 capsules should be about l or 2 inches in diameter. Very 
 useful glass dishes and capsules are made out of old retorts, 
 receivers, and flasks, in the manner to be described hereafter 
 (1212) ; and they will admit of the application of heat carefully 
 applied. It is not advantageous to purchase glass dishes for 
 the preparation of solutions ; they are so brittle and liable to 
 fracture from heat, as to be both expensive and dangerous 
 to the experimenter's results. 
 
 372. Flasks are very useful. Those made of flint glass 
 should vary from an ounce to a quart in capacity ; the neck 
 
 should expand at the mouth, or a 
 
 A projecting ring should be formed 
 
 I \ ( f on it, that the flask may be held 
 safely by that part without danger 
 of slipping. They should be ex- 
 amined with respect to thickness, and the most uniform should 
 be chosen, provided they be not so thick as to be liable to 
 
Sect. VI] FLORENCE FLASKS STIRRERS. 169 
 
 rupture by heat, or so thin as to burst by the weight of the 
 fluid, or by handling when filled. The thinnest that are of 
 sufficient strength should be selected. The bottoms should be 
 particularly observed : they are frequently much thicker than 
 the other parts, and then almost invariably break when placed 
 upon the sand bath or over a lamp. The thickness of a flint- 
 glass flask from half a pint downwards in size, should be about 
 that of an ordinary Florence flask : when larger they should 
 be somewhat thicker. The indications by which irregular or 
 excessive thickness is judged of, are dependant upon peculiar 
 appearances of the reflection and refraction of light, and are 
 best learned from an ocular examination of a good and of a 
 decidedly bad flask. 
 
 373. Florence flasks are very useful vessels, and for most 
 purposes are superior to flint-glass flasks. They are always 
 thin, and require careful handling when filled with a fluid, or 
 they will be crushed from the attempt to support the weight. 
 If resting upon the bottom they should be supported by a 
 large surface (68). It is seldom that they are knotty, but 
 should that be the case, the flask ought not to be subjected to 
 the action of heat, lest it should fly. Liquids should never be 
 put into a cracked flask or glass vessel, for the purpose of 
 being heated. Florence flasks may-be obtained of two sizes, 
 by application to oilmen, or to foreign wine-merchants : the 
 pints having been used to contain olive oil, the quarts to hold 
 wine. 
 
 374, Besides these vessels, stirrers are frequently required 
 in the progress of these operations. They should be made of 
 solid glass rod, and not of tube. The diameter may vary from 
 the quarter to the one-third of an inch ; the length from six 
 to ten inches. After being cut off from the glass rod, the ends 
 should have the sharp edge round them removed by a fine, 
 or a dull file ; or they should be softened in the blow-pipe 
 flame (1154), and in that case some should be left round at 
 the extremities, and others conical, each having its particular 
 uses (70). Mr. Phillips bends them very slightly in the blow- 
 pipe flame, which prevents their rolling off' the table. Enamel 
 rod is sometimes used for this purpose, but glass is harder 
 and not so brittle. Thick glass tube is not good, because 
 
170 SOLUTION IN THE MORTAR ACTION OF HEAT. [Sect. VI. 
 
 the sealed end is apt to crack off in hot solutions, and then 
 the cavity opened is a receptacle for dirt. 
 
 375. All these utensils are equally useful for evaporation 
 and other processes, as for solution s, requiring in these cases 
 generally no other qualities than those before mentioned. 
 This being understood they will not be referred to again. 
 
 Proceeding now to the operations of solution, the following 
 method is very ready, and of constant use in the laboratory 
 relative to salts and similar substances, which are entirely 
 soluble, and form a solution of sufficient strength without 
 the application of heat. The substance should be put into 
 a clean mortar, a little water be added, and by the action 
 of the pestle the solid matter reduced to a thin paste ; this is 
 done in a few moments, more water should then be added, and 
 the whole stirred together, in consequence of which the finest 
 particles will rapidly disappear. When upon continuing the 
 trituration, the fresh portion of small powder which is pro- 
 duced does not seem to dissolve, the whole should be allowed 
 to stand a moment, the fluid poured into a glass or jar, the 
 residuum triturated, water added, and the process continued 
 until the whole is dissolved. The solution when all together 
 should stand a few minutes, to deposit any minute particles 
 that may not have been dissolved ; or a little water added to it, 
 and the whole agitated, when it will immediately become clear 
 or nearly so. If there be occasion it should then be filtered, 
 and in this way a solution nearly saturated, and always strong 
 enough for ordinary laboratory uses, may be made in a few 
 minutes. 
 
 876. This method of facilitating solution by mechanical 
 division is very useful in numerous cases. If one substance 
 be embarrassed or enveloped by another, it is thus more easily 
 exposed to the solvent; and from the great utility of this 
 practice when chemical solvents are used, as acids or alkalies, 
 arises the necessity of having mortars which are competent, as 
 before mentioned (309), to resist the action of these and similar 
 substances. 
 
 377. The use of heat in assisting solution is very great, and 
 though heat and division may in many cases be resorted to 
 almost indifferently for effecting the required end, yet the 
 
Sect. VI.] SOLUTION HEAT SATURATION ASCERTAINED. 171 
 
 student should understand that they attain the object in diffe- 
 rent ways, that he may know in peculiar cases when to apply 
 the one and when the other. Division is favourable merely 
 by increasing the surface of contact between the solvent and 
 the body to be dissolved ; thus offering an immense number of 
 points where the action may simultaneously be exerted, and 
 in this way bringing it sooner to a close : whereas heat acts 
 directly by increasing the power of the solvent, and enabling 
 it to take up a larger quantity, and incidentally by causing a 
 multitude of currents in the liquid, by which fresh portions 
 are continually brought into contact with the body to be dis- 
 solved. Hence heat does not merely expedite the action, and 
 in that way do what comminution effects ; but it does actually 
 increase it, and cause a greater portion of the solid body to be 
 dissolved than would otherwise be the case. 
 
 378. Perhaps the simplest application of heat is that re- 
 quired to obtain a solution saturated when cold. It would 
 take a long time, for instance, to prepare a saturated aqueous 
 solution of white arsenic, by contact of the powder with water, 
 or even by agitation ; but by boiling the water with the pow- 
 der for half an hour, leaving it to cool, and afterwards filtering 
 it, a saturated solution will be immediately obtained. The same 
 is the case, though not so strikingly, with more soluble sub- 
 stances, as sulphate of potash, nitre, &c., and in these instances 
 the object is generally effected by warming the pulverized 
 substance with the water in an evaporating basin or flask, over 
 a lamp or sand-bath, or by using warm water with trituration 
 in the mortar. With the exception of the two or three salts 
 which are scarcely more soluble in hot water than in cold, the 
 attainment of the object should be ascertained by observing 
 whether the hot solution has deposited any portion of the solid 
 substance during its cooling : if it has, it proves the saturation, 
 if it has not, there is reason to doubt it, and heat with more of 
 the solid substance in powder should again be applied. 
 
 379. An easy method of testing this point of saturation, 
 even Avhilst the solution is hot, is to dip a glass rod into the 
 liquor, and by means of it to transfer a drop to a cold glass 
 plate (1348) : if a deposition of crystals or solid substance 
 appear in a few moments, then the solution will be saturated 
 
* ' 
 
 172 SOLUTION HEAT HOW APPLIED. [Sect. VI. 
 
 when cold. If they do not appear immediately, still the stu- 
 dent should not be satisfied , until he has stirred the drop with 
 the platina spatula, and repeatedly struck the glass beneath 
 the solution with the metal ; this will frequently cause a pre- 
 cipitation of crystals to take place, which would not otherwise 
 have appeared except in a long time, and they equally indicate 
 that the solution when cold will be saturated. Ultimately the 
 solution should be filtered, if necessary, to separate any me- 
 chanical impurity. 
 
 380. When the object of applying heat to increase the 
 solvent power is not simply to obtain a saturated solution, but 
 to accelerate a process which, either from the previous combi- 
 nation of the substance with other bodies, or the want of action 
 at ordinary temperatures, would be tedious and imperfect, if 
 not urged by all the means at command ; the application 
 has to be continued for a longer time, and frequently in 
 vessels which will retain the vapour more perfectly than a 
 basin. The ebullitions and digestions which are sometimes 
 continued for a long period, are processes of this kind, and the 
 choice of the vessel will depend upon the circumstances at- 
 tending the action. Basins and open vessels are convenient, 
 because they afford a ready access to the liquid, either for the 
 purpose of removing portions for examination when necessary, 
 or for stirring and agitation. For this reason, when the dis- 
 persion of a little vapour, or even of a little of the substance 
 by ebullition is of no consequence, basins are very convenient, 
 and they are necessarily used when the substances are operated 
 upon in such a form as prevents their introduction into flasks. 
 But when it is desirable to retain the vapour as much as pos- 
 sible, as whilst using acids, or when it is necessary that all 
 loss from ebullition be avoided, or all possible contact of ex- 
 traneous substances prevented, then flasks are most useful, and 
 especially Florence flasks. Hence almost all solutions relative 
 to analyses, if they require the aid of heat and occupy time, 
 are most safely made in flasks. The selection of a basin or a 
 flask in any particular case must be left to the judgment and 
 experience of the operator. 
 
 381. In these and similar cases, all sudden applications of 
 heat, especially to glass vessels, should be avoided. A glass 
 

 Sdct. VI.] SOLUTION IN BASING 173 
 
 flask, unless it be very thin, when filled with a cold fluid, and 
 set suddenly in a hot sand-bath, is almost sure to break. If 
 it be required to heat a basin in a sand-bath, the bottom 
 should previously be dried, for if wet, the water by contact 
 with hot sand becomes rapidly converted into vapour, which, 
 causing a slight explosion, sometimes throws the sand into the 
 vessel. The elevation of temperature is accelerated by cover- 
 ing the basin and preventing evaporation. This is often con- 
 veniently done by putting a second basin somewhat larger 
 over it, its cleanliness having been previously ensured. If the 
 fire or sand-bath be such that it is advisable to obtain the heat 
 as rapidly as possible, no fear of injury being entertained, then 
 on putting down the basin it should not be set upon the top of 
 the sand, or pressed down a little way only, but the sand 
 should be removed with the iron spatula before mentioned 
 (174) to the sides, the basin set down upon the bottom of the 
 bath, or with only a very thin layer of sand intervening, and 
 then the sand returned round the sides of the basin. The 
 thickness of sand which may be allowed to remain between the 
 bath and the bottom of the basin, must be left to the judgment 
 of the experimenter, being proportionate to the heat of the 
 fire under the bath, the previous heat of the sand, and the 
 quantity and nature of the substance to be heated. It is in 
 general advisable not to heap the sand round the sides of the 
 basin to a greater height than the solution inside, at least if 
 the sand be hot, or likely to become so during the operation ; 
 for it then sometimes makes the part of the dish above the 
 solution very hot, and when ebullition happens and raises fluid 
 over it, the sudden change occasions fracture, or gives rise to 
 the production of much steam, which endangers the boiling 
 over of the contents of the vessel. 
 
 382. If it become necessary to add water or a cold liquid 
 to the contents of a hot basin upon the sand-bath, the ad- 
 ditions should be made with great care, for if the cold liquor 
 be poured at once into the hot, it will pass through it, and 
 striking against the bottom of the hot basin, will very pro- 
 bably break it. Hence, to avoid too sudden a change of tem- 
 perature, the cold liquid should be added slowly, and poured 
 into different parts of the hot fluid. 
 
 - 
 
174 SOLUTION IN FLASKS BOILING. [Sect. VI. 
 
 383. When a flask is put upon the bath, it should be sunk 
 more or less deep according to the heat of the sand and the 
 heat required, and hotter or cooler parts of the bath may be 
 selected'for the same reasons. Hence one advantage of the 
 table-furnace before described (169), whose sand-baths present 
 every required degree of temperature. If a situation be too 
 hot for a flask, making its contents, for instance, boil very 
 rapidly, the heat is easily diminished by raising up the flask 
 more or less, and allowing the sand to sink under it ; this not 
 only causes a thicker stratum of sand to intervene between the 
 bottom of the bath and the flask, but also removes a part of 
 the flask out of the sand altogether. 
 
 384. When a flask on the bath is to have its contents 
 heated as rapidly as possible, it is frequently safer, instead of 
 endeavouring to apply a stronger heat at the bottom to pre- 
 vent dissipation of heat above. This is very usefully effected 
 by a tin cone about seven inches in diameter at its base, six 
 inches high, and having a hole where the apex would other- 
 wise be, about an inch in diameter, through which the neck 
 of the flask may pass. This case, slipped over the flask, 
 
 and resting at its lower edge on the sand, 
 forms a hot chamber round the upper part ; 
 the air within it actually assists at times to 
 heat the flask and its contents, and in all 
 cases materially interferes to prevent cooling. 
 Even the space left open round the neck may be closed when 
 desirable, by passing a piece of card, with a hole cut in it, over 
 the neck, that it may rest on the upper edge of the cone. 
 
 385. When a flask in a state of ebullition on the bath, seems 
 on a sudden in danger of boiling over, it should instantly be 
 lifted up if possible, but at the same time the operator should 
 blow with his mouth against that part of its surface which is 
 above the level of the fluid. This will generally cause conden- 
 sation of the steam within, the ebullition will diminish, and the 
 contents be secured. An expedient of this kind will often save 
 the contents of a flask when the neck, from being full of froth, 
 is too hot to be touched by the hand ; upon its descent the 
 neck will become cool, and may be laid hold of. When flasks 
 are upon the sand-bath, a list ring or two (68) should be on 
 
Sect. VI.] 
 
 TRIPODS RETORT STANDS. 
 
 175 
 
 one side, ready for the reception of the flask in case of emer- 
 gency. 
 
 386. When a small charcoal fire or a lamp is the source of 
 heat, the basin or flask has to be supported above 
 it. This may be done either by a ring tripod, as 
 delineated in the wood-cut, or by what are called 
 retort stands. With the tripod the height is fixed, 
 and hence the lamp or furnace may require elevat- 
 ing. For this and numerous other purposes of 
 adjustment in the laboratory, the wooden blocks 
 before described (20) are continually of use. Re- 
 tort-stands are sold by the instrument-makers, and consist of 
 an upright brass rod fixed on a heavy turned foot, and fur- 
 nished with rings, which being each fixed to an arm, and that 
 to a socket, the latter passes freely up and down upon the 
 brass rod, and is made tight at any particular height by a 
 screw-nut at the back (448. 465). In this way the facility is 
 obtained of fixing the projecting rings at any height required, 
 and as several of different sizes accompany each retort stand, 
 vessels with globular bottoms, or indeed of many other forms, 
 may be supported at any required height. It is easy by these 
 stands to support the flasks or basins at the proper distance 
 above the lamp or furnace. When, from the weight of the 
 vessel and its contents, it is too heavy for the arm, or would 
 cause the stand itself to tip over, then two stands may be used 
 on opposite sides, the ring of one being placed under the other, 
 and the flask or basin on the uppermost. These stands are 
 generally made with small circular brass feet, filled with lead, 
 but which still are insufficient to retain the whole upright when 
 a heavy vessel is on the ring. It is much better to make the 
 foot of a piece of stout board, about twelve 
 inches in length, six inches in width, and an 
 inch thick. The upright rod should be fixed 
 about one inch and a half from one end of it, 
 the lamp or furnace should be placed upon 
 it, and the ring of course in a corresponding 
 direction. Such an arrangement is perfectly 
 steady,' and cannot be overset by any weight 
 which it is strong enough to bear. When 
 
17G FLASK CRUCIBLE FURNACE TIN CONE. [Sect. VL 
 
 the usual stands only are at hand, it may now and then be 
 necessary to put on a second ring in an opposite direction to 
 the first, and to add weights for the purpose of equipoising the 
 whole. 
 
 387. When a flask will not fit very well, it may be hung 
 up above the lamp flame by a cord, for which the common 
 shape of the neck is well adapted : this arrangement may often, 
 on other accounts, be desirable. 
 
 388. When a crucible furnace is used it should always be 
 placed on a tile, and not immediately upon the wooden table 
 or stand, lest, during a long operation, it should become heated 
 to the bottom and burn the wood beneath (1357). The tile 
 also catches hot falling ashes or sparks, which would burn the 
 wood, and it facilitates the removal of the furnace in the hottest 
 state without inconvenience. A lamp requires no precautions 
 of this kind. When operating with flasks and retort-stands, 
 care should be taken that a flask, which, with its contents, has 
 been heated, be not suddenly put upon a cold ring, and that a 
 cold flask just charged be not placed over the fire upon a hot 
 ring; in both cases the bottoms of the flasks will probably 
 come out, and the contents be lost. 
 
 389. When it is desired to keep a flask with its contents in 
 a state of ebullition over a lamp, it may generally be effected 
 by adjusting the flame. But a facility is gained by having 
 the heat somewhat greater than is sufficient when the lamp is 
 under the centre of the flask, and adjusting the effect by mov- 
 ing the lamp a little on one side. The application of the heat is 
 smaller or greater in proportion as the lamp is removed from 
 the centre ; but at the same time, being applied on one side, a 
 cooling process goes on more decidedly at the other than 
 before ; and this, with the uniformity of the current established 
 within, makes the whole operation more regular. 
 
 390. If the effect obtained by a lamp is hardly sufficient, 
 and yet from circumstances is the most desirable source of 
 heat, the tin cone (384) is then a very essential adjunct. 
 When slipped over, and allowed to rest upon the flask, it con- 
 fines an atmosphere of very hot air about the upper part, by 
 which the time of heating is shortened, and in many cases it 
 assists in the attainment of a temperature which could not 
 
Sect. VI.] SOLUTION HOOD. 177 
 
 otherwise be acquired. The cone should be guarded at the 
 upper part within either by a layer of thick paper, thin paste- 
 board, or some such substance, or by a ring of cork, to prevent 
 the metal from touching the glass ; a circumstance which might 
 now and then, from difference of temperature, produce fractures. 
 The exterior should be preserved clean and bright. 
 
 391. In many cases of solution, the vapours emitted, either 
 from their acid nature or noxious qualities, are highly inju- 
 rious ; wherefore it is desirable, as much as possible, to convey 
 them away, and to prevent their mixture with the atmosphere 
 of the place. Hence the use of the large hood before referred 
 to (10), which, receiving such vapours, conducts them into the 
 flue. A hood to be useful should descend low, and as closely 
 as possible over the place from whence fumes are to be carried 
 off, but this necessity often makes a large hood inconvenient. 
 To be effectual, it should also have a good draught passing 
 through it. 
 
 392. A temporary moveable hood is a useful appendage to 
 
 the table-furnace before described (169). It 
 consists of a cone having its lower diameter 
 equal to that of the round sand-bath (171), 
 supported on three short legs to rest within 
 the edge of the bath, and opening above into 
 a funnel- pipe, which, by three bends at right 
 angles, is made to terminate opposite the fire 
 door. The pipe is conveniently formed, in 
 two or three pieces, the whole being of copper ; the cone itself, 
 and the pipe and joint above, may be made of copper, or very 
 advantageously of stone-ware. When placed upon the sand- 
 bath, with the door of the fire partly open, and the end of the 
 pipe opposite the aperture, such a draught is occasioned 
 through the whole as will carry off any fumes which may be 
 liberated beneath it into the chimney. 
 
 393. The inside of a hood of this kind should be kept clean, 
 to prevent the possibility of dirt falling from it into the vessels 
 beneath. When the vessel is a flask, an additional security is 
 obtained by covering the mouth loosely, either by inverting 
 over it a short tube, closed at one end, and sufficiently large, 
 or by placing upon it a convex fragment of old glass from a 
 
 N 
 
178 SOLUTION PRECAUTIONS. [Sect. VI. 
 
 retort or flask. When the vessel is a basin, it may, in some 
 cases, be similarly guarded by another basin, placed over it as 
 before-mentioned (274) ; when that cannot be done, the clean- 
 liness of the hood should be particularly attended to. 
 
 394. When the contents of a flask evolve vapour spon- 
 taneously, or require but little heat to produce them, the flask 
 may be placed upon a listed ring (68), in an inclined position, 
 and have its mouth directed to the ash-pit of the furnace : the 
 draught will carry away the fumes whilst it is in that position, 
 and, at intervals, it may be placed for a few minutes together 
 on the sand-bath. Where the spare flues exist, which have 
 been before referred to (5, 168), they are very useful in carry- 
 ing off vapour. The mouth of a flask brought near to one, 
 will deliver all its vapours into the flue, and from the height of 
 the latter, it is easy to arrange the flask, with its lamp or fur- 
 nace, in a proper position. When the portable hood, just re- 
 ferred to (392, 168), is adapted to the aperture of the flue, 
 which may easily be effected when the pipe, as mentioned, is in 
 two or three shifting pieces, nothing more can be desired ; for, 
 so arranged, a good flue is competent to carry off all the fumes 
 from any basin which the hood can cover. Where the table- 
 furnace is favourably situated, as against the side of the labo- 
 ratory, no difficulty occurs in using a piece of pipe, which may 
 be put up in a moment, and connect a moveable hood over any 
 part of the sand-bath, with the flues behind. 
 
 395. Besides these general directions for the process of solu- 
 tion, there are numerous precautions requisite to ensure ac- 
 curacy, when results of the utmost precision are required, as in 
 cases of analysis ; amongst which are the following. If the 
 quantity of solid matter operated upon has been weighed, it is 
 of consequence that not a particle be lost in introducing it into 
 the flask, supposing such a vessel to be used. The experi- 
 menter should not venture to pour it into the neck directly 
 from the glazed paper in which it may have been weighed (61), 
 or from any vessel that may contain it, but should use a small 
 clean funnel for the purpose. If dry, the powder will probably 
 pass freely through it, without adhering to the glass; but 
 before removing the funnel, it should be washed with a little 
 water, which will carry down any adhering particles. If, in 
 
Sect. VI] SOLUTION EFFERVESCENCE. 179 
 
 passing through the funnel, some of the powder has struck 
 against and adhered to the inside of the neck of the flask, that 
 should also be washed down to the bottom with a little water. 
 The water which is used for these purposes should be distilled, 
 and indeed in all cases where accuracy is required, equal care 
 should be taken on that point. It is much to be regretted 
 that any laboratory should be so far restricted in the use of 
 distilled water as not to have sufficient for every case of solu- 
 tion, whether for refined analyses or the most ordinary experi- 
 mental processes (26). 
 
 396. When effervescence happens in the flask, precautions 
 should be taken that none of the solution be lost. During a 
 cold effervescence, as of carbonate of lime in an acid, the break- 
 ing of the bubbles will throw up a shower of particles, many 
 of which will ascend several inches perpendicularly. In these 
 cases, it will be right to incline the flask at an angle of about 
 45, for then the rising drops will meet with and break against 
 the side of the flask, and be retained. At other times, when 
 strong currents of vapour or gas are produced at the same 
 time with this dispersion from the breaking of bubbles, many 
 of the particles may be carried away by the current, even when 
 the flask or vessel may be considerably inclined. In these 
 cases, the addition of the acid, or the application of heat, 
 should be made cautiously, that the current may not become 
 so rapid, and attain such power as to do harm. For the same 
 reason, operations which are liable to occasion much effer- 
 vescence, should be performed in flasks of the largest size, that 
 the current of gas within may have less velocity, and that the 
 particles may have room and time to fall. 
 
 397. On pouring solutions from glasses, flasks, or basins in 
 the ordinary way, it is scarcely possible to operate, so that, on 
 ceasing to pour, and returning the vessel to its first position, a 
 small portion of the liquid shall not flow down the outside ; or 
 if successfully done once, there is no certainty that it can be 
 performed whenever required. A failure of this kind occasions 
 a loss of substance, which, when repeated, is quite incompatible 
 with the accuracy of analytical processes ; but it may be 
 avoided by very simple means. A clean glass rod (374) is to 
 be dipped into the solution to be poured, so as to have its sur- 
 
 N 2 
 
180 
 
 SOLUTION POURING USE OF A ROD. [Sect. VI. 
 
 face at the end wetted, and then, the vessel being inclined, the 
 rod is to be applied in a vertical or highly inclined position, so 
 that its wet surface shall touch the lip or edge from which it is 
 intended to pour. When, by further 
 motion of the vessel, the fluid at last 
 runs over its edge, it will proceed down 
 the rod, being conducted by it in any 
 required direction. When a sufficient 
 quantity has in this way been removed, 
 the vessel is to be restored to its first 
 position, the rod not being withdrawn 
 until the fluid is decidedly below the 
 inside edge ; all that is without will be 
 confined to the surface of the rod, not 
 \*/ a particle having flowed down the out- 
 
 side of the basin. The rod may be 
 
 left in the solution until a fresh portion is to be poured ; or if 
 no more be required, may be washed by a little water from 
 the dropping bottle (402), which, being added to the original 
 solution, prevents the loss of a single particle of the con- 
 tained substance. 
 
 398. This application of the rod is not merely useful in 
 preventing loss or waste, but also in conducting the fluid in 
 particular directions, when other means are wanting. A solu- 
 tion, or liquid of any kind, which wets the rod, may be poured 
 very accurately and securely into a narrow-mouthed bottle by 
 it, if a funnel be not at hand, and occasionally it even sur- 
 passes the funnel in convenience. Thus in pouring successive 
 small quantities of a valuable fluid, a rod enables it to be done 
 safely, and at the same time with considerable minuteness, by 
 allowing a very small stream to flow from its end, the vessel 
 being in contact with the rod, but a little way above it ; be- 
 tween each operation of pouring, the rod is conveniently and 
 securely placed in the fluid. With a funnel, a much larger 
 surface is moistened, which drains for some time after, and the 
 quantity is by no means so well estimated as by the former 
 method : neither in the intervals of pouring can the funnel be 
 so conveniently disposed of as the rod. 
 
 399. If upon any sudden emergency the pouring has to be 
 
Sect. VI.] SOLUTION MINUTE OPERATIONS. 181 
 
 performed without the guiding rod, and yet loss of the substance 
 would be of consequence, then put the lip from which the fluid 
 is to flow, against the further side of the mouth of the vessel 
 which is to receive, inclining the latter if necessary at the time. 
 
 400. The operations which have been described have fre- 
 quently to be performed on a very minute scale (915). Hence 
 the use of small earthenware dishes, platina capsules, and 
 especially fragments of broken flasks (371), which, from their 
 concave form, are exceedingly convenient for experiments upon 
 drops of fluids. In operations of this kind, heat is applied, 
 either by a small spirit-lamp flame, obtained by pulling down, 
 the cotton before the lamp is lighted, or by touching the glass 
 with the hot sand of the bath, or even by letting it stand upon 
 the hotter part of the furnace plate. Instead of flasks, tubes 
 are used in similar operations for making minute solutions, the 
 general management of which will be described in Sect, xvi; 
 (917). : 
 
 401. Instead of pouring out the fluid, it has now to be 
 transferred in portions, each less than a drop, and this is best 
 done by dipping a glass rod into the solution, and then, whilst 
 more or less adheres to it, according to the quantity wanted, 
 to touch a clean glass plate or a piece of a flask with it, and 
 allowing the adhering portion to run down. If but little be 
 required, only a small length of the rod should be dipped in, 
 and if still less be required, even that small portion should be 
 allowed to drain for a moment or two, before the rod is brought 
 into contact with the substance to be moistened. On the con- 
 trary, if a large quantity be wanted, two or three inches of the 
 rod should be dipped in, and the adhering fluid quickly trans- 
 ferred to the desired place ; or if the most be wanted that the 
 rod can lift, it should, upon being dipped, be taken out hori- 
 zontally, and carried adroitly in that position to the place 
 required, taking care, by slight but proper motions of the rod, 
 to prevent such accumulation of the fluid in one spot as to 
 cause a drop. By these means, a glass rod may be made to 
 carry very different quantities of fluid, affording great facilities 
 in the practice of minute chemistry. 
 
 402. There is an instrument which cannot be dispensed with 
 in the laboratory, and which, in the order of our arrangement, 
 
182 DROPPING-BOTTLE. [Sect, VI. 
 
 first comes into service in the present chapter it is the drop- 
 ping-bottle. Its use is to supply small quantities of water, 
 and the laboratory should be furnished with two of them, one 
 to deliver large and rapid drops, or a small stream, the other 
 to supply very minute portions for such experiments as those 
 just referred to. The larger one may be a bottle holding 
 about half a pint, and should have a good smoothly cut cork 
 fitted into its mouth. A piece of strong glass tube, of an in- 
 ternal diameter not more than the eighth of an inch, should 
 be selected and drawn out, so as to have a 
 contracted aperture, which, at the same time, 
 should be bent on one side ; the piece of tube 
 should be about two and a half inches long, 
 and fitted tightly into the cork, its extremity 
 not passing inwards beyond the cork ; and it 
 is an advantage that the surface of the latter should be slightly 
 concave or conical, as in the accompanying section. Lastly, a 
 notch is to be cut in the side of the cork, diminishing from 
 above downwards, so that when the latter is in its place, the 
 notch may form a passage into the bottle, with a narrow open- 
 ing at the inner surface. This slit is to be on that side of the 
 cork from which the upper extremity of the tube inclines. 
 
 403. The bottle is to have distilled water put into it, and 
 being then placed in different positions, it will supply a stream 
 of water variable in its quantity at pleasure. If inverted, it 
 will be found that a small stream will flow out at the beak, 
 and a current of air enter at the notch to supply its place. If 
 the bottle be inclined, keeping the notch uppermost, the 
 stream will not be so rapid, and in consequence of the dimi- 
 nished perpendicular height of the column of water tending to 
 descend, occasioned by bringing it nearer to a horizontal posi- 
 tion, the stream will at last break into single successive drops, 
 which by a still further motion of the hand also cease to fall. 
 If a small portion of water be required to make a solution, it is 
 readily supplied even to single drops, and smaller quantities 
 are easily lifted and transferred as before described, by a glass 
 rod (401). Or if a stream be wanted to wash the solution 
 from a rod or a funnel, or to wash out a glass, it is instantly 
 obtained. By allowing the stream or drops to fall from a 
 
Sect. VI.] DROPPINGf-BOTTLE SOLVENTS. 183 
 
 greater or smaller height, variations in the descending, and 
 consequently washing force, are produced ; this may even be 
 increased occasionally, by a downward jerking motion of the 
 hand, which will throw out forcible independent jets of water. 
 
 404. It is proper to have a smaller dropping-bottle ready 
 for use, because, from the infinite variety in the quantities to 
 be operated upon by the chemist, such an instrument will at 
 times be found advantageous. By making the tube smaller, a 
 similar set of capabilities to those just described, but with a 
 smaller stream of water, are obtained, and a minute quantity of 
 a rare substance of which it is desired to save every atom may 
 be operated with, yet without more dilution than is absolutely 
 necessary. 
 
 405. The selection of solvents for particular substances is 
 an important point, which must, however, in a great measure 
 be left to the judgment and knowledge of the student. If the 
 object be to ascertain the properties of a substance by working 
 with its solutions, water should be first tried. If it have no 
 action, alcohol may be used, and after that ether, pyroligneous 
 ether, and finally, on some occasions, oils. As a general rule, 
 those solvents are to be preferred which are evaporable, and 
 may therefore be dissipated by heat, and which at the same 
 time least affect the chemical powers of the substance to be 
 dissolved. In these properties, and in economy, water sur- 
 passes every other body that can be used. 
 
 406. Mixtures of water and alcohol are frequently useful, 
 where neither water nor alcohol alone is applicable. Thus if 
 muriate of soda and sulphate of lime were mixed together, the 
 muriate is best dissolved by water ; this, however, would occa- 
 sion the solution of a portion of the sulphate of lime, whereas 
 by a mixture of one part of alcohol and two or three parts of 
 water, a solvent is produced which will separate the former 
 salt and reject the latter. 
 
 407. When an aqueous solution of a vegetable substance 
 has been made, which on examination is found to contain dif- 
 ferent substances, some soluble in alcohol and others not (and 
 there are few infusions of vegetables that do not yield such a 
 mixture), it has to be subjected to the action of alcohol for the 
 purpose of effecting a separation. The first step is concentra- 
 
184 SOLVENTS SELECTED APPLIED. [Sect. VI. 
 
 tion by evaporation ; but it is advisable not to carry this to 
 dryness, or as far as may be without injury to the substance, 
 and then to act by alcohol ; for generally a soft mass is 
 obtained, upon which alcohol acts only imperfectly except in a 
 long period, because the last portions of soluble matter are 
 protected by the mass of insoluble substance. It is better to 
 suspend the evaporation when the substance is a thick fluid, 
 and then to add a small quantity of alcohol ; which, although 
 it will cause a partial solution and partial precipitation at first, 
 will, upon being stirred, mix with the fluid, and be over- 
 powered as it were by the water still remaining, so that the 
 precipitated portion will be redissolved, and the whole again 
 rendered fluid. This should be repeated twice or thrice, 
 stirring each time, and keeping the mixture of uniform con- 
 sistency ; a precipitation will gradually take place, increasing 
 as the proportion of alcohol is increased. The particles thus 
 rejected as insoluble will be nearly free from any mixture of 
 substance soluble in the alcohol, if at least there be no chemi- 
 cal affinity interfering, and thus a ready solution of the one 
 part, and its separation from the other, may be effected. The 
 quantity of alcohol added must be such as at last to surpass 
 by many times the quantity of water left at the close of the 
 evaporation, otherwise its powers will be diluted, and a com- 
 plete separation of that which is soluble from that which is 
 insoluble will not be obtained. Hence the evaporation should 
 be carried as far as possible, so that the residue be fluid and 
 will mix readily. If it be so thick that it clots upon adding 
 the first portion of spirit, a few drops of water must be added. 
 The solution should be in such a state that the first portion of 
 alcohol, equal to about a fourth of the bulk, should cause pre- 
 cipitation, which disappears upon stirring ; the second portion 
 cause a turbid liquor after stirring ; the third, an increase of 
 turbidness but still no clotting; the fourth, when an equal 
 volume has been used, a separation of the precipitable part in 
 softer or harder masses. When three or four times the volume 
 has been added, it will generally be found that the separation 
 is complete. 
 
 408. Some of the acids frequently act as mere solvents : their 
 power apparently not being due to any combination effected 
 
Sect. VI.] SOLVENTS USE OF ACIDS. 185 
 
 between them and the substance by which a change of cha- 
 racter is produced. Thus acetic acid dissolves caoutchouc, 
 and acetic, nitric, muriatic, and some other acids, dissolve 
 phosphates and borates. Muriatic acid dissolves sulphate of 
 lead, and to a slight degree muriate of silver, and many other 
 such actions will be observed in the course of experimental 
 investigations, all of which should be remembered, and may in 
 turn be put to important uses. 
 
 409. When acids and other energetic chemical substances 
 soluble in water are used, either as simple solvents or as pro- 
 ducing compounds by combination, attention should be paid 
 in their selection to certain general advantages which each 
 possesses. Nitric acid is distinguished as a chemical solvent 
 by the solubility of almost all the salts which it forms; by its 
 imparting oxygen to metals generally, so as to bring them into 
 a soluble state ; and by its ready separation from all its com- 
 pounds at a sufficiently high temperature, three circum- 
 stances of very great importance. When used, care should be 
 taken that it is sufficiently diluted: very strong nitric acid 
 will sometimes seem to have no power over a body at common 
 temperatures, when upon the addition of a little water, action 
 will immediately commence. This circumstance never occurs 
 with acid which has been diluted with one half its bulk of 
 water. Any further dilution, therefore, can only be required 
 to moderate chemical action, and not to commence it. Muriatic 
 acid yields salts generally soluble, though some of them are 
 but slightly so ; and muriate of silver not at all so in water. 
 Many of the resulting compounds are fixed at a red heat, 
 some few sublime, some are decomposed. The muriatic acid 
 has the advantage of being separable from the bodies it has 
 combined with by solutions of silver. Sulphuric acid forms 
 many insoluble salts, but it has the advantage of being removed 
 readily by solutions of barytic salts. The circumstance of its 
 producing insoluble salts makes it valuable as a chemical 
 solvent for those bodies with which it combines and remains in 
 solution, inasmuch as it facilitates their separation from the 
 others. Hence it is frequently added to solutions made by 
 muriatic and nitric acids, and displacing these, they are after- 
 wards separated by heat. It should not be used in its concen- 
 
186 SOLVENTS ALKALIES. [Sect, VI. 
 
 trated state, but more or less diluted, or the same effect will 
 occur as with nitric acid. Acetic acid forms soluble salts with 
 all the substances with which it combines; and it may be 
 burnt off by heat, with access of air. 
 
 410. When an alkaline solvent is required, ammonia, if 
 effectual, is most convenient, because of its ready volatility and 
 dissipation when uncombined, and the volatility of all its ordi- 
 nary salts, except the phosphate, borate, and those containing 
 metallic acids. When ineffectual, the fixed alkalies must be 
 resorted to. 
 
 411. It is necessary that the student be on his guard 
 respecting certain variations in the solubility of bodies arising 
 from the presence of other matters. He will continually find 
 that small portions of substances generally considered as inso- 
 luble in water will remain in neutral solutions when some other 
 substance is present, or because of slight mutual decomposi- 
 tion ; and he will also frequently find that matter usually con- 
 sidered as readily soluble, is so with difficulty when in contact 
 with substances with which it is not apparently in combination. 
 Thus water boiled upon muriate of potash and phosphate of 
 baryta will be found to contain more baryta than if boiled 
 alone upon the phosphate ; and on the contrary, if oxide of 
 iron and alumina be precipitated together from a solution, it 
 will be found much more difficult to dissolve the alumina by 
 solution of potash than if it had been thrown down alone. 
 
 412. The alkaline earths are remarkably soluble in solutions 
 of sugar, and also, though to a less degree, in solutions of 
 extract and other vegetable matters : hence they are retained 
 in solution at times in very unexpected situations, and might 
 give rise to much uncertainty in the appearances and characters 
 of other substances, unless the experimenter were aware of the 
 general fact. Platina is not itself soluble in nitric acid, even 
 when spongy, and in its most comminuted form, but when 
 alloyed in small quantities with metals dissolved by that acid, it 
 becomes soluble with them, and, in consequence, appears now 
 and then in situations where it is not expected. 
 
 413. Tartaric acid or tartrates have an extraordinary power 
 of rendering many metallic oxides soluble, which are not so by 
 other acids without it; and still more in holding them in 
 
Sect. VI.] SOLVENTS ALKALIES VARIATIONS. 187 
 
 solution when such substances are added as in ordinary cir- 
 cumstances effect their separation. The oxides of bismuth, 
 antimony, tin, and titanium, are easily dissolved by acids when 
 tartaric acid is present ; and being present, ammonia no longer 
 has the power, upon its addition, of separating the oxides of 
 iron, titanium, manganese, cerium, cobalt, nickel, lead, anti- 
 mony, and the earths, alumina, magnesia, and yttria, from 
 their solutions, and, in certain cases, even potash or soda fail 
 so to do. Great advantage may be taken of this property 
 occasionally, but sometimes it is equally disadvantageous in 
 preventing the usual action of re-agents *. 
 
 414. A very numerous class of aqueous solutions is pro- 
 duced by metallic salts. These, in consequence of the varied 
 quantity of oxygen with which many of the metals can com- 
 bine, are susceptible of changes dependent upon the oxygena- 
 tion of the metal whilst the state of solution is continued. 
 These changes are eminently useful in fitting the solutions in 
 one way or another for experimental purposes. If the object 
 be to oxidize the metal, whether to render it soluble, or for 
 any other purpose, the agents to be employed are the acids 
 generally, nitric and nitromuriatic acids especially, chlorine 
 and chlorate of potash, and, in some peculiar cases, even alka- 
 lies. No metal will dissolve in water or an acid until it is 
 combined with oxygen, and, in obedience to this law, sulphuric 
 and phosphoric acids, and perhaps muriatic acid, frequently 
 cause the decomposition of water for the oxygenation of the 
 metal. Nitric acid is often decomposed, supplying a portion 
 of its own oxygen to the metal with which it is in contact. 
 Proto-salts in solution are frequently converted into per-salts 
 by it, and also by nitro-muriatic acid and chlorine. A 
 proto-sulphate, muriate, or nitrate of iron, may be converted 
 into a per-salt by a little nitric or nitro-muriatic acid and 
 heat ; and a proto-nitrate by heat alone. The same agents 
 are equally effectual in converting proto-salts of tin into per- 
 salts. In these cases of conversion care should be taken that 
 no acid be added that will interfere with the future experi- 
 ments, or that may not be dissipated by heat. 
 
 415. The influence of alkali in causing oxygenation may 
 
 * Aiinales de Chimie, xxiii. 356. 
 
188 METALLIC SOLUTIONS HOW AFFECTED. [Sect. VI. 
 
 be observed by putting a little oxide of chrome or a salt of 
 chromium into a solution of alkali, so that the latter may be 
 in excess ; by evaporation to dryness in a platina capsule, and 
 heating the mixture with access of air, the oxide of chrome will 
 absorb oxygen, and become chromic acid, through the influ- 
 ence of the alkali, with which it will ultimately combine. 
 
 416. If deoxidizing agents be required for the metal in 
 solution, then an efficient one is most likely to be found 
 amongst such bodies as alcohol, ether, sugar, gum, &c. Of 
 the known metals, per-salts of manganese are reduced to the 
 state of proto-salts by being boiled with alcohol or ether, and 
 become quite colourless: solutions of platina and palladium 
 are actually reduced by boiling with alcohol. The per-oxides 
 of lead and manganese, when mixed with any of the bodies 
 enumerated and an acid, are reduced to the state of protoxides, 
 and dissolved if the acid be such as to form soluble salts. If 
 a chromate have excess of acid added to it, with a little of any 
 of the same substances, and be heated, it loses oxygen and 
 becomes oxide of chrome, which, with the excess of acid, forms 
 a salt. These facts are mentioned generally rather than par- 
 ticularly, that being combined with the pupiPs previous know- 
 ledge, they may assist him in surmounting a difficulty, and in 
 devising the most expedient process by which he may attain 
 his objects. The processes of analysis and research require to 
 be so infinitely varied under different circumstances, that every 
 possible action and every practicable expedient is necessarily 
 resorted to in turn to enable the experimenter to proceed. 
 
 417. The general principles and directions given with 
 respect to the solution of inorganic matter, will apply to a 
 great extent to that of organic substances. The few differences 
 that occur depend upon the situation of the matter to be dis- 
 solved, and upon its destructible nature. The active prin- 
 ciples to be separated are generally in small quantity compared 
 to that of the inert enveloping substance, and the latter is often 
 easily affected by powerful agents, such as acids and alkalies, 
 and converted into bodies which, though useless, are soluble, 
 and would contaminate the solution. Hence it is necessary to 
 select such agents as, at the same time that they act with 
 energy on the principles to be dissolved, have no power over 
 
Sect. VI.] SOLUTION OF ORGANIC MATTER. 189 
 
 the accompanying matter. Acids and alkalies are therefore 
 objectionable. Indeed a still more cogent reason exists for 
 their rejection in general, namely, a reaction upon, and de- 
 struction of, the peculiar principles themselves. Hence a fre- 
 quent recurrence to such solvents as water, alcohol, and ether, 
 either cold, or aided by heat ; and if acids or alkalies are used, 
 they should be diluted and applied only after the other sol- 
 vents have exhausted their powers, or for the separation of 
 known principles to which their action is favourable. 
 
 418. M. Robinet has lately recommended the use of neu- 
 tral saline solutions in particular cases*, stating that a separa- 
 tion of principles may be sometimes effected by them, where 
 water dissolves the whole or acts only imperfectly. 
 
 419. The original vegetable or animal substance, if dry, 
 may be rasped or bruised (333, 357), so as to be divided into 
 small pieces, but not generally into powder. If the action 
 required be but short, hot water poured over the substance in 
 a basin may be sufficient : but if a longer time be required, 
 the mixture must be retained in a sand-bath, or over a lamp, 
 as before. When hot water is merely poured upon the sub- 
 stance, the process is named Infusion. When the heat is con- 
 tinued for some time by the application of fire, Decoction ; and 
 when it consists of pouring cold or warm water on the sub- 
 stance, and allowing it to stand for some time, it is called 
 Maceration. 
 
 420. A very excellent and useful process of solution is 
 called Lixiviation. It is applicable only to such substances 
 as, from their porous nature, are permeable to water, and 
 consists in the separation of a soluble body from an insoluble 
 one by washing. For this purpose the mixture is to be loosely 
 arranged, and water added till it fills all the cavities, and 
 covers the surface of the mass. In the laboratory it may be 
 conveniently performed in the small way in a funnel, and shall, 
 therefore, be so described. Suppose it were necessary to wash 
 the salts from a quantity of ashes : a funnel of sufficient size 
 should have the lower aperture stopped by a cork, and should 
 be supported on a stand, so that it may steadily retain its pro- 
 per position. A few pieces of the ash, of such size that 
 
 * Annalea de Chiraie, xxx, 208. 
 
190 SOLUTION LIXIVIATION. [Sect. VI. 
 
 they shall not pass through the neck of the funnel, should be 
 introduced in the first place, to prevent the descent of the 
 matter to be placed over it. Having added pieces rather 
 smaller, until the surface exposed in the funnel is an inch in 
 diameter, the rest should be crushed in a mortar to a coarse 
 powder, or rather to small pieces or grains, and put into the 
 funnel above that previously arranged. If the substance be 
 such that it will not afford lumps of sufficient size or strength 
 to remain in the neck of the funnel and support the rest, then 
 its place should be supplied by some pieces of broken glass, 
 which may be continued to the height before mentioned, and 
 which, while they support the substance, afford abundant pas- 
 sages for the fluid when required. Being thus far arranged, 
 hot or cold water is to be poured into the funnel according to 
 circumstances, its quantity being such that it will just cover 
 the mass. The whole is to be left in that state for a time 
 proportionate to the solubility of the substances present. The 
 water which has penetrated the fragments will gradually dis- 
 solve the salts, and forming a heavy solution, will descend in 
 the free spaces, changing situations with the water not yet 
 saturated. In this way a solution will be produced of much 
 greater strength below than above, and the upper part of the 
 mass will be washed almost perfectly at the first operation. 
 When sufficient time has been allowed, according to the quan- 
 tity and nature of the salt, and the manner in which it is en- 
 veloped, the cork beneath should be withdrawn, and one-half 
 or two-thirds of the solution suffered to run out gradually, not 
 hastily, lest greater disturbance of the solid matter in the fun- 
 nel be occasioned than is necessary or advantageous. The 
 cork is to be replaced, fresh water added above, so as not to dis- 
 turb the arrangement : and being left as before for a time, the 
 second solution should then be withdrawn, and this operation 
 repeated till the water which passes is perfectly free from salts, 
 or contains so little as to make further attention unnecessary. 
 
 421. As before remarked, this operation can only be per- 
 formed on such substances as permit access of water to all parts. 
 When the particles fall together, or adhere slightly, and so 
 prevent contact of the water, and choke up the channels, then 
 recourse is sometimes had to the intermixture of inert matter, 
 
Sect. VII.] DISTILLATION COMMON STILL. 191 
 
 as hay, straw, coarse sand, or broken glass ; but it is better in 
 such cases, when they occur in the laboratory, to put the sub- 
 stance into a basin or glass with excess of water, and by agita- 
 tion every now and then, effect the solution in the usual way. 
 
 SECTION VII. 
 DISTILLATION. SUBLIMATION. 
 
 422. DISTILLATION and sublimation have the same object, 
 and require nearly the same means ; both consist in the con- 
 version of a body into vapour, its transference in that state, 
 and consequent separation from other substances, and its ulti- 
 mate condensation. The difference generally consists in the 
 state assumed by the vapours when condensed ; if the product 
 be solid, the process is called sublimation ; if liquid, distilla- 
 tion. All that is required is, that the substance to be distilled 
 or sublimed should be raised to such a temperature, that it will 
 assume the gaseous form, and in this form conducted into a 
 receptacle of such temperature, as to cause its resumption of 
 the fluid or solid state. 
 
 423. Simple as is the process in theory, there are few that 
 are liable to greater variety of arrangement. The range of 
 temperatures at which different bodies rise in vapour is very 
 extensive ; for sulphurous acid or chlorine assumes that state 
 at temperatures below the freezing point of water, whilst mer- 
 cury or zinc require one verging upon, or even surpassing, a 
 red heat. Thus, on the one hand, very low temperatures are 
 required to effect condensation, and, on the other, very high 
 ones to cause the requisite vaporization. The vessels and the 
 apparatus to be employed must not only be adapted to these 
 points, but also effectually to meet the innumerable varieties in 
 the quality and quantity of the substances operated upon (924). 
 
 424. The common still will serve best to exemplify the ordi- 
 nary points requiring attention in the process of distillation. 
 It may be used both for water and alcohol, and if the labora- 
 tory be not otherwise supplied with distilled water, must con- 
 
192 DISTILLATION USE OP THE STILL. [Sect. VII. 
 
 tinually be had recourse to for that necessary article (26). 
 The still consists of a metal boiler to contain the water to be 
 purified ; to this is adapted a head, which terminates in a beak, 
 and the latter is made to fit into the commencement of a spiral 
 tube called the worm, fixed in a tub, the whole of this part 
 being called the refrigerator. The process consists in raising 
 the water into vapour in the still, and condensing that vapour 
 in the worm ; the condensed water runs out, and is received at 
 the lower extremity, which ought, in all cases, to be left open. 
 
 425. It will be necessary to preserve a sufficient fire under 
 the boiler during the distillation, not merely to produce ebul- 
 lition, but also to cause the water to boil rapidly, so as to afford 
 a quick succession of vapour, otherwise the operation will be 
 very tedious. It is important, in all cases, to keep the top of 
 the still hot, or the vapours will condense there, and, flowing 
 down the sides to the water below, will be again vaporized, 
 and cause great waste of heat. For this reason it is useful, 
 when the top is exposed to the air, to cover it with a dry cloth, 
 this precaution being continued to the descending part of the 
 beak or pipe. It is also necessary to observe that this pipe be 
 sufficiently capacious for the passage of the steam to the con- 
 denser without any obstruction : every thing in this part of the 
 apparatus should be arranged so as to generate vapour with 
 great rapidity, and to convey it with corresponding readiness 
 to the worm. The student must not forget that as the water 
 is distilled, its quantity will diminish in the vessel, and should 
 be replenished before any injury arises from its deficiency. 
 
 426. The vapour having reached the worm is there to be con- 
 densed ; and therefore the worm is put into a tub and surrounded 
 with cold water, the low temperature of which causes the sub- 
 stance to lose its elastic form, and flow out in the liquid state. 
 From the quantity of heat communicated to the refrigerating 
 water, which is greater as the operation is more successfully 
 carried on, it will become necessary to change it readily and 
 quickly, and many contrivances have been resorted to for this 
 purpose, amongst the best of which are those that supply a 
 constant stream of cold water to the bottom of the tub, and 
 draw off an equal quantity of hot from the top. Whatever the 
 arrangements are, the water must never be allowed to become 
 
Sect. VII.] DISTILLATION STILL RETORTS. 193 
 
 hot, or if it does so at the surface, it should be but moderately 
 warm at two or three inches beneath ; for, although in some 
 cases it may happen, that when the upper half of the water is 
 hot, the lower half may still be sufficient to condense the steam, 
 yet inconveniences often arise. Amongst these is occasionally 
 one of more consequence than mere failure of condensation ; 
 this is, the obstruction occasioned to the passage of the steam, 
 when it has to force its way uncondensed through several coils 
 of small hot pipe, and which, at times, may become so great 
 as even to cause the forcing up of the head of the still. As 
 before mentioned, any obstruction to the free liberation and 
 condensation of the steam interferes with the effectual working 
 of the still, and causes a consequent loss of heat and expense 
 of fuel. 
 
 427. The water which flows out at the end of the worm 
 should never be more than warm. It may be received and 
 preserved in stone bottles, and should always be tested, that 
 its purity may be known. The end of the worm should not 
 usually be allowed to dip into water, so as to close the aper- 
 ture, as in that case, from irregularities in the liberation of 
 steam, much agitation is now and then produced; and, at a 
 moment of inattention, the water which has been distilled may 
 actually return back into the boiler, from a partial condensa- 
 tion therein. 
 
 428. The vessels in which most laboratory distillations are 
 effected, are retorts (16) and flasks (372). Retorts are of every 
 size and shape, and of very various materials ; those made of 
 glass are equal to all operations which may be conducted at 
 temperatures less than that at which the glass softens, and by 
 luting may be used at much higher. They admit of constant 
 observation of the materials within, are acted upon or injured 
 by very few substances, and may be cleaned, generally, with 
 facility. Their great point of failure is that of brittleness, 
 which endangers both the apparatus and its contents. 
 
 429. With regard to the general form of glass retorts, it is 
 not of any very great consequence, as respects their use in dis- 
 tillation and sublimation : they will be required with necks of 
 very different lengths and dimensions, and with bodies of 
 various proportion as relates to the necks ; the general propor- 
 
 O 
 
194 DISTILLATION RETORTS THICKNESS. [Sect. VII. 
 
 tions may be nearly those of the accompanying figure. But 
 the case is different when they are 
 intended for exhaustion, as in nu- 
 merous pneumatic experiments (866) ; 
 for having then the pressure of the 
 atmosphere to support on their ex- 
 : -d terior surface, their form should be 
 
 carefully attended to. Retorts that are carelessly bent in the 
 making, are liable to two imperfections of form, which fre- 
 quently weaken them so much as to render them unable 
 to bear exhaustion; the one is a flattening of the convex 
 surface at a, and the other is a sharp fold or double in 
 the glass at the opposite part 6, which expands the two sides 
 (at c), so that a section made through those parts would 
 have a resemblance to a long flat ellipsis. Such a shaped 
 retort will rarely bear the pressure of the atmosphere on 
 the flattened parts, but will crack during exhaustion at c 
 and the opposite corresponding side, or will be shattered 
 and crushed to pieces. Retorts should therefore be gene- 
 rally chosen sufficiently convex in all parts, the degree of 
 curvature of one part passing gradually into that of the 
 neighbouring portions, as is represented in the figure. Such 
 a retort, though very thin, will bear exhaustion with perfect 
 safety ; and that a sufficient number may be on the shelves 
 when required, let all be selected with a view to such an 
 application. 
 
 430. With regard to thickness, retorts should be examined 
 as directed for glass flasks (372) ; the bulb should be uniform, 
 or nearly so, throughout : if there be any difference, the part 
 at d should be thinnest, gradually thickening to the neck. 
 All should be rejected of which the part at d is thicker than 
 elsewhere, the application of heat being almost sure to break 
 them. The general thickness should be that of flasks of 
 about the same capacity, except that small retorts are better 
 rather thicker in proportion to their size, or even occa- 
 sionally as thick as the large ones, because they are more fre- 
 quently subjected to temperatures at which glass becomes 
 soft. All retorts with spots or grains of sand in the part 
 to be heated should be rejected; they are liable to fly at 
 those places. 
 
Sect. VII.] DISTILLATION RETORTS STOPPERS. 195 
 
 431, The sizes of retorts, on the shelves, should vary, in 
 the capacity of their bulbs, from two ounces to two pints. 
 A few large ones may be at hand, on a bye-shelf, for par- 
 ticular uses. 
 
 43. Retorts are either tubulated or plain. When tubu- 
 lated (465) they are more likely to crack, from the irregularity 
 of form and thickness of glass at the juncture, than when 
 plain ; but, being very convenient in particular cases, by 
 allowing easy access to the interior of the retort, some will 
 be required. The aperture should be in such a position as to 
 open into the body of the retort freely, admitting a funnel 
 or a rod into it without interfering with the neck, and yet 
 as little beyond the curve where the neck commences as 
 possible. The tubulature is safest when it is not much thicker 
 than the retort at the part where they join, but should 
 thicken upwards, and be sufficiently strong to admit of 
 having a glass stopper ground into it in a tight and secure 
 manner. When the tubulatures are put on like a thick knot 
 of glass, they soon break off, and the retort is of course 
 destroyed. 
 
 433. In all cases where ground-glass stoppers are used, 
 and they are very numerous, though this of the tubulated 
 retort is the first we have arrived at, they should be ex- 
 amined, and the accuracy of the grinding ascertained. 
 They should be so ground as not to be liable to fix and 
 become imrnoveable, and be so accurate as to remain air-tight 
 for months and even for years, when a little pomatum, or, 
 rather, hard tallow is put round them. A stopper should 
 be slightly conical, so that, when introduced, it may at once 
 obtain its place, and bear on every part of the ground 
 surface. Being moved round in its situation, it should feel 
 perfectly steady and firm in the aperture, in every part of 
 the revolution ; and more accurately to prove the regularity 
 in the hole and the stopper, by which they come in contact 
 in all parts, the stopper should be pressed sideways in dif- 
 ferent directions, and in different parts of the revolution, 
 to find out, if possible, any one position in which it shakes 
 a little in its place ; none such ought to occur. This ascer- 
 tained, a little tallow should be put upon the stopper, both 
 
 O 2 
 
196 DISTILLATION CHARGING OF RETORTS. [Sect. VII. 
 
 that and the aperture being clean and dry, and being then 
 again introduced and turned round, a film of the tallow will 
 intervene between the two surfaces of glass, which, at the same 
 time that it occasions perfect freedom of motion in the stopper 
 as regards its turning round in the hole, does not at all render 
 it less firm and steady in its bearing than before; and it 
 perfectly closes the passage, so that no portion of liquid or of 
 gas can pass between them. If a stopper is not tight, it is 
 easy rendered so by grinding (1230). 
 
 434. Finally, with reference to the state of the retort, it 
 should be observed, that no retort, when once cracked in any 
 part near the bulb, should be used in cases where heat has to be 
 applied to liquid contents. Their use must then be confined to 
 cold operations, or to sublimations in unimportant experiments. 
 
 435. A student has many points to attend to relative to the 
 charging of retorts, or the method of introducing substances 
 into them. If a substance in the state of lumps or of powder 
 is to be put into a plain retort, and it is required that the neck 
 be preserved in a clean state, the best preparatory step is to 
 insure the cleanness and dryness of the retort (1251, 1252), 
 so that no portion of the substance shall have any tendency to 
 adhere to the glass. If it be a powder, it should fall down 
 one side of the neck ; being introduced, if there be occasion, by 
 a small clean funnel (395). It should not be thrown down 
 in a careless way, while the neck is held in a perpendicular 
 position : by holding the retort in an inclined position, the 
 powder is less separated, and adheres less to any part of the 
 internal surface. If it be in lumps, they should be made to 
 slide down one by one, the neck being inclined at an angle of 
 40 or 45, If held more upright, or the pieces be heavy, 
 there is a probability of their passing through the retort by 
 their momentum. The retort must not be held with the 
 bottom of the bulb downwards, for then the pieces as they 
 pass from the neck will fall suddenly upon, and almost cer- 
 tainly break it ; but it must be turned half way round, so that 
 as the piece descends it may pass over that part which, when 
 the retort is in its right position, forms its internal upper sur- 
 face. In this manner masses of metal and other heavy sub- 
 stances may be introduced without endangering the vessel. 
 
Sect. VII.] DISTILLATION RETORTS. 197 
 
 When the retort is tubulated, precautions relative to keeping 
 the neck dry and clean are not so necessary, because there is 
 no occasion for soiling it. The powder may be introduced by 
 a funnel as before, and even washed in with a little water 
 (395) ; and masses may be introduced also at the tubulature, 
 not dropping them, but allowing them to slide in safely. 
 
 436. No instruction is necessary for the introduction of 
 liquid, if a little waste, or the soiling of the vessel, be unim- 
 portant points ; but when either of these are of consequence, 
 the student should be acquainted with the methods of avoiding 
 them. If the neck is to be preserved clean, as is often the 
 case when acids are introduced, the end is easily obtained with 
 the tubulated retort, by the use of a funnel with a beak so nar- 
 row and long, that it may pass into the body of the vessel. A 
 few moments should be allowed for the funnel to drain, and it 
 should at last be drawn out adroitly immediately after a drop 
 has fallen, and before another is ready to descend ; and during 
 its removal the wet beak should be held so steadily as not to 
 touch the side of the tubulature. 
 
 437. If the retort be not tubulated, then a funnel with a 
 long narrow beak, sufficient to pass down the neck of the re- 
 tort, and to reach the bulb at the end, must be used ; or if such 
 a funnel be not at hand, and the case is imperative, a piece of 
 glass tube, rather longer than the neck, may be employed for 
 the purpose, the fluid being carefully poured down the inte- 
 rior of the tube. In using the long-necked funnel or the 
 tube, care should be taken that the end do not dip into the 
 fluid already in the retort, for the exterior should be preserved 
 clean and dry, that its removal may be effected without soiling 
 the neck. For this purpose, when the funnel or tube has 
 drained a few moments, it should be inclined with the retort, 
 until the neck is nearly in a horizontal position, or even has 
 passed it a little ; that which was the lower end will now be 
 the upper ; and the fluid, still adhering to the inner surface, 
 instead of flowing as before to the extremity, and gathering 
 there in a drop, will tend to return upon its former course, 
 leaving the end almost dry. In this state the tube or funnel 
 may easily be withdrawn from the retort, without any risk of 
 soiling it, if its extremity be prevented from touching the 
 glass ; for no further dropping can take place. 
 
198 DISTILLATION- SIZE OF RETORT. [Sect. VII. 
 
 438. The size of a retort must be regulated by the quan- 
 tity of substance to be used, and by the kind of action expected 
 to occur. If the contents be fluid or semi-fluid, and the libe- 
 ration of gas or ebullition be expected, the charge should not 
 occupy more than one-half or one-third the capacity of the 
 bulb ; or if the action be likely to be rapid, not so much : but 
 if no expansion or swelling take place, nor any commotion by 
 which particles may be thrown over ; or if, in other cases, 
 although portions are liable to be thrown into the neck, it be 
 desirable to act on as much of the substance introduced as pos- 
 sible, the charge may then occupy much more of the body of 
 the retort. 
 
 439- The general methods of applying heat to glass retorts 
 is the same with those adopted for heating flasks (381, &c.) ; 
 and the spirit-lamp (199, 201), hot air (269), water, steam, 
 and sand-baths (258, 271, 381, 176), oil-lamps (212, 386), 
 and small crucible furnaces (386), may all be used in turn, 
 with the precautions before given. Sometimes a little varia- 
 tion is required, dependent upon the following circumstances. 
 In certain forms of distillation the heat is applied merely to 
 excite and increase chemical action ; this is the case in the pro- 
 duction of several gases from mixed materials ; and in such 
 cases, when the temperature has attained the necessary point, 
 the application of heat must be diminished, until it is merely 
 sufficient to preserve the temperature already acquired. In 
 other cases a greater resemblance exists to the process of distil- 
 lation already described (424) , and it is required not merely 
 to allow a certain temperature, but to communicate heat for 
 some time with more or less rapidity, 
 that the liquid in the retort may be 
 converted into vapour, and carried over. 
 Hence the necessity of a command over 
 the fire, so that it may be increased or 
 diminished at pleasure. 
 
 440. The oil-lamp is of great service 
 in chemical distillations, from its ready 
 management, but sometimes scarcely 
 
 yields heat enough for the performance of quick operations. 
 In such cases the upper part of the retort should be covered, 
 to prevent its being cooled by contact of the air, and this can 
 
Sect. VII.] DISTILLATION RETORTS HEATED. 199 
 
 often be effectually done by a thick paper or card-board cone, 
 with a broad notch to admit the neck ; this interferes with a 
 ready change of the air at the top of the retort, and saves 
 much heat, which would otherwise escape at that part from the 
 condensation of the vapour within. 
 
 441. The evolution of vapour is in many cases very much 
 facilitated by the addition of substances having apparently no 
 chemical action ; and the process of distillation is not only thus 
 facilitated, but rendered possible and easy, in cases where 
 otherwise it would be almost unattainable. If diluted alcohol, 
 spirits of wine, wine, or certain alcoholic solutions be distilled 
 in glass vessels, the vapour is frequently evolved with diffi- 
 culty ; the contents of the retort at one moment not boiling at 
 all, and at another bursting throughout into a mass of vapour 
 and fluid, which fills the whole body of the vessel. This en- 
 dangers the sudden expulsion of part of the substance, causing 
 serious derangement of the process, and is also accompanied 
 with such agitation of the fluid, such bumping and shaking of 
 the retort, as at times actually to endanger the safety of the 
 whole: for when the vapour is formed, it is with such force as 
 to produce a dull explosion. This is prevented by the intro- 
 duction of a few angular or fragmented pieces of solid matter 
 into the retort, of such nature as not to be acted upon by any 
 of the substances present. For this purpose metallic substances 
 are the best ; a piece of platina foil cut by scissars into 
 narrow slips, so as to resemble a fringe, or seven or eight 
 inches of silver, platina, or copper wire pressed up loosely, or 
 platina and silver filings are then very useful. So also is a 
 fragment of cork or a piece of torn cartridge paper, any of 
 which will generally cause the regular and tranquil evolution 
 of vapour, and occasion the distillation to proceed quietly and 
 satisfactorily. 
 
 442. The same effect takes place with sulphuric acid when 
 distilled in glass vessels, but, from the weight of the fluid and 
 the high temperature employed, with more force and more 
 danger to the retort. In this case the ill consequences which 
 would result from the fracture of the vessel are much increased 
 by the highly corrosive power of the substance at exalted 
 temperatures. If, however, a piece of platina foil be intro- 
 
200 IRREGULAR EBULLITION PREVENTED. [Sect. VII. 
 
 duced into the retort, the operation proceeds quietly, the 
 vapour rises readily, and, with the exception of the high heat 
 necessary, the distillation goes on as freely as that of water. 
 
 443. The student should be cautioned against the sudden 
 introduction of these promoters of vaporization, whilst the 
 fluids are hot. If, upon the occurrence of bumping during a 
 distillation of alcohol, sulphuric acid, or any other fluid, in 
 glass vessels, a piece of any one of the substances mentioned 
 were suddenly introduced by the tubulature, it is probable that 
 the consequent burst of vapour would be so instantaneous and 
 strong as to do more harm than the bumping itself. The 
 safer method is to remove the source of heat for a moment, then, 
 opening the tubulature, to introduce a platina wire, letting it 
 touch only the surface of the fluid at first, and introducing 
 more of it as the ebullition occasioned by it ceases; when 
 that is over, the wire should be withdrawn, the cork, the pla- 
 tina, or whatever, according to the nature of the fluid within, 
 has been selected, be introduced, the stopper closed, heat ap- 
 plied, and the distillation proceeded with. 
 
 444. The effect of these promoters is best observed upon 
 sulphuric acid. If two or three ounce-measures of strong 
 sulphuric acid be put into a clean glass flask and heated over 
 a small charcoal fire, as soon as the acid begins to boil, 
 it will exhibit the irregularity described. The foil is then to 
 be dropped in, and its power of forming vapour will be suf- 
 ficiently visible. Sulphuric acid will boil several degrees lower 
 in a glass vessel containing a piece of foil, than in one not so 
 assisted. Professor Oersted has stated, that the introduction 
 of brass wire into brandy very much accelerates the process of 
 distillation*; and Dr. Bostock has noticed similar effects with 
 regard to ether f. For these and other facts I must refer to 
 the authority quoted beneath. 
 
 445. The products evolved in distillatory operations may 
 be considered generally as of two kinds ; vapourous, or such as 
 may be condensed at ordinary pressure by the low tempera- 
 tures we can command ; and gaseous, or such as resist these 
 means, and hence have been called permanently elastic. 
 
 * Annals of Philosophy, New Series, ix, 157. f Ibid, ix. 196. 
 
Sect. VII.] DISTILLATION RESULT RECEIVER. 201 
 
 Since the general relation of gases and vapours to each other 
 lias been distinctly explained and confirmed by experiment, 
 this division is known to be very unscientific, but it is con- 
 venient in operations, and, being generally retained in chemical 
 language, there can be no objection to it in this place. The 
 operations of distillation here verge upon pneumatic manipu- 
 lation ; but as, in consequence of the peculiar means required 
 for the retention and transference of that form of matter, all 
 processes relative to gases will be more conveniently con- 
 sidered together, the further directions in this chapter will be 
 confined entirely to such operations as relate to condensable 
 substances. 
 
 446. Retorts being used for the purpose of raising sub- 
 stances into vapour, receivers become necessary for their con- 
 densation. Receivers are vessels which perform a cooling as 
 well as a retaining office, and are as variable in their kinds as 
 retorts. Sometimes a simple tube is used, at others flasks, 
 globes, and bottles ; these receive the vapours, condense them, 
 and retain the resulting fluid. On other occasions the re- 
 ceiving apparatus is more complicated in form ; one part serving 
 to condense the vapours, and another to contain the products. 
 These varieties and the methods of managing them will be best 
 illustrated by examples. 
 
 447. The simplest arrangement of retort and receiver is 
 to introduce the beak of the former, when charged, into the 
 
 mouth of the latter, which may be a 
 flask or globe (372), and then proceed 
 to distil. This is an arrangement 
 readily made, and in constant use in experiments upon inexact 
 quantities. The receiver is frequently retained sufficiently 
 cold by the air to condense the vapours ; or, if it be desirable 
 to increase the refrigerating power, it may easily be done by 
 putting the globe into a basin of cold water. During the dis- 
 tillation the globe may be turned now and then, to bring diffe- 
 rent parts into contact with the water in the basin ; and if at 
 times it becomes quickly heated from a rapid production of 
 vapour, the cooling power may be increased by covering the 
 upper surface with a -doubled piece of filtering paper, and 
 pouring a little water, at intervals, over it. Water, and most 
 
202 DISTILLATION CONDENSATION. [Sect. VII. 
 
 substances not less volatile than it, may in this way be distilled 
 in ordinary experiments, with very little loss. Nevertheless, 
 as the vessels are open, and the cooling process is not fitted for 
 the condensation of a sudden or large production of vapour, 
 the arrangement should not be used except in experiments in 
 which the substances remaining in the retort are the same with 
 those which are condensed, or where a little loss of matter is 
 of no consequence. 
 
 448. On other occasions, although an open apparatus may be 
 convenient or necessary for the ready substitution of one receiver 
 for another, yet great cooling power may be required. An 
 arrangement requisite for the distillation of sulphurous acid 
 will illustrate some of the means which, either separately or in 
 conjunction, are then advantageously applicable. The retort 
 in which the sulphurous acid is generated, is attached, by a 
 caoutchouc connecter (840), with a bent piece of glass tube of 
 
 the form represented in the figure, 
 and that again by another caout- 
 chouc connecter, with a second 
 bent tube^ also figured in the cut. 
 The first tube is to be placed in a 
 glass or other vessel, convenient 
 for holding a frigorific mixture 
 (454) ; the second is for the pur- 
 pose of conducting the gas into the receiver, and is represented 
 as passing into a small stoppered flask. These tubes should be 
 of sufficient diameter to allow of the free passage of all the 
 gas that may be liberated, and the first or cooling tube should 
 be so large as also to retain all the fluid that may be condensed 
 there, and yet allow free passage for the uncondensed gas. 
 
 449. The caoutchouc or India-rubber connecting pieces are 
 easily made, and are of such constant use in attaching tubes 
 and apparatus for the conveyance of vapours and gases, that 
 a number of them, from an inch to two inches long, and from 
 a quarter to half an inch in diameter, should be kept ready in 
 a box or drawer (1122). They are most easily made of the 
 sheet caoutchouc, prepared by Mr. Hancock *, which is about 
 
 * Mr. Hancock resides in Goswell Mews, Goswell-street Road. 
 
Sect. VII.] DISTILLATION CAOUTCHOUC CONNECTERS. 203 
 
 the tenth or twelfth of an inch thick, and may be had in pieces 
 ten or twelve inches square. A piece of this caoutchouc, 
 about an inch and a half square, is to be slightly warmed till 
 it becomes flexible and soft, and then put round a glass rod or 
 other cylindrical body, rather smaller than the intended tube ; 
 the projecting edges are to be pinched together, and when 
 they have slightly adhered, cut through with a pair of very 
 sharp, clean scissars ; this will remove the superfluous caout- 
 chouc, will expose perfectly clean surfaces upon each edge, and 
 leave the two edges slightly adhering together. The junction 
 is to be completed by immediately bringing these edges into 
 contact throughout the whole extent of cut surface; which 
 may be done by applying a thumb-nail upon each side the 
 section, and pressing the surfaces together,the glass rod within 
 supporting the caoutchouc, and thus assisting to obtain the 
 desired adhesion. This operation, if neatly performed, will 
 cause the cut surfaces to apply so accurately to each other, that 
 no part of either will appear. When firmly pressed together 
 whilst warm, the adhesion is such that the tube will tear else- 
 where as readily as at the junction. The tube should be made 
 so loose that it will easily slip off the glass rod. If the caout- 
 chouc has been stretched to make the edges meet, and the tube 
 consequently fits closely to the rod, it will frequently adhere 
 so tightly as to be difficult of removal ; but this may be ob- 
 viated either by putting a little flour over that surface of the 
 caoutchouc which is to be the inside of the tube, and which 
 prevents its adhesion to the glass ; or by wrapping a piece of 
 paper first round the mould ; or by using a thin tube instead 
 of a glass rod, and breaking it to pieces when the tube ip 
 finished, if it should happen to adhere. Great care is neces- 
 sary, in using the flour, that none get to the surfaces to be 
 joined, for any kind of dirt or extraneous substance prevents 
 the adhesion, and the tube is rendered imperfect. On the 
 other hand, when the tube is finished, and it is desirable to 
 prevent the adhesion from pressure of the sides within, then a 
 little flour, chalk, or other dry powder is very useful. 
 
 450. If Hancock's sheet caoutchouc cannot be obtained, the 
 tube may be made of thin bottle India-rubber. For this pur- 
 pose, the smallest and thinnest bottles should be chosen, selecting 
 
204 DISTILLATION CAOUTCHOUC CONNECTERS. [Sect. VII. 
 
 from them, when cut up, only the most straight and uniform 
 pieces that can be obtained. They should first be softened by 
 being placed in a warm situation for some hours and rubbed 
 frequently, or by being boiled for half an hour ; then, being 
 dried, they may be formed into tubes. The caoutchouc in bot- 
 tles is more rigid and stiff, and less adhesive, than that in 
 sheets, and for this reason, greater pressure and more care are 
 generally required in making the joint firm and tight; the 
 tubes will probably require warming two or three times on the 
 rod during the operation of pressing the edges together, and 
 perhaps, also, compression of the joint by a pair of pincers. 
 
 451. Although these tubes have been described as cylindri- 
 cal, yet they are frequently useful of a conical form to connect 
 tubes or apertures of different sizes (844). There is no ordi- 
 nary agent, except perhaps chlorine and strong nitric and sul- 
 phuric acids, which act upon them ; hence they are very gene- 
 rally applicable. When tubes are connected by them, as in 
 the present case of sulphurous acid, one of these flexible con- 
 necters should be selected of a size near to that of the tube to 
 which it is to be adapted. If small, it easily admits of exten- 
 sion, and is then slipped over the ends and tied with two or 
 three turns of fine twine or thread, which should not be drawn 
 tight, or it will cut the caoutchouc ; indeed, when the tube has 
 required a little expansion to make it pass over the glass, it 
 contracts with sufficient force to form a joint impervious to gas 
 at ordinary pressure; very little stress, therefore, upon the 
 thread is sufficient to secure any joint in a perfect manner. If 
 the caoutchouc tube be a little too large, so contractile and 
 manageable is the substance, that tying is quite sufficient to 
 make it tight. 
 
 452. Where the object, as in the present case, is merely to 
 connect different parts of an apparatus, the ends of the glass 
 tubes should be from the eighth to the fourth of an inch apart 
 within the caoutchouc connecters. This is quite sufficient, in 
 ordinary cases, to allow of that flexibility in complicated glass 
 apparatus which is so valuable as permitting motion and the 
 minute adjustments of one part, without endangering another. 
 
 453. The apparatus for a distillation of this kind at low 
 temperatures being thus connected, and ready for an opera- 
 
Sect. VII.] DISTILLATION CAOUTCHOUC CONNECTERS. 205 
 
 tion, the next step is to apply the necessary means of cooling 
 the parts where condensation is to be effected. For this pur- 
 pose some ice should be pulverized, the glass a half filled with 
 it, and then nearly filled up with water. For the glass b, 
 where the actual condensation is to take place, a more powerful 
 cooling mixture must be prepared ; for this purpose ice and 
 salt should be used, the glass being filled with the mixture to 
 within half an inch of the top. 
 
 454. In making this mixture, a little ice should first be put 
 into a mortar, and having been broken small, during which 
 operation the mortar will have cooled considerably, should 
 have about a fourth of its bulk of salt added and rubbed with 
 it : fusion of much of the ice will take place, and a cold of 
 will be produced. After a few minutes this portion is to be 
 thrown away, for, being fluid, it would not long retain its low 
 temperature in a warm atmosphere, and its use should, there- 
 fore, be confined to cooling the mortar and pestle. The ope- 
 rator should now proceed to pound ice and salt together for a 
 mixture to be used in the distillation. The quantity of salt 
 used should be about one- half the weight of the ice, or nearly 
 one-third its bulk ; this is far more than the water from the 
 ice can dissolve, but the excess is necessary, to insure, with 
 facility, the cold of 0, as long as ice continues undissolved. 
 The pulverization of the ice, and its mixture with the salt, 
 should not be discontinued as soon as the temperature in the 
 mortar is at 0, but continued, consistently with a quick opera- 
 tion, until the ice is as small as possible ; otherwise, after being 
 put into the glass, and standing for a time, a quantity of liquid 
 will form, the solid salt will sink, the lumps of ice float, and it 
 will be found difficult by stirring to keep the temperature down 
 to ; whereas, if the ice be in fine particles, when, from the 
 production of brine, a partial separation does ta'ke place, very 
 little stirring will be sufficient to keep the temperature at 0, 
 until nearly all the ice be dissolved. The state of the mixture 
 in the mortar is most advantageous when, with a due propor- 
 tion of salt, it contains most solid ice in a small state. 
 
 455. Neither a cold mixture, nor ice and water, should 
 be poured suddenly into a glass at common temperatures : it 
 is safer to cool the glasses previously by putting a few pieces 
 
206 DISTILLATION REFRIGERATION. [Sect. VII. 
 
 of ice into them, and then, upon removing the ice, to introduce 
 the mixtures. The receivers, which are to be placed in the 
 cooling mixture, should also have their temperatures lowered 
 gradually; this is easily effected by allowing them to remain 
 for a few moments among the loose ice. 
 
 456. It may be observed that so long as the glass a contains 
 ice mixed with water, the water will be at 32 or nearly so ; 
 and in the glass 6, if stirred now and then, the temperature of 
 the whole will remain nearly at 0, so long as both ice and salt 
 in any quantity remain in the solid state. But if the operation 
 should continue until nearly the whole of the ice in both is 
 dissolved, it is better not to wait till all has disappeared, but, 
 whilst a fifth or sixth part remains, to prepare a fresh mixture 
 for 6, and, removing part of the water from a, to replace it 
 by ice. 
 
 457. These cooling mixtures receive heat so rapidly from 
 the atmosphere, especially in summer, as often to have their 
 power exhausted in one-half or one-third the time during 
 which they would remain effectual if such influence were 
 prevented. When operations, therefore, of any kind in which 
 refrigerating mixtures are used, are continued for a long time, 
 it is highly advantageous to prevent the effect as much as 
 possible, that the trouble, expense, and loss of time attendant 
 upon the frequent renewal, may be avoided. All that is 
 necessary is to hinder the access of air, either by wrapping a 
 dry flannel or cloth round the sides of the cooling vessel, 
 or even a large sheet of paper three or four times loosely round 
 it, so as to form a cylinder, which is to be tied with pack- 
 thread (1343) . This case should rest upon the table beneath, 
 so as to prevent as much as possible the passage of air at the 
 bottom : not that small apertures need be attended to, but free 
 way for a descending current should not be permitted. The 
 tops of the vessels may be covered temporarily by laying on 
 them loosely a card or a couple of cards with notches, to 
 receive the tubes. Small portions of freezing mixtures may in 
 this way be preserved for hours together, at 0, in the middle of 
 summer. In hot weather, merely putting the glass containing the 
 refrigerating mixture into a glass jar is very useful, for the latter 
 retains a bath of cold air around the former which retards the 
 
Sect. VII.] DISTILLATION SULPHUROUS ACID. 207 
 
 alteration of temperature very greatly. The jar should be 
 covered with a card, or paper, to keep the atmosphere within 
 in a quiescent state. 
 
 458. Having made the proper preparatory arrangements, 
 the distillation of the sulphurous acid may be commenced and 
 carried on. The gas being liberated from any of the usual 
 materials in the retort, passes first through the bent tube re- 
 tained at a temperature of 82 by the ice and water. Several 
 advantages result from the use of this vessel. In the first 
 place, water brought over with the gas is in part condensed 
 and retained ; in the second, the temperature of the gas is 
 reduced to 32, and consequently its condensation more easily 
 effected in the receiver at 6; in the third, being evolved in a 
 warm state, much of the heat which must necessarily be ab- 
 stracted from it before it will assume the liquid form, is re- 
 moved here, where the refrigerating agent (ice and water) is 
 easily restored, and consequently less of the cooling power of 
 the mixture in b is required for its ultimate condensation, and 
 the latter remains effectual for a longer time. 
 
 459. Leaving the part of the apparatus at a, the sulphu- 
 rous acid travels on to 6, and there enters the receiver. 
 Being heavy, it soon displaces the air ; and then, coming in its 
 unmixed state against the sides of the receiver at 0, it is 
 condensed, and assumes the liquid form. This condensation, 
 as the student will know from his scientific sources of chemical 
 knowledge, evolves heat, and will consequently tend to raise 
 the temperature of the mixture around the receiver: in this, 
 and in all similar operations, a thermometer should therefore 
 be immersed in the mixture, to indicate whether its tempe- 
 rature is such as it ought to be. 
 
 460. It will be found advisable, in all cases where the 
 substance distilled is so volatile as to require these low tempe- 
 ratures for its condensation, to collect it in small receivers; not 
 only that it may soon come into contact with their cold sides 
 during condensation, but also that it may be in convenient 
 portions for operating with in experimental investigations 
 (924, 929). The vessel in which the body is condensed should 
 generally be that in which it is afterwards preserved ; and as, 
 in most experiments, the quantity in one vessel will (unless 
 
208 SMALL RECEIVERS ELONGATED RETORT. [Sect. VII. 
 
 with peculiar management) be used at once, it is better in the 
 first instance to receive the substance in such small portions as, 
 being sufficient for each time, shall leave no overplus; so that 
 waste may be avoided. Operating in this way, it will be 
 necessary to change the receivers frequently: this is easily 
 done in consequence of the flexibility of the arrangements. 
 Those receivers which are to replace in succession such as are 
 sufficiently full, should be preserved cool by a mixture in a 
 separate glass. 
 
 461. The receivers may in many cases be small flasks or 
 stoppered bottles, but the latter are generally so thick at the 
 bottom as to fly to pieces when one of them containing such a 
 volatile body as sulphurous acid is opened, in consequence of 
 the sudden cold produced by its evaporation. Very useful 
 receivers for these purposes will be described in Sect. xvi. 
 
 46&. The various circumstances necessary to an effectual 
 arrangement for a distillation of this kind have now been 
 described minutely. It will be unnecessary to point out the 
 applicability of parts only of the arrangements their uses in 
 the present instance will be so evident as to indicate their 
 sufficiency in other cases ; and though a particular form of the 
 tubes has been described, yet the parts may easily be altered 
 and arranged at pleasure. 
 
 463. There is, however, one point with respect to the retort 
 worth suggesting, as it will often be found useful. It is the 
 advantage derived from an elongation of the neck of the retort 
 itself at the table blow-pipe (1179, 1176), by softening and 
 
 drawing it out sometimes almost to a 
 
 ^ capillary tube ; and also by bending 
 
 ^V it in different directions upwards or 
 \ downwards. Opportunities are thus 
 obtained of delivering the products of 
 
 the distillation through minute apertures, and upon particular 
 spots, in a very advantageous manner. Similar opportunities 
 of course exist with respect to the tube which terminates the 
 distillatory apparatus (448). 
 
 464. In the apparatus and arrangements hitherto described, 
 the passage is free from the retort to the air, and in the distil- 
 lation of sulphurous acid it will generally be found that much 
 
Sect. VII.] 
 
 DISTILLATION CLOSE APPARATUS. 
 
 209 
 
 of the substance escapes and is lost. In some operations this 
 is carefully to be avoided : thus in the distillation of wine for 
 the purpose of ascertaining the quantity of alcohol it contains, 
 if vapour be lost, alcohol is lost^ and the results are inaccurate. 
 In other cases, as in the preparation of concentrated hydro- 
 cyanic acid, though the exact quantity of the product is not 
 required, yet being valuable and also deleterious to the lungs, 
 it is desirable to prevent loss as much as possible. Some 
 arrangements will, therefore, now be described tending to 
 secure all the results, and allowing at the same time of the 
 introduction and illustration of other contrivances. 
 
 465. Let us suppose the object were to distil some wine for 
 the purpose, as already intimated, of separating the alcohol it 
 contains from the other principles, that its quantity may be 
 accurately estimated ; and let us consider it as having been 
 introduced into a tubulated retort with the precautions already 
 described to prevent soiling the neck (437), and with the intro- 
 duction also of some clipped platina foil and two or three pieces 
 of cork which may have little pieces of platina foil stuck into 
 
 them (441). The wood-cut 
 represents this retort con- 
 nected with a quilled re- 
 ceiver which is to assist in 
 the condensation, and of 
 which the quill descends into 
 a flask which is to receive 
 the distilled spirit. The 
 retort should have a neck 
 of comparatively consider- 
 able length ; for, by a con- 
 trivance to be described, a 
 
 large portion of it is to serve as a refrigerator. If from 14 to 
 
 18 inches long it will answer the purpose. 
 
 466. The retort and receiver are connected by a cork, and 
 it is better that the neck of ihe retort and the opening of the 
 receiver should be of very different dimensions, than that they 
 should nearly fit. If the aperture of the receiver be about 
 two inches in diameter, it will be large enough to admit the 
 necks of most retorts. A bung of good cork (1331), chosen 
 
 P 
 
210 RETORT AND RECEIVER CONJOINED. [Sect. VII. 
 
 of such size that it will fit tightly into the aperture of the 
 receiver, should be pierced as before described (67), the hole 
 being of such dimension, that, when the neck of the retort is 
 thrust tightly into it and then connected with the receiver, the 
 beak may pass in about as far as is represented in the wood- 
 cut. If the cork be good, well cut, and the hole neatly made, 
 this junction will be air-tight, or nearly so, and may be made 
 quite secure by drawing a slip of moist bladder tightly round it 
 several times, and tying it on by a few turns of twine. 
 
 467. The flask should be of such a size as to permit the 
 quill of the receiver to approach close to, or to touch the bot- 
 tom. It should be immersed in a jar of water, and a few 
 pieces of ice should be put into the jar and allowed to float on 
 the surface, for the purpose of keeping the temperature at or 
 below 40. The flask, whilst empty, will be so much buoyed 
 up by the water, as to press against the end of the quill if its 
 aperture be large enough to admit the latter so far through it ; 
 but this should be prevented, as it endangers the bottom of 
 the flask. A little slip or wedge of wood introduced between 
 the quill and the flask at the neck, will retain the latter, so 
 that the end of the quill may be about a quarter of an inch 
 from the bottom. So much pure water should be put into the 
 flask as to rise just high enough to close the aperture of the 
 quill. 
 
 468. Both receiver and flask are in this way adapted for 
 refrigeration ; but the intention is not to effect the principal 
 condensation there, but to insure the retention of all the spirit 
 by liquefying such portions as may pass the neck, where the 
 condensation is principally to be effected in the manner now to 
 be described. A little loose tow should be drawn out into a 
 sliver, wetted, and wrapped twice round the neck of the retort, 
 the ends being so long that they may be twisted together 
 beneath, with a few threads of the tow pulled out from the 
 part that has already passed round, and hang down for about 
 four or five inches in length. The ring of tow which thus 
 surrounds the neck should be placed about half an inch or an 
 inch above the junction before mentioned, as at a (465) ; it 
 should be moderately tight round the glass, and should be 
 carefully separated from the bladder or cork beyond, so as to 
 
Sect. VII.] REFRIGERATION ON RETORT NECK. 211 
 
 have no part in contact with it, touching indeed nothing but 
 the neck. A single piece of filtering paper should then be 
 selected, long enough to reach from about half an inch above 
 the tow to the part where the neck begins to turn and blend 
 with the body of the retort, and wide enough to go two-thirds 
 or nearly the whole way round the neck : it should not pass 
 
 quite round, as it then does not 
 apply itself so readily in the wet 
 and dry state to the glass. Being 
 /' (^ laid on the neck of the retort and 
 
 moistened, it will adapt itself to 
 
 the glass, adhere closely to it, and will serve the office of con- 
 veying water to every part to which it is applied ; and it should 
 be observed that all parts of this surface is of such inclination, 
 that the fluid condensed within will run into the receiver, and 
 not return again to the body of the retort. 
 
 469. The water is to be supplied to this paper from a filter 
 in a funnel placed above (534, Sic.), in such a position that 
 the drops shall have to fall about half an inch or an inch, which 
 assists in spreading the water over the paper, and also shall 
 descend upon the paper a little way from its upper extremity. 
 If they fall on to its edge, or on to the glass, a few particles 
 may splash upon the hotter parts of the retort, or portions 
 may run down its outside. Water should be put into the 
 filter in such quantity, that it may descend sometimes in a 
 small stream, and sometimes in rapid drops : it will wet the 
 paper and the glass under it, and running down to the tow, 
 will there descend and be caught in a basin placed beneath, 
 not a particle passing beyond the tow to endanger the intro- 
 duction of any portion into the flask, either by soaking through 
 the bladder, or by running down the outside of the receiver 
 and the quill. 
 
 470. Still, however, the water, in its tendency to descend, 
 will not wet all parts of the paper fully and equally if it be 
 of much extent ; and the upper surface of the lower end incurs 
 
 the risk of being sometimes dry. This is avoided, 
 \Sr~ ^/ and the paper freely wetted in all parts by the use 
 
 of another piece of filtering paper folded as here 
 drawn. Being placed with its two lower edges upon a moist 
 
 P2 
 
212 DISTILLATION PERFORMED. [Sect. VII. 
 
 surface, it will absorb water, the two sides or flaps will bend down, 
 and, accommodating themselves to the wet surface beneath, 
 will adhere to it, and the central part will stand up in a ridge, 
 leaving an acute angled space between it and the moistened 
 surface. Being, therefore, applied to the neck of the retort, it 
 adheres, is stationed there like a saddle, and answers the pur- 
 pose of a channel for the water. Its proportions and position 
 may be gathered from the former wood-cuts. The water 
 which drops upon the neck, just above its upper opening, 
 partly enters into the channel there formed ; and whilst about a 
 third of it is carried through, and delivered at the lower end 
 of the channel over the upper surface of the neck, the rest 
 flows out along the sides of the saddle, and being distributed 
 all over the paper adhering to the glass, keeps it thoroughly 
 wet and even flowing with moisture. 
 
 471. All is now prepared for distillation : heat is to be 
 applied to the retort, and when the upper part becomes 
 warm, the filter must be supplied with water, so that the con- 
 densing arrangement on the neck may be constantly and fully 
 moistened. Upon commencing ebullition, the temperature of 
 the neck will rise, water will rapidly evaporate from the moist 
 paper, and care must be taken that the supply be sufficient, 
 not merely to keep the paper fully wet, notwithstanding the 
 evaporation, but to have a surplus running off in a small 
 stream from the tow. The distillation should not be hurried, 
 and the quilled receiver should never be more than warm 
 about the part where the retort is inserted. If it become hot, 
 or if vapour enters it visibly from the retort, rising and causing 
 rapid condensation over the whole of the upper surface and 
 elevating its temperature, then either more water must be suf- 
 fered to fall upon the neck, or if that be fully moistened, and 
 still does not effect a sufficient condensation, the heat must be 
 diminished. 
 
 472. The tightness of the j unction between the retort and 
 receiver will be rendered evident upon the application of heat, 
 by the expansion of the air within, and its passage from the 
 bottom of the beak in bubbles through the water. This will 
 continue until much of the air is expelled, and the retort and 
 part of the neck is filled with vapour. As the distillation pro- 
 
Sect. VII.] DISTILLATION TIGHTNESS, ETC. 213 
 
 ceeds, the condensed liquid will flow down to the water in the 
 flask and mix with it. The first portion which rises is the 
 most volatile ; but, combining with the water, and being di- 
 luted by it, and its temperature being reduced at the same 
 time to about 40, no appreciable portion will escape. As 
 the quantity of fluid increases, the quill will be more deeply 
 immersed, but this is of no consequence : the fluid will rise 
 and fall in it, and occasionally when the heat slackens, or 
 when fresh water has been put into the filter, the conden- 
 sation within may be such that nearly all the contents in 
 the flask may pass up into the globe, and even air enter 
 it. This is of no importance ; there is abundant space in the 
 globe for the liquid, so that it cannot be drawn back into the 
 retort, and it even has the advantage of cooling that vessel ; 
 in a few minutes the expansion within will cause it again to 
 return into the flask, and probably a portion of the air pre- 
 viously absorbed may now be expelled. When about five- 
 sixths of the contents of the retort have passed over, all the 
 alcohol will have been separated, and the operation may be 
 concluded : the diluted spirit in the flask or flasks, if a second 
 has been required, being reserved for the prosecution of the 
 intended experiments. 
 
 473. It is sometimes necessary in distillatory processes to 
 keep a part of the neck hot, for the purpose of preventing the 
 condensation of the vapours there. This is readily effected 
 by wrapping it in two or three folds of dry flannel or cloth, or 
 even paper, the envelope being loose and tied with twine. 
 
 474. The refrigerating arrangement (468), although de- 
 scribed of such a size as to occupy nearly the whole of the 
 neck, may vary in extent and form, and be applied to other 
 apparatus, as well as the neck of a glass retort. 
 
 475. In other cases of distillation, it may be required to con- 
 dense the liquid products out of contact with other substances, 
 and yet to retain the uncondensed portions, so as to pass them 
 through water, or, if gaseous, to conduct them to their proper 
 receptacles. The accompanying figure will illustrate a case 
 of this kind, which may be supposed to be a distillation of 
 nitric acid from nitre and sulphuric acid. The retort contain- 
 ing the charge is connected wih a globular receiver of the form 
 
214 CONDENSATION OF PRODUCTS. [g ec t. VII. 
 
 a, from which a bent tube proceeds, and passes into the Woulfe's 
 
 bottle b (844). The junctions be- 
 tween the receiver and the retort 
 and tube are best made by ground 
 ' glass joints; but if that plan can- 
 not be adopted, other means must 
 be resorted to. Good pierced corks will answer the purpose, 
 the junction being made vapour-tight, either by some glazier's 
 putty put over it, or a paste of linseed meal (1031), or a little 
 plaster of Paris ; and where the neck or tube nearly fits the 
 aperture, it may be made tight without a cork by plaster 
 of Paris alone ; the open space being first closed by rather a, 
 thick paste of it, and the joint made smooth and tight outside 
 by a thinner portion (1]08). The plaster will resist the action 
 of the acid vapours ; cork and other substances will be some- 
 what acted upon, but with care will cause no injury to the 
 results. If bodies, not corrosive, are distilled in this way, 
 these precautions, as to the nature of the closing substances, 
 are not necessary (Sect, xviii). 
 
 476. The receiver a, and the bottle b may, one or both, be 
 cooled, according to the temperature produced by the vapour, 
 being for that purpose immersed in jars or pans of water ; the 
 neck of the retort may, occasionally, be cooled as before by 
 paper and the filter (468). Caution must be used in applying 
 that method however to such substances, as, from the high 
 temperature at which they boil, produce very hot vapours, lest 
 the differences of temperature be so great as to break the glass. 
 Bodies, not more fixed than water, may, when distilled in glass 
 retorts, have that process applied ; but, when substances re- 
 quiring higher temperatures, for example, nitric acid or oil of . 
 turpentine, are distilled, then hot water should be put into the 
 filter instead of cold, or the refrigeration should be carried on 
 further down the neck, where the contents are of a lower 
 temperature. 
 
 477. At the commencement of the operation, it is supposed 
 that the receiver a is clean and dry, and that the bottle b con- 
 tains water enough to cover the end of the tube. In the dis- 
 tillation, therefore, any product condensed in the neck of the 
 retort, or in the receiver, will be retained in an undiluted and 
 
Sect. VII.] DISTILLATION PRODUCTS UNDILUTED. 215 
 
 unmixed state; but the portions, which, from their particular 
 nature, or the comparatively high temperature of those parts, 
 remain uncondensed, will be conducted into the bottle, and 
 their condensation facilitated by the solvent powers of the 
 water, or the still lower temperature which may there be ap- 
 plied. If any gaseous matters are evolved, they may be con- 
 ducted away by a second tube, and treated as hereafter to be 
 described (748). 
 
 478. There are one or two additions now and then required 
 to this and other arrangements, in consequence of occasional 
 peculiar circumstances to which they are subject. It may be 
 observed, that if partial condensation of the vaporous atmos- 
 phere in the retort and receiver takes place, the solution in the 
 bottle b will be forced back into the receiver a, and mix with 
 its contents (475). One method of avoiding such an effect is 
 by the use of Welter's safety tube. This instrument is figured 
 
 in the wood-cut, and may be fixed in the tubu- 
 lature of the retort. Mercury is to be introduced 
 until it fills about one-fourth of the little bulb, 
 and the tube by its side, to the same height ; 
 this closes the passage, but admits of a variable 
 column of metal, according to the pressure 
 within the retort and receiver. Whenever 
 there is condensation within, the external air 
 has a tendency to enter by forcing the water 
 up the tube c (in the former wood-cut), and 
 the mercury into the ball d (of the present) , and will gain en- 
 trance where the fluids exert 'the least pressure. Hence it is 
 necessary to have the height of the tube c above the water in 
 the bottle 6, more than fifteen times that, from the bend of the 
 safety tube at e, to the level of the mercury, when nearly the 
 whole of it is in the bulb 5 for in that case, the air will enter 
 by passing through the mercury in the bulb, and not by forc- 
 ing the water into the receiver at a. 
 
 479. Should it be impossible, from some limiting circum- 
 stance, to establish this proportion of 1 to 15 or more in the 
 height of the column of mercury and fluid, then, in place of 
 mercury, water may be used in the safety tube, provided that 
 if a little were to enter the retort it would occasion no injury, 
 
216 DISTILLATION TUBE OF SAFETY. [Sect. VII. 
 
 but then the height from e to the top of the safety tube should 
 be two or three times the quantity by which the tube c (475) 
 dips into the fluid in the bottle, otherwise the pressure of the 
 gaseous contents may, on some occasions, force a passage out 
 through the safety tube, and derange the regularity of the 
 experiment. 
 
 480. It is to be observed, that a few bubbles of air entering 
 by the safety tube, are more effectual in preventing further 
 contraction of the vapours within the retort, than the entrance 
 of the whole of the water by the tube c would be. These 
 bubbles come at once into the hottest part of the vessels, are 
 there much expanded, and at the same time actually lessen 
 that tendency of the vapour to condense, which is at the 
 moment threatening the mischief; whilst, on the contrary, the 
 water on entering would rapidly increase the tendency to con- 
 densation, both by cooling the receivers and by its absorbent 
 power over the vapours, with which it would be brought in 
 contact. It will generally be found in such cases, that when 
 one drop of water has entered, the rest will rush violently 
 after it. 
 
 481. Another arrangement of a safety tube may now and 
 then be adopted, but being more applicable to gaseous mani- 
 pulations will hereafter be described (847). 
 
 482. A contrivance something resembling the safety tube 
 just described, is often useful in feeding a retort with fluid 
 during the progress of distillation. For this purpose a piece 
 of tube may be bent into the form of a double syphon, as in 
 the figure, and fixed into the tubulature of the retort. Acid 
 
 poured into it will rise in the first two por- 
 tions to the height of the second bend, and 
 then further additions will flow into the ves- 
 sel. The part a should be of sufficient length 
 to contain a column of fluid, heavy enough 
 to counteract any pressure outwards that 
 may occur within : its length should be at 
 least twice that of the middle portion. Its 
 upper extremity should be opened out at the 
 blow-pipe table into a funnel form, and the tube should be so 
 large, that the fluid may be poured down without carrying 
 
Sect. VII.] DISTILLATION TEMPORARY APPARATUS. 217 
 
 air-bubbles with it. If it be so small that air mixes with the 
 passing fluid, the relative weights of the columns are deranged, 
 and sometimes the acid thrown back and even out of the ap- 
 paratus. 
 
 483. A sufficient number of instances have now been ad- 
 duced, to illustrate the different arrangements that are useful 
 in distillations performed with glass retorts. But little has 
 been said relative to the methods of supporting the different 
 
 parts in their respective positions. The delineations, 
 and the descriptions relating to flasks (386) , retort 
 stands (386), bricks (24), rings (68), wooden blocks 
 (20), &c. being sufficient for the purpose. When 
 these conveniences are wanting, very useful tripods 
 may be made, by tying three sticks together at the 
 middle, and confining them beneath by string, to 
 prevent them from slipping down. 
 
 484. In cases of necessity, Florence flasks may often be 
 substituted for retorts in distillation ; a neck being formed of 
 
 a piece of bent tube, and attached to 
 the flask by a good sound cork, made 
 tight by accurate fitting without blad- 
 der or lute. Corks thus circumstanced 
 sometimes swell by the heat and moisture, so much as to en- 
 danger the neck of the flask, and if it be discovered, by the 
 expansion of the part outside, that such danger is to be appre- 
 hended, the cork should be partly withdrawn and in that way 
 relieved. 
 
 485. Before leaving the consideration of distillations, which 
 may be performed at temperatures easily borne by glass, there 
 are one or two remarks to be made in addition to those already 
 given. There are some cases in which, although the heat ne- 
 cessary for the operation may be easily sustained by glass 
 retorts, circumstances will make it advisable to prefer retorts 
 of other substances. In the preparation of fluoric acid, a vessel 
 of lead will be superior : glass would then be easily acted upon, 
 and at the same time that the retort would be destroyed, the 
 product obtained would not be pure, but a combination, 
 with part of the vitreous matter. There are some sub- 
 stances which, though sufficiently volatile, are very difficult of 
 
218 DISTILLATION DIFFERENT SUBSTANCES. [Sect. VII. 
 
 distillation in glass vessels. Of such kind are bone oil, Dip- 
 pie's animal oil, sometimes naphtha, and some of the common 
 essential oils, when free from water. These are distilled with 
 great facility in a tin plate or copper retort, but as they fre- 
 quently require a high temperature, the vessels should not be 
 soldered, but be either brazed, or the joints lapped over and 
 then made tight by a small quantity of solder. 
 
 486. The essential oils are generally distilled with water : 
 they rise in conjunction with its vapour, at a temperature far 
 below that at which they would distil alone. Advantage may 
 be taken of this circumstance in many cases where the contact 
 of water is of no consequence ; and bone oil, naphtha, and 
 other substances of that kind, may be distilled in a similar 
 manner. It is to be remembered, however, on future occa- 
 sions, that the substances generally retain a small portion of 
 water, which, unless removed, may be injurious in particular 
 experiments. 
 
 487. In small distillations, other cooling agencies, besides 
 those mentioned (447, 448, 465), are useful. With this view, 
 alcohol, ether, carburet of sulphur, and even sulphurous acid, 
 are employed ; being dropped upon the condensing vessel, they 
 effect their object by rapid evaporation. These are more par- 
 ticularly serviceable in small operations, where the substances 
 are distilled by cooling the receiver, instead of heating the 
 retort. Processes of this kind will be described and illustrated 
 in Section xvi. on Tube Chemistry. 
 
 488. As a heated tubulated retort cools, it is advisable to 
 loosen the stopper from time to time, lest the differences of 
 contraction, from previous difference of temperature, should 
 cause it to become fixed so tightly that it cannot be removed 
 without risk of breaking the vessel. 
 
 489. In operations of distillation requiring temperatures so 
 high that glass would melt, either earthenware or iron retorts 
 must be used, or the glass must be protected and strengthened 
 by an exterior coating of lute (1084, 1093). Notwithstanding 
 the fusibility of glass, and its liability to chemical action at 
 high temperatures, and in a softened state, it is still, when 
 coated, often superior to earthenware, because of the perme- 
 ability by air of the latter substance when hot, and its great 
 
Sect, VII.] DISTILLATION AT HIGH TEMPERATURES. 219 
 
 risk of fracture at high temperatures, either during the heating 
 or cooling ; and it is often preferable to iron, because, though 
 liable to chemical action, it is generally less so than that metal. 
 For the choice of the lute, and the method of applying it, see 
 Section xviii. Lutes, Cements, 8cc. 
 
 Glass retorts should be coated at a leisure time, and several 
 of them kept ready for use in a warm place (16), Their per- 
 fect dry ness is then secured, and time is allowed for the stop- 
 ping of any cracks that may have been formed. 
 
 490. When perfectly dry, and prepared for the fire, and 
 charged with the materials to be distilled, they then require to 
 be adjusted and supported in a furnace that they may be 
 heated. They should not be allowed to hang from the neck 
 as is frequently permitted in ordinary distillations, but must 
 be sustained from beneath, that when the glass is red-hot and 
 soft, there may be as little stress or weight to disturb its form 
 
 as possible : for the lute is generally so much 
 cracked by the heat, that though it will 
 adhere to the glass and hang together, it 
 gives on the whole very little strength unless 
 supported below ; it even, by its weight, 
 sometimes does more harm than good. A very excellent sup- 
 port, on many occasions, is a small round crucible filled with 
 sand, and placed on the bars of the furnace, the bottom of the 
 retort being allowed to rest upon it. At other times, a couple 
 
 Eof bars of iron, crossing the furnace, are used, and now 
 and then stands, either of wrought or cast-iron, of the 
 form figured, and of different sizes. The upper wood-cut 
 represents the section of a coated glass retort, placed within a 
 crucible furnace (158), and supported on a crucible. The 
 furnace is notched at the side to admit of the passage of the 
 retort neck. 
 
 491. Earthenware retorts are made of very different ma- 
 terials. The ware is sometimes close and compact, like that 
 of Wedgwood, that the vessels may be but little permeable to 
 air, and sometimes more open and coarse, like the red or brown 
 ware, being then less liable to crack in the fire. They should 
 be heated very gradually, and also cooled with the same pre- 
 cautions, if it be desired to save them from fracture ; but it is 
 
220 DISTILLATION SUBLIMATION. [Sect. VII. 
 
 scarcely worth the attempt to use an earthenware retort a 
 second time, because of the difficulty of ascertaining the clean 
 state of the inside, and from the almost inevitable existence 
 of fissures. In some cases earthenware retorts may be ren- 
 dered tight, i. e., impermeable to air, by washing their sur- 
 faces with a solution of borax, or rather with a cream of 1 
 part powdered borax, % of finely-pulverized glass, and water. 
 These materials fuze and cover the surface with a glaze, which 
 effectually prevents the passage of air. 
 
 492. Earthenware retorts should rarely be put naked into 
 the fire ; when luted, as has been directed with regard to glass 
 retorts (489, 1084), a great degree of security beyond what 
 they possess when naked, is afforded. They should be care- 
 fully dried before being heated, and if washed with the mix- 
 ture of powdered borax, glass, and water, previous to the 
 application of the lute, are rendered impermeable to air or 
 vapour. 
 
 49B. Small iron retorts are more frequently used for the 
 distillation of oxygen and carbonic oxide gases, than for any 
 other purpose. They are usually in the form of bottles having 
 an iron tube fitted to them by a ground joint, which answers 
 the purpose of a neck. By frequent use, this joint oxidizes, 
 scales, and is no longer quite tight ; it may then be rendered 
 so by mixing up a little fine lute, as Cornish clay, into a thin 
 paste, with either water or oil, and putting it round the tube 
 before it is thrust into its place : in these cases the retort 
 should be introduced very steadily and carefully into the fire, 
 lest by shaking, the joint should be loosened. As little of the 
 oiled substance should be allowed to pass within the retort as 
 possible. 
 
 494. Distillations with the iron retort are best effected by a 
 coal or coke fire. The table-furnace fire (169) answers per- 
 fectly well, the tube of the retort being brought out either at 
 the door, or through the rings put on above, in place of the 
 sand-bath (176). 
 
 Sublimation. 
 
 495. The apparatus for sublimation in the laboratory, con- 
 sists generally of tubes, flasks, retorts, capsules, and crucibles. 
 
Sect. VII.] SUBLIMATION ALEMBIC FLASKS. 22 1 
 
 Those which are adopted in manufactories being confined to 
 particular operations, are therefore constructed of such mate- 
 rials and form, as fit them for their exclusive purposes. The 
 use of tubes in the sublimation of small quantities, will be 
 considered hereafter. (935, Sec.) Such substances as are of 
 moderate volatility, like naphthaline, iodine, camphor, chloride 
 of carbon, gallic acid, &c., may be sublimed in glass retorts; 
 the vessel being heated by a lamp or sand-bath, or small fur- 
 nace, and the neck introduced into a large globe or flask, for 
 the condensation of the vapours. The flask may either be 
 cooled or not, according to the circumstances of the case, the 
 means being those before described. (447, &c.) Florence flasks 
 are frequently superior to retorts for these purposes, and being 
 placed in an inclined position, their necks may be introduced 
 into receivers, as has been directed with respect to the beak of 
 the retort (447.) 
 
 496. The alembic is frequently used with advantage in the 
 sublimation of substances of moderate volatility. Its con- 
 venience consists in the facility with which the products and 
 residue of the sublimation may be removed. There is nothing 
 peculiar in its use requiring notice. 
 
 497. Florence flasks are useful in sublimations, which re- 
 quire a higher temperature than the substances just referred 
 to, such, for instance, as calomel, cinnabar, &c. Being charged 
 with the proper materials, they may then be bedded in the 
 sand-pot (176), and surrounded by the sand to a height more 
 or less above the level of the materials within, according to the 
 volatility of the substance. A red heat may then be applied, 
 and the products condensed in the upper part of the flask ; or 
 
 received into another flask, having 
 a wide neck ; or with the neck 
 cut short and placed over the first. 
 ) Sometimes a large tube, with its 
 end bent, so as to pass over the 
 neck of the flask, is a very con- 
 venient condensing vessel. The joint may be wrapt with dry 
 paper, and tied with twine, the other end of the tube should be 
 drawn out and contracted (1179), so as to enter a globe, in 
 which vapours, not condensed in the tube, may be caught and 
 finally rendered solid. 
 
222 SUBLIMATION IRON POTS. [Sect. VII. 
 
 498. When Florence flasks can be heated in a sand-pot, 
 they do not require luting, but if they are exposed to a naked 
 fire, must then be strengthened by an exterior coat of clay 
 (1084), 
 
 499. Some sublimations are most conveniently performed by 
 putting the substance into a basin (369), which is then to be 
 covered with another containing water ; the application of heat 
 to the lower causes the evolution of vapours, which are con- 
 densed against the bottom of the upper. Such sublimations 
 as can be effected by the heat of an oil lamp are well con- 
 ducted in this manner. Sometimes small platina capsules 
 (371) are more advantageous. Indigo is best sublimed, after 
 it is bruised, by being put in small quantities into a platina 
 capsule covered by a larger one (371), and the lower heated 
 strongly by a spirit lamp. The upper should be kept at 
 about 212 ; or a little below, by moistening it with a piece of 
 wetted bibulous paper. After some time the sublimed indigo 
 will be found forming a layer of crystals upon the under 
 surface of the upper capsule. 
 
 500. Iron and earthen crucibles are useful for the sublima- 
 tion of bodies that have no action upon them. The crucible 
 may, in the first place, be charged, and after being covered by 
 a large vessel to condense the vapours, heated in a sand-bath ; 
 or, being previously heated, it may be set upon a stone or 
 brick, and after the substance is thrown in, it may be covered. 
 Benzoic acid, naphthaline, and other such bodies, may be sub- 
 limed from them into proper vessels. 
 
 501. The necks of broken retorts are frequently useful for 
 conducting the vapours which rise during sublimations in 
 crucibles, &c. They are conical, and occasionally so large at 
 the retort end, that they easily cover a small crucible standing 
 in the sand-bath. The sand, if heaped, will often serve suffi- 
 ciently to close the lower end of this conductor, and the upper, 
 being introduced into a flask or globe, conveys the vapours 
 into them, which are thus removed so far from the source of 
 heat as to be easily condensed. 
 
 502. Finally, cast-iron pots (176) are sometimes in use for 
 the purpose of effecting sublimation ; but they require to be 
 covered with a head and tube, for the purpose of leading the 
 
Sect. VIII.] PRECIPITATION ITS OBJECTS. 223 
 
 vapours to a vessel sufficiently large to receive and condense 
 them : or the pot being so set as to have a level surface con- 
 tinued from the edges on all sides, a box or large vessel may 
 be inverted over the whole^ and the condensation effected in 
 the space within. 
 
 503. It is much to be regretted that the chemist cannot 
 obtain glass retorts, and other vessels which have to resist high 
 temperatures, of green bottle-glass, and of all the forms and 
 sizes he requires. Large glass retorts, for the purpose of con- 
 centrating sulphuric acid are made of it, and sometimes smaller 
 ones may be obtained : but an abundant variety, from two pints 
 to an ounce in capacity, are required in the laboratory of 
 research. Even green glass tubes are rarely to be procured, 
 and are not permitted to be made without the special leave of 
 the Board of Excise. The green glass bottles, retorts, &c., 
 that are frequently met with in London, are either flint or 
 plate glass, neither of which have the hardness and difficult 
 fusibility of green wine bottle glass. 
 
 SECTION VIII. 
 
 PRECIPITATION. 
 
 504. PRECIPITATION is valuable as a mode of separating sub- 
 stances, and consists in changing them from a soluble into an 
 insoluble state. It always depends upon altering the relation 
 of the solvent to the substance it holds in solution; this being 
 effected sometimes by changing the state of the solvent, as 
 when water is added to a solution of resin in alcohol, or alcohol 
 to a solution of gum in water ; and at other times by causing 
 a change in the body dissolved, as when sulphuric acid is 
 added to a solution of baryta to precipitate the earth, or 
 ammonia to a solution of iron to precipitate the oxide. It is 
 often practised to render the presence of a substance visible, 
 and forms an essential part of analytical and other processes, 
 as well in the discovery of bodies (912, &c.), as in their separa- 
 
224 PRECIPITATION VESSELS, [Sect. VIII. 
 
 tion and estimation. Any substance added to a solution to 
 cause a separation in the solid form of matters present, has 
 received the general name of precipitant, and the substance so 
 separated is called a precipitate. 
 
 505. Many of the vessels useful in the processes of preci- 
 pitation have been already described as glasses (368), basins 
 
 (369), and flint-glass and Florence flasks (372, 
 373) ; but there are two kinds which particu- 
 larly deserve mention here. The one is a small 
 cylindrical glass standing on a foot, about one 
 inch in diameter and two and a half in height ; 
 it is very useful in testing mineral waters and solutions by 
 precipitation, for which reason, two or three dozen of them 
 should be in the laboratory stock. The other is of the kind 
 called Phillips's precipitating glasses. These are of a trun- 
 cated conical shape, as represented in the wood-cut, and are 
 peculiarly useful in the management of precipitates, in conse- 
 quence of the facility with which they allow the solid matter 
 to fall to the bottom of the liquid. The precipitate, as it 
 descends, meets with no obstruction from the sides of the glass, 
 tending indeed rather to shrink from than adhere to it ; the 
 fluid, on the contrary, tends to rise in the space left, and thus 
 in numerous cases great facility of separation is obtained. 
 They should be provided of three or four different sizes, 
 having about the capacity, for instance, of two, four, and eight 
 ounces (118). Jars of this form have already been described 
 (368). 
 
 506. When in the progress of investigation it is required to 
 know whether a substance in solution will be precipitated by 
 certain tests, the latter are to be added, and the whole purposely 
 mixed or suffered to become so spontaneously. If immediate 
 separation take place, the question is answered ; but if other- 
 wise, the results are not to be thrown away, and the inquiry 
 decided in the negative ; but the mixture is to be allowed to 
 stand for some hours, and then again examined, If no appear- 
 ance of precipitation be produced, a heat is to be applied, 
 approaching to 212 ; perhaps precipitation may occur during 
 the application of this temperature, and if so, the point is 
 ascertained ; but if not, the operator must still persist, by 
 
I 
 
 Sect. VIII.] PRECIPITATION WHEN COMPLETED. 225 
 
 allowing the mixture to cool to common temperature, and then 
 observe it for the last time. For want of perseverance of this 
 kind, possible precipitations are often considered as impossible. 
 Dr. Wollaston's test of the presence of potash in water is fre- 
 quently thought to be ineffectual, merely from the hasty man- 
 ner in which the experiment is made. 
 
 507. Very frequently liquids containing precipitates in such 
 small quantities as merely to have an opalescent or slightly 
 milky appearance, are to be examined and perhaps compared 
 with each other in colour, turbidness, &c. In these cases it is 
 often advantageous to examine them by reflected light, as that 
 thrown back by a sheet of white paper, for which purpose the 
 glasses containing the precipitates may be placed on white 
 paper, or at other times a piece of paper may be held behind 
 them at an angle such as to reflect light from the sky-light or 
 window. The tints and appearances of several glasses in a 
 row are very well compared with each other by such means, 
 and the process is often of value in comparative testing. 
 
 508. Precipitations are generally effected by substances with 
 which, from previous experience, they are known to occur; 
 and manipulative instruction merely relates to the best method 
 of obtaining those expected results, arid of thus securing the 
 separation of the whole of a substance held in solution, in pro- 
 cesses instituted for its purification, or for the analysis of its 
 compounds. It is to be understood that these operations are 
 generally best performed in Phillips's test-glasses (505). 
 
 509. It is frequently necessary to add a precipitant to a 
 solution, until no further effect is produced. Upon com- 
 mencing the addition, it is easy to observe the formation of the 
 precipitate ; but when the mixture becomes milky or thick, 
 the student is unable to perceive whether the additions he 
 makes actually cause increased separation, or whether they are 
 useless. As soon as this happens, it is better to desist from 
 adding the precipitant, and, after stirring the whole so as to 
 mix it thoroughly, to allow it to stand a few minutes ; a sepa- 
 ration of the precipitate from the liquid will take place at the 
 surface, and allow the removal of a small portion of the clean 
 fluid, either by pouring it out into a little glass (397), or by 
 dipping a rod into it, and transferring a drop or two to a glass 
 
 Q 
 
226 PRECIPITATION TESTED. [Sect. VIII. 
 
 plate (70). This done, a small quantity of the precipitant is 
 to be added to the liquid so separated, and notice taken 
 whether any precipitate is produced; if not, enough has been 
 added to the large portion ; but if a further effect takes place, 
 the portion removed is to be restored, the glass or valve being 
 washed by the dropping-bottle (402) ; more of the precipitant 
 is to be added, and the whole again stirred up and examined 
 as before, until it has in this way been ascertained that no 
 further addition will produce any precipitation. 
 
 510. If the separation of the precipitate be slow, it is not 
 necessary at all times to wait till the fluid at the surface be 
 quite clear ; for when opalescent, the further effect produced 
 by the precipitant in the trials may often be observed ; it is 
 only when approximating to a sufficient addition of the pre- 
 cipitant, that perfect clearness in the portion removed is 
 required. When the precipitate sinks rapidly, it will be unne- 
 cessary to remove any portion for trial ; for the liquid, being 
 clear, or nearly so, to the depth of an inch or two, may be 
 tested by dipping a glass rod into the precipitant and bringing 
 it to the surface: the small quantity of the test thus conveyed 
 will show, during its descent through the clear part, whether 
 more is required or not. 
 
 511. Sometimes the solution contains so much precipitable 
 matter, that before a sufficiency of the precipitant has been 
 added; the whole is thick, and even pasty. In nearly all such 
 cases, the whole ought to be diluted; for not only is the fluid 
 part in such small quantity, when compared with the solid, 
 as to be inseparable by the usual means, but the mixture 
 cannot be made with such facility as to insure uniformity 
 in every part; without which, uncertainty with respect to 
 the addition of the precipitant will be occasioned. But if, 
 from peculiar circumstances, it is desirable to avoid dilution, a 
 small portion of the mixture must be diluted in a little glass, 
 and tried as before : the quantity of water thus added to the 
 general mass, when the portion tried is returned, will be no 
 object. 
 
 512. The precautions just given with regard to the undue 
 addition of the precipitant, only relate to those cases where 
 either an exact equivalent to the substance to be precipitated 
 
Sect. VIII.] PRECIPITATION TESTED FACILITATED. 227 
 
 is required, or the precipitant itself is valuable, or the super- 
 fluous addition of it would complicate and burden the solu- 
 tion so as to embarrass future operations. If a peculiar salt 
 of baryta existed in solution, and it were required to obtain 
 the acid pure by precipitating the earth in combination with 
 sulphuric acid, then any excess of the latter, above the 
 exact quantity necessary to neutralize the baryta, would 
 remain in solution and contaminate the peculiar acid: in 
 such a case, therefore, the precautions above described must 
 be used, and it is better, when the precise point required is 
 nearly attained, to dilute the precipitant (the sulphuric acid, 
 in this instance) , so that less risk may be incurred of adding 
 too much at once. 
 
 513. If the object be merely to save a valuable precipitant, 
 as nitrate of silver when used for muriatic acid, or to keep 
 the remaining solution as free from extraneous substances as 
 possible, then the trouble of very delicate testing, as before 
 described (509), may be of more consequence than the use 
 of a little excess ; and in such cases, when near the point, 
 such a quantity may be added as is known somewhat to sur- 
 pass it. But when the precipitant is cheap, does no harm if 
 added in excess, and when none of the points above mentioned 
 require attention, it is better not to lose time in minute ope- 
 rations, but to add a considerable excess at once : and indeed 
 in many experiments it will be found that this excess is either 
 necessary for the perfect separation of the substance, or advan- 
 tageous as very much facilitating it. The student who is 
 commencing his experimental operations should in all cases 
 practise the method directed (though without attending to 
 great exactness), until he is so far acquainted with the nature 
 of the ordinary chemical precipitants, such as acids, alkalies, 
 and salts, as to form a tolerably correct notion of the suffi- 
 ciency or insufficiency of the quantity added by the appear- 
 ances it produces. 
 
 514. Solutions to which precipitants have been added are 
 easily mixed in glasses or small jars, by agitating with the 
 rods or stirrers before mentioned (374) ; but where they are 
 bulky, and occupy deep vessels, the mixture is better effected 
 by immersing a small glass tube sufficiently long to reach 
 
 Q2 
 
228 PRECIPITATION HEAT FACILITIES. [Sect. VIII 
 
 the bottom of the jar, and blowing air down it with the 
 mouth, so as to make it pass through the fluid in bubbles. 
 These being made to ascend through different parts of the 
 solution, the whole soon becomes uniformly mixed. The ex- 
 treme upper end of the tube should be placed quite within the 
 mouth, and not in contact with the lips, tongue, or any other 
 part ; so that nothing but air or aqueous vapour may pass 
 down it. 
 
 515. When rods or tubes are used to stir mixtures which 
 contain weighed or valuable substances, the adhering fluid 
 should be washed off into the vessel by the dropping-bottle 
 (402), that nothing may be lost; or, if required several 
 times, they may in the intervals be placed with their ends in 
 a small glass, and ultimately both glasses and stirrers washed 
 as before (509) . 
 
 516. Precipitates do not often require heat for their forma- 
 tion or separation, but in particular cases it is very serviceable : 
 basins (369) and flasks (372) are used for the purpose. If a 
 basin is to be used for the application of heat, the precipitate 
 may be thrown down in it ; but if a flask is preferable, the 
 precipitation is generally better effected in a glass or jar, and 
 the mixture afterwards transferred to the flask. More com- 
 mand of the fluid, and easier access to it, are obtained in an open 
 than in a closed vessel. The heat of the sand-bath is gene- 
 rally sufficient in these cases. 
 
 517. A few commonly-occurring precipitates are affected 
 by peculiar circumstances, which may be usefully pointed out 
 in this place. Chloride of silver, continually produced in the 
 separation of muriatic acid or chlorine by nitrate of silver, has, 
 when abundant, its separation facilitated by agitation. When 
 the liquid containing it is stirred, or poured backwards and 
 forwards from one vessel into another, the chloride adheres, 
 forming heavy flocculi, which, in a few seconds, fall to the 
 bottom, leaving the fluid nearly clear ; whereas, without such 
 agitation, it would require from half an hour to two or three 
 hours to produce an equal effect. It falls also more readily 
 when an excess of the nitrate of silver, or of nitric acid, is pre- 
 sent ; for which reason these substances may occasionally be 
 added with advantage. Heat assists its separation. 
 
Sect. VIII.] PRECIPITATION PECULIAR CASES METALS. 229 
 
 518. The separation of sulphate of baryta from the fluid 
 containing it, is very much facilitated by the addition of a 
 little nitric acid in excess where it can be permitted, and also 
 by heat. The two together are highly useful in many ana- 
 lytical processes. 
 
 519. Prussian blue, or rather the blue ferro-prussiate of 
 iron, constantly produced in testing for iron, falls much more 
 readily in solutions containing a considerable proportion of 
 salts or uncombined acids, than in such as are nearly free from 
 them : and for this reason, the addition of a little muriatic acid 
 is often advantageous. When recently precipitated this sub- 
 stance is soluble in pure water. 
 
 520. The oxide of tin, formed by the action of nitric acid 
 and tin, can hardly be washed with pure water, because of its 
 suspension ; but a little common salt added causes it to separate 
 easily, and may be used in cases where it does or can do no 
 injury. 
 
 521. Carbonate of lime, when thrown down from a solution 
 by an alkaline carbonate, has a loose bulky form, which in the 
 course of a short time alters, and the substance becomes a fine 
 gritty powder, rapidly settling to the bottom of the supernatant 
 fluid. This change, which is advantageous to the separation 
 of the precipitate, is facilitated by the application of heat. 
 The solution from which the lime is to be precipitated as a 
 carbonate should not have much acid in excess, for then much 
 carbonic acid is evolved upon adding the precipitant, and, if 
 cold, much carbonate of lime at first remains in solution. The 
 application of heat causes the separation of this portion, but 
 then a large part of it adheres as a crust to the vessel, and 
 occasions trouble in its accurate separation. For this reason 
 it is generally better to add alkali in the first place to neutralize 
 the excess of acid, and then to add the carbonate. Ammonia 
 and the carbonate of ammonia are the substances generally 
 preferred for the purpose. 
 
 522. Some of the metals are now and then precipitated 
 from their solutions in the metallic state by other metals. 
 Thus silver is thrown down by copper, copper by iron, lead 
 by zinc, &c. In these cases it is best to retain the solution 
 in an acid state by the addition of a little excess of the same 
 acid as that with which the metal is combined. Silver is 
 
230 PRECIPITATION METALS. [Sect. VIII. 
 
 generally precipitated from its solution in nitric acid. The 
 excess of nitric acid increases the rapidity of action, in conse- 
 quence of the electrical effect which occurs as soon as any silver 
 is precipitated, and at the same time tends to prevent any pre- 
 cipitation of copper on the silver, or any separation of oxide 
 of copper. Copper is best precipitated by iron from its solu- 
 tion in sulphuric acid. The excess of that acid has scarcely 
 any action on the copper once precipitated, and very effectually 
 retains all the iron in solution. Lead is readily precipitated by 
 zinc from any of its soluble salts : the excess of acid is not so 
 necessary in this case ; but if the solution be weak, nitric or 
 acetic acid is still advantageous. 
 
 523. Dr. Wollaston has devised a very beautiful method of 
 precipitating one metal by another, or rather by two others 
 combined into a voltaic circuit. This process will be de- 
 scribed in Section xvii., on Electricity (1065). 
 
 SECTION IX. 
 
 FILTRATION, DECANTATION, WASHING, SEPARATION 
 OF FLUIDS. 
 
 FILTRATION is a process purely mechanical. From its 
 nature it can only be effected where the substances to be sepa- 
 rated are such as will not dissolve each other ; and in almost 
 all cases it is requisite that one of them be in the fluid, and the 
 other in the solid state. It has the advantage of requiring no 
 chemical change in the bodies to which it is applicable. It is 
 of extensive service in chemical research, and is often supple- 
 mentary to precipitation. 
 
 525. Filtration is a process analogous in its nature to sifting, 
 and is performed by putting the mixed substances into a vessel 
 sufficiently porous to admit the passage of one substance, but 
 close enough to retain the other. As before mentioned, the 
 substances to be separated are usually fluids and solids ; hence 
 bodies permeable to fluids are those required for the filter. 
 Unsized paper, cloth, flannel, tow, sponge, sand, pulverized 
 
Sect. IX.] FILTRATION VESSELS STANDS. 231 
 
 glass, flints, porous stones, earthenware, and many other sub- 
 stances, are used on different occasions ; but the first is almost 
 exclusively used in the laboratory, a few of the others now and 
 then being resorted to only on particular occasions. 
 
 526. Funnels are continually necessary to support the paper 
 through which filtration is to take place. The ordinary fun- 
 nels required in the laboratory for the passage of fluids answer 
 the purpose very well, and they are of use for supporting filters, 
 when, from their necks being broken off, they are otherwise 
 unserviceable. They may be either of glass, or good Wedg- 
 wood, or other earthenware ; those of glass are to be preferred, 
 because the progress of the filtration and the state of the filter 
 can be better ascertained in them. Metal funnels should not 
 be allowed in the laboratory. 
 
 527. No other glass vessels than the precipitating and test 
 glasses (505), and the jars (368), already described, are re- 
 quired. Stirrers will be necessary ; and the platina spatula, the 
 platina-bladed pocket-knife (62), and sometimes other spa- 
 tulas, are very useful in moving precipitates. 
 
 528. The funnels containing filters may frequently be sup- 
 ported by the glass or jar intended to receive the filtered fluid, 
 and at other times by the rings of retort stands. But not- 
 withstanding these facilities, so frequently is the operation 
 required, that a laboratory should be supplied with at least 
 one filtering stand of considerable size (12). The end of such 
 
 ~ a stand is represented in the woodcut. 
 It should be 15 inches wide, 3 or 4 
 feet long, and have an interval between 
 the bottom and top of 12 inches. The 
 top should have a number of round 
 holes made in it at intervals of 6 
 inches, differing in diameter from 1^ to 3 inches ; two or three 
 small ones of half an inch or an inch in diameter being inter- 
 mixed. The whole should be well made and firm, so as to 
 support considerable weights ; the top having frequently to 
 answer the purpose of a table, and to sustain jars full of solu- 
 tions, as well as to bear funnels and filters. 
 
 529. It is no easy matter for the chemist to obtain unob- 
 jectionable filtering paper; and yet it is of such importance in 
 
232 FILTERING PAPER EXAMINED. [Sect. IX. 
 
 reference to the duties it has to perform, that he should not 
 spare pains to procure the best possible. It should be so 
 porous as to admit the free and ready passage of fluids ; so 
 close as to retain the finest solid particles ; so strong as to bear 
 the weight of a considerable quantity of fluid ; and so pure as 
 to give nothing to the solution, or, if heated with the sub- 
 stance retained upon it, to occasion no mixture of ashes. 
 Some chemists use plate paper, i. e., the paper of copper-plate 
 printers. It is very porous, and yet there are few precipitates 
 that will pass through it ; at the same time it is often tender, 
 generally yields a considerable quantity of ashes when burnt, 
 and is inapplicable for minute filters when very small quan- 
 tities of fluid only are to be worked upon, because of its thick- 
 ness and consequent waste of the portion of solution imbibed 
 by it. 
 
 530. It is amongst the thinner varieties of unsized paper, or 
 white blotting-paper, kept by some of the large stationers, that 
 the chemist will probably find the kind best suited to his pur- 
 pose. It should be so strong, that a single filter of it, capacious 
 enough to hold a pint of water, should not break with that 
 quantity, even though some degree of agitation be given to 
 the funnel containing it. Its porosity, that is to say, its com- 
 parative freedom from size (for all is sized in a slight degree), 
 may be judged of by holding it to the tongue, and observing 
 how it absorbs moisture ; and by a cautious pull its strength 
 may be ascertained whilst in such moistened state. The 
 student who is unused to the examination of papers, will, 
 however, better judge of its capability of allowing fluid to 
 pass, by actual trial with water ; a pint filter, filled with 
 clean water, should allow the fluid to run in a considerable 
 stream. 
 
 531. The best method of judging of the purity of paper is 
 to burn it and examine its ashes : the fewer it yields, the better 
 is it adapted for filters. A demy sheet should not yield more 
 than one and a half or two grains of ashes altogether. If it 
 contains more, their solubility or insolubility should be ob- 
 served, that the student may be aware of the impurities that 
 may probably be imparted to solutions in very delicate experi- 
 ments. In minute cases of investigation, sulphuric acid may 
 
Sect. IX.] 
 
 FILTRATION FILTERS -PLAIN. 233 
 
 frequently be traced to the sulphate of lime existing in the fil- 
 tering paper. 
 
 532. Filtering paper should be cut ready for use into dif- 
 ferent sizes : a demy paper furnishes useful sizes for filters, 
 when the sheet is separated into four, or six, or nine parts; 
 and parcels of each of these sizes being prepared, they should 
 have a string passed through the corners, and be preserved for 
 use in a clean place. This previous arrangement of the paper 
 is very convenient, as readily supplying the sizes that will be 
 wanted, and in preventing the waste that would occur by care- 
 lessly tearing up a sheet each time a filter is required. 
 
 533. On preparing a filter, the piece of paper should be 
 first examined, by looking through it against the light, to as- 
 certain that it is free from holes. The simplest filter is made 
 by folding the paper twice in opposite directions, in such 
 manner as to bring the four corners together, and by opening 
 
 one corner from the other three, so as to pro- 
 duce an irregular conical cavity. Such a filter 
 being put into a funnel, and then filled with 
 water, will immediately permit its passage : 
 but from the similarity of form between the 
 filter and the funnel, and the close adhesion of the former to 
 the latter, over by far the greater part of its surface, consider- 
 able obstruction is opposed to the passage of the fluid, and the 
 operation is retarded. For this reason different contrivances 
 have been recommended, to separate the filter here and there 
 from the funnel, and allow passages for the fluid. Lavoisier 
 recommended small glass rods put into the funnel before the 
 filter is introduced, so as to lie down and against the sides. 
 Straws are used in a similar way, and they certainly open 
 channels in their immediate neighbourhood, by which the fluid 
 may flow. By other chemists, ribbed funnels are recommended ; 
 but it is difficult to find a funnel so deeply ribbed as to sup- 
 port the paper in such a manner that it shall not touch the 
 glass in every part ; and if they do not perform this, they are of 
 no use. 
 
 534. The best expedient by far is, to fold the filter in such 
 a manner that ribs may exist in the paper itself ; and this may 
 be done, so as not only to allow numerous free passages for the 
 
234 FILTRATION FOLDED FILTER. [Sect. IX. 
 
 fluid between the filter and the glass, but also to allow of ready 
 transmission through its whole surface, and not of one-half 
 only and even that imperfectly, as in the former case (533). 
 For this purpose, the paper is first to be doubled, and in this 
 state is again to be folded in half, each half folded into quar- 
 ters, and each quarter into eighths, the folds being all on the 
 same side, and radiating at equal distances from the middle of 
 the folded edge to the other edges. The woodcut represents 
 the doubled paper thus divided into eight 
 parts. Each eighth is now to be divided 
 into half by folds in the opposite direction, 
 but in lines still originating at the same 
 centre, which makes the doubled piece resemble a child's paper 
 fan, both when closed and when a little open : it is represented 
 by the accompanying figure. Whilst in this 
 state, the projecting corners should be taken 
 off by a knife ; folding the whole up tight 
 like a closed fan, and making the section at 
 about a. Being now allowed to expand a 
 little, the originally doubled sides are to be 
 separated from each other for the first time, but without dis- 
 turbing the angles or bending the ridges or ribs formed in 
 them. Having opened it sufficiently to separate the cut edges 
 from each other, it will be found that the. paper is equally 
 divided into parts forming alternate external and re-entering 
 angles, except at the two edges b b, where two external angles 
 come together. Here the intervening portion of paper between 
 the two contiguous external angles should be folded, by 
 bringing the latter together and creasing the paper down, so 
 as to form a re-entering angle between them : this should be 
 done at both places. Then opening the paper 
 sufficiently to bring the bottom into proper shape, 
 by thrusting out the part which is convex within, 
 so as to make it project externally, the filter is 
 completed, and, being put into a funnel, is ready 
 for use. Its appearance, when perfectly formed, 
 is represented by the accompanying woodcut. 
 
 535. It is necessary, in making these filters, that the folds 
 be not continued to the point, but that they should stop about 
 
I 
 
 Sect. IX.] FILTRATION FILTERS. 235 
 
 half an inch short of it (see the last figure), for if completed 
 to the bottom, the frequent action of the fingers in folding 
 \vill so far break down and destroy the texture of that part, 
 that a hole probably will appear before the filter is finished ; 
 or if not, it will be so weakened as to be unable to bear a 
 quantity of fluid without breaking. Hence that part of the 
 filter will, during the folding, assume a concave form ; and 
 the regularity of the folds, which by practice may be easily 
 attained, must be strictly attended to in the upper part, but 
 may be dispensed with at the lower. When opened out, 
 therefore, for the completion of that part, before the filter is 
 put into the funnel, all that will be required is to push that 
 side of the bottom outwards which is convex inwards, doing it 
 so carefully as to cause no injury. The folds of the filter 
 should be distinct and sharp an effect which should be obtained 
 by a single decisive pressure, and not by much fingering. No 
 wrinkle or mark should appear in a well-made filter except 
 the folds described, and the portion of paper between the folds 
 should be as stiff as when first taken up. The filter should be 
 handled lightly during the whole of the operation, and never 
 be opened out more than is represented in the last figure. It 
 is best to keep the folds as close, and the whole filter as com- 
 pact, as possible ; dropping it loosely into the funnel, and per- 
 mitting the fluid poured in to do the office of opening it out. 
 It should be so regularly made, that, when thus expanded by 
 the fluid, the external angles of the folds should touch the 
 glass at equal distances from each other, except at two oppo- 
 site places where smaller divisions exist ; and unless a large 
 quantity of fluid be present, the angles at the upper part 
 should remain nearly as sharp when the liquid is introduced as 
 they were before. Below, they gradually pass into the rounded 
 surface forming the centre or bottom of the filter, which 
 will be about the size of a sixpence or shilling, according to 
 the dimension of the funnel in that part. These filters leave 
 such free space between themselves and the glass as to admit 
 of the passage of fluid to a far greater extent than is neces- 
 sary ; and no obstruction being placed against the external 
 surface of the paper, the whole acts in the filtration, and that 
 in the most favourable manner. 
 
236 FILTRATION ARRANGEMENT PERFORMED. [Sect. IX. 
 
 536. Of these two kinds of filters, which may be distin- 
 guished as the plain and the folded, sometimes the one and 
 sometimes the other is preferable. When the object is to 
 cleanse and purify the fluid, that being the valuable part, it is 
 most rapidly and effectually attained by a folded filter ; but 
 when the precipitate is the part required to be taken care of, it 
 is generally desirable not to spread it over the irregular and 
 extensive surface of such a filter, but, by using a plain one, to 
 retain it on a surface of only half the extent. It is then like- 
 wise of such uniform thickness in every part, as best to admit 
 of the operation of washing, by having successive portions of 
 water passed through it ; and when the filter is opened out, the 
 precipitate is delivered in one continuous portion, and not 
 divided into many parts, as happens with the folded filter. 
 
 537. When a single filter is judged too weak to hold the 
 mass of fluid it is required to sustain, a double one should be 
 used. If the filter is to be a folded one, then a double thick- 
 ness of paper is to be taken ; but if plain filters are used, the 
 two should be made separately, and put one into the other, 
 in such a manner that the three thicknesses of the one may 
 come against the single thickness of the other. Occasionally it 
 is proper to strengthen the bottom of the filter^ which, not 
 being supported by the glass, has to support the greatest 
 column of fluid, but not so as to obstruct the upper part, 
 where a filtration as free as possible is required. In such a 
 case a smaller filter is to be added to the exterior of the large 
 one, so that it may not interfere with the precipitate within, 
 when it is necessary to remove it from the paper. 
 
 538. When the substance collected upon a filter is such that 
 heat can do it no harm, and that therefore it is resolved to 
 burn the filter for the sake of procuring all the substance, then 
 use a double filter, the inner one on which the precipitate is 
 disposed being of India-paper. 
 
 539. The filter and funnel being ready, and placed on the 
 stand in one of the holes before mentioned (528), over a glass 
 ready to receive the liquid, the mixture to be filtered is to 
 be introduced. It should not be poured from a great height, 
 nor upon the middle of the filter, but down the side, the force 
 of its descent being diminished as much as possible by good 
 
Sect. IX.] FILTRATION WASHING A PRECIPITATE, 237 
 
 management, lest it break a hole through the paper: for the 
 same reason it is better to pour it down the rod (369). If the 
 first portions of fluid which pass be not clear, they should 
 be returned into the filter, and a second glass be placed 
 beneath : the solid matter in the liquid to be filtered will soon, 
 by adhering against the paper, cause clear filtration, except 
 perhaps in one or two particular cases, as with precipitated 
 oxide of tin, &c., on which occasions a double thickness 
 of paper must be used. On changing the vessels beneath 
 the filter, for the removal of the clear solution, it should be 
 done so that no drop be lost. By inclining the empty vessel, 
 its edge may be brought under the funnel before the full 
 one is removed ; and in no case should a vessel be left under 
 the filter, in which there is not sufficient room for the contents 
 of the latter if it should break. Such an accident ought not 
 to occur, but ought always to be provided against. 
 
 540. Supposing a precipitated substance is to be filtered 
 from the solution containing it, and then washed, the mixture 
 may be poured in all at once, or added successively. In 
 the former case, as the fluid passes through, the precipitate 
 forms a soft mass lying upon the paper, but hollow in the 
 middle ; in the latter, this hollow nearly disappears, from the 
 successive portions of solid matter added. The first state 
 is the most advantageous for the operation of washing, when 
 it is necessary for the removal of the portion of solution 
 retained by the mass on the filter. For this purpose the 
 vacant space should be filled with water, that it may pass 
 through and displace the solution ; and this should be done 
 before the part within has drained to the utmost, and whilst 
 it is still soft and bulky, for the water then finds easier access 
 to all its parts. This water having passed, a second and third 
 portion should be added, and the washing thus repeated, until, 
 by testing the liquid which passes, it is found to be perfectly 
 pure, or to contain so little matter as to render the rest 
 unimportant. 
 
 541. Sometimes the mass, though light, is adhesive: it 
 may then very advantageously be stirred up with the added 
 water, but great care must be taken that the filter be not 
 broken in the operation. The top of a quill feather may be 
 
238 FILTRATION WASHING FILTERS, [Sect. IX. 
 
 used for the purpose. At other times as much fluid as pos- 
 sible having passed through, the filter with its contents may be 
 put into a fresh portion of water, the paper removed, and the 
 precipitate being stirred up with the water, the whole may be 
 put upon ar new filter. These processes are applicable when a 
 quantity either of the substance in solution or of the preci- 
 pitate^ being required in a pure state^ it is desirable to avoid 
 loss as much as possible, without being particularly accurate. 
 The student should understand^ that when a precipitate in its 
 moist state occupies a large portion of the space within a filter, 
 it is impossible, except in very long periods of time, to wash it 
 perfectly merely by passing water through it, because of the 
 greater facility of passage which the water will find in one 
 direction rather than another. When the precipitate forms 
 but a thin layer, or when it can be completely stirred up from 
 the bottom by a jet of water (403, 547), or a feather it maybe 
 well and perfectly washed. 
 
 542. It is advisable in all cases of washing in filters, where 
 accuracy is necessary, to make the filter of such a size as to 
 drop entirely within the funnel, and to cover the latter with a 
 clean basin. This protects the upper moistened parts of the 
 filter from evaporation, which would cause the slow but con- 
 tinual ascent of portions of the fluid from below, and conse- 
 quently a deposit of the substance there. In slow filtrations 
 a considerable quantity of the substance in solution would be 
 accumulated in the upper part of the filter, instead of being 
 washed away. 
 
 543. It is necessary, in certain cases, first to moisten the filter 
 with water. When aqueous solutions of vegetable matter, 
 which are thick and adhesive, are to be cleansed by this pro- 
 cess, the filter should be thus prepared. The advantage will 
 be found very considerable with solutions of sugar. In the 
 filtration of alcoholic vegetable solutions, the filter should 
 always be previously moistened with pure alcohol. Fixed or 
 essential oils, or naphtha, and similar bodies, in mixture with 
 water or aqueous solutions, in which they are not soluble, may 
 be separated from the latter by a paper filter, previously 
 moistened with pure water. In some few cases the other sub- 
 stance may be made to separate by passing through the paper, 
 
Sect. IX.] HOT FILTRATIONS MINUTE OPERATIONS. 239 
 
 the filter having been previously imbued with a portion of it 
 in a state of purity. 
 
 544. Sometimes hot filiations are to be performed. Oils 
 filter better hot than cold : tallow and cocoa-nut oil may be 
 passed through paper when hot ; and many solutions must be 
 filtered at high temperatures, because of the greater solubility 
 of the ingredients under those circumstances. In these cases 
 the fluids should be heated in a flask or basin before they are 
 poured into the filters; and the filter funnels being placed in 
 the glasses or jars, and, after the fluid is poured in, covered 
 over with a basin or glass plate, the whole should be enveloped 
 in a piece of flannel or a dry cloth. If, from the length of the 
 operation or other causes, the flannel or cloth be not efficient, 
 it may be dispensed with ; and the glass and filter, being placed 
 on a warm part of the sand-bath, should be covered with a 
 box or vessel large enough to rest on the sand, and thus form 
 a hot-air-chamber for the process. When the operations are 
 upon a small scale, a paper cone (1343) is sufficient to cover 
 the vessels on the sand-bath and keep them hot. These filtra- 
 tions may very often be conducted with great facility by means 
 of a current of hot air directed against the vessels (269). 
 
 545. In filtrations of alcohol, or alcoholic solutions, the 
 funnel should be put into the glass, and covered as before 
 mentioned (542), that evaporation may be prevented as much 
 as possible. In all filtrations for analysis the filter should- be 
 covered in the same manner, to prevent accumulation of sub- 
 stances in the upper part of the paper. These covers should 
 in no case touch the filter, but merely rest upon the edges of 
 the funnels. 
 
 546. When working upon minute quantities, filters as small 
 as possible are used, that but little of the fluid may be ab- 
 sorbed. When of such size as will result from a piece of 
 paper three inches square or less, they are better not folded, 
 but plain (533, 536), and may then be supported without a 
 funnel upon the mouth of a small test-glass (505). When a 
 lipped Phillips's test-glass is to be used, nothing more is re- 
 quired than to select one having a diameter at the mouth of 
 about one inch and a quarter, or less, according to the size of 
 the filter ; from one half to a third of which, when in its place, 
 
240 FILTRATION WASHING BOTTLE. [Sect. IX. 
 
 s to be left above the edge of the glass. In arranging the 
 filter, the triple or stronger side should be placed opposite 
 the lip, that the form may be retained, and the space at the 
 lip left open for the passage of air outwards, as 
 the fluid passes into the vessel. These filters 
 should never be filled to a height much above 
 the edge of the glass, otherwise the weight will 
 sometimes bend the paper over the outside, and derange the 
 whole. If the glass used has no lip, then a double fold must 
 be made in the single side of the filter, so as to make a portion 
 from the top to nearly the bottom project inwards and appear 
 like a sharp ridge. When put into the jar, this will form a 
 notch as it were in the side of the filter, by which the air may 
 find a passage outwards. It is necessary in these small filtra- 
 tions that the air-passage be attended to and kept open; 
 should it be badly formed, or, from the quantity of fluid within, 
 be pressed against the glass, or stopped up by the abundance 
 of liquid which passes through the filter, either filtration will 
 cease, or the fluid, not being able to enter the glass, will flow 
 over and down the outside, and be lost. 
 
 547. The dropping-bottles (402) will be very useful in all 
 these filtrations, especially those on a minute scale ; and there 
 is another bottle, recommended by Berzelius, which is also 
 useful. It is formed much like the dropping-bottle, but the 
 cork 'has no notch in the side, being inserted air-tight, and 
 the glass tube has a small aperture. When about half or 
 two-thirds filled with water, it is to be inverted, and then, by 
 applying the mouth to the aperture, air is to be forced in 
 through the tube and water, and condensed as much as pos- 
 sible in the upper part: when the mouth is removed, this 
 compressed air forces out the water in a small stream, which 
 continues for some time, and which, directed against the sides 
 of the filter, washes the precipitate from the paper, and accu- 
 mulates it at the bottom. It is necessary in many cases to 
 collect the precipitate at the bottom of the filter as much as 
 possible; and, for this purpose, besides the dropping-bottle and 
 Berzelius's bottle, a syringe (560) may also be employed. 
 This instrument is easily made from a piece of glass tube at 
 the blow-pipe table (1181), and is very effectual in cleansing 
 the sides of the filter. 
 
Sect. IX.] DECANTATIOtf SYPHON ITS USE. 241 
 
 548. When a filter is required so large that paper alone has 
 not strength sufficient, a piece of cloth should be fastened by 
 the edges to a slight square frame of wood, so that it may hang 
 loosely ; a sheet of filtering paper should be laid over it, and 
 the fluid to be filtered placed upon that. 
 
 549. When the object is hastily to filter a fluid for the pur- 
 pose of removing pieces of dirt, then a little loose tow at the 
 bottom of the funnel, or a piece of sponge slightly thrust in, 
 is often sufficient for the purpose. Upon some few occasions 
 filters for acids are required. These are generally recom- 
 mended of powdered glass, being arranged somewhat in the 
 manner described for lixiviation (420) . Pieces of glass are 
 put into the neck of the funnel ; upon these smaller fragments, 
 then again other layers of particles diminishing in size, until a 
 moderately fine powder has been used, the top being finished 
 by a layer of small fragments, to prevent disturbance by 
 pouring. The pieces of glass should be well cleaned before 
 pulverization, and, when arranged, some water should be 
 passed through the filter, to remove alkali or other matters that 
 may be separable from the glass, which should be that of wine- 
 bottles, and not flint glass. 
 
 Another mode of separating a fluid from the finely-divided 
 solid matter it may contain, is to allow the latter to deposit, 
 and then to remove the former. This is called decant ation ; 
 it is a process much superior to filtration in many analytical 
 experiments, and recommended in preference both by Lavoi- 
 sier and Berzelius. 
 
 550. If the fluid be poured off, it should be done from a 
 lipped jar (368, 397), and with a very steady hand, that as 
 much may be removed as possible, before the deposit at the 
 
 bottom be disturbed. But a better method by far is, 
 to use a syphon. Let a piece of glass tube, about 
 0.3 of an inch internal diameter, 22 inches in length, 
 and of sufficient thickness to bear ordinary laboratory 
 work, be bent at the blow-pipe table, so that one 
 limb shall be about two inches longer than the other ; 
 the extremities should be contracted at the lamp 
 (1166, 1175), until about 0.2 of an inch in diameter. 
 So formed, when filled with fluid and held as in the figure, but 
 
 R 
 
242 DECANTATION USE OF SYPHON. [Sect. IX. 
 
 with one aperture closed by a finger, the fluid will not fall out 
 at the other, because of its smallness ; and yet the larger 
 diameter of the body of the syphon will permit a more rapid 
 passage of fluid than would otherwise take place. When this 
 instrument is to be used to separate the liquid in a jar from 
 the deposit lying at the bottom, the syphon is to be inverted 
 and inclined, so that the orifice of the shorter leg shall be 
 higher than the other : it is then to be filled with water from 
 the dropping-bottle, taking care that no bubbles of air are in- 
 cluded, which is easily done by holding the beak of the bottle 
 against the side of the aperture ; and when the water has filled 
 the longer leg it is to be closed by a finger, and more water 
 added till the other leg also is full. Keeping the finger tight 
 upon the orifice that no air may enter it, the syphon is to be 
 inverted, so as to bring it into its acting position ; the shorter 
 leg is to be introdued into the fluid 5 and then, by withdraw- 
 ing the finger, the fluid is to be suffered to run out into a ves- 
 sel placed to receive it. 
 
 551. The current may at any time be diminished, or pre- 
 vented altogether, by applying the finger partly, or closely, 
 against the exterior aperture, and thus complete command in 
 that respect be obtained. As the surface of the fluid descends 
 in the jar and approaches the sediment, care must be taken 
 that the immersed end of the syphon be not brought so near 
 the deposit as to cause any disturbance of it ; and towards the 
 last, by diminishing the current and inclining the jar very 
 slowly and steadily, the endeavour should be to remove as 
 much clear fluid as possible, without drawing away any of the 
 precipitate. This may be done, so that not above a cubic inch 
 of clear fluid need be left behind. The syphon is best held in 
 the right hand during the operation, at about the middle of 
 the exterior leg. A degree of government over the current 
 may be obtained by inclining the syphon, so as to bring the 
 aperture of the external leg nearly to a level with the surface 
 of the fluid in the jar, but in all cases it should be kept some- 
 what below the latter. The jar should be placed in a steady 
 position during the operation, and it is proper to raise it till 
 nearly on a level with the eye. The top of the filtering stand 
 (528, 12) answers very well for these occasions. 
 
Sect. IX.] DECANTATION WASHING. 243 
 
 552. When a very deeply-coloured solution is to be drawn 
 off, so dark indeed as to hide the end of the syphon when in 
 the middle of the fluid, that end should be brought close to 
 the side of the glass, and a lighted candle held on the outside 
 near it ; in this way the precipitate, the depth of the clear 
 part, and the orifice of the syphon may be seen, when they 
 cannot be observed by any other means. 
 
 553. Washing by decantation is much more easily and 
 effectually performed than by filtration, but it requires more 
 water, and hence one great use of a plentiful supply of distilled 
 water (26) in the laboratory. After having drawn off the 
 clear solution, it is merely necessary that the jar be filled up 
 with water, the whole mixed either by a stirrer or by blowing 
 (514), the mixture left to settle, the clear fluid decanted, and 
 fresh water added ; the operation is to be repeated until what 
 is removed contains no soluble matter. Phillips's test glasses 
 (505) and jars (368) are very useful in these washings, because 
 of the facility with which the precipitate falls in them to the 
 bottom. Some solid substances contract into a smaller space 
 than others, but even the most bulky should have so much 
 water added to them, as to enable five-sixths to be drawn off 
 after twelve hours standing. During the time that the deposi- 
 tion is taking place, the glasses or jars should be covered to 
 keep out the dirt. The bottoms of footed glasses (368, 1222) 
 answer this and many other useful purposes ; when, therefore, 
 such glasses are broken, the upper part should be chipped 
 away, and the bottoms reserved in a drawer. 
 
 554. When the substance has been sufficiently washed, and 
 - is left with as little fluid upon it as possible, it may, according 
 
 to the requisite circumstances of the case, be poured into a 
 basin and evaporated, (as will be described in Section xi. 590, 
 See.) or poured into a filter to remove more of the fluid, or the 
 water may be removed by means of bibulous paper. There 
 are many bodies, such as chloride of silver, oxide of copper, 
 carbonate of lime, sulphate of baryta, and others, which readily 
 fall in water and occupy but a small space ; and which, having 
 been washed, are best freed from the remaining water in the 
 latter method. For this purpose they should be transferred 
 carefully into a small evaporating basin, using the dropping- 
 
 R 2 
 
244 WASHING PAPER AND COTTON PRECAUTIONS. [Sect. IX, 
 
 bottle for washing in the last portions (402, 547), and allowed 
 to settle to the bottom, an effect which is accelerated by mode- 
 rate warmth ; then folding up a piece of filtering paper two or 
 three times, its end should be applied cautiously to the surface 
 and suffered to imbibe part of the water ; this done, it must 
 be taken out, the wet end pulled off, and the edge again in- 
 troduced, as in a process formerly described (69), observing 
 that no solid matter be disturbed during the operation. By 
 taking the precautions formerly given (69) ; by inclining the 
 basin a little, and by similar attentions, which will suggest 
 themselves at the moment, nearly the whole of the water may 
 in this way be removed without disturbing the substance. 
 
 555. The formation of a syphon by a few threads of mois- 
 tened cotton, or by a piece of folded and bent filtering paper, 
 is now and then very convenient for the gradual separation of 
 a fluid. If a basin contain a mixture of fluid and solid matter, 
 and the cotton or the piece of paper be bent over the edge, so 
 that the inner end is in contact with the fluid, and the outer 
 end lower than the inner, the fluid will gradually be abstracted 
 by a syphon action, and the solid matter left nearly dry. A 
 little temporary syphon of this kind is often very useful in re- 
 frigerating and other operations ; being connected with a vessel 
 of water, it will supply a small quantity of that fluid constantly 
 during a long period of time. 
 
 The precautions given to ensure an easy separation of 
 a precipitate (517 521) must be attended to in washing par- 
 ticular bodies. Prussian blue should always be washed with 
 dilute muriatic acid (519), and sulphate of baryta with weak 
 nitric acid, and, if possible, with warm water (518). 
 
 556. It will be observed that the process of lixiviation 
 already described (420) is in reality a washing process. What 
 has been said relative to it will be abundantly sufficient to 
 direct its application to substances generally when necessary. 
 
 557. There are numerous cases in chemistry where immis- 
 cible fluids are to be separated from each other. Many of 
 these are not difficult, especially where the substances are un- 
 important or valueless ; but sometimes great care is required, 
 because of the value of the bodies, or their dangerous nature. 
 A case of separation by filtration has already been pointed out 
 
Sect. IX.] SEPARATION OF FLUIDS SEPARATORS. 245 
 
 (543). In other circumstances the two fluids may be poured 
 into a wet funnel (if at least one of the two be water, or an 
 aqueous solution), closed by a good cork beneath, and left to 
 remain on the filtering stand until separated : by partly with- 
 drawing the cork, the lowermost may be almost entirely re- 
 moved from the upper. Glass vessels, furnished with a stop- 
 cock beneath, are made for this purpose. Their use is evident, 
 and requires no description. 
 
 558. Another serviceable instrument is a glass tube with a 
 bulb an inch in diameter blown in it, and drawn out 
 below to a moderately fine aperture (1197, 1179). The 
 aperture being immersed in either the upper or under 
 liquid, the mouth is to be applied above, with the pre- 
 cautions before mentioned (514), and the air withdrawn, 
 when the liquid consequently will enter. The finger 
 being then placed on the upper end of the tube, so as 
 to close it, the instrument may be removed, and the 
 
 fluid within transferred to any convenient vessel. 
 
 559. A useful vessel for the separation of a small quantity 
 of valuable fluid may be made of a piece of glass tube from the 
 third to a quarter of an inch in diameter, by drawing it out in 
 
 one part until it becomes capillary (1176), 
 and turning it up as in the figure. The point 
 a must be closed in the flame of the spirit 
 lamp, the mixed fluids poured into the tube, 
 and suffered to remain till separated. The 
 point a is to be broken so as to open an aper- 
 ture, and then by inclining the instrument, 
 first one fluid, and afterwards the other, may be decanted. 
 The fluids will issue drop by drop into the vessels placed to 
 receive them, and the surface of contact of the two in the fine 
 tube is so small, that scarcely an appreciable portion of the 
 valuable one need be wasted. The pouring, or transference 
 rather, is more steady and regular when the beak a is placed 
 against the side of the receiving vessel, so that no drop is 
 formed, but a continuous minute stream. 
 
 560. Finally, glass syringes, such as have already been 
 mentioned (547), are very advantageous in the removal and 
 separation of fluids. Such an one as that figured in the wood- 
 
246 SYRINGES CRYSTALLIZATION. [Sect.X. 
 
 cut may be used for instance in the management of the chloride 
 
 of nitrogen *. The tow wrapped 
 round the wire which forms the 
 piston, is made sufficiently tight 
 by being moistened with water, 
 and when not inconvenient, a little water may be retained both 
 above and below it. The beak of the syringe being brought 
 near the globules of the chloride, and the piston moved up- 
 ward, the substance enters, and may be collected by holding 
 the instrument in the position in which it is figured. It may 
 then be transferred to other situations, and, if required, be 
 made to issue from the jet perfectly free from moisture. This 
 is effected by holding the syringe with its beak downward 
 against a piece of filtering paper, then depressing the piston, 
 till the water, which may be before the chloride, is expelled, 
 and, when the latter is on the point of issuing, by removing 
 the instrument from the damp paper and ejecting the pure 
 substance into the desired place, by a further depression of the 
 piston. Other heavy fluids may in the same way be separated 
 from the liquids in which they lie; and light fluids may in 
 like manner be drawn up and removed, but then excess of 
 water must not be left below the piston, and a bubble of air 
 should be allowed to intervene between it and the substance to 
 be taken into the instrument. 
 
 SECTION X. 
 CRYSTALLIZATION. 
 
 561. CRYSTALLIZATION is a very useful and valuable process 
 in the laboratory. It enables us in many cases to purify 
 bodies with great precision; thus by crystallizing the car- 
 bonate of soda, a pure salt is obtained, which affords a very 
 available source of pure soda ; by crystallizing the acetate and 
 the nitrate, similarly pure sources of the alkali are furnished. 
 * Braude, Manual of Chemistry. 
 
Sect. X.] CRYSTALLIZATION ITS APPLICATION. 247 
 
 Potash, in various states useful for combinations, and free from 
 other alkalies or earths, is obtained by crystallizing the bi-car- 
 bonate or the bi-tartrate of potash, or nitre. Pure magnesia 
 is obtained from a crystallized sulphate ; pure baryta from a 
 crystallized nitrate ; pure oxide of nickel from its sulphate ; 
 and pure nitric and muriatic acids are obtained from nitre and 
 common salt, previously rendered free from other bodies by 
 this process. A second object attained by crystallization, is 
 the very definite and convenient state conferred upon sub- 
 stances by it. A third, the peculiar but precise forms and 
 appearances which it generally imparts to them : these serve as 
 characters, by which known bodies may be recognized, or by 
 which substances before confounded together may be distin- 
 guished from each other. 
 
 562. Crystallization is always effected in the laboratory by 
 bringing the particles of solid bodies into a mobile state, either 
 by solution, fusion, or vaporization. It is not to be under- 
 stood that these are the only methods by which crystalline form 
 or structure can be conferred, for there are sufficient proofs to 
 shew that a body not crystalline may become so without 
 changing its state of solidity. The crystallization of cooling 
 basalt, as in Mr. Watts' experiments *, or of heated glass, or of 
 barley sugar, or even the spontaneous change of brass wire, which 
 in a few years becomes brittle, are all effects of the latter kind. 
 
 563. Considering first the most common case, that of crys- 
 tallization from an aqueous solution, it is generally performed 
 in one of two ways, by cooling a hot solution, or by slowly 
 evaporating a cold one. For the due application of the first 
 and most useful method, it is necessary that the substance 
 should be more soluble in hot water than in cold ; and the first 
 object is to obtain a hot solution of sufficient strength to deposit 
 crystals when of a common temperature. This may be pro- 
 cured as already directed (378), or a weak solution may be 
 evaporated (590, &c.), till of sufficient strength. A very con- 
 venient mode of ascertaining when the solution is strong enough 
 to crystallize, is, to transfer a drop of it by a rod (70), to a cold 
 glass plate, and observing whether it deposits crystals as the 
 temperature falls (379). 
 
 - * Philosophical Transactions, 1804, p. 282. 
 
248 CRYSTALLIZATION FROM WATER. [Sect. X, 
 
 564. When a proper solution is made, and filtered if neces- 
 sary, it is to be allowed to cool undisturbed, and the more 
 gradually this is done, the larger will be the deposited crystals. 
 The vessels may be either basins (369), pans, or such other as 
 may be convenient, having regard to the quantity and quality 
 of the fluid. They should resist chemical action, and gene- 
 rally be of glass or earthenware. They should not be shallow, 
 unless a rapid crop of crystals be required, and then they are 
 to be left open. A depth of fluid about one half or one third 
 of its horizontal width, is the most convenient for the quanti- 
 ties usual in the laboratory. The vessel should be covered 
 over, to prevent evaporation at the surface, where otherwise a 
 crust of crystals would frequently form, disturbing the regula- 
 rity of the rest. When it is required to cool the whole slowly, 
 it should be covered with a flannel, or cloth, or a cone of paper 
 (1343). Generally speaking, when the solution is strong in 
 the first instance, agitated during cooling, and the temperature 
 diminished rapidly, the crystallization is quick, confused, and 
 irregular, and the crystals small : but when the solution is of 
 moderate strength, the cooling allowed to go on slowly, and 
 the whole retained in a quiescent state, the crystallization is 
 regular, and the crystals are large and distinct. The parti- 
 cular proportions and habitudes of each substance can only be 
 gained by experience. 
 
 565. Crystallizations to be effected by spontaneous or very 
 slow evaporation, require a solution saturated at common tem- 
 peratures. This may be obtained as before mentioned (378), 
 and must have more surface exposed during the process than 
 was required in the former method. Evaporating basins (369) 
 answer this purpose very well. The solution should be put 
 into a dry place, where there is a sufficient access of air to 
 carry off the vapour which will gradually rise from it, and 
 must then be left for a much longer period than in the former 
 case. It is advantageous, if the place be so clean that no dust 
 can fall into the solution to disturb or contaminate it, to leave 
 the vessel uncovered ; but if danger be apprehended on that 
 point, it must be covered either with a thin dry cloth, stretched, 
 so as not to incur any risk of its sinking into the solution, or 
 else by filtering paper. When, however, an evaporating solu- 
 
Sect.X.] CRYSTALLIZATION PAPER COVERS. 249 
 
 tion is thus covered, the process is considerably interfered with, 
 and much more time required. 
 
 566. These vessels, as well as glasses, and many others 
 having round apertures, are occasionally very conveniently 
 covered with paper; for which purpose a piece of paper, so 
 large as to overlap the vessel from half an inch to an inch on 
 every side, being placed over the aperture, should be folded 
 down on one side against the vessel. Then a second fold, an 
 inch from the first and partly overlapping it, is to be made ; a 
 third upon that, and so on, until the folds have reached round 
 the aperture. These hold each other down, and the last may 
 be fastened by screwing it up tightly, the whole being done 
 somewhat in the manner that a grocer finishes his paper case 
 for a small quantity of sugar. The temporary cover thus 
 formed fits the mouth of the vessel tightly, is strained level over 
 its surface, incurs no risk of sinking into the solution beneath, 
 and being held on by the ledge formed from the succession of 
 folds, is not easily displaced or disturbed. 
 
 567. It is by the process of slow evaporation that the largest 
 crystals are obtained. A few of perfect forms should in the 
 first place be selected, and these being placed in the solution, 
 increase in size as the evaporation proceeds, and ultimately 
 become very large. They must be turned every day, that all 
 sides may receive increments of solid matter in succession. 
 
 568. An advantageous process between the two now de- 
 scribed may often be resorted to; it consists in placing a 
 moderate or weak solution on the sand-bath, in the evening 
 when the fire is going out, heaping the sand round the basin, 
 and leaving the whole until the morning. The evaporation is 
 somewhat hastened, and at the same time the temperature falls 
 very slowly ; and thus in many cases a fine crop of crystals 
 may be obtained in a short period. 
 
 569. For most substances the first method (563) is pre- 
 ferable; thus acetate of lead, sulphate of soda, nitre, &c., are 
 better so crystallized ; but for a few others, the second (565) 
 is most advantageous, and such are common salt, borax, Ro- 
 chelle salt, sulphate of potash, Sec. 
 
 570. A very interesting, and, in some cases, useful process, 
 is the gradual conversion of several small crystals into one 
 
250 LARGE CRYSTALS FROM SMALL ONES. [Sect. X. 
 
 large one. Dr. Wollaston, who communicated it to me, per- 
 mitted me also to describe it. If a small quantity of sul- 
 phate of nickel in solution, with a slight excess of acid, be 
 evaporated in a watch-glass, it will probably, on cooling, yield 
 a crop of numerous small crystals ; but if set aside for a few 
 weeks in a place subject to the changes of atmospheric tempe- 
 rature, its appearance will gradually alter, the small crystals 
 disappearing, the larger increasing, until ultimately only one 
 or a few large ones are left. This effect depends on the greater 
 extent of surface exposed by the small crystals, as compared 
 to their mass, than by the larger crystals ; so that when any 
 increase of solvent power in the surrounding fluid is occasioned 
 by a slight increase of heat in the atmosphere, the small crys- 
 tals dissolve to a greater extent than the others ; but, upon 
 the decrease of temperature, the deposition is equal upon all. 
 In this manner the small ones are gradually dissolved, and 
 the large ones become larger. Thus sometimes a separation 
 from impurities, a perfection of form, or a crystal of magnitude 
 is obtained, which cannot be had by other means. The same 
 effect may often be observed in solutions confined in glass 
 bottles, as in oxalic acid, nitrate of mercury, acetate of lead, 
 &c. ; the small crystals which were formed when the solutions 
 were first made being gradually converted into others of con- 
 siderable magnitude. 
 
 571. Other solvents than water must be used for substances 
 not soluble in that fluid, and, at times, even for some that are. 
 Alcohol is applicable to the crystallization of potash, choleste- 
 rine, urea, sugar, &c. Alcoholic solutions are generally crys- 
 tallized by spontaneous evaporation, unless indeed the solution 
 has been introduced into a retort, for the purpose of distilling 
 part of the spirit, and then the remaining fluid is generally best 
 left in the retort to cool and crystallize. Ether, oil of turpen- 
 tine, and pyroligneous ether, are now and then employed in 
 experiments on unknown substances, for the purpose of dis- 
 covering characters by which they may be distinguished. 
 
 572. The influence exerted over one substance by the pre- 
 sence of another, which often materially affects the appearances 
 of crystals and crystallizations, must now be noticed. Nitre, 
 when crystallizing from solutions containing much common 
 
Sect. X.] CRYSTALLIZATION CAUSES INFLUENCING FORMS. 251 
 
 salt, is frequently rough upon its surface, or constituted of a 
 number of crystals, forming a friable, instead of a compact, 
 mass. Common salt, when crystallized from a solution con- 
 taining urea, or in urine, assumes an octohedral form. It has 
 also the same form, though imperfectly, when crystallizing at 
 the surface of a solution during evaporation. The appearances 
 of several salts are altered when crystallized in animal or vege- 
 table infusions. The most remarkable instance of the kind, 
 and one which deserves notice here in consequence of the great 
 apparent difference produced, although not likely often to 
 happen accidentally, is when strong sulphuric acid has acted 
 upon some of the products of distilled or decomposed oil. If 
 one part of the substance obtained by the compression of oil 
 gas, and which always exists as vapour in it, be mixed with 
 eight or ten parts of strong oil of vitriol, a dark liquor is pro- 
 duced ; from this, when diluted with water, filtered, and con- 
 verted, by the addition of carbonate of potash, into a sulphate 
 of potash, a salt is obtained, which, upon crystallization, is 
 nacreous, in the form of scales, and has nothing in its appear- 
 ance common to sulphate of potash. It is, however, that salt, 
 and is thus affected by a substance which sometimes does not 
 amount to a two hundredth part of the salt present. The 
 same substance has still greater power over the sulphate of 
 copper, and in increased quantities (still comparatively very 
 small) influences the appearances of a great many saline 
 bodies. 
 
 573. Sometimes crystallization is not effectual for the sepa- 
 ration of salts. When the sulphates of iron and copper are 
 in solution together, crystals will be obtained resembling those 
 of sulphate of iron, but with very variable proportions of sul- 
 phate of copper in them, the latter salt being present at times^ 
 in great quantity ; on other occasions triple salts are formed^ 
 as frequently occurs with nickel. But these, and a knowledge 
 of many more extraordinary circumstances attending crystalli- 
 zation, must be left to be obtained by reading and experience. 
 
 574. When salts which may be separated from others by 
 crystallization have been obtained from impure solutions, they 
 always retain a portion of the impurities, and require to be 
 
252 CRYSTALLIZATION INDICATED EXAMINED. [Sect. X. 
 
 redissolved and r eery stall ized, before they can be considered 
 as approaching to purity. In particular cases even a third 
 crystallization is necessary. 
 
 575. When experiments are proceeding upon an unknown 
 substance or a mixture of substances, to ascertain whether it 
 will crystallize or not, they are generally made as distinctly 
 and effectually upon a small scale as a large one, and often 
 indeed with more success (916). Thin fragments of Florence 
 flasks are useful ; as are little dishes, capsules, watch-glasses, 
 and the glass plates already briefly mentioned (1348). Some- 
 times merely by dipping a rod into the hot solution, and 
 allowing the surface thus wetted to dry in the air, it may be 
 observed from the striated, regular, or uniform appearance, 
 whether the substance has crystallized upon it. At other 
 times, a drop of the cold solution may be put upon a flat 
 glass plate, and the latter placed on a warm part of the table 
 furnace, that the liquor may slowly evaporate, and from the 
 examination of the spot of solid matter left, a judgment may 
 be formed. But perhaps the most decisive evidence is to be 
 gained by leaving a drop or a small portion in a piece of Flo- 
 rence flask to evaporate spontaneously at common tempera- 
 tures ; or, if the substances dissolved are deliquescent, by 
 evaporating them under the air-pump receiver (583). The 
 crusts of solid matter thus produced should be examined with 
 care ; as well with a powerful eye-glass as by the naked eye ; 
 sometimes by holding the glass plate in the sun's ray whilst it 
 is regarded sideways, or by the light from a candle reflected 
 by it to the eye, or by looking through the crust and glass, 
 not directly at the light, but at a back ground close to it. In 
 all these trials appearances which resemble crystallization 
 should be closely scrutinized, for the manner in which a film 
 cracks or scales, or the way in which the surface of a fluid in 
 small quantities is drawn by contraction, is often such as to 
 occasion appearances so deceitful as to make it absolutely 
 necessary to refer to an eye-glass. 
 
 576. Mr. Daniell has introduced a process of dissection *, 
 which, though not concerned in the production of crystals, is 
 
 * Quarterly Journal of Science, i. 24. 
 
Sect. X.] CRYSTALLIZATION BY DISSECTION FUSION. 253 
 
 frequently of great advantage in developing them from amor- 
 phous masses, and shewing the relation of forms one to another. 
 It consists in putting a mass of the substance into a fluid 
 capable of dissolving it, which gradually removing the exterior 
 parts, reveals the interior in their symmetric arrangement. 
 When the substance is moderately soluble, like alum, a lump 
 of it should be put into water, equal to about its own bulk in 
 quantity, and in such a vessel that the fluid may rise a little 
 above its surface, and should be left for several days in a quiet 
 place of uniform temperature. It will then be found, upon 
 examination, that crystalline forms have been developed by 
 the solvent action of the water. 
 
 577. Bodies but slightly soluble, as sulphate of potash, may 
 have more water put over them. On the contrary, such as are 
 very soluble, in place of being immersed in water, should be 
 put into a solution of the same substance, which having been 
 saturated, has afterwards been slightly diluted to occasion a 
 solvent action. Substances not soluble in water, but soluble 
 in acids, without effervescence, may be successfully examined 
 in the same manner. 
 
 578. As before mentioned, the crystallization of some sub- 
 stances may be effected by fusion, when solution is scarcely 
 applicable, and thus, many metals, sulphur, spermaceti, &c., 
 may be made to assume crystalline forms. The process only 
 succeeds well with large quantities, and may be illustrated by 
 reference to lead or bismuth. The metal is to be put into an 
 iron ladle and melted, the ladle removed from the fire and 
 placed on the sand-bath, where, though the bottom may be 
 kept warm, the heat is not such as to prevent the top from 
 congealing. When a solid crust has formed, holes should be 
 broken through it at two opposite parts near the edge, with a 
 hot iron rod, and the fluid metal rapidly poured out. When 
 that which remains in the ladle is examined, it will be found 
 crystallized in the interior. A crucible may be used in place 
 of an iron ladle for metals ; a glass flask or an evaporating 
 basin for sulphur, spermaceti, or similar substances. When 
 the experiment is made with sulphur, the temperature should 
 not be raised too high, or the fluid will thicken and become 
 adhesive. 
 
254 CRYSTALS BY VAPORIZATIONS-EXAMINED. [Sect.X. 
 
 579. When crystals are to be obtained by vaporization, 
 the general directions given with regard to sublimation (495, 
 &c.) are to be followed ; it is to be observed, however, that the 
 more slowly and regularly the crystals are formed, the finer are 
 the forms obtained. It is easy to sublime and crystallize 
 such bodies as camphor, iodine, naphthaline, Sec., but with 
 those which demand a higher temperature, as calomel or 
 corrosive sublimate, good crystals can be obtained only by 
 operating with large quantities. The crystallization of indigo 
 is best effected as already described (499.) 
 
 580. In examining crystals, with a view to recognize their 
 general form and appearance, or the existence of any particular 
 plane, it may be observed that the eye should be assisted by an 
 eye-glass, and sometimes by placing the crystals in the sun's 
 light, or in the light of a lamp, or candle, that the reflection 
 from the planes, as they come into particular positions, may 
 render them evident 5 and it may also be observed, that where 
 small crystals or fragments of substances are to be taken up 
 and examined by the eye, a soft cement, composed of two parts 
 yellow wax and one part turpentine, is very useful (1125). 
 A little piece of this, softened between the fingers, may be 
 fixed on the end of a pencil or a small stick, and formed 
 to a point, or a small roll of the substance itself may be 
 pointed at the end, and the particle being touched by this 
 point immediately adheres to it, and may be examined with 
 perfect ease. 
 
 581. With reference to the use of the goniometer, espe- 
 cially the accurate instrument of Dr. Wollaston's invention, 
 and also to the determination of the forms of crystals them- 
 selves, these constitute a part of that extensive, important, and 
 mathematical branch of knowledge now known by the name 
 of Crystallography; and for such information as relates to 
 the use of the instruments required in it, the student is re- 
 ferred to the paper by Dr. Wollaston in the Philosophical 
 Transactions for 1809; Phillips' Elementary Introduction 
 to Mineralogy; and Brooke's Introduction to Crystallo- 
 graphy. 
 
Sect. XL] EVAPORATION ITS NATURE PROCESSES. 255 
 
 SECTION XI. 
 EVAPORATION DESICCATION. 
 
 582. EVAPORATION is a process so simple in its nature, and 
 common in its performance, as to be comprehended generally 
 by every one. The ordinary vessels required for it are 
 basins of earthenware (369), one or two of silver and lead 
 (371), a crucible and capsules of platina (371), Florence 
 flasks (373), fragments of flasks (1213), and watch-glasses. 
 The basins and capsules of earthenware should be thin at the 
 bottom, but all these vessels have been sufficiently described in 
 the section upon Solution. 
 
 583. Of evaporation, at common temperatures, that which 
 is performed spontaneously has been referred to in treating of 
 crystallization (565), and the necessity of a clean airy place, 
 or of covering the vessels, insisted upon. But the process has 
 been very much assisted and hastened by the use of desiccators, 
 and in the hands of Mr. Leslie * has been carried to an extent 
 in its power and application, surpassing every previous expec- 
 tation. Mr. Leslie's process consists in placing the fluid to be 
 evaporated in a basin so as to expose considerable surface, 
 under the receiver of an air pump, accompanied by another 
 basin, containing a substance which has strong attractive 
 powers for water. Sulphuric acid, having a surface of from 
 twice to thrice that of the fluid to be evaporated, may be used. 
 These should be so placed that the first basin may be sup- 
 ported over the second ; and both being covered by a receiver 
 as small as can be conveniently used, it is to be exhausted, 
 and the operation left to . itself. The air being absent from 
 within the receiver, a ready liberation of vapour from the 
 water, equivalent in tension to its temperature, takes place ; 
 but this vapour is as rapidly condensed upon coming into con- 
 tact with the sulphuric acid, and in its place supplied by fresh 
 vapour from the water, which in turn is condensed as before. 
 
 * Supplement to Ency. Britannica. Art, Cold, 
 
256 EVAPORATION LESLIE'S METHOD. [Sect, xi, 
 
 Thus the process goes on, the water travelling in the form of 
 vapour from the basin to the sulphuric acid, where it combines 
 and resumes the liquid state. 
 
 584. This process of evaporation and consequently of desic- 
 cation, is valuable, not merely as avoiding any necessity for 
 elevation of temperature, but as actually causing considerable 
 depression, and is for this reason useful in numerous cases 
 where delicate organic substances, which might be injured, 
 even by moderate heat, require drying. For its operation, all 
 that is necessary is, to replace the basin of water by the sub- 
 stance to be dried ; whether it be fibre, or a filter with a 
 precipitate upon it, or a portion of washed precipitate in a 
 basin, or a solution. All these or any other substances, in 
 basins, may be supported by a little tripod with glass legs, 
 standing in the dish of sulphuric acid. 
 
 585. In the general arrangement of this process, it is ne- 
 cessary that the pump be in such order, and the receiver 
 fitted so accurately to the plate, that the vacuum may be 
 retained for days together. It is also necessary that the sul- 
 phuric acid be not allowed to become too dilute by frequent 
 use. It is most powerful when first introduced, should be 
 stirred up now and then when the receiver is opened, and 
 had better be replaced by fresh acid when diluted with a 
 fourth or fifth its weight of water. Care should be taken 
 to prevent all contact between the acid and the bodies to be 
 dried ; and the student should be aware, that upon the first 
 exhaustion after the introduction of fresh acid, there is gene- 
 rally the evolution of a little air, which, forming bubbles 
 at its surface, break and throw up minute drops. Care 
 should be taken that these drops cannot reach the substance to 
 be dried. 
 
 586. Although the arrangement described is the most 
 powerful, it may not always be the most convenient. The 
 substance to be dried may be in a glass or bottle ; which may 
 stand in the dish containing the acid, or the acid itself may be 
 in a glass by the side of the substance ; but in all cases the 
 acid should be in a very open vessel, for if in a close one, its 
 small surface soon becomes diluted and rendered ineffectual ; 
 and moreover, as there is also a tendency in the process to 
 
Sect. XL] EVAPORATION BY DESICCATORS. 257 
 
 accumulate the portion of air left in the receiver in the vessel 
 containing the acid, it retards the condensation, and conse- 
 quently the operation. 
 
 587. Mr. Cooper has a method of setting several of these 
 operations, on a small scale, at work at one time. It consists 
 in the use of glass plates, in addition to the receiver and its 
 contents. These plates, like those referred to (575, 1348), 
 are of thick plate glass, but each has a small hole drilled 
 through it at about one fourth the diameter from the edge. 
 
 These plates, with a little pomatum or oil between 
 them, are perfectly air tight, and two thus prepared, 
 being placed together, with the holes coincident, 
 allow a free passage for the air through them, but by 
 being turned a little way round one upon the other, 
 the holes are separated, and the passage closed. Mr. Cooper 
 places a jar with an open ground top upon the plate of the air 
 pump, on it two of the glass plates with the holes coincident, 
 and the basin of sulphuric acid with its glass and receiver upon 
 the upper plate. The pump is then worked, both receivers 
 are exhausted, and when in that state the plates are moved 
 one upon the other, so as to close the communication, air is let 
 into the lower receiver, and the upper receiver, with its con- 
 tents standing upon the two plates, is set aside for a few 
 days or a longer time, as may be required. Instead of using 
 the lower receiver, the plates may be put directly upon the 
 air pump, the aperture in it coinciding with those in the 
 plates. 
 
 588. More imperfect, but yet very useful processes, may be 
 practised without the aid of an air pump. If the acid and the 
 substance to be dried be placed in a proper position upon a 
 glass plate of sufficient size, rubbed with pomatum, and a re- 
 ceiver covering them, accurately closed upon the plate, then, 
 by raising the receiver, introducing the flame of a spirit lamp 
 for a moment, and suddenly replacing it accurately upon the 
 glass, as is practised by cuppers, an exhaustion will be ob- 
 tained, imperfect it is true, but which still will usefully facilitate 
 the evaporation. 
 
 589. Even without any process of exhaustion, evaporation 
 at common temperatures may be carried on by the use of 
 
 s 
 
258 EVAPORATION BY DESICCATORS TO DRYNESS. [Sect. XI. 
 
 desiccators, more rapidly in close vessels than in the open air, 
 unless, indeed, a current be taken advantage of; and a wide- 
 mouthed stoppered bottle, or a jar placed over or in a basin, 
 will at times supply the want of better apparatus. In these 
 cases sulphuric acid, chloride of calcium, carbonate of potash, 
 quick lime, and similar absorbents, may be used. A basin of 
 quick lime, with a moist precipitate placed above it, and the 
 whole covered with a jar or receiver, will soon dry the pre- 
 cipitate. 
 
 590. When there is no objection to the application of heat, 
 evaporation may be rapidly effected by its assistance. The 
 heat being supplied in one or other of the numerous methods 
 already referred to in distillation (section vii.) and solution 
 (section vi). 
 
 591. If the evaporation is to be performed at temperatures 
 under ebullition, the vessel used should be an open one, as a 
 basin (369), and have free access of air, that the aqueous 
 vapour may be removed from the surface of the liquid by the 
 aid of the atmosphere, as fast as it is produced (943). When 
 crusts form on the surface, they should be broken down, for 
 they interfere much with the evolution of vapour, acting indeed 
 the same part as a cover, or the film of oil before mentioned 
 (260) ; the effect which before was advantageous being now 
 injurious. 
 
 592. If the evaporation be required to dryness, as is com- 
 mon in cases of analysis, great care is necessary when the solid 
 matter begins to be in such proportion to the liquid as to form 
 a thick mixture. The circulation which took place throughout 
 is now interrupted, and the heat will frequently increase at the 
 bottom of the basin until above the boiling point of the solu- 
 tion, before it can pass by conduction through the crust above 
 it. Then occurs the sudden evolution of small portions of 
 steam, which cause sputtering and petty explosions, and throw 
 the substance about. In such cases it is necessary to stir the 
 substance continually, that by mixing the whole together, the 
 one part may be prevented from rising to too high a tempera- 
 ture, and the other be more readily evaporated to dryness. It 
 assists also in making way for the steam from the lower part, 
 and materially facilitates the desiccation. It is even necessary, 
 
Sect. XI.] EVAPORATION BASINS FLASKS. 259 
 
 when part of the matter has become so dry as to harden into 
 lumps, to use a pestle in place of a glass rod, and by rubbing 
 the lumps down and mixing them with the moist parts, to 
 bring the whole gradually into the state of an uniform dry 
 powder. When this is done for analysis, great care must be 
 taken not to lose any portion of that which adheres to the rod 
 or the pestle : it must be scraped off with the platina spatula, 
 and the rod and pestle being washed with a little water, the 
 liquid must be reserved to be added to the rest in due time. 
 
 593. Sometimes when substances which dry hard, as a solu- 
 tion of common salt, are left to evaporate without stirring, they 
 form a cake, between which and the bottom of the basin por- 
 tions of steam are generated, with a force not merely sufficient 
 to throw out a part of the contents, but actually to cause 
 violent explosions, breaking the basin to pieces, and dispersing 
 the substance in all directions. This is entirely prevented by 
 frequent stirring. When, from the habits of the salt, no fear 
 is entertained of such an occurrence, stirring may be dispensed 
 with in operations not requiring exactness, the evaporating 
 basin being then covered by another to prevent the loss of any 
 small particles thrown up. The upper must then be retained 
 in a heated state, which may be done by filling it with sand, 
 otherwise the desiccation will not proceed, for the vapour con- 
 densing upon the cold cover will return to the substance below 
 in drops. 
 
 594. If the fluid is to be evaporated at a boiling tempera- 
 ture, there is no necessity for its being done in an open vessel, 
 though it is always most rapidly so performed. It may then 
 be effected either in basins or flasks. In the latter case the 
 dry results are not so easily removed, but that is often of no 
 consequence, and occasionally flasks present decided advantages. 
 The analysis of a mineral water often requires that large quan- 
 tities of fluid be evaporated : these being too great for intro- 
 duction at one time, are introduced by successive portions; 
 and, as much time is required, the evaporation should be per- 
 formed so as to avoid the dispersion of any part, and pre- 
 vent the entrance of fumes or other extraneous matter. The 
 quart Florence flasks are then very useful ; the boiling, and 
 consequently the evaporation, may proceed rapidly in them on 
 
 S 2 
 
260 EVAPORATION IN BASINS PRECAUTIONS. [Sect. XL 
 
 the sand bath, fresh portions of water being added as that in 
 the flask diminishes, until all is reduced to a small quantity, 
 which may then be decanted, the flask washed out, and this last 
 and concentrated portion treated as the analysis may require. 
 
 595. The entrance of dirt at the small aperture of the flask 
 may be prevented by rolling up a piece of paper into a conical 
 form, and putting it loosely into the mouth as a stopper, or 
 covering it in the manner of an extinguisher. Either method 
 will allow free passage for the vapour. 
 
 596. When evaporations are going on at the boiling tempe- 
 rature in a basin, it is still more requisite that the vessel be 
 covered, inasmuch as the ebullition will more probably throw 
 small portions of fluid out, and dirt and vapours are more likely 
 to find their way in. The best cover is a second basin put 
 over the first and retained hot (593) ; or if the evaporating dish 
 be small, one of the bottom covers (553), or a watch-glass may 
 be used. It is necessary in all these evaporations, as M. Ber- 
 zelius has observed, that the cover dip downwards, so that any 
 fluid condensed on it may return to that below, and not run to 
 the outside of the vessel : for the particles of matter in solution 
 being thrown up and caught by the cover, are thus returned 
 to the place from whence they came ; whereas in the other 
 case, they would be carried to the outside and lost. The steam 
 makes its way out at the lip of the basin. The necessity dur- 
 ing these close evaporations of keeping up the heat, will be 
 evident from the observations already made (425) . 
 
 597. With a view to particular substances in a mineral 
 water, which it is feared may be confounded with any thing 
 that by possibility could be separated from the glass of a 
 Florence flask by long boiling, it is sometimes required to 
 carry on the evaporation in a metallic vessel. A deep silver 
 crucible, or vessel, is probably the best apparatus that will 
 present itself, though one of platina would be better. The 
 vessel must be perfectly clean, and covered with a silver or 
 platina dish in the manner just described (596). The water 
 must be added in successive portions. 
 
 598. When heat is applied by a sand-bath to a basin during 
 evaporation, the precautions pointed out (381, 382) are to be 
 observed. When the temporary hood (392) is in use, care 
 
Sect. XL] EVAPORATION DESICCATION OF POWDERS. 261 
 
 must be taken that the inside be clean, that nothing may fall 
 from it to contaminate the substance in the basin beneath. 
 
 599. Solutions of animal and vegetable substances are fre- 
 quently to be evaporated and dried, until they become free 
 from water or retain but a small portion of it. In these cases, 
 if the heat be that of a sand-bath or lamp, the temperature is 
 ultimately apt to increase to such a degree at the bottom of the 
 basin, as to cause injury to the substance. The solution, or 
 extract, should be constantly stirred as it thickens, and as a 
 thermometer cannot be applied so as to indicate the heat at the 
 bottom^ another method must be adopted for that purpose. 
 Sir Humphry Davy recommends .that a chip of wood be re- 
 tained in contact with the exterior of the basin at the bottom. 
 When the temperature is powerful enough to char the wood, 
 it is sufficient to cause injury to the contents of the vessel, and 
 upon the first indication the latter should be removed. A few 
 slips of paper laid between the basin and the sand, when a 
 sand-bath is used, answer the purpose very well, and indicate 
 by their changes the power of the temperature to which the 
 basin is subject. As some substances decompose by heat before 
 others, it is advantageous to have corresponding indications ; 
 and if slips of worn calico be used, they will undergo a change 
 at temperatures much below those which affect paper. In 
 cases, therefore, where more care is required, the former sub- 
 stance should be used instead of the latter. 
 
 600. Similar care is required in the desiccation of organic 
 substances in a pulverulent or divided state, and they should 
 be continually stirred, if the bottom of the vessel containing 
 them be liable to an injurious elevation of temperature. 
 
 601. When substances in powder, not subject to injury 
 from an occasional high temperature, are placed upon the 
 sand-bath to dry, they should be covered with paper (566) to 
 keep out dust. Or if loose covers be more convenient, a glass 
 bottom (553), or another basin, will answer the purpose; but 
 in these cases the cover is to be removed now and then, to 
 allow the escape of vapour, and should be dried before being 
 replaced. 
 
 602. In cases of desiccation, it is frequently required to 
 know whether all the water that can be dissipated has risen, 
 
262 TEST OF DRYNESS WARM AIR-CHAMBER. [Sect XI. 
 
 or whether vapour be still passing away. A very excellent 
 and delicate mode of determining the point is to cover the 
 dish with a cold glass plate or basin ; if dimness appear, it 
 shews that vapour is rising. The test-glass must sometimes 
 remain nearly a minute, or until it is warm, before a conclusion 
 may be drawn, such an interval being necessary to make the 
 presence of vapour visible when in small quantity. Powders, 
 supposed to be hygrometric, or to have absorbed moisture 
 from the air, may be heated in a small basin, and tested by 
 this method, and the dryness of extracts, and many other 
 bodies, may be ascertained in a similar manner. 
 
 603. Evaporations are frequently performed on a small 
 scale (948), and will occasionally be carried on in capsules or 
 on small plates (1348), or in fragments of Florence flasks; 
 and the spirit-lamp (199), the sand-bath (173), and the hot 
 plate of the table-furnace (171), will be in constant requisition 
 as sources of heat. 
 
 604. The importance of a current of air in facilitating eva- 
 poration, generally, by removing the moist atmosphere and 
 allowing fresh vapour to rise with greater facility, is so well 
 known, that it will be needless to urge its application in every 
 case where it can do no harm, and is on other accounts admis- 
 sible. 
 
 605. A warm air-chamber, when it can be obtained, is highly 
 useful for desiccation, evaporation, and similar purposes. It 
 should not consist merely of a cavity or closet, but should 
 admit of a thorough draught of air. One that has been con- 
 structed by Mr. Cooper is the best in its principle, and most 
 convenient in its application, in the laboratory of research, 
 with which I am acquainted. It consists of an inclosed space 
 placed near the furnace, so as to receive some warmth from it, 
 but rendered fully efficacious in the operations for which it is 
 intended, by a current of hot air traversing it. This air is 
 heated by passing round an iron plate at the back of the fur- 
 nace, and enters the air-chamber at the top ; another passage 
 for its exit commences at the bottom, in a situation as far as 
 possible from the former opening, and is continued until it 
 joins the flue of the furnace at a convenient place. Thus the 
 hot air is made to descend, and spread through the chamber 
 
Sect. XL] DESICCATION WARM AIR-CHAMBER. 263 
 
 by the draught of the flue. A damper is inserted for the con- 
 venience of opening or closing the communication at pleasure, 
 and entrance is gained to the chamber by a door which closes 
 accurately and is fastened by a button. 
 
 606. A warm air-chamber may be made of brick-work, 
 metal, or even wood, and may be placed in any convenient 
 part near the furnace. An excellent situation for it in the 
 table-furnace (169, 172), exists within the walls and beneath 
 the flue, where the arrangements necessary for heating the 
 current of air will be ready and obvious. Projecting spikes 
 should be fastened into one or two sides of these chambers, to 
 hold a tin plate or a board, to form a temporary shelf when 
 required. 
 
 607. Precipitates, filters, and other moist substances put 
 into such a chamber, are readily and safely dried. The hot 
 air causes evaporation of the water, whilst the current removes 
 the rising vapour. The chamber is very useful in effecting 
 the slow evaporation of liquids (565, 568), and also for hot 
 filtrations (544), when the entering current of air is of a tem- 
 perature sufficient for the purpose. 
 
 608. In cases of necessity, a similar chamber may be made 
 by passing the stream of heated gaseous products from a small 
 crucible furnace (269) into one side of a box, and allowing an 
 aperture on the other side, or at the bottom, for its exit : but 
 as dust may pass with the air, it is necessary that the sub- 
 stances to be evaporated or dried be covered with bibulous 
 paper (566). An Argand lamp (270) may be applied in the 
 same manner as the furnace ; and in this case even a band-box 
 may be used for the chamber, the hot air entering by a two- 
 inch tube with a funnel termination at one side (1342), 
 and passing out by an opening at the other side, or in the 
 bottom. The chamber should not be too large in proportion 
 to the lamp, but of such dimensions as to be retained at a 
 considerable temperature, and then the water formed during 
 the combustion of the oil will not be deposited : and though it 
 will diminish the drying power of the air, in cases of evapora- 
 tion, it will still leave it in a very useful state. 
 
 609. Where filters with precipitates upon them are to be 
 dried, one useful method is to put them upon a clean tin plate, 
 
264 DESICCATION BY ABSORPTION. [Sect. XI. 
 
 with a piece of filtering paper intervening or not, according to 
 circumstances, and placing the plate over the sand-bath at a 
 part where its temperature may be sufficiently raised. The 
 sand may be removed from, or arranged over the bottom of 
 the bath at this part, so as to regulate the heat communicated 
 to the tin plate, which should never be such as to char paper; 
 and at other times, when no furnace or sand-bath is in action, 
 the plate may be heated by an oil-lamp placed beneath (SI 2, 
 270). These arrangements will often be found very useful. 
 
 610. Precipitates which have been separated or washed in 
 a filter may have a considerable quantity of the fluid removed 
 from them by being placed upon an absorbent body. A large 
 mass of chalk with a flat surface is exceedingly useful for this 
 purpose, when the fluid to be removed is water; and a sheet 
 or two of filtering paper folded up into several thicknesses may 
 be used when the fluid is acid, alkaline, or saline. When the 
 filter with its contents is to be transferred, it should first be 
 loosened at the sides, by inclining the funnel, and then either 
 lifted out by the edges and laid upon the absorbent body, or if 
 too heavy to admit safely of such a method, it should be 
 slipped out of the funnel by inclining the latter, its motion 
 being assisted at the same time by a slight pull. If the filter 
 be a simple one (533), the side thus laid on the absorbent 
 surface should be that which is single, and then the folds are 
 easily opened, and the filter with its contents laid out. If the 
 chalk be used, it should be separated from the filter by an 
 intervening piece of bibulous paper. 
 
 611. After a time proportionate to the nature and quantity 
 of the precipitate, the latter will be found dried to a certain 
 degree. Many precipitates admit of the operation being 
 hastened by folding the filter over them, laying several folds 
 of bibulous paper upon it, and applying pressure with the 
 hand. When the paper has become wetted, dry paper is to 
 replace it, and the operation renewed. This expedient must 
 not be adopted unless the precipitate have so much consistency 
 as to bear the pressure without being forced out at the edge 
 of the filter. After an operation of this kind, the filter with 
 its contents may be removed to the warm air chamber (605), 
 or the hot plate (609), and dried in the usual manner. 
 
Sect. XL] DESICCATION BY ABSORPTION. 265 
 
 612. The solid contents of small filters (546) are fre- 
 quently dried with advantage in the above manner between 
 folds of paper. It often happens that the substance, though 
 in small quantity, is rare or valuable ; in which case the fol- 
 lowing method may be adopted for the prevention of loss. 
 After being pressed once or twice, it will form a layer within 
 a fold of the filter, the paper being above and beneath, and 
 adhering slightly. Fold one edge of the paper quite back, 
 and then pull it, stripping as it were the paper off the precipi- 
 tate ; this may be done without disturbing the moist cake of 
 solid matter : then double the filter with its contents, making 
 the fold pass through the middle of the precipitate, by which 
 it will also be doubled up, and being pressed a little, will so 
 far adhere that the paper may be bent back and stripped off 
 as before, without disturbing the substance ; in this way the 
 cake is reduced to half its original extent, but doubled in 
 thickness, and by repeating the operation, the precipitate, 
 however small in quantity, may be collected from the different 
 parts of the filter into one compact portion. 
 
 613. Before quitting the subject of desiccation, it may be 
 remarked, that moistened crystals or other "substances in small 
 fragments, are frequently put into funnels to drain, and that 
 the required effect is hastened, and also carried to a greater 
 extent, than it otherwise would be, by inserting a folded slip 
 of filtering paper into the neck of the funnel, so that its upper 
 end may touch the bottom of the collection of crystals, and its 
 lower project a little beyond the funnel. Thus situated, it 
 enables the liquor to drain away to a greater extent than 
 would otherwise take place. 
 
 614. M. Robinet* has very much improved this process of 
 draining crystals, by passing a current of air through them. 
 If the crystals be put into a funnel with its neck obstructed by 
 a ball of cotton wool, and the funnel be then fixed in one 
 aperture of a double-mouthed bottle, whilst a tube is attached 
 to the other, air may be drawn by the tube through the funnel 
 and its contents, into the bottle, and will carry with it the 
 mother- water, or adhering moisture, in such an effectual man- 
 ner as perfectly to cleanse the most silky crystals. 
 
 * Annals of Philosophy, New Series, xii. 460. 
 
266 COLOURED TESTS CABBAGE RED. [Sect. XII. 
 
 SECTION XII. 
 COLOURED TESTS NEUTRALIZATION. 
 
 615. THOSE very important chemical substances, acids and 
 alkalies, in a free state, possess the power, even in very small 
 quantity, of effecting certain general and regular changes in 
 the tints of some vegetable colours. The distinctness of the 
 change and facility with which it is produced have occasioned 
 the colours to be used as tests of the presence of these bodies 
 when uncombined or in excess, and are now of such con- 
 stant service as to be indispensable in the laboratory. They 
 are prepared for use in a state of solution, or fixed upon 
 paper; the preparations being called test solutions, or test 
 papers. 
 
 61 6. The only substance of the kind perhaps worth keeping 
 in solution is an acid infusion of red cabbage. For its prepa- 
 ration, one or more red cabbages should be cut into strips, and 
 boiling water poured upon the pieces ; a little dilute sulphuric 
 acid is to be added, and the whole well stirred : it is then to 
 be covered and kept hot as long as possible, or, if convenient, 
 should be heated nearly to boiling for an hour or two in a 
 copper or earthen vessel. The quantity of water to be added 
 at first should be sufficient to cover the cabbage, and the sul- 
 phuric acid should be in the proportion of about half an ounce 
 of strong oil of vitriol by measure to each good sized plant. 
 This being done, the fluid should be separated and drained off, 
 and as much more hot water poured on as will cover the solid 
 residue, adding a very little sulphuric acid. The whole is to 
 be closed up, and suffered to stand until cold, and then the 
 liquid poured off and added to the former infusion. The 
 cabbage may now be thrown away. The infusion is to be 
 evaporated to one-half or one-third its first bulk, poured into 
 a jar, allowed to settle, and the clear red fluid decanted and 
 preserved in bottles. The residue may have water added to 
 it, the solid part be allowed to subside, the clear liquor drawn 
 off, evaporated, and added to the former, or it may be dis- 
 
Sect. XII.] BLUE FLUID LITMUS PAPER. 267 
 
 missed altogether. This solution will keep for a year. When 
 required for use, the acid of a small portion of it should be 
 neutralized by caustic potash or soda (not by ammonia), when 
 it will assume an intensely deep blue colour, and will, in most 
 cases, require dilution with twelve or fourteen parts of water. 
 The red liquor of pickled cabbage will, occasionally, answer the 
 uses of the solution, and is, when required for service, to be 
 neutralized in a similar manner. 
 
 617. Test papers are far more advantageous for use than 
 liquids : two of them in general application and delicacy sur- 
 pass the rest, these are litmus and turmeric papers. For the 
 preparation of the former, some good litmus is to be rubbed 
 to powder with hot water in a mortar, the mixture poured into 
 an evaporating basin or a flask, and water added until the pro- 
 portion is about half-a-pint for each ounce of litmus. It is to 
 be covered up so as to remain warm for an hour, after which 
 the clear liquor is to be decanted, and fresh hot water poured 
 on to the residue. This is to be covered up as before, suffered 
 to stand, and the liquid evaporated. The operation is to be 
 repeated a second time, and if much colour appears to be 
 removed, even a third. The first solution is to be kept apart 
 from the second and third, which may be mixed. The first 
 portion will not require evaporation, but the others are to be 
 so far reduced in quantity, that when a piece of filtering paper 
 is dipped into them, and dried, they will impart to it a blue 
 colour of sufficient intensity for use. 
 
 618. Paper is then to be dipped into the prepared solution. 
 The paper should in all cases be bibulous, and not sized (530), 
 so that fluid dropped upon it should be instantly absorbed. 
 Sized paper often presents a fairer tint of colour upon the sur- 
 face, but is by no means so delicate as a test. The paper 
 should be of a good colour, that the tint may not be injured ; 
 of sufficient thickness not to become almost transparent when 
 wet ; and particular care should be taken that it be free from 
 earthy matter, especially carbonate of lime, and alkalies. It 
 may be examined as to these points in the manner recom- 
 mended for filtering paper (530). 
 
 619. The paper selected should be cut into pieces of a size 
 convenient to be dipped, somewhat less, for instance, than half 
 
268 LITMUS PAPER TURMERIC PAPER. [Sect. XII. 
 
 a sheet of post paper. The litmus solution should be poured 
 into a dish or soup-plate, and the paper should be drawn 
 through it piece by piece, in such a manner that the fluid may 
 be in contact with both sides, and then having been held to 
 drain a few seconds, it should be hung on lines of thread or 
 twine to dry, in a convenient place. No fumes of acid or 
 burning charcoal should have access to it, for they injure the 
 colour ; and as soon as the paper is dry it should be taken 
 down, and laid together. The tint ought to be a full blue, or 
 if light, not faint or undecided : it may be judged of by 
 touching a piece of the paper with a very weak acid, and ob- 
 serving whether the red colour produced is vivid, and a strong 
 contrast to the blue tint of the rest of the paper. If the solu- 
 tion should have been made so dilute as to produce too weak 
 a tint, the paper may be dipped a second time, but this is to 
 be avoided if possible, as it involves a second exposure to 
 the air. 
 
 620. It may happen from the suspension of fine particles 
 of litmus in the solution, that the tint is not so clear as was 
 required, but has a dusky appearance. This is unpleasant, 
 but is not injurious; the fine particles of litmus testing the 
 presence of an acid nearly as well as the stained paper. 
 
 621. When the paper has acquired its proper colour and is 
 dry, it should immediately be tied up closely in stiff paper, 
 and preserved from the air and light : the latter injures and 
 destroys its colour, and the former, from the carbonic acid and 
 other occasional substances it contains, injures the colour, and 
 consequently the sensibility of the paper. 
 
 622. Turmeric paper is to be prepared in a similar manner. 
 A hot infusion of finely-bruised or coarsely-ground turmeric 
 is to be made, by boiling one ounce of the root. with ten or 
 twelve ounces of water for half an hour, straining through 
 a cloth, and leaving the fluid to settle for a minute or two. 
 The liquid should be of such strength that paper, when dipped 
 into it and dried, should acquire a fine yellow colour. The 
 paper should be of the kind before described (618). No par- 
 ticular care is required during drying, relative to exposure to 
 air, except that acid and alkaline fumes should not have ac- 
 cess, as they may transfer injurious matter to the paper, and 
 
Sect. XII.] TEST PAPERS USE OF HOW APPLIED. 269 
 
 diminish its delicacy. When dry it should be wrapped up 
 and preserved with care. 
 
 623. The stock of test-papers should not be left lying about 
 the laboratory for general use, for then much is torn up care- 
 lessly and wasted, and much more spoiled by floating fumes. 
 But a piece of each should be cut into slips about six inches 
 in length, and half an inch in width, and either put into a 
 stoppered bottle, with dark paper pasted round it to prevent 
 the entrance of light, or, what is more convenient, tied up in a 
 case of cartridge paper, the slips projecting about half an inch 
 at each end, that one, either of litmus or of turmeric, may be 
 withdrawn at pleasure. 
 
 624. In using these test-papers with a fluid suspected to 
 contain free acid or alkali ; or, knowing that one of these sub- 
 stances is predominant, to ascertain which is so, all that is 
 necessary is to moisten them with the liquid, and observe the 
 change : if the fluid be acid, the blue colour of the litmus will 
 immediately become red ; if alkaline, the yellow colour of the 
 turmeric will be changed to a brown. The moistening may 
 be effected by dipping the paper into the liquid, but a better 
 method is to touch the edge of the slip with a rod dipped in 
 the fluid (374). In the latter case there is no risk of conta- 
 mination to the fluid from the paper, and only a very minute 
 quantity of the liquid is used at once. 
 
 625. These trials must be made by day-light ; artificial 
 light not permitting that just estimation of the changes by 
 which the presence of a small excess of acid or alkali is to be 
 determined. As the proportion of free acid or alkali di- 
 minishes, the intensity of the new tint produced upon the 
 paper is also diminished, and when in very small quantity it 
 requires considerable attention before a decision can be ar- 
 rived at. The test paper should occasionally be touched with 
 pure water in the immediate neighbourhood of the part where 
 the solution has been applied ; for any change in appearance 
 that may have occurred, not due to mere moistening, is then 
 readily perceived. 
 
 626. Although acid is -generally tested for by litmus paper, 
 and alkali by turmeric paper, yet the former is sometimes 
 used advantageously for the latter purpose, being first slightly 
 
270 COLOURED TESTS NEUTRALIZATION. [Sect. XII. 
 
 reddened either by exposure to the air, or by momentary 
 contact with muriatic acid fumes. When the paper thus 
 modified is used instead of turmeric paper, to detect a free 
 alkali, that substance is indicated by the restoration of the 
 original blue colour. Litmus paper is best slightly reddened 
 for this use, by putting a drop or two of muriatic acid into 
 a large jar, allowing it to stand a few minutes, and then 
 bringing the paper towards the mouth of the jar, or carefully 
 placing it within ; so soon as the blue tint has become slightly 
 reddened, the paper should be removed for use. If too much 
 acid be imparted to the paper, the delicacy of its indications is 
 injured, because of the greater quantity of alkali required to 
 neutralize the acid, and restore the blue colour. For the same 
 reason a paper free from alkali or carbonate of lime has been 
 recommended for the preparation of these tests (618), for these 
 impurities combining with a minute portion of acid, neutralize 
 it, and thus prevent that delicacy of indication which the test 
 paper ought and may be made to possess. 
 
 627. Litmus contains a portion of alkali, and so also does 
 litmus-paper, in consequence of which it becomes insensible to 
 liquids very weakly acid, when applied in the small quantities 
 above directed, because the acid present in the drop is neutra- 
 lized by the alkali of the paper, and therefore has no effect on 
 the colour : but in these cases there can be very little free acid, 
 and if absolute certainty as to its existence, or not, be required, 
 it is then better to cut some little squares of the test-paper, 
 the one-tenth or one-twentieth of an inch in size, to put one of 
 these into the liquid, and move it from place to place. If 
 there be the smallest trace of free acid present, the alkali of 
 the paper is quickly neutralized, and then the blue colour 
 changed to red. 
 
 628. Neutralizations are best effected with the assistance of 
 heat, especially if a carbonate be used, or if precipitation occur 
 during the operation. The carbonic acid in the first case is 
 dissipated, and in the latter the combination is more rapidly 
 and perfectly effected. Evaporating basins (369) are highly 
 useful for these purposes, their contents being easily stirred, 
 and the rod used for that purpose also applied to moisten 
 the test paper when required. The solution to be neutralized 
 
Sect. XII.] COLOURED TESTS FALLACIES. 271 
 
 should not be very strong, and the substance added should be 
 diluted (511), upon approaching the point of neutralization, if 
 it be accurately required, for the reasons before given. The 
 successive trials on the test paper should be made down one 
 edge, and occasionally contrasted with the effect produced by 
 water (625). On very delicate occasions this comparative trial 
 should be made with hot water, heated in a small basin by the 
 side of the larger one containing the solution. Great care 
 should be taken that the paper be not brought into contact 
 with acid fumes during the trial; or much error may inad- 
 vertently be occasioned. 
 
 629- Sometimes precipitations are to be effected in neutral 
 solutions, by the addition of an alkali or an alkaline carbonate, 
 it being desirable to have as little excess of the latter as pos- 
 sible. Turmeric paper is then required, and the operation 
 should be performed by heat as before mentioned ; but instead 
 of adding the precipitant gradually to the whole of the solution, 
 until slight indications of an alkali in excess appear, it is better 
 to reserve a small portion of the solution, and then rapidly 
 rendering the rest slightly alkaline, afterwards to add the small 
 portion by degrees, testing with the turmeric paper until the 
 point is as nearly attained as required. The small remaining 
 part may then be precipitated, by adding alkali carefully and 
 continuing to test it, and finally adding it to the larger 
 portion. 
 
 630. There are many substances which affect the colour of 
 test papers, and especially of turmeric paper, either inde- 
 pendently of the free acid or alkali they contain, or with ap- 
 pearances different to those described ; which, if unknown, 
 might sometimes lead to error. Solution of boracic acid, 
 whether strong or weak, gradually changes turmeric paper, 
 producing a tint resembling that occasioned by an alkali ; and, 
 if previously mixed with the common acids, produces still 
 stronger tints of red and reddish-brown. The borates occasion 
 the same effect, especially when mixed with acids, and some 
 of the tints very much resemble those produced by alkalies. 
 Strong oil of vitriol, and muriatic acid gas, redden turmeric 
 paper, but the redness is removed by the addition of water. 
 Ammoniacal gas, on the contrary, does not redden turmeric 
 
272 ALKALIMETRY TUBE PREPARED. [Sect. XII. 
 
 paper, unless there be sufficient water present in the paper to 
 dissolve the gas. The salts of iron, tin, and uranium, the 
 muriates of zirconia, zinc, antimony, and manganese, and the 
 nitrate of bismuth, when in moderately strong solution, pro- 
 duce tints in turmeric paper, resembling those occasioned by 
 excess of alkali*. It should be remarked, for the instruction 
 of those who, meeting with a difficulty of this kind, may resort 
 to paper stained yellow by rhubarb, that it also is affected in 
 the same way, though not so generally, but that, with particular 
 care, it is a very excellent test of the presence of alkalies. 
 
 631. Alkalimetry at present consists in an estimative process, 
 dependant upon neutralization and the use of the test papers 
 just described ; the object being to ascertain the quantity of 
 free alkali or of carbonate contained in any impure specimen, 
 as for instance, in that produced by the first rough process for 
 their preparation. Descroisilles first resorted to neutralizing 
 power for this purpose, but the extent to which the application 
 has been improved by chemists since his time may be seen in 
 modern works *f-. 
 
 632. Let a tube, closed at one end, of about three-fourths 
 of an inch internal diameter, and nine inches and a half in 
 length, have 1000 grains of water weighed into it ; then 
 let the space it occupies be graduated into 100 equal parts, 
 by the processes formerly described (129, &c.), and every ten 
 divisions numbered from above downwards. At 23.44 parts, 
 or 76.56 parts from the bottom, make an extra line a little on 
 one side, or even on the opposite side to the graduation, and 
 write at it with the scratching diamond (128) Soda; lower 
 down at 48.96 parts, make another line, and write potash ; 
 still lower at 54.63 parts, a third line marked carl, soda ; and 
 at 65 parts a fourth, marked carb. potash. It will be ob- 
 served that portions are measured off, beneath these marks, in 
 the inverse order of the equivalent numbers of these sub- 
 stances, and consequently directly proportionate to the quan- 
 tities of any particular acid, which will neutralize equal weights 
 of the alkalies or their carbonates. As these points are of 
 
 * Quai-terly Journal of Science, xiii. 315, xiv. 234. 
 
 } Ure's Dictionary of Chemistry, introduction, p. xiii. Henry's Elements of 
 Chemistry, eighth edition, ii, 512. 
 
Sect. XII.] ALKALIMETRY ACID PREPARED. 273 
 
 great importance, it will be proper to verify them by weighing 
 into the tube first 350, then 453.7, then 510.4, and lastly 
 765.6 grains of water, which will correspond with the marks if 
 they are correct. Or the graduation may be laid down from 
 the surface of the four portions of fluid when weighed in with- 
 out reference to where they fall upon the general scale. The 
 tube is now completed, except that it should be observed 
 whether the aperture can be perfectly and securely covered by 
 the thumb of the left hand, and if not, or if there be reason to 
 think it not ultimately secure, then it should be heated and 
 contracted until sufficiently small. (Sect, xix.) 
 
 633. Diluted sulphuric acid must now be prepared to be 
 used with the tube. When of a specific gravity of 1.1268, it 
 will be very nearly, if not accurately, of the strength required ; 
 and this may be obtained by mixing one part by weight of 
 oil of vitriol of specific gravity 1.82, with four parts of water. 
 If, when cold, the specific gravity of this diluted acid be as 
 above mentioned 1.1268, it must be nearly, if not exactly, of the 
 strength required ; but before being admitted into use, should 
 be examined experimentally. Assuming it^ however, as being 
 absolutely correct, it will be found that a quantity measured 
 into the tube up to any one of the four marks described, is 
 sufficient to neutralize 100 grains of the dry alkali or carbo- 
 nate set down at the mark ; consequently, if water be added in 
 the tube, thus filled up to any one of the marks, until the 100 
 parts are full, and the whole uniformly mixed, one part of such 
 diluted acid will neutralize one grain of the alkali or carbonate 
 named at the mark, up to which the tube was first filled with 
 the acid of specific gravity 1.1268. 
 
 634. When a specimen of potash, barilla, or kelp, is to 
 be examined by this instrument, 100 grains are to be weighed 
 out, dissolved in warm water, filtered, the insoluble portion 
 washed, and the solution added to the rest ; by this process 
 the alkali will be separated from carbonate of lime, or other 
 insoluble matters, which otherwise might cause errors in the 
 estimation. The alkaline solution is to be put into a basin on 
 the sand-bath, and then the tube and acid prepared. For this 
 purpose some of the acid, of specific gravity 1.1268, is to be 
 poured into the tube until it rises up to the mark indicating 
 
 T 
 
274 ALKALIMETRY PROCESS DESCRIBED. [Sect. XII. 
 
 the substance to be tested for ; potash or carbonate of potash 
 for the potash or pearlash of commerce, and soda or carbonate 
 of soda for barilla or kelp : then water is to be added carefully 
 (402), until the hundred parts are filled, and closing the tube 
 with thejfinger, its contents are to be perfectly agitated and 
 mixed. 
 
 635. The alkali in the basin is now to be neutralized with 
 the acid in the tube. After having once placed the thumb of 
 the left hand over the aperture of the tube, it is not to be again 
 removed ; but inverting the tube by turning the hand so that 
 the thumb and the mouth of the tube are downwards, the acid 
 is to be let out gradually into the alkaline solution, by relaxing 
 the thumb and admitting a succession of small bubbles of air ; 
 the hot solution beneath is to be continually stirred, so as to 
 mix the acid instantly with the whole, and the operator must 
 proceed with increased caution as the point of neutralization is 
 approached. Very small quantities of the acid may be added, 
 by slightly relaxing the thumb so as to permit a minute quan- 
 tity, less than a drop, to flow to its extremity, and touching it 
 with the glass rod ; the final adjustment may thus be made 
 more accurately, than by dropping the acid from the lip of the 
 tube. The process must be carried on until the alkali is 
 found by the test papers to have been exactly neutralized 
 (625, 627) : then the tube must be inverted, the thumb re- 
 moved, drawing its under surface over the edge of the tube, so 
 as to leave as much as possible of the fluid that otherwise might 
 adhere to it, and having allowed the sides to drain, it must be 
 observed how many parts of acid have been used, the number 
 of which will indicate the number of grains of the alkali or 
 carbonate, contained in the 100 grains of the impure alkali 
 operated with. 
 
 636. With respect to the proper strength of the acid (633), 
 it is to be examined in the following manner : crystals of bi- 
 carbonate of potash are to be fused in a platina crucible, the 
 fluid poured out upon a clean, cold metal plate, and a piece of 
 the resulting solid, estimated to be 70, 80, or 100 grains, 
 weighed in water (72) ; in this way a known weight of pure 
 carbonate of potash will be obtained in solution. The solution 
 is then to be diluted, heated, and neutralized by acid from the 
 
Sect. XII.] ALKALIMETRY VERIFICATION OF THE ACID. 275 
 
 tube diluted as before described (633), from the mark of car- 
 bonate of potash. If it be found that as many parts of the 
 acid have been used as of grains of the carbonate weighed out, 
 the acid is of proper strength : if more acid has been used, it 
 is too weak; if less has been sufficient, it is too strong. Sup- 
 pose for instance that 100 grains of the salt (fuzed carbonate 
 of potash) had been used, and that 90 parts of the acid were 
 sufficient ; 'ihen these 90 parts ought to have occupied the 100, 
 and consequently the 100 parts contain one-tenth too much 
 acid, in consequence of the experimental acid itself containing 
 one-tenth more than it ought to do. Hence the latter must be 
 diluted with such a quantity of water as will make nine volumes 
 into ten, or by one-ninth its volume ; for as the 90 parts used 
 are to the 100 parts they ought to have occupied, so is any 
 number of parts by volume of the acid under trial, to the num- 
 ber of parts which it ought to occupy. The difference between 
 the two last numbers will give the quantity of water in volumes, 
 to be added to the acid expressed by the first of them, in order 
 to correct it and make it of proper strength. On the contrary, 
 if it were found that the 100 parts were insufficient, and that 
 10 parts more of similar acid were required, then there is too 
 much water by one-eleventh of the whole in bulk, the correc- 
 tion for which would be one-tenth more of the 35 parts of acid 
 put into the tube up to the mark 65 carb. potassa. This 
 tenth is 3.5 parts, but as only a fifth of that or 0.7 parts is acid, 
 therefore 0.7 parts by weight of the same oil of vitriol that was 
 used before must be added for every 35 parts of the mixed 
 acid. The correction in any other case may be easily made, 
 by considering that the number of parts over a hundred which 
 are necessary to saturate the 100 grains of carbonate of potash, 
 are proportionate to the quantity of oil of vitriol which must 
 be added to bring the experimental acid to proper strength : 
 thus if 136 parts of the diluted acid were used, then thirty-six- 
 hundredths more of the weight of oil of vitriol already used 
 must be added; and the quantity of oil of vitriol that was 
 added at first being known to be one-fifth by weight (633), 
 the additional quantity required is easily ascertained. These 
 corrections are not strictly accurate, but sufficiently so to meet 
 
 T 2 
 
276 ALKALIMETRY PRECAUTIONS REQUIRED. [Sect, XII. 
 
 even the exaggerated cases put of a difference of 10 parts, and 
 to bring it within the limit of errors of experiment. 
 
 637. Sometimes instead of using test papers, a little of the 
 neutralized "Blue cabbage liquor (616), or of infusion of litmus 
 may be put into the alkaline solution ; the former immediately 
 assumes a green tint : and by attending to the change effected 
 by the addition of the acid, and noticing the point when blue- 
 ness is again restored to the cabbage-colour, or when the 
 litmus becomes reddened, the indication of neutrality is suf- 
 ficiently evident and accurate for general purposes. The test 
 by papers is, however, more precise. 
 
 638. Some of the impure sources of potash and soda used 
 in the arts, contain amongst other substances sulphuret and 
 sulphite of alkali. Both these occasion errors in the mode of 
 estimation above described, to obviate which MM. Welter 
 and Gay Lussac^ advise, that after the soluble parts have 
 been separated by water, a little chlorate of potash should be 
 added to them, the whole evaporated and heated to redness. 
 This converts the sulphuret and sulphite into neutral sulphate,, 
 and then upon redissolving the whole, the caustic and carbo- 
 nated alkali may be ascertained as before described. 
 
 639- A process of neutralization, quite the same in principle, 
 may be adopted for the purpose of estimating the strength of 
 acids, but from circumstances it is not often used, and being 
 easily comprehended from the above directions, claims no 
 further notice here. Acetic acid is at present the substance 
 which most frequently requires some such estimation as the 
 above, both because its specific gravity varies very little with 
 its strength, and because it is much in use in the arts in an 
 impure state. Dr. Paris has pointed out the exact agreement 
 between the equivalents of acetic acid and carbonate of lime, 
 and has proposed to estimate the strength of this acid, by 
 allowing it to act upon a known weight of fragments of carbo- 
 nate of lime, and ascertaining the quantity dissolved, which 
 will at once express the quantity of pure acid present. Vine- 
 gar, however, or impure acetic acid is not very readily neu- 
 tralized by pieces of carbonate of lime. 
 
 * Annales de Chimie, xiii. 212. 
 
Sect. XII.] ACIDIMETRY' MINERAL ACIDS. 277 
 
 640. In the same manner muriatic, nitric, and any other 
 acid, which forms a neutral soluble salt with lime, and has had 
 its equivalent number well ascertained, may be estimated, and 
 its strength become known. Thus let 500 grains of the acid 
 be put into a basin or flask with 100 grains of marble in frag- 
 ments, and after the first effervescence is over, warmed, and 
 the neutrality ascertained ; the solution is then to be poured 
 off, and the remaining pieces of marble washed, dried, and 
 weighed. The number of grains of carbonate of lime dis- 
 solved in muriatic acid multiplied by 0.74, indicate the num- 
 ber of grains of dry acid by which it has been dissolved ; and 
 the number dissolved in nitric acid multiplied by 1.08, also 
 represent the equivalent of dry nitric acid, or the quantity pre- 
 sent in the solution submitted to experiment. 
 
 SECTION XIII. 
 CRUCIBLE OPERATIONS FUSION REDUCTION. 
 
 641. OPEN vessels, intended to receive bodies to be subjected 
 to high temperatures, have received the name of crucibles. 
 They are very various in form and material, both for the sake 
 of economy and to fit them for peculiar uses. By far the 
 greater number are formed of earthen ware ; they are cheap, 
 they resist a high temperature, and also the action of most 
 bodies which, from their fixedness, admit of or require the 
 application of heat. They must, however, be distinguished 
 from each other. 
 
 642. Ordinary English crucibles are easily scratched by a 
 knife or glass, and break with a granular crumbling fracture. 
 They are useful for many common purposes, may be had of a 
 triangular or circular form, with covers of the same material, 
 and are cheaper than any others. They will bear a bright red 
 heat, but will not resist a very high temperature ; for in it they 
 soften and froth, and frequently occasion the loss of their con- 
 
278 CRUCIBLES HESSIAN CORNISH. [Sect. XIII. 
 
 tents. In consequence of their approach to fusibility when 
 hot, fluxes render them quite fusible, for which reason they 
 will not retain these agents long. The latter find rapid entrance 
 and access to the interior in consequence of the porosity and 
 softness of the vessels, which, of course, allows easy penetration 
 by the fluid : after being heated for a short time with a 
 coloured flux, and then cooled and broken, the extent to which 
 these agents penetrate them may be readily observed. 
 
 643. Hessian crucibles very far surpass the common English 
 vessels in resistance of high temperatures and the action of 
 fluxes. When powerfully heated even to softening, they do 
 not become vesicular. They are triangular, but are not ac- 
 companied with covers, a want very often felt in the laboratory. 
 They are usually .of a brown colour, are harder than English 
 crucibles, scarcely yielding to a knife or to glass; they are 
 more compact, and are interspersed with black particles ; the 
 fracture is sharper. The price is about 7d. for the nest of five 
 or six crucibles. 
 
 64)4. Cornish crucibles. Round crucibles of different sizes 
 are made in Cornwall, for the use of the assay masters, and 
 are plentiful there, but not common in London. They may 
 be bought of Mr ? Beauchamp, 22, Grafton-street^ Soho. They 
 are equally good with the Hessian crucibles. They resist a 
 very high temperature, and on softening do not become vesi- 
 cular and frothy. They agree with the Hessian crucibles in 
 hardness, fracture, and in all points except colour, being white 
 or nearly so ; covers of the same material may be obtained. 
 
 645. Wedgwood's crucibles are made of a close white ware, 
 and hence, though thin, it is difficult to dissolve them, and 
 they retain fluxes at moderate temperatures longer than other 
 crucibles. They are round, well formed and finished, and 
 their covers fit with considerable accuracy. They are liable to 
 crack when heated, or if this be prevented by care, they fre- 
 quently do so in cooling, which renders it necessary to use 
 much caution during change of temperature. They bear a 
 moderately high heat, surpassing in that respect the common 
 English crucible, but not equalling the Hessian or Cornish. 
 
 646. Blue pots or black-lead crucibles are made of a mix- 
 ture of coarse plumbago and clay, and are generally of large 
 
Sect. XIII.] CRUCIBLES MOST REFRACTORY. 279 
 
 si/e, being intended principally for use in the arts. They 
 bear a higher temperature than the English crucible, are not 
 so liable to crack when suddenly heated or cooled, and resist 
 the action of fluxes better than most others at moderate fur- 
 nace temperatures ; but as they contain abundance both of 
 iron and charcoal, they cannot be used in experiments where 
 either the one or the other would be injurious. Covers to 
 these crucibles of the same material may be obtained. 
 
 647. Attempts have been made to improve earthenware 
 crucibles, but as yet none equalling the Hessian in the power of 
 sustaining a high temperature unchanged have been produced 
 in this country except the Cornish. Those made by Marshall * 
 and Anstey f are said to approach in some properties to the 
 blue pots. They are made of Stourbridge clay and pulverized 
 coke ; Anstey's are not baked previous to use. These vessels 
 bear temperatures equal almost to those which are sustained 
 by a Cornish or Hessian crucible, and with care are but little 
 subject to crack in the fire. They are principally in use as 
 melting pots. 
 
 648. Of all these varieties the Hessian and Cornish crucibles 
 are the most valuable in the laboratory. They are generally 
 used singly, and uncoated, but on particular occasions it is 
 advantageous to place one in another, and by taking two 
 successive ones from a nest, a double crucible may thus be 
 obtained, which is not very clumsy. They should not be put 
 simply one into the other and then used, but Stourbridge clay 
 (1101), mixed with water into a smooth and rather soft paste, 
 should be put at the bottom and about the inside of the larger, 
 in such quantity that, on introducing the smaller, and applying 
 pressure, it may come in contact with the clay in every part, 
 the excess being thrust out at the edge between the two vessels. 
 It requires some power to force in the smaller crucible and 
 displace the excess of clay. This object is best effected 
 by placing the crucibles with the mouths downward on a 
 table, and pressing on the bottom of the larger, whilst a little 
 twisting or lateral motion is given, until its edge is also in 
 contact, or nearly so, 'with the table. The two crucibles being 
 thus by the intervening clay compacted into one, must be put 
 
 * Trans, Soc, Arts. xU. 52. f Ibid, xliii, 32. 
 
280 CRUCIBLES OF CHARCOAL LINED. [Sect. XIII. 
 
 into a warm place (605) and left for some days to dry. They 
 must not be used in a damp state. 
 
 649. A Wedgwood's crucible is sometimes advantageously 
 luted, and is then not so liable to crack by the heat as if un- 
 protected. Or, sometimes one may be placed as a lining 
 within a Cornish crucible ; but being more delicate, less force 
 must be used than in the case above (648), and the paste of 
 Stourbridge clay is to be made somewhat thinner. 
 
 650. Charcoal crucibles are very convenient for certain 
 operations of reduction. Klaproth recommends that they be 
 formed by making a cavity in a piece of well burned charcoal, 
 answering to the size of the substance to be operated with, 
 with a charcoal stopper to close the mouth. The charcoal 
 vessel is then to be fitted into a common clay crucible, which 
 last is to be well covered and luted. 
 
 651. Stoppers or covers may be made out of solid charcoal, 
 and as that of alder wood does not crack or fly to pieces when 
 heated, it is best adapted for the purpose ; but it is requisite 
 previously to heat the charcoal to a high degree, in consequence 
 of the contraction which that substance undergoes, and which 
 appears to be proportionate to the temperature it is submitted 
 to. Charcoal made as it usually is, by mere ignition, when 
 fitted and then subjected to high heat, will be considerably 
 deranged, from the contraction occasioned by a greater tempe- 
 rature; but if previously strongly ignited this derangement is 
 avoided. 
 
 652. For a similar purpose it is often advantageous to line 
 crucibles with charcoal. The charcoal should be pulverized, 
 and the more compact and close the lining is required, the 
 finer should be the powder; for in consequence of the porosity 
 of charcoal its powder lies in a much smaller space than the 
 solid or coarsely pounded substance. It is to be mixed with 
 weak gum water, not putting so much as to make it adhere, 
 but forming with it a moist powder ; the crucible is to be lined 
 with a coat of this, from the fourth to the half of an inch 
 or more in thickness. The cavity is to be finished by a 
 smooth mould, or rather core, as the end of a pestle or a 
 properly formed piece of wood ; and having pressed the lining 
 as hard as possible with this, it is to be withdrawn carefully, 
 
Sect. XIII.] CRUCIBLES PLATINA SILVER. 281 
 
 first giving a little rotatory or lateral motion, so as to set 
 it free from the lining without causing derangement. The 
 crucible is then to be set in a warm place to dry (605). 
 
 653. Amongst metallic crucibles, those formed of platina 
 are most generally useful : they should be accompanied by 
 covers of the same metal. They are usually made with a flat 
 bottom meeting the sides at a sharp angle, and then have the 
 advantage of standing steadily ; but they are peculiarly liable 
 to injury at this angle, not only because they are often thinner 
 there than elsewhere, but from blows upon the outside, and 
 from endeavours by means of hard instruments to loosen their 
 contents. The substance adhering to it should, on account of 
 the value of a platina crucible, be loosened as much as pos- 
 sible by solution, and afterwards removed by smooth or blunt 
 bodies, as glass rods, or spatulas. By making the crucible 
 with a round bottom, or egg-shaped, the disadvantages attend- 
 ing the angle are avoided, but the inconvenience of not standing 
 by itself is incurred. It is however, when hot, easily sup- 
 ported in the sand-bath, and when cold, either there or on the 
 top of a test-glass (505). The two forms are equally well 
 supported in the furnace. 
 
 654. Platina capsules have been before referred to (371). 
 They are useful in heating bodies either in the furnace or by 
 the spirit-lamp, and often supply the place of crucibles. When 
 a cover is wanted, one will serve that purpose to another, or 
 even to the platina crucible itself; and the crucible cover may 
 be useful in conjunction with the capsules. 
 
 655. A platina crucible may often be inserted with advan- 
 tage into a Cornish one, but it is better not to introduce any 
 intervening substance. The metal crucible is thus protected 
 from impurities in the fuel, and from the forcible action of 
 the tongs in moving it into and out of the furnace. 
 
 656. A silver crucible and cover is a useful vessel ; it may 
 in many cases be used instead of the platina crucible, and 
 being of a cheaper metal, may be formed of larger size. It is 
 of great service in the evaporation of mineral waters, and 
 various solutions. It should be of pure silver. It should be 
 carefully attended to when heated, because silver fuses at a 
 full red, or rather yellow heat; and because in a furnace, 
 
282 CRUCIBLES GOLD METALLIC. [Sect. XIII. 
 
 amongst the fuel, there are frequent air-ways and currents of 
 small extent, by which one part of a crucible is rendered much 
 hotter than another. It should be understood, that as the 
 heat approaches the fusing point, there are certain temperatures 
 at which the crucible will appear quite whole and sound, even 
 when it is so friable and brittle, that if held at one edge, its 
 weight is sufficient to break a piece out. Hence it is best 
 never to trust it in any other than the crucible furnace (158), 
 where it can be most conveniently watched, and where the 
 heat is not so liable to rise unobserved as in a close furnace. 
 It may sometimes be put with advantage into a Cornish or a 
 Wedgwood crucible. 
 
 657. Klaproth, who has the merit of first applying fixed 
 alkalies to the analysis of minerals by heat, found silver and 
 platina crucibles so much acted upon by them, as to be induced 
 to make, and earnestly to recommend, a vessel of pure gold 
 for this purpose. Such a crucible is by no means liable to the 
 same kind or extent of injury as the former, but is very fusible 
 in the fire. 
 
 658. No other furnace fuel than charcoal should ever be 
 used to metallic crucibles. The sulphureous fumes which rise 
 from coke and coal injure them ; and iron and other sub- 
 stances present do not merely form slags, which adhere to the 
 vessels and soil them, but actually corrode and destroy them. 
 
 659. These crucibles gradually deteriorate and become 
 injured by successive operations : platina frequently rises into 
 blisters, which are exceedingly inconvenient, not merely as 
 weakening the vessel, but as forming cavities ; portions of the 
 matter fuzed in the crucible are retained in these cavities, and 
 being very difficult of removal, often remain and cause injury 
 by contaminating the future operations. The surface of the 
 metal, also, gradually becomes roughened, and the whole is 
 rendered more or less brittle. The purest platina undergoes 
 these changes in time, partly perhaps from the fumes of the 
 fuel in the furnaces, or the slight, but successive action of the 
 substances heated in it. Silver crucibles change much more 
 rapidly, and after some time acquire a crystalline structure 
 and become very brittle. 
 
 660. An iron crucible is occasionally required ; though but 
 
Sect. XIII.] CRUCIBLES APPROPRIATED. 283 
 
 seldom for experiments of ignition. On the whole, though a 
 more fusible material, it is better of cast than of wrought metal. 
 
 661. When, in the absence of crucibles, an extemporary 
 vessel of this kind is required, it may either be a tobacco- 
 pipe, or a piece of green glass tube luted, or a china cup or 
 its fragments. 
 
 662. In the appropriation of metallic crucibles to particular 
 uses, it is to be observed that fusible metals, or compounds of 
 metals likely to be reduced, must never be heated in vessels of 
 silver, gold, or platina; otherwise alloys will be formed, the 
 crucible destroyed, and its contents lost. Even several chlo- 
 rides which are unchanged in and cause no injury to glass, 
 will, when heated in platina under ordinary circumstances, 
 injure it. This is the case with chloride of lead, which being 
 partially reduced, the crucible becomes lined with an alloy of 
 lead, and seriously injured. It is the same with oxide of lead 
 and many compounds containing that metal, such as flint glass. 
 These crucibles should be used, therefore, only with infusible 
 substances in mass or powder, or with such fluids as will not 
 act upon them. In analyses the chemist is frequently obliged 
 to heat alkalies in them, because no other vessels resist their 
 action so well. Caustic alkalies act at a high temperature 
 upon both platina and silver, though not rapidly : the action 
 is much increased by free access of air, and seems to be 
 dependant in part upon the formation of a portion of the per- 
 oxide of the alkaline metal, oxygen being afterwards trans- 
 ferred from it to the crucible. The carbonated alkalies do not 
 act upon either, but they cannot be fused safely in silver, from 
 the high temperature they require. When charcoal is mixed 
 with the carbonated alkalies, action takes place slowly on pla- 
 tina, perhaps in consequence of the formation of a portion of 
 potassium. 
 
 663. When the characters exhibited by earthy bodies, upon 
 being heated, are to be ascertained, the earths must not, as 
 Klaproth has shewn, be put into earthen crucibles*. Vitri- 
 fication frequently takes place, in consequence of an action 
 which occurs at the surface of contact, when it would not hap- 
 pen in crucibles of charcoal or metal. 
 
 * Klaproth's Analytical Essays, vel. ii., pp. 35, 36. 
 
284 CRUCIBLES EARTHEN HEATED. [Sect. XIII. 
 
 664. Earthen crucibles are best adapted for the retention of 
 metals at high temperatures, and consequently for all experi- 
 mental attempts to reduce them ; but there are certain liabili- 
 ties to which they are subject, of which the student must be 
 aware. The action of fluxes upon them has been already 
 noticed (642), and it is such that they will not stand in the fire 
 beyond a certain time, proportionate to the temperature and 
 dissolving power of the flux. They also occasionally yield 
 substances to the bodies heated in them ; thus platina heated 
 highly with charcoal in an earthen crucible, will be found to 
 have combined with silicon, if at least the temperature has been 
 carried up to the fusing point ; and either wrought or cast- 
 iron, in like manner heated intensely in an earthen crucible, 
 will be found to have acquired silicon, and perhaps aluminum. 
 
 665. Finally with reference to the selection of these vessels, 
 it is generally best to reject an earthen crucible that has once 
 been used, except it be large, in good condition, and required 
 for a repetition of a former process. For the numerous small 
 and varied experiments made in the laboratory, it is always 
 advisable to commence with clean vessels, and to throw them 
 away when done with, lest any impurity should be communi- 
 cated to an important result. The cheapness of crucibles 
 removes the charge of extravagance from such a practice ; one 
 failure in an experiment is of more consequence than the 
 second use of several earthen crucibles. 
 
 666. The apparatus for the application of heat requisite for 
 crucible operations, as lamps, furnaces, &c., have been already 
 described (Sect, iv.) ; so that now there remains but to notice 
 such circumstances as peculiarly relate to their use with cruci- 
 bles. The small and the large spirit lamps (199, 205, 228) 
 answer well for platina crucibles and capsules, when the heat 
 they communicate is sufficient ; for no fumes arise which can 
 occasion injury to the metal. If the tranquil flame of the 
 lamp be hardly sufficient, the broken flame obtained by the 
 blow-pipe before described (283, 245) may be used. The 
 
 crucible may be conveniently sup- 
 ported by a piece of iron-wire, bent 
 so as to form a ring at each end, 
 one about two-thirds of an inch and the other one and a quarter 
 
Sect. XIII.] 
 
 CRUCIBLES HEATED JACKETS. 285 
 
 inch in diameter, separated by a straight line seven inches in 
 length ; the wire should be pushed, before being bent, through 
 a couple of phial corks, which, when brought to the middle of 
 the straight part, serve as a handle, and prevent the hot metal 
 from burning the hand. 
 
 667. The heating power of the tranquil flame is much 
 
 economised, and the temperature of 
 the crucible increased, by using a 
 jacket like that represented partly in 
 section and partly in perspective in 
 the wood cut. It is to be made of 
 sheet copper or iron, open at the top 
 and bottom, and within it, three pro- 
 jecting slips of iron-plate are to be 
 fixed by rivets, intended to support 
 the crucible on their edges. This jacket is to be sustained on 
 the ring of a retort stand, the crucible placed within it, and 
 the spirit-lamp beneath. The supporting slips should be of 
 such dimensions as to leave a space of about the third of an 
 inch between the crucible and the jacket, in which the flame 
 moving tranquilly, wraps itself around the crucible, and as no 
 flickering motion takes place, every portion is thus effectually 
 applied. The loss of heat from the crucible by radiation and 
 contact of cold air, is very much diminished, and this is still 
 further lessened when the cover is on the crucible. A very 
 important difference in the temperature of the contents of a 
 metallic crucible, depends upon the circumstance of the cover 
 being on or off. The spirit-lamp used to heat the crucible 
 must bear some proportion to the size of the vessel, and the 
 quantity of its contents. The two mentioned (199, 205) are 
 sufficient for most purposes when platina crucibles are used. 
 
 668. The jacket is also of highly advantageous application 
 in the use of an oil (212, 213) or gas-lamp (215), and is often 
 economical in distillations, evaporations, &c. A second, on a 
 larger scale, must then be used for the larger sized retorts, 
 and it should not have supporting slips within, but the jacket 
 and retort should be sustained independently of each other; for 
 otherwise the edges, from the rapid manner in which they be- 
 come heated, would often occasion the fracture of the glass. 
 
286 CRUCIBLES HEATED FURNACES ARRANGEMENT. [Sect. XIII. 
 
 669. In considering the relations of furnaces to the crucibles 
 that may be heated in them, it is hardly necessary to notice 
 the table-furnace (169). Any crucible less than six inches in 
 height, and four inches in diameter at the top, may be heated 
 to full redness in it. It may be set on the fuel and raised now 
 and then when needful by tongs, or be put upon a square 
 piece of soft brick about an inch thick, placed upon the bars. 
 As before mentioned, coke should be the fuel used (192), and 
 a cover (of common English ware or black lead) should be 
 applied, when the highest heat is required ; the furnace-door 
 should be shut, the ash-door open, plenty of fuel around and 
 upon the crucible, and all extra flues communicating with the 
 chimney closed. 
 
 670. When a crucible is to be heated in a crucible-furnace 
 (158), the grate should be placed in it not less than half way 
 from the top (160). The furnace should be of such a size 
 as to allow at least two inches of space for fuel all round 
 the crucible, when the latter is two inches in diameter or less, 
 and somewhat more if it be so much as three inches in di- 
 ameter: this will permit the supply of fuel in sufficient quantity 
 to produce a strong heat. When a fire is to be lighted in the 
 furnace, a few pieces of charcoal may be put into a common 
 fire, and when ignited placed in the crucible furnace, and 
 being afterwards covered by charcoal, the combustion will 
 soon become sufficiently vivid. If the crucible to be heated be 
 of platina, it may be placed on the fuel, the cover put on, 
 and charcoal added to the sides. Unless a strong heat be 
 required, it will not be necessary to place fuel over the cru- 
 cible, but if there be occasion for a high temperature, the fuel 
 is to be piled up, and even the flue (165) used. As the fuel 
 sinks, it must be re-adjusted with the tongs, the crucible 
 raised, and, if the heat has not been continued long enough, 
 fresh fuel is to be added. The crucible should never be al- 
 lowed to sink to the grate. If it contains a soft or pasty 
 substance, it should be carefully watched, to prevent its posi- 
 tion from being deranged, or the cover displaced. It will 
 acquire the highest temperature when about an inch and a 
 quarter from the grate, equally distant from the sides of the 
 
Sect. XIII.] ARRANGEMENT IN THE FURNACE FUEL. 287 
 
 furnace, covered with about an inch of fuel, and with the 
 temporary flue over it. 
 
 671. If the heat is to be continued longer than during the 
 combustion of one charge of fuel, a stand should be used for 
 the crucible. This may be a small crucible about one inch 
 and a half high, turned upside down, with a little sand or 
 clay between it and the experimental crucible; or an English 
 cylindrical crucible with the mouth upwards, either empty 
 or filled with sand ; or a small round pillar of soft brick (1354). 
 It should be put into its place, the furnace lighted, the cru- 
 cible arranged, the fuel added, and the heat raised. The fuel 
 should not be suffered to burn down very low, nor should 
 much be added at once ; but the addition should be gradual 
 and continual, that the crucible may never be left exposed to 
 the air if the experiment has in the first instance required it to 
 be covered. Cold fuel suddenly diminishes the temperature of 
 that part of the fire with which it comes in contact, which if 
 it occur where the crucible itself is situated, causes injurious 
 variations in its temperature. 
 
 672. The temperature of a furnace should never be al- 
 lowed to rise and fall suddenly and irregularly, whilst an ope- 
 ration is going on. Such changes are liable to affect the tem- 
 perature of the crucible, and even to cause its fracture. 
 
 673. The utmost heat that can be given to a crucible is to 
 be attained in the laboratory by such a blast-furnace as has 
 been already described (184) ; the fuel being coke or coke and 
 charcoal, (187, 191, 193.) When of the dimensions specified, 
 it will heat a crucible three inches and a half high, and two 
 inches and three-quarters in its upper diameter, very highly ; 
 and one not more than one inch and three-quarters diameter at 
 the top, intensely. To acquire the most powerful heat, the 
 crucible should be raised about one and a half or two inches 
 from the grate, and covered with at least the same depth of 
 fuel. Hence arises a necessity for supports and covers, capable 
 of resisting intense temperatures. The best supports would be 
 crucibles made of the Cornish or Hessian clay, of a cylindrical 
 form, from one and a half to two inches in height, and from 
 half an inch to an inch internal diameter ; the closed end being 
 put upon the grate, and the bottom of the crucible on or into 
 
288 CRUCIBLES SUPPORTED COVERS. [Sect. XIII. 
 
 the aperture above, where it would be steadily retained. But 
 in the absence of such supports, recourse must be had to 
 Cornish or Hessian crucibles, and one being selected with a 
 flat bottom, it must be placed upside down, with the mouth 
 upon the grate. From the irregular form of the bottoms of 
 these crucibles, and the necessity of choosing them as narrow 
 as possible, that the fuel may be close to all parts of the cruci- 
 ble to be heated, the latter is necessarily, when simply placed 
 upon the stand, very tottering ; it is, therefore, generally ad- 
 visable to lute the crucible and stand together with a little 
 Stourbridge clay, a small portion being put between the two 
 surfaces, and more at the side, so as in fact to make the two 
 vessels into one, their bases being attached together. Such 
 luting must be well dried for a day or two before it is placed 
 in the furnace (1084). 
 
 674. With respect to covers, the arrangement is more diffi- 
 cult, in consequence of the absence of those necessary accom- 
 paniments to Hessian crucibles, and the uncertainty attending 
 the supply of them with Cornish crucibles. Suppose that iron 
 or steel is to be heated without contact of carbonaceous or ex- 
 traneous substances of any kind. A common English cover 
 will not answer the purpose, because it will melt and run into 
 the crucible. A larger crucible of the same kind may be 
 turned over it, and luted at the edges ; but this inconveniently 
 increases the size of the mass to be heated, which, when the 
 highest temperature is required, should be as small as possible. 
 A smaller crucible of the same kind may be inverted and put 
 inside the other, and the interval filled by a luting of Stour- 
 bridge clay ; but the heat contracts the " lute, the fissures of 
 which may receive particles of fuel and slag. This is the more 
 probable, because in all cases of a blast in the furnace from 
 below upwards, there is an eddy in the stream of air above the 
 crucible, which stands as a fixed obstacle in the current, and 
 which causes the return and accumulation of numerous small 
 particles upon the top. 
 
 675. The method that has been found to answer best, is to 
 beat up some Stourbridge clay with water into a stiff paste, to 
 make it into a cake the fourth of an inch thick, to put it over 
 the top of the crucible, to press it down with a common English 
 
4 
 
 Sect. XIII.] CRUCIBLE IN FURNACE FIRE LIGHTED. 289 
 
 cover of proper size, so as to force a cake of the damp clay into 
 the crucible, and cut off the excess by its edge, and then to 
 finish by luting the edge of the cover and the side of the cru- 
 cible together. This is to be done before the crucible is luted 
 upon its stand, and the whole is to be well dried previous to being 
 used. When heat is applied, the internal cover of lute becomes 
 baked, and though it diminishes in size, yet from the form of 
 the crucible, it seldom sinks down to the charge ; and if the 
 English external cover soften and fuse, it is still supported on 
 the former, and generally serves to keep out impurities. 
 
 676. When the crucible is of charcoal, or is lined with char- 
 coal, and consequently has a charcoal stopper inside (651), the 
 common cover may be put directly over it and luted ; and 
 even in plain crucibles, when charcoal is not injurious, an in- 
 ternal cover of it, formed out of one or several pieces, may be 
 used instead of the plate of lute, and the ordinary cover then 
 put over it. 
 
 677. The furnace being clean and in order, and the crucible 
 with its luted cover and stand dry, the latter is to be placed 
 steadily on the grate of the furnace ; a few pieces of lighted 
 charcoal are to be dropped in and covered by cold charcoal to the 
 depth of two or three inches, and the whole left until the com- 
 bustion has spread amongst the fuel ; the air will find sufficient 
 access through the aperture beneath. When the crucible 
 becomes warm, coke is to be added so as to cover it, and the 
 temporary flue (165) is to be adjusted, to assist the draught. 
 When the fuel is nearly red-hot an inch or two below the sur- 
 face, more coke is to be added until it rises about two or three 
 inches above the crucible, the flue is then to be replaced, and 
 the combustion to proceed until the crucible itself is red hot. 
 This will occupy perhaps an hour, and require attention only 
 at the short intervals when coke is to be added. The course 
 described is adapted to the object of raising the heat steadily 
 and gradually to redness ; it may be well to explain, that the 
 coke should not be put on until the crucible has been some- 
 what warmed by the charcoal, to prevent the deposition upon 
 it of the water driven -from the fuel. Having attained a red 
 heat, the flue must be removed, the bellows applied (185, 188), 
 
 u 
 
$ 
 
 290 CRUCIBLE IN BLAST-FURNACE 'DEFENDED. [Sect. XIII. 
 
 # 
 
 slowly at first, and more powerfully as the heat rises, until the 
 highest point required, or that is possible, be attained. 
 
 678. It is very desirable that the heat should be raised 
 regularly, and sustained steadily. For this reason the blast 
 should not be variable, but uniform. As the combustion goes 
 on the fuel will generally fall freely, but it should be touched 
 now and then by the tongs or an iron rod, in order that, if 
 hollow places should occur, they may be filled up without 
 delay. The fuel should never be allowed to burn away very 
 low and then a large quantity of cold fuel piled on ; but it 
 should be supplied at small intervals, the top of the crucible 
 never being left uncovered, except purposely, to observe that 
 it has not melted down. Cold fuel should not be allowed to 
 come in contact with it ; even bright red-hot fuel will cool a 
 white-hot crucible. All these precautions in heating the cru- 
 cible are necessary, to insure the fullest advantage that may be 
 attained in the short time which an operation in this furnace 
 generally requires. When the crucible is large, or double, or 
 is lined with charcoal, or contains a considerable charge, it is 
 some time before it acquires a temperature approaching to that * 
 of the fuel on the outside ; and if the heat has been raised in 
 an intermitting manner, or if the fuel, after being allowed to 
 burn low, has been replenished by cold portions, the furnace 
 may have appeared very hot occasionally, and yet no propor- 
 tionate effect be obtained within the crucible. 
 
 679. When very high temperatures are required, as in the 
 fusion of platina or rhodium, the crucibles become so soft as to 
 sink and fold like leather, and the results are often lost. This 
 is sometimes due in part to the pressure of the fuel upon the 
 crucible, and may be prevented by hanging a shelter over it. 
 A long narrow English pot, having a mouth a little larger than 
 the crucible to be heated, is to be selected, and a hole made 
 through its bottom ; by passing an iron rod with a hooked end 
 through this hole, the pot may be suspended in an inverted 
 position over the crucible and within half an inch of it, thus 
 preventing the contact of the fuel with its top. Care will be 
 requisite that the expansion of the rocl and vessel, as the heat 
 rises, should not cause the latter to press upon the crucible. A 
 
Sect. XIII.] CRUCIBLE MOVED TONGS IGNITION. 291 
 
 great depth of fuel is, on these occasions, to be preserved in 
 the furnace round the shelter, to compensate as much as pos- 
 sible for its effect in diminishing the temperature ; and this, 
 with a little more than common application of the bellows, is 
 always sufficient for the purpose. In this way many crucibles 
 and their contents have been saved, which, from the average of 
 experiments without the shelter, there is reason to believe 
 would have been lost. 
 
 680. When an operation in this furnace is considered as 
 concluded, it is best to withdraw the bellows, and to let the 
 temperature sink a little before the crucible is disturbed, other- 
 wise the heat will be unbearable, and the vessel, from its soft- 
 ness will be liable to injury. If allowed to cool entirely in the 
 furnace no harm results, and occasionally much advantage. 
 
 m 
 
 
 
 681. Whether this or any other furnace be used, care is 
 
 necessary in moving the crucibles with the tongs when in the 
 fire, or in putting them in and taking them out. If heavily 
 laden, and nipped by the tongs at one edge, they should not 
 be held too upright, lest the weight break them. Attention 
 should also be paid that no impurity be communicated to 
 their contents, from the tongs or from the fuel, by awkward 
 management. If the charge is fluid, as in analytical processes, 
 ^ the tongs should never touch any part of the inner surface 
 where the fused matter has adhered, lest they not only convey 
 , impurity, but remove a part of the charge. 
 
 682. The following general remarks upon the objects of 
 these operations may be useful. If the object be the ignition 
 of a mixture for analysis, or the desiccation of analytical pro- 
 ducts, then a platina crucible with its cover, raised either by 
 the lamp or the charcoal furnace to a moderate red heat, is 
 sufficient. When the substance is to be weighed, or the loss 
 
 of weight ascertained, the crucible is first to be counterpoised, 
 then weighed with the substance in it, afterwards heated and 
 j ^ weighed again to ascertain if there be loss. The remaining 
 substance is then to be removed, and the crucible weighed for 
 the last time, to see .that the counterpoise continues correct. 
 Or if it be a substance to be dried, as silicia, it is first to be 
 weighed, then heated carefully and weighed with the crucible 
 after it has been heated ; the substance is then to be removed, 
 
 ** ' ,*t * U2 
 
292 ALLOYS PRECAUTIONS IN MIXING FLUXES. [Sect. XIII. 
 
 the crucible wiped, and the diminution of weighed ascertained, 
 In that way the quantity of dry matter it contained may be 
 estimated better than by transferring the substance itself to 
 the pan and weighing it, or if the latter be done, the weight 
 may be verified by the former method : for it is easier to re- 
 move and clean all the substance out of the crucible, than to 
 put it all into the balance pan. If a substance to be fused or 
 dried decrepitate by heat, it should first be pulverized (315), 
 or in less precise cases the crucible should be covered. If the 
 object be to observe the changes that may take place in bodies 
 by heat, attention must be paid to the precaution pointed out 
 by Klaproth (663) and others, as to the mutual action of the 
 crucible and the substance. ^ 
 
 683. When the end to be obtained is the mutual action of 
 bodies, then the crucible, being charged, is to be heated gra- 
 dually, fluxes being used as seldom as possible ; for although 
 they are very advantageous in cleansing the reduced metal, 
 and assisting its separation from embarrassing impurities, they 
 corrode and weaken the crucible, as before mentioned (642), 
 In making alloys, the metals are to be well agitated together ; 
 for in some cases, even when apparantly miscible and well 
 mixed, there is, as Mr. Hatchett has shewn, a remarkable ten- 
 dency to separation*. In the preparation of alloys, and the 
 fusion of some metals, it is advantageous to cover the surface 
 of the metal with pieces of charcoal, to prevent oxidation. In 
 these cases a loose cover should be put on after the charcoal, 
 to hinder the access of air, and prevent combustion as much 
 as possible. 
 
 684. When, in an analytical process, potash is to be used, 
 which alkali may be added as carbonate, then the bicarbonate 
 is very serviceable, for it will fuse down without ebullition, an 
 effect which always takes place if the carbonate is used, or even 
 pure potash, and is often injurious. 
 
 685. Fluxes are very frequently required in cases of chemical 
 action amongst metallic compounds at high temperatures, and 
 often cannot be dispensed with. Their use is to protect the 
 substance from the air ; to dissolve impurities which would 
 otherwise be infusible ; and to convey active agents, as char- 
 
 * Philosophical Transactions, 1803. 
 
Sect. XIII.] WHITE FLUX BLACK FLUX CRUDE TARTAR. 293 
 
 coal and reducing matter, into contact with the substance 
 operated upon. 
 
 686. White flux is made by deflagrating a mixture of equal 
 parts of nitre and cream of tartar in a large earthen crucible, 
 heated red-hot at the bottom. The mixture should be intro- 
 duced in successive small quantities, the combustion of one 
 portion being allowed to arrive nearly to a termination before 
 another is thrown in, or the substance will be blown out of the 
 crucible. That part of the flux which has been in contact 
 with the sides of the crucible, when removed from it, should 
 be separated from the rest, and preserved apart ; a little earthy 
 matter being usually derived from the vessel, which, though 
 ordinarily of no importance, may be of consequence in delicate 
 experiments. The flux should be retained in a closed jar or 
 bottle. It consists almost entirely of carbonate of potash, the 
 nitric acid of the nitre and the combustible tartaric acid of the 
 tartar having both been destroyed ; indeed the process has for 
 its object the preparation of a carbonate of potash from the two 
 salts used. This flux disintegrates ordinary earthy or stony 
 matter, dissolves silica, separates acid and sulphur from metals, 
 assists in the oxygenation of many metals, and dissolves many 
 metallic oxides. When charcoal is present it decomposes por- 
 tions of the flux and yields potassium, which sometimes combines 
 with the metals beneath. Antimony, bismuth, and some other 
 metallic bodies thus become highly alloyed with potassium*. 
 
 687. Black flux is made from a mixture of one part nitre 
 and two parts crude tartar, deflagrated as before in a crucible, 
 hot enough to cause feeble combustion ; the result should not be 
 raised to so high a temperature as to cause fusion. From the 
 quantity of tartar used, this flux contains an excess of charcoal 
 resulting from the tartaric acid ; hence it differs from the white 
 flux with which it would otherwise agree, in containing a 
 reducing agent. The charcoal frequently assists in converting 
 metallic oxides into metals by abstracting the oxygen. The 
 flux yields potassium in the manner before mentioned. 
 
 688. Crude tartar, argol, or cream of tartar, when decom- 
 posed by heat, yields a carbonaceous carbonate of potash. It 
 is used sometimes with advantage as a flux, from the accuracy 
 
 * Serullas : Journal de Physique, xci. 123, 170. xciii. 115. 
 
* &t 
 
 I 
 
 294 SAL ENIXUM BORAX GLASS FLUX. [Sect. XIII. 
 
 *. 
 
 ^v ~^ .A? ^ 
 
 with which it may be mixed with the pulverized substance 
 whilst in the state of tartar. ' The intimate manner in which * 
 the charcoal and potash of this flux are mixed, causes the evo- ^ 
 lution of much potassium. The action of these carbonaceous 
 potash fluxes is influenced by the potassium evolved, the re- 
 ductions frequently depending to a considerable extent upon it. 
 
 689. Nitre is a salt frequently added to the contents of a 
 crucible for the purpose of communicating oxygen to some of 
 the metals, and converting them into oxides. Potash is left, 
 which operates as a solvent of the oxides produced, and acts, 
 generally, as the fluxes already described. If the substances 
 present be such as easily combine with oxygen, the nitre 
 should be added carefully and gradually, lest a violent and 
 sudden action be occasioned. 
 
 690. Sal Enixum is an acid sulphate of potash formed in 
 the manufacture of nitric acid. It is powerfully corrosive and 
 cleansing in the crucible, and acts at first as an acid from the 
 excess which it contains. This excess is soon either neu- 
 tralized or driven off, and, when charcoal is present, often 
 occasions the production of a sulphuret, which, being injurious 
 in certain experiments, is then to be avoided. 
 
 691. Borax being a more expensive salt than the former, is 
 a flux more rarely used, and only for the cleansing or melting 
 of the most valuable metals, such as gold, rhodium, &c. It is 
 a ready solvent of metallic oxides generally, and yet does not 
 act so rapidly upon earthenware crucibles as potash, or alka- 
 line fluxes containing carbonate of potash. It has little or no 
 action on silver, gold, or platina crucibles. 
 
 69S. All these fluxes act upon earthen crucibles, some more 
 than others. They are not used with metallic crucibles except 
 to dissolve adhering impurity, and to cleanse them. 
 
 693. Common flint glass is a very good flux in many cases, 
 and exerts but little action on earthen crucibles. But it con- 
 tains much oxide of lead, which is reduced if any charcoal or 
 combustible substance be present, and even by the access of 
 smoke. Many metals, as iron, zinc, &c., and several ores, 
 also reduce portions of the lead, and thus the buttons of these 
 metals beneath such a flux become contaminated. 
 
 694. Green bottle glass is a very serviceable flux at high 
 temperatures, but when charcoal is present, it yields iron; 
 
Sect. XIIL] 
 
 USES OF FLUXES OF CHARCOAL. 295 
 
 even traces of silicium and alumium have been observed in 
 iron, previously pure, after being heated with it. 
 
 695. These fluxes are sometimes pulverized and mixed with 
 the ores or other substances to be acted upon, before being intro- 
 duced into the crucible, and sometimes are gradually thrown 
 into the crucible afterwards. The method to be adopted must 
 depend upon the different circumstances of the substance to be 
 operated with, the flux, and their mutual action. It is neces- 
 sary that care be taken upon first introducing the crucible into 
 the fire that the heat and action be moderate, lest from the 
 ebullition which ajways takes place in consequence of the libe- 
 ration of either gas or moisture, a part of the flux should flow- 
 out, and thus a portion, even of the valuable part of the con- 
 tents, be lost. As the ebullition diminishes, more of the mix- 
 ture (if any remain) may be added, and when all is in, and the 
 charge is less agitated, the heat may be raised until the metal 
 be fused ; or if an action is going on, until the flux itself be- 
 come quiet and tranquil ; a result which generally indicates 
 the cessation of chemical action. 
 
 696. In consequence of the very common occurrence of 
 metals in the state of oxide, their deoxygenation is most fre- 
 quently the object of a crucible operation, and carbon in one 
 form or another is the agent generally resorted to. It is for this 
 reason that tartar and black flux are so valuable as fluxes. 
 Charcoal is frequently added to the oxide to be reduced, in 
 quantity greater than that contained in the flux; sometimes 
 indeed no flux at all is used, it being actually injurious from 
 its affinity for oxides, and from being in opposition to those 
 affinities which assist in reducing the metal. A charcoal 
 crucible, or a crucible lined with charcoal, is useful for the 
 reduction of some oxides, as that of iron for instance*, and also 
 for the deoxygenation of sulphates and their conversion into 
 sulphuretsf ; but in other instances, when the oxides are 
 infusible, and yet cannot be thus reduced by cementation as it 
 were, the charcoal may be pulverized and mixed with the 
 oxide, and the mixture introduced into the crucible. In these 
 cases it is generally "best to use a crucible lined with a thin 
 coat of charcoal. 
 
 * Berthier. Annales de Chimie, xxvii. 24. f Journal des Mines, vii. 421. 
 
296 FURNACE TUBE OPERATIONS. [Sect. XIV. 
 
 697. There are several substances which occasionally surpass 
 charcoal as reducing agents ; sometimes because they mix 
 more intimately with the oxide in powder, and at others 
 because they either are fluid, or melt when heated ; and being 
 absorbed, are present every where in the mass, and when de- 
 composed leave charcoal wherever they have had access ; but 
 they should be such bodies as bear a high heat without being 
 dissipated, or when decomposed leave much carbon. Of this 
 kind are starch, gum, sugar, wax, spermaceti, oil, fat, tar, and 
 pitch. 
 
 SECTION XIV. 
 FURNACE TUBE OPERATIONS. 
 
 698. THE operations to be described in this chapter are 
 such as require a high temperature, like those just referred to, 
 but being performed with substances in either the gaseous or 
 vaporous state, require another description of apparatus 
 for their confinement and subjection to the necessary heat. 
 The vessel now to be adopted is a tube, and by its means 
 either gases or vapours may be subjected alone to great heat, 
 or they may be passed over solid or fluid bodies previously 
 raised to a high temperature. On both these accounts the 
 methods about to be described are very common and useful. 
 
 699. Different tubes are required for different occasions. 
 They are frequently made of earthenware ; these resist a 
 high heat, except that they are liable to crack in the fire ; 
 but this fault may in part be guarded against by previously 
 luting them, for the reasons and in the manner directed with 
 respect to earthen retorts (491, 1084). In addition to the di- 
 rections there given for luting, it may be observed, that, with 
 respect to tubes, the lute, after being put on as stiff and as 
 tightly as possible, may be surrounded by a long slip of sam- 
 pler or open canvass, running round it in a spiral manner, so 
 that each fold may overlap the last (1094) : this will retain 
 the lute in its place during desiccation, and prevent the oc- 
 
f 
 
 % - 
 
 Sect. XIV.] FURNACE TUBES IRON P1ATINA. 
 
 - 
 
 ' 
 
 
 currence of cracks*. The porosity of earthenware has been 
 before mentioned (489, 491), and if necessary must be guarded 
 against as much as possible by washing the tube with borax, 
 &c., as already directed (491). But when the loss of a part 
 of the gas is of little importance, as when it is passed into 
 a tube to operate upon the substance within without reference 
 to quantity, then the porosity of the tube does not much 
 interfere. Wedgwood's tubes are of pure ware, but very 
 liable to crack. Tubes of the same material as that used in 
 the manufacture of common English crucibles are not so 
 subject to this failure, but are more porous. Black lead tubes, 
 or such as^are made of a mixture of clay and plumbago, are 
 least liable to crack of any, but sometimes communicate iron, 
 and are very porous. These tubes are frequently bent into 
 the form of a narrow U, when they may be readily introduced 
 into the mouth of a common furnace, the two ends and aper- 
 tures being outwards, and close together. When straight it is 
 advantageous to guard them in the furnace by a semi-cylinder 
 of tin-plate, and at times they are conveniently strengthened 
 by being passed through a cylinder of plate-iron, roughly 
 turned into a form which may serve as a casing. 
 
 700. Iron tubes are constantly useful. A gun-barrel, when 
 convenient as to size, answers the purpose very well. When 
 larger or smaller tubes are necessary they must be forged for 
 the occasion. If required for a long operation, or at a tem- 
 perature above a red heat, they should be protected from the 
 fire either by luting (699)? or by being passed through a black 
 lead tube. Iron tubes are generally adapted for the decompo- 
 sition of organic substances, as oils, &c., or water, or potash 
 by charcoal or iron, or of gases that have little or no action 
 upon the metal, as ammonia and carburetted hydrogen. 
 
 701. A platina tube can scarcely be dispensed with in the 
 laboratory, because of the very high temperature it will bear, 
 and the few instances in which it interferes with the substance 
 passed through it : substances may be heated together in it 
 which cannot be so treated in any other kind of vessel. Chlo- 
 rine, sulphur, and the metals, are almost the only bodies which 
 affect it ; oxygen and acid gases have no power of action on it. 
 
 * Mr. Cooper's Practice and Suggestions. 
 
**w 
 
 "--." 
 
 298 FURNACE TUBES COPPER GLASS. [Sect. XIV. 
 
 Those are best which are drawn, and have no joint down the 
 side, but they are the most expensive. Those which are 
 turned or bent, and soldered with gold, will not bear the high 
 temperature of the former, and it is impossible to make a joint 
 without solder, which will continue tight. The platina tube 
 may often be used with advantage as a retort, by the adapta- 
 tion of a plug to one end, which may be removed or replaced 
 at pleasure. 
 
 70. A bored copper tube is frequently used when a platina ^ 
 tube is not at hand, but it is limited as to the temperature it 
 will sustain, and also as to the substances which may be passed 
 through it. 
 
 703. Glass tubes are perhaps the most generally useful of 
 all. They allow operations performed in them to be watched 
 up to a red and even a yellow heat, and some kinds of glass 
 resist the action of most chemical agents likely to be brought 
 into contact with them in this form. The best tubes are those 
 :P4rv*mad| of green bottle glass, they require care in heating, but 
 resist the action both of heat and chemical agents much better 
 than those of flint glass. The latter include in their composi- 
 tion both alkali and oxide of lead, substances which are liable 
 
 be acted upon in many experiments. They soften also, and 
 are easily expanded, and collapsed at a red heat, but to com- 
 pensate in part for these bad qualities, they may be obtained 
 any where, whereas green glass tubes are very scarce. When 
 of small size they are readily bent into form, and arranged by 
 a spirit-lamp and mouth blow-pipe. Glass tubes may, like 
 those of 'earthenware, be strengthened by luting, but it is 
 ^* generally so desirable to witness the action going on within, 
 that a semi-cylinder of tin plate, or of earthenware, will be 
 ^t f un( ^ a more advantageous support. 
 
 I *ft)4. The method of connecting these tubes, when in the 
 furnace, with parts of other apparatus by which the gas or 
 vapour is either to be introduced or conveyed away, must vary 
 with the substance of the tubes. They should be of such 
 ength as to leave the ends projecting sufficiently far from the 
 furnace, to be either of moderate temperature, or to allow of 
 the application of cooling processes ; which, however, should v % 
 only be applied to metallic tubes, and then with caution. 
 
 *> * 
 
 ****** * ,; * 
 
*%.* 
 
 * ***_.. 
 
 Sect. XIV.] FURNACE TUBES JUNCTIONS HEATED. 299 
 
 When the tubes are metallic, terminating pieces with ground 
 joints or screws may be brazed or welded on, and thus junc- 
 tions are easily effected ; and in these cases if the ends be hot, 
 washers of card should be applied at the screw (830), and not 
 such as are made of oiled leather ; for the latter gradually 
 decompose and become unsound. It is often of use in opera- 
 tions with the gun -barrel, to terminate it at each end by a stop- 
 cock, of which the outer extremity has been formed into a 
 ground socket ; perforated wooden or cork plugs, formed at 
 one end so as to fit tightly into these sockets, and at the other 
 into a screw, may then be used as adapters ; while they com- 
 plete the junction, they prevent the transmission of heat. 
 
 705. If the tube be of earthenware or glass, and the extre- 
 mity be cool, the junction may be effected by fitting on a cap 
 (833), or by a perforated cork, or by caoutchouc connectors 
 (449), or by any of the processes already described, or to be 
 described in the sections on gaseous manipulation, and on lutes 
 and cements. If the terminations be hot, the object must be 
 attained by applying some of the methods described in the 
 latter section. 
 
 706. When vapours are to be passed through a heated 
 tube, it will be necessary to generate them in a little boiler or 
 a retort, connected with one end of the tube. In such a case 
 the joint must be capable of bearing the heat requisite for the 
 existence of the vapour, and the neck of the retort and the asso- 
 ciated part of the tube should be wrapped up in flannel or <^(t < 
 paper (473), that loss of heat, and consequent condensation of 
 
 the vapour there, may be prevented as much as possible. 
 
 707. The adaptation of furnaces to the heating of these 
 tubes will be readily understood. When crucible furnaces 
 are used, the tube should be placed in two notches (158) cut 
 in opposite sides, so as to bring the upper part of the tube 
 below the level of the edges, and the grate should be raised to 
 within one inch and a half of the tube itself. If one furnace 
 be scarcely wide enough to heat a sufficient length of tube, a 
 second may be arranged by its sides, the tube passing through 
 the notches and lying over both. It is easy, by piling the 
 charcoal over the edges of the furnaces where they touch, to 
 heat the tube there ; and a brick or tile, or other body, should 
 
JFV* *dl* * 
 
 ***MmF 
 jpPW 
 
 *:IB.' 
 
 300 TUBES HEATED SPIRIT-LAMP. [Sect. XIV. 
 
 be put on each side, bearing against the two furnaces, for the 
 purpose of interfering with, and as far as may be, preventing 
 the current of air, which will otherwise pass towards the junc- 
 tion of the two crucibles, and in ascending tend to cool the 
 tube at that part. 
 
 708. By placing two bricks edgeways, across a loose square 
 grate, four, five, or six inches distant from each other, a space 
 is left between them, which makes an excellent tube-furnace ; 
 it may, by the use of several bricks, be arranged to heat any 
 fr A Desired length of tube. Charcoal is to be the fuel used. But, 
 when a much higher heat is necessary, and even the application 
 J<* of a blast required, as in the preparation of potassium, it is 
 J^ * better to build up a temporary furnace with bricks and mortar, 
 setting the tube in its proper position in the course of the 
 work ; and as the brickwork is not required, nor is likely to 
 be, of much durability, it will be safe, before putting a fire 
 in, to tie it round with iron wire. When the heat is to be 
 raised to a high degree, it will be proper to introduce a stay 
 or two, pieces of black lead tube for instance, as supporters to 
 the lute. 
 
 
 4 709. A small piece of glass tube may be heated in a spirit- 
 lamp, and a greater portion in the oil-lamp (212). The tube 
 may either go through holes in the sides of the chimney, just 
 
 above the top of the flame, or it may be bent thus II so as 
 
 to pass down the chimney, until the lowest part of the tube is 
 just above the flame. The concentric double- wick oil-lamp 
 (213), or the large spirit-lamp (205, 206), answers for these 
 purposes very well. 
 
 710. The lamp which surpasses all others for the ignition 
 of a length of tube, is that invented by Mr. Cooper *, and 
 figured in the accompanying wood- cut. It consists of a frame 
 ten or eleven inches long, which, being raised upon four feet, 
 has an aperture from end to end of 0.8 or 0.9, of an inch in 
 width. It is furnished at each end with a wire support, 
 adjustable in its height, and bent at the top into a convenient 
 form for retaining a tube in a horizontal position. The lamps 
 
 * Transactions of the Society of Arts, xli., p. 56. Quarterly Journal, xvii., 
 p. 232. 
 
* * 
 
 m * * 
 
 COOPER S LAMP-FURNACE, 
 
 301 
 
 Sect. XIV.] 
 
 are two in. number, and stand on the frame, one on each side 
 the aperture. They have each ten burners passing obliquely 
 
 I 
 
 
 upwards from one edge and inclining towards those of the 
 other lamp, over the aperture before mentioned. Each burner 
 is 0.8 of an inch in length, half an inch wide, and about that 
 distance apart from its neighbours, and the lamps may be put 
 so near to each other as to leave the two sets but little asunder, 
 or they may be removed to a greater distance. Small uprights 
 are fixed on the top of the lamps between the burners : there 
 is also a feed-pipe to each lamp closed by a cork, and each 
 burner is furnished with a cap, to cover it and prevent the 
 evaporation of alcohol when the lamp is not in use. The 
 whole of this apparatus is made of tin-plate and iron-wire. 
 
 711. The trimming of the lamps is performed by selectii 
 some straight Argand lamp cottons, and cutting off so much 
 from both edges of the folded cotton as will divide it into two 
 pieces, each of proper width to pass down the burners. The 
 waxed end is introduced first, and the cotton thrust in until it 
 touches the opposite side at the bottom ; this is easily done, 
 and then the excess of cotton above is to be cut off with scis- 
 sors. The caps are then put on, and alcohol introduced at the 
 feeding aperture, until the lamps are two-thirds or three-fourths 
 full, when they are ready for use. 
 
 712. A platina tube of half an inch in diameter may be 
 heated to full redness by this lamp-furnace in a few minutes. 
 For this purpose it is to be' sustained at the two ends by the 
 wire supports already mentioned, these being adjusted so as to 
 leave an interval of about an inch between the tube and the 
 

 APPLICATIONS. [Sect. XIV. 
 
 double line of wicks beneath. The lamps are then to be 
 lighted and the cottons adjusted, until the flames reach and 
 * wrap about half way round the tube. The lamps should be 
 placed so as to leave about half an inch between the two rows 
 of wicks ; so that air passing upwards from beneath the frame, 
 and through the aperture before mentioned, may ascend be- 
 tween the flames and assist in supporting the combustion. The 
 flames will coalesce over this aperture, and also from side to * 
 side, so as to furnish a powerful and continuous line of intense 
 
 fheat, by the time they have ascended to the tube. By un- 
 covering and using only so many wicks as are beneath, and 
 proportionate to, the part of the tube to be heated, a certain 
 part of its length may be subjected to a high temperature 
 at once. 4MR^ B| * 
 
 '713. It is desirable in numerous cases to apply the flame 
 ^successively from one end of the tube to the other. On these 
 occasions the operation must commence with all the wicks un- 
 covered. As many are then to be lighted as may at first be 
 requisite, and to prevent the combustion from spreading to 
 he contiguous uninflamed wicks, a slip of tin-plate, about 
 three-fourths of an inch high, is to be placed across under the 
 tube, and supported by the burners and the upright pieces 
 10) already mentioned. The heat having been continued 
 sufficiently long on the one part, the temporary tin division is 
 to be removed farther on, more wicks are to be lighted, and if 
 any of those at the opposite end are now unnecessary, a simi- 
 lar plate of tin should be put between them and those which 
 are still to continue in combustion, and the former extinguished 
 by a sudden slight puff of the breath. 
 
 i* - 714. Mr. Cooper has occasionally constructed the lamps in 
 such a manner, that each burner has its separate receptacle of 
 alcohol, so that in place of one long lamp like that described, ** 
 it appears to consist of many small lamps, standing side by 
 side, but independent of each other. When only a part of the 
 tube is to be heated at once, a few only of the lamps are 
 lighted, and these, without using the rest, are easily moved one 
 way or the other, and their flames applied successively under 
 all parts of the tube. 
 
 715. The lamps cannot heat a greater length of tube at 
 
 
 w^ 
 
4 iW 
 
 A^ 1t & ^ JL ' 
 
 Sect, xiv.l COOPER'S LAMP FURNACE. 303 
 
 - 9* 
 
 once than is equal to the length of the frame ; but there is no 
 difficulty in putting two or more frames together end to end, 
 and in that manner igniting any extent of tube. If it be re- 
 quired to heat a tube longer than the frame, but in successive 
 portions, it is easily done by shifting the tube itself through 
 the apertures in the wire supporters by which it is held (710). 
 716. When small metal tubes, or moderately- sized tubes 
 of glass 'are to be heated, a single row of wicks is required, 
 which must be advanced a little to the edge of the aperture, 
 that the flames may rise up just beneath the tube. Green 
 glass tubes are constantly in use with this apparatus, and in 
 some cases, when the advantage of seeing the interior is of no 
 consequence, it is advisable, for many reasons, to inclose them 
 in a tube of copper foil (1351) ; this supports the glass when 
 so hot as to become soft, confines and prevents it from being 
 expanded into bulbs by the pressure of gas within, and assists 
 in conducting the heat uniformly over the tube. It also con- 
 veys heat to those parts of the tube not yet subjected to the 
 flame, and by gradually warming, prepares them for its ap- 
 plication ; so that no sudden change of temperature is ever 
 occasioned, and the tube is consequently more safely heated. 
 This external case is made of a slip of copper foil, about an 
 inch or an inch and a half wide, and so thick that twenty-five 
 or thirty folds squeezed by pincers may be equal to about the 
 tenth of an inch . The foil, after being flattened , should be rolled, 
 up tightly into a small cylinder, bound with a piece of wire, 
 and heated to dull redness for a moment, to destroy the degree 
 of rigidity given to it by pressure between the rollers. Being 
 then cooled and opened out, it is to be wrapped close round 
 the part of the tube to be heated in a spiral, one fold over- 
 lapping another at the edge. When so much of the tube is 
 enveloped as is required, the extra length of foil is to be torn 
 off, and the end kept tight upon the tube by a turn or two 
 of thin wire. The case thus formed is more or less thick, 
 and consequently strong, in proportion to the degree in which 
 the turns are folded over each other. If a fold overlap the 
 previous one by one half, then the case will be of double thick- 
 ness ; if it overlap two thirds, of triple thickness ; if it overlap 
 but a little at the edges, the case will consist of little more than 
 a single thickness of foil. 
 
n 
 
 ** 
 
 ' *&*r % v *.*** - 
 
 304 . TUBE DECOMPOSITION. [Sect. XIV. 
 
 ^^^^Bp^ rf.* . -5 -^Jf* L^ 
 
 ^ '^ #* j*Br 
 
 717. Glass tubes, whether guarded in this way or not, 
 generally require support in the middle to prevent them from 
 bending. This support is given by a moveable stand, made 
 of a piece of iron wire fixed perpendicularly into a leaden 
 bottom, and terminating above in a loop or ring, or sometimes 
 in a crutch. This wire passes up the aperture between the 
 lamps, and may be moved along the tube between the flames 
 into the most effectual or convenient position. Even short 
 pieces of tube closed at one end may be supported by means of 
 it and heated ; it is also useful in the arrangement of other 
 tubes as well as those which are straight. 
 
 718. When gases or vapours are to be passed through tubes 
 at high temperatures, for the purpose of effecting their decom- 
 position, it will be advantageous to increase the surface of con- 
 tact, and also to break the uniformity of current within. 
 Broken rock crystal, or flint, answers this purpose very well 
 with glass or earthenware tubes. The crystal or flint should , 
 be divided in a mortar into coarse particles, if the tube be 
 large, or if much deposited matter be expected from the decom- 
 position ; or into smaller, if the tube be small, or if but a 
 slight action, accompanied with little deposit, be anticipated. 
 
 * m .Afc.crumpled piece of wire should be thrust into the tube near 
 one end, a few large pieces of the broken substance dropped 
 in at the other to rest upon 'the wire, and afterwards, that 
 ich is considered of a proper size is to be poured in. 
 If two or three larger pieces, and then more wire be added, 
 they will retain the charge in its place ; but the wire should 
 be such as will not injure the experiment, for which reason 
 *&& also 8^s better to place it generally out of the heated part. 
 Platina wire answers the purpose for small glass tubes, and 
 will rarely occasion harm. 
 
 719. Some substances have singular powers in influencing 
 the decomposition and even combination of gaseous bodies and 
 
 Vkt % vapours, although they have no apparent tendency to com- 
 bine with either the compounds or their elements ; and it is 
 for this reason that tubes of different substances operate dif- 
 ferently upon the gases passed through them. If ammoniacal 
 gas be passed into a red hot iron tube, it will be easily decom- 
 posed into nitrogen and hydrogen gases ; but if it be passed 
 
 .*** 
 
Sect. XIV.] TUBE DECOMPOSITION. 305 
 
 through a glass tube, as Gay Lussac has shewn, it resists an 
 equal and even a much higher temperature, with scarcely any 
 change. This effect may perhaps be dependant, as MM. 
 Despretz and Savart have endeavoured to show, upon an 
 actual combination occurring between the metal and some of 
 the substances present ; but whatever the cause, it may be 
 taken advantage of without the necessity of having tubes 
 formed of the materials, it being sufficient to introduce them into 
 glass tubes in the manner before described for rock crystal 
 (718) ; it will be found that a glass tube charged with broken 
 iron turnings, will as effectually cause the decomposition of 
 ammonia as one of iron. 
 
 720. The power of spongy platina is such that it occasions 
 the combination of oxygen and hydrogen, even at common 
 temperatures, producing ignition and explosion. When its 
 action is diminished by mixture with earthy bodies, it is again 
 increased by elevation of temperature. Spongy platina also 
 causes the union of oxygen and oxide of carbon at common 
 temperatures ; the decomposition of nitric oxide by hydrogen ; 
 and the combination of both the elements of olefiant gas with 
 oxygen, at temperatures above 572. For further illustrations 
 of this power of the metals, see Dulong and Thenard's paper 
 in the Annales de Chimie, xxiii. 440. 
 
 721. The vapour of water passed over iron heated in tubes 
 is decomposed, the metal becomes oxidized, and hydrogen gas 
 is evolved. In this case the higher the temperature, the more 
 rapid is the action. The steam should be raised from a small 
 boiler, and not in too large a quantity, as great excess tends 
 to cool the tube considerably. If one-third or one-half of 
 what is passed into it be decomposed, it is in sufficient pro- 
 portion. The iron for small experiments may very conve- 
 niently be clean turnings, beaten into small pieces in a mortar. 
 They lie close, expose much surface, and keep open a free 
 passage for air. 
 
 722. The vapours of alcohol and ether may be decomposed 
 in a similar manner : iron assists but is not necessary, but rock 
 crystal, or some substance affording surface (718) should be 
 introduced. The results vary with the temperature. Nearly 
 all the vapour that is sent in should be decomposed. It may 
 
 X 
 
306 TUBE DECOMPOSITIONS COMBINATIONS. [Sect. XIV. 
 
 be generated in a little boiler, or in a flask or retort, and 
 caoutchouc junctions may be used, even with ether. 
 
 723. Olefiant gas, nitrous oxide, and some other gases, are 
 decomposed by being passed through heated tubes. If the 
 general facts are only to be observed, the gases may be intro- 
 duced from the retort evolving them, or forced in from a 
 bladder or an air-tight caoutchouc bag (820, 821), and the 
 contents may even be received in similar vessels at the other 
 end of the tube: but if accurate experiments upon precise 
 quantities are required, then two mercurial gazometers (809) 
 should be connected with the tube, that nothing may be lost. 
 
 724. Many oxides may be reduced in part or entirely when 
 heated in tubes, by passing certain gases or vapours over them. 
 Protoxide of manganese is best obtained in this way from 
 a pure peroxide, or from the oxide precipitated from a pure 
 salt ; hydrogen passed over it at a red heat reduces every 
 particle to the state of dry protoxide, and the progress of the 
 change from one end of the tube to the other is beautifully 
 exhibited. Oxides of titanium, tungsten, chromium, iron, See., 
 are often usefully treated in this manner ; and besides hy- 
 drogen, other reducing agents may be used. Ammonia has 
 equal power with hydrogen, and sometimes, from the nascent 
 state of the hydrogen in it, is superior to the simple gas. 
 The vapours of alcohol, ether, naphthaline, and camphor, may 
 be used, where it is probable that carbonaceous matter will 
 favour the desired effect. 
 
 725. Many combinations are effected with great advantage 
 in a heated tube. Thus oxygen is easily combined with 
 baryta, and the peroxide of barium formed. The heat should 
 be a dull red ; no oxygen will pass till the whole of the earth is 
 peroxidized. In such cases, the end of the tube at which the 
 oxygen passes out does not require to be connected with any 
 apparatus: a glowing match should now and then be applied 
 to it, and when the presence of pure oxygen is evident, the 
 operation is finished. 
 
 726. Sulphur may be combined with platina, and phos- 
 phorus with lime, in a tube apparatus, with great convenience. 
 The platina in the spongy state, or the quick lime, are to be 
 placed in the tube, and heated to dull redness ; the tube should 
 be slightly inclined, and the higher end lengthened so far from 
 
Sect. XIV.] 
 
 TUBE COMBINATIONS. 307 
 
 the furnace or lamp, as to be only warm. If turned up, it is 
 an advantage, and the aperture there should be fitted by a 
 good cork. When the tube is sufficiently heated, a piece of 
 sulphur in the one case, or a piece of phosphorus in the other, 
 is to be dropped or thrust in at this end, and the aperture 
 immediately closed by the cork. A small spirit-lamp flame 
 will melt the substance, and cause it to run down to the warm 
 part, where it will gradually become vapour; and though a 
 part may distil back (which is of no consequence), the greater 
 portion will be sent over the platina or lime within : the pro- 
 gress of the change will easily be observed. When the first 
 portion of substance has combined, a second is to be intro- 
 duced ; the aperture being rapidly opened and closed, so that 
 no current may be allowed to occur in the tube, and this pro- 
 cess is to be continued until the substance within is entirely 
 converted into sulphuret or phosphuret. Great care is, of 
 course, required in handling the phosphorus ; pieces not more 
 than one-third or the half of an inch in length, should be intro- 
 duced at once into tubes half an inch in diameter. They 
 should first be dried, then dropped in rapidly by a pair of 
 forceps, lest the temperature of the tube should be sufficient 
 to inflame them. In wiping phosphorus dry, it should be 
 rolled between two or three folds of cloth or filtering paper, 
 every part of its surface being pressed but not rubbed ; and 
 when thus dried, it must not be held in the uncovered hand, 
 but be inclosed in cloth or paper, and be taken out from 
 them by the forceps. This is to be done at some little dis- 
 tance from the furnace or lamp, and when the phosphorus is 
 carried towards the heat, the operation should be conducted 
 quickly, though steadily, that no time be allowed for the tem- 
 perature of the substance to rise so high as to cause its inflam- 
 mation before it be in the required situation. 
 
 727. Titanium may be combined with chlorine by passing 
 the gas over the metal in a heated tube*. The alkaline 
 earths may be decomposed by passing chlorine over them in 
 the same manner, oxygen being then evolved, and their bases 
 remaining combined with the chlorine f : numerous other che- 
 
 * Mr. George, Annals of Philosophy, New Series, ix. 18. 
 t Sir H. Davy, Phil, Trans. 1811, p. 12. 
 
 X 2 
 
308 WATER PNEUMATIC TROUGH. [Sect. XV. 
 
 mical actions of the most important kind may be effected by 
 this mode, in a manner the most convenient possible for obser- 
 vation. When the substance used and the results produced 
 are equally fixed, small platina trays, formed by doubling a 
 piece of foil, may be used for containing them ; they are easily 
 introduced into the tube and withdrawn again by a wire bent 
 into a hook at the extremity. Every facility is afforded for 
 conducting away the results, whether solid, fluid, or gaseous ; 
 and in by far the great number of cases, those excellent flexible 
 connectors formed of caoutchouc (449) are of perfect and 
 easy application. 
 
 SECTION XV. 
 
 PNEUMATIC MANIPULATION, OR MANAGEMENT OF 
 
 GASES. 
 
 1. Pneumatic Troughs, Jars, fyc. 
 
 728. THE first apparatus necessary for the experimental prac- 
 tices to which this chapter relates, is the pneumatic trough, 
 with its accompanying jars. We are indebted to Priestley for 
 the invention of this useful vessel, and for much of the appa- 
 ratus which is used in conjunction with it. 
 
 729. The common pneumatic trough is a vessel constructed 
 so as to retain water, and of such dimensions that large jars 
 may be filled in it ; and it is finished with shelves or supports 
 beneath the surface of the water, on which vessels may firmly 
 stand. The trough is frequently so contrived, that the shelf 
 is of considerable extent, and the deeper part> which may be 
 called the well, made of such dimensions as just to allow the 
 filling of the largest jar required for use. This is of no con- 
 sequence as regards the level of the water, and its alteration 
 by filling jars, and raising them upon the shelf; but it is of 
 importance that the well should be sufficiently large. There 
 should be width and breadth enough for two or three jars to 
 be immersed at once, and sufficient depth to permit the in- 
 version of any jar or tube beneath the surface, likely to be in 
 use at the trough. The shelf also of the large trough should 
 
Sect. XV.] 
 
 WATER PNEUMATIC TROUGH, 
 
 309 
 
 =// 
 
 be of sufficient size to hold several jars of gas at once. If 
 the surface of water be 19 inches by 28, and a well be formed 
 at one end of 14 inches by 10, and 12 inches in depth, so as to 
 leave a continuation of the shelf surface on three sides of the 
 well, of two inches and a half in width, it will be found suffi- 
 ciently large for almost every purpose. 
 
 730. Such a trough is best made of japanned copper, and 
 supported in a wooden frame, so as to stand about 39 inches 
 from the ground. Two depressions like small wells, should 
 
 be made in the shelf, each about 
 seven inches long, two wide, and 
 one and a half deep ; they should 
 be placed with one of their nar- 
 rowest ends about one inch and 
 a half from the end of the shelf 
 which is furthest from the well, 
 and about eight inches apart. 
 These depressions are to receive 
 the beaks of retorts delivering 
 gas into jars placed over them ; 
 and it is advantageous to have 
 a flap fixed to this end of the trough frame, which, turned up or 
 down at pleasure, may be used when there is occasion to sup- 
 port a retort stand or other apparatus required in the evolution 
 of gas. This trough should be filled with water until it is one 
 inch and a quarter, or one inch and a half above the shelf. A 
 stop-cock should be fitted into the bottom of the well, by which 
 the water may be drawn off when it has become acidified or dirty. 
 
 731. These principal troughs are sometimes made of wood, 
 
 but never with advantage, because 
 of their complexity of form, and the 
 consequent difficulty of keeping the 
 numerous joints tight. They are 
 often on a smaller scale, and when 
 the chemical establishment altogether 
 is small, are then more in proportion 
 to the rest of the apparatus. A 
 very useful and usual table trough 
 is of a circular form, and about two 
 feet in diameter, internally divided 
 
310 WATER PNEUMATIC TROUGHS. [Sect. XV. 
 
 into three parts ; the middle part is seven inches deep, and 
 forms the well, the other parts on each side four inches deep, 
 and are the shelves ; a moveable shelf, with holes in it, extends 
 from side to side across the well, and serves to support such 
 jars as are receiving gas from the beaks of retorts placed 
 under the holes. 
 
 738. Besides a principal trough, several smaller ones are 
 required for the preparation of particular gases, as for example, 
 chlorine, when warm water is required ; or sulphuretted hydro- 
 gen, which contaminates water, and would discolour metallic 
 troughs. These may be either of metal or earthenware, and 
 need not have fixed shelves. An earthenware foot-bath makes 
 an excellent trough ; and even a washhand basin, or moderately 
 sized evaporating pan, is at times sufficiently large, very 
 portable, and offers advantages. 
 
 733. Trivets are used with these smaller troughs to sup- 
 port the jars. They are best made of cast-iron, in the form 
 of very open grates, either square or round, and raised by 
 means of three or four feet; they should be of different 
 heights, from half an inch to two inches, and when very dry 
 should be covered with a good coat of black varnish, or made 
 hot almost to visible redness, and then brushed over with oil ; 
 the oil is in this way decomposed, and leaves the metal covered 
 with a very permanent varnish. These trivets answer the 
 purpose of shelves when required, and also support the jars 
 when filled with water, so that the beak of a retort, or the end 
 of a tube, may be introduced beneath them. 
 
 734. When the small troughs are used, so much water must 
 be present as at all times to cover the trivets an inch or more 
 in depth. Small and narrow jars may be filled in them with 
 water, but larger jars are generally filled more conveniently at 
 the large trough, or in a pail, and then transferred in the 
 manner to be shortly described (753). If during their use 
 the water rise so high in them as to endanger the steadiness of 
 the jars containing gas standing in them, a part must be 
 removed. The facility with which extemporaneous troughs 
 may at any time be contrived, will be evident from what has 
 been said relative to these smaller arrangements. 
 
 735. Water which has been taken from a deep well, from a 
 cistern into which it has been thrown through the exertion of 
 
Sect. XV.] MERCURIAL TROUGH DIMENSIONS. 311 
 
 much power, and from other situations, frequently contains so 
 much air in solution as to interfere with the purity of gases 
 standing over it in the pneumatic trough ; for when in the 
 smaller quantities it is relieved from the pressure and other cir- 
 cumstances which favoured the absorption of air, and now 
 evolves it again in numerous bubbles. Hence water which 
 presents this appearance to any extent when put into the 
 trough should be avoided, or else its probable influence should 
 be remembered, that upon particular occasions it may not, 
 through inadvertence of the operator, introduce inaccuracy 
 into pneumatic experiments. 
 
 736. Water troughs are calculated for the reception and 
 retention of gases not soluble, or alterable by water, but not 
 for the many which are affected by that fluid. Dr. Priestley 
 was the first who recommended the use of mercury; and 
 though its weight and opacity are disadvantageous, that metal 
 is still so superior to any thing else, as to be constantly used 
 in these cases. Being expensive as well as heavy, it is neces- 
 sary that the troughs in which it is used should be as small as 
 possible, consistently with the performance of experiments, and 
 at the same time of a material that will resist the action of the 
 metal. They have been made of wood and of marble, but 
 varnished cast-iron, which is now generally adopted, is by far 
 the best substance. In principle and in the arrangement of 
 the parts, they resemble water troughs. Newman's large 
 mercurial trough will allow the use of a jar two inches and 
 two-tenths in diameter, and nine inches in length; it has 
 seventy-six square inches of shelf room very well arranged, 
 and also a mercurial gasometer attached to it at one extremity. 
 It requires from 60 to 70 Ibs. of mercury for the free per- 
 formance of experiments. 
 
 737. Newman has also a much smaller trough for the use, 
 
 though in a confined manner, of jars 1.5 
 inches in diameter, and six inches in 
 length ; it has only thirty square inches 
 of shelf room. It requires 20 Ibs. of 
 mercury to fill it, with a jar standing on 
 the shelf. When working with jars of 
 gas over this trough, the metal requires transferring backwards 
 
312 MERCURIAL TROUGH JARS. [Sect. XV. 
 
 and forwards, because of the difference in level made by the 
 descent or the elevation of a jar-full, but it is very useful in 
 facilitating operations on small quantities, either in tubes or 
 small jars. 
 
 738. A mercurial trough should always stand in a tray, and 
 likewise have a cover to keep out dust and dirt, when not in 
 use. Its place, as before, described, should be upon the table 
 groved round the edge (12), that waste of mercury may be 
 avoided as much as possible. When the metal is spilled it is 
 best collected by being swept together and then gathered up 
 by a card. A card will even gather it well up from the sur- 
 face of baize. If only occasionally in use, it is better to keep 
 the mercury in stone bottles, than by constant exposure in the 
 trough to render it liable to accidents and loss. 
 
 739. The jars which accompany, or are required with, 
 pneumatic troughs, are of various kinds. Plain jars should 
 be from twelve to sixteen inches in length, two and a half 
 or three inches in diameter, of such thickness (about one- 
 eighth or one-tenth of an inch) as to withstand the general 
 
 liabilities of use, and ground at the edges, so as, 
 when moistened or greased, to be closed accurately 
 by a flat glass plate. Those for the mercurial 
 trough should be from four to eight inches in 
 length, one and a half or two inches in diameter, 
 and as thick as the former, that they may safely 
 bear their weight of metal when filled and in use. 
 These also should be ground at the edges. 
 
 740. Stoppered jars have an aperture above, fitted with a 
 ground-glass stopper, and resemble stoppered bottles without 
 bottoms. They are required of different sizes, and should be 
 larger in diameter than the plain jars ; the proportions may be 
 gathered from the figure in the preceding wood-cut. Such as 
 are less than three inches and a half in diameter should be 
 ground at the lower edge, and all ought to be ground flat at 
 the top, for the convenience of closing them occasionally by a 
 glass plate (1348), instead of the stopper. It is useful in 
 public laboratories, and often in private ones, to have a second 
 set of stoppers for several of these jars, the stoppers having a 
 projecting knob beneath, to which a deflagrating spoon, or a. 
 
Sect. XV.] PNEUMATIC JARS STOPPERS TRANSFER JARS. 313 
 
 taper, or other article, may be attached by a wire. When it 
 is required that any one of these should be introduced into the 
 gas already confined in a jar by the first stopper, it is to be 
 attached to the second, and introduced rapidly after the re- 
 moval of the first stopper, and the jar closed by the stopper to 
 which it is suspended. When these second stoppers are not at 
 hand, corks will often answer the purpose very well, the wire 
 which supports the article introduced being thrust through 
 them : but being combustible, they will not answer for defla- 
 grations in oxygen gas, unless their lower surfaces be pre- 
 viously guarded by a plate of sheet lead or iron. In all defla- 
 grations the ^spoon or combustible should for many reasons be 
 put as low down in the jar as possible. A good cork will 
 occasionally form a very tight and excellent stopper to an open 
 jar which has not been ground. 
 
 741. The stoppers of jars, and indeed all ground-glass stop- 
 pers, should be of considerable thickness where the lower and 
 upper parts are connected ; for sometimes considerable strength 
 is required to loosen them from their places, in consequence of 
 difference of temperature, the hardening of some substance 
 around them, or other circumstances. For the method of 
 loosening stoppers thus fixed, see Sect. xx. (1263.) Stoppers 
 should never be put into pneumatic jars without having been 
 previously touched by a little pomatum or tallow (433), so as 
 to make them fit easily but closely, and this should be renewed 
 whenever from use or cleaning there is occasion for it. Neither 
 should they be put into jars or bottles in a heated state ; the 
 latter frequently then contract on the stoppers, and it becomes 
 almost impossible afterwards to move them. 
 
 742. Capped or transfer jars are such as, being open above, 
 
 have a cap cemented upon them, the latter being sur- 
 mounted by a stop-cock. They allow of easy com- 
 munication with other apparatus, by adopters and 
 screws. They should be of four or five different sizes, 
 and a large and a small one should be graduated. A 
 small capped jar or two should be provided for the 
 mercurial trough, of the dimensions before given (736). These 
 jars should often be examined, to ascertain the tightness of the 
 cap and stop-cock, by which they are closed. This is best 
 
314 GLASSES TUBES FUNNELS DISHES. [Sect. XV. 
 
 done by nearly filling them with water or mercury, according 
 to the trough to which they belong, without moistening the 
 stop-cocks, placing them on a steady part of the trough, ob- 
 serving where the level of the water or mercury stand inside, 
 and leaving them for half an hour or an hour. If at the end 
 of that time the level be unchanged, the jar is tight, and in that 
 respect in order. 
 
 743. The lipped glasses before described (368, 505) both 
 large and small, are very useful as jars when operations are 
 carried on at the small troughs, or with small quantities of gas ; 
 and tubes closed at one end will frequently be required for the 
 same purposes. These tubes may be of any length less than 
 10 or 12 inches, and of any diameter; some may be plain, but 
 several should be graduated (1ST) for the estimation of small 
 quantities of gas. Those which are too wide to be closed per- 
 fectly by the finger, should be ground at the edge so as to be 
 closed, when required, by a glass plate (1348). The others 
 should be level, or nearly so, at the mouth, and not irregular 
 from bad cutting or from fractures. 
 
 744. None of these vessels when cracked should ever be used 
 at the mercurial trough, for they are not only rendered very 
 weak and are easily destroyed by a slight blow near the cracked 
 part, but often suffer the gas to pass slowly through the fis- 
 sure. They should rarely be used at the water-trough, except 
 in very common experiments j for, notwithstanding cracks 
 when moistened are frequently air-tight, though not so when 
 dry, yet they as often leak, especially when the water does not 
 adhere to their surface, or when the gas within is subjected to 
 those sudden movements which frequently occur in experi- 
 ments ; besides these risks, the jars are easily broken, and the 
 gas consequently lost. 
 
 745. In addition to the vessels already described, small and 
 moderately-sized funnels, with narrow necks, will be required 
 to assist in the transference of gas into vessels having narrow 
 apertures; and dishes will be necessary for the removal of jars 
 containing gas, from one place to another. These dishes may 
 be of glass or earthenware, as evaporating dishes (369), or 
 of metal, being then best made of sheet copper, with a flat 
 bottom and upright edge. Even common soup plates and tea 
 
Sect. XV.] PRODUCTION OF GAS GAS BOTTLE. 315 
 
 saucers will answer the purpose extremely well. The glass 
 plates before referred to (740, 1348) are in constant use in 
 closing the mouths of such jars as, not being too large, have 
 ground edges. 
 
 Q. Production, retention, and transference of Gases. 
 
 746. The manner in which gas is evolved is very variable. 
 It is frequently liberated during distillations in iron, earthen- 
 ware, or glass retorts : these processes have been described, and 
 all that is now necessary to be referred to is the fact, that such 
 apparatus must terminate in a beak, which may either be 
 directly plunged into the fluid of the pneumatic trough, or 
 lengthened by a tube which may have its extremity placed in 
 a similar situation. Gas is sometimes produced by tube opera- 
 tions (704, 718, &c.), and the manner of leading it away by 
 tubes to the trough will be evident. 
 
 747. When the liberation of gas takes place at common tem- 
 peratures and immediately the materials are in contact, as of 
 hydrogen from diluted sulphuric acid and zinc, or of carbonic 
 acid from muriatic acid and pieces of marble, then glass retorts 
 are sometimes used, and on other occasions gas bottles and 
 flasks. The adaptation of retorts to these purposes is simple 
 and evident. Gas bottles are vessels intermediate in their 
 character between flasks and bottles, being thickened at the 
 
 neck and having pieces of bent tubes fitted to 
 them by ground joints ; the bottle therefore 
 represents the body of a retort, and the bent 
 tube the neck. When the materials are in- 
 troduced, the tube is put into its place, and 
 its open extremity immersed in the water of 
 the pneumatic trough. When a common Florence or white 
 flask has to perform the office of a generator, it must have a 
 piece of bent tube fitted to it by a good cork (484), and this 
 will answer every purpose required. 
 
 748. The open neck or tube by which the gas is ultimately 
 delivered, whether it belong to a retort, a tube apparatus, or a 
 complicated arrangement of vessels, is to be immersed in the 
 water of the pneumatic trough. When the vessel is a mere 
 retort or gas bottle, it is easily arranged in a convenient situa- 
 
316 COLLECTION OF GAS WITHOUT LOSS. [Sect. XV. 
 
 tion, being supported in its place by a stand (386) ; and move- 
 able apparatus of any kind may generally be arranged on a 
 table near the trough, so as to have the necessary juxta-posi- 
 tion. If from circumstances the apparatus disengaging gas is 
 fixed, and cannot be brought to the trough, as may happen 
 for instance in the distillation of oxygen gas in an iron retort, 
 or in complicated experiments of research, then either the neck 
 must be prolonged by connecting tubes of glass, or small pneu- 
 matic troughs must be used ; these, being portable, may easily 
 be placed in the vicinity of the apparatus. It is often neces- 
 sary in these cases to collect large quantities of gas over a small 
 trough ; and this is easily effected by transferring the jars 
 (753, 758) as they are filled, to the larger trough, and replac- 
 ing them by such as are filled with water. 
 
 749. A prime object in preparing gases is generally to col- 
 lect the pure portions only ; and it becomes necessary to expel 
 the common air of the retort or gas bottle, before the particular 
 gas is collected. For this reason the first portions may be 
 thrown away ; but as a general rule, it is better that these 
 should be collected in ajar, and then rejected, rather than, by 
 leaving the beak of the retort exposed to the air, to allow them 
 to escape at once into the atmosphere. By collecting them, it 
 is known when twice or thrice the contents of the retort has 
 passed out ; after that, the gas may be collected for use : by 
 suffering them to escape from the beak, the estimation of the 
 quantity rejected, and the probability of the air being all dis- 
 placed, is vague and uncertain. When a quantity of gas has 
 been allowed to escape, sufficient to justify the opinion that 
 what is afterwards evolved is nearly or quite free from air, the 
 future portions may be collected in jars for use, as is imme- 
 diately to be described ; but the order of these jars should still 
 be attended to, for which reason it is well to mark them one, 
 two, three, four, &c. as they are filled, and then, in case a por- 
 tion of gas perfectly free from atmospheric air be required, the 
 third or fourth jar may be resorted to instead of the first or 
 second. 
 
 750. On other occasions it is important to collect all the gas 
 that may be evolved, that its quantity may be measured. It 
 is then frequently necessary to collect every bubble of gas that 
 
Sect. XV.] 
 
 COLLECTION OF GAS JARS FILLED. 317 
 
 comes from the retort, including the common air itself. Then 
 after having estimated the whole of the gaseous products, the 
 capacity of the retort, and the volume of solid or liquid matter 
 it may have received as a charge, it becomes easy to ascertain 
 the volume of air, and consequently the volume of pure gas 
 evolved. In this case the jars are to be numbered as they are 
 filled ; for though the first contains much atmospheric air, and 
 perhaps also the second a little, the others are filled with a pure 
 gas, which may be preserved for use. The operation of col- 
 lecting and estimating the whole of a gas is delicate, and re- 
 quires considerable variation, according to the nature of the 
 gas, and the bodies from which it is to be evolved. These 
 points would be improperly introduced into the description of 
 elementary operations, but will be referred to again in a more 
 advanced part of the volume. 
 
 751. The trough being filled with water as before described 
 (729, 734), and the apparatus arranged ready for the evolution 
 of gas, a jar is to be selected, which we will consider for the 
 present as a plain one (739), and being immersed in the water 
 of the trough with its mouth inclined a little upwards, so as to 
 allow the air to escape, is to be filled with water. It is then 
 to be raised upright with its mouth downwards, and will be 
 found to remain full of the fluid so long as the mouth is 
 retained beneath the surface of the water ; it may in that situa- 
 tion be placed upon the shelf of the trough, or upon a trivet. 
 If placed over an aperture in the shelf, or with its edge pro- 
 jecting a little way over the well, there will be no difficulty in 
 so arranging the beak of the retort, that the bubbles of gas 
 escaping from it shall ascend into the jar, and, accumulating at 
 the top, gradually displace the water, which will descend and 
 mingle with that in the trough. When the jar is nearly full 
 of gas, a second is to be depressed in the well of the trough, 
 filled with water, and placed on the shelf by the side of the 
 first : when the gas in the first is within half an inch of the 
 mouth, it is to be moved on one side, the second put into its 
 place, and filled in like manner with gas. Or if the retort or 
 vessel be moveable and the jars large, it will be better to place 
 the second jar over another aperture, or projecting conveniently 
 over the edge of the shelf by the side of the first, and to 
 
318 COLLECTION OF GAS TRANSFERENCE OF A JAR. [Sect. XV. 
 
 transfer the beak of the retort from the first to the second, 
 rather than to endeavour suddenly to move them : then after 
 displacing the full jar, the final adjustment of the retort and 
 second jar may be leisurely made. In this way jar is to 
 succeed jar, until the action in the retort has ceased, or until 
 sufficient gas has been collected. 
 
 752. The filling of the jars with water in the well of the 
 trough must be so conducted, that none of the air passing 
 from them shall enter into the jars already filled with gas. 
 For this reason, when a jar is full of gas, it should be put 
 so far upon the shelf, that its mouth may be entirely closed; 
 and in filling the fresh jar with water its mouth is to be turned 
 away from the gas jars already in use. The mouth of ajar 
 is not to be immersed first, so as to cause the air to burst 
 forth in large bubbles ; but the closed end should be first de- 
 pressed, and the water suffered to flow in, and the air to pass 
 out, smoothly. 
 
 753. If the trough in use be a small one, there may not be 
 shelf room in it for the jars as they are filled, in which case 
 it will be proper to transfer them to another place. For this 
 purpose an evaporating or glass dish, or a common plate (745) 
 is to be selected, of sufficient size freely to receive the mouth 
 of the jar, and allow water to remain around it; this dish 
 is to be put into the water about an inch beneath the surface, 
 and the jar moved until its mouth is received into it; this 
 being done, the jar and dish are to be raised together out of 
 the trough, and placed safely on one side. The water in the 
 dish will confine the gas, just as well as the water in the 
 trough, the dish in fact becoming a small trough for the time ; 
 all that is necessary is, to preserve the portion of water which 
 accompanies the jar at such a height that the mouth of the 
 latter may never be uncovered. Very little depth of water is 
 required ; so that this point be attended to, a common kitchen 
 plate will answer the purpose exceedingly well. The jar of 
 gas thus removed may either be left in that state, or may be 
 transferred to another trough by immersing the dish and 
 mouth of the jar into the water of the second trough, and then 
 removing the dish. 
 
 754. Sometimes also it will happen, from the smallness of 
 
Sect. XV.] COLLECTION OF GAS TRANSFER JARS. 
 
 319 
 
 the trough, that there is not room to fill the jar with water. 
 It may then be filled in a pail, or in the large trough, and 
 transferred in the manner just described, by means of a 
 plate or dish, to the trough at which the gas is to be liberated. 
 The long jars already described (739), which are ground 
 at the ends, are very advantageously transferred by the 
 help of a glass plate (1348) : which, dipped into the water 
 and held tightly against the mouth, is in its moistened state 
 quite secure, and will safely retain the contents of the jar 
 during transference, whether they be water or gas or both. 
 
 755. Such is the manipulation with plain jars : it is the same 
 with stoppered and other vessels, except in occasional variations 
 in the mode of filling them with water. A stoppered jar may 
 be filled with water by removing the stopper, depressing the 
 jar in water in an upright position until entirely immersed, and 
 then replacing the stopper: it may be afterwards raised and 
 used as a plain jar. Transferring jars, or such as, having a 
 cap cemented to their upper aperture, are finally closed by 
 a stop-cock (742, 827), frequently require to be filled with 
 such care as to avoid the introduction of any water into the 
 stop-cock. This may be done by sinking the jar steadily in 
 water, allowing the air to issue out at the cock, until the fluid 
 has risen into the cap, and very nearly as high as the aperture 
 of the cock itself; then by closing the latter the water is re- 
 tained in the jar. 
 
 756. When there is not sufficient depth of water in the 
 trough to admit of this process, another method may be 
 adopted. It is to apply the lips to the upper end of the stop- 
 cock, and to withdraw the air by the force of the lungs and 
 mouth. This may be done at one, or at several times, a clean 
 cloth being placed over the stop-cock to prevent its contact 
 with the lips. As the water approaches the cap, its ascent 
 should be moderated, and when within a very small distance 
 of the cock, it should be arrested altogether by closing the 
 latter. 
 
 757. It is evident that these transfer jars cannot be filled 
 with water by inclining them in the trough, without intro- 
 ducing the fluid into the stop-cock, although its entrance may 
 be excluded from the upper half by closing it with the 
 
320 LEVEL OF WATER DECANTATION OF GAS. [Sect. XV. 
 
 finger. When filled with water they ought to be moved with 
 care, lest any portion should be thrown up into the stop-cock ; 
 and when placed to receive gas, the first bubbles should 
 be admitted with equal caution, one by one, or as they break 
 within they will splash the liquid into the aperture above. 
 When the fluid has descended below the cap, so as to 
 be in sight, there is but little danger of this happening, and 
 the operation may proceed more rapidly. If pure gas is to 
 be collected in these jars, it is necessary that the first few 
 bubbles should be expelled through the stop-cock, that they 
 may carry away the common air from it; this expulsion is 
 effected by sinking the jar up to the neck in water, opening 
 the cock, and refilling the vessel with fluid. It can only be 
 done in a trough or vessel deep enough to allow of sufficient 
 depression. 
 
 758. During the collection of gas in a small trough (748), 
 the jars being filled at another place with water (754), there 
 is of course a rapid alteration at the surface of the water 
 in the trough, from the continual addition of that fluid from 
 each jar. In such cases it is necessary to lade the water 
 out, and to return it to the vessel from whence it was taken, 
 and from which the jars were filled. Considerable care is 
 sometimes required on this point, in order that the level of 
 the water may not rise too far above the surface of the trivet 
 or shelf. If the depth of water be inadvertently allowed to 
 increase, and at the same time the gas be permitted to collect 
 in the jar until the latter is almost full, it will frequently 
 happen that the jar, becoming buoyant, will fall over and its 
 contents escape. Jars, generally, should not have the water 
 depressed to within less than half an inch of their edges, the 
 level within being then nearly the same as that without. 
 
 759. After having succeeded in collecting gases over the 
 trough, the next facility to be acquired is the decantation of 
 them from one vessel to another, either in large or small por- 
 tions, or with vessels of different sizes. In decanting gas from 
 jar to jar, which is the simplest case of this kind, the operation 
 is easy, and in reality is only an inverted pouring, the gas or 
 air being poured upwards through water from one vessel to 
 the other. The jar into which the gas is to be introduced, is to 
 
Sect. XV.] DECANTATION OF GAS INTO JARS BOTTLES. 321 
 
 be filled with water, and placed in the usual way with its 
 mouth upon the shelf of the trough, as if it were to receive 
 the gas from a retort ; it is then to be brought forward over 
 the well, removing two-thirds or three fourths of the mouth 
 from off the shelf, so that though the jar is supported by one 
 edge, another jar may with ease be brought towards it, and 
 turned up beneath its mouth. This done, and the jar retained 
 steadily in the left hand (that being usually most convenient 
 for the purpose), the second jar (containing the gas to be de- 
 canted), and which must previously have been placed on the 
 shelf of the trough, is to be brought forward by the right 
 hand, and, being depressed in the well, is to be approximated 
 to the first jar, and inclined so that, while its mouth is elevated 
 in relation to the closed extremity, it may be made to pass 
 under the mouth of the first jar, in order that when the gas, 
 because of the further inclination, issues out in bubbles it may 
 ascend into the latter. The top of the jar to be emptied is 
 then to be depressed until the whole is under and full of water, 
 but this must be done gradually and steadily; the gas not being 
 suffered to pass out suddenly, or in large quantities, for then 
 
 the magnitude of the bubbles causes them to interfere in their 
 o 
 
 ascent with the descent of the water, and portions are frequently 
 thrown outside. In all practice of this kind, the experimenter 
 should endeavour to obtain a habit of steady and success- 
 ful manipulation ; and even when care may not be required 
 for the particular experiment, he should be anxious to acquire 
 dexterity, that when it is of importance, no chance of failure 
 may be incurred. When the form of the trough is that de- 
 scribed (729), it is advantageous to bring the jar full of water 
 over the corner of the well, for its weight is then more safely 
 supported by the two sides of the shelf above, and the mouth 
 of the jar whose gaseous contents are to be transferred, may 
 more readily and certainly be conducted beneath the first jar, 
 by means of the angle existing in the well. 
 
 760. When the gas is to be transferred from large into 
 smaller jars, or into bottles, more care is required than in 
 the case just described. A jar with a large mouth delivers 
 bubbles of considerable lateral extent ; and when these rise 
 towards an aperture, it is to be remembered they cannot enter 
 
 y 
 
322 TRANSFERENCE OF GAS FUNNELS TUBES. [Sect. XV. 
 
 it, unless there be space for the passage outwards of an equal 
 bulk of water at the same time ; if there be not, they will fre- 
 quently be broken and part of the gas be carried outside and 
 lost. In these cases funnels are highly useful, and especially 
 in filling bottles : the funnel, being inverted and immersed in 
 the water, is to have its beak introduced into the mouth of the 
 bottle filled with water, and the gas, being decanted into the 
 funnel, is readily and safely conducted into its proper place. 
 The difficulty of the operation is at first increased, because 
 attention is to be given to the funnel and the bottle at the 
 same moment; for the former and the mouth of the latter 
 must both be retained under water, and the edge under which 
 the jar is to be brought is necessarily much deeper in the trough 
 than if no funnel had been used. 
 
 761. Instead of a funnel, a lipped jar or glass (368) may 
 be employed in the transfer as an intermediate vessel. These, 
 although they have wide mouths, deliver narrow bubbles of air 
 by the lip, and to that owe their advantages. All that is re- 
 quisite is, to bring the lip into such a position that, as the jar or 
 glass is inclined, the lip may be the highest part of the mouth, 
 and the gas consequently tend to flow out there. 
 
 762. The manipulation with jars and glasses is compara- 
 tively easy to that which occurs in transference of gas from 
 them to tubes, or from tubes to each other ; and yet this latter 
 practice is continually required in the laboratory, especially in 
 eudiometrical and analytical operations. One circumstance 
 with tubes which occasions difficulty, in addition to the nar- 
 rowness of their mouths, is, their contracted capacity within, 
 by which the easy passage of a bubble of gas upwards, and 
 water downwards, at the same time, is interfered with ; this 
 effect is greatest in tubes of the smallest diameters. 
 
 763. No great difficulty will occur in the transference of gas 
 from a tube to another that is wider. The second tube is to 
 be filled in the usual manner with water, and held in the well 
 
 of the trough, in a considerably inclined 
 position ; the tube containing the gas is to 
 be brought near it, the upper edge of its 
 mouth inserted as it were into the mouth of 
 the first, and then its position slowly altered, until the gas 
 
Sect. XV.] TRANSFERENCE OP GAS TUBES HOW HELD. 323 
 
 passing towards the mouth be gradually delivered in distinct 
 bubbles into the first tube. During this transfer, the mouth 
 of the second tube should be retained as much as possible 
 within the first ; the latter should not be raised to a perpen- 
 dicular position, but be considerably inclined, for then the 
 edge of its mouth meets better with, and is adapted to those 
 of the second tube, so as to confine the gas, and the motion of 
 the bubbles is less sudden and less subject to derangement. 
 Occasionally, it is advantageously placed in almost a horizontal 
 position, its closed extremity being but little raised. One 
 bubble of gas should be allowed to rise to some height in the 
 tube before another is permitted to follow. 
 
 764. When the delivering tube is larger than the receiving 
 tube, more care is required in the transfer. The first tube 
 should be inclined as before, and the upper edge of the mouth 
 of the second placed within it, and to assist in uniting as it 
 were the two tubes for the moment, the finger and thumb 
 of the left hand (which holds the receiving tube) should be 
 applied at the sides of the junction, so as to confine the gas 
 and prevent its escape laterally. For this purpose, and gene- 
 rally indeed in tube transference, the tube is best held in the 
 hand, with its open extremity passing out between the thumb 
 and fore finger, so that when sustained in the water in an in- 
 clined position, the back of the hand may be upwards, the 
 hand being as it were over the vessel ; the tube is then easily 
 supported by the two or three last fingers of the hand, and the 
 fore finger and thumb are left at liberty to guide the mouths 
 of the vessels, or to close the lateral opening, as has been just 
 described. At other times it may be held as a pen is retained 
 in the hand, the mouth being confined and guided between the 
 thumb and two fore fingers, but there is then less facility in 
 elevating or depressing it to different angles. The tubes 
 should at all times be retained by a light and easy, though 
 secure hold, and not in a stiff rigid manner, and the arms may 
 often be allowed to rest with advantage on the edge of the 
 trough, whilst the hands are immersed in the water. 
 
 765. An intermediate lipped glass should be used for the 
 transference of gas from a large jar to a tube. No difficulty 
 will be found in transferring from a lipped glass to a tube. 
 
 Y 2 
 
324 TRANSFERENCE OF GAS MEASUREMENT. [Sect. XV. 
 
 The tube being filled with water is to be held under the sur- 
 face, as before described (763) ; the lip is to be introduced 
 into it, the junction made by the fingers if necessary, as in the 
 former case, and the gas allowed to pass in distinct bubbles. 
 It will be found easier to transfer from a glass that is from a 
 third to five-sixths full of gas, than from one containing more 
 or less. When a glass is nearly empty, it is often exceedingly 
 difficult to transfer from it into a narrow tube. Advantage 
 may, therefore, occasionally be taken of the circumstance above 
 mentioned, by replenishing the glass with gas. 
 
 766. Finally, small funnels may, when requisite, be used 
 for the transference of gas into tubes, the procedure being 
 exactly the same as that before described (760). Tubes con- 
 taining gases are easily transferred from one trough to another, 
 or to other situations, merely by closing their mouths with the 
 finger or thumb, and carrying them to the required situation. 
 The student should very early attain the habit of closing the 
 mouth of a tube by the finger with facility and security. The 
 accurate manipulation of gas in tubes, so that none shall escape 
 and be lost, is often essential in experiments of research, where 
 only small portions of gas are evolved, yet require to be ex- 
 amined as to many properties. 
 
 3. Measurement of Gases. 
 
 767. There are two cases of the measurement of gases. 
 Either a bulk of gas is to be accurately measured, or the sepa- 
 ration of a certain volume from a larger quantity is required. 
 The mode of determining the bulk of gas received in a plain 
 jar may be first considered. The jar must stand steadily on 
 the shelf of the trough ; three pieces or slips of waxed or oiled 
 paper are then to be attached by a little wax (1125) and slight 
 pressure, at equal distances on the outside of the jar, so that 
 they may just adhere, and serve to mark the height of the 
 water within, by their upper edges. The jar is then to be 
 removed from the shelf and depressed in the well until the 
 surfaces of the fluid within and without coincide, and the ope- 
 rator should observe how far this change of position has altered 
 the coincidence of the three pieces of paper with the surface 
 of the water within, taking care that the jar be held upright 
 
Sect. XV.] MEASUREMENT OF GAS IN JARS. 325 
 
 during the observation, so that any difference maybe the same 
 at each mark. The jar should then be replaced upon the 
 shelf, and the situation of the paper marks raised by a quan- 
 tity equal to that which it was observed they were too low, 
 when the gas was levelled. This may easily be done by the 
 eye, the elevation of the marks being made now just as much 
 above the gas within as they were too low when the jar was 
 depressed in the well. The jar should again be sunk in the 
 well until the inner and outer surfaces of the fluid are level ; 
 the correspondence of the marks with the level should be 
 observed, and the process carried on in this manner until the 
 adjustment is perfect : the papers are then to be pressed more 
 forcibly against the glass, that their adhesion may be secured. 
 The gas is now to be transferred (759) into a graduated jar 
 (742) , to be depressed also in the well until the inner and outer 
 surfaces of the water being level, the gas within may be subject 
 only to the pressure of the atmosphere ; the graduation is then 
 to be observed, and a direct determination immediately made 
 of the quantity of gas contained in the jar. 
 
 768. In this operation the jar should be held perfectly 
 upright, and the use of the double or triple graduation before 
 recommended (118, 150) will be evident, from the facility with 
 which it is now ascertained by inspection, whether the jar is in 
 its right position, and, consequently, whether the determination 
 by the different graduations accord, as ought to be the case ; if 
 not, they may easily be made to do so by inclining the jar a 
 little one way or the other, and the volume should not be con- 
 sidered as ascertained until both or all the scales agree. 
 
 769. In reading off the height of gas in jars, and also in 
 adjusting the paper marks already referred to, the observation 
 should be taken not from any part of the curved surface of the 
 water close to the glass (121), but from the general and un- 
 disturbed level within ; and when, in equalizing the pressure 
 within and without the jar, that surface is necessarily brought 
 low and beneath the level of the eye, the student should not be 
 satisfied with a casual and oblique glance, but should also 
 lower his eye and bring it as nearly as possible to a level with 
 the surface itself. When the jar is thus lowered in the well, 
 without resting any where upon its edge, and sustained only 
 
326 MEASUREMENT OF GAS READING OFF. [Sect, XV. 
 
 by the hand, great assistance and steadiness may be gained by 
 holding and pressing it as it were into one corner of the well, 
 sustaining it in part by friction against the sides : further 
 assistance may be gained also by supporting the wrist or arm 
 on the edge of the trough. 
 
 770. If an accident happen in transferring the gas, or after- 
 wards in the graduated jar, before the volume is ascertained, 
 a record of the quantity is preserved by the three waxed 
 paper marks (767), and hence their great use : if no accident 
 happen, they still serve to verify the measurement. For the 
 latter purpose the jar is to be removed from the trough, set 
 with its mouth upwards, and then water measured in (120) 
 until it is filled by that fluid to the extent that it before was by 
 gas. If the quantity of fluid thus introduced accord with the 
 measurement of the gas, an assurance is gained of the accuracy 
 of the determination. 
 
 771. When the gas is collected in the first instance in a 
 graduated jar, it may of course be measured in it, as has just 
 been described, transference being then avoided ; hence an 
 advantage, in many cases, in receiving gas, requiring to be 
 measured, directly in such jars. 
 
 772. If the gas to be measured is contained in ungraduated 
 tubes, the process, though a little varied, is the same in prin- 
 ciple. The level within and without is to be equalized, and 
 the height of the gas marked with a file (132), or by a slip of 
 waxed paper put round the tube like a ring. The gas is then 
 to be transferred into a graduated tube (743), levelled (769), 
 and its volume determined by the graduation. Both in the 
 marking and observing, particular attention is to be paid to 
 the curve of the water, for the considerations which were for- 
 merly insisted upon (135), as important in graduating, are 
 now equally important in observing. The practice there men- 
 tioned of always reading in the same manner, should be par- 
 ticularly attended to (121), and by a little experience the point 
 on the graduation, which may be considered as that which 
 would coincide with the surface, supposing the gas and water 
 to meet by a plane, may be ascertained very accurately from 
 mere inspectiou. The tube in which the gas was first con- 
 tained, arid which was marked by the file or paper, may after- 
 
Seft. XV.] MEASUREMENT OF GAS TEMPERATURE. 327 
 
 wards be measured up to the mark by water or mercury from 
 a graduated tube (125, 127) ; or if very small, the mercury 
 may be weighed, the precautions with regard to convexity of 
 the surface not being forgotten (135). 
 
 773. In all estimations of the bulk of gas, the temperature 
 by the thermometer, and the pressure as indicated by the baro- 
 meter, should be observed and registered in the laboratory note 
 book (1290). No considerable difference should be allowed to 
 exist between the temperature of the air and water at the time 
 of the experiments ; if it be more than a degree or two, it 
 should be corrected by altering the temperature of the water. 
 The registered temperature should be that of the water ; and 
 great care should be taken in handling the jars, that their tem- 
 perature be not made to differ from the observed one. For 
 this reason they should be held lightly by the thick part of the 
 neck, and not grasped at the sides, lest a temporary change of 
 temperature and consequently of volume should be induced, 
 which in certain cases might occur just as the volume of the 
 gas was under determination. The barometer should be an 
 accurate one, or, if inaccurate, the difference in altitude between 
 it and a perfect instrument should be known, and always 
 allowed for, as a necessary correction. In observing this in- 
 strument it should be supported perpendicularly, the eye being 
 level with the surface of the mercury ; it should be observed 
 whether the mercury be concave or convex, and after having 
 observed its height, the instrument should be slightly tapped 
 to allow free motion to the metal, until tapping produces no 
 change. If the experiments are long, the barometer is to be 
 observed two or three times during their continuance, that no 
 unperceived alteration may occur to vitiate the results. 
 
 774. In measuring out a required quantity of gas, no diffi- 
 culty will occur with large quantities. A graduated jar is to 
 be filled with water, and the gas passed into it (759) until 
 there be nearly enough. The additional portions are then to 
 be added more carefully, at first from a lipped glass (765), 
 and when the quantity is almost sufficient, from a tube. The 
 water within and without the jar is to be brought to the same 
 level at every examination of the bulk on the scale. Many 
 depressions of the jar in the water, for the equalization of pres- 
 
328 MEASUREMENT OF GAS ADJUSTMENT. [Sect. XV. 
 
 sure, will not be required, a facility of adjustment being ob- 
 tained, by attending to the quantity apparently necessary 
 when the level is so equalized. Thus, if it is found when the 
 jar is depressed that the level of the water within is one divi- 
 sion higher on the scale or graduation than it ought to be, then 
 on raising it to the shelf, gas is to be added until the level is 
 depressed by one division, without respect to the particular 
 part of the division with which it may happen in that state to 
 coincide ; upon restoring the equality of level, the quantity 
 will be found very nearly accurate, and the portion that is 
 necessary to make it quite so, may now very well be estimated, 
 and accurately added at the next trial. 
 
 775. The advantage of using the tube for the addition of 
 the last portions is, that much smaller bubbles may be delivered 
 into the jar, and the final adjustment be more accurately made. 
 If the aperture of a tube at the trough containing gas be closed 
 by the fore finger (of the right hand), whilst it is held by the 
 thumb and other fingers, and inclined under the water, with 
 the mouth upwards, so that the gas within would escape but 
 for the finger, then if the finger be relaxed a very little at the 
 lower edge, so that a small quantity of water may flow in, and 
 the mouth be immediately closed as before, it will be found, 
 that at each operation a bubble of air will be expelled from the 
 tube, the dimension of which will depend on the degree in 
 which the finger was withdrawn, and on the quantity of water 
 consequently admitted. In this manner bubbles smaller than 
 a pin's head may be obtained, and consequently a very minute 
 quantity of gas may be added, whereas risk of adding too 
 much in one large bubble is incurred, if the gas be let out from 
 a tube not thus guarded by the finger, or from a glass or jar. 
 
 776. In measuring quantities in tubes, for eudiometrical and 
 other experiments, more care is required than is usually neces- 
 sary with large quantities, because general proportions and 
 results are frequently deduced from very small volumes. In 
 these cases standard or unit measures are often useful, and 
 being equally filled again and again, afford a series of equal 
 volumes. In filling them, however, it is not sufficient that 
 gas be passed into them until they overflow, for from the co- 
 hesion of the water, and other circumstances, this will take 
 
Sect. XV.] MEASUREMENT OF GAS MEASURES. 329 
 
 place when the measure contains very different quantities, 
 and it will in almost all cases be rather more than full, the 
 gas projecting beyond the edge of the tube. When there- 
 fore such measures are made out of tubes (142), it is usual 
 to close them when full of gas by the finger, the excess being 
 thus thrown off; but, inasmuch as the skin when dry or 
 soaked, or when slightly or forcibly pressed, enters more or 
 less into the opening of the tube, an inaccuracy is occasioned 
 unless the operator be careful always to make the applied 
 part of the finger assume the same convexity, and the mea- 
 sure used be of small diameter. With these precautions this 
 is a very good mode of measuring. These tubes are some- 
 times closed by stoppers so adjusted, as to leave a capacity 
 of the proper measurement, and occasionally larger mea- 
 sures, amounting to the half or the whole of a cubic inch, 
 are made of bottles carefully stopped and adjusted for the 
 purpose (125). 
 
 777. In using measures of this sort a surplus of gas is to be 
 introduced, the stopper put into its place, and the excess 
 thrown out ; but in introducing the stopper it must be done 
 in such a manner as to exclude water as much as possible from 
 the measure. It should be introduced at first obliquely, one 
 edge being a little higher than the other, whilst the measnre 
 itself is quite perpendicular. It should be observed that the 
 gas descends on all sides of the stopper, or at least that no large 
 quantity of water is carried up on one side; and this being the 
 case it may be thrust into its place, the extra bubble of gas 
 thrown off, and that within the measure used as required. If 
 the measure be inclined, and the stopper put in carelessly, it 
 will be found in most instances that a quantity of water has 
 been carried up into the bottle or measure, on the bottom of 
 the stopper, notwithstanding the considerable excess of gas that 
 was first introduced. 
 
 778. Mr. Cavendish used a measure for these purposes, 
 
 consisting of a piece of glass tube closed at one 
 end and fitted into a brass collar, with a flat 
 slider passing through it ; this, when thrust for- 
 wards in a direction at right angles to that of the 
 tube, closed its mouth, and included a space accurately ad- 
 
330 MEASUREMENT OF GAS MEASURES. [Sect. XV. 
 
 justed to half a cubic inch. When used, the slider was opened, 
 and a surplus of gas passed into the tube, the slider was then 
 closed, the excess of gas beneath it thrown away, and the 
 included and accurately measured volume retained for use. 
 
 779. When in consequence of the nature of the experiment 
 and of the measure used, the operation does not consist in ac- 
 curately filling a measure or tube, but in filling it to a certain 
 mark only, as for instance, to the fifth or the tenth division on 
 the graduation (and in general this will be the kind of mea- 
 surement required in tubes), a little excess of gas above what 
 is wanted should be put into the tube, and the adjustment 
 effected by closing the mouth with the finger, and letting out 
 minute bubbles in the manner just described (775). The 
 tube is to be returned to an upright position occasionally, and 
 the quantity left examined as to its accordance with the gradua- 
 tion in the required place. If by accident too much gas has 
 been thrown out, a little more must be added, and the adjust- 
 ment proceeded with as before. If the gas be valuable or 
 in minute quantity, then the small bubbles ejected should not 
 be thrown away, but caught in a little tube held over them, 
 and reserved for other experiments. A very quick and ac- 
 curate adjustment of a required quantity of gas may in this 
 way be obtained. 
 
 780. In observing the volume of gas in a tube, after hav- 
 ing brought the internal and external surfaces of water to a 
 level, the necessity of lowering the eye to the level of the 
 water may be avoided by closing the mouth of the tube with 
 the finger, and then raising it out of the water to the height of 
 the eye; but the act of closing the tube must be so performed, 
 that the pressure of the finger does not compress the gas 
 within, and raise the level above its proper place. If the 
 finger be applied to all parts of the edge at once, and then 
 pressed hard, this effect will almost certainly take place. To 
 avoid it, the finger should not be applied directly against the 
 mouth of the tube, but a little obliquely, pressing it hard 
 against the part of the edge it first meets, and then folding it 
 over, so as to cover the mouth gradually from one side to the 
 other: the pressure at last upon the whole edge being less than 
 that with which the operation began. In this manner the tube 
 
Sect. XV.] GAS COLLECTED MERCURIAL TROUGH. 331 
 
 may be closed without any change of level, and it should be 
 observed during the operation, that this is the case. When 
 the habit is once attained the practice is quick, and in long sets 
 of pneumatic experiments the operator is enabled by it to avoid 
 some degree of fatigue. 
 
 781. The barometer and thermometer should be attended 
 to in all these experiments, unless the latter are brief, or are 
 such as to require merely relative portions of two gases, their 
 absolute quantities being unimportant. 
 
 782. The operations which have been described have all 
 been illustrated by reference to the water trough, and to gases 
 permanent over it. They are the same in principle as those 
 which will be necessary in experiments at the mercurial trough 
 (736), with those gases which, being soluble in w r ater, cannot 
 be preserved over that fluid. The first point the student has 
 to remember at the mercurial trough is, the excessive weight of 
 the fluid with which he is working, and its influence in his 
 operations, either as coinciding with or opposing the pressure 
 of the atmosphere. If the extremity of a retort, or the mouth 
 of an apparatus, delivering gas, be immersed, for example, an 
 inch, in the water trough, and another to the same depth in a 
 mercurial trough, the pressure upon the interior of the ap- 
 paratus, which is so little as to be unimportant in the first case, 
 becomes of consequence in the second, being nearly fourteen 
 times greater. The latter, if unattended to, might derange 
 and burst open joints made by soft cement or lute ; might 
 force the evolved gases through bladder or junctions quite tight 
 to the pressure of water ; and might blow out a tube or retort 
 heated to redness, as in the preparation of oxygen gas from the 
 chlorate of potash, which would have suffered little or no 
 change at the water trough. Hence the beak of such apparatus 
 should be immersed to no greater depth in the mercury than is 
 necessary to insure the safe delivery of the gas into the jar 
 placed to receive it. Hence also the shelf of the trough should 
 not be covered with mercury to a greater depth than is neces- 
 sary to secure the mouths of vessels placed upon it; and jars, 
 if supported by other means, as by trivets or stands, in small 
 or temporary troughs, should be so arranged that their mouths 
 may not be too far below the surface whilst receiving gas. 
 
332 MERCURIAL TROUGH JARS FILLED. [Sect. XV. 
 
 783. The mercurial jars are, as before described (739), to be 
 strong, and ground at the edges. If they are lipped, which is 
 very desirable in many cases for the advantage of transferring, 
 the lip should be level with the rest of the edge, so as to bear 
 upon a flat surface at the same time with the other parts ; and 
 not, as is usually the case, retiring outwards towards the bottom 
 of the jar, so as to leave a space between the lip and a glass 
 plate applied to the mouth. The jars may be filled, either by 
 inverting them in the mercury of the trough itself (751), or 
 with mercury from another vessel ; in the latter case the mouth 
 is to be closed by a glass plate (1348), the jar afterwards in- 
 verted, and its mouth immersed in the metal of the trough, 
 and the plate withdrawn. But when jars containing mercury 
 are thus closed either for the purpose described or the trans- 
 ference of gas, a strong hold on the plate must be retained, to 
 prevent its displacement by the weight of metal upon it. 
 
 784. In moving a jar partly or entirely filled with mercury, 
 from one part of the trough to another, great care should be 
 taken to prevent its receiving any sudden blow or jerk, for 
 though slight in appearance, it might, from the weight of the 
 mass moved, suffice to break the jar; upon such occasions the 
 whole weight of mercury suddenly descends, sometimes derang- 
 ing every thing in the trough, besides occasioning the loss of 
 the metal and the escape of the gas. The jars are, under these 
 circumstances, most liable to injury by slight blows against 
 each other, or against the iron of the trough, when they take 
 place upon the edges or sides. 
 
 785. When a mercurial jar contains gas it may be removed 
 from the trough, as already mentioned (739, 783), by a glass 
 plate ; but if it contain a considerable quantity of mercury, it 
 is safer to effect the transfer by a little evaporating basin (745, 
 753.) 
 
 786. When a capped jar is to be filled with mercury, by 
 the assistance of the mouth (756), the jar should be inclined 
 as much as possible, to diminish the height of the column 
 of air within it, as well as the labour attending the opera- 
 tion ; then, by applying the mouth to the stop-cock, and using 
 it to exhaust, in a manner almost the reverse of that described 
 for blow-pipe practice (222, &c.), the air may be withdrawn, 
 
Sect. XV.] MERCURIAL TROUGH GAS TRANSFERRED. 
 
 333 
 
 and the mercury gradually raised until it fills the jar. Relief 
 should be afforded to the mouth by closing the stop-cock occa- 
 sionally during the operation ; the cloth should generally be 
 applied over the aperture (756), and no moisture should be 
 allowed to enter the stop-cock. 
 
 787. The transference of gas from vessel to vessel under 
 mercury, is the same in principle with transference under 
 water, but differs from it in consequence of the opacity and 
 weight of the fluid ; the first of which prevents the experi- 
 menter from watching the motion of the gas, and obliges him 
 to work in the dark, whilst the second causes the bubbles 
 which leave the decanting jar to be thrown up through the 
 fluid with considerable force. Great care is therefore required 
 in these operations, and especially with tubes. The relative 
 and desired position of the mouths of the vessels must be 
 judged of principally by feeling with the fingers. The de- 
 pression of the decanting tube should be very slow and gra- 
 dual. The escape of the first bubble should be watched ; if it 
 ascends into the receiving tube, all is well, and the position of 
 the mouths should be steadily retained ; but if it escape into 
 the air, the position should be changed. Generally speaking, 
 the mouth of the decanting vessel ought to be farther under 
 the mouth of the receiving vessel than is required in water. 
 When tubes are the vessels employed, the use of the fingers in 
 closing the sides (764) is often highly advantageous. 
 
 788. There is one circumstance in which water and mer- 
 curial troughs essentially differ, and of which the student 
 should be fully aware, as it will account to him for many acci- 
 dents that otherwise might occur at the commencement of his 
 experience, in the transferring and collecting of gases, and en- 
 able him in most cases to avoid them. This consists in the 
 property which water has of wetting and adhering to the sur- 
 faces of the jars and apparatus concerned in operations at the 
 pneumatic trough, which is not possessed by mercury. Hence 
 it is that portions of gas expelled from apertures under water, 
 rise in distinct bubbles through the fluid about them ; for the 
 adhesion of the water- to the solid substances generally in use 
 is greater than that existing between its own particles. It is 
 not so, however, with mercury ; that metal docs not come into 
 
334 ESCAPE OF GAS IN MERCURIAL TROUGH. [Sect. XV. 
 
 such close contact with glass or other substances as to adhere, 
 and hence it often happens that the gas ejected from the aper- 
 ture, instead of being thrown as a bubble into the fluid metal, 
 suddenly returns round the edge, and passes up in a stream 
 between the vessel and the mercury. It is in this way diffused 
 for a moment in thin films over a large surface, and ultimately 
 escapes at the ring, where the surface of the mercury ought to 
 be in contact with the vessel from which the gas is thrown out. 
 The collection or retention of the gas in such cases is utterly 
 impossible, its passage in the form of bubbles being necessary 
 for that purpose. 
 
 789. This insidious emission of gas takes place with little or 
 no disturbance of the mercury, and is sometimes quite imper- 
 ceptible. It can only occur when the vessel delivering the gas 
 proceeds from above downwards, in the manner of a jar, or the 
 beak of a retort, or a descending straight tube ; so that when 
 the extremity of a tube is curved, and made to turn up under 
 the surface of the mercury, it is avoided. It is very usual 
 with dirty vessels, and may often be prevented by wiping them 
 clean : this is especially the case with the beaks of retorts de- 
 livering gas. It is more likely to occur in dirty than in clean 
 mercury (1278). In such cases, though it may not take place 
 immediately, it frequently will after the lapse of a short time, 
 the agitation of the mercury apparently collecting a film, or 
 diminishing the adhesion between the metal and the glass. 
 Wiping the glass with a clean cloth, even whilst under the 
 metal, is then a remedy. 
 
 790. Some gases have a tendency to occasion this effect 
 more than others, and amongst them may be quoted fluoboric 
 and silicated fluoric acid gases, and euchlorine. The necks of 
 retorts delivering these gases should be wiped occasionally. 
 The effect happens more readily when the sides of the vessel 
 or delivering tube approach to perpendicularity, than when 
 they are much inclined, so as to approximate a horizontal 
 position ; and finally, it often occurs between the fingers and 
 the mercury, the transpired matter on the surface of the skin 
 apparently facilitating the effect. Hence when the fingers 
 are brought into contact with the gas in transferring ope- 
 rations, they should, when the effect is likely to occur, be 
 bent upwards under the mercury as much as possible. 
 
Sect. XV.] MERCURIAL TROUGH TRANSFERENCE OF GAS. 335 
 
 791. It frequently happens that small quantities of gas are 
 to be taken from larger portions and transferred to other situ- 
 ations. This is constantly the case in analytical and eudio- 
 metrical experiments, where small volumes are required in 
 tubes or narrow vessels. Another common case is the trans- 
 ference of a small portion of gas from a jar over water into a 
 vessel over mercury, the transmission of water at the same time 
 being avoided. As these operations are frequent, several use- 
 ful contrivances have been invented to facilitate them. 
 
 792. A common method of transferring a little gas from 
 the water to the mercurial trough in the dry state is, to fill 
 a tube with the gas over water, to close it by the finger, then 
 removing it from the trough, to wipe the outside of the tube 
 and hand dry, taking care that the gas be securely retained 
 during the operation. The tube is afterwards to be carried to 
 the mercurial trough, the finger to be removed, and a little 
 piece of bibulous paper, tightly rolled up, introduced through 
 the mercury into the gas. By re-applying the finger, so as to 
 close the tube, and shaking the piece of paper about within, 
 it imbibes a large portion of the water, and the gas may after- 
 wards be decanted into another tube filled with mercury, with- 
 out any risk of water passing with it, for the fluid will be 
 retained by the paper or by adhesion to the glass. The gas 
 is thus obtained in a dry state, or at least without the presence 
 of any fluid water. With regard to its hygrometric state, it, 
 of course, still remains saturated with aqueous vapour. 
 
 793. A very useful contrivance for the same purpose, due 
 to Mr. Cavendish, is thus described by Dr. Henry*. " A 
 tube eight or ten inches long, and of very small diameter, is 
 drawn out to a fine bore, and bent at the end so as to resemble 
 the italic letter /. The point is then immersed in quicksilver, 
 which is drawn into the tube till it is filled, by the action of 
 the mouth. Placing the finger over the aperture at the 
 straight end, the tube filled with quicksilver is next conveyed 
 through the water with the bent end uppermost, into an in- 
 verted jar of gas. When the finger is removed, the quick- 
 silver falls from the tube into the trough, or into a cup placed 
 
 * Elements of Experimental Chemistry, i, 22. 
 
336 
 
 PEPYS S TRANSFEREE. 
 
 [Sect. XV. 
 
 to receive it, and the tube is filled with the gas. The whole 
 of the quicksilver, however, must not be allowed to escape, but 
 a column must be left a few inches long, and kept in its place 
 by the finger. The tube is to be removed from the water, 
 and dried by an assistant with a towel or with blotting paper ; 
 the point of the bent tube is then to be introduced into the 
 aperture of the tube standing over quicksilver, and on with- 
 drawing the finger from that aperture, which is now upper- 
 most, the pressure of the column of quicksilver, added to the 
 weight of the atmosphere, will force the gas from the bent 
 tube into the one standing in the mercurial trough." 
 
 794. Mr. Pepys has invented a very useful instrument for 
 the transference of small quantities of gas from one vessel to 
 
 another over the trough, which he permits me 
 to describe. It is made of a piece of glass 
 tube, about half an inch in diameter, and five 
 inches long, attached to a piece of smaller 
 diameter, which, after bending as in the 
 figure, terminates in a chamber at a, which, 
 being cylindrical for the greater part of its 
 length, terminates in a capillary tube and 
 aperture. A small piston, rendered air-tight 
 by tow and tallow, is fitted into the cylin- 
 drical tube ; it is moved by a rod and ring, the rod pass- 
 ing through a box which closes the upper aperture of the 
 instrument, but which should not be air-tight. A portion of 
 mercury is placed above the piston, and the space between it 
 and the capillary opening of the chamber is filled with the 
 same metal when the piston is in the position depicted. Upon 
 raising the piston, the mercury follows it, and descends into 
 the chamber a, the space left by it being immediately filled 
 with the air or gas which has access to the capillary opening. 
 The rod has a graduation upon it, by which it is known when 
 a tenth of a cubical inch of air has entered the chamber. 
 
 795. The following is the mode of using this instrument. 
 Suppose the object be to transfer a little gas from a jar to a 
 eudiometer tube, both standing over the same trough : the 
 piston is to be depressed until the mercury entirely fills the 
 chamber a, even up to the aperture ; that end is to be dipped 
 
Sect XV.] MERCURIAL TROUGH TRANSFERER. 337 
 
 into the mercury in the trough, and passed under the edge of 
 the jar containing the gas ; it is then to be raised above the 
 surface of the mercury within, and the piston lifted : this will 
 cause the descent of the mercury in the chamber a within the 
 jar, which consequently will be replaced by the gas surrounding 
 it. As soon as enough has entered, the motion of the piston 
 is to be suspended, the aperture of the instrument depressed 
 into the mercury, the piston raised a very little for the purpose 
 of drawing a globule of mercury into the capillary part, the 
 chamber a again elevated into the jar to ascertain that this has 
 been done, and then the instrument removed through the 
 mercury away from the jar. The portion of gas within it will 
 be confined both above and below by the metal, and when it is 
 to be transferred to the eudiometer tube, all that is necessary 
 is, to introduce the capillary opening into the mouth of the 
 tube, and to depress the piston. The gas is immediately 
 ejected from the chamber, and in a manner so much under 
 command, that it is easy to throw up just that quantity which, 
 by the graduation on the eudiometer tube, or on the stem of 
 the instrument, is known to be required for the experiment. 
 When measuring by the graduation on the instrument itself, it 
 is necessary to bring the level within and without the jar from 
 which the gas is taken, to the same height, or else the gas 
 measured will not possess the same volume at common pressure. 
 796. The same instrument is equally useful in removing 
 portions of gas from a jar over water, and conveying them, in 
 a dry state, to a jar or tube over mercury. Being full of mer- 
 cury, it is to be introduced into the jar as before ; water rarely 
 adheres in any quantity to the summit of the capillary termina- 
 tion, or if a drop should, a slight lateral shake throws it off. 
 By raising the piston, the mercury in the chamber falls and 
 the gas enters ; to confine it there, the instrument should 
 receive a cautious jerk, so as to throw the mercury up towards 
 the capillary opening ; it will be found easy to make a globule 
 adhere there, and when that is the case, by depressing the 
 piston, to cause it to enter into the capillary part so as to close 
 it perfectly. The instrument is then to be removed from the 
 jar and water, wiped dry, and the gas conveyed into the 
 required vessel, as before. 
 
 z 
 
338 MERCURIAL TROUGH GAS MEASURED. [Sect. XV. 
 
 797. The instrument described and figured (151), is used 
 by Dr. Hare in transferring accurately measured portions of 
 gas from one vessel to another over mercury. Its use is easy, 
 and will be understood from the description given of the 
 instrument. When full of mercury, the beak is introduced 
 under the edge of the jar into the gas above, and by with- 
 drawing the rod a certain number of degrees, an equal volume 
 of the gas enters, and is easily transferred to any other vessel 
 at pleasure. 
 
 798. The general processes for measuring gas over mercury, 
 are the same with those already directed for similar operations 
 over water (767) ; the propriety of marking the jar or tube, 
 before any attempt to estimate the volume, is even greater here 
 than on the former occasion, because of the greater risk of the 
 gas escaping in transference, or of the occurrence of other 
 accidents. When regulating the quantity in a tube (775), the 
 finger is not of the service in this as in the former case, for the 
 reasons already stated (788, 789) ; but to make the utmost use 
 possible of it, with the least risk of accidental escape of the 
 gas, it should be held in a bent position under the mercury, 
 rising upwards to the extremity and not from it, that the chances 
 of escape of the gas may be diminished (789). It is in cases 
 where these difficulties with gas over mercury occur^ that 
 the instruments just described are particularly useful. 
 
 799. When the gas to be measured is in a tube, the advan- 
 tage of the process (767, 772) , in which the height is marked, 
 the gas transferred and thrown away, and its volume ascer- 
 tained by the weight of mercury replacing it (126, 131), is 
 much greater over the mercurial than over the water trough, 
 simply because it dispenses with the somewhat uncertain 
 operation of transferring the gas under mercury. But the 
 experimenter must then remember the cautions already given, 
 with regard to the opposite convexities of the mercury, when 
 it is at first confining the gas, and afterwards replacing it 
 (135) ; and besides marking the true bulk with care, he 
 should be equally careful in estimating the quantity of mer- 
 cury which is to replace it. 
 
 800. In all measurements and estimations of gas over mer- 
 cury, particular attention should be given to bring the metal 
 
Sect. XV.] MERCURIAL TROUGH LARGE JARS. 339 
 
 inside and outside the vessel to the same level ; or if there be 
 not sufficient depth of mercury for the purpose, the height of 
 the surface in the jar or tube above that in the trough should 
 be accurately measured and noted down. This becomes a 
 deduction necessary to be made from the observed height of 
 the barometer, when the volume of the gas is to be corrected, 
 and its true bulk at mean temperature and pressure ascer- 
 tained (883). 
 
 801. In experiments requiring the use of a large jar at the 
 mercurial trough, it is frequently desirable to possess the means 
 of raising or lowering the surface of the mercury in it without 
 moving the jar. Thus, if such a jar were placed over the 
 trough, and it were required to raise the mercury within an 
 inch or two, as in Lavoisier's experiment on the analysis of air, 
 it is easily done by passing one leg of a glass syphon under the 
 mercury into the jar, applying the mouth to the other and 
 withdrawing air (786). When the mercury is sufficiently 
 raised, the end of the syphon in the mouth is to be closed by 
 the tongue, which must not be removed before the other end 
 has been withdrawn from the jar, through the mercury, by the 
 same way in which it was introduced. Or if, during an experi- 
 ment, the gas has been absorbed, and the mercury stands very 
 high in a large jar, so as to require care in letting so heavy a 
 mass down, a syphon may be introduced as before, and air 
 allowed to pass into the jar through it, the mercury falling 
 gradually as the air is allowed to enter. To prevent the mer- 
 cury entering into the syphon during the transit of its extre- 
 mity through the metal, that end should be closed by intro- 
 ducing a plug of twisted paper into it, or paper should be 
 wrapped about it ; either will be sufficient to keep the metal 
 out, without stopping the passage for the air. 
 
 4. Of larger and independent Vessels, for the retaining and 
 storing of Gas. 
 
 802. Numerous vessels have been contrived for the reten- 
 tion of gas, independently of the use of jars, or of the water 
 or mercurial trough, and it is necessary that the student be 
 acquainted with the principles and uses of many of them. All 
 
 Z 2 
 
340 
 
 GASOMETER CONSTRUCTION USE. 
 
 [Sect. XV. 
 
 have their respective conveniences; some consisting in great 
 capacity, others in facility of operation, and others, again, 
 in their security as to the retention of particular gaseous 
 bodies. 
 
 803. Gasometer. The vessel usually thus designated may 
 be compared to a large jar suspended in a trough, of size just 
 sufficient to allow its entire immersion in an upright position. 
 The gas- vessel, or bell, instead of resting on a fixed support, 
 is suspended by cords or chains passing over pullies, and 
 having weights at the opposite extremities to counterbalance 
 the vessel. The trough, cistern, or tank, as it is called in large 
 instruments, is nearly filled with water, which remains constant 
 in quantity, the aerial capacity within the gas-vessel being 
 increased or diminished by raising or lowering it in the water ; 
 it is thus adapted to the quantity of gas it may contain. The 
 passage of the gas to and from the gasometer is effected along 
 pipes permanently fixed. A single pipe is sufficient in the 
 simplest form of instrument, and this commencing at any con- 
 venient place on the exterior of the tank, is conducted through 
 its bottom, and made to rise so high within, that its extremity 
 shall be above the surface of the water. By connecting the 
 external aperture with proper apparatus, 
 gas may be made to pass from it into the 
 gasometer, or from the gasometer into the 
 apparatus. The accompanying wood-cut, 
 presenting a section of this instrument, will 
 illustrate its principle, and assist the com- 
 prehension of the annexed directions for its 
 use. The actual construction of the in- 
 strument, and its numerous variations in 
 form and adjustments, make no part of 
 our subject. Gasometers were formerly 
 much more used in the laboratory than 
 at present, and great care was paid to their construction, for 
 the purpose of obtaining an uniform pressure. They may 
 be made of a great variety of materials. They have of 
 late years been constructed of enormous size in coal gas 
 works, and beautifully arranged with regard to their system 
 of pipes. 
 
Sect. XV.] GASOMETER ADJUSTMENT OF PRESSURE. 341 
 
 804. There is nothing difficult or particular in the use of a 
 gasometer. The water in the tank should never rise so high 
 as to endanger its running into the passage pipe, it being 
 necessary that this should be preserved perfectly free. If 
 water should, perchance, get into the pipe, it may be drawn 
 out at the lower stop-cock. The gas-vessel should be of such 
 depth as to sink entirely into the water when required, and is 
 advantageously contracted above into a small chamber, in- 
 tended to receive the end of the pipe, and thus to allow of the 
 expulsion of nearly all the air except the small portion the 
 pipes may contain. When it is to be filled with gas, the cocks 
 should be opened, the bell depressed, until it be as empty of 
 air as possible ; one of the cocks is to be shut, and the other 
 connected by a tight joint, with the apparatus delivering gas. 
 This may be a retort, or a bladder, or a funnel placed in the 
 water trough, or in any other vessel. When the operation is 
 over, or the gasometer sufficiently full, the stop-cock is to be 
 closed, and the junction to be disunited. 
 
 805. When the gas within the gasometer is required for use, 
 it may be taken out at that stop- cock which is most convenient. 
 If it be desired to fill a bladder, it should be attached to the 
 end of the stop-cock ; or if a jar over the pneumatic trough is 
 to be filled, a piece of tube should replace the bladder, and its 
 open extremity pass into the water of the trough under the 
 jar (748) ; or if it be required to pass a stream of the gas 
 through a blow-pipe (251), the blow-pipe should be attached 
 to the end of the tube just mentioned. 
 
 806. The entrance or exit of gas to and from the gasometer, 
 is governed principally by the pressure exerted upon the con- 
 tents of the vessel ; this being again dependant upon the pres- 
 sure exerted by or through the bell itself. If the hand press 
 upon the bell it presses also upon its contents ; in consequence 
 of which the water on the outside rises to a higher level than 
 that inside, and the gas tends to issue by any open channel, 
 and with a force proportionate to the pressure. On the con- 
 trary, if the bell be forcibly raised by the hand, the previous 
 pressure is diminished, and to such an extent as to make it less 
 than that of the atmosphere on the exterior ; the level of the 
 water without falls, and becomes lower than that within, and if 
 
342 GASOMETER EXAMINED MERCURIAL. [Sect. XV. 
 
 any passage be open, the air will enter into the gasometer, 
 being forced inwards by the superior external pressure. 
 
 807. These variations and arrangements of the pressure on 
 the contents of a gasometer are very important, but in practice 
 they are effected by the addition of weights either to the bell 
 or to its counterpoise, or the inverse subtraction of them, which 
 has the same effect. Any arrangement of weights which makes 
 the bell preponderate, increases the pressure in proportion to 
 that preponderance ; the reverse arrangement diminishes the 
 pressure. Now, on receiving gas into the instrument, care 
 should be taken that the preponderance of the bell should be 
 no more than what is easily overcome by the effort of the gas 
 to pass in, and it may sometimes be almost entirely removed 
 with advantage. On the contrary, when the gas in the vessel 
 is to be used, a pressure outwards is required, more or less, 
 according to the force which opposes the transfer ; thus, but 
 little pressure will enable it to pass from the gasometer into the 
 air, or into a bladder in the air, though more will be necessary, 
 when it has to be thrown out through an aperture at the depth 
 of two or or three inches or a foot under water. 
 
 808. When a gasometer is received from the instrument- 
 maker, it should in the first place be examined as to tightness. 
 This is done by putting water into the cistern, then half filling 
 the bell with air, closing the apertures, loading the bell con- 
 siderably so as to occasion much pressure outwards, and leav- 
 ing it so for some hours. If at the end of that time the bell 
 has not sunk below its first position, it indicates the tightness 
 of the instrument. 
 
 809. A mercurial gasometer is the same in principle as those 
 already described, but in order to avoid the weight and ex- 
 pense which would arise from filling the cistern with mercury, 
 its interior is principally occupied by a core, allowing space 
 enough between it and the sides of the cistern for the jar, and 
 for mercury to make it tight. The first instrument of this 
 kind has been described by Mr. Clayfield*, and was con- 
 structed of glass. To Mr. Pepysf we are indebted for an 
 excellent instrument of this sort made of iron, and having a 
 
 * Davy, Researches, Chemical and Philosophical p. 573. 
 f Phil. Mag. v. 154. 
 
Sect. XV.] GASOMETER MERCURIAL PEPYS 5 USE OF. 343 
 
 very convenient arrangement for the introduction of gases from 
 retorts. This has been connected by Mr. Newman with his 
 
 large mercurial trough*. 
 The accompanying sec- 
 tional diagram will illus- 
 trate the arrangement by 
 which the gasometer is 
 charged : the iron core and 
 the sides of the cistern may 
 be distinguished, and the 
 jar is seen half full of gas, 
 and closed by a stop-cock 
 above. The core is tra- 
 versed by a perpendicular 
 passage consisting of a 
 glass tube cemented into 
 its place, which being open 
 above into the bell of the 
 gasometer, terminates be- 
 neath in a stop-cock. To this a small funnel is attached by a 
 screw cap cemented upon it ; and beneath the funnel is placed 
 a glass cup or dish containing mercury, and raised so high as 
 to cover the edge of the funnel, about the third or fourth of an 
 inch in depth. It, in fact, is a small mercurial trough, by 
 means of which the gas from the retort is made to pass into the 
 funnel, and from thence through the core into the jar above. 
 On commencing operations after the gasometer has been filled 
 with mercury, the jar found to be in order, the stop-cocks clean 
 and moveable, and the trough beneath arranged, the first step 
 is to open both stop-cocks, and to depress the jar in the mer- 
 cury until all the air is excluded, then closing the upper cocks 
 to leave the jar to itself. The buoyancy of the glass in the 
 mercury will cause a tendency to rise, and cause also the ascent 
 of the mercury a little way in the funnel beneath, above the 
 surface of that in the dish. If, after leaving it an hour or two 
 in this state, it be found that the jar has not risen higher than 
 at first, the tightness of the instrument is ascertained. The 
 beak of the retort, or the end of the tube delivering gas, is 
 
 * Quar. Jour, of Science, i. 185. 
 
344 
 
 GASO'METER PEPYS 5 GAS-HOLDER. 
 
 [Sect. XV. 
 
 then to be passed beneath the edge of the funnel, the gas al- 
 lowed to enter the latter, and the jar will be seen to rise at 
 every bubble. When as much as is equal to the contents of 
 the funnel, and the tube of the gasometer has entered, the 
 upper cock is to be opened, and the jar depressed, its contents 
 thrown out, the cock shut, and the gas collected as before. 
 This is to be done once or twice more, to insure the rejection 
 of all common air, and then the future portions of gas are to 
 be collected and preserved for use. When the gasometer is 
 full, the retort is to be removed, the lower stop-cock shut, the 
 temporary trough taken away, and the included gas reserved 
 until required. When wanted, it is to be drawn off from the 
 upper stop-cock, the apparatus being connected with it in the 
 usual manner. 
 
 810. The gasometer has been to a great extent super- 
 seded by another instrument, also the invention of Mr. 
 Pepys*, which can hardly be dispensed with in the labora- 
 It has been called a gas-holder, and is' a valuable 
 vessel for the retention of a stock 
 of oxygen or any other gas, which 
 is in constant requisition. It is 
 usually made of japanned copper, 
 and consists of a close cylindrical 
 vessel, surmounted by a circular 
 trough of the same diameter, but 
 comparatively of small depth ; a 
 pipe a, proceeds from the bottom 
 of the trough, and passing through 
 the top of the air-chamber, de- 
 scends until near the bottom, where 
 it terminates in an open extremity. A second pipe, 6, also 
 passes downwards from the trough, but merely enters into 
 the top of the air-chamber. Both these are closed by stop- 
 cocks,/, h, placed between the trough and the chamber. A 
 stop-cock, g, is also inserted into the top of the air-chamber 
 on one side, and finally a short piece of wide pipe, c, enters 
 through the side of the air-chamber near the bottom, and 
 is placed obliquely, so that the highest part of the edge 
 * Phil. Mag. xiii. 153. 
 
Sect. XV.] PEPYS* GAS-HOLDERHOW FILLED. 345 
 
 of the inner aperture shall be lower than the lowest part 
 of the edge of the outer aperture, by at least half or three 
 quarters of an inch. It is closed and made air-tight occa- 
 sionally by a plug which screws into the aperture. A glass 
 tube is cemented into two sockets at d and e, which opening 
 into the air-chamber, render the tube in fact a part of that 
 cavity ; its use is to indicate the quantity of water, and con- 
 sequently the quantity of gas, within. All the joints and 
 seams should be perfectly air-tight; this point may be ascer- 
 tained in the following manner. The aperture c being closed 
 by its proper plug, the three cocks above are to be opened, 
 and water poured into the trough and allowed to descend 
 into the air-chamber until it is full; the vessel is then to be 
 inclined a little, the lateral stop- cock being raised upwards 
 so that the air may escape by it until water only issue. This 
 and the other stop-cocks are then to be closed, and the guage 
 observed to ascertain whether the vessel be full of water, 
 or if a bubble of air be at the top, to mark the place where 
 it stands. The plug at c is then to be unscrewed and re- 
 moved. The water cannot escape there in consequence of 
 the manner in which the pipe c is inserted, unless the air 
 finds access inwards above at the same time; and if there 
 should be any leak, the weight and tendency of the water 
 to descend will draw the air through it. Upon standing 
 therefore a few hours, it will be easy to ascertain by the guage 
 whether the vessel be tight : i. e. whether any air has gained 
 access, or any water has run out excepting the first small 
 portion. 
 
 811. The process of filling this vessel with gas is exactly 
 the same in principle as filling a jar over the pneumatic 
 trough. The stop-cocks are to be closed, the aperture c 
 opened, and the beak of the retort or the tube delivering gas 
 is to be introduced at c; the gas will bubble up through the 
 water and displace the fluid. Provision, however, is to be 
 made to convey away the water. For this purpose the gas- 
 holder may be filled near the sink, and the water allowed to 
 run out ; or if it has to be brought towards the furnace, as 
 in the making of oxygen gas, it may be mounted on a stool, 
 and the water received into a pail placed beneath the open- 
 
346 PEPY'S GAS-HOLDER TRANSFERENCE. [Sect. XV. 
 
 ing. In such cases it will be found useful to hang a piece 
 of wet tow about the tube conducting the gas, so as to be 
 in contact with the edge c ; this will lead the water into the 
 pail (468). 
 
 81S. The descent of the water, and therefore the quantity 
 of gas introduced, is indicated by the guage. When the gas 
 bubbles out at c, the vessel can retain no more: the tube or 
 retort is to be withdrawn, the plug screwed up tight, and in 
 that state the gas is securely confined, and may be preserved 
 for many months provided water is retained in the trough above. 
 
 813. No difficulty occurs in transferring the gas from this 
 vessel into any other that may be required. The lower aper- 
 ture is, in these cases, of no use, and is to be kept closely shut. 
 Upon opening the stop-cock of the pipe a, the water will flow 
 down it to the bottom of the air-chamber until such time as, 
 having accumulated there, the gas above is compressed by a 
 force equal to the weight of the column of water in the tube 
 and trough. No more water will then descend unless the 
 stop-cock f or g be opened, when the gas will immediately 
 rush out, urged on by the column of water in the tube, and 
 the water above will supply its place. The process, therefore, 
 of filling a jar or a bladder, or passing the gas through a tube, 
 is very simple. In transferring it to a jar, for instance, the 
 latter must be first filled with water, inverted (753) in the 
 water of the trough, and placed over the aperture of the pipe 
 b ; then having opened h as before described for the purpose 
 of causing pressure on the gas within, the stop-cock/ is to be 
 carefully opened, when the gas will rush up and quickly fill 
 the jar. The water from the jar descends into the trough to 
 supply the place of that which passes into the air-chamber. 
 The cock f is to be closed as soon as enough gas has passed 
 out, when h is to be shut, the jar of gas transferred and used 
 as may be required. Or suppose that a bladder is to be filled 
 with gas : the common air is first to be thrown out, the bladder 
 attached to the cock </, pressure is to be given by opening h, 
 then g is to be cautiously opened, and the bladder to be filled ; 
 the water which is necessary being supplied to the trough 
 above from a jug or pail ; finally, the cocks g and h are to be 
 shut, and the bladder removed. 
 
Sect. XV.] PEPYS* GAS-HOLDER TRANSFERENCE. 347 
 
 814. It is sometimes necessary to introduce gas from a 
 bladder into the gas-holder. In that case the full bladder is 
 to be attached to the cock </, all the cocks being closed ; the 
 plug at c is to be opened, and then the cock at g cautiously 
 turned to allow the gas to pass in, the water at the same time 
 passing out ; the cock is then to be closed, and finally the 
 plug c. 
 
 815. If the transfer of gas is to be effected through a tube, 
 as for instance, in arranging the oxygen blow-pipe (251), or 
 supplying inflammable air to a jet, the pipe must be attached 
 to the cock y ; the pressure of water given as before, and the 
 emission of gas regulated by the extent to which the stop-cock 
 g is opened. 
 
 816. The inventor has provided, even for occasions on 
 which a greater pressure than that of two feet of water may be 
 required, by associating a long tube and funnel with the instru- 
 ment. This being screwed into the mouth of the pipe a, 
 where it enters the trough above, and retained full of water, 
 subjects the gas in the instrument to the pressure of a column 
 four feet in height, and is occasionally very useful. 
 
 817. It requires no particular skill to make one of these air- 
 holders out of a good cask by the addition of a few tubes, 
 cocks, and a funnel : but it must always be retained moist. 
 
 818. It is essentially necessary that in all the transfers of 
 gas from the instrument, an abundance of water be retained 
 in the trough above, to supply the place of that which passes 
 into the air-chamber. It is also necessary to be aware of the 
 possible introduction of common air with the water, even when 
 there is considerable depth in the trough. When the gas is 
 passing rapidly out at the lateral stop-cock, and consequently 
 the water rapidly descending through the tube, it will, if 
 unattended to, frequently acquire a rotary motion, which, from 
 mechanical causes easily explained, will at last produce an 
 aperture commencing at the surface of the water and descending 
 to the very bottom of the tube. Down this, air is rapidly 
 carried by the descending water, which, mixing with the gas 
 in the instrument, deteriorates it, and with inflammable gases 
 may lead to dangerous results. Hence this rotary motion, 
 when observed, should be disturbed. The formation of the 
 
348 GAS-VESSELSBLADDERS. [Sect. XV. 
 
 central channel for air may easily be prevented by allowing a 
 large bung or a piece of light wood to swim on the surface of 
 the water. If rotation does take place, it will draw the floating 
 mass to the centre, and prevent the air from passing down by 
 hindering the formation of a channel, if water be plentifully 
 supplied. 
 
 819. When gas-holders are to be left for several weeks or 
 longer with gas in them, it is advantageous to put a board over 
 the water in the cistern or upper part. It prevents the evapo- 
 ration of the fluid too rapidly, and retains all in order. 
 
 820. Amongst vessels for the retention of gas may be 
 classed bladders and bags' they are very useful in many 
 receiving or transferring operations, or when subjected to 
 pressure, in supplying a constant stream of gas for a length of 
 time. Bladders of different sizes are required. The necks 
 should be softened by water, opened, drawn over the lower 
 part of a cap similar to a retort cap (833), and tightly tied 
 with twine. A stop-cock screwed into the cap renders the 
 vessel complete. If the bladders are used in a dry state, the 
 mechanical action to which the membrane is subjected during 
 expansion and contraction, and otherwise, soon breaks the 
 substance, and they become useless. To prevent this, and 
 also to remove their rigidity, which is inconvenient, bladders 
 are commonly moistened before being used. This renders 
 them very conveniently flexible for present purposes, but they 
 become more and more rigid each time they are wetted and 
 dried, and soon break into holes. A bladder may be made to 
 continue tight for a considerable period by pouring a little oil 
 into it at first, and allowing it to become saturated. It is not, 
 then, to be wetted for use, and is at no time so pleasant to 
 work with as a wet bladder. Bladders should be kept in a 
 moderately expanded state, not tightly blown, nor on the con- 
 trary compressed together ; and this is more particularly neces- 
 sary with those bladders which are wetted each time they are 
 used, and are laid aside in a moistened state. Bladders are 
 not perfectly tight to gases, and are less so when dry than 
 when moist ; consequently gases should not be retained long in 
 them, and never longer than is absolutely necessary. Hydro- 
 gen passes through them more rapidly than any other gas. 
 
Sect. XV.] GAS-BAGS CAOUTCHOUC GAS-BOTTLES. 349 
 
 821. Gas-bags are made of oiled silk, or of two layers of 
 woven material, having between them a layer of caoutchouc or 
 India rubber, which serves to bind the whole into one imper- 
 vious substance ; they are furnished with a cap and stop-cock, 
 like the bladders just described. Those made of oiled silk 
 are seldom tight, and rapidly increase in porosity. Those 
 manufactured with caoutchouc are superior, and when the 
 substance has been prepared for this purpose with a thick coat 
 of that peculiar body, may be made permanently air-tight. It 
 is, however, to be understood, that the fabrics sold as water- 
 proof, and stated to be made so by caoutchouc, are not suffi- 
 ciently air-tight for these applications. These bladders and 
 bags are useful in transferring gases from vessel to vessel, as 
 between jars and air-holders ; and when filled and covered 
 with a weighted board, they will supply a constant stream of 
 gas for a length of time. 
 
 822. Caoutchouc or India rubber bottles are useful vessels 
 in particular circumstances, and may be had at the instrument- 
 makers ; their uniform expansion in all directions having been 
 previously ascertained. It is necessary to introduce the gas 
 by a condensing syringe, in consequence of the force required 
 to dilate the bottle ; but being introduced, the spontaneous con- 
 traction of the caoutchouc upon it is very useful in forcing it 
 out through the stop-cock, and hence the particular uses of 
 these bottles (252). A bottle, at first not more than three 
 inches in diameter, may be extended till it contains half a 
 cubic foot of gas or more, and upon allowing its contents to 
 escape, will contract to nearly its original size. 
 
 823. Those who endeavour to prepare these bottles for 
 themselves, will not succeed with more than one in four or five. 
 They should be selected of uniform thickness, and without 
 external marks or depressions; those which are lightest in 
 colour are generally best. They should be heated in hot 
 water, or in steam, for an hour or two, and then rolled between 
 the hands until they become perfectly flexible ; when cold they 
 should be tied upon caps, having a stop-cock and a syringe 
 attached; the air is then to be gradually thrown in. The 
 bottle, when fully distended, generally becomes thin at one 
 place first ; if upon expansion by air this thinness extends to 
 
350 GAS-BOTTLES EXAMINED FILLED. [Sect. XV. 
 
 the neighbouring parts, all is well ; but if it increase rapidly 
 and partially, there is little chance of the bottle being made 
 useful. The air should be introduced in successive portions, 
 a lapse of time being allowed after every few strokes of the 
 piston, especially during the first expansion. Caoutchouc 
 bottles, thus fully expanded and rendered thin, should not be 
 exposed to heat on one side only or partially, for the heat, 
 diminishing the cohesive attraction, allows the neighbouring 
 parts to contract by distending the heated part, which, 
 becoming gradually thinner, at last burst into a hole. 
 
 824. Finally, glass bottles are frequently of great service in 
 the retention and preservation of gases, and more especially 
 of chlorine gas, which cannot be retained for any length of 
 time over water, in which it dissolves, or over mercury, on 
 which it acts. The bottles should be wide-mouthed and accu- 
 rately stoppered (433), their capacities being from four or six 
 ounces to a quart. The necks and the stoppers should in the 
 first place be wiped dry, a little tallow or lard applied to the 
 stopper, and the latter moved round in its situation, so as to 
 disperse the tallow over the ground surfaces, and render the 
 stopper easy in its motion and at the same time air-tight. The 
 bottles should then be filled with gas as if they were jars (751), 
 the stoppers put in under water, and pressed into their places, 
 and then the bottles be stored away in a dark place of nearly 
 uniform temperature, in an inverted position, and with the 
 stopper and neck immersed in water. This may be done by 
 providing earthenware jelly pots, or similar vessels, one for each 
 bottle. When water is put into these, and the bottles inverted 
 in them, the gas is rendered perfectly secure, and may be pre- 
 served for months, and even years. These receiving vessels 
 may be conveniently made out of fractured wine bottles, when 
 they remain sound towards the bottom, the upper part being 
 cut off by a hot iron or otherwise (1214). 
 
 825. Dry bottles may be filled with such gases as, being 
 either much heavier or lighter than atmospheric air, are at the 
 same time soluble in water, and cannot be collected over that 
 fluid. For light gases, such as ammonia, the bottle to be filled 
 is to have its stopper greased, and is then to be placed in a 
 vertical position, with the mouth downwards over the end of the 
 
Sect. XV.] DRY GASES STOP-COCKS. 351 
 
 tube or retort neck delivering the gas, which at the same time 
 is to be directed upwards, until it touches the bottom of the 
 bottle ; the light gas occupies the upper part of the vessel at 
 first, and gradually displaces the air : ultimately, from the 
 addition of fresh portions above, it flows out at the mouth of 
 the bottle, and when by applying a slip of moistened turmeric 
 paper to the aperture, it is judged from the change produced 
 that the gas in the bottle is nearly or quite pure, the tube or 
 retort is to be gradually withdrawn, with as little disturbance 
 of the gas within as possible, and the stopper instantly put into 
 its place. 
 
 826. Many gases, such as muriatic, sulphuric, or carbonic 
 acid gas, are on the contrary conducted downwards to the bot- 
 toms of bottles placed with their mouths upwards, which when 
 they freely overflow with gas at the mouths, are to be with- 
 drawn and quickly stopped. The overflowing of the muriatic 
 acid gas is known by the fumes which seem to issue from the 
 mouth of the bottle. The fullness of vessels receiving sul- 
 phurous or carbonic acid gases may be ascertained by bringing 
 a lighted taper carefully near the mouth, the rapidity and ap- 
 pearance of its extinction being a sufficient indication. In all 
 these cases it is necessary to allow an excess of gas to pass 
 through the bottles, and to continue the introduction of fresh 
 gas even after the bottle is supposed to be full, a portion being 
 willingly thrown away to ensure the greater purity of that 
 which is retained. The gases above mentioned may readily 
 be collected, especially in small bottles, intermixed with not 
 more than between a fiftieth and a hundredth part of com- 
 mon air. 
 
 5. Connexion and Communication. 
 
 827. Having already had occasion to mention caps and stop- 
 cocks, it will be necessary more particularly to consider the 
 general uses and arrangement of these and other pieces of 
 apparatus, intended to facilitate the connexion or disjunction 
 of different instruments, or the different parts of a complicated 
 arrangement. Laboratory stop-cocks are usually made of brass, 
 and are terminated by a male screw at each end rising from a 
 flat shoulder, so that the intervention of a washer, or collar of 
 
352 STOP-COCKS EXAMINED TIGHTNESS. [Sect. XV. 
 
 leather (830) renders them, when screwed up into their proper 
 apertures, perfectly air-tight. The plug of the cock should 
 be very accurately ground into its socket, that no air may pass 
 it. It is usually held in its place by a collar and screw, so that 
 the experimenter can take it out, examine it, and apply a little 
 wax or fat, whenever there may be occasion. The passage 
 through the cock should not be more than one-eighth of an 
 inch in diameter, and is even advantageously smaller where it 
 passes through the plug, for then its section upon the plug and 
 socket is diminished, and the tightness and security of the cock 
 increased. 
 
 828. These stop-cocks are necessarily subject to injury 
 during use, many gases, as chlorine, ammonia, Sec, having 
 powerful action upon the metal: they should be frequently 
 looked at, examined, and the plug lubricated (827, 433). It 
 is often necessary to cleanse the air-way, and remove such ob- 
 structing matter as has either collected or been formed there. 
 This may be done with a stiff wire ; but particular care should 
 be taken, in such operations, that the plug itself, or its socket, 
 be not scratched, or the apertures formed by the air- way upon 
 their surfaces injured, which would soon destroy the tightness 
 of the instrument, and render it useless. The plug when 
 turned round in its socket should move easily and steadily, 
 allow of no shake in any direction, and not permit air to pass. 
 For this purpose, even when new, a little wax or grease should 
 be applied. Tallow is the substance usually resorted to, but a 
 mixture of two parts yellow wax and one part sweet oil is 
 much better, since it preserves the tightness of a stop-cock that 
 is slightly injured, longer than tallow or pomatum. The plug 
 and socket of a foul stop-cock should be cleaned with a cloth, 
 and not with a hard instrument. 
 
 829. If the plug adhere, as though, from chemical action or 
 otherwise, it had become so fixed as to be almost immovable, 
 its screw and collar are to be removed, and by tapping the end 
 with wood (not with metal) attempts are to be made to drive 
 it out of its place. If it resist this, and also some degree of 
 force applied to turn it, a little oil is to be dropped in at each 
 end of the stop-cock, and also applied to the end of the plug, 
 and then the whole should be warmed and left for an hour or 
 
Sect. XV.] STOP-COCK WASHERS. 353 
 
 two, when it may generally be moved. The plug of an old 
 stop-cock commonly requires more wax or tallow than a new 
 one ; this should not be allowed to accumulate in the air- way, 
 where it is of no use, but a little piece being put upon each 
 side of the clean dry plug, the latter is to be introduced into 
 the socket, equally clean and dry, and then turned round a few 
 times to effect its equal and proper distribution. When chlo- 
 rine or ammonia has passed through the stop-cocks, the sooner 
 they are looked at and aired or washed as occasion may require, 
 the better. 
 
 830. Washers or collars are round pieces of soft substances, 
 as leather or paper, which, having holes in the middle, are 
 passed over the male screws of the stop-cocks, so that when 
 the latter are connected with other apparatus, the washers are 
 between their shoulders and the sides of the aperture into 
 which the cocks are screwed, and make the joints impervious. 
 They are usually punched out of thin boot or shoe leather, and 
 the pieces being soaked in oil for a day or two and then cleaned, 
 are ready for use. It is better for many purposes to use wax 
 instead of oil on these occasions. Yellow wax should be 
 melted and the washers put into it for five minutes; when 
 taken out, they are to be allowed to drain a moment or two, 
 and suffered to cool. When required for use, they should be 
 rendered flexible by the warmth of the hand, before they are 
 put into their places. Such collars will occasionally remain 
 tight for hours together at a pressure of from ten to thirty 
 atmospheres, when an oiled washer would inevitably have 
 leaked ; and they are more secure and constant even at com- 
 mon pressures. 
 
 831. When the joint has to bear a temperature near to or 
 above 21 2, one or more thicknesses of card answer the purpose 
 of a collar better than leather. Sheet caoutchouc (449), similar 
 to that prepared by Mr. Hancock, may be formed into excel- 
 lent collars for particular occasions, but it is necessary to be 
 cautious in screwing up the joint. Caoutchouc, from its elas- 
 ticity, becomes readily adapted to the surfaces immediately 
 upon contact, so that but little pressure renders the joint per- 
 fectly tight. On the contrary, were the cock tightly screwed 
 up, the force would be sufficient to press out nearly all the 
 
 2 A 
 
354 RETORT CAPS EXAMINED ATTACHED. [Sect. XV. 
 
 caoutchouc at the edges of the joint ; this although it would 
 not destroy the tightness of the arrangement, would be of no 
 use, and would injure the collar and spoil it for future service. 
 All dirt should be removed from the surface of the shoulders 
 before the collars are put on, or otherwise it will occasion irre- 
 gular pressure, and interfere with the tightness of the joint. 
 
 832. Some variations in the ordinary chemical stop-cock 
 have been recommended, but have not been received into 
 common use. Mr. Griffiths advises that the air-way be lined 
 by a tube of platina, so as to prevent, to a considerable degree, 
 the action of gases and other substances passing through or 
 retained in it *. Signor Crivelli has combined a conical metallic 
 valve with the stop-cock, for the purpose of rendering it more 
 tight and manageable when employed to retain gases under 
 great pressure (*. 
 
 833. Retort caps are cylinders of thin brass plate, contracted 
 at one extremity by the insertion of a thick ring, in which a 
 female screw is cut, and turned flat at the end so as to screw 
 up tightly against the shoulder of the stop-cock. These caps 
 are of various diameters to fit tubes and necks of retorts of 
 different sizes. The flat extremity at the head of the cap, 
 which screws up against the shoulder of the stop-cock, should 
 have two or three concentric grooves (merely deep lines) 
 turned in it, which will render its bearing against the collar 
 more air-tight and secure. These lines or grooves should be 
 kept free from dirt by having a point run along them occa- 
 sionally, and the worm of the screw should also be preserved 
 clean and free from obstructing matter. 
 
 834. Caps are fastened upon the ends of tubes or retorts 
 with a particular cement (11 S3), in the following manner. 
 One is to be selected of such size as to admit the tube and 
 allow a space for cement about the thickness of a card, or a 
 little more, but the cap should never be so small as itself to 
 gripe the glass, or any larger than is necessary to allow room 
 for cement to surround the glass. The cement should be 
 heated to fluidity on the sand-bath, but not to a greater de- 
 gree ; the cap should be warmed over a candle or lamp until 
 
 * Transactions of the Society of Arts, xlii. p. 29. 
 f Quarterly Journal of Science, viii. p. 346, 
 
Sect. XV.] RETORT CAPS CONNECTERS. 355 
 
 it is hot enough to melt cement, and then that part of its in- 
 terior which is intended to come against the glass, namely, the 
 sides of the cylinder, should be covered with the hot cement, 
 applied by a piece of stick. The cap being then laid on its 
 side by the sand-bath to keep it from cooling, the end of the 
 tube or retort is next to be warmed, and a coat of cement 
 applied on the exterior, over every part which is to come into 
 juxtaposition with the cap, but the other parts are not to be 
 unnecessarily soiled ; so much cement is to be left adhering to 
 the glass, that with what there is in the cap, there may be an 
 excess above the quantity that can be retained between the 
 glass arid metal when the two are fitted together. When the 
 cap, glass, and cement, are all so warm that the latter is fluid, 
 or very soft, the cap is to be placed upon the tube, thrust into 
 its right position, receiving a little rotatory motion at the same 
 time, to distribute the cement equally over all parts, and is 
 afterwards to be set aside to cool. When this is well per- 
 formed, the retort neck, or tube, should pass along until it be 
 stopped by the inside of the shoulder ; no cement should soil 
 its interior, or project within the cap, but it should fill every 
 part between the glass and cap, to make a firm, tight junction, 
 and project in a ring from the edge of the cap over the exterior 
 of the glass. The superabundance is easily removed by a 
 knife, and the annular surface left made smooth and tight by 
 a hot wire passed rapidly over it. If a piece of cement, 
 pushed on by the edge of the glass, project in the inside of the 
 cap, it should, when nearly cold, be cut off by a knife, and 
 removed, so that no loose fragment may remain in the retort 
 or tube. 
 
 835. When there is a deficiency of apparatus, and caps are 
 wanting, their place may be supplied for the time by corks. 
 Thus, if there be no cap large enough for the aperture of a 
 jar or tube, a very good cork may be selected, made to fit 
 tightly into the aperture, a hole pierced through it, and the 
 cock screwed into this hole ; care being taken that the cork be 
 not divided or torn to pieces by the force applied. This may 
 be done so as to be quite tight, or if a small leak occur, a little 
 soft cement (1125) will make all secure. 
 
 836. Connecters are short perforated pieces of metal, tra- 
 
 2 A 2 
 
356 STOP-COCKS AND CAPS. [Sect. XV. 
 
 versed by a female screw, and terminated by flat surfaces at 
 the ends, so as to screw tightly against the shoulders of stop- 
 cocks (827). They have on their extreme surfaces concentric 
 grooves, like those on the ends of retort caps (833), to meet 
 and hold against the collars. Their use is to connect together 
 stop-cocks or other parts of apparatus terminated by male 
 screws, and hence their name. They are best made square on 
 the exterior, being then more firmly held in the hand, or by a 
 key, when tightly screwed. The clean state of the worm, of 
 the screw, and of the grooves, should be attended to (833). 
 The want of these connecters may at times be supplied by a 
 sound perforated cork (835, 1331). 
 
 837. The screws of all these stop-cocks, caps, and con- 
 necters, should be cut with the same thread, so as readily to 
 fit each other ; several of each should be ready for use, and 
 preserved in a drawer appropriated to the purpose (25) ; those 
 which are old or leaky are to be repaired or rejected, and the 
 rest kept clean and in good order. 
 
 838. The tightness of stop-cocks, as well as that of their 
 junctions with connecters and caps, and also of caps when 
 cemented upon retorts, may be determined in several ways. 
 If, for instance, it be required to ascertain whether a stop-cock 
 is tight, it may be screwed to the plate of an air-pump, and 
 the pump worked until the gauge indicates considerable ex- 
 haustion. If, without further working of the pump, this indi- 
 cation continue unaltered for some time, it is a proof that the 
 stop-cock is tight. Or the cock may be screwed into the top 
 of a capped jar (742) standing in the water-trough, the water 
 raised in the jar to near the top, its situation marked whilst 
 the jar stands on the shelf, and then again after several hours : 
 if it remain unchanged the cock is tight. Or a still simpler 
 method, and on the whole a very good one, is, to close the 
 cock, to apply one end to the mouth, to exhaust the air within 
 the small cavity as much as possible by the mouth, and closing 
 the aperture by the lip or tongue, to allow it to be forced 
 against the cock by the pressure of the atmosphere. If, after 
 a few minutes, the adhesion remains sensibly undiminished, it 
 is a proof that the stop-cock is sufficiently tight to resist the 
 passage of air under considerable pressure. 
 
Sect. XV.] CONNECTION OF TUBES PAPER TUBES. 357 
 
 839. If it be required to ascertain whether a cap has been 
 fixed upon a retort, so as to be quite air-tight, all that is neces- 
 sary is to screw in a stop-cock before ascertained to be secure, 
 to attach this to the air-pump, and then to exhaust ; if the 
 gauge remain for some time as high as it was raised by the 
 exhaustion, all is tight, or if it fall, air finds admission. The 
 same trial may be made, though not so rigorously, by attach- 
 ing the retort and stop- cock to a transfer or capped jar, nearly 
 filled with water, and standing on the shelf of the pneumatic 
 trough, and then opening the communication. The level of 
 the water, after the first depression, should be marked, and if 
 it fall not soon afterwards, it is a proof of tightness under 
 pressures equal to that of the column of water in the jar. 
 
 840. The apertures of tubes are frequently made to com- 
 municate with other apertures very advantageously by con- 
 necters of caoutchouc, the formation and application of which 
 have already been described (449). When of a conical shape, 
 they connect apertures of different dimensions, conferring great 
 flexibility and security upon the apparatus (844). 
 
 841. Tubes for the conducting of gas and vapour, though 
 frequently formed of rigid materials, as glass, metal, or por- 
 celain, (699? &c.) are also sometimes advantageously con- 
 structed of flexible substances. Tubes of caoutchouc three 
 or four feet or more in length, are easily made from Han- 
 cock's sheet caoutchouc, in the manner already described (449), 
 small tubes of six or eight inches long being joined at the 
 extremities, by surfaces freshly cut with a clean sharp knife. 
 Mr. Hancock also makes flexible air-tight tubes of any length, 
 of canvass and other fabrics, imbued with caoutchouc in the 
 liquid state : similar flexible tubes are likewise manufactured 
 of canvass and oil boiled with litharge, &c. 
 
 842. It may be useful for the student to know, that very 
 excellent tubes may be formed of pasted paper, sufficiently 
 tight to be serviceable on an emergency in numerous experi- 
 ments upon large quantities of aeriform substances, such as 
 coal-gas, fire-damp, carbonic acid, &c. They should be made 
 by rolling three or four thicknesses of paper round a glass 
 tube, a rod, or a wire, one half of the paper being pasted so as 
 to cause at least the two outer folds to adhere throughout. If 
 
358 
 
 SOLUTION OF GASES WOULFE S BOTTLES. [Sect. XV, 
 
 after they are made they be brushed over with oil, or being 
 first warmed, with melted wax, they become very tight. A 
 tube very nearly tight enough to hold gas under small 
 pressures may be made simply by rolling up smooth writing 
 paper, and tying it round with thread. When such a tube is 
 wanted for the conveyance of fluids, the paper may be first 
 oiled or waxed, and then rolled into form (1337). 
 
 843. When tubes are used for the ready and rapid con- 
 veyance of gas, it is desirable that they should be of sufficiently 
 large dimensions. No difficulty occurs in the usual course of 
 laboratory experiments, but in the arts, and sometimes in 
 large experiments upon the transmission of gas, air, or steam, 
 much annoyance has risen from the contracted dimensions of 
 the tubes employed. 
 
 844. In numerous cases of solution or chemical action 
 exerted upon or by gases, there is occasion to pass the gas 
 over successive portions of other substances, and these, when 
 liquid, are best placed for this purpose in an arrangement 
 of vessels first devised by Glauber, but which with some 
 modifications, has since received the name of Woulfe's appa- 
 ratus (475, 959). 
 
 In the general arrangement^ a series of close vessels are 
 placed side by side, connected by tubes, which originating 
 from the top of those which precede in the series, descend to 
 
 the bottom of such as suc- 
 ceed * as in the delineated 
 bottles a, 6, c, and the tubes 
 1, , 3. The gas is supposed 
 to be delivered into the bot- 
 tle a, by the tube 1. After 
 having acted upon the water or solution there, it passes out 
 by the tube 2, into the bottle 6, and from thence by the 
 third tube to the bottle c. Now it is necessary in this ar- 
 rangement that the junctions of the tubes with the bottles be 
 air-tight, or the pressure exerted upon the gas by the fluid 
 through which it is to pass will cause it to escape. These 
 junctions are made in various ways. The tubes may some- 
 times pass through corks, and be tied round with bladder, 
 or be luted (465, 475, 1100, &c.), as has already been de- 
 
Sect. XV.] WOULFE'S BOTTLES JUNCTIONS. 359 
 
 scribed; or the joints may be ground air-tight, another mode 
 of effecting a junction, which has been noticed (475). But 
 these and similar junctions give a stiffness and rigidity to 
 the whole apparatus, which in consequence of the compa- 
 rative slenderness of the tubes, and the size and weight of 
 the parts connected by them, involves considerable risk of 
 fracture to the former, or at least of derangement at the 
 joints by very slight shaking or motion given to the latter. 
 Hence it is desirable to have flexible or moveable junctions, 
 and this is well effected by the use of such caoutchouc 
 tubes or collars, as they may be called, as, being of a 
 conical form, may be tied at the upper edge round the centre 
 tube, and at the lower round the tubulature (451), as is repre- 
 sented at the tubes 2 and 3, bottle 6. These may be used 
 with most gases, chlorine being perhaps the only one likely 
 to be passed through a Woulfe's apparatus that will act upon 
 them. 
 
 845. Another very excellent though more expensive mode 
 of forming a moveable junction, is represented by tube 3, bofc- 
 tie c. A wide tube is selected and fixed air tight, either by 
 grinding or otherwise, into the tubulature ; it descends nearly 
 to the bottom, and is cut off oblique] y, so as to present an 
 oblique aperture. The connecting tube 3, is made to pass 
 down this tube, and having its end turned a little on one 
 side, though not enough to prevent its being easily drawn 
 up and down, that inclination causes the gas to be thrown 
 off laterally, and to pass under the edge of the large tube, 
 and through the solution, into the space above. An arrange- 
 ment of this kind is rapidly mounted and dismounted; for 
 the instant the conducting tube is inserted in its place, it is 
 air-tight. It is necessary, in all such arrangements, that the 
 fluid in the bottle (c) should rise above the aperture of the 
 wide tube, and that the extremity of the conducting tube 
 should descend below it. 
 
 846. Considering the joints as being properly made in any 
 of these methods, let us illustrate the uses of the arrange- 
 ment by supposing muriatic acid gas to be thrown into the 
 apparatus by tube 1 ; it will pass into the water, and be 
 immediately dissolved; but as from the continual additions 
 
360 WOULFE'S BOTTLES USE SAFETY TUBES. [Sect, XV. 
 
 of fresh gas the liquid becomes saturated, a part of the gas 
 will pass into the upper part of the bottle, and propelling the 
 air before it, will enter the bottle b by tube 2. Here it will 
 operate exactly as in the first bottle a, if the arrangement be 
 the same and the gas be conducted into the fluid : but if, as in 
 the figure, this be not the case, it will, after acting upon and 
 saturating the fluid as much as practicable by the surface, pass 
 on in a similar manner to the third bottle, and from that to 
 wherever the fourth tube may lead. 
 
 847. Such is the simple operation ; but it is liable to fre- 
 quent variations, which are to be met by particular con- 
 trivances. Amongst the most essential of these is the appli- 
 cation of safety-tubes, intended to admit air when, from 
 any cause, the pressure within is so far diminished as to be 
 considerably less than that of the atmosphere. Suppose for 
 instance that the currents of gas into the bottles a and b were 
 stopped while solution was still going on : as the water dis- 
 solved the gas above it, the atmospheric pressure would force 
 the fluid from the bottle c up the third tube into the bottle b, 
 and if it reached the aperture of the second tube, even in part 
 into the bottle a. If the operation had occasioned the evo- 
 lution of heat, a mere depression of temperature within the 
 bottle might produce the same effect, and in this manner 
 cause great derangement of the liquid and the failure of the 
 experiment. 
 
 848. All this may be avoided by the use of the small 
 safety- tube d, first applied by M. Lavoisier from an idea 
 suggested by M. Hassenfratz*. It passes through a tight 
 joint into the bottle, and has its lower extremity immersed in 
 the liquid to the depth of half an inch or more. When the 
 absorption before described takes place, air passes down the 
 tube, enters the bottle, and prevents the recession of the liquid 
 from the other bottles. No air can at any time escape there, 
 but any pressure exerted from within outward is indicated, and 
 even measured, by the elevation of a column of fluid in the 
 tube: in this way such tubes are highly useful in shewing the 
 state of things within. Another tube of safety called Welter's 
 has been already described (478), which, being fixed into the 
 
 * Traite Elementaire de Chimie, 453. 
 
Sect. XV.] 
 
 361 
 
 middle tubulature of the bottle^ will render that just mentioned 
 needless. 
 
 849. When the bottles are connected in the manner de- 
 scribed (845 tube 3, bottle c,) by a fixed large tube, the latter 
 becomes a tube of safety, permitting the entrance of air when- 
 ever the external pressure is much above that within. 
 
 850. On first setting an apparatus of this kind to work, the 
 student should be attentive to the quantity of water in the 
 bottles, and the depth to which the extremities of the con- 
 necting tubes are immersed. Supposing the immersion to be 
 two inches in each of the bottles a and c, it makes a pressure ox 
 four inches, which has to be overcome by the gas passing into 
 the apparatus through the first tube. From inattention, this 
 pressure may be very considerably increased, and to such an 
 extent as to interfere with the arrangement of the apparatus in 
 which the gas is evolved ; in consequence of which, lutings may 
 be deranged, and even the vessels burst. Hence as a general 
 rule, the conducting tubes are not to be immersed more than is 
 needful. 
 
 851. Upon numerous occasions it is not necessary to im- 
 merse the tubes at all, especially in the large way; conse- 
 quently, apparatus may then be used for the liberation of the 
 gas, which would be quite inadmissible were any pressure to 
 be exerted within it. This is particularly the case with mu- 
 riatic acid, for the solution formed by that gas in water being 
 heavier than either the water or weaker solution beneath it, 
 falls to the bottom. Hence in a muriatic acid gas arrangement,, 
 the delivering tube may terminate above the surface of the 
 water as in bottle b ; the water, as it dissolves the gas, will 
 descend, and this change of place will go on until it be fully 
 saturated. On the contrary, with ammonia the reverse is the 
 case, the solution of that substance being lighter than water; it 
 is essential therefore that this gas be delivered at the bottom of 
 the bottle, that it may always come first into contact with the 
 weakest portions of solution. 
 
 852. In several cases the gas is conducted to the bottom 
 of the fluid, that the bubbles in their ascent may cause agi- 
 tation, and thus favour the solution. This is necessary in 
 dissolving chlorine in water, and is advantageous with am- 
 moniacal and sulphurous acid gases. 
 
362 NOOTH'S APPARATUS. [Sect. xv. 
 
 853. Although three bottles are figured in the wood -cut, 
 often not more than one is required at a time, and the two or 
 three tubes, in place of being passed each through a separate 
 tubulature, may be put through three holes in a cork adapted 
 to the mouth of an ordinary bottle; and the junction be made 
 good by soft cement or other means. A wide-mouthed jar, or 
 bottle, will occasionally make a very good Woulfe's apparatus ; 
 and a large stone bottle often answers the same purpose even 
 in chemical manufactories. 
 
 854. Dr. Knight of Aberdeen avoids much of the trouble 
 resulting from a stiff Woulfe's apparatus, by supporting the 
 different bottles each on sand, placed in a bowl or cup of com- 
 mon stone ware. That quantity of motion is then allowed 
 which is sufficient to compensate for the casual alteration of 
 the position of the parts ; the tubes are saved from injury, and 
 the whole works well and pleasantly. 
 
 855. An apparatus invented by the late Dr. Nooth, and 
 distinguished by his name, is occasionally used for the purpose 
 of making a solution of carbonic acid. It is rather complicated, 
 is of no general use in the laboratory, and does not require 
 particular description ; but it may be prudent to caution those 
 who possess it, against generating gas afresh in the lower 
 vessel without first ascertaining that the valve between that 
 and the second is in right order. This is easily done by lifting 
 the upper vessel from the lower, raising it over the head, 
 and applying the mouth to the lower aperture of the valve 
 tube ; if the muscles of the cheeks have not power to raise this 
 valve and blow air through it, the apparatus should not be 
 used. The valve is always out of order when it cannot thus 
 be raised; .and from inattention to this circumstance, appa- 
 ratus of the kind has^ in two or three cases, been blown to 
 pieces. 
 
 856. Solutions of muriatic acid, ammonia, and sulphurous 
 acid, are generally retained upon the shelves. Solution of 
 chlorine is often wanted, but is not usually preserved. It is 
 readily formed by opening a bottle of chlorine (824) in an 
 inverted position under water, allowing a little of the fluid to 
 enter, replacing the stopper, and then agitating the contents of 
 the vessel ; in a second or two it is again to be opened under 
 
Sect. XV.] 
 
 GASES MIXED AIR-PUMPS. 363 
 
 water, when more of the fluid will enter ; it is then to be re- 
 stopped and re-agitated, fresh water admitted, and the process 
 thus continued until the bottle is half full. By further agita- 
 tion, nearly all the gas may be taken up by this quantity of 
 water, but air should be admitted now and then to supply the 
 place of the gas dissolved. In opening the bottle, either 
 under water or in the air, the stopper is not to be removed 
 farther than just sufficient to allow the ingress of the air or 
 water, otherwise loss of the solution or of the gas is occa- 
 sioned. 
 
 857. Before leaving the description of those operations which 
 relate directly to the transference and removal of gases, it will 
 be proper to observe that, although in making mixtures of 
 gases they will become uniform without agitation if sufficient 
 time be allowed, the period required will be very long, 
 extending even to hours, in narrow vessels. If hydrogen be 
 thrown up into a wide jar half full of oxygen, so as to fill it, 
 and no further agitation be given, the mixture^ after a lapse 
 of several minutes, will be of different composition above and 
 below. Hence the propriety in all cases of mixture, of agi- 
 tating the gases well together. This precaution is more par- 
 ticularly necessary in those eudiometrical or analytical pro- 
 cesses, which require the mixture of gases in tubes or narrow 
 vessels. 
 
 6. Air-pumps, Syringes, and the operations performed with 
 
 them. 
 
 858. Air-pumps and syringes are instruments of great ser- 
 vice and constant use in the laboratory, but are in their con- 
 struction and reparation so necessarily the work of the instru- 
 ment-maker, as to render needless here every thing relative to 
 these points. The air-pump is required not merely in the 
 exhaustion of receivers for experiments with atmospheres of 
 less pressure than those ordinarily occurring, but also for the 
 removal of air from retorts, flasks, globes, &c., that other 
 gaseous bodies may be introduced. A good syringe will 
 answer the same purpose to a very considerable extent, when 
 the air-pump is absent. It has the great advantage of com- 
 bining the power of condensing air (822) with that of exhaust- 
 
364 AIR-PUMP TIGHTNESS OF. [Sect. XV. 
 
 ing it, at a very little additional expense. All the screws by 
 which the attachment of other apparatus to the pump or 
 syringe is to be effected, should be cut with the same thread 
 as that adopted for the stop-cocks (742, 804, 810, 827), that 
 the screws thus used may fit each other without difficulty. 
 
 859. The student has to observe that the pistons of these 
 instruments are well oiled, move easily and tightly, and that 
 all the fixed joints are so perfect, as to prevent leakage of air 
 at any of the screws or junctions. The tightness of the pump 
 is easily ascertained by screwing a stop-cock into the air aper- 
 ture upon the plate, closing it, and then working the pump 
 until the gauge indicates considerable exhaustion. When the 
 pistons are in order, the experimenter feels, as he moves the 
 handle, that he withdraws air each time a piston rises, and he 
 can also perceive without difficulty that less and less is removed 
 at each successive stroke. The diminution should proceed 
 until none can be withdrawn by further operations ; and this 
 useless condition of the piston when at work, which is judged 
 of by the hand (862), should coincide with the stationary and 
 highest state of the gauge, indicative of the exhaustion within. 
 If after some time the gauge continues to indicate the same 
 exhaustion, it is a proof that no air can pass into a receiver 
 fixed tightly upon the plate and similarly exhausted ; and if 
 upon working the pistons, the same absence of air is indicated 
 beneath them as when the exhaustion was first effected, it is a 
 proof that no air passes by them into the lower part of the 
 pump cylinders. 
 
 860. The plate of an air-pump should be perfectly flat, and 
 ground so smooth that a little pomatum may render a receiver 
 with ground edges quite tight when placed upon it. It should 
 be secured from injury by a tin cover put over it at all times 
 when not required for experiment ; for very slight blows with 
 bard substances produce serious harm by the depressions they 
 occasion. 
 
 861. The tightness of a syringe piston, when its other parts 
 are accurately fitted, may be judged of by drawing the piston 
 as far back as possible, then closing either the exhausting or 
 condensing aperture by a stop-cock, carrying the piston forward 
 to the end of the cylinder, if that may be done, and retaining 
 
Sect. XV.] AIR-PUMP SYRINGE EXHAUSTION. 365 
 
 it there a minute or two. This motion condenses the air 
 before the piston, and rarefies that behind it ; and if the piston 
 be not quite tight, the air will pass it, whilst it is forcibly held 
 forward, and consequently when the hand is removed, the 
 piston will not return, as it ought, to the top of the cylinder, 
 or to the place from whence it was displaced. If there be 
 leaks at the joints of the syringe, then the effect above 
 described may be produced, although the piston be tight. In 
 either case the imperfection of the instrument is ascertained, 
 and it should be sent to a workman to be repaired. 
 
 862. A syringe has not the advantage of an attached gauge 
 like that of the pump, hence exhaustions made by it are ne- 
 cessarily judged of by the feel of the piston when in motion. 
 As soon as the quantity of air removed at each stroke has 
 diminished to nothing, the exhaustion is as complete as pos- 
 sible. This indication is the same as that already described 
 with the air-pump (859), but may be more distinctly explained 
 in consequence of one piston only being in action. It depends, 
 generally, upon the effort made by the air to lift and pass 
 through the valve in the piston, as the latter presses upon it. 
 On first working the syringe, this happens immediately the 
 piston is advanced ; but as the air is more and more rarefied 
 by exhaustion, the piston has to descend further and further, 
 before the portion in the cylinder beneath is sufficiently com- 
 pressed to lift and pass the valve. It is the particular effect 
 of lifting the valve which, becoming sensible to the hand in 
 ordinary air-pumps and syringes, supplies the indication in 
 question ; this is easily felt and observed, but difficult clearly 
 to describe. 
 
 863. When the instrument is absolutely bad, and cannot be 
 replaced or repaired, the student must compensate for the 
 imperfections as far as he can, by interposing a stop-cock 
 between it and the retort, flask, or other vessel, (which indeed 
 in most experiments of this kind is necessary for other reasons,) 
 and close the communication as soon as, by rapidly working 
 the instrument, he has effected the best exhaustion he can 
 attain. 
 
 864. Air-pumps and syringes should be preserved from 
 injury, likely to arise from mechanical violence or chemical 
 
366 SILK VALVE EXHAUSTED VESSELS. [Sect. XV. 
 
 action. They are best secured, not in the laboratory, but in 
 the place appropriated to the balance (29) > and other appa- 
 ratus, liable to injury from acid fumes. And if in cases of 
 emergency any gas has been passed through them, which 
 exerts the slightest action on the metal, leather, silk, or oil, the 
 instrument should be quickly worked in the air as soon as it 
 can be liberated from the experiment, that the injury may, if 
 possible, be prevented by the instant removal of all the gas ; 
 or it should be immediately dismounted and cleaned. 
 
 865. The oiled silk valve generally applied in these instru- 
 ments is exceedingly simple in construction, but liable to go 
 out of repair quickly, especially if certain gases or vapours 
 have passed it, on the other hand it is repaired with great faci- 
 lity, and its description may, therefore, be useful. It consists 
 of an aperture of small diameter made in a part of the metal 
 of the piston or of the extremity of the barrel, the aperture 
 terminating on a flat surface \ a strip of silk is put over this 
 surface, and the aperture and its ends being passed down the 
 sides of the metal, a turn or two of thread is taken round them 
 which confines the strip to its proper place. As the air or gas 
 passes through the hole against the silk it easily escapes under 
 its edges, but as the air tends to proceed in the opposite direc- 
 tion, it presses the silk slip against the aperture, and stops all 
 passage. When the valve is out of order from the derange- 
 ment of the silk, nothing is more easy than to remove the latter 
 and tie another slip in its place. 
 
 866. The pressure upon the exterior of vessels exhausted 
 of air is about I5lbs. upon every square inch of their surface, 
 and with large vessels it accumulates to an enormous extent. 
 For this reason the form of such as are intended to sustain 
 this pressure, must be particularly attended to, especially 
 when, as in usual laboratory operations, they are of glass. 
 Air-pump receivers are always made of curved forms, and 
 particular directions have already been given with regard to 
 the proper form of retorts (429) which are to be exhausted. 
 A retort is so convenient for the retention of solid or fluid 
 matter during exhaustions; for the reception of sufficient 
 gaseous matter to act upon the substance within ; for its al- 
 lowing the heating of the substances in the gas even whilst 
 
Sect. XV.] VESSELS EXHAUSTED CARE REQUIRED. 367 
 
 on the air-pump, and for the opportunity it affords of viewing 
 all that passes ; that it is in constant request in experiments 
 of this kind, where gaseous bodies are acting on each other, or 
 on fluids or solids (429). Well-formed flasks and globes 
 are also in constant use, as bearing exhaustion, and readily 
 allowing the mixture of gases in them ; a common Florence 
 flask (373) will, from the general perfection of its form, 
 sustain perfect exhaustion, notwithstanding its thinness, and 
 these, with globes and retorts, are easily attached to the pump 
 or syringe by means of caps and stop-cocks (827). 
 
 867. Particular care is necessary with all exhausted glass 
 vessels, that no sudden blow, even though slight, take place 
 on the exterior, especially with sharp edged or hard substances, 
 for the slightest fracture of the surface leads to the destruction 
 of the whole. A retort, flask or globe may be destroyed 
 merely by laying it down hastily upon a table, especially if a 
 particle of sand or any other hard substance be beneath it; 
 and a slight blow with a glass rod or metal wire, which would 
 do no harm to the apparatus in its usual state, will now shiver 
 it to pieces. 
 
 868. On exhausting glass vessels for the first time, they 
 should, after being attached to the pump or syringe, be co- 
 vered with a cloth, before the exhaustion is effected. If they 
 burst by the mere pressure of the external atmosphere, the 
 fragments are then prevented from flying to any distance. 
 Pieces which may have fallen upon the plate of the pump, or 
 have entered into the stop- cock by which the vessel has been 
 attached, are to be carefully and immediately removed, that no 
 injury may be caused by them to the ground metallic surfaces, 
 or to other parts. 
 
 869. The general process for removing the air from a 
 vessel, and for replacing it by any required gas, is an easy 
 one, and will be readily understood from description. The 
 gas is to be collected in a transfer jar (755), over water or 
 mercury, according to its nature, and a connecter screwed 
 to the upper end of the jar stop-cock. The vessel to be ex- 
 hausted must have a cap fitted securely to its neck (833), 
 and a stop-cock screwed into the cap, and then, being at- 
 tached by means of the cock to the air-pump or syringe, it is 
 
368 VESSELS FILLED WITH GAS. [Sect. XV. 
 
 to be exhausted, and the cock closed. This done, the vessel 
 is to be separated from the pump and attached to the jar by 
 means of the connecter, the stop-cock of the jar being screwed 
 tightly into it ; the lower of the two cocks, which now in- 
 tervenes between the jar and the exhausted vessel, is to 
 be opened, then the upper one gradually, and the gas slowly 
 admitted, until the vessel be full, or sufficient has passed in. 
 
 870. If the volume of gas which enters is to be ascertained, 
 it will be necessary to equalize the level within and without the 
 jar (767), but this must not be done until the temperature 
 within the globe is the same as that of the surrounding air. 
 When air rushes into an exhausted vessel, it first occasions a 
 depression of the temperature within, but afterwards an eleva- 
 tion (effects dependant upon well known causes). To prevent 
 therefore the interference of any accidental temperature thus 
 produced, the level within and without is to be equalized, the 
 stop-cock shut, and the apparatus left for a few minutes ; after- 
 wards the level is again to be equalized, the stop-cock opened, 
 and at the same time the surface of the water in the jar 
 observed ; its motion indicates that the temperature within has 
 changed : again, the vessel must be closed, left for a time, and 
 then examined, and when after the lapse of five minutes no 
 change in the level is produced by opening the stop-cock, it is 
 a proof that the temperature within is the same as that of 
 the atmosphere. This done, the stop- cocks are to be finally 
 closed, and the retort or vessel removed and used as the 
 experiment may require. 
 
 871. It sometimes happens that when the gas to be intro- 
 duced has been collected over water, a drop or two of that fluid 
 adheres near the upper aperture, and, if the gas be allowed to 
 pass with violence, is carried forward into the exhausted vessel 
 by the current. Care should be taken to prevent this, for which 
 reason, in addition to other precautions, it is useful to intro- 
 duce a little piece of crumbled filtering paper into the top of 
 the connecter, so that when the second stop -cock is screwed 
 into its place, the paper may lie loosely between the apertures 
 of the two. It will catch any drops of water that may be 
 carried up, and prevent their entrance into or beyond the 
 second stop-cock. 
 
Sect. XV.] VESSELS FILLED WITH GAS SYRINGE. 
 
 369 
 
 872. The general process of the introduction of gases con- 
 nected with the use of the air-pump is required in the weighing 
 of gases ; in the mixing of those which are affected by water 
 or mercury, or afford results so affected ; and in the exposure 
 of particular substances to gases or vapours. Where, however, 
 actions of the latter kind are exerted spontaneously, as is often 
 the case with chlorine, it is frequently sufficient to put the 
 substance into a tube closed at one end, and having opened a 
 small bottle of chlorine, quickly to introduce the tube and 
 close the bottle. Substances are also very often advantageously 
 exposed to gases in tubes in the manner already described 
 (698, &c.) 
 
 873. With regard to those operations in which the com- 
 pression of gases, instead of their expansion and exhaustion, is 
 required, they are performed by means of the syringe already 
 spoken of (858, &c.) ; but the vessel is now to be screwed to 
 the end from which the gas is to be forced out, and the oppo- 
 site aperture is to be connected by a tube, or otherwise, with 
 a gasometer, or other vessel containing the gas. When the 
 syringe is worked, it draws the air out of the latter vessel, and 
 forces it into the former. Suppose the operation were to con- 
 dense oxygen to the amount of four or five atmospheres into 
 a brass globe, for the purpose of making a blow-pipe (252) ; 
 the globe is first to be attached to the syringe, and to have 
 the air exhausted from it; then to be detached, and the same 
 aperture of the syringe connected with the vessel, which is to 
 supply oxygen gas. It is now necessary to expel the air con- 
 tained in the syringe and pipe; one stroke of the piston is 
 sufficient to remove that in the syringe, and a second will gene- 
 rally expel all that was contained in the pipes, if they be of 
 moderate size. The exhausted globe is then to be attached 
 to the exit aperture of the syringe, and all the cocks being 
 opened, oxygen will immediately pass into the globe, and fill 
 it nearly to atmospheric pressure; the piston is then to be 
 worked, and as much more oxygen thrown in as may be re- 
 quired ; finally, the stop-cocks are to be closed, and the appa- 
 ratus dismounted. The quantity of gas introduced may be 
 judged of by that which has disappeared from the jar or vessel, 
 if it be visible and can be appreciated. 
 
 2 B 
 
370 STRENGTH OF GLASS VESSELS. [Sect. XV. 
 
 874. Retorts and flasks will not bear so great a pressure on 
 their interior as on their exterior, and many that will bear 
 exhaustion with perfect safety, will burst long before they have 
 received one additional atmosphere. Even the force of the 
 mouth is adequate to the bursting of thin Florence flasks. 
 Hence the glass vessels intended to retain gases under pressure 
 must be thick, or of small diameter. Small globes are useful 
 in such experiments, and also small tubes carefully closed at 
 one end, and well annealed. According to some experiments 
 of Mr. Brunell, a uniform flint glass tube, its thickness being 
 ten, and its internal diameter eighteen, sustained an internal 
 pressure of 135 atmospheres of 14 Ibs. each, when applied in 
 a regular and careful manner. Hence the strength of other 
 glass tubes may easily be calculated by the rule of proportion, 
 for if the glass be but one half this thickness, it will resist only 
 half that number of atmospheres. No force should be exerted 
 in experiments surpassing one-third, or at most one-half of the 
 calculated strength ; and, indeed, it is rarely that glass tubes 
 are so uniform in structure or so well annealed as to have near 
 the strength indicated in the experiment. 
 
 875. When small globes or tubes are fitted with caps for 
 the purpose of connecting them with a syringe, in order to 
 subject them to internal pressure, it is necessary that particular 
 care be taken in fastening on the cap that it may remain tight 
 and firm. The outside of the neck should in such cases be 
 roughened by a file, and the junction of it with the inside of 
 the cap by cement very carefully and accurately made (833). 
 Cement so warm as to be in a state of thick fluidity should 
 afterwards be put over the outside of the cap and the glass 
 beyond, and drawn-out tow wound round it, so as to pass 
 obliquely backwards and forwards from the glass to the cap, 
 and back upon the glass again. This should be covered en- 
 tirely by more cement, and will help much to bind the vessel 
 and cap together. At other times a band of thin open canvas 
 may in the same manner be buried in the cement, passing 
 once or twice round the joint ; or cloth or thick muslin may be 
 used for the same purpose ; but whatever it is, it should be 
 thoroughly soaked in, and completely covered by, the cement. 
 
Sect. XV,] CORRECTION OF THE VOLUME OF GASES. 371 
 
 7. Correction of the Volume of Gases for Temperature 
 and Pressure. 
 
 876. In all the processes relative to volumes of gases, 
 directions have been given that the temperature and the baro- 
 metric pressure be noted at the time (781, 888). This is 
 for the purpose of making such corrections as shall enable 
 the operator to compare the results obtained at one time with 
 those obtained at another. When the temperatures of gases 
 have been raised whilst the pressure upon them remains the 
 same, they expand in bulk ; and when their temperatures are 
 lowered, they contract, but the bulk is determinate for every 
 temperature. On the other hand, if the temperature be constant 
 when the pressure is varied, then variations in bulk are also 
 occasioned, the volume increasing as the pressure is diminished, 
 and decreasing as it is increased, whilst it still remains constant 
 and determinate for every particular degree of force so ap- 
 plied. Now as atmospheric temperature and pressure vary 
 continually, it is evident that experiments made at different 
 times must, v occasionally, differ as to the volume of gas they 
 require, and, consequently, it would be inaccurate to compare 
 these different volumes without ascertaining the influence of 
 temperature and pressure upon them ; the latter must, there- 
 fore, be observed and registered. This being done, it is easy 
 to apply corrections by which the volume of gas used at any 
 one time can be truly compared to that used at another ; 
 for as the bulk is determinate for any given temperature and 
 pressure, it is only necessary to correct the bulk of the one 
 portion to the temperature and pressure of the other, or to 
 select two fixed points of this kind, and in every case to reduce 
 the observed volume of gas to what it would be at these points ; 
 the results will then be perfectly consistent. 
 
 877. The points usually adopted in this country, and dis- 
 tinguished as mean temperature and pressure, are for tempe- 
 rature 60 of Fahrenheit's scale, and for pressure 30 inches of 
 mercury. Hence, when necessary, gas observed at any other 
 temperature and pressure has to be reduced to the volume it 
 would occupy at these points. This may be done in the fol- 
 lowing manner : 
 
 2 B 2 
 
372 CORRECTION FOR TEMPERATURE. [Sect. XV. 
 
 Correction for Temperature. 
 
 878. It appears by the experiments of MM. Gay Lussac 
 and Dal ton, that all gases and vapours of whatever nature, 
 when not in contact with liquids, are affected equally in their 
 volume by changes of temperature, the increase in volume for 
 every additional degree of heat of Fahrenheit's scale being 
 f^Q part of the volume at 32 Fahrenheit, and the decrease for 
 every diminution of temperature of one degree being also ^J^ 
 part of the volume at 32 Fahrenheit. This known, it is easy 
 to calculate how much a volume of gas at a given temperature, 
 60 Fahrenheit, for instance, would be increased or diminished 
 by a change of one or more degrees. For though it is not, for 
 one degree, a -^ part of the bulk at 60, the proportion is 
 easily ascertained by adding 28, or the number of degrees of 
 the observed gas above 32 to 480, which producing 508, in- 
 dicates that jl-g part of the bulk at 60 is to be considered as 
 the increase or diminution for every degree of change. For 
 conceive 480 parts of gas at 32 : at 33 they become 481 
 parts; at 34, 482 parts; at 60, 508 parts; the . increase at 
 each degree being ^ of the volume at 32, and, consequently, 
 such part of the volume at any other temperature, as is indi- 
 cated by adding the number of degrees above 32 to 480. 
 
 879. The rule for correction to be applied to an observed 
 volume of gas is, therefore, to add to 480 the number of degrees 
 above 32 ; to divide the observed volume by this sum, which 
 gives the expansion or contraction for each degree at the ob- 
 served temperature ; to multiply this by the number of degrees 
 between the observed temperature and the temperature to which 
 the gas is to be corrected, which will of course indicate the 
 whole expansion or contraction ; and then to subtract this, if 
 the observed be above the corrected temperature, or to add it, 
 if the former be below the latter ; thus allowing for the con- 
 traction or expansion which would actually take place, if the 
 temperature of the gas were really to be brought to the point 
 to which by calculation it may thus be corrected. 
 
 880. As an illustration, suppose 100 cubic inches of gas at 
 70 Fahrenheit are to be corrected to mean temperature, or 60. 
 The difference between 70, the observed temperature, and 
 
Sect. XV.] CORRECTION FOR PRESSURE. 373 
 
 32, is 38, which added to 480 = 518 ; the 100 inches divided 
 by 518, gives 0.19305 of a cubic inch as the whole expansion 
 for each degree; and this multiplied by 10, the difference 
 between 70 and 60, gives 1.9305 cubic inches as the whole 
 expansion ; which, subtracted from 100 cubic inches, leaves 
 98.0695 cubic inches as the volume which would be occupied 
 by the gas at 60 Fahrenheit. 
 
 881. Or, again, suppose the 100 cubic inches were observed 
 at 50 instead of 70, then the expansion per degree is obtained 
 by adding 18, or the difference of 32 and 50 to 480 : this 
 equals 498, and dividing 100 cubic inches by this, we obtain 
 0.2008032 of a cubic inch as the expansion per degree at 50 ; 
 and this multiplied by 10, the difference between 50 and 
 60 = 2.008032 cubic inches, which would be the whole ex- 
 pansion for the 10 from 50 to 60. Being added to 100, it 
 makes 102.008032 cubic inches as the corrected volume of gas. 
 The decimals have in these instances been calculated much 
 farther than will be necessary except in particular experiments, 
 merely with a view of shewing the difference in the amount of 
 the corrections required for an equal number of degrees at 
 different temperatures. 
 
 Correction for Pressure. 
 
 882. Boyle and Hooke were perhaps the first to observe 
 that the volumes of gases varied inversely in proportion to the 
 pressure exerted upon them, although the law, having been first 
 distinctly announced and enlarged upon by Marriotte, has 
 received his name. Its truth at high pressure, although some- 
 times doubted, has been confirmed by the results of Oersted *, 
 and still more recently by those of MM. Dulong and Aragof, 
 and no one has any doubt of its being accurately true at such 
 pressures as occur naturally and are indicated by the baro- 
 meter, and also at the greater variations dependant upon the 
 difference of level of the fluid within and without a jar stand- 
 ing over the mercurial or water-trough (767, 782). 
 
 883. A pressure of 30 inches of mercury, as observed by an 
 accurate barometer, has been assumed as the mean height or 
 barometric pressure) and volumes of gas observed at any other 
 
 * Phil. Mag. Ixviii. 102. f Bib. Universelle, xlii. p. 338. 
 
374 CORRECTION FOR PRESSURE. [Sect. XV. 
 
 pressure (780), frequently require to be corrected to what they 
 would be at this point. For this purpose it is only necessary 
 to compare the observed height with the mean height, or 30 
 inches, and increase or diminish the observed volume inversely 
 in the same proportion. Thus, as the mean height of the 
 barometer is to the observed height, so is the observed volume 
 to the volume required. As an instance, suppose that 100 
 cubic inches of gas have been observed when the barometer 
 stood at 30.7 inches : then, as 30 inches, or mean height, is to 
 30.7 inches, or observed height, so is 100, or the observed 
 volume, to a fourth proportional obtained by multiplying the 
 second and third terms together and dividing by the first: 
 thus, 30.7 X 100 = 3070, which divided by 30 = 102.333 cubic 
 inches ; this would be the volume of the gas at 30 inches of 
 barometric pressure. Or, consider the gas as observed at 28.9 
 inches of the barometer : then 30 inches, or mean height, is to 
 28.9 inches, or observed height, as 100 is to 96.333 cubic 
 inches, that being the result of 28.9 multiplied by 100 and 
 divided by 30, according to the rule. Again, suppose a 
 quantity of gas amounting to 20 cubic inches standing over 
 mercury in a jar, the level of the metal within being 3 inches 
 above that without, and the barometer at 29.4 inches (800). 
 Then the column of 3 inches of mercury within the jar, coun- 
 terbalancing 3 inches of the barometric pressure, instead of 
 being 29.4 the latter is effectively only 26.4, and the cor- 
 rection will be as 30 inches is to 26.4 inches, so is the 20 
 cubic inches observed to 17.6 cubic inches, the volume which 
 the gas would really occupy if the mercury were level within 
 and without the jar, and the barometer were at 30 inches. 
 
 884. It is constantly necessary to make corrections both for 
 temperature and pressure in the same volume of gas. It 
 matters not which correction is made first, the result being the 
 same in either mode. Thus for instance, 100 cubic inches 
 observed at the temperature of 40 Fahr. the barometer being 
 at 28 inches, if first corrected for pressure, become 93.33 
 cubical inches : and then for temperature become. 97.158469, 
 which is the true volume. Or, if first corrected for temperature, 
 it becomes 104 09836, and then for pressure, it becomes as 
 before 97.158469 cubic inches. 
 
Sect. XV.] 
 
 375 
 
 885. Dr. M. Hall has constructed an instrument* which he 
 has called an Aerometer, intended to give at once a correction 
 for changes in the temperature of the atmosphere; in the 
 barometrical pressure ; in the external and internal heights of 
 the fluid in the pneumatic trough ; and when this trough con- 
 tains water, for the elevation and precipitation of aqueous 
 vapour. It consists of a bulb of glass 4J cubic inches in 
 capacity, attached to a long tube whose capacity is 1 cubic 
 
 inch. This tube is inserted into another tube of 
 nearly equal length, and supported on a stand, as in 
 the figure. The first tube may be sustained at any 
 height within the second by means of a spring at the 
 upper part. Five cubic inches of air at mean tem- 
 perature and pressure are introduced into the bulb 
 and tube, of the latter of which it will occupy one- 
 half ; the other half, and part of the tube into which 
 it is inserted, are to be occupied by the fluid of the 
 pneumatic trough, either water or mercury. The 
 point of the tube at which the air and fluid meet, is to be 
 marked 5, and the upper and lower half divided into 5 equal 
 parts, indicating tenths of a cubic inch each. The external 
 tube is to be marked by a scale of inches. 
 
 886. When the volume of a gas confined over the pneu- 
 matic trough in jars is to be corrected by the indications of 
 this instrument, the difference between the levels of the fluid in 
 the jar and in the trough is to be measured, and the same 
 difference occasioned in the external and internal heights of the 
 fluid in the aerometer. The gas in the instrument, and that 
 in the jar, are then precisely in the same condition, and by 
 observing the volume of the former, the latter may be cor- 
 rected. Thus if it be 5.2 cubic inches in the aerometer, and 
 74 cubic inches in the jar, then as 5.2 is to 5, the volume in 
 the instrument at mean temperature and pressure, so is 74 to 
 71.15, the corrected volume of gas in the jar. 
 
 8. Weighing of Gases or Air. 
 
 887. The process of weighing a gas, which of all others is 
 simplest in principle, is, to exhaust a light globe or flask, 
 fitted with a cap and stop-cock for the purpose, then exactly 
 
 * Quarterly Journal of Science, v. 52. 
 
376 
 
 WEIGHING OF GAS OR AIR. 
 
 [Sect. XV. 
 
 to counterpoise it (64.65), to attach it to a graduated transfer 
 jar containing the gas to be weighed (755), and after allowing 
 as much as will enter to pass in, permitting the temperature to 
 become that of the atmosphere (870), and equalizing the 
 pressure within and without the jar, to estimate the volume 
 that has entered, by the graduation. Then on weighing the 
 vessel, it may be ascertained how much it has increased in 
 weight, and the increase will of course be the weight of the 
 observed volume of gas. 
 
 888. Globes or flasks of the kind required are sold by the 
 instrument-maker. They should be perfectly clean and dry 
 when used, nothing being allowed to adhere to the outside that 
 may alter their weight during the process. The temperature 
 should be noted, and its equality carefully preserved during 
 the experiment; for this reason, the globe should be handled 
 with all the delicacy possible (773). The pressure of the 
 barometer is likewise to be noted. If the gas be in a jar 
 standing over water, it must be let in carefully (871), the little 
 piece of paper before recommended being introduced into the 
 connecter ; and it is advisable to let a small quantity of gas 
 pass out there before the parts are closely screwed together, 
 that the common air in them may be removed. 
 
 889. Gas when standing over water becomes saturated with 
 aqueous vapour, tjie quantity being proportional to the tem- 
 perature. In these cases, a part of the volume observed, and 
 also a part of the weight, is due to the vapour, which therefore 
 must be ascertained before the true weight of the gas under 
 examination can be determined. The following table exhibits 
 the proportion by volume of aqueous vapour existing in any 
 gas standing over or in contact with water at the corresponding 
 temperatures, and at mean barometric pressure of 30 inches. 
 
 40 
 
 .00933 
 
 51o 
 
 .01380 
 
 61o 
 
 .01923 
 
 71 
 
 .02653 
 
 41 
 
 .00973 
 
 52 
 
 .01426 
 
 62 
 
 .01980 
 
 72 
 
 .02740 
 
 42 
 
 .01013 
 
 53 
 
 .01480 
 
 63 
 
 .02050 
 
 73 
 
 .02830 
 
 43 
 
 .01053 
 
 54 
 
 .01533 
 
 64 
 
 .02120 
 
 74 
 
 .02923 
 
 44 
 
 .01093 
 
 55 
 
 .01586 
 
 65 
 
 .02190 
 
 75 
 
 .03020 
 
 45 
 
 .01133 
 
 56 
 
 .01640 
 
 66 
 
 .02260 
 
 76 
 
 .03120 
 
 46 
 
 .01173 
 
 57 
 
 .01693 
 
 67 
 
 .02330 
 
 77 
 
 .03220 
 
 47 
 
 .01213 
 
 58 
 
 .01753 
 
 68 
 
 .02406 
 
 78 
 
 .03323 
 
 48 
 
 .01253 
 
 59 
 
 .01810 
 
 69 
 
 .02483 
 
 79 
 
 .03423 
 
 49 
 
 .01293 
 
 60 
 
 .01866 
 
 70 
 
 .02566 
 
 80 
 
 .03533 
 
 50 
 
 .01333 
 
 
 
 
 
Sect. XV.] WEIGHING OF GAS OR AIR. 377 
 
 890. By reference to this table, which is founded upon 
 the experiments of Mr. Dalton and Dr. Ure, and includes 
 any temperature at which gases are likely to be weighed, the 
 proportions in bulk of vapour present, and consequently of 
 the dry gas, may easily be ascertained. For this purpose 
 the observed temperature of the gas should be looked for, 
 and opposite to it will be found the proportion in bulk 
 of aqueous vapour at a pressure of 30 inches. The volume 
 to which this amounts should be ascertained and corrected 
 to mean temperature. Then the whole volume is to be 
 corrected to mean temperature and pressure (876) , and the 
 corrected volume of vapour subtracted from it. This will 
 leave the corrected volume of dry gas. It has been ascer- 
 tained in a manner approaching to perfect accuracy, that a 
 cubic inch of permanent aqueous vapour corrected to the 
 temperature of 60, and a mean pressure of 30 inches, 
 weighs 0.1929 grains. The weight therefore of the known 
 volume of aqueous vapour is now easily ascertained, and 
 this being subtracted from the weight of the moist gas, will 
 give the weight of the dry gas, the volume of which is also 
 known. 
 
 891. As an illustration, suppose a gas standing over water 
 had been thus weighed, and that 220 cubic inches at the 
 temperature of 50 Fahr., and barometric pressure of 29. 4 
 inches had entered into the globe and caused an increase in 
 weight of 101.69 grains. By reference to the table it will be 
 found that at the temperature of 50, the proportion of 
 aqueous vapour in gas standing over water is .01333, which 
 in the 220 cubic inches will amount to 2.933 cubic inches, 
 which corrected to the temperature of 60, becomes 2. 942 
 cubic inches. The whole volume corrected to mean tem- 
 perature and pressure (878, 883) will be found to equal 
 219.929 cubic inches, from which, if the 2.942 cubic inches of 
 aqueous vapour present be subtracted, it will leave 216.987 
 cubic inches as the volume of dry gas at mean temperature 
 and pressure: 2.942 cubic inches of aqueous vapour weigh 
 .5675 grains, for 2.042x0.1929=0.5675; this subtracted 
 from 101.69, the whole weight leaves 101.1225 grains, which 
 is the weight of the 216,987 cubic inches of dry gas ; and by 
 
378 WEIGHING OF GASES THEIR DESICCATION. [Sect. XV. 
 
 the simple rule of proportion, therefore, it will be found that 
 100 cubic inches of such gas, when dried and at mean tem- 
 perature and pressure, will weigh 46.603 grains. 
 
 892. It is not necessary in this experiment that the globe 
 or flask be perfectly exhausted of air before the gas be 
 admitted, all that is necessary in that respect being, that the 
 quantity of gas which enters, and the corresponding increase of 
 weight, be known. For the same reason it is not necessary 
 that the globe be filled, provided the quantity which does enter 
 is ascertained upon the graduation of the jar when the level is 
 the same inside and outside; and that no alteration of the 
 quantity in the globe be allowed before the weighing is com- 
 pleted. The state and quantity of the gas is estimated in the 
 jar, and it is there that the temperature and pressure should 
 be attended to. It is essentially necessary that the tem- 
 perature of the gas over the water should have been steady for 
 some time before the experiment be made, and that it do not 
 change until the gas has entered the globe and the stop-cock is 
 securely closed. After that, a little variation of temperature is 
 of no consequence, so that nothing passes into or out of the 
 globe until the conclusion of the experiment. The globe, as 
 before said (888) , should be clean and dry. 
 
 893. Some experimenters prefer drying the gas before it is 
 weighed, and thus in fact weigh a known volume, not of a 
 mixture, but of pure gas. Now gases are dried in various 
 ways. One method is to pass them through a glass tube, con- 
 taining substances having powerful attractions for water. It 
 is a simple and a useful process, and therefore proper to be 
 described here, though not conveniently applicable to the mode 
 of weighing a gas as above directed, because of the greater 
 difficulty of measuring the quantity of gas which enters. 
 The tube may be about half an inch in diameter, and from 12 
 to 20 inches long ; it should have a piece of wire pressed into 
 a loose ball, thrust into one end of it, to prevent fragments 
 falling through. Chloride of lime should be heated and 
 fused in an earthenware crucible, a temperature below that 
 of visible redness being quite sufficient for the purpose, then 
 poured upon a clean metallic or stone surface, and as soon 
 as it has solidified, broken up and put into stopped bottles. 
 
Sect. XV.] DESICCATION OF GASES SUBSTANCES USED. 379 
 
 This chloride being divided into a mixture of large and small 
 fragments is to be introduced rapidly into the tube, until the 
 latter is nearly full ; the apparatus is then ready for use. The 
 tube may be connected with the jar, gasometer, or other 
 vessel, containing or evolving the gas, by caoutchouc con- 
 necters (449), or in any other convenient way; and so much 
 gas should be passed through it as effectually to expel all the 
 common air before the globe or vessel to be filled with the dry 
 gas be attached. That being done, the gas should be allowed 
 to pass slowly, 100 cubical inches having from 10 to 20 
 minutes allowed for their passage through such a tube as that 
 described, though if the period be lengthened, no injury is 
 occasioned. If the tube be shorter, or of smaller diameter, 
 more time should be proportionately allowed. 
 
 894. Instead of chloride of lime, fused potash, or fused 
 carbonate of potash may be employed, but it is to be remem- 
 bered that ordinary potassa fusa generally evolves a little 
 oxygen during its solution, and hence may occasionally be 
 exceptionable. Chloride of lime will not answer for ammonia, 
 or for sulphurous and some other acid gases. Potash, or 
 carbonate of potash, answers perfectly well for ammonia, but 
 not for acid gases. Sulphuric acid is a very excellent desic- 
 cator for many gases, and may be used in a tube by first 
 curving the tube, then filling it with fragments of glass or rock 
 crystal, and afterwards pouring in so much concentrated oil 
 of vitriol as shall moisten the fragments, but not cause ob- 
 struction to the passage of the gas. By moving the tube a 
 little from time to time, the acid is made to pass from place to 
 place, it becomes mixed, and it remoistens the fragments, 
 which from the previous quiescent state of the apparatus may 
 have drained considerably. This substance is effectual with 
 almost all gases except ammonia. 
 
 895. In any case where tubes like these are to be used for 
 drying the gas to be weighed in the manner already described, 
 and consequently requiring to be measured, the gas must be 
 delivered from a graduated jar, and after the quantity which 
 is to expel the atmospheric air has passed through, and the 
 exhausted vessel is attached to the end of the drying tube, the 
 level within and without the jar should be equalized and the 
 
380 DESICCATION OF GASES METHODS. [Sect. XV. 
 
 quantity of gas noted ; and again also, when so much gas has 
 passed from the jar as has sufficed to fill the globe, and when 
 its temperature is the same as that of the surrounding air. 
 It will, however, be evident that in these cases the quantity 
 that has entered the globe is not equal to that which has left 
 the jar, for a certain volume of vapour has been abstracted. 
 This must be ascertained by noticing the temperature of the 
 moist gas, and correcting its volume to the pressure of 30 
 inches of mercury ; then ascertaining by the table (889) the 
 proportion of vapour which was present in the volume which 
 left the jar, and which is to be subtracted from the corrected 
 volume, and the remainder will be the volume of dry gas 
 which has entered the globe. 
 
 896. Desiccating tubes, similar to those which have been 
 described, are very convenient for drying gas in numerous 
 cases, without reference to the operations of weighing, and 
 where no account of volume is kept. They may be of various 
 sizes, some indeed not more than five or six inches in length, 
 and the fourth or fifth of an inch in diameter. The tube 
 should be drawn out at one end to a conical form, with a 
 capillary opening ; the desiccating substance should be intro- 
 duced, and the other end drawn out in a similar manner to the 
 former. The capillary apertures are easily sealed hermetically 
 by holding them for a moment in a flame, and the tubes may 
 be preserved in that state until wanted. When required, the 
 ends should be broken off, so as to open small apertures, and 
 the tube should be attached to the gas apparatus by caoutchouc 
 connecters (449), or in any other manner, so as to permit the 
 gas to pass through it. When the operation is finished, and 
 the tube dismounted, the gas within may be blown out by bel- 
 lows, or drawn out by the mouth, the ends of the tube be 
 sealed as before, and the tube itself reserved for use another 
 time. It will in this way be repeatedly serviceable, until so 
 much water has been abstracted by it as to injure its desic- 
 cating power. The drying effect of these tubes is in all cases 
 increased by lowering their temperature, which may very con- 
 veniently be done when the tube is bent, as has been mentioned 
 with respect to sulphuric acid (894), by dipping the bent part 
 into a mixture of ice and salt (454) . 
 
Sect. XV.] DESICCATION OF GAS BY SULPHURIC ACID. 381 
 
 897. In other cases, gas confined over mercury, either at the 
 trough or in a gasometer, may be dried by desiccating sub- 
 stances, as chloride of lime, previously placed within the jar : 
 or gas dried by being passed through the desiccating tubes 
 (893), may be conveyed into a graduated jar over mercury, 
 thence transferred into the exhausted globe, and may actually 
 be measured in its dry state. 
 
 898. A sulphuric acid bath, or gasometer, may be used 
 with great advantage in the desiccation of particular gases, as 
 chlorine, or in very important experiments. For this purpose 
 a graduated transfer jar should be' selected, and a common 
 glass jar for the retention of fluids ; the latter of a size just 
 
 sufficient to receive the former, and allow it free 
 motion. The latter jar is to be filled with sulphuric 
 acid except about an inch of the top, when if the 
 transfer jar be depressed in it, whilst the air escapes 
 above (755), it will become filled with the acid. 
 The gas to be dried is then to be introduced by the 
 stop-cock, the connection of the apparatus being 
 made by caoutchouc tubes, or otherwise, as may be 
 convenient. As the sulphuric acid must not rise into the cap 
 or stop-cock, and as air will consequently occupy those places, 
 it is needful, after the gas has passed in to the depth of an 
 inch or a little more, to detach the jar and throw out that por- 
 tion, by which means very little of the common air will remain. 
 The apparatus is now to be re-attached, the gas introduced as 
 before, and allowed to accumulate in the jar. When the jar 
 is nearly full, the stop-cock is to be closed, and the gas left 
 over the sulphuric acid for an hour or two. During this time 
 the jar may rest on the sulphuric acid ; or if there be any 
 danger of an overflow, the jar may be blocked up by a cork 
 put between it and the outer jar, or it may be supported in 
 part by a string tied to the stop-cock and made fast to a nail 
 or some other projection. When the gas is dried, it is to be 
 used in any way that may be desired, being transferred through 
 the stop-cock and its quantity measured upon the graduation, 
 after the level of the sulphuric acid within and without the jar 
 has been equalized. 
 
 The original mercurial gasometer of Mr. Clay field, without 
 
382 WEIGHING OF GASES THOMSON'S METHOD. [Sect. XV. 
 
 tubes (809) , is an excellent instrument for the desiccation of 
 gas over sulphuric acid, being altogether of glass. 
 
 899- The desiccators mentioned, namely, chloride of cal- 
 cium, potash, carbonate of potash, and sulphuric acid, are 
 adapted for all gases, one being applicable when another is 
 not. Sometimes dry lime in tubes is used in slow processes, 
 but has no advantage over those bodies, except that it is more 
 economical in large experiments. 
 
 900. Returning to the methods of weighing gases: Dr. 
 Thomson has published one* which, being exceedingly simple 
 in principle, relates to the determination of their relative spe- 
 cific gravities, and requires description. The globe or flask 
 (888), with its stop-cock, is to be weighed as accurately as 
 possible, then exhausted and weighed again. The loss of 
 weight sustained is equal to the quantity of common air drawn 
 out, and is less or more according to the size of the flask and 
 the goodness of the exhaustion. The flask is then to be filled 
 with the gas whose specific gravity is wanted (869). All the 
 precaution necessary, according to Dr. Thomson, is, to take 
 care that no particles of water or mercury (supposing the gas 
 to be standing over mercury) insinuate themselves into the 
 flask. It is obvious that the volume of gas which will enter 
 the flask will be precisely equal to the volume of common air 
 that has been previously drawn out of it by the air-pump. 
 The flask thus filled with the gas, whose specific gravity is to 
 be known, is now to be weighed, and the increase above its 
 weight when exhausted, gives exactly the weight of the gas 
 introduced. This weight divided by the weight of the com- 
 mon air removed by the pump, gives the specific gravity of 
 the gas, that of air being assumed as unity or 1 ; and this is 
 done without any measurement, or the necessity of any correc- 
 tion for temperature, or for the height of the barometer, which 
 remain unchanged during the short time of the experiment. 
 
 901. Notwithstanding the simplicity of the principle, how- 
 ever, much caution and even correction is necessary, without 
 which it would be unsafe to recommend the process to the 
 student. It is especially requisite that no gas of a preceding 
 experiment remain in the globe ; for which reason, after one 
 
 * Annals of Philosophy, xv. 232. 
 
Sect. XV.] WEIGHING OF GASES PRECAUTIONS. 383 
 
 experiment is finished, or before another has commenced, the 
 globe or flask should be exhausted many times, air being 
 admitted after each time ; or if access to the interior be easy, 
 much air should be drawn or blown through it. 
 
 902. The air which is in the globe is the same as that of 
 the atmosphere at the time it was introduced, and is therefore 
 liable to all the variations to which the atmosphere itself is 
 subject. Now the weight of a given bulk of the atmosphere 
 at the same temperature and pressure, varies at different times, 
 because of the variable proportions of water and perhaps other 
 substances which it contains. It is not often saturated with 
 moisture, and is never quite dry, and would require both 
 hygrometrical experiment and calculation for a knowledge of 
 its true state at any particular period. By reference to 
 Daniell's tables of observation, it will be found that a differ- 
 ence in the dryness of the air, amounting to 20 degrees of the 
 hygrometer when the air was at the temperature of 60 degrees, 
 has been observed within three days, there being at one time 
 1.053 cubic inches of vapour present in 100 cubic inches of 
 the air, and at another 1.98 cubic inches: a difference of .9^7 
 cubic inches of vapour (uncorrected for temperature) having 
 occurred in that short period. 
 
 903. If the air in the globe were dried, it would then be 
 almost constantly the same in weight ; for its two important 
 ingredients vary very slightly if at all, and the difference in 
 their weight is so small as to make these variations of no con- 
 sequence. The carbonic acid in the air is in very small quan- 
 tity, and though variable can hardly interfere, except under 
 particular circumstances. It may on very important occasions 
 be removed by alkali. 
 
 904. No choice can be permitted in this process, as to passing 
 in the gas in a dry or a moist state ; it must of necessity be 
 dry. For though, if admitted when saturated, the proportion 
 of the vapour may be deduced from the temperature by refer- 
 ence to the table (889) , and its specific gravity may be con- 
 sidered as known, yet as the whole volume of gas introduced 
 is unknown, and the specific gravity is as yet unknown, there 
 is no way of ascertaining the actual weight or volume of the 
 vapour present, without which the correction for moisture can- 
 
384 WEIGHING OF GASES CORRECTIONS REQUIRED. [Sect.XV. 
 
 not be applied ; it is, therefore, necessary that the gas should 
 be dried (893) by some one of the processes already described, 
 and then, if the air in the globe be dried also, without knowing 
 the volumes and without correction for barometer or thermo- 
 meter (provided they do not change during the experiment) , 
 the relative specific gravities of air and the gas may be ascer- 
 tained, and by similar experiments, of air and any other gas. 
 Thus, suppose the globe by exhaustion lost 45.28 grains, and 
 by admitting dry oxygen gas gained 50.7 grains, 50.7 -f- 45.28 
 = 1.1197 the specific gravity of that oxygen gas, common air 
 being 1. Then clearing out the globe, and replacing its con- 
 tents by pure dry air (901), suppose the experiment repeated 
 with dry sulphurous acid gas, the globe losing this time only 
 40.25 grains, and gaining by the entrance of the sulphurous 
 acid 90.37 grains, then 90.37 + 40.25 = 2.245 the specific 
 gravity of sulphurous acid, air being 1. 
 
 905. But if the volume of the gas admitted be measured 
 (887), it may then be saturated with moisture; but now the 
 temperature and pressure must be known. The temperature 
 being known, the volume of the aqueous vapour admitted 
 with the gas may be ascertained by reference to the table (889, 
 891) ; and then, being corrected for temperature, its weight 
 also may be ascertained ; and by subtraction of it from the 
 whole weight gained, the weight of the dry gas admitted is 
 known. Now diminishing the weight of the common air taken 
 out by a proportion equal to the volume of the vapour in the 
 gas, the rest is the corresponding weight of air of a bulk equal 
 to that of the dry gas, and dividing the latter by the former, 
 the specific gravities are ascertained. The proportion in bulk 
 between the gas and the vapour mixed with it, required in the 
 latter part of this calculation, is to be obtained by correcting 
 the whole volume of gas to the pressure of 30 inches, and then 
 subtracting the volume of vapour from it. 
 
 906. On the whole, it is better perhaps in this method that 
 both the air and the gas should be saturated with aqueous 
 vapour, the temperature being known, and the same for both. 
 This is easily done by exhausting the globe or flask, and filling 
 it with common air from a receiver over the same water as the 
 gas ; then counterpoising it, exhausting it more or less, ascer- 
 
Sect. XV.] WEIGHING OF GASES PRECAUTIONS. 385 
 
 taining the loss of weight, supplying the place of the air taken 
 out by the gas, observing the quantity admitted and weighing 
 it again. Thus the equal volumes of moist air and gas, their 
 weights and temperature, become known ; from the quantity 
 and temperature of either, the volume of aqueous vapour at 
 the pressure of 30 inches may be deduced by the table (889), 
 and is the same for both. The weight of this, when reduced 
 to mean temperature, may easily be ascertained, and that being 
 equally subtracted from the observed weights of the common 
 air and the gas, leaves the actual weights of equal dry volumes 
 of air and of the gas ; from which the specific gravity is easily 
 deduced as before by division. 
 
 907. As an illustration of this method, suppose the globe to 
 be filled with air from over water, then balanced, afterwards 
 exhausted, and the loss of weight found to be 34.6 grains ; on 
 letting in the moist gas, suppose that 112 cubic inches entered, 
 and that the gain of weight was 52 grains, the temperature 
 being 52 Fahrenheit, and the barometer at 29.2 inches. At 
 52, the proportion of aqueous vapour in volume is, 01426, 
 which, of 112 cubic inches, is 1.597 cubic inches ; this quan- 
 tity corrected to mean temperature = 1.623 cubic inches ; and 
 this equals 0.313 grains of aqueous vapour ; the subtraction of 
 this weight equally from the weights of the moist air and gas, 
 leaves 34.287 grains for the weight of dry air, and 51.687 
 grains for the weight of an equal volume of dry gas. In this 
 way any slight errors in measuring are important, but care is 
 requisite as to the constancy of temperature. 
 
 908. In all experiments upon the weight of gases, it will be 
 proper to leave the globe full of pure common air ; all remains 
 of the gases which have been in use, having been removed be- 
 fore the apparatus is put away. 
 
 2 C 
 
386 TUBE CHEMISTRY TUBES REQUIRED. [Sect. XVI. 
 
 SECTION XVI. 
 TUBE CHEMISTRY. 
 
 909. FREQUENT occasion has occurred in the preceding parts 
 of this volume for the description of apparatus formed partly 
 or altogether of glass tube. The object of this section is to 
 shew the important uses of apparatus of that description. 
 The facility with which it supplies the absence of many com- 
 plicated instruments ; the consequent economy and readiness 
 of chemical practice ; and the peculiar advantages of it when 
 rare and valuable substances are under examination, are the 
 inducements to collect the information upon this subject into 
 one focus. 
 
 910. The material required for the construction of this kind 
 of apparatus is glass tube of half an inch in diameter, or less, 
 and of different degrees of thickness. The most useful sort 
 is quill tube, the glass being of the thickness of card or thin 
 pasteboard. Three-square or edge files are required for 
 cutting the tube into lengths. If the table blow-pipe and 
 lamp (242) be not at hand, most, and indeed all the apparatus 
 may be made by a spirit-lamp and a mouth blow-pipe (216). 
 To these should be added a drawer full of tubes, closed at one 
 end, of various diameters, and all lengths from one inch to five or 
 six. The fragments of tubes, which are continually occurring, 
 should be worked up into these forms at every opportunity, 
 according to the direction to be given in Section XIX. (1165, 
 SEC.) and are then ready for use. 
 
 911. These tubes answer all the purposes of test-glasses, 
 and in the small way precipitates are made, preserved, and 
 washed very conveniently in them. They are easily supported 
 in a tumbler or wine-glass, or they may be supplied individu- 
 ally with stands, by inserting them in perforated corks (67). 
 Those who frequently use them will find a tube-rack very 
 convenient. It may be formed of two boards, one supported 
 two or three inches above the other, and the upper pierced 
 with holes to admit the tubes. Or a very simple one may be 
 
Sect. XVI.] PRECIPITATION WASHING. 387 
 
 made of a board a foot in length and six inches in width, 
 having a piece of coarse wire trellis about three inches above 
 it, supported at the corners by upright pieces of strong wire. 
 The apertures in the trellis serve to receive and retain the 
 tubes. A dropping-bottle (402) is necessary in experiments 
 with these tubes, for the supply of small quantities of water, 
 or for washing precipitates from the sides. 
 
 912. When in precipitating or testing (504, &c.) agitation 
 is required, it may be given by closing the tube with the 
 finger, and shaking the contents together from top to bottom. 
 Or, if the finger be likely to communicate impurity, and so 
 interfere with the experiment, or be itself liable to injury, then 
 a clean glass rod, about half the diameter of the tube, if raised 
 and lowered in the fluid, will readily and perfectly mix it. 
 Occasionally, with corrosive fluids, the tube may be held 
 rather stiffly at top in one hand, and the fore-finger of the 
 other passed rapidly backward and forward by the bottom, so 
 as to strike it each time, and thus give rapid agitation to the 
 contents, if they are not in too great quantity. Such ordinary 
 agitation as would effectually mix fluids in a glass or bottle, is 
 insufficient for the same purpose in these narrow vessels, espe- 
 cially when the depth of fluid is more than an inch. 
 
 913. When delicate testing operations are in progress, tubes 
 are exceedingly convenient, owing to the facility with which a 
 little of the fluid to be tested may be compared with the por- 
 tions to which tests have been added. It is scarcely possible 
 that the slightest change can pass unnoticed when the two are 
 examined by each other. 
 
 914. The ivashing and separation of small quantities of 
 insoluble fluids and fusible solids, is well effected in tubes. 
 An extemporary instrument for the former purpose, made of 
 tube, has been already described (559). In consequence of 
 the facility with which heat may be applied, it is easy to melt 
 a fusible body in a tube ; thus naphthaline may be fused with 
 water or a solution of potash, and if mixed well, and after- 
 wards left to separate and cool, it will be obtained in a cleansed 
 state and a very convenient form. In such cases it is advan- 
 tageous to let two pieces of wire remain in the tube until all 
 is cold : one is to pass through the naphthaline into the water 
 
 2 C 2 
 
388 TUBE CHEMISTRY SOLUTION. [Sect. XVI. 
 
 beneath ; the other, bent at the lower end, is to be placed in 
 the naphthaline, and retained there by turning the upper part 
 of it over the edge of the tube. If the straight wire be first 
 pulled out, a passage for air is opened, in consequence of which 
 the piece of naphthaline may itself be drawn out with facility 
 by the second wire. Wax, camphor, and other equally fusible 
 bodies may be experimented with in the same manner. 
 
 915. As already observed, these tubes will bear heat, its 
 application being easy and convenient either by sand-baths, 
 spirit-lamps, or other means. Hence they supply the place 
 of flasks (400) as well as glasses, and many operations (259) 
 both hot and cold, as those of solutions, digestions, &c., may 
 be performed in them with numerous advantages, amongst 
 which is the important one of easily witnessing what is going 
 forward. Solutions in acids are readily effected (400, Sec.), 
 and the action upon a substance, or the changes in the ap- 
 pearance of the solid and fluid may be watched at every 
 moment in the most advantageous manner. 
 
 916. The surface of a body which has been partly acted 
 upon, is frequently better seen in a tube when surrounded by 
 fluid, than it can be even in the air ; and this is still more 
 particularly the case with such bodies as change in the air, 
 or that cannot be washed or dried without injury. For this 
 reason the crystallizations which are formed from hot solutions 
 as they cool in tubes, are more advantageously examined in 
 that way than in any other (575) ; and as the cooling can be 
 retarded to almost any degree, either by wrapping the hot 
 tube, with its contents in flannel, or else immersing it in a 
 large quantity of hot matter, and enveloping the whole, this 
 method is often superior to any other. 
 
 917. The arrangement of tube-baths for the conveyance of 
 limited temperatures either by the intermedium of water, so- 
 lutions, or metals, has already been described with sufficient 
 explicitness (259, 263, 265). 
 
 918. Tubes when heated sometimes acquire temperatures 
 which make them untenable in the unguarded hand ; this 
 inconvenience is easily obviated by folding a piece of paper 
 about three inches square three or four times in one direction, 
 so as to form a band of eight or twelve thicknesses, passing 
 
Sect. XVI.] HEATING TUBES BOILING. 389 
 
 this round the tube near the top, and twisting the two 
 ends together into a handle. The conducting power of the 
 paper is so small, that such a handle prevents the passage of 
 any heat by which the hand might suffer inconvenience. A 
 very convenient handle may also be made of a sound cork 
 perforated so as to form a ring, which is to be cut through 
 with a knife in one place. Half a dozen of these will supply 
 handles to most tubes ; they merely require to be slipped upon 
 them, and will clasp the vessel like a spring. Occasionally, a 
 piece of square or angular cork, or the half of a rounded cork, 
 or one that does not fit tightly, being inserted in the mouth of 
 the tube, forms a useful handle (1174) ; these are more par- 
 ticularly required in sublimations, where the whole of the 
 surface of the tube is, if possible, to be exposed to view. 
 
 919. In consequence of the small diameter, and, therefore, 
 small sectional area of tubes, they are much stronger relatively 
 to internal pressure than larger vessels, such as flasks of the 
 same thickness. An advantage is thus gained in some cases 
 of solution or digestion in certain fluids, as alcohol, ether, and 
 even water, because it enables the experimenter to subject the 
 substances to temperatures as high as the boiling points with- 
 out loss of the fluid (400), or occasionally to temperatures still 
 higher (99) , the ebullition going on as it were under pressure. 
 This is easily performed with alcohol, ether, and similarly vola- 
 tile fluids, in tubes of four, five, or six inches in length, and 
 of such diameter as to be readily and perfectly closed by the 
 finger. Suppose a tube of this kind, one-third filled with 
 alcohol, and held tightly between the thumb and second finger 
 of the left hand, its orifice being closed by the fore-finger of 
 the same hand. The fore-finger is to be relaxed, and the 
 heat of a spirit-lamp applied until the alcohol begins to boil ; 
 the fore-finger is then to be reapplied closely, and it will be 
 found that the flame of the lamp, applied at intervals, is quite 
 sufficient to keep the temperature up to the boiling point. No 
 alcohol can evaporate, for the finger has power sufficient to 
 retain the vapour even were its force equal to two atmospheres, 
 and the tube itself is also strong enough to resist the same 
 force. 
 
 920. This operation is very advantageous when valuable 
 
390 TUBE CHEMISTRY BOILING UNDER PRESSURE. [Sect. XVI. 
 
 and volatile solvents are in use ; it is therefore worth while to 
 refer to those points which indicate the state and temperature 
 of the fluid, and which make the practice easy. If the fluid 
 be one which, like alcohol, when at or above its boiling point 
 is at a temperature inconvenient to the hand, then, if all the 
 common air were allowed to pass out of the tube before closing 
 it, the whole tube would become heated by the vapour rising 
 from the hot liquid beneath, and the fingers would be injured ; 
 but by not allowing all the air to escape, that portion which is 
 retained in the tube is always forced to the top by the succes- 
 sive formation and condensation of the vapour below, and in- 
 terfering with the passage of the hot vapour to the part which 
 it occupies, it preserves that portion of the tube at compara- 
 tively low and very bearable temperatures. The part thus re- 
 tained at a low temperature is proportionate to the quantity 
 of air confined in the tube ; this quantity is usually a proper 
 one if the tube be closed just after the alcohol has begun to 
 boil, and before the upper part of the tube has been heated. 
 If too much air has been expelled, and the tube is found to 
 become hot above, the application of the flame must be sus- 
 pended a moment or two, the whole suffered to cool below the 
 boiling point, the tube opened, the upper part cooled slightly 
 by a piece of moist paper or a cold finger, and then the fore- 
 finger is to be re-applied to close it as before. 
 
 921. The state of the fluid within is in part indicated by 
 the pressure of the air or vapour on the finger, the latter 
 being urged away from the tube by a force proportionate to 
 the degree of heat above the boiling point, and being drawn 
 inwards when the heat is below that point. Generally, there- 
 fore, the finger alone will serve to ascertain whether the tem- 
 perature is above or below the point of ebullition ; but as the 
 force required is, after operating for some time at high pres- 
 sures, such as to diminish the sensibility of the finger to smaller 
 pressures, it sometimes happens that on lowering the tempera- 
 ture, the period at which it attains that of ebullition in the 
 atmosphere cannot be distinguished. This point is, however, 
 easily recognised by relieving the pressure of the finger slightly ; 
 should the quiescent fluid below then burst into ebullition, it 
 is a proof that its temperature is higher than the boiling point 
 
Sect. XVI.] TUBE CHEMISTRY DISTILLATIONS. 391 
 
 at atmospheric pressure, but should it remain quiescent until 
 the finger is entirely removed, its temperature will be known 
 to be below that point. 
 
 922. During long digestions, as in the solution of difficultly 
 soluble bodies, a tube bent into the form represented in the 
 
 figure is very advantageous. The acid 
 or other fluid which is volatilized and 
 distilled over into the part at 6, is easily 
 returned upon the substance at a, by elevating the open end 
 of the tube, and is made to re-act upon it ; a little piece of 
 moistened paper may be applied at b, or that part may be 
 cooled by a refrigerating mixture, or by immersion in water. 
 This arrangement is most frequently useful in the solution of 
 substances but slowly acted upon in acids, as certain metals or 
 metallic ores. 
 
 923. The above process also illustrates the use of tube 
 apparatus in distillation, the part a answers to the retort, and 
 the part b to the receiver of the usual apparatus (447). The 
 fluid to be purified or distilled may be poured into the tube, 
 and the latter being held upright, and the finger placed over 
 the aperture, heat should be applied below and vapour raised ; 
 this will condense upon the sides of the tube and flow down, 
 carrying with it that portion of the fluid which, in pouring, 
 adhered to the side ; this should be done till it is observed that 
 the vapour rises nearly to the top before it condenses, and 
 insures the cleansing of the whole tube. This preliminary 
 operation is intended simply to wash the adhering portion of 
 the introduced fluid to the bottom of the apparatus, that no- 
 thing may remain at b to contaminate the distilled products. 
 The tube is then to be placed as in the figure, the proportion 
 of the vessel and the charge being such, that the latter shall 
 not occupy more than half that part of the tube. Heat being 
 then gradually applied near the top of the fluid, the latter 
 should be distilled over into the angle at 6, which is now to be 
 cooled by wet paper, water, or some other means. If the dis- 
 tillation be unsatisfactory, it is easy to return the product and 
 repeat the operation ; if satisfactory, then by applying a file 
 at c (1152) the tube is readily divided, and the rectified por- 
 tion obtained in the bent part, constituting a separate vessel. 
 
392 'TUBE CHEMISTRY DISTILLATION RETORTS. [Sect. XVI. 
 
 Distillation is frequently performed in a tube-appa- 
 ratus, precisely similar to the ordinary retort and receiver. 
 A piece of tube sealed at one end, and then bent as in the 
 figure, forms what is called a tube- 
 retort (1175). Fluid substances are 
 easily introduced into it through a little 
 tube funnel, made by heating the middle of a piece of tube 
 about two inches long, and half an inch in diameter, by the 
 lamp, and then drawing it out into a capillary tube and sepa- 
 rating it of a proper length, (1176, 1181), A receiver for 
 such a retort is made of a piece of straight tube of larger dia- 
 meter closed at one end (911). The beak of the tube-retort 
 is merely inserted an inch or more into the tube-receiver, the 
 junction is left open, and the latter is cooled, 
 if required, in any of the usual ways, (447, 
 453, &c) . Occasionally it is advantageous 
 to draw out the beak of the retort into a 
 capillary form, as has been before described 
 (463, 1179) ; it will then enter into vessels 
 having small apertures and necks. Some- 
 times it is very useful to contract the necks of tube-receivers 
 in a similar manner, as will hereafter be more evident (929). 
 
 925. When a larger tube-retort is made use of, it is often 
 
 useful to draw out and contract the 
 neck, for the purpose of diminishing 
 its capacity, and consequently the quan- 
 tity of vapour which it can contain ; a 
 common narrow-necked phial then makes an excellent receiver. 
 
 926. The tube-receiver is frequently varied in form with 
 advantage, by making it of a bent piece of tube open at both 
 ends, and when one end of it is formed as at b in the following 
 figure, it is exceedingly convenient for pouring out minute 
 
 portions of the liquid contained in it without 
 waste ; for by bringing the small extremity 
 b against a glass rod or a plate, and inclining 
 
 the receiver, as little or as much of the fluid may be delivered 
 
 as is required. 
 
 927. These tubular vessels may be supported with facility, 
 
Sect. XVI.] DISTILLATION ARRANGEMENT. 393 
 
 sometimes upon the table across two or three pieces of glass 
 tube, or rod, or upon listed rings (68), or in the air upon 
 the edge of glasses placed side by side, 
 upon retort stands. The arrange- 
 ments are so simple that no difficulty can 
 occur with respect to them. The receivers may be cooled by 
 wet paper, or by placing them in water in a glass or Wedg- 
 wood's dish, or by putting them into a hole in a piece of 
 ice, into which a little salt may be occasionally introduced (454). 
 
 928. In cases of distillation upon a small scale, where, be- 
 sides a fluid product, a gas is also expected and required to 
 
 be collected (746, &c.), the tube 
 may have the accompanying 
 form given to it. If it be re- 
 quired to distil the first product a second time for its further 
 purification, it should at first be distilled into a receiver of the 
 second form, and that operation finished, the retort is to be 
 removed, a small flame applied by the blow-pipe to the narrow 
 part of the receiver at a, which, when soft, is to be drawn out 
 
 and sealed hermetically (1167, 
 1190). The second rectifica- 
 tion is to be made either by 
 neat to b, and plac- 
 ing another receiver at c, or by 
 turning the tube into the position it would take if this page 
 were inverted, applying heat at a, and distilling into the bend 
 at d. 
 
 929. A very convenient vessel, answering the purpose both 
 of receiver and bottle, may be made of tube. For this purpose 
 a piece of tube, about the third of an inch in diameter, four 
 inches long, and sealed at one end, is to be softened in a flame 
 at about an inch from the open extremity, and when uniformly 
 heated all round, it is to be removed from the flame and drawn 
 out, so as to form a long narrow neck (1176). The substance 
 to be distilled into it, such as sulphurous acid (461, 924), or 
 chloride of phosphorus, is to be conducted by a fine tube, simi- 
 lar to that already described (463, 924), which is to terminate 
 the distillatory apparatus, being either drawn out upon the end 
 of the retort or joined with it by a caoutchouc connecter (449) 
 
394 TUBE CHEMISTRY RECEIVERS THEIR USE [Sect. XVI. 
 
 
 
 When sufficient fluid has been distilled into the receiver, the 
 capillary neck of the distillatory apparatus 
 c / should be withdrawn, the tube softened about a 
 by a small flame and drawn off, so as to leave 
 the termination there with a fine aperture ; then 
 it is to be softened again at 6, and bent as in 
 the second figure. The aperture at c is easily 
 closed by holding it for a moment in the edge 
 of a flame, and the contents of the vessel, how- 
 ever valuable they may be, are securely re- 
 tained. When a portion is wanted for experi- 
 ment, the extreme point should be nipped off 
 so as to make an aperture, and the tube should be inclined 
 until b becomes the highest part ; so much of the fluid as may 
 be required should be thrown by a little agitation into the neck 
 about 6, where it will remain in a short column ; but by ap- 
 plying the hand to the thicker part of the tube, the air will 
 expand and force out the fluid in the neck, on to any spot to 
 which the aperture at c may have been directed. In this 
 manner the smallest quantity of the fluid, or the whole, may 
 be used at once ; and enough having been removed, the tube 
 is again to be placed in a more upright position, its extremity 
 sealed, and the whole put aside until again wanted. 
 
 930. These receivers are very useful for retaining valuable 
 and volatile fluids, and are the best that can be used for 
 such bodies as sulphurous acid (461). If that substance be 
 confined in ordinary bottles, a great quantity is suddenly 
 volatilized each time the bottles are opened, and from the 
 instantaneous cold produced, the bottoms generally break 
 and fall out: but if it be preserved in vessels like those 
 described, they may be of sufficient thinness to bear this sud- 
 den depression of temperature without fracture, and may 
 even be cooled previously with facility by a piece of ice and a 
 little salt (487, 927). Sulphurous acid may be preserved in 
 such tubes in small portions for single experiments, or if in 
 large quantity, it is easy to distil or transfer it as has been 
 described. When used for sulphurous acid, they must of 
 course be retained in a refrigerating mixture during the dis- 
 tillation (454), they must be continued in this mixture whilst 
 
Sect. XVI.] 
 
 COOLED RECTIFICATIONS. 395 
 
 the top piece is withdrawn (929), and also whilst the bend is 
 given to them, if that be required. It is also necessary that 
 they be sealed when thus cooled, for it cannot be done after 
 they are exposed to the air (1189, 1191, &c). The best 
 method is to prepare the small aperture by drawing off the 
 extremity, to lift the tube into the air, then to apply the flame 
 of the lamp, which will not as yet seal it, and afterwards to lift 
 up the freezing mixture, or depress the tube in it, still ap- 
 plying the flame of the lamp: as the cold condenses the internal 
 vapour the current outwards will cease, and the extremity will 
 close; instantly withdraw the lamp so that the glass shall 
 harden, and then the receiver may be taken out of the cold 
 mixture, and preserved in a glass or tumbler (911), in a place 
 at ordinary temperature. Should there be a doubt of the 
 sealing being perfect, bring a little ammonia near the ex- 
 tremity ; if no fumes are produced all is secure, if there be 
 fumes the same operation of sealing as that just described must 
 be resorted to. 
 
 931. Successive rectifications may be made in the same 
 tube, by bending it with several angles as in the annexed 
 figure; such an apparatus was found of great service in 
 experiments upon the fluids obtained by the compression 
 of oil gas. The fluid is to be introduced at the open ex- 
 
 a tremity a, so as to lie in the 
 angle 6, then applying a 
 small blow-pipe flame, the 
 glass should be softened at the neck, drawn out and sealed, 
 the capillary termination at /being open. On moderately 
 heating 6 and cooling c, a distillation of the more volatile part 
 will take place, the latter collecting at c; after a time, by keep- 
 ing 6 and c warm and cooling d, a reptification of the product 
 at c may be effected, and this distillation may be again 
 repeated upon the product at d by condensing in r. By 
 forming the angles of the tube as in the figure, the results may 
 be returned and redistilled ; for upon raising the end /, the 
 product in c will first return to 6, then that in d, and finally 
 that in e : so that if the substance be sufficiently freed from the 
 denser parts only after the third or fourth distillation, the 
 products in c and d may be returned to b and redistilled as 
 
396 TUBE CHEMISTRY RECTIFICATIONS. [Sect. XVI. 
 
 before, that in e being retained separate : during such experi- 
 ments e should be preserved very cold. 
 
 932. In experiments with the oil gas liquor, distillations 
 of this kind were often to be performed in close vessels, 
 that dissipation of the more volatile parts might be prevented. 
 In such cases after having introduced the fluid to b and sealed 
 the end , the end of f was raised till it was the highest point, 
 the fluid in the lower extremity heated until combustible 
 vapour issued at/", and then a small flame applied whilst the 
 temperature of the other parts was allowed to fall ; the vapour 
 within soon condensed, the extremity was instantly closed by 
 the lamp, the lamp itself removed, and the tube left hermeti- 
 cally sealed. Then collecting all the fluid to the end 6, the 
 distillations and rectifications were performed, and when fluid 
 had collected in e, it was easy by opening the end / under 
 mercury, to ascertain whether it was sufficiently volatile to rise 
 as gas at ordinary pressure, and when it did so the gas was 
 collected in jars with facility. 
 
 933. It will be unnecessary to refer minutely to the capa- 
 bility of transferring backwards afforded by different in- 
 clinations of the parts of the tubes: by angles different to 
 those mentioned, the fluid may be first returned from e to d, 
 then from d to c, and so on. By bending the tube at l } as 
 
 is represented in the accompanying 
 wood-cut, so that the tube from I to 
 
 Jr ^ n shall be in a plane perpendicular 
 
 to that which includes the part from 
 g to I, the power is obtained of re- 
 turning the products from k to h, or from m to k inde- 
 pendently of each other; and thus the more fixed and more 
 volatile parts may both be returned and re-distilled with- 
 out mutual interference. The student will easily compre- 
 hend these forms of tubes and their advantages by bending 
 a piece of wire into the directed or desired shape, and ob- 
 serving the position of its parts as he inclines it in different 
 directions. 
 
 934. Valuable volatile substances are frequently purified 
 with [great advantage by distillation in vacuo in tube retorts. 
 A common tube retort (924) is to be softened and drawn out 
 
Sect. XVI.] DISTILLATION IN VACUO SUBLIMATION, 
 
 397 
 
 near the open end, like the extremity a of the figure, page 394, 
 the fluid is to be introduced, the neck to be drawn off by a 
 small flame, and a minute aperture left ready for sealing (929) ; 
 the retort being held with this aperture upright, the substance 
 below is to be heated till the tube is full of vapour (932), and 
 the aperture sealed as before described (1190). When the 
 tube is cold, the substance is to be collected to one end, and 
 the distillation effected either by raising its temperature or by 
 cooling the opposite extremity. When the distillation is to be 
 slow, the difference of temperature thus caused between the 
 two ends should be slight, when quick, it must be greater. A 
 very convenient method in slow operations is to pass the end of 
 the tube retort containing the substance through a cork, and 
 ^^- _/? to fix it in the mouth of an open air-jar ; 
 
 this is to be supported by a retort stand 
 or two bricks, or otherwise, and a spirit- 
 lamp with a small flame is to be placed 
 under it: an atmosphere of heated air 
 ."-Jr '-[ is thus formed within the jar, which 
 
 ^S"^ warms the tube more or less according 
 
 to the arrangement, and effects the distillation. The ex- 
 ternal or condensing end of the tube may be cooled either 
 by the air, or by water (447, 468), or by refrigerating 
 mixtures (454, 487) . 
 
 935. The uses of tubes in sublimation will be evident from 
 what has been already said of that process (495) , and of their 
 application to distillation. Any volatile body, as camphor, 
 calomel, &c., placed at the bottom of a straight tube closed 
 at the lower end and heated, will sublime and condense in 
 the cooler upper part ; after which the tube may be cut with 
 the utmost facility (1152) between the sublimed part and the 
 residuum, and the former obtained in a pure state. 
 
 936. In these operations the successful condensation of the 
 vapour is materially influenced by several little circumstances 
 requiring attention: these, when the substance is easily con- 
 densed, and the upper part of the tube is retained sufficiently 
 cool by mere contact of -the air, relate simply to position. The 
 nearer the tube is held to a vertical position, the greater will 
 be the length heated by the ascending flame, and on the 
 
398 TUBE CHEMISTRY SUBLIMATION. [Sect. XVI. 
 
 contrary, the nearer to a horizontal position, the Jess will be 
 the extent thus elevated in temperature. Advantage may 
 be taken occasionally of both these circumstances. In sub- 
 liming cinnibar, arsenic, calomel, or any other body requiring 
 a high heat for the formation of its vapour, the vertical 
 position of the tube is the best, the place of condensation 
 being then farther removed from the place where the crude 
 substance lies, and the crystals themselves being better formed 
 in consequence of the vapour losing its high temperature 
 less rapidly; but with such substances as iodine, naphthaline, 
 camphor, corrosive sublimate, and bodies whose vapours are 
 either formed at low temperatures, or which condense into 
 a liquid before solidifying, the position of the tube should 
 be nearly horizontal, that the place of condensation may 
 not be too much heated for its office, nor so inclined as to 
 occasion the immediate descent of the portion of fluid con- 
 densed there. 
 
 937. Occasionally it will even be necessary to cool the place 
 of condensation; this may be done by a damp finger, or by a 
 piece of tin or copper foil wrapped round it (1356), or by a 
 slip of wet paper folded over it (447) and moistened from 
 time to time. A very convenient and useful method of con- 
 densation, when it- is required quickly to remove a portion of 
 the substance out of the subliming vessel, is to introduce the 
 end of a smaller tube, closed below, and containing a little 
 water, into the subliming vessel. But this must be done only 
 with such substances as rise at low temperatures and condense 
 readily, for example, iodine, camphor, naphthaline, &c. ; for if 
 very hot vapours, as those of mercury, were to come in con- 
 tact with such a cooled tube, they would probably break it, 
 and cause inconvenience from the dispersion and mixture of 
 the water. The substance condenses on the exterior of the 
 introduced tube, and may be withdrawn with it. A tube 
 filled with mercury may be used for condensation in a similar 
 way, or even a cold glass or metal rod ; but the condensation 
 should in these cases never be continued so long as to heat the 
 rod, or the condensing tube and its contents, very highly, for 
 then their efficacy fails. If they become hot, they should not 
 be withdrawn in that state with the substance upon them, but 
 
Sect, XVI.] SUBLIMING TUBES. 399 
 
 their temperature first allowed to descend so as not to occasion 
 volatilization, or serious loss of the substance, when brought 
 into the open air. 
 
 938. Sublimation may frequently be effected very simply 
 and conveniently by condensing the vapours in a tube placed, 
 not within, but over the subliming vessel, a short but larger 
 one being inverted over the mouth of the latter, and the con- 
 densation taking place principally in it. In place of this 
 second tube a flask or phial may be used. A very convenient 
 form of condensing tube for heavy vapours, or easily fusible 
 
 substances, as iodine, napththaline, &c., 
 is that of the annexed figure, the bent 
 tube being of such diameter as freely to 
 pass over the subliming tube, but not 
 larger : the condensation takes place principally in the upper 
 part of the middle portion of the tube, and the refrigeration 
 may be effected in the most convenient manner either by moist 
 paper or immersion in water (447). 
 
 939. Berzelius has upon particular occasions used an open 
 tube for sublimation, the length being about six inches, the 
 
 diameter half an inch or more, and the 
 position an inclined one. When a sub- 
 stance is heated in the lower part of the 
 tube, an upward current of air carries the vapours forward into 
 the cooler part, where, if condensable under the existing tempe- 
 rature and circumstances, they assume the liquid or solid form. 
 The air has access to such a tube or may be shut out by the 
 finger at pleasure, and any combustible body heated in it may 
 consequently be burnt if required; this circumstance occasioned 
 the introduction of the tube into use. A crude mixture con- 
 taining much sulphur with a little selenium, being put into 
 the lower part and heated, the sulphur inflamed, and forming 
 sulphurous acid, passed away ; the selenium sublimed, and 
 condensed in part in the upper portion of the tube, and a 
 fixed impurity remained in the place of the mixture. The 
 portion of selenium might afterwards be sublimed or otherwise 
 examined, and many of its properties ascertained. It is in 
 the continually varying experiments of investigation and re- 
 search, that such practices and facilities as these are resorted 
 
400 BODIES HEATED IN VAPOURS. [Sect. XVI. 
 
 to. They are found of essential advantage where the object 
 is rather to effect the separation of bodies supposed to be 
 present, with a voluntary loss of part, than merely to purify 
 one substance from another in such manner as to preserve the 
 whole. Both objects are important in turn, and both may 
 be attained by one or other of the processes and practices 
 described. 
 
 940. Tubes are exceedingly convenient for the heating or 
 even igniting of numerous substances, in the vapours of vola- 
 tile bodies, which are either solid or fluid, at common tempe- 
 ratures. If a small piece of naphthaline be put into a tube 
 closed at one end, and held in an inclined position, and the 
 bottom be heated, the naphthaline will melt, sublime, condense 
 above, and descend to the lower end in a stream ; but as soon 
 as it reaches the hot part it will be re -volatilized, to be re-con- 
 densed above, and to flow down as before. In these circum- 
 stances the bottom of the tube may be heated red-hot for half 
 an hour or longer, being filled during the whole time with the 
 vapour of naphthaline nearly pure. The same may be effected 
 by a little management, easily to be acquired by practice, with 
 alcohol or ether, or sulphur, or even iodine, and indeed with a 
 numerous set of important chemical agents. It will be evident, 
 that any fixed substance placed in the bottom of the tube, 
 may, under these circumstances, be heated to redness for a long 
 time in the vapour of the volatile body, and thus the facility 
 of acting on metals, metallic oxides, and other bodies, by such 
 agents as those mentioned above, is obtained. Nor is it con- 
 fined to these cases, for the vapour of sulphur, for instance, 
 may be heated to redness, mixed with the vapour of ether or 
 of napthaline ; or these latter substances may be raised to a 
 red or a white heat, for the purpose of effecting their decom- 
 position ; and a great variety of important experiments may 
 be thus performed, to the full satisfaction of the experimenter. 
 
 941. Those who work much with tube apparatus will have 
 frequent occasion to dry precipitates or powders contained in 
 tubes, or even to evaporate fluids to dryness in them. These 
 processes may be performed with more facility than is generally 
 imagined, but require peculiar though easy arrangements 
 and precautions. Suppose, as the simplest case, that a portion 
 
Sect. XVI.] 
 
 DRYING OF PRECIPITATES. 401 
 
 of moist powder, a precipitate for instance, contained in a tube, 
 is to be dried : a paper handle should first be adapted to the 
 tube (918) , and then heat applied to volatilize the water. The 
 first portions of vapour will condense on the interior of the 
 tube and form drops, which descending, may sometimes cause 
 the fracture of the hot glass below ; to prevent this the tube 
 is to be held in a position nearly horizontal, so that the drops 
 shall have but little tendency to descend, and a piece of fil- 
 tering paper is to be folded lengthways and introduced into 
 the tube, as far as the commencement of that part which is 
 too hot to permit of condensation. This piece of paper, lying 
 upon the lower internal surface of the tube, is sufficient to 
 absorb all the liquid that may condense, and does not interfere 
 with the passage outwards of that part of the water which is 
 still in the state of vapour. When all the water is driven 
 from the substance, the paper may be withdrawn, bringing 
 away the moisture with it. 
 
 When the desiccation is performed in long tubes, it is ad- 
 vantageous to wrap paper or tow round the upper part, to 
 keep them hot, and prevent as much as possible the condensa- 
 tion of the vapour. When from any circumstance a drop has 
 collected in the upper part of a tube, and is in danger of 
 running down and causing injury, either by cracking the glass 
 or by its chemical action, it may readily be removed by bring- 
 ing the end of a piece of folded or rolled bibulous paper into 
 contact with it. 
 
 94$. When the contents of tubes have been thus dried, the 
 tubes themselves are often left filled with aqueous vapour, and 
 their sides in a damp state. But these small portions of water 
 are easily removed whilst the tube is warm, either by blowing 
 or drawing air through it. For this purpose one end of a long 
 narrow tube is to be introduced, the mouth applied to the 
 other end, and air blown through it ; this will rapidly take up 
 the warm water, and carry it out into the atmosphere. Still, 
 however, the tube remains filled with air from the lungs, 
 which, being in a moist state, would, on the falling of the tem- 
 perature, cause a dampness and deposition ; to prevent this, a 
 portion of air is to be drawn by the mouth through the long 
 narrow tube before its removal, which air, as it must pre- 
 
 2 D 
 
402 TUBE CHEMISTRY EVAPORATION. [Sect. XVI. 
 
 viously have entered into the outer tube from the surrounding 
 atmosphere, will effectually remove all portions of that from 
 the mouth which had been left there. This process of drawing 
 the air of the atmosphere through vessels, is a very ready and 
 useful expedient in many cases where vessels are to be dried, 
 but it should never be resorted to if any deleterious vapours 
 or gases are present, as they are then conveyed into the lungs : 
 a pair of bellows should on such occasions be used to propel 
 the air. 
 
 943. When a comparatively large quantity of water is to be 
 evaporated from tubes upon the sand-bath, at temperatures 
 below ebullition, it is ordinarily a very slow process, in con- 
 sequence of the limited access of air to the interior (591), 
 except some expedient be adopted to facilitate its entrance and 
 exit. A very generally convenient one is to insert one end of 
 an open bent tube, as in the figure ; a cur- 
 rent of air is thus established either in the 
 one direction or the other, and the aqueous 
 vapour readily removed. A more con- 
 venient evaporator is a bent tube open at 
 both ends, as in the annexed figure, which 
 being set in the sand-bath, or otherwise 
 heated, so as to have one limb rather 
 hotter than the other, has a current spon- 
 taneously established through it. The evaporation proceeds 
 with readiness and facility ; the dry results are very easy of 
 access, and yet little danger of their dispersion during the pro- 
 cess is incurred. 
 
 944. With reference to tube pneumatic apparatus, the 
 advantages which it supplies to those who know how to use 
 them are equally great with other applications of tubes in the 
 construction of apparatus. It is surprising to observe how 
 many of the ordinary, and even refined, experiments of modern 
 pneumatic chemistry may be repeated satisfactorily with an 
 evaporating basin for a pneumatic trough, and with retorts, 
 receivers, and other vessels, formed of tubes (728, &c). 
 
 945. The tube retort has been already described (924), and 
 the modification produced by drawing out the neck after 
 having introduced the material has been referred to (924), 
 
Sect. XVI,] PNEUMATIC APPARATUS RECEIVERS. 403 
 
 This variation is often of great service: thus if an oxide of 
 silver or of mercury were to be decomposed by heat, and the 
 gas collected, it would be advisable to put it into a piece of 
 straight tube closed at one end, and then applying heat above 
 the containing part, to draw the tube out into a narrow neck 
 (925) from four to six inches in length ; this should be bent 
 near to the body, by holding it over the flame of a small spirit- 
 lamp. Such a retort approaches more closely in its form to 
 the ordinary vessel than the common tube retort, and it will 
 be useful, not merely in the instances mentioned, but in most 
 cases where the materials are solid, and remain so, or do not 
 swell much, during the action of heat upon them. 
 
 946. Tube air-jars or receivers are merely tubes closed at 
 one end, and cut off level at their mouths (1152). They 
 may be long, or short, plain, or graduated. Funnels for the 
 transference of liquids into retorts, or gas into tubes over 
 water or mercury, are easily made of a piece of wide tube, as 
 before described (924). An evaporating basin filled with 
 water makes an excellent trough; it should have a slip of. 
 heavy metal, such as sheet lead, laid at the bottom, against 
 which the mouths of the tube receivers may rest, whilst they 
 recline above against the side of the basin. The tubes are 
 thus prevented from slipping to the bottom, or changing their 
 inclined and proper position for a horizontal one, which would 
 endanger the loss of gas. 
 
 947. Oxygen, a small quantity of which in a pure state is 
 often required, is conveniently and economically made even in 
 the large and well furnished laboratory, from chlorate of 
 potash, in a tube retort. Euchlorine is generally, if not al- 
 ways, best made in a tube retort, but then another variation is 
 advantageous, which is useful also in numerous other cases. 
 The retort itself is to be a piece of plain tube, about half 
 an inch in diameter, two or three inches in length according to 
 circumstances, and closed at one end : the mouth is to be fitted 
 with a good perforated cork, having a small tube fixed into it, 
 which, after proceeding about an inch upwards from the cork, 
 is to turn off nearly at right angles for about three inches, and 
 then return to its first direction for about the eighth of an inch. 
 This piece of tube is the neck of the retort, whilst the wide 
 
 2 D 2 
 
404 TUBE CHEMISTRY GASES EUCHLORINE. [Sect. XVI. 
 
 short piece is the body; and the latter having received its 
 charge, the cork is to be put in and made tight by soft cement, 
 after which the distillation may be proceeded with, and the gas 
 evolved and collected. 
 
 948. In reference to the distillation of euchlorine, and of all 
 other explosive substances, the student should be aware of the 
 caution required to prevent accidents, in case explosion should 
 occur. Whenever such an effect is probable, the vessel should 
 be surrounded with tow or cloth, that if it break the frag- 
 ments may be retained; and during distillation the side of 
 the apparatus, or that part which is guarded by the tow, 
 is to be turned towards the eyes, that they at least may be 
 out of danger. It is not easy to wrap tow regularly and 
 tightly round a clean glass tube, from its tendency to slip 
 over the surface; but the difficulty is obviated, by rubbing 
 the outside of the tube with soft cement, or a very little 
 turpentine with a piece of tow or cloth, so as to render it 
 slightly adhesive to the fingers. 
 
 949. When a mercurial trough is required, it may be made 
 either of an evaporating basin, or an earthenware crucible, or 
 even of a glass or cup, according to circumstances; the first 
 being most convenient for transference, the latter for collect- 
 ing gas, delivered from retorts or tubes. The apparatus 
 delivering gas should always be made to turn up at the end, 
 as has been described of the euchlorine retort, that the gas 
 may be fairly thrown off, and into the mouth of the receiving 
 vessel (947). 
 
 950. A very convenient mercurial receiver* of the form 
 represented in the annexed figure, may be made of tube from 
 
 half to three-quarters of an inch in diameter, and 
 from four to ten inches in length. It is closed above 
 but open at the lower extremity. It is to be filled with 
 mercury when inclined, by pouring in the metal at the 
 mouth, and is then to be suspended or supported in the 
 position represented, with an evaporating basin beneath 
 it. The small tube delivering gas is to be introduced at 
 the mouth, so far as to allow the bubbles to pass into the tube, 
 and the mercury to flow out into the basin below. When the 
 * First suggested, I believe, by Mr. Cooper. 
 
Sect. XVL] TUBE CHEMISTRY MERCURIAL RECEIVER. 405 
 
 mercury has descended nearly to the flexure, the operation 
 should be stopped. 
 
 951. The gas thus collected may be examined as to a great 
 number of its characters without the help of any other tube, 
 or of any transference but what may be obtained by moving 
 it from one part of the tube to another. For instance, the 
 finger may be placed on the aperture, in contact with the 
 metal, so as to exclude all air and close the mouth of the 
 receiver; then inclining the vessel, a bubble of gas may be 
 made to pass round the bend towards the finger : this done, 
 upon restoring the upright position of the receiver the larger 
 portion of gas will still be in the upper part, but a quantity 
 varying from a quarter to three-quarters of an inch in extent, 
 according to the will of the operator, will be confined between 
 the mercury and the finger, quite unconnected with the larger 
 portion. This quantity may be tried as to inflammability by 
 bringing a lighted taper near the aperture, and immersing it in 
 the gas the moment the finger is removed. Suppose this trial 
 made and the consequent knowledge acquired ; then by pouring 
 in mercury, so as to fill the small space now unoccupied, 
 re-applying the finger and re-inclining the tube, another 
 portion of the gas is brought into a situation similar to the 
 former; this may be examined as to smell, and its odorous 
 or inodorous nature ascertained. Again filling the space with 
 mercury, and repeating the operations as before, a third por- 
 tion of gas can be brought to the mouth of the tube, and this 
 may be examined as to whether it is heavier or lighter than the 
 atmosphere, if from the two previous trials it appeared to differ 
 in quality from common air: thus, if after leaving the mouth 
 open a short time, the atmosphere around being quiescent, 
 the gas or a part of it still remains in the tube, it must be 
 heavier than air, whereas if all signs of it have disappeared, it 
 is a proof of its lightness as compared with that standard. In 
 a similar manner trial may be made of the solubility of the gas 
 in water, by filling up the space left by the last experiment 
 with water instead of mercury, or at least in part by water, 
 and then bringing a bubble of gas to that part as before; if it 
 instantly disappear, it indicates considerable solubility, if it 
 does not at all diminish, it shows comparative insolubility. If 
 
406 TUBE CHEMISTRY MERCURIAL RECEIVER. [Sect. XVI. 
 
 a solution be actually formed, then upon removing the finger 
 it may be examined as to its acid or alkaline nature, or other 
 properties. 
 
 95%. In these and similar experiments great care should be 
 taken that no water pass beyond the bend into the tube, for 
 which reason but little water should be put in at once ; there 
 should be sufficient mercury between it and the angle to replace 
 the bubble of gas which is to be brought to the mouth, and the 
 inclination of the tube should be carefully attended to, that no 
 water inadvertently pass backward into the higher part. When 
 the trial of solubility is over, the water should be taken from 
 the mouth of the tube, first by a folded piece of bibulous paper, 
 and afterwards with tow upon a wire. Trials may afterwards 
 be made with lime-water or alkaline solutions, their action 
 upon a part or the whole of the gas being in this way easily 
 observed. 
 
 953. Thus the gas may be divided into many successive 
 portions, and submitted to numerous examinations; and should 
 it so happen that a part is absorbed by water and a gas left 
 which could not be properly examined whilst in a state of 
 mixture, then, after having made the proper experiments upon 
 the mixture, a little water may be let into the body of the 
 receiver, and shaken with it, to absorb the soluble gas, and 
 the finger being removed from the aperture, either under mer- 
 cury or water, those fluids will enter and supply the place of 
 the absorbed substance. The insoluble and purified remainder 
 may now be examined in successive portions exactly in the 
 manner just described. 
 
 954. In numerous cases gas may actually be retained and 
 examined in the tubes in which they have been generated ; 
 and no use of simple tubes is more important than the useful 
 indications they furnish when substances are heated in them 
 and the evolved vapour or gases examined at their mouths. 
 Thus when a little piece of animal matter is heated in a small 
 tube, it is easily ascertained, by a slip of turmeric paper at the 
 mouth of the vessel, whether ammonia is evolved : or if sulphur 
 be heated with a vegetable substance, the appropriate tests 
 applied in a similar manner will show whether sulphuretted 
 Jiydrogen gas be extricated Several of the properties of oxygen 
 
Sect. XVI.] OXYGEN CARBONIC ACID EUCHLORINE. 407 
 
 are exhibited by putting a little chlorate of potash or oxide of 
 mercury into the bottom of a glass tube, and applying heat so 
 as to evolve oxygen ; the source of heat may be removed after 
 sufficient gas has been liberated to fill the space above, and 
 that may be judged of in the one case by the ebullition of the 
 chlorate, and in the other by the appearance of metallic mer- 
 cury. The gas may then be examined as to its power of sup- 
 porting combustion, and that being done, the impure mixture 
 remaining after the experiment may be blown out, and by a 
 fresh application of heat another portion of pure gas evolved. 
 
 955. Carbonic acid gas may be examined in a similar man- 
 ner in a tube, at the bottom of which is a piece of marble and 
 a little dilute muriatic acid ; and so also may muriatic acid 
 gas, sulphurous acid gas, chlorine, and euchlorine, very con- 
 veniently. Perhaps, with regard to the latter gas, this is the 
 safest way for a tyro to examine its properties. A little pul- 
 verised chlorate of potash and strong sulphuric acid should be 
 put into the bottom of such a tube, the acid first, and the 
 chlorate in successive small quantities; euchlorine will gra- 
 dually rise and fill the lower part or the whole of the tube, the 
 gas appearing of a deep yellow colour. Occasionally the 
 liberation may be hastened by the warmth of the hand, or a 
 little warm water, the mouth of the tube being directed from 
 the operator. By warming the upper part of the tube with a 
 small lamp-flame, or by immersing a hot wire into the gas, its 
 explosive nature will be observed, the disappearance of colour 
 remarked, and even the chlorine and oxygen liberated may be 
 recognised by their proper qualities. Afterwards, if a little 
 more time be allowed or warmth applied, a fresh portion of 
 euchlorine will be evolved from the materials for another expe- 
 riment. The weight of the gas may now be observed by 
 pouring it from the generating tube into another tube, or a 
 wine-glass. It will descend through the air like water. 
 Whilst pouring, the air should be left undisturbed, and the 
 tube from which the gas flows not quite inverted, but raised 
 with the closed end only a little above the horizontal line. If 
 a piece of copper leaf (1351) be put into the receiving-tube or 
 wine-glass, it will be seen that the euchlorine has no action 
 upon it, and if then the separation of its elements be effected by 
 
408 TUBE CHEMISTRY KERR'S TUBE. [Sect. XVI. 
 
 touching the gas with a hot wire, it will also be seen that the 
 metal will burn in the chlorine set free. Thus a very exten- 
 sive and instructive set of experiments on this curious com- 
 pound may be made with no other apparatus than tubes. 
 
 956. There are certain chemical actions which take place 
 between solids and fluids, where the fluid, from its price, is of 
 no great consequence, and may be used instead of water for 
 collecting the gas evolved during the action. This is the case, 
 for instance, when a formiate is acted upon by sulphuric acid 
 to shew the immediate evolution of carbonic oxide ; and also 
 when the same acid is made to act by heat upon oxalic acid, to 
 shew the evolution of carbonic oxide and carbonic acid : many 
 similar cases occur. These actions may very conveniently be 
 effected in a form of tube first described by Mr. Kerr*. A 
 simple tube, closed at one extremity, is to be bent near the 
 middle, but rather towards one end, in 
 such a manner that when placed as in 
 the figure, the vertex on the lower side 
 shall not be directly under that on the 
 upper side, but nearer the closed end ; this is easily effected 
 during the bending by making one part softer than another, or 
 by blowing it out as is to be described (1197). The part from 
 a to b being then filled with the sulphuric acid or the acting 
 fluid, the substance to be acted upon is to be dropped in at c, 
 and will descend into the acid at d. When the action com- 
 mences, either at common temperatures or by applying a little 
 heat, the gas formed at d will ascend in the closed limb and 
 cause the fluid to occupy the other. The experiment should 
 be made over a basin of water, that the acid may occasion 
 no harm if a little should be spilt ; and when the tube is full, 
 or the action has ceased, the acid should be replaced by water 
 or mercury, and the gas examined. To replace it by water, 
 it is only necessary to immerse the tube in that fluid, and then 
 
 * Edinburgh Philosophical Journal, x. 53. Mr. Kerr has the merit of first describ- 
 ing the utility of the bent tube above referred to, and of making the important im- 
 provement in the position of the vertices. This tube, without that improvement, 
 and all other tubes described in this section, except the modification suggested 
 by Mr. Kerr (957), have been in use in the laboratory of the Royal Institution 
 for many years, and it was supposed were resorted to in most other laboratories 
 of research. 
 
Sect. XVI,] , KERR'S APPARATUS. 409 
 
 to raise the closed end, so that the acid may pour out of the 
 tube and have its place supplied by the water : to replace it 
 by mercury, it is necessary to pour mercury into the open 
 limb, allowing the sulphuric acid to flow over, and also, if 
 there be any portion in the closed limb of the tube in conse- 
 quence of the insufficiency of the gas to fill it, to displace it 
 by inclining the tube carefully, so that it may flow over the 
 mercury between it and the glass into the other, or open limb, 
 without allowing any gas to follow. In this way all the sul- 
 phuric acid may be removed, except that portion which adheres 
 to the glass, which may be cleared away from the greater part 
 of the open limb after the mercury has been poured in, by 
 wiping the glass first with a little plug of wet tow upon the 
 end of a wire, and afterwards by dry tow. When the acid has 
 been replaced by water or mercury, the gas may be examined 
 in successive portions in the manner already described (950). 
 
 957. Mr. Kerr suggests an improvement of this tube*, by 
 making it of the accompanying figure, with an aperture at a, 
 stopped with a ground stopper, or a 
 cork covered with wax. Its use is 
 the same as that of the former, but 
 it affords a further facility of trans- 
 ferring a little gas from it to another 
 vessel without interfering with the fluid in the apparatus. As 
 the gas collects in the closed limb, the small quantity of fluid 
 remaining in the short part is to be turned out, by inclining 
 the tube, and this may be done safely from the mutual in- 
 clination of the parts, without spilling any of the acid at the 
 open extremity. When gas is to be transferred from this 
 vessel to a separate one, as a small tube-jar, the inferior end 
 of the descending part of the closed branch is to be dipped 
 beneath the surface of water or mercury, according to the 
 nature of the gas ; and when the stopper or cork is taken out, 
 the gas will issue forth, or may easily be made to do so, by 
 raising the extremity more or less in the water, or by rendering 
 the column of liquid in the other leg more or less vertical, or 
 slightly urging the gas forward by the mouth. When suf- 
 
 * Edinburgh Philosophical Journal; x. 251. 
 
410 TUBE CHEMISTRY COLLECTION OF GASES. [Sect. XVI. 
 
 v 
 
 ficient gas has been transferred, the stopper or cork is to be 
 replaced, and the circumstances are then nearly as they were 
 at first. 
 
 958. Tubes thus intended for the production of gas over 
 the acid from which it is evolved, are often advantageously 
 bent into a form, which may be described, by assuming them 
 to have been coiled obliquely in the manner of a long-threaded 
 screw, about a triangular prism, of which the planes are one 
 inch wide, so that each straight portion of tube is an inch and 
 a half or two inches long. It will be found, if sufficient acid 
 be introduced to fill one and a half of the straight portions of 
 the tube, and the substance to be acted upon, as oxalic acid, 
 be introduced with it and heated, that by inclining the tube 
 in different directions, relative to a horizontal axis supposed 
 to pass through the prism about which it was moulded, the 
 whole tube, with the exception of the last divisions at the open 
 end, may be filled with gas. It is confined safely during the 
 revolution by the quantity of acid within, which, as the gas 
 increases in volume, travels before it from one end of the tube 
 to the other. When full of gas, the acid may be replaced by 
 water (956), and the gas conveniently examined in successive 
 portions, in a manner similar to that already particularized 
 (950). It would be tedious to explain minutely all the 
 motions and positions required in working with these useful 
 tubes; these, as well as their form, will easily be understood, 
 by bending a piece of wire as described (933). The facility 
 with which the gas may be managed in them may be easily 
 acquired, by putting some water and a little air into such 
 tubes, and observing their relative positions and changes of 
 place whilst the tubes are in motion. 
 
 959. A minute apparatus, resembling WouhVs (475, 844) 
 in its powers and uses, is easily formed of a piece of tube, one- 
 
 third or one-half of an inch in 
 width, bent as in the figure. The 
 gas should be passed in at a, and 
 will bubble up through the water at c and d, and if soluble 
 will form solutions. If it be required that the gas should 
 come into contact with a large surface of water, one of the 
 lower bends should be extended in a horizontal position, as at 
 
Sect. XVI.] WOULFE'S APPARATUS GASES CONDENSED. 411 
 
 d. If the tube be bent as in the second figure, then the por- 
 ^\ (r\\ /^\ /^\ /? tions of fluid in the four lower angles 
 xid) \^7 IL/ (Ll/ may be removed in succession, be- 
 ginning either with the strongest or weakest ; or, for compari- 
 son, they may be removed alternately from either extremity ; 
 all that is necessary being the careful elevation of one or other 
 end of the tube (931,933). 
 
 960. The extremities or apertures of tubes are frequently 
 to be closed for a short time during operations ; thus, after a 
 substance has been placed in an open tube, it may be desirable 
 to close one or both ends, to prevent the establishment of a 
 current of air through it when heated, or the dispersion and 
 loss of volatile but condensable substances. The opening may 
 be closed in the temporary manner required, either by the 
 finger, or a cork, or a piece of cement, according to circum- 
 stances, and may be opened with equal facility when necessary. 
 
 961 . The readiness and the ease with which gases are passed 
 over substances in tubes, either at high or low temperatures, 
 have been already fully pointed out (709, &c.) ; those practices 
 indeed form an important part of tube chemistry. Detached 
 instructions and instances of this kind may be referred to by 
 means of the Index. 
 
 962. It was by an apparatus constructed entirely from 
 tubes, that chlorine and many other of the gases were first 
 distinctly condensed ; and the results sufficiently indicate the 
 value of such arrangements. It will be advantageous briefly 
 to describe the method of condensing one of the gases which 
 are most easily rendered fluid, as cyanogen, and point out the 
 attentions necessary in making the same experiment with those 
 which, requiring higher pressures for the purpose, involve the 
 risk of greater danger. 
 
 963. The tubes chosen should be of such thickness as is suffi- 
 cient to resist thrice the pressure that is expected to be exerted 
 (874). A piece of about eight inches long is to be selected, and 
 its extremity sealed (1165, 1175) ; then, being softened in the 
 lamp, at about five inches from the closed end, it is to be bent, 
 not sharply, but obtusely and roundly, until the two limbs 
 make an angle of about 130 or 140 (1154). Some cyanuret 
 of mercury is to be pulverized and dried in an evaporating 
 
412 TUBE CHEMISTRYGASES CONDENSED. [Sect. XVI. 
 
 basin, on the sand-bath, or over a lamp, at temperatures which, 
 being above that of boiling water, are insufficient to decompose 
 the salt, or at least to cause much change ; it is to be rendered 
 quite dry (60S), may be allowed to become a little brown, and 
 is then to be introduced into the tube until it fills three-fourths 
 of the closed limb. The open limb is afterwards to be wiped 
 clean, if there be occasion, with a wire and tow, and then to 
 be heated and drawn off (9^9, 1176), so as to leave the tube 
 with only a minute aperture. 
 
 964. The apparatus is now to be filled with an atmosphere 
 of cyanogen, and then sealed hermetically ; the part containing 
 the cyanuret is therefore to be heated in the flame of a spirit- 
 lamp, until enough cyanogen has been evolved to expel all the 
 atmospheric air. This may be ascertained by bringing the 
 aperture towards a flame, when if the small jet of gas which 
 issues is found to be combustible, it indicates that the 
 tube is filled with cyanogen. Cease to decompose any more 
 cyanuret, and by introducing the contracted extremity of the 
 tube into the lamp, seal it hermetically (1190). This is the 
 more easily done in consequence of the gradual diminution of 
 temperature in the tube, which causes the cyanogen within to 
 contract in bulk, and allows the soft glass to coalesce and 
 thicken. Then permit the whole to cool before proceeding to 
 the evolution and condensation of the cyanogen. 
 
 965. The tube is next to be supported on a retort stand, 
 or on pieces of wire, in a position proper for distillation, that 
 is with the vertex uppermost, and the two extremities nearly 
 in the same horizontal line. A piece of wet bibulous paper is 
 to be wrapped round the short and empty limb, which is to 
 retain the condensed cyanogen, and the flame of a spirit-lamp 
 carefully applied to that containing the cyanuret, so as to de- 
 compose the compound : the progress of the operation may be 
 judged of by the discoloration, fusion, and ultimate solidification 
 of the cyanuret. This process must not be carried on rapidly, 
 or the heat allowed at any time to rise so high as to sublime 
 much mercury : the appearance of globules of sublimed mer- 
 cury to any extent in the upper part of the long limb, is a 
 proof that the heat has been higher than was necessary or 
 proper. The heat should never be allowed to rise considerably 
 
Sect. XVI.] CONDENSATION OF CYANOGEN. 413 
 
 in the part of the long leg above the place of the cyanuret ; 
 and if the condensation of cyanogen in the shorter limb is so 
 rapid as to make the moistened paper sensibly warm, or the 
 water from it visibly evaporate, the operation must be 
 retarded. The progress of the condensation should be 
 observed by slipping the moistened paper off the end of the 
 tube occasionally, restoring it immediately the information has 
 been obtained. 
 
 996. In this way cyanogen may be condensed without the 
 slightest risk of explosion, the pressure within never rising 
 above five or six atmospheres, and when all is cold, being not 
 more than four atmospheres ; half an inch or more in depth 
 of the liquid will be obtained in the shorter end of the tube. 
 When left for some days the fluid generally returns to the 
 black mass remaining in place of the cyanuret, the substance 
 having apparently an attraction for it resembling that possessed 
 by hygrometric bodies for water. But upon repeating the 
 distillation as just described, a very moderate heat is sufficient 
 to separate the cyanogen, and to exhibit it in a pure and iso- 
 lated form. 
 
 967. Such is an instance of the condensation of a gas in 
 tubes, which any one may repeat. It will easily be under- 
 stood that, in the condensation of gases requiring higher pres- 
 sures, the risk of explosion from the bursting of the vessels is 
 comparatively greater. To diminish the danger as much as 
 possible, certain general precautions should be attended to. 
 The tubes chosen should be sufficiently strong, and be esti- 
 mated according to the directions before given (874) . They 
 should be regular and uniform, and free from the specks or 
 minute cracks to which thick tubes are frequently liable. 
 Upon sealing the ends and bending the angle, the parts heated 
 should be exceedingly well annealed ; for which purpose the 
 glass should be withdrawn gradually from the flame, and not 
 allowed to cool suddenly, otherwise the tubes will have a ten- 
 dency to crack or fly at these unannealed places, even without 
 pressure, and are then unsafe for the experiments. For this 
 reason the tubes when sealed at one end and bent, should be 
 laid aside for a week or two, and afterwards examined in all 
 positions with regard to light $ if any cracks or fissures appear, 
 
414 TUBE CHEMISTRY GASES CONDENSED. [Sect. XVI. 
 
 however minute, the tube should be rejected. The bend 
 should be gradual and not sudden, that great flattening or 
 distortion there may not injure the general form of the tube; 
 when bent irregularly and left in a wrinkled state, there is 
 usually an irregular tension of the different parts when cold, 
 which renders the glass exceedingly apt to crack. On sealing 
 the end of the tube at first, it should be observed that it be 
 left of a thickness equal to that of any other part, that it may 
 have sufficient strength. On drawing out the other extremity 
 also, for the purpose of finally closing the tube, the conical 
 part, and the capillary tube which terminates it, should be 
 allowed to thicken a little in the flame, that it also may have 
 sufficient strength. It will easily be understood, that the tube 
 being of smaller diameter in that part than elsewhere does not 
 require the thickness of the other parts ; but if it be drawn 
 out without attention to this point, it may be rendered so thin 
 as to give way to the force afterwards exerted (1178). It 
 should also be observed in closing the aperture, that the extre- 
 mity be compact and firm, and not blown out or left in a thin 
 film. All the directions necessary for effecting these objects 
 relative to the sealing and bending the glass securely, will be 
 given in Section XIX, (1179, 1183, &c.) 
 
 968. The operation of condensation should always be con- 
 ducted slowly. The condensing end of the tube should be 
 well cooled (9^7, 454) ; in experiments where gases difficult 
 of condensation are operated upon, it is of essential importance 
 that the heated and the cooled parts of the tube should not 
 approximate closely, but that portions of intermediate tem- 
 peratures should intervene, so that the temperature shall 
 change gradually and not suddenly from one end to the other. 
 
 969. A tube containing the result of an operation may 
 generally be preserved for years, without any further change 
 or injury than what may be rectified by cooling the receiving 
 end, or moderately warming the other extremity. But one 
 or two instances have occurred, where tubes have burst some 
 months after an experiment has been made in them. They 
 should always be handled with great caution. Any sudden 
 contact with a hard substance, in the manner of a tap or blow, 
 should be avoided with the utmost care; and if from the 
 
Sect. XVI.] 
 
 CONDENSATION OF GASES. 415 
 
 exertion of the internal pressure or other causes a crack should 
 gradually appear in any part of the tube, such tube should 
 never be examined, except with every precaution, even though 
 it may seem to be secure, and have retained the gas for months 
 or years as well as at first. 
 
 970. After the addition of some further brief instructions, 
 this part of tube manipulation may be dismissed. Cyanogen 
 and ammonia may be evolved and condensed in dry tubes. 
 So also may sulphurous acid ; or at least the part in which 
 the gas is condensed, may be retained dry, but the arrange- 
 ment is different to that for cyanogen and similar gases. 
 When the straight piece of tube selected is sealed at one extre- 
 mity as described (962), mercury is to be put into it for 
 about the depth of an inch, and over that the most concen- 
 trated sulphuric acid is to be introduced through a small tube 
 funnel to the depth of about three inches, so as not to soil the 
 upper part of the vessel (924). An inch and a half or two 
 inches above this the tube is to be bent as before described 
 (962), and two or three inches farther on is to be contracted. 
 Then holding the tube as vertical as may be, the mercury is 
 to be heated very carefully in the sulphuric acid, until suffi- 
 cient sulphurous acid gas has been evolved to eject the common 
 air of the apparatus ; this will be ascertained by the well- 
 known smell of the acid, or by the fumes which it will yield 
 when the aperture is brought near to paper moistened with 
 ammonia. The operator must then cease to evolve more gas, 
 and having allowed the temperature of the tube to fall, until 
 scarcely any gas passes out at the aperture, the capillary extre- 
 mity of the tube should be introduced into the flame of a lamp 
 for a moment, that it may fuse and become sealed (1190) ; 
 but it should instantly be withdrawn, that it may cool without 
 being expanded by the gas, which is still slowly evolved 
 within. The tube and its contents are then to be cooled by a 
 little water, or ultimately even by ice and water, which will 
 cause such condensation of the gas within as to make the 
 internal pressure less than the external ; and this being the 
 case, if the sealed termination be not sufficiently strong, it 
 may be again introduced into the flame, the glass softened and 
 allowed to coalesce into a thicker mass. The distillation and 
 
416 TUBE CHEMISTRY CONDENSATION OF GASES. [Sect. XVI, 
 
 condensation of the gas may then be proceeded with, according 
 to the directions already given (965) . 
 
 971. Many of the gases, such as muriatic acid, carbonic 
 acid, sulphuretted hydrogen, Sec., are evolved from materials 
 which, liberating gas the moment they come into contact, 
 must not be brought together in the tube of condensation 
 before the second extremity is securely sealed up ; as that can 
 only be done whilst the gas or air has no tendency to pass out 
 of the tube. The procedure necessary in such cases may be 
 briefly illustrated in the instance of muriatic acid : the tube is 
 to be closed and bent as already described (962), except that 
 the curve is to be near the closed end, so that the shorter leg 
 may be the closed one. The latter is then to be filled by 
 means of a tube funnel with sulphuric acid, to within the half 
 or the third of an inch of the bend, especial care being taken 
 that none of the acid touch the inner surface of the longer leg: 
 a piece of thin platina foil is to be crumpled up loosely, and 
 thrust up the long limb until near the bend, and afterwards 
 long angular fragments of muriate of ammonia, cut with the 
 grain from a lump (319), are to be put up the tube by a wire, 
 until it is full to within an inch of the open end : these are 
 prevented from passing into the sulphuric acid by the inter- 
 posed piece of platina foil, and are required of an angular 
 form, that the acid may easily flow afterwards between them 
 and the glass. Being so far arranged, the open end of the 
 tube is to be sealed hermetically ; during which operation, the 
 apparatus must be held in a position nearly horizontal, that 
 no contact of the sulphuric acid with the muriate of ammonia 
 may take place (1188). That being done the tube must be 
 allowed to cool, and then placed in a corner with the acid end 
 upwards ; the acid will immediately flow past the platina foil, 
 and upon the salt beneath, rapid action will take place and 
 much gas appear to be evolved. The action will gradually 
 seem to diminish almost entirely, because the pressure within 
 increasing continually for some time, the bubbles will thereby 
 be reduced into a smaller bulk. The tube should be left in 
 this position for some days, or even a week, at the end of 
 which time a very limpid fluid will be perceived here and 
 there, occupying cavities in the dense acid sulphate of ammonia. 
 
Sett. XVI.] USE OF TUBES TO CONTAIN SUBSTANCES. 417 
 
 The tube being placed in a distilling position, and the shorter 
 leg cooled (447, 924, 934), the limpid fluid will pass over into 
 it, and its characters may then be observed. The pressure 
 will be about forty atmospheres at a temperature of 50. A 
 tube of half an inch internal diameter and ten inches long, 
 will, in such an experiment, resist and support a pressure 
 upon its internal surface of above 6000 Ibs. 
 
 972. In all cases where the condensation of a highly elastic 
 gas is to be effected, the tube should be filled as nearly as pos- 
 sible with the materials, that the space for aeriform matter 
 may be the less ; or else it may happen that the quantity of 
 gas evolved from the substances is not enough to do more 
 than fill that space with an atmosphere, equal to or less in 
 density than that required before fluid will be deposited. 
 
 973. One constantly valuable use of tubes is for the reten- 
 tion and preservation of different substances, for which purpose 
 they may often be used instead of phials and bottles, and are 
 not unfrequently superior to them. The tubes in the drawer 
 already spoken of (910) will in these cases be had recourse to, 
 but they are improved and strengthened, by softening and 
 turning the edge of the aperture outwards, so as to make it 
 like a phial mouth ; they then allow the cork, which is to be 
 used for closing them, to be applied with more force. When 
 deliquescent substances, or such as would be injured by access 
 of air, are to be preserved in them, the cork should, either 
 before or after its insertion, be covered with wax, or, which is 
 better, because it is not liable to crack and separate, soft 
 cement (1125). The arrangement and economical use of 
 tubes intended to receive and contain small quantities of 
 valuable fluids have already been described (929). 
 
 974. A tube, different in its kind from either of these, is 
 exceedingly useful for the preservation of such portions of 
 valuable fluids or solids as, being intended for specimens, may 
 be left undisturbed for long periods of time, and consequently 
 may be sealed up hermetically. The tubes selected for this 
 purpose should be rather thicker than usual, that they may 
 
 2 E 
 
418 TUBE CHEMISTRY- WRITING ON TUBES, [Sect. XVI. 
 
 bear packing when required, or be laid with other things 
 without injury. They should be perfectly clean previous to 
 the introduction of the substance, and when sealed up at the 
 end last closed, the termination should be made thick and 
 strong in the manner described in Section XIX. (1184, &c.) 
 The substance thus permanently secured may be preserved 
 for years without change or injury, and can always be readily 
 examined as to its appearance, and external characters. Its 
 name, with the date, and other necessary circumstances, should 
 be written upon the exterior of the tube with a scratching 
 diamond (128). 
 
 975. Writing in this manner with the diamond is best 
 done by laying a book or board of equal thickness with 
 the tube upon the table, and holding the latter in the angle 
 formed by the two, by which steadiness is given to it: the 
 diamond should be held in a vertical position during the writ- 
 ing, and the hand retaining it should be rested on the book. 
 Upon trying to write on a piece of flat glass with a scratching 
 diamond, turning the latter round slightly at the same time, 
 it will be found that one position of it is more advantageous 
 than any other, the writing being then performed with greater 
 facility: this being ascertained, a notch or mark should be 
 made on the handle of the diamond, so that at any future 
 time this favourable position may be immediately given to it. 
 
 976. When tubes are required for the conduction of gas or 
 vapour, it has been already shown that in cases of emergency 
 such as are made of paper (247, 272, 841) may be substituted 
 for those of glass or metal. It is often advantageous to render 
 the paper difficult of combustion, that the accidental, and 
 at times even necessary, approach of flame may not occa- 
 sion injury. This may be done by washing the paper with 
 a strong solution of alum, or phosphate of soda, or common 
 salt, or better still with alkali or carbonated alkali, provided 
 these do not interfere afterwards with the uses of the tube, 
 or paper, or the substances which are to be passed through 
 them (1337). 
 
 977. Such are some of the numerous applications of 
 tubes for the performance of chemical experiments. Many 
 
Sect. XVII.] ELECTRICITY. 419 
 
 variations of the forms mentioned will suggest themselves in 
 practice as affording facilities in particular cases. It would 
 have occupied far too much room to have enumerated all 
 that have been found useful ; and indeed throughout this 
 chapter general forms have been referred to and described 
 rather than particular ones; for their uses and properties 
 once known, the variations will easily be understood. The 
 economy and exceeding facility afforded by this kind of 
 apparatus in situations distant from the usual sources of 
 more perfect instruments, and its superiority in some cases 
 over any other that has yet been devised, is sufficient to 
 recommend it to full and general attention: and when com- 
 bined with the use of a few fragments of glass and paper 
 vessels, as is hereafter to be described (1335), places in the 
 hands of every one, whatever his situation may be, opportu- 
 nities of pursuing chemical researches to a very considerable 
 extent. 
 
 SECTION XVII. 
 ELECTRICITY. 
 
 978. IN consequence of the very general and close asso- 
 ciation of chemistry with all the other sciences, the chemist is 
 often obliged to work with instruments, and to make arrange- 
 ments which, although they seem essentially to belong to other 
 pursuits, are at times highly influential over his own. The 
 powers of Electricity, amongst others, are so closely allied to 
 those of Chemistry, and possess such vast influence in aiding 
 or opposing them, that the experimenter in this science is con- 
 tinually resorting to them in his peculiar and ever varying ex- 
 aminations of matter. For this reason so much of the manage- 
 ment of electrical machines and apparatus as is frequently 
 required in the laboratory will be described in this section, and 
 the circumstances necessary to facilitate investigation, or secure 
 
 success, will be particularly pointed out. 
 
 2E2 
 
420 ELECTRICAL MACHINE EXCITED. [Sect. XVII* 
 
 1. Ordinary Electricity. 
 
 979. The common electrical machine is of constant use for 
 the passing of sparks or currents of electricity through gases, 
 for charging ajar, or for conferring particular states of electrical 
 tension upon insulated bodies. When required for use it 
 generally wants some degree of preparation to bring it into 
 strong action. In favourable weather, merely wiping the 
 machine with a warm linen cloth, and afterwards with a silk 
 handkerchief, is sufficient for the purpose ; but usually, and 
 especially in damp weather, it will require warming. This 
 may be done occasionally by placing it before a fire and turn- 
 ing the handle at intervals, that all parts may be exposed to 
 the heat ; but it is more advantageous, as well as safer, to 
 attain the same end by placing the machine in a current of hot 
 air ; or if it be required for continued use in one particular 
 place, to pass a stream of hot air against and about it. A 
 machine may be very effectually warmed by placing it over a 
 sand-bath or hot iron plate of a temperature not more than 
 212, by which not only does the plate or cylinder, but also 
 the glass insulations become thoroughly warm. At other 
 times a current of air heated by a crucible furnace (269) may 
 be conveniently conveyed to the machine, the warm air being 
 occasionally conducted by paper pipes (1337). Another ex- 
 pedient, and a very good one with cylinder machines, is to 
 place a chemical lamp (212) with a low flame beneath the 
 cylinder, and to support a plate of metal about six inches 
 square nearly an inch above the chimney of the lamp (270). 
 This plate prevents the ascent of the comparatively small hot 
 current of air from the lamp (which would heat the cylinder 
 in spots only, and those far too highly), it becomes itself hot, 
 warms the air lying upon it, and thus produces a large current 
 moderately heated, which surrounds the cylinder on all sides 
 and thoroughly warms it. 
 
 980. During the warming of a machine, care should be 
 taken to give it as equable a temperature as possible, and it 
 should be continually watched that no part becomes so hot as 
 to melt the cement used in its construction. The warmth of 
 
Sect. XVII.] ELECTRICAL MACHINE WARMED. 421 
 
 the insulating parts should be particularly attended to ; for in. 
 damp weather a machine which will appear to be in excellent 
 action and give out long electrical brushes from its cylinder or 
 plate, will often scarcely give a spark from the conductor, 
 because of the dampness of the insulating glass pillar. 
 
 981. Whilst a machine is being warmed it should be wiped 
 with a dry cloth or a silk handkerchief; the rubbers should be 
 examined, all dust taken from them, and amalgam applied 
 if required : this may be known by observing whether the 
 amalgam has broken away, or has, by age and disuse, con- 
 creted into a hard brittle mass that will not adapt itself, or 
 present a good surface, to the passing glass. If the cylinder 
 have many spots of amalgam upon it, and several of them 
 large, they should be removed : they may easily be scraped off 
 by the thumb-nail or a piece of wood. A few small spots 
 appear rather to increase than, diminish the activity of the 
 machine, and the silk which proceeds from the rubber to a 
 certain distance over the glass, is far better when from use it 
 has become impregnated with amalgam, than when it is quite 
 clean and free from that substance. It is often advantageous, 
 especially when the machine is required in haste, to hold a 
 piece of silk with some amalgam upon it against the plate or 
 cylinder, whilst it is turned, and also to rub up the surface of 
 the amalgam upon the rubber with the same amalgamated silk. 
 To apply the amalgam to the silk, it is necessary first to put a 
 little tallow upon the latter, after which the amalgam will 
 adhere. The amalgam itself should be rubbed in a mortar 
 with a little tallow, before it be considered fit for any use 
 about the machine. The rubbers should press lightly against 
 the glass. The silk proceeding from them over the cylinder is 
 better unoiled than oiled. 
 
 982. When the machine is in good order, the prime con- 
 ductor away, and the handle turned, it should send out an 
 uninterrupted series of brushes from the edge of the silk, with 
 continual sparks flying round the glass. The appearance pre- 
 sented by bringing the knuckles near the edge of the silk is a 
 very good indication of the exciting power of the machine. 
 These effects should take place without causing considerable 
 friction between the glass and the rubber and silk, or, if there 
 
422 PLATE ELECTRICAL MACHINES. [Sect. XVII. 
 
 be much, it should be from adhesion between the glass and the 
 silk, and not from the pressure of the rubber. In that case it 
 is .easily diminished, and the labour of turning lessened, by 
 folding back the silk more or less, so as to lessen the part in 
 contact with the glass, 
 
 983. Upon putting the prime conductor into its place, and 
 continuing the motion, sparks two or three inches in length 
 should fly rapidly from it to the knuckle, or to a clean brass 
 ball held near it. For these trials of the length of spark, 
 and for discharges, where the passage of a spark is necessary 
 in other circumstances, a metal ball is better than the knuckle 
 or back of the hand ; the hairs, moisture, and adhering fila- 
 ments of the latter, frequently diminish the effect. 
 
 984. The machines, when out of use, should be set aside in 
 a dry room or cupboard, away from the fumes of the labo- 
 ratory (29), and it is advantageous to throw a coarse linen 
 bag over them as a cover to keep off dirt, and, to a certain 
 extent, moisture and fumes. 
 
 985. The manner in which plate machines are mounted, 
 namely, by an axis passing through the middle of the plate, 
 made tight by collars or screws, generally causes an irregularity 
 of tension, by which a tendency to crack from the centre is 
 produced. This renders the machine liable to injury from 
 circumstances otherwise unimportant ; and warming it too 
 much at the middle before a fire, or partially only, or slight 
 mechanical strains, cause cracks to originate there, which, 
 though small at first, gradually extend till they reach the cir- 
 cumference, unless means be adopted to stop their progress. 
 This is best done by directing an instrument- maker to drill a 
 small hole through the glass, a little in advance of the crack, 
 and in its course. When the crack reaches the hole it gene- 
 rally stops, and the plate is saved for a time till other cracks 
 are formed, which gradually weaken, and finally destroy the 
 machine. 
 
 986. The machine is used to give sparks directly from its 
 conductor : these, when passed through eudiometers, either 
 inflame the mixture of gases within, or occasioning chemical 
 changes of a slower kind, require to be repeated a great 
 number of times. A spark of sufficient intensity to inflame 
 
Sect. XVII.] EUDIOMETER SPARKS PASSED. 423 
 
 a combustible gaseous mixture, may often be taken from a 
 machine to one of the wires of an ordinary eudiometer, the 
 other wire being in contact with the finger or connected with 
 the earth through conducting matter. But it will occasionally 
 be found exceedingly difficult to succeed in the experiment 
 solely from inattention to some slight circumstance about the 
 arrangement. The wires which are fixed into a detonating 
 eudiometer are so placed as to have their inner extremities at 
 a small distance from each other. These terminations are not 
 always finished off with sufficient care, the wires being either 
 simply cut by pliers, or, if filed into shape, are still left with 
 some projecting corner or irregularity. Sometimes the wires 
 themselves are too thin. 
 
 987. All these circumstances tend to make an electric dis- 
 charge pass rather as a coarse brush, or as a succession of 
 minute sparks, than as one decided luminous flash. This 
 tendency is still further increased if the exterior ends of the 
 wires are also small, or are only turned into a little loop ; and 
 it will then be found almost impossible to send a spark from 
 the prime conductor in an undivided state through the interior 
 of the tube. When defects of this kind are found to exist, 
 they may be partially remedied by putting a ball half an inch 
 or an inch in diameter upon the wire, which is to be brought 
 near the conductor ; this ball will receive a large distinct 
 spark, and will transmit it from the one wire to the other 
 within the eudiometer in a single discharge, even though the 
 latter were to terminate almost in points. 
 
 988. Sometimes a eudiometer which permits a spark to pass 
 with perfect facility, through gas confined in it over mercury, 
 will not with gas over water. The film of water with which 
 the interior of the instrument is moistened interferes in this 
 case, and conducts the electricity of a spark given in the ordinary 
 manner, to such an extent as to prevent its passage from point 
 to point of the wires within. In these cases the application of 
 the large ball on the outside (987) will often remedy the evil, 
 by enabling a more powerful spark to be drawn from the 
 machine. If it has not this effect, the charge of a Leyden jar 
 must be used : the ball in these cases need not necessarily be 
 fixed upon the eudiometer, it may be hung from it by wire, 
 
424 LEYDEN JAR ITS PROPERTIES. [Sect. XVII. 
 
 or the knob of a discharging rod, the metal of which is held 
 against the end of the eudiometer wire, may be substituted, or 
 it may be arranged in many other ways. The necessary 
 points to be attended to are, that the ball and the eudiometer 
 wire make an undivided metallic communication, the whole of 
 which is insulated, and that the spark be received by the ball. 
 
 989. In all these eudiometric explosions, the other wire of 
 the tube must be in communication through a finger, or a 
 chain, or some conducting matter with the ground. The 
 whole of these operations are effected with admirable facility 
 by a single person, with the detonating eudiometer of Dr. Ure 
 (999). 
 
 990. A Leyden jar of the capacity of a quart will be suffi- 
 cient for all ordinary laboratory purposes. The ball should be 
 at least an inch in diameter, and with the wire and wooden 
 top should be so firmly fixed to the jar, that the latter may be 
 placed in any required position without fear of their falling, or 
 being deranged. For the same reason the connexion between 
 the ball and the coating within should be made by wire and 
 not by a chain, that the communication may be perfect in 
 every position. The jar when new should be warmed and 
 wiped on the outside, and then examined relatively to certain 
 points, and first as to its freedom from the fault of permitting 
 spontaneous discharge. The jar being held by its exterior 
 coating should have its knob placed in contact with the 
 machine when in good order, and should be as highly charged 
 as possible. If the jar does not discharge itself, or permit a 
 spark to pass over the external uncoated glass, it is in that 
 respect good ; if it discharge spontaneously, but only when 
 very highly charged, it is moderately good ; if it discharge 
 spontaneously with readiness and freedom, even with com- 
 paratively low electrical charges, it is bad. This fault may 
 sometimes be cured by paring away half an inch or more of 
 the exterior coating at the upper edge, so as to make the dis- 
 tance between it and the wire of the ball greater ; or by re- 
 moving some accidental angular projection or point on the wire 
 or wooden top, which has facilitated spontaneous discharge. 
 
 991. If a jar prove good when tried as above, it should then 
 be examined as to its powerof retaining a charge undiminished. 
 
Sect. XVII.] LEYDEN JAR DISCHARGED BY A WIRE, 425 
 
 For this purpose the jar should be highly charged, and thea 
 immediately discharged by the discharging rod, the length ,. 
 brilliancy, and sound of the spark, being at the same time 
 observed. It should then be charged to the same degree as. 
 before, and being removed from the conductor, should be left 
 a minute in the air before it be discharged, and the spark again 
 observed and compared with the former. It will readily be 
 seen whether in consequence of standing for the minute the 
 spark is smaller, and also whether the diminution has been 
 much or little. 
 
 99&. There are no jars which do not lose considerably, even 
 in a short interval of time, if very highly charged, but if only 
 moderately charged, they should suffer much less dissipation 
 of electricity, and ought to yield a spark of considerable force 
 after a lapse of five minutes. A jar of the size above men- 
 tioned, when dry and warm and well charged, should, after a 
 lapse of ten minutes, give a spark at least half an inch in length 
 to the ball of the discharging rod, the ball being one third of 
 an inch in diameter. 
 
 The retention of the charge by an electric jar in chemical 
 experiments is frequently of great importance, from the 
 unavoidable delays which often occur before the spark can 
 be passed. 
 
 993. A jar for eudiometrical experiments is much more 
 conveniently discharged by a wire, than by the usual glass- 
 handled discharger. A piece of copper wire about one- 
 twentieth of an inch in thickness should be connected with 
 the outside coating, by being passed round the body of the 
 jar, and made tight by twisting it, the piece left to act as a 
 discharger being about 18 inches in length. The loose end 
 should be coiled up into a flat spiral of a couple of turns, 
 to prevent its acting as a mere point, or if a little metallic ball 
 or a very small bullet be fixed upon it, the arrangement will 
 be more complete. This wire performs the part of a dis- 
 charger whenever required, and being in constant contact with 
 the outside, and also very flexible, it may be adapted to nearly 
 every possible occasion. Suppose, for instance, that the 
 machine will not yield a spark sufficiently powerful to inflame a 
 mixture of gases in an eudiometer tube (986), and that a dis- 
 
426 MANAGEMENT OF A EUDIOMETER. [Sect. XVII. 
 
 charge is requisite, the jar must be charged and then discharged 
 in the following manner. The loose end of the attached wire 
 is first to be placed and retained in contact with one of the 
 eudiometer wires, and then the ball of the jar approached 
 to the other wire ; the discharge will immediately be made 
 through the instrument without any risk of inconvenience to 
 the experimenter, even though he hold the wire and jar in his 
 hand during the operation. 
 
 994. There are certain points in the management of a 
 eudiometer, relative to the method of holding it during an 
 explosion, which require the attention of the student. The 
 common detonating eudiometer is a short glass tube closed at 
 the upper extremity, and having two pieces of platina wire 
 passing near that extremity through the glass, so that their 
 inner terminations are within a very short distance of each 
 other. These wires, being made parts of the metallic com- 
 munication of a charged jar as before described, conduct the 
 electricity, and cause a discharge to be effected through or 
 between them. The gas to be subjected to the spark is 
 generally such a mixture as will inflame. It is to be trans- 
 ferred into the tube over water or mercury, according to 
 circumstances (762, 788) , and the lower open end of the eudi- 
 ometer is necessarily retained in the water or mercury during 
 the experiment to confine the gas. 
 
 995. When the gas has been introduced, the outside and 
 upper part of the eudiometer is to be wiped clean and dry, 
 so that no water or mercury may adhere to it. The instru- 
 ment should then be held firmly and upright, which is perhaps 
 best effected by grasping it with the first three fingers on the 
 one side, whilst the thumb and little finger are pressed against 
 it on the other. The hand should be about the middle of the 
 tube, and out of the way of the wires above, that the knob 
 of the charged jar may not come near it during the experi- 
 ment. The tube should be supported by the hand alone, its 
 lower end not being allowed to touch the bottom of the vessel 
 in which it stands during the explosion, lest it strike against 
 it with such force as to be broken or injured. It is ad- 
 visable, wherever it can be done, to apply a finger of the 
 unoccupied hand with slight force to the bottom of the 
 
Sect. XVII.] EUDIOMETER DETONATION OF GASES. 427 
 
 detonating tube under the fluid at the moment of explosion: 
 this allows the descent of the water or mercury during the 
 explosion, but as contraction takes place it is drawn against 
 the aperture, and prevents the fluid rushing in at once. By 
 withdrawing it gradually, the water or mercury is admitted 
 in a more tranquil manner than would otherwise be the 
 case; and indeed the impetuosity of the action is altogether 
 restrained, and the probabilities of loss of the contents of the 
 eudiometer diminished. 
 
 996. As before mentioned relative to a spark from the con- 
 ductor (986, &c.), so also here if the wires be pointed, a ball 
 may be advantageously used ; and if the interior be so moist as 
 to transmit all the electricity of a small or moderate charge, 
 then a large charge must be passed. 
 
 997. The proportion of gas which may be detonated with 
 safety in an eudiometer tube, depends considerably upon 
 the explosive power of the particular mixture under exami- 
 nation, and also upon the quantity detonated at once. A 
 mixture of oxygen with carbonic oxide expands, when in- 
 flamed, with much less force than a mixture of oxygen with 
 hydrogen or olefiant gas ; and a large quantity will of course 
 expand with more force than a smaller. But besides con- 
 sidering the efficiency of the eudiometer tube in resisting the 
 expansive force, occasioned by detonation, the experimenter 
 has also so to proportion the quantity of gas, that whilst 
 expanding there shall be abundant space in the tube to retain 
 the products under their greatest volume and agitation, that no 
 loss may occur. No more gas should be introduced into a 
 tube for detonation than will occupy a sixth of its capacity at 
 common temperatures, and, generally, it will be safer and 
 advisable to employ much less. 
 
 998. In operations with the ordinary eudiometer tube, two 
 persons are usually required, one to hold and manage the 
 instrument, the other to pass the electric discharge. The 
 second person may however be dispensed with by a little 
 contrivance. The jar may be placed upon the table with 
 its knob in contact with the prime conductor of the machine, 
 and with a wire of two feet in length, made fast to one of the 
 eudiometer wires, that sufficient motion may be allowed in 
 
428 URE'S EUDIOMETER HOW USED. [Sect. xvn. 
 
 connection with its outside. One end of another wire of equal 
 length is to be attached to the second eudiometer wire, and 
 the other end made fast to a metallic ball, which is to be 
 placed within half an inch of any part of the prime con- 
 ductor. The ball with its wire, though it is not essential, 
 may be insulated with advantage, and for this purpose it 
 may be supported on the mouth of a glass or a bottle, 
 raised upon a stool or other convenient support (20). The 
 operator may then hold the eudiometer tube (994) in one 
 hand, and turn the machine with the other: when the charge 
 in the jar has acquired such intensity as to pass over the 
 half inch of air between the conductor and the ball, the jar 
 will be discharged through the eudiometer wires. The hand 
 which holds the tube should be, as before mentioned, clear 
 of the wires (995) ; and it is proper not to touch the outside 
 of the jar or any of the wires during the experiment, lest from 
 some unperceived circumstance the discharge should be made 
 through the body. 
 
 999. Dr. Ure's eudiometer* (989) renders the experi- 
 ment easy of performance by a single person. This instru- 
 ment is furnished with wires in the usual manner, but is 
 bent, so that the open extremity is turned 
 up nearly as high as the closed one. It is to 
 be filled with water or mercury, and the gas 
 transferred into it in the ordinary manner; 
 then, being placed upright, part of the fluid 
 in the open leg is displaced by inserting a 
 glass rod, or in some other manner. The 
 open leg being grasped by the hand, the 
 thumb is to be placed tightly over the aperture, so as to close 
 it, and at the same time to touch one of the wires; a spark 
 taken from the conductor to the other wire passes through the 
 gas, inflaming it, and is conducted off by the thumb and hand. 
 The gas in expanding depresses the fluid beneath it, whilst 
 the air in the part closed by the thumb acts as a spring to 
 restrain the violence of the explosion. If a charge from a 
 jar (993) is to be passed, then the thumb must not be allowed 
 to touch the wire whilst closing the aperture ; when the jar is 
 * Edinburgh Philosophical Transactions, 1818. 
 
Sect. XVII.] ELECTRICAL BATTERY ELECTROMETER. 429 
 
 charged, the wire connected with the outer coating is first to be 
 hooked upon the eudiometer wire nearest the thumb, and 
 securely retained there, so as not to slip during the experiment, 
 and then the knob of the jar is to be brought to the other wire, 
 and the gas will be inflamed. 
 
 1000. It will be unnecessary particularly to describe the 
 arrangements of a battery, which belong principally to 
 the electrician. Whenever its use is required in the labo- 
 ratory, it should be ascertained that all the outside coatings 
 are well and securely connected together by metallic sub- 
 stances, as wires or sheets of metal; that the internal coat- 
 ings are in proper connection with each other, through their 
 appropriate mountings and wires; that no wire or thread, 
 or conducting matter of any kind, extend in any way from 
 the case or externally coated parts of the jars, towards the 
 knobs and wires connected with the insides ; and that no 
 filamentous or pointed substance, nor any projecting metallic 
 body remain in the neighbourhood of the battery during the 
 time it is in use. 
 
 1001. If a Henley's electrometer be used to shew the pro- 
 gress of the charge, it should be so placed that, as the index 
 moves, it shall not approach to any ball, or wire, or surface 
 charged similarly to itself, but recede from it ; if placed upon 
 the end of the conductor, therefore, the index should be 
 allowed to move outwards and away from the conductor, and 
 not in a direction over it towards its more central parts; the 
 latter would interfere with the free indication of the instru- 
 ment, and sometimes even render it quite useless. 
 
 1002. When a battery is in use, the operator should beware 
 of discharging it accidentally by means of his own person ; 
 for though the shock might do no bodily harm, it might cause 
 involuntary movement, and the derangement of an important 
 experiment: being therefore once well and securely arranged, 
 the wires and metallic connections should not be unnecessarily 
 approached after the charging has commenced, until after the 
 explosion. 
 
 1003. When a battery has been used, the experimenter 
 should beware of the residual charge. During the time occu- 
 pied in charging a battery, a diffusion of electricity takes 
 
430 TEMPORARY ELECTRICAL JARS DISCHARGER. [Sect. XVII. 
 
 place over that part of the uncoated glass which is near the 
 edge of the foil ; this is not entirely removed on the discharge 
 of the coated part, but afterwards gradually returns to the 
 coatings and recharges the battery, occasionally to a consider- 
 able extent : hence if, after the discharge of a battery, it be 
 left a few minutes with its internal coating uncommunicated 
 with the earth or with the exterior coating, it will be found, 
 upon applying the discharger, to afford a considerable spark. 
 
 1004. When a regular electrical jar cannot be obtained, an 
 excellent substitute may be formed from a large thin medicine 
 phial, by filling it two-thirds or three-fourths with metallic 
 filings, coating the outside to the same height with pasted tin 
 foil, and closing the mouth by a cork, thrust in nearly to a 
 level with the top of the neck ; a thick wire is to be passed 
 through the cork so that one end shall enter the filings, and 
 the other project about three inches above the cork ; a bullet 
 or other convenient metallic ball is to be attached to its ex- 
 tremity. A ready substitute for a jar may also be made of a 
 piece of thin glass tube of large diameter, coated on the inside 
 and outside with tin foil, to within two inches of each end, and 
 furnished with a knob and wire connected with the inside 
 coating as just described. A plate of crown glass coated on 
 both sides with tin foil to within an inch and a half of the 
 edges, also makes a good substitute, but requires care in the 
 handling, lest it be discharged through the fingers. 
 
 1005. A still simpler, although not so effectual an instru- 
 ment, is the original Leyden bottle. Fill a thin Florence 
 flask two-thirds full of water, put a nail or wire through a cork 
 in the mouth, so that the metal dip into the water an inch or 
 two; let its outer end terminate in a coil or ball (993). Wipe 
 the flask dry, grasp the lower part in the palm of the hand 
 and fingers, and then charge it from the machine. It will now 
 give a very considerable discharge ; but the discharge should 
 be made immediately after the charge, and the whole arrange- 
 ment acts better if it be warmed beforehand. The water on 
 the inside and the hand on the outside are the coatings of the 
 bottle. 
 
 1006. A very effectual and cheap discharger is made of a 
 piece of thick wire about twelve inches long, curved, terminated 
 
Sect. XVII.] ELECTROPHORUS ITS CONSTRUCTION USE. 431 
 
 by a bullet at each end, and supported in the middle by a stick 
 of sealing-wax as a handle ; in many cases even the stick of 
 sealing-wax is not required to complete the discharger (993). 
 
 1007. The electrophorus is an instrument which would not 
 claim the attention of the chemist, but that, being easily con- 
 structed with materials obtainable in almost every place, it 
 may be rendered effectual in supplying the want of an elec- 
 trical machine for usual laboratory purposes. A sheet of tin 
 foil is to be laid smoothly in the bottom of a flat dish, so that 
 its edges may rise up all round ; or it may be laid upon a flat 
 surface, with its edges rising up against the inside of a hoop 
 placed to confine them. Equal parts of common resin, shell- 
 lac, and Venice turpentine, are to be mixed together, and heated 
 in a metallic vessel, the mixture being retained in a state of 
 fusion at temperatures from 230 to 240, until all evolution 
 of vapour has ceased, and the fluid is quiet. It is to be allowed 
 to cool until it thickens, and is then to be poured tranquilly, 
 so as to avoid the formation of air bubbles, upon the tin foil 
 laid out as before described, so that, when cold, it may form a 
 cake one-third or one-half of an inch in thickness. The tin 
 foil should ultimately be trimmed round the edge, and, if 
 convenient, a board attached to the cake to serve as a bottom, 
 and prevent accidental fracture or injury. This is one part 
 of the electrophorus (1011). 
 
 1008. The second part may be a piece of flat deal board, 
 one-third or one-half of an inch in thickness ; less in size than 
 the cake of resin, by an inch, or an inch and a half on every 
 side, and with the edges rounded and smoothed. This board 
 is to be covered with pasted tin foil, smoothly laid on, espe- 
 cially at the edges, and all asperities rubbed down. The 
 smoothest and flattest side is to be appropriated to meet the 
 surface of the resinous plate : a piece of glass tube, about 
 seven or eight inches long, is to be fixed perpendicularly on 
 the middle of the other side to serve as a handle ; and towards 
 the edge on the same side should be fixed a piece of thick 
 brass or other wire, about two inches long, curved outwards, 
 and terminated at its upper extremity by a smooth metal ball. 
 This is the cover of the electrophorus (1011). 
 
 1009. Before using this instrument, the resinous plate 
 
432 ELEeTROPHORUS-^EXCITED ITS POWERS. [Sect. XVII. 
 
 should be warm and dry and placed upon its board in a con- 
 venient horizontal position, with the tin foil on its lower sur- 
 face, connected by a chain or wire with the floor of the place, 
 or with neighbouring metallic bodies. A piece of warm dry 
 flannel is to be doubled up loosely, so as to form a roll about 
 ten inches long ; one end of the roll is to be held in the hand, 
 and the other being swung round in an inclined direction, by 
 a quick motion of the wrist, is to strike the surface of the 
 plate in an oblique manner each time it passes, so as to pro- 
 duce an effect between that of a rub and a blow. This is to 
 be done over the whole surface of the warm resinous plate, by 
 which it will be excited electrically to a considerable degree. 
 Having previously warmed the cover of the electrophorus, it 
 should now be lifted by the handle and placed on the middle 
 of the plate ; if the knob of the cover be touched when all is 
 in order, a spark will pass between it and the finger. The 
 cover is then to be lifted by the handle in a horizontal direction, 
 and when two or three inches above the plate, the knob upon 
 it is again to be touched by the finger or a ball, when a spark 
 much stronger than the former will be occasioned ; the cover 
 is again to be put down, when a third spark will pass between 
 the knob and the knuckle ; being again lifted as before, a 
 spark as strong as the second may be taken from it : similar 
 effects will follow for a long time by repetitions of the process. 
 All the sparks which pass immediately after putting the cover 
 down are negative as to the approximated ball or knuckle, and 
 those which pass after taking it up are positive. 
 
 1010. When the electrophorus is in good order, the sparks 
 taken after lifting the cover are quite sufficient to inflame the 
 greater number of explosive mixtures operated upon in eudi- 
 ometers. All that is necessary is, to substitute the knob of 
 the cover for the conductor of the electrical machine. If a 
 stronger spark be required, a jar must be charged : this may 
 be done either positively or negatively at pleasure. For the 
 first purpose it is only necessary to bring the knob of the elec- 
 trophorus cover into contact with the knob of the jar immedi- 
 ately after raising it from the plate ; upon doing this thirty or 
 forty times in succession, the jar will be charged positively : if 
 the ball of the jar be applied to the knob of the cover each 
 
Sect. XVII.] ELECTROMETER BENNETTS. 433 
 
 time the latter is put clown, until several sparks have passed, 
 it will become negatively charged. It must be understood, 
 that to obtain strong positive sparks, it is necessary to touch 
 the cover when on the resinous plate with a finger or other 
 conducting body, which must be removed before the cover is 
 raised ; and that to obtain the strongest negative sparks, the 
 cover, when raised, should always be discharged of all its 
 electricity against the hand or some other convenient conductor, 
 before it is again placed on the plate. The cover must always 
 be in a good state of insulation, when it is put down to give 
 negative sparks, or when it is taken up to give positive sparks ; 
 and inasmuch as ordinary glass has a powerful tendency to 
 attract moisture to its surface, and thus becomes a bad insu- 
 lator, it is advisable to varnish the glass tube handle with 
 sealing-wax dissolved in spirit of wine, or to construct the 
 handle of a stick of sealing-wax or other resinous matter. 
 
 1011. Instead of a resinous electrophorus plate, that part 
 of the instrument may be made of a sheet of thin crown-glass, 
 the metallic base (1007), which is essential as a bottom for 
 the apparatus, being tin foil pasted and attached to it. A 
 large plate of mica without fissures, coated in the same manner 
 with tin foil on one side, makes a most excellent electrophorus. 
 The cover (1008), instead of a board, may consist of a plate 
 of tin having its edges turned up round a thick wire, that no 
 sharp edge or angle may be presented outwards. These parts 
 are to be used exactly in the manner already described ; but if 
 glass be the substance employed, it must be well warmed at 
 first, and kept warm during the experiments. It is most 
 powerfully excited by being rubbed with a piece of silk, having 
 some amalgam spread upon it (981 ) ; this should be passed 
 briskly over its surface backward and forward, and at last 
 slidden rapidly off at the edge, so as not to rest upon any one 
 part of the glass, as it would then discharge that portion of its 
 surface. 
 
 1012. Bennetts gold leaf electrometer, as improved by 
 Singer, is highly useful in the laboratory, for the facilities 
 it affords of detecting electricities of low tension, and deter- 
 mining their kind. These are constantly developed by chemi- 
 cal action ; by the voltaic pile ; and by other causes which are 
 
 2XF 
 
434 ELECTROMETER SINGER*S. [Sect. XVII. 
 
 related to chemical science. This instrument, as improved by 
 the application of Singer's mode of insulating the cap and 
 gold leaves, will, when warm and dry, retain a charge for 
 hours. It would be improper to enter minutely into its appli- 
 cations ; but repeated experience that its indications are not 
 generally well understood by persons having occasion to use it, 
 induces me to describe more particularly the kind of change 
 it receives under different circumstances, and the precautions 
 requisite in interpreting the appearances. 
 
 1013. If an insulated portion of conducting matter, as a 
 brass ball at the end of a glass handle or silken thread, be 
 electrified, and then placed in contact with the cap of the 
 electrometer, the cap and leaves will immediately partake of 
 the electricity of the ball, and the leaves will diverge. If the 
 charge in the ball be of considerable intensity, the leaves will 
 be torn to pieces by their mutual repulsion, and the attrac- 
 tion of the sides of the glass jar; but if the intensity be 
 small, the leaves will diverge moderately, so as not to touch 
 the glass ; and the degree of divergence will be in some pro- 
 portion to the intensity of the charge communicated. The 
 appearances will be the same whether the electricity communi- 
 cated be positive or negative. 
 
 1014. The circumstances will be different if the body 
 brought in contact with the electrometer is an electrified por- 
 tion of what is usually called non-conducting matter ; if for 
 instance it be a stick of sealing-wax rubbed with flannel, 
 instead of a metallic ball. If highly electrified, this will cause 
 the same disturbance and appearances in the leaves during its 
 approach as the ball ; if moderately electrified it will, when in 
 contact with the cap, cause the usual appearance of divergence 
 in the leaves, but upon removing it, the leaves, instead of 
 remaining diverged, will either collapse, or remain very slightly, 
 and frequently uncertainly, electrified. This is a consequence 
 of the non-conducting power of the wax ; and the method of 
 transferring electricity to the electrometer in such a case is, to 
 draw the excited parts of the wax over the edge of the cap ; 
 small portions will be communicated, and the electrometer 
 will be left electrified similarly to the wax. Such a process is, 
 however, very uncertain ; for if the electricity of the wax be 
 
Sect. XVII.] ELECTROMETER HOW USED. 435 
 
 weak, the friction of the substance against the electrometer cap 
 will sometimes generate an electricity stronger than that pre- 
 viously existing on the surface of the wax, and the elec- 
 trometer will become charged, not by the previous electricity 
 of the wax, but by that produced during its friction against 
 the cap. 
 
 1015. This difficulty may, however, be avoided in most cir- 
 cumstances, simply by bringing the electrified non-conductor 
 into contact with the cap, and retaining it there during the 
 experiment; for the electricity which in this way is made by 
 induction to exist in the leaves, and causes their divergence, is 
 the same as that which would exist over the whole of the cap 
 and leaves, if the electricity of the wax could be transferred to 
 them. 
 
 1016. Such are the circumstances relating to the charge of 
 the electrometer, by bodies brought into contact with it, and 
 communicating to it part of the electricity they previously 
 possessed. As before mentioned, when highly electrified, 
 they cannot be so applied to the instrument without tearing the 
 leaves to pieces ; but they may then, when held at a distance, 
 be made to diverge the leaves by induction, and even to com- 
 municate a charge to the instrument, and thus enable it to 
 exhibit divergencies when the inducing electrified body is re- 
 moved. The effects thus produced by induction are the same 
 in kind and nearly in extent, whether the electrified body be a 
 mass of conducting or non- conducting matter, so that in this 
 respect the metallic ball and the stick of wax are equal ; the 
 only difference being in the kind of electricity produced, which, 
 with bodies charged positively, is the reverse of that occasioned 
 by such as are charged negatively. 
 
 1017. When an electrified substance is placed at such a 
 distance from the cap of the electrometer, as to occasion con- 
 siderable divergence, and is retained there for a few minutes, 
 the divergence of the leaves will generally diminish, and the 
 more rapidly as the instrument becomes cold or the glass damp, 
 as the leaves are ragged, or any part of the cap angular and 
 pointed. On removing gradually the electrified substance to 
 such a distance that it can no longer affect the instrument, it 
 will be found that the leaves will collapse at first, and after- 
 
 2 F 2 
 
436 ELECTROMETER DIVERGED. [Sect. XVII. 
 
 wards expand again more or less, according as they had lost 
 more or less of their first divergence. This ultimate divergence 
 of the leaves will be due to a charge of electricity in the in- 
 strument, of the opposite kind to that of the inducing or 
 approximated body. 
 
 1018. If no effect of this kind takes place, and there be no 
 diminution of the first divergence, nor any ultimate change, then 
 the insulation and goodness of the electrometer is proved by a 
 powerful test. This being ascertained, then, if whilst the elec- 
 trified body is in the neighbourhood, and the leaves diverged, 
 the cap be touched by the hand, or any other conducting 
 substance communicating with the earth, the divergence of the 
 leaves will instantly cease. In this state of the instrument, if 
 the communication be broken, so as to leave the cap and leaves 
 insulated, they will still remain collapsed ; but if the inducing 
 electrified body be now removed from the situation in which it 
 at first caused the divergence, the leaves will immediately di- 
 verge, and the electrometer become charged with electricity of 
 the opposite kind to that of the inducing body. The degree 
 of charge thus given to the instrument will be in proportion to 
 the degree of divergence induced in the leaves before they were 
 made to collapse by the touch of the finger. 
 
 1019. In the case in which a weakly electrified non-conduct- 
 ing substance was directed to be laid on the cap of the electro- 
 meter (1015), to occasion a divergence by electricity like its own, 
 it may be observed that, if, during the experiment, the cap be 
 touched by the fingers, and the electrified body afterwards re- 
 moved, the leaves will first collapse, and then diverge with 
 opposite electricity, although at the commencement of the 
 experiment they were diverged with the same electricity as that 
 of the body to be examined. 
 
 1020. If therefore the electricity of an excited body is to be 
 examined, the leaves of the electrometer are in the first place 
 to be diverged. This may be done with the same electricity, 
 by bringing the body, if weakly electrified, into contact with 
 the cap, leaving it there if of non-conducting matter (1015), 
 or removing it after contact if of conducting matter (1013) ; 
 or, if strongly electrified, by approaching it so near as to cause 
 a sufficient divergence of the leaves, and retaining it there until 
 
Sect. XVII.] ELECTROMETER ITS INDICATIONS. 437 
 
 the conclusion of the experiment. On other occasions however 
 with strongly excited bodies, it may be convenient, either be- 
 cause of their size or other circumstances, to communicate a 
 charge of the opposite kind, in the manner described (1018) ; 
 then upon determining what that kind is, in the manner to be 
 immediately described, the electricity of the originally elec- 
 trified body will of course be known to be opposite to it. 
 
 1021. The tests of the kind of electricity by which the leaves 
 are diverged, are of the following nature. A stick of sealing- 
 wax rubbed with warm flannel becomes negatively electrified ; 
 a tube of warm glass rubbed with a dry silk handkerchief, or, 
 better still, with a piece of silk, having a little amalgam upon it 
 (981), becomes positively electrified; both these excitations 
 being so strong, as to make the leaves of an uncharged electro- 
 meter diverge, whilst the wax or glass is at a considerable dis- 
 tance. If one of these excited substances be brought near the 
 cap of an electrometer already diverged, it will either cause the 
 divergence to increase or diminish. The divergence will in- 
 crease if due to electricity of the same kind as that of the body 
 approached, but will diminish if of the opposite kind ; so that 
 the electricity of the body approached being known, that of 
 the electrometer will also be known, and consequently that of 
 the excited body which had originally caused its divergence. 
 The sealing-wax for instance is rendered negative by flannel : 
 being approached to a diverged electrometer it may cause the 
 leaves to collapse ; the conclusion to be drawn is, that the elec- 
 trometer leaves were in a positive state : being approached to 
 another diverged electrometer it may increase the divergence, 
 in which case it will indicate that the leaves of the electro- 
 meter were in a negative state. An excited rod of glass brought 
 to these electrometers would make the first diverge still more, 
 and would cause the second to collapse, in both cases indicating 
 the same states as the wax. 
 
 1022. Some precaution is required with respect to the 
 manner in which these excited rods are to be applied. The 
 electrometer being diverged, the wax or glass is to be excited 
 at such a distance as to have no influence over the instru- 
 ment ; the most strongly excited part of the wax or glass is 
 then to be gradually approached to the cap, the hand and all 
 
438 ELECTROMETER. [Sect. XVII. 
 
 other unnecessary" conducting bodies being kept out of the 
 way as much as possible, or at least not moved in the neigh- 
 bourhood of the electrometer during the experiment. As 
 soon as the rod begins to affect the leaves (even though the 
 distance be two or three feet), the effect must be watched, and 
 then their collapse or further divergence will become evident 
 immediately on moving the rod a little way to or from the 
 instrument. It is this first effect that indicates the kind of 
 electricity in the electrometer, and not any stronger one ; for 
 although, if the repulsion be increased from the first, no 
 approach will cause a collapse to take place except the actual 
 discharge of the leaves against the sides of the glass, yet 
 where collapse is the first effect, it may soon be completed, 
 and a repulsion afterwards occasioned from a too near approach 
 of the strongly excited test tube. It is, therefore, the first 
 visible effect that occurs, as the test rod is made to approach 
 from a distance, that indicates the nature of the electricity; 
 and when this effect is observed, the rod should not be brought 
 nearer, so as permanently to disturb the state of the electro- 
 meter, but should be removed to a distance, and again ap- 
 proached, for the purpose of repeating and verifying the pre- 
 ceding observation. 
 
 1023. It is to be understood, that the approach of the test 
 rod, though it affects the divergence, causes no permanent 
 change of the electricity in the instrument, unless it be brought 
 much too near, and cause considerable disturbance of the 
 leaves. The electrometer will remain, after a good experiment, 
 in the same state as at first (1018). 
 
 1024. When the body to be examined is so strongly elec- 
 trified that it may not be brought near to the electrometer, 
 but has been placed at such a distance as to affect it (1020), 
 and left there to cause a proper divergence, then its place 
 should not be directly over but rather on one side the cap, 
 that the test tube, when applied, may be brought towards the 
 instrument on the other side ; the originally electrified body 
 and the test tube being retained in directions as widely apart 
 as they conveniently can be. 
 
Sect. XVII.] VOLTAIC ELECTRICITY ACID. 439 
 
 %. Voltaic Electricity. 
 
 1025. Great variety in the forms of the Voltaic pile, trough, 
 or battery have been introduced at different times, of which a 
 knowledge may be obtained from elementary works on Che- 
 mistry or Electricity, and from particular memoirs on the 
 subject. The information here to be conveyed does not con- 
 cern these varieties of form so much as the management by 
 which they are to be rendered serviceable and effectual in the 
 performance of experiments. This management, though it 
 be spoken of generally, will be described with reference, prin- 
 cipally, to the ordinary form of apparatus, in which the plates 
 being arranged in sets of ten each, and fixed to a bar of wood, 
 are inserted into earthenware troughs, as suggested by Dr. 
 Babington. 
 
 1026. Troughs are usually charged with a diluted mixture 
 of acids, which; when the plates are immersed, confers power 
 and activity upon the arrangement. A mixture of a proper 
 strength is obtained by adding two parts in bulk of oil of 
 vitriol and one part of common nitric acid to 80 or 100 parts 
 of water, the whole being well stirred together until equally 
 mixed. Its power should in all cases be ascertained before it 
 is poured into the troughs, by dipping a piece of clean zinc 
 into a little of it in a glass and observing the degree of action 
 exerted upon the metal. A stream of bubbles should be dis- 
 engaged so small that their size can hardly be distinguished by 
 the naked eye, and which, as they rise up through the fluid, 
 should be carried freely in different directions by the cur- 
 rents in the fluid itself. If the action be so strong as to 
 evolve bubbles of a considerable size, which rapidly rise to 
 the surface, and are numerous, the acid must be diluted. 
 If, on the contrary, little or no chemical action can be per- 
 ceived, the charge must be strengthened by the addition of 
 acid. Although the above charge is recommended for ordinary 
 use, it may frequently be necessary when more energetic action 
 is required to increase the proportion of acid accordingly. 
 
 1027. If the proportion of the two acids differ from the 
 above, then the indications by bubbles varies also. The sul- 
 
440 VOLTAIC TROUGH QUANTITY OF FLUID. [Sect. XVII. 
 
 phuric acid causes the formation of bubbles and gas ; the 
 nitric acid tends to prevent the formation of either when pre- 
 sent within certain proportions with the sulphuric acid, and a 
 mixture which evolves much gas from zinc may consequently 
 have the evolution lessened by the addition of nitric acid, 
 although at the same time its exciting power in the Voltaic 
 trough is increased. Hence it is often useful to increase the 
 proportion of nitric acid, for the purpose of avoiding the pro- 
 duction of much gas or vapour from the battery during the 
 experiments. 
 
 1028. The cells are to be filled to within half an inch of 
 their upper edges ; when the plates are in their places the 
 mixture should not flow from one cell into another. The 
 fluid in the cells may be levelled and made equal in all by 
 raising the trough on one side, so that the liquid may 
 flow from one cell into another over the divisions; its pas- 
 sage from the trough is prevented by the height of the 
 edges of the latter all the way round above the level of the 
 divisions. This superior height of the edges of the trough is 
 attended to in all constructions of Voltaic apparatus with cells, 
 whether formed of earthenware or whether the cells are made 
 by the plates themselves set at equal distances and cemented 
 into a trough of wood. 
 
 1029- When the plates of the battery are separate from the 
 troughs and are to be immersed after the latter are charged 
 with fluid, great care is necessary that they be properly in- 
 troduced ; the zinc and copper plates of two contiguous pairs 
 are to be placed in the same cell, but not the zinc and copper 
 plates of the same pair. There is no fear of erring on this 
 point with Wollaston's double coppers, but when the copper 
 plates are single, considerable risk of this kind is incurred. 
 It is also essential that the plates be arranged in the same 
 relative position, i. e. all the zinc plates in one direction, and 
 all the copper plates in the other. When by accident 10 pairs 
 of plates are turned the wrong way in a battery of 100 or 
 more, they do considerably greater harm than merely results 
 from the loss of their own power, and the neutralization of 
 that of 10 other pairs. It is always advisable so to arrange 
 a battery that, whatever the number of troughs may be, the 
 
Sect. XVII.] TROUGHS ARRANGED ACTION TESTED. 441 
 
 two extremes of the series should be within two or three 
 feet of each other. The troughs may stand very well on dry 
 boards ; and no material loss of power will occur, if, in the 
 convolution of the battery, the rows are two feet apart, unless 
 indeed the series be very extensive. Damp ground or damp 
 boards occasion considerable loss in the power of extensive 
 batteries, especially if the intervals between the rows are 
 small, and the wires of communication for the experiments 
 thin and long (1036). 
 
 1030. When the battery is charged, and the plates im- 
 mersed in the acid, the good order of the whole is to be 
 ascertained by fastening two wires to the extreme plates to 
 serve as poles, twisting their ends round two pieces of well 
 burned box-wood charcoal (1033), and bringing these together. 
 An immediate discharge of electricity will take place^ pro- 
 ducing an exceedingly brilliant spark of light, which will be 
 larger or smaller in proportion to the size and power of the 
 battery. If therefore it be wanting altogether^ or by no 
 means equal to what was anticipated from a trial with a 
 single trough in the same manner^ then the obstruction, or 
 whatever it may be that interferes, is to be sought for by the 
 following method. 
 
 1031. A piece of copper wire about the ^ of an inch in 
 diameter, and four or five feet in length, is to have one end 
 twisted round a piece of box-wood charcoal, and the other 
 brightened ; then beginning at one extremity of the battery, 
 the bright end is to be pressed tightly against the last plate 
 with one hand, whilst by means of the other the corner of 
 some plate, as far off as can be conveniently reached, is to 
 be touched with the charcoal at the opposite extremity. If 
 the spark be as brilliant as could be expected, it will prove 
 the perfection of the arrangement through the portion tried. 
 The bright end of the wire is then to be brought to the plate 
 last touched, and a second portion of the battery tried in 
 the same manner, until the whole has been tested. If, durino- 
 the trial, the discharge of any portion seems imperfect, or 
 is altogether wanting, then keeping the bright end of the 
 wire against the plate with which it was in contact at the 
 time of the failure, every fifth or sixth plate is to be tried 
 
442 VOLTAIC BATTERY EXAMINED CHARCOAL. [Sect. XVII. 
 
 backwards with the charcoal, which is to approximate at 
 each remove that to which the bright end is applied, and 
 it will be found that on a sudden the discharge is effected, 
 though with less force, because of the smaller number of 
 plates between the ends of the wire. Whenever this discharge 
 occurs, it points out the place where, from some derangement 
 or untoward circumstance, the obstacle to the action of the 
 battery exists. 
 
 1032. The battery is to be examined at this point, and it 
 will be found that a plate is in the wrong trough ; or that acid 
 is wanting ; or that a wire lies across to some other part of the 
 arrangement ; or that the metallic communication is bad, the 
 zinc plate being either broken or injured by corrosion ; or 
 some other cause for the obstruction will be found. This 
 must be removed, or if it be of such a nature that it cannot 
 immediately be corrected, either the trough where it occurs 
 must be rejected, or a good metallic connection by thick copper 
 wire (1034) must be made between the plates on different sides 
 of the obstruction, so as to allow an efficient and concurring 
 action of the rest of the battery. This trial of the battery 
 need not necessarily be made on portions of four or five feet, 
 but when, from the convolution of its course, an opportunity 
 is offered of connecting the battery across, more extensive 
 portions may be tried, as, for instance, one half at a time, 
 and thus the half containing the obstruction may be at once 
 discovered. 
 
 1033. The charcoal used in these and similar experiments, 
 with the Voltaic battery, is made from box-wood, which being 
 cut into pieces, having a length of two inches, and a thickness 
 of about a quarter of an inch, are to be charred in close vessels. 
 The wood may be packed in an earthenware crucible, and 
 being well covered over with dry sand, should be heated until 
 it ceases to flame. Although the greater part of such char- 
 coal will conduct electricity almost as well as metals, some 
 pieces will probably fail. Before being set aside, therefore, for 
 use, it should be examined by a single trough, a wire being 
 brought from each end of the trough against the opposite ends 
 of each piece of charcoal in succession. Such as easily con- 
 duct the electricity, and yield a brilliant spark, are to be pre- 
 
Sect. XVII.] TROUGHS CONNECTED PRECAUTIONS. 443 
 
 served in a stoppered bottle ; those which afford a small spark, 
 or none, should be rejected. 
 
 1034. When two or more troughs are to be connected, and 
 the instrument-maker has not furnished the necessary means, 
 attached to the sets of plates, the arrangement should first 
 be examined to ascertain that the plates of both troughs are 
 placed in the same relative position and order, and when that 
 is the case they may be connected, and considered but as one 
 trough. The connexion should be made by a single or double 
 copper wire, one fifth of an inch in diameter ; and the operator 
 should not be satisfied with merely bending the wire, so that 
 the ends may drop into the two cells containing the plates to 
 be connected, but should bring them into firm and close con- 
 tact with the plates in those cells, so that a good metallic com- 
 munication may exist between them. If the ends of the wires 
 merely dip into the fluid charge of the cell, which, in com- 
 parison to the metal of the apparatus, is a bad conductor of 
 electricity, then all the electricity has to pass from the fluid to 
 the wire by a very small surface ; it has consequently to pass 
 through a great length of the badly-conducting body, and also, 
 near the wire, has to be compressed as it were into a small 
 mass of it : both of which are circumstances causing obstruction 
 to its course, and waste of power in the battery. But, on the 
 contrary, if the wire touch the metallic plate, the electricity then 
 passes, comparatively without obstruction. Nor is it retarded 
 importantly when the wires are soldered to plates equal in size 
 to those of the troughs, even though they may not touch the 
 trough plates, for then a large surface of metal is afforded for 
 contact with the liquid, and, consequently, for the trans- 
 mission of the electricity : the stratum of fluid between the 
 communicating plate and the trough plate is, virtually, not a 
 fifth or sixth of its former quantity ; and the additional plates 
 also are active, like the other plates of the trough. When 
 these communicating wires with plates at their extremities are 
 not at hand, ordinary wires are to be used, and brought into 
 contact with the plates already in the cells : this is easily done 
 by bending the wires, so that when introduced into the cells 
 they may act as springs, and press against the plates. 
 
 1035. The two extremes of the whole arrangement are 
 
444 VOLTAIC BATTERY POLES POLE W*RES. [Sect. XVII. 
 
 called the poles, and require to be connected in various ways 
 with the solids and fluids to be acted upon, according to the 
 nature of the experiments. Metallic rods or thick wires are 
 usually made to proceed from these extremes, and, as long 
 as they remain in communication with them, are often termed 
 the poles. It is essential that these pole-wires should com- 
 municate with the extremes of the battery, either by plates at 
 their extremities, equally large with those of the battery, or by 
 actual and good metallic contact with the end plates of the 
 series. The simple immersion of their extremities in the fluid 
 of the extreme cells should never be considered as sufficient 
 (1034). 
 
 1036. These poles or terminal wires should be of consider- 
 able thickness. Copper wire (1034) one fifth of an inch in 
 diameter, answers the purpose very well in ordinary cases. 
 In experiments, when, from the rigidity of such wire, it may 
 be found necessary to complete the communication with the 
 substance to be experimented upon by a smaller wire, still 
 the thicker one should be continued as far as possible, and 
 the small wire made short. Even the large wires, which 
 conduct the electricity from the battery to the substance 
 under examination, should be as short as convenient ; for 
 though with electricity of considerable intensity they may seem 
 to cause no obstruction, yet when of slight power they will 
 offer considerable resistance. Metals themselves vary much in 
 their power of conducting electricity, but no one of them is 
 more advantageous for the purpose of effecting Voltaic com- 
 munications than copper (1347) : it is easily drawn into wire ; 
 is very flexible ; has a high conducting power ; and when pure 
 and in a state of rest, exhibits no magnetic effects, and conse- 
 quently does not interfere with the magnetic phenomena occa- 
 sioned by a current of electricity passing through it. 
 
 1037. When Voltaic electricity is resorted to for its chemical 
 power over imperfectly conducting matter (on which only it 
 has hitherto been rendered efficient), the substance to be acted 
 upon is placed between the two poles or extremes of the wires, 
 being made the medium of conducting communication from the 
 one to the other. These extremes are best formed of platina, 
 which, of all the metals, is the one least acted upon by the sub- 
 
Sect. XVII.] POLES THEIR SIZE COMMUNICATION. 445 
 
 stances likely to be operated with or evolved. The nearer 
 those extremes or acting poles are to each other, i, e. the smaller 
 the portion of imperfectly conducting matter between them, 
 the more powerfully is it affected ; and the same holds good 
 to a certain extent with respect to the size of these poles, for 
 the greater the surface of their contact with the matter to be 
 decomposed, the greater is the action, provided the distance 
 between the two surfaces be not increased. (1052, &c.) 
 
 1038. These remarks are intended to apply to an extent 
 of the acting surfaces, considerably less than the size of the 
 plates of the battery, and they become more applicable, when 
 the substance acted upon is a worse conductor of electricity. 
 Thus suppose a battery of 100 pair of plates of four inches 
 square to be in use, and water were to be placed between the 
 poles for decomposition ; then, instead of holding the poles, 
 which may be two small platina wires, in the water, point to 
 point, half an inch apart, it would be better to hold them side 
 by side at the same distance. It would be better still to use 
 two slips of platina foil instead of the wires, placing them 
 parallel to each other in the water, and half an inch apart ; and 
 if, instead of half an inch, the distance were one fourth of an 
 inch, or still less, the effect would be proportionably increased. 
 Every increase in size of these slips, until they were at least 
 two-thirds the size of the plates in the battery, would also be 
 advantageous, by increasing the surface of action without 
 materially diminishing its intensity. But if instead of water a 
 very strong solution of potash were the substance to be acted 
 upon, then though the general effect would be the same, and 
 the advantage very striking by the substitution of small plates 
 of foil for wire, it would cease if the plates were as large as 
 those of the battery, or even of a size, which would be bene- 
 ficial if water alone was used. 
 
 1039. It is essentially necessary that the metallic communi- 
 cation between the battery and the acting poles, or the ex- 
 tremes of the wires, should be good and perfect. In any 
 place where a permanent junction may be allowed, it is best 
 to effect it by sound metallic soldering or brazing. Where a 
 temporary junction only is required, it is effected by bringing 
 the clean surfaces into close contact, and retaining them so for 
 
446 VOLTAIC BATTERY METALLIC CONTACT. [Sect.XVII. 
 
 the time by pressure or otherwise. Wires may be twisted 
 together, their surfaces being first well cleaned and brightened ; 
 or if, from their thickness, they are stiff and rigid, they should 
 be first slightly twisted together, and then bound round by 
 twenty or more turns of clean copper wire of smaller size. 
 Either in twisting or in binding wires, two or three loose 
 turns must never be considered as sufficient, but the two 
 pieces must be so twisted or bound together, as to have the 
 steadiness of one piece. 
 
 1040. When a junction is required to be made and broken 
 again frequently, as happens in many electro- chemical and 
 electro-magnetical experiments, it should be done at one place 
 only in the metallic communication. The ends of the wires 
 should be perfectly clean, and when put across each other for 
 the purpose of effecting the communication, should be held 
 tightly in the hand, or pressed together by a weight placed 
 upon them for the time ; or in peculiar situations, such a bend 
 must be given to the wires that they may act as springs and 
 press against each other. It is often advantageous to amal- 
 gamate the surface of these ends, for then, if they be moistened 
 with a little mercury, the fluid metal causes a perfect contact 
 over a comparatively large surface at the point where the 
 wires meet, the moment they are connected together. 
 
 1041. Clean copper wires are readily amalgamated on the 
 surface, by washing them with a solution of nitrate of mer- 
 cury, then rinsing them in water and afterwards dipping them 
 in mercury. When the experiments are of long continuance, 
 it is convenient to put about a quarter of an ounce, in bulk, 
 of mercury into a cup or glass, with half an ounce by measure 
 of moderately strong solution of nitrate of mercury ; on clean- 
 ing the curved end of the wire a little, dipping it into the 
 nitrate, and moving it about in contact with the solution and 
 the metal beneath, it will quickly amalgamate, after which it 
 should be removed into another glass containing water, with 
 a little mercury at the bottom, the adhering solution washed 
 off, and the wire dried by a piece of bibulous paper. This 
 method is very convenient for ensuring the amalgamation and 
 perfect contact of chain or link joints, by which the necessary 
 mobility of part of the metallic communication in electro-mag- 
 
Sect. XVII.] JUNCTIONS REQUISITES. 447 
 
 netic experiments is attained. The ends of wires thus amal- 
 gamated, if not well washed, frequently oxidate, and become 
 covered in a few days with a thick crust of badly conducting 
 matter. If, from the duration of the experiments, this be 
 inconvenient, the wires should be amalgamated, not by nitrate 
 of mercury, but by the use of a little tallow and metallic mer- 
 cury, putting the tallow, with a few globules of the metal, on 
 a piece of chamois leather, and rubbing the wire with it until 
 the adhesion is effected. Wires thus prepared do not tarnish 
 or become foul nearly so soon as those prepared in the former 
 method. 
 
 1042. Where flat surfaces are to be brought into contact, 
 the intervention of a little mercury is very useful, but the 
 surfaces should previously be well cleaned, and if amalga- 
 mated, the contact is more secure. A cup of mercury is also 
 convenient for making metallic communications, which require 
 to be broken frequently, for which purpose the ends of the 
 two wires to be connected should be cleaned, amalgamated and 
 dipped into the metal. The wires may be readily arranged, 
 so that one may be displaced and restored, without the slight- 
 est shake or disturbance of the apparatus, and the perfection 
 of the contact is ensured every time the wire is replaced. 
 
 1043. The importance of these four points, namely, accu- 
 rate metallic contact ; sufficiency of thickness in the conducting 
 wires; their shortness; and also extent of surface where a 
 good conductor and a bad one are in contact, should never be 
 forgotten in practice ; and though one or the other, or most 
 of them, may now and then be of little consequence in parti- 
 cular experiments, yet attention to them is always useful, and 
 often essential. This is especially the case in electro-magnetic 
 experiments, where electricity in great quantity but of low 
 intensity is frequently the subject of investigation. One per- 
 son will not be able to perform electro-magnetic revolutions 
 and motions with five or six troughs, which another, by atten- 
 tion to these circumstances, will effect with a single pair of 
 small plates. 
 
 1044. In all experiments with large batteries it is advisable 
 to retain only one of the poles in the hand at a time, unless 
 indeed they are previously in communication with each other 
 
448 VOLTAIC BATTERY DECOMPOSITIONS. [g ec t. XVII. 
 
 by good conducting matter, or by large surfaces and masses of 
 badly conducting substances. The pole-wires should be pre- 
 served distinct from each other in all parts of their course, so 
 that no accidental discharge and consequent waste of power 
 may take place between them. For this reason both should 
 not be allowed to come in contact with the same piece of metal 
 or wire, or be connected by good or even moderately con- 
 ducting matter. All their energies should be preserved un- 
 impaired until they are exerted upon the substance placed 
 purposely for decomposition between their extremities. 
 
 1045. In all cases the experiments should be prepared as 
 far as possible before the battery is put into action, that 
 none of its power may be unnecessarily wasted during such 
 preparation. 
 
 1046. The methods of subjecting substances to the poles of 
 the battery for the purpose of effecting their decomposition, 
 and of collecting the results, are very numerous. If the sub- 
 stance be a fluid, for example water or a saline solution, it 
 may be put into a glass, and the two platina poles (1037) 
 immersed in it : the nearer they are brought to each other the 
 more powerful will be the action. Tubes will answer the same 
 purpose. They may be prepared very conveniently for such 
 experiments by closing one end, but with a platina wire 
 
 passed through it, extending nearly to the 
 other end. This may be done by passing the 
 wire through a cork, and using that cork to 
 close the tube ; or by sealing the platina wire 
 into the tube, and at the same time closing its 
 extremity in the manner to be described in 
 Section xix. (1201). Such a tube being fixed 
 on a cork (67) with its open end uppermost, 
 may be filled with the fluid, and then, if one pole be brought 
 into contact with the external end of the tube wire, and the 
 other pole immersed in the fluid, action immediately com- 
 mences. In all these arrangements it is necessary, that how- 
 ever near the poles may approach each other, they should not 
 be in contact, for then all chemical action on the surrounding 
 fluid ceases. 
 
 1047. When the quantity of fluid to be acted upon is small, 
 
Sect. XVII.] VOLTAIC DECOMPOSITION GASES COLLECTED. 
 
 449 
 
 a watch-glass, or a piece of broken flask or retort, is very con- 
 venient as a receiver, or when a drop only of the fluid can be 
 spared, a glass plate (1348) will support it. The poles are 
 on such occasions to be brought towards each other on oppo- 
 site sides of the drop, and the effect minutely examined and 
 noted. 
 
 1048. With a view of increasing the acting surfaces, a pla- 
 tina capsule may be used to receive the fluid : one pole is then 
 to be placed in contact with the exterior of the capsule, and 
 the other dipped into the fluid within. Even the surface of 
 this immersed pole may be extended by attaching a piece of 
 platina foil to it. When the experiment is to be continued for 
 some time the immersed pole may be supported and kept from 
 contact with the capsule, by putting a little piece of glass, or in 
 delicate experiments, a fragment of rock crystal into the solu- 
 tion, allowing the wire or foil to rest upon it. 
 
 1049. When the products of the experiment are gaseous, 
 they are best collected by the use of tubes similar to those 
 already described (1046), but placed in an inverted position. 
 If such a tube be filled with a saline solution for instance, and 
 inverted in a portion of the same solution in a glass or other 
 vessel, not of metal, then by dipping the negative pole of a 
 
 battery into the fluid of the vessel, and con- 
 necting the wire of the tube with the posi- 
 tive pole, action will take place, and the 
 oxygen evolved from the water of the solu- 
 tion at the positive pole will be collected in 
 the tube. If in place of one such tube two 
 be used, both standing in the same vessel, 
 and their wires connected" with the poles of 
 the battery, the gases evolved at those 
 poles are collected separately in the tubes. 
 Or if both poles be introduced into the same tube (1203), 
 then the gases are collected in a state of mixture. 
 
 1050. A very convenient form of tube for the collection 
 and examination of the gases evolved in small experiments, by 
 either one pole or the other, is shewn by the figure. The tube 
 is first to be filled with the solution to be acted upon, and then 
 held in the position represented. The kind of gas collected 
 
 2 G 
 
450 VOLTAIC DECOMPOSITION FLUIDS. [Sect. XVII. 
 
 is dependent upon the pole which is made fast to the wire 
 at a ; the other is [to be inserted at 6, but not so far as to 
 allow any of the gas from it to pass round the 
 bend into the tube ; the fluid will flow out of 
 the mouth of the tube as the gas is evolved at 
 the pole a. When the vessel is sufficiently full 
 of gas, the pole b is to be removed, and the gas 
 examined as described (950), or else, if neces- 
 sary, transferred and examined in a more mi- 
 o nute and accurate manner. 
 
 1051. In the arrangement of these tubes, and in all decom- 
 positions of solutions^ it is better to use platina foil for the ter- 
 mination of the poles, than wire, because of the greater surface 
 of contact presented by such a pole to an imperfectly con- 
 ducting substance (1038). For tubes, therefore, which have 
 platina wires fused into them, the wire should be thick, and 
 the extremity, for a length nearly equal to that of the tube, 
 flattened out into foil; or a piece of platina foil should be 
 prepared for the pole inside the tube, and be made fast to a 
 piece of wire, either by close contact or gold soldering, before 
 the latter is put through and fused into the glass (1201). 
 
 1052. In all arrangements relative to the decomposition of 
 water or aqueous solutions by Voltaic electricity, the young 
 experimenter should keep in mind the effects dependent upon 
 variations in the quantity and situation of the fluid. The 
 fluid, as compared with the metal of the poles, is a very im- 
 perfect conductor, and when in large quantity, offers a serious 
 obstacle to the passage of electricity of the low intensity gene- 
 rated by the Voltaic pile : and yet in proportion as this passage 
 is free or obstructed, is the action more or less energetic and 
 effectual. The necessity for bringing the poles near to each 
 other has therefore been insisted upon (1088), that the column 
 of fluid which intervenes between them may be as short as 
 possible. But the injurious effect which occurs by contracting 
 the width of this column has not yet been pointed out. 
 
 1053. Suppose that the poles of the battery are two platina 
 wires, and that they have been immersed in a saline solution 
 contained in a glass, and placed half an inch apart ; gas will 
 be evolved, and a certain degree of action will be observed. 
 
Sect. XVII.] OPPOSITE POLES PRECAUTIONS. 451 
 
 If then a plate of mica be cut into such a form that it will 
 serve, when introduced into the glass vertically, to divide the 
 solution into two parts, each containing a pole, and if a notch be 
 then cut in the mica somewhat wider than the immersed wires, 
 and of equal depth with them, so that when returned into its 
 place there shall be a passage for the solution through the 
 notch, directly between the two poles, and of equal size with 
 them, or even rather larger, it will still be found, though the 
 distance between the poles is exactly the same as when no 
 mica was present, that their action is very greatly diminished. 
 This effect is entirely due to the contraction of the thickness 
 of the connecting column of imperfectly- conducting fluid ; and 
 if the mica were of considerable thickness, so as to extend the 
 notch into a channel of half or three-quarters of an inch in 
 length, then, notwithstanding its width and depth would be the 
 same as before, the poles would hardly exert a perceptible power. 
 
 1054. All this may be easily understood by considering that 
 what the fluid wanted in conducting power had been partly 
 made up by its mass, and that by diminishing this mass, the 
 channels of communication had been in a great measure closed ; 
 but this is very often forgotten in the construction of appa- 
 ratus, and in conducting of experiments. When two poles 
 rise through the bottom of a glass, they may act perfectly 
 well ; but if a tube of glass be put over each, to collect the gas 
 evolved, the circumstances are entirely altered. There are 
 very few parts of the opposite poles that are now virtually as 
 near to each other as before, and those farthest up the tubes 
 are removed to a distance equal to the length of the line which 
 might be drawn from the end of one pole to the edge of the 
 tube containing it, across, to the edge of the other tube, and 
 upwards, to the extremity of the pole within it. Besides this 
 increased length, the thickness of the intervening and con- 
 ducting mass of fluid is very much diminished also, being 
 equal to the diameter of the tubes only, whereas, before, it was 
 in some parts equal to the diameter of the glass containing the 
 solution and poles. 
 
 1055. A similar influence is exerted to a great extent in 
 experiments where the poles are placed in different vessels. 
 These vessels require to be connected by syphon tubes filled 
 
 2 G 2 
 
452 VOLTAIC BATTERY AQUEOUS SOLUTIONS. [Sect. XVII. 
 
 with the solution, or by moistened threads of cotton or ami- 
 anthus. If these bridges of communication be small, much 
 power will be wasted, which would be active were larger tubes 
 or bundles of fibres applied ; and besides making them large, 
 they should, for the reasons before given, also be as short 
 (1052) as the other circumstances of the experiment will allow. 
 Generally, with regard to the fluid intervening between the 
 poles of the battery, the endeavour should be in all cases to 
 make it virtually as short, and, if the expression may be used, 
 as massive as possible, no more insulating or retarding matter 
 being allowed to occupy the space between the poles than can 
 possibly be helped. 
 
 1056. Aqueous solutions generally have greater conducting 
 power than pure water, and advantage may be taken of this 
 circumstance in effecting the decomposition of water, and even 
 of some other bodies. It will be found that a battery which 
 will scarcely act upon water, so as to evolve sensible portions 
 of gas, will appear to acquire twice or thrice its former power 
 by putting a little common salt, sulphate of soda, or almost 
 any saline body, into the water under decomposition. A small 
 quantity only is required, one part of a saturated solution of 
 these salts to six or eight parts of water producing a great 
 effect. These solutions are very useful as tests of the ex- 
 istence of a Voltaic current, capable of effecting chemical 
 changes. When substances are so arranged, that it is sup- 
 posed an electrical current of some intensity is produced, all 
 that is required to ascertain the correctness of the opinion is, 
 to bring a wire from each end of the arrangement, and im- 
 merse their extremities in a drop of a weak solution of salt ; if 
 gas be evolved, it is a proof the opinion is well founded. 
 
 1057. The plates of a voltaic battery should be removed 
 from the action of the charge at every considerable inter- 
 mission of the experiments. The acid rapidly dissolves and 
 destroys the zinc plates during the time it is in contact with 
 them, and though the degree of action may not be of such 
 importance as to justify the raising of the plates during the 
 cessation of experiments for a minute or two, or even for a 
 longer time in particular circumstances, yet they should never 
 unnecessarily be left to the action of the charge, when the 
 
Sect. XVII.] VOLTAIC BATTERY SIZE. 453 
 
 electricity they evolve is not actively employed on other bodies. 
 When five or ten minutes intervene between one experiment 
 and another, it is worth while raising the plates of a battery of 
 ten or twelve troughs, or less, from the cells ; this affords the 
 additional advantage of an increase of action upon their re- 
 immersion, due in some way to draining or exposure to air. 
 Instrument-makers sometimes hang the plates to a frame, 
 which being suspended by a cord, and connected with a lever, 
 allows the whole to be raised or depressed at pleasure ; and 
 Dr. Hare has constructed a trough *, in which the cells being 
 formed by the metallic plates (1028), the charge is poured oil 
 and off at pleasure, by a quarter revolution of a handle. 
 
 1058. Although it is highly advantageous to operate with a 
 large battery, as for instance of 100 pair of plates four inches 
 square, when such can be had, and when the object is to 
 render the experiments and other results evident at a distance, 
 yet such a power is by no means always necessary. Even the 
 repetition of the most refined and admirable experiments may 
 be made with a battery no way comparable to one of this size, 
 if the object of the experimenter be only to satisfy himself or 
 those close to him, and if he use the precautions as to contact, 
 vicinity, &c., already given. A single trough, of ten pairs of 
 plates four inches square, will suffice to repeat nearly all the 
 experiments that have yet been made on the decomposition of 
 bodies in solution, and all those relating to electro-magnetism. 
 Nor is it essential that a greater power should be used in many 
 new investigations. In the same manner, a small trough with 
 40 or 50 pairs of plates, one inch square, will be found a very 
 useful instrument in a laboratory not affording the opportunity 
 of working with a larger arrangement ; and the habit of expe- 
 rimenting with small apparatus, and on a minute scale, is 
 highly valuable for the independence, which it gives to the 
 philosopher, of larger, more expensive, and consequently 
 scarcer instruments. 
 
 1059. Where copper and zinc in sheets can be obtained, 
 (and there is now scarcely a large town in England without 
 them,) a Voltaic arrangement may easily be constructed. The 
 metals are to be cut into single plates of equal size, two inches 
 
 * Philosophical Magazine, Ixiii. 241, 
 
454 VOLTAIC ARRANGEMENTS. [Sect, XVII. 
 
 square for instance, and are then to be arranged as a pile 
 with equal-sized pieces of flannel dipped in dilute acid (1026) 
 in the order zinc, flannel, copper; zinc, flannel, copper; 
 zinc, flannel, copper; until twelve or more pairs of me- 
 tallic plates have thus been put together. Such an arrange- 
 ment should be made in a plate, that any acid exuding from it 
 may be caught and retained. The surfaces of the contiguous 
 metallic plates should be clean, that the contact between them 
 may be good. To ensure this, it is convenient to solder the 
 plates together at their edges into pairs, each comprising a zinc 
 and a copper plate. On building these up with the inter- 
 vening flannels, the order will be copper, zinc, flannel; copper, 
 zinc, flannel; copper, zinc, &c. The wires, which, when 
 attached to the top and bottom of this pile, serve as its poles, 
 should be clean and in good contact with the end plates, and 
 then a pile of twenty of these pairs will be found to have very 
 considerable power, and be competent to the performance of a 
 great number of experiments. 
 
 1060. The nature of the poles of an ordinary battery may 
 be determined by inspection of any one of the pairs of metallic 
 plates employed in its construction. The end of the battery 
 on the zinc side of the pair examined is the positive pole ; 
 the end on the copper side of the same pair is the negative 
 pole. This holds good wherever the pair may be in the bat- 
 tery, or however far the ends may be removed. 
 
 1061. Electro-magnetic, and many other experiments rela- 
 tive to the transmission of electricity through good conduc- 
 tors, such as the metals, and the effects produced thereby, 
 often require for their performance Voltaic arrangements, 
 consisting of a few large plates rather than many small ones. 
 It is easy to arrange the ordinary troughs, consisting often 
 pairs of plates four inches square, so as to produce intensity 
 or quantity at pleasure. Thus if four of these troughs were to 
 be used for chemical experiments, it would be best to place 
 them end to end in their proper order, so as to form a bat- 
 tery of forty pairs of plates four inches square, connecting 
 them if necessary in the manner described (1034) : but if 
 large plates and few in number be more advantageous, then 
 these four troughs may be arranged so as to form a battery 
 
Sect. XVII.], ELECTRO-MAGNETIC EXPERIMENTS. 455 
 
 equivalent to one of ten pair of plates eight inches square. 
 For this purpose they must be placed with their sides to- 
 gether, their similar ends being in 
 the same direction ; and they should 
 be connected by two thick pieces of 
 copper wire, bent according to the 
 figure, in such a manner that the lower angles of one piece will 
 enter the four terminal cells at one end of the battery; this, 
 if in perfect contact with the plates (1034), will connect them 
 together. The second piece will perform the same office at the 
 other ends of the troughs, and the projecting terminations of 
 these wires are to be used as the poles of the battery. 
 
 1063. A single pair of plates is sufficient for the performance 
 of nearly all electro-magnetic experiments, and a combina- 
 tion of this kind may be constructed with great facility by 
 those who possess a piece of plate zinc and a piece of plate 
 copper. They require merely to be put near each other in a 
 jar or vessel of dilute acid, and connected by a wire. The 
 plates may be conveniently tied together with a couple of 
 pieces of glass rod or tobacco-pipe between them, to prevent 
 metallic contact. A thick wire a few inches in length should 
 be attached to each plate, to act virtually as the poles (though 
 they are not really poles according to the usual acceptation 
 of that word in Voltaic electricity), and these wires or poles 
 should be connected by the experimental wire, which, though 
 thinner than the former, should not be unnecessarily long. 
 This arrangement has been described as formed of flat pieces 
 of zinc and copper plate, but any shape may be given to them, 
 so that their relative position is the same: they may be 
 coiled ; or even a copper vessel may be used instead of a cop- 
 per plate, and then the jar for containing the acid may be 
 dispensed with altogether. 
 
 1063. The double copper arrangement described by Dr. 
 Wollaston is excellent for ordinary experiments, and may 
 easily be constructed. It consists of a plate of zinc surrounded 
 on both sides by a. plate of copper, so that a surface of the 
 latter is brought into opposition with both surfaces of the zinc. 
 This arrangement when immersed in acid is very powerful ; a 
 zinc plate of less than an inch square being able to effect the 
 
456 DR. WOLLASTON'S ARRANGEMENT. [Sect. XVII. 
 
 ignition of fine platina wire, the deflection of the magnetic 
 needle, and most of the electro-magnetic experiments. 
 
 1064. It is necessary the student should be informed that 
 instruments consisting of a single pair of plates have no che- 
 mical action. 
 
 1065. Dr. Wollaston's beautiful Voltaic arrangement for 
 the precipitation (523) of certain metals, is so instructive, and 
 in many cases so useful, that it must not be here omitted. It 
 was devised for the separation of cadmium from the solution of 
 the ore or metal under examination, after all that could be 
 precipitated by zinc alone (522) had been thrown down. The 
 solution rendered slightly acid was put into a platina crucible, 
 and a rod of zinc also introduced, so as to rest on the bottom 
 and at the edge of the vessel : this formed a Voltaic combina- 
 tion with the platina and the fluid ; electro- chemical action 
 took place, and the cadmium was precipitated on the platina, 
 which was the negative part of the arrangement. When the 
 separation of the cadmium had been completed, the zinc was 
 removed, the solution poured out, the crucible with the cad- 
 mium adhering to it washed with distilled water ; then a little 
 nitric acid being used, it dissolved the latter metal without 
 causing any injury to the platina. 
 
 1066. A very usual problem which the chemist has to solve 
 is, whether a substance be a conductor of electricity or not, or 
 what is the degree of conducting power which it possesses 
 with regard to electricity. Whether it conduct like a metal 
 or not may be ascertained in the following manner. If a piece 
 of zinc and a piece of silver be placed one above and the other 
 below the tongue, and the edges be then brought into contact, 
 a peculiar taste will be perceived at the moment, which will be 
 repeated every time the contact is broken and renewed. If, 
 instead of bringing the zinc and silver in direct contact, a 
 piece of metal, as a wire, intervene, the taste will still be per- 
 ceived ; but if the interposed substance be a body not metallic, 
 or one of those numerous substances which, though they con- 
 duct electricity, are less efficient than the metals, a piece of 
 wet paper for instance, a piece of starch, or even a piece of 
 galena, then no taste will be occasioned. The experiment 
 should therefore be made first with the zinc and silver, and 
 
Sect. XVII.] CONDUCTING POWER EXAMINED. 457 
 
 having succeeded, the substance to be tried should be placed 
 between the two metals and the attempt repeated ; the pro- 
 duction or non-production of taste will immediately indicate 
 whether it conducts electricity or not. All the pure metallic 
 bodies, and all combinations of them with each other, conduct 
 electricity so well as to occasion the taste ; but as yet no other 
 substance has been ascertained to do so, nor even any of the 
 definite compounds of metals with other substances, as sul- 
 phur or oxygen. Dr. Wollaston's method of preventing 
 accidental contact of the zinc and silver on one side of the 
 substance to be tried is very useful * : it is to cut a hole in 
 a piece of card, and lay the doubtful body in this hole be- 
 tween the other metals ; its contact and retention in its place 
 is secured, and the accidental contact of the known metals 
 perfectly prevented, 
 
 1067. Evidences of the conducting power of solutions and 
 transparent fluids are of the following kind. If on placing 
 a small portion between the Voltaic poles, gas be evolved, or 
 metals or other substances separated, or any change effected 
 which would not have taken place by mere contact of the liquid 
 and the metal of the pole distinct from the battery, such action is 
 a proof that a current of electricity is passing, and consequently 
 that the fluid is a conductor ; and the energy of the action is 
 to a certain degree an indication of the degree of conducting 
 power. A small Voltaic battery is sufficient for this purpose. 
 
 1068. It is, however, possible, though not usual, that no 
 apparent change may take place, notwithstanding the body is 
 a conductor, equally good with those fluids which suffer de- 
 composition ; this is the case with fluid chlorine. In such 
 instances, besides the portion of fluid to be tested, there should 
 be in another vessel a portion of a solution of salt ; one of these 
 should be connected with one pole of the battery, the other 
 with the other pole, and a piece of platina wire should be bent 
 so as to dip into both portions of fluid, and its ends should be 
 brought near to the ends of the poles immersed . There are thus 
 two portions of matter. ready to be decomposed by the electric 
 current : if the decomposition is seen by the liberation of gas to 
 proceed in the solution of salt, it is a proof that the other fluid 
 
 * Philosophical Transactions, 1823, p. 20. 
 
458 CONDUCTING POWER ROUSSEAU'S TEST. [Sect. XVII. 
 
 is a conductor of electricity sufficient for this purpose : if no 
 decomposition take place in the solution, then the other fluid 
 will not permit Voltaic electricity of this intensity to pass, and 
 is in that respect a non-conductor. 
 
 1069. The same kind of trial serves for such solid bodies as 
 are not comparable to metals with regard to this property, they 
 being then substituted for the liquid in this experiment, and 
 the solution of salt acting the part of a test as before. It will 
 in this way be found that several of the native and artificial 
 compounds of the metals and other bodies conduct electricity, 
 though by no means with a readiness sufficient to answer the 
 test of taste first proposed (1066). 
 
 1070. Again, there are very many substances which, though 
 so inferior in conducting power as to appear perfect insulators 
 by these modes of trial, will yet shew many degrees of it by 
 more powerful tests, that is, by electricity of higher intensities. 
 These are generally classed amongst very bad conductors, and 
 are most readily examined perhaps by the gold leaf electrometer 
 (1012.) If the electrometer be diverged, and its cap then touched 
 by any substance held in the fingers, or at the end of a wire, 
 it will be discharged, and the leaves collapsed with more or less 
 rapidity, according to the conducting power of the substance. 
 If the leaves retain their first divergence, it is a proof of the 
 entire absence of conducting power as far as our tests usefully 
 extend. For the application of this method to a liquid, the 
 latter should be placed in a convenient vessel, a capsule or tube 
 for instance, connected by a wire or the hand with the earth, 
 and then a piece of bent wire, well insulated by a stick of seal- 
 ing wax or gum lac, is to be made to touch the cap' of the 
 electrometer by one end, and the surface of the fluid by the 
 other. If the leaves collapse entirely, it is a proof that the 
 fluid conducts electricity. 
 
 1071. M. Rousseau * has devised a very ingenious varia- 
 tion of this test. He brings one end of a dry electric column 
 into contact with the cap of the electrometer, and retains it 
 there. This occasions a divergence of the leaves to an extent 
 dependent upon the power of the pole. He then connects the 
 cap of the electrometer with the earth through a portion of the 
 
 * Aiinales de Chimie, xxv. 373. 
 
Sect. XVII.] VOLTAIC BATTERY ITS USES. 459 
 
 fluid or substance to be tried, and observes to what extent this 
 reduces the previous divergence of the leaves. If the diver- 
 gence be entirely destroyed, it shews a conducting power 
 which is considerable, as compared to that of most bodies which 
 may be tried by this method ; if but slightly diminished, it 
 indicates but little conducting power. Decided distinctions 
 may be established between even the different oils by this 
 method. 
 
 1072. Although the great use of the Voltaic pile is to effect 
 chemical change by means of the peculiar power of its poles, it 
 is often otherwise applicable. When the discharge of a power- 
 ful battery is made through air between two pieces of charcoal, 
 the heat is very intense, and is extended over a larger space 
 than when the discharge takes place between two pieces of 
 metal. To this temperature any gas may be subjected in 
 which the discharge is made and the effects upon it may be 
 observed. Carburetted or sulphuretted hydrogen are thus 
 decomposed. Other gases examined in the same manner 
 would probably present peculiar phenomena. 
 
 1073. By transmitting the Voltaic current through thin 
 wires, they are heated, ignited, and fused. This effect sup- 
 plies a means of conveying, or rather of producing and 
 applying heat in situations in which it could not otherwise be 
 excited, and thus facilitates certain refined experiments. Sub- 
 stances having wires passed through them may be placed 
 within globes under water, or in remote situations, and then be 
 heated, ignited, and exploded: eudiometers have been con- 
 structed in which a fine wire passing across the cavity has 
 been ignited by a Voltaic battery, and thus used to inflame the 
 included mixture of gases. 
 
 1074. The insulation of substances is frequently required 
 in electro- chemical investigation, and numerous methods must 
 be resorted to, according to the circumstances of experiments. 
 When an insulating plane is required, a plate of mica is the 
 best substance for the purpose, then a plate of resin or wax, 
 or, in their absence, a -plate of warm glass. In all similar 
 insulations, the substance to be supported should be placed so 
 far from the edges of the insulating planes, as to be independent 
 in its electrical state of the neighbouring bodies ; and it is also 
 
460 ELECTRICITY INSULATION. [Sect. XVII. 
 
 convenient to support the insulating planes themselves upon a 
 glass jar or other vessel, in those cases at least where the state 
 and degree of electricity of the insulated substance is to be 
 minutely examined. For if the insulating plane lie on a table 
 or other conducting body, it allows of induction through it ; 
 and thus, without any actual communication, permits the 
 electricity of the body upon it to be influenced in an uncertain 
 and variable manner. For the same reason when a body is 
 insulated for minute and delicate examination, no projecting 
 mass of conducting matter should be allowed to exist in its 
 immediate neighbourhood, because of the influence which will 
 then be exerted upon it by induction through the air. 
 
 1075. When glass pillars, or stools with glass legs, or a 
 common glass (368), is used for insulation, they should always 
 be well warmed and dried, and glass apparatus which is con- 
 stantly appropriated to this use should be varnished with a 
 solution of sealing-wax in strong alcohol. Ordinary glass has 
 such an attraction for water, that at common temperatures its 
 exposed surface is constantly moistened to a certain degree ; in 
 consequence of which it becomes a conductor of electricity of 
 such tensions as are sensible by the gold leaf electrometer, and 
 is therefore a bad insulator. A glass rod well warmed and 
 rubbed, and then left exposed to the air to cool, will be found, 
 after a few hours, capable of discharging a gold leaf electro- 
 meter, solely by the film of moisture on its surface ; for if glass 
 be examined in an unexceptionable manner, it has not itself 
 those conducting powers at common temperatures. Resins are 
 very superior to glass in this respect, and hence the use of the 
 varnish recommended. 
 
 1076. In experiments upon the manufacture of glass for 
 optical purposes, I have found that with such as contained no 
 alkali, but consisted of silica, boracic acid, and oxide of lead, 
 the insulation was so perfect as to equal if not surpass that of 
 lac resin *. This glass is not at present in use, but may here- 
 after, because of this and other properties, be very useful in 
 electrical investigations. 
 
 1077. When a small mass of solid matter is to be insulated 
 by a handle, it may be effected by a piece of white silk 
 
 * Philosophical Transactions, 1830, p. 49. 
 
Sect. XVIII.] LUTES CEMENTS THEIR NATURE. 461 
 
 thread dipped into and stiffened by melted gum-lac, or by a rod 
 or thread of the same resin. This substance is easily melted 
 and drawn out into threads of different diameters, and surpasses 
 every other in insulating power at common temperatures. 
 
 1078. If a body is to have a suspensive insulation, then silk 
 thread or cord may be advantageously resorted to, but in such 
 cases white silk should be used. Black silk frequently con- 
 ducts as well as a moistened thread, and coloured silks are 
 often very inferior in this respect to white, in consequence of 
 the dye stuff they contain conferring a certain degree of con- 
 ducting power. 
 
 1079. There are no particular instructions required in rela- 
 tion to electro-magnetic experiments beyond those which have 
 already been given. The contacts should be carefully attended 
 to; the part of the connecting wire which is experimented 
 with removed and preserved as far as it can be from other 
 parts of the wire, and from the battery, that the needle or 
 apparatus experimented with may be subject to no other 
 influence than that of the wire alone. The magnets used 
 should be strong ; their magnetic poles well determined, and not 
 irregularly diffused over the steel of which the magnets con- 
 sist. The points of support for the magnetic needles should 
 be attended to (1390, 1398), and the needles should be in an 
 active state. 
 
 SECTION XVIII. 
 LUTES-CEMENTS. 
 
 1080. IT is intended in this Section to comprise such an ac- 
 count of Lutes and Cements, with the methods of applying 
 them, as shall enable the student to select that whicli is most 
 fitted for his particular purpose, and make it answer the re- 
 quired end with the greatest success. 
 
 1081. Lutes are soft 'adhesive mixtures, principally earthy, 
 used either for closing apertures existing at the junction of 
 different pieces of apparatus, or for coating the exterior of 
 
462 LUTES APPLIED. [Sect. XVIII. 
 
 vessels which are to be subjected to a high temperature ; the 
 latter application being either for the purpose of strengthening 
 them and preventing their fracture (489) > or for repairing a 
 fracture, or to prevent the contact of the air. There are but 
 few lutes used for the latter purpose ; and the success of the 
 operation, which is usually called coating, is generally more 
 dependent upon the manner in which it is performed than upon 
 the lute itself. But those which have been applied for the 
 purpose of rendering junctions tight are very numerous, in 
 consequence of the variety of vapours which require to be con- 
 fined, and the difference of temperature to which they are 
 occasionally subjected. The term luting has occasionally been 
 confined to this application. 
 
 1082. The lutes which are used for junctions pass by 
 degrees into cements ; the two sets of bodies, if considered as 
 distinct, being frequently convertible in their uses into each 
 other. For this reason both will be comprised in this Section, 
 and also such other applications of these substances as may be 
 useful in the laboratory. 
 
 1083. The vessels which require coating are generally re- 
 torts, flasks and tubes, sometimes crucibles and other vessels. 
 Occasionally the temperature to be sustained is very high, at 
 other times a high red heat only is to be provided against ; and 
 in other instances the coating is rather for the purpose of ren- 
 dering vessels impervious to air (4-91, 492), than to defend them 
 from, or strengthen them in the fire. 
 
 1084. When the coating must sustain a very high tempera- 
 ture, as in the preparation of potassium by the gun-barrel, or 
 in the attachment of a crucible to its support, it should be 
 made of the best Stourbridge clay, no other earthy substance 
 found in this country being so capable of resisting fire without 
 softening or fusion. 
 
 1085. The lute is to be made into a paste, varying in 
 thickness or composition according to the opinion of the ex- 
 perimenter, as will immediately be pointed out. The paste 
 should be beaten until it is perfectly ductile and uniform, and 
 a portion should then be flattened into a cake of the required 
 thickness, and of such size as shall be most manageable with 
 the vessel to be coated. If the vessel be a retort or a flask, it 
 
Sect. XVIII.] COATING OF A VESSEL. 463 
 
 should be placed in the middle of the cake, and the edges of 
 the latter raised on all sides, and gradually moulded and ap- 
 plied to the glass: if it be a tube, it should be laid upon one 
 edge of the plate, and then applied by slowly rolling the tube 
 forward. In all cases the surface to be coated should be rubbed 
 over with a piece of the lute dipped in water, for the pur- 
 pose of slightly moistening and leaving a little of the earth upon 
 it ; and if any part of the surface becomes dry before the lute 
 is applied, it should be remoistened. The lute should be pressed 
 and rubbed down upon the glass successively, from the part 
 where the contact was first made to the edges, until all air 
 bubbles are excluded, and an intimate adhesion effected. If the 
 lute be inconsiderately and carelessly pressed upon small sur- 
 faces, as by the thumb or a finger, it will frequently extend 
 laterally, become of greater dimension than the vessel beneath, 
 and consequently will form a kind of bag about it, with air 
 intervening. This must be avoided by moderating the pressure, 
 making it more general, and applying it so that the coat rather 
 tends to thicken than otherwise ; and if an air bubble should 
 accidentally be formed, the endeavour should not be to expel the 
 air by passing it along between the coat and the vessel to the 
 edge of the luting, but by a hole to be pricked with a pin 
 through the luting over the bulb. 
 
 1086. When one cake of lute has been applied, and is not 
 large enough to cover the whole required surface, another 
 must be adapted in a similar manner. Particular care must 
 be taken in joining the edges ; for which purpose it is better 
 to make them thin by pressure, and also somewhat irregular 
 in form, and if at all dry they should be moistened with a 
 little soft lute. Afterwards they should be well pressed toge- 
 ther, that the adhesion may be as perfect there as in every 
 other part. 
 
 1087. If from irregularity in the form of the vessel coated, 
 as for example about the neck of a retort, the thickness of 
 lute, after a little pressure and moulding, should be somewhat 
 uncertain, it may easily be ascertained by passing a needle 
 through it, and observing the depth to which it penetrates. 
 The minute hole thus formed is rarely of consequence, and 
 may be obliterated by a little pressure towards it upon the 
 
464 LUTES THEIR STATE. [Sect. XVIII. 
 
 lute in the immediate vicinity. The general thickness may be 
 from one-fourth to one-third of an inch. 
 
 1088. Being thus luted, the vessels are afterwards to be 
 placed in a warm situation over the sand-bath, or near the 
 ash-pit of the furnace, or in the sun's rays. They should not 
 be allowed to dry rapidly or irregularly, and should be moved 
 now and then to change their positions. When dry they 
 should never again be allowed to become damp. 
 
 1089. With respect to the best state of the lute, there is 
 considerable variety of opinion and practice. The object is to 
 diminish the contraction which the moist clay undergoes, first 
 in drying in the air, and afterwards when heated in the fire. 
 By some, the clay is beaten into a very fine and uniform paste 
 with water, just so much of the latter being added as to make 
 the mass ductile and capable of application ; it is then applied 
 to the surface of the retort or tube in the manner described, 
 until it forms a coat upon its surface, from the fourth to the 
 half of an inch in thickness, according to the size of the vessel, 
 and the degree of strength required in the coating. During 
 the drying this coating will crack ; these cracks are to be care- 
 fully filled up with a portion of the same lute, again dried, and 
 again repaired if necessary, until the exterior appears sound 
 and perfect. 
 
 1090. Others apply their lute in a much softer and more 
 ductile state. This facilitates the operation, but upon drying, 
 the cracks are generally larger, and though these may be 
 filled up, and the whole exterior made to appear sound and 
 perfect, it will be evident that the separation of the coating 
 from the vessel, which must necessarily occur during the con- 
 traction of the clay, must proceed to a greater extent with the 
 latter kind of luting than the former. 
 
 1091. When vessels thus luted are introduced into the 
 fire and highly heated, further contraction of the aluminous 
 coating takes place. If the vessel itself be iron or earthen- 
 ware, it does not give way to the diminished bulk of the 
 coating, but actually expands beneath it, and thus new divi- 
 sions in the coating are produced ; the former partial adhesion 
 of it to the vessel is much diminished, and its tendency to 
 separate and fall off in fragments is much increased. When 
 
Sect. XVIII.] LUTES COATED VESSELS CRACKING. 465 
 
 the coated vessel is glass, this does not happen to such an ex- 
 tent, for the heated glass yields and gives way to the contrac- 
 tion of the coating, which, if it retain its unity and form until 
 the glass has softened, actually becomes an earthenware vessel 
 lined with vitreous matter (489). 
 
 1092. To prevent cracking during desiccation, and the 
 consequent separation of the coat from the vessel, some che- 
 mists recommend the introduction of fibrous substances into 
 the lute, so as mechanically to increase the tenacity of its 
 parts. Horse dung, chopped hay and straw, horse and cow 
 hair, and tow cut short, are amongst the number. When 
 they are used they should be added in small quantity, and it 
 is generally necessary to add more water than with simple lute, 
 and employ more labour to obtain an uniform mixture. It is 
 best to mix the chopped material with the clay, before the 
 water is put to it ; and upon adding the latter to effect the 
 mixture at first by stirring up the mass lightly with a pointed 
 stick or a fork : it will then be found easy by a little manage- 
 ment to obtain a good mixture without making it very moist. 
 If the fibres be long, more than an inch in length for instance, 
 it will be almost impossible to mix them uniformly with the 
 lute, and they will interfere much with its after application. 
 Hay cut to the length of one-half or one- third of an inch, is a 
 very good substance for the purpose. 
 
 1093. Retorts coated with lute thus prepared may be dried 
 gradually without the production of any considerable cracks 
 on the surface. The effect of these intermixed substances is 
 not merely to confer additional tenacity on the lute, but to 
 give a direction to the separations which are formed during 
 the contraction occasioned by drying, so that, ultimately, in- 
 stead of having the lute in three or four pieces, with large 
 open cracks intervening, the separation has resulted in nu- 
 merous minute fissures. These do not, however, prevent the 
 whole from adhering together as one coating ; the removal of 
 any one part of the coating far from its original situation 
 during the contraction from drying is thus avoided, and the 
 places of adhesion between the tube and the vessel are more 
 generally dispersed and more numerous than before. 
 
 1094. A similar object is sometimes obtained by applying 
 
 2 H 
 
466 COATING ITS LIABILITIES IN THE FIRE. [Sect. XVIII. 
 
 a bandage of coarse canvas or other open wove cloth over the 
 surface of the freshly- applied lute (699). Thus a tube, when 
 coated, may have a moistened slip of such canvas carried round 
 it, the edges of each turn being allowed to overlap consider- 
 ably, the whole being afterwards rubbed with a little moist 
 lute, so as to make the adhesion between the wrapper and the 
 coat perfect. When dried, the lute does not crack, and the 
 coating remains whole, but it has a tendency to split when in 
 the fire in the direction of the edges of the folds. Where the 
 form of the vessel is such as to prevent the application of a 
 slip of cloth, tow, or hemp, drawn out into lengths, may be 
 used for the same purpose ; but it must be carried over the 
 surface in different directions, or the cracks will not be pre- 
 vented, but merely a direction given to them. The tow en- 
 velope should be afterwards well moistened with soft lute, so 
 as to adhere closely to, and form one mass with, the coating. 
 
 1095. The most serious evil to which the lute or coating 
 is liable, is cracking in the fire ; and unfortunately this evil 
 increases with the heat, and, consequently, is greatest when the 
 coating, if good, would be most valuable and serviceable. A 
 luting of pure clay contracts much more in the fire than a 
 luting of clay mixed with as much sand as it will contain with- 
 out entirely losing its plasticity and tenacity. The mixture of 
 sand with the lute, however, renders it more fusible ; and 
 hence, though this is a very useful expedient when the vessel 
 to be luted has not to support more than a bright red or a 
 yellow heat, it is not applicable with equal, or with any ad- 
 vantageous effect, when very high temperatures are to be 
 sustained. In the latter cases it has been found advantageous 
 first to heat a portion of the clay intensely, then to break it 
 small and use it instead of sand, adding so much to the recent 
 clay as shall leave the mass, when moistened and beaten, with 
 such a degree of plasticity and adhesion as to allow of its ap- 
 plication. If access can be had to a glass-house, the frag- 
 ments of the broken glass pots may be pulverized and used 
 instead of the heated clay, particular care being taken that all 
 parts with glass upon them, or with the exterior glaze which 
 occurs upon glass pots, be rejected. Or pulverized Hessian 
 or Cornish crucibles may be used for the same purpose ; but 
 
Sect. XVIII.] COATING LUTING OF JOINTS. 467 
 
 old crucibles, when soiled by flux or other impurities, must not 
 be so employed. 
 
 1096. Lute which has had fibrous substances diffused 
 through it (1092) does not separate by contraction and fall off 
 so readily as that which is altogether earthy, probably because 
 the contraction is compensated by smaller fissures in greater 
 number. Those fibrous matters which have comparatively 
 large apertures, as hay, straw, dung, &c., appear to be the 
 best, and lute which has been mixed with one-third its weight 
 of pulverized coke, according to Mr. Marshall's method of 
 making crucibles (647), has appeared to be improved in cases 
 where the luting had no great weight or mechanical power to 
 resist. 
 
 1097. The liability to crack by heat in all these coatings is 
 diminished by their being washed over when dry with oil. 
 
 1098. Retorts, flasks, and other vessels of irregular forms, 
 are sometimes coated by being dipped into a thick cream of 
 the lute with water, and sprinkling dry lute over them during 
 desiccation ; when dry they are again to be immersed in the 
 thin paste and re-sprinkled, and the process repeated until the 
 coat which they have received is of sufficient thickness. 
 
 1099. All coated vessels should be supported as much as 
 possible when in the fire (490), to prevent or retard the de- 
 rangement or separation of the lute in consequence of its 
 weight. 
 
 1100. The methods of luting joints vary according to the 
 joint or aperture to be closed, and the kind of lute to be em- 
 ployed. In the time of Lavoisier, accurate joints were more 
 essentially necessary than at present. The general directions 
 then given were, to fix the apparatus firmly, and to cement it 
 tightly and stiffly by strong luting. In this way many com- 
 plicated instruments were combined into one great apparatus, 
 so rigid in all its parts as to render it almost impossible to 
 retain every junction perfectly close. The number of these 
 junctions has, in later times, been very much diminished, and 
 the introduction of elastic caoutchouc connecters (449) has 
 almost entirely removed that rigidity which was so dangerous 
 to the apparatus and fatal to its soundness. 
 
 1101. The following are brief accounts of various lutes 
 
 2 H 2 
 
468 WINDSOR LOAM-~WILLI8*S LUTE. [Sect. XVIII. 
 
 and cements that may be advantageously used in different 
 circumstances. 
 
 Stourbridge clay : it should be ground to fine powder ; is 
 highly useful in coating retorts, tubes, &c., and in effecting 
 junctions between crucibles and their stands. It is to be ap- 
 plied in the manner already described (1084). It sustains a 
 higher heat than any other English lute. 
 
 1102. Windsor loam: obtained at Hampstead, &c. It is a 
 natural mixture of clay and sand in such proportions as to 
 make an excellent lute, though it will not resist the heat sus- 
 tained by Stourbridge clay. It is frequently used for the 
 lining of furnaces, pots, &c. 
 
 1103. These lutes are also very useful for making the hot 
 joints of metallic vessels tight, as, for instance, the iron tube 
 which is attached to an oxygen bottle for the purpose of con- 
 veying away the gas. These joints are generally ground air- 
 tight at first, but by use in the fire soon become unsound. 
 When that is the case, a little smooth and rather soft lute 
 should be mixed up, put round the end of the tube, and the 
 latter pressed into its place. Care should be taken in moving 
 the apparatus afterwards that no agitation or blow be given 
 it, so as to derange the junction and break the continuity of 
 the lute. 
 
 1104. Willis's lute. When earthenware retorts (491) are 
 required to be rendered impervious to air or vapours, Mr. 
 Willis directs that an ounce of borax be dissolved in half a 
 pint of boiling water, and as much slacked lime added as will 
 make it into a thin paste. This is to be spread over the 
 retort with a brush, and when dry, a coating is to be applied 
 of slaked lime and linseed oil beaten together until it becomes 
 plastic. This will dry sufficiently in a day or two, and is then 
 fit for use. Earthenware retorts thus prepared may be used, 
 it is said, several times with safety, the coating of lime and oil 
 being renewed each time. 
 
 1105. Mixtures of pulverized borax with the clay lutes 
 above described, or with common clay, form fusible fluxes, 
 which are often useful in glazing over the surfaces of vessels so 
 as to close their pores. About one-tenth by weight of borax 
 is sufficient for the purpose. The mixture made into a thick 
 
Sect. XVIII.] FAT LUTE CEMENT PLASTER OF PARIS. 469 
 
 paste with water may be laid on with a brush, and the vessel 
 should be handled carefully until the heat has attained redness, 
 lest the slightly adhering crust should be knocked off pre- 
 vious to its fusion. 
 
 1106. Fat lute is applied to the junctions of apparatus which 
 are liable to considerable elevation of temperature, or to pre- 
 vent the escape of corrosive vapours (475) . It is prepared by 
 beating dried and finely pulverized clay (pipe-clay or Cornish 
 clay) with drying linseed oil, until the mixture be soft and 
 ductile. It is to be closely applied to the junction intended 
 to be made tight, the glass or other substance being first 
 wiped perfectly dry. If the joint has to sustain heat, the lute 
 will soften ; it then requires to be confined by strips of bladder, 
 which being put round it, should be tied tightly above and 
 below the mass of lute, and afterwards two or three turns of 
 twine passed round the middle part. When moisture or 
 vapours escape between this lute and the vessel, it is very 
 difficult to close the leak, and hence the great importance of 
 making a dry tight joint at the commencement. Glaziers 1 
 putty resembles fat lute, and may be used for similar purposes. 
 
 1107. Parker's cement is a brown powder, which should 
 be preserved for use out of contact with the air. When mixed 
 with water into a thin paste, it gradually sets, and becomes 
 quite solid and hard. It may be used occasionally with ad- 
 vantage in making joints tight, either at common or mode- 
 rately high temperatures. It may be rendered quite tight by 
 being brushed over with a melted mixture of equal parts of 
 wax and oil. It resists a red heat sufficiently well to make it 
 a useful coating for glass retorts or tubes upon numerous occa- 
 sions. 
 
 1108. Plaster of Paris, when mixed into a thick cream 
 or thin paste with water, sets after a short time and becomes 
 solid. It is best mixed by putting a little water into a cup, 
 sprinkling the powder into it, and stirring the mixture. It 
 may be used for the same purposes as Parker's or Roman 
 cement (475), being. generally superior to it in convenience; 
 and may be made air-tight in the same way by washing it 
 with oil or wax and oil, and should also be preserved from 
 the air when in powder. When Plaster of Paris is mixed up 
 
470 LUTES LIME AND EGG. [Sect. XVIII. 
 
 with very weak glue instead of water, it is somewhat longer 
 before it solidifies, but ultimately makes a very hard and 
 strong lute. 
 
 1109. A lute of Plaster of Paris may be raised to dull red 
 heat without injury, but if oiled or waxed to prevent the 
 passage of vapours, it will not support so high a temperature 
 unchanged. 
 
 1110. Caustic lime, mixed with various mineral and vege- 
 table substances in solution, affords numerous cements and 
 lutes, which when dry are hard, and impervious to vapours. 
 The lime should be well burnt, and slaked with just sufficient 
 water to make it fall into a dry powder ; after which it should 
 be preserved in a close bottle until wanted. One of the most 
 powerful of these cements is obtained by using white of egg 
 diluted with its bulk of water. The fluids are to be beaten 
 together until the mixture pours with perfect liquidity. This 
 is best effected by means of a little stick made to rotate by 
 rolling it between the hands, and having at its lower end a 
 cross piece, the arms of which, when in motion and immersed 
 in the liquids, effectually mix them. This being done, the dry 
 slaked lime in powder is to be added by sprinkling in such 
 quantities, that the whole when mixed shall have the consist- 
 ency of thin paste. This should be done quickly, after which 
 the mixture should be put upon slips of cloth and applied 
 round the junction to be luted, and a little of the dry lime 
 should be sprinkled over the exterior. The substance soon 
 hardens and adheres strongly. 
 
 1111. This cement is often conveniently applied by moist- 
 ening slips of cloth with white of egg beaten up without the 
 addition of water, and then sprinkling the lime in powder over 
 it in such quantity as to make a moist paste on the cloth. 
 The slips should be immediately applied to the junction, a 
 little lime being shaken over the exterior. 
 
 1112. In place of white of egg, a moderately strong solu- 
 tion of glue may be used ; or the serum of blood; or diluted 
 blood ; or a mixture made by rubbing down very poor cheese 
 with water in a mortar, until of the consistency of cream. 
 
 1113. If a leak take place through or by one of these lime 
 lutes during an operation, no difficulty occurs in stopping it 
 
Sect. XVIII.] JRON CEMENT WHITE LEAD BLADDER. 471 
 
 by the application of a fresh portion of the lute, which adheres 
 readily and perfectly, and is not liable to the difficulty which 
 occurs with fat lute. They will bear a heat approaching to 
 visible ignition without injury. 
 
 1114. Iron cement. This mixture is used for making per- 
 manent joints generally between surfaces of iron. Clean iron 
 borings, or turnings, are to be slightly pounded, so as to be 
 broken but not pulverized ; the result is to be sifted coarsely, 
 mixed up with powdered sal ammoniac and sulphur, and 
 enough water to moisten the whole slightly. It is then to be 
 rammed or caulked into the joints, and the latter drawn 
 together as tightly as possible. The proportions are, 1 sul- 
 phur, 2 sal ammoniac, 80 iron ; and no more should be mixed 
 than can be used at once. 
 
 1115. White lead ground up with oil, when spread upon 
 slips of cloth, is very useful for making joints tight, especially 
 those of metal, glass or other tubes. The lead when laid on 
 the cloth should be made to penetrate it. The slips should be 
 drawn tightly round the joint, and then bound with twine, 
 the ends of the joints being tied first, and afterwards the 
 middle. Sometimes tow is used with the white lead instead 
 of cloth ; it should then be so laid over the joint as to allow 
 the fibres to pass each other and the joint obliquely, that lateral 
 strength may be given to it. 
 
 1116. Bladder. Moistened bladder is in constant requisi- 
 tion in the laboratory for closing joints ; when soaked for 
 some time in water either warm or at common temperatures, it 
 becomes clammy, is very adhesive, and adheres well to glass. 
 It should be cut into slips of the proper size, and then applied 
 as a bandage to the place. It does not always require the 
 application of twine to keep it in its situation, so that occa- 
 sionally, when inconvenient, tying may be dispensed with. 
 
 If after being soaked it be wiped dry with a cloth and then 
 moistened on the surface with white of egg, its adhesion is 
 increased, and the use of twine rendered quite unnecessary. 
 
 1117. Paste and Paper are frequently useful in making 
 joints. The paste should be well boiled and thick. It is 
 better to use bibulous than sized paper, for the paste more 
 freely enters its pores and incorporates with it, and the joint is 
 
472 LUTES PASTED PAPER LINSEED MEAL. [Sect. XVIII. 
 
 less permeable ; but from the greater tenderness of such paper 
 when moist, more care is required in handling the pasted slips 
 and applying them. If sized paper be used, the pasted surface 
 should be doubled inwards, then redoubled several times, and 
 left for a few minutes to soak : evaporation is thus prevented, 
 and the paste and paper preserved moist. When opened out, 
 the pasted surfaces should not be separated from each other, 
 until the doubled paper has been cut into slips of the size 
 required. 
 
 1118. Paper which has been pasted, and has been allowed 
 to dry without having been folded together, is very useful in 
 the laboratory. A slip of it moistened on the pasted side and 
 allowed to soak for a few moments, is ready for application to 
 a joint, or in any other situation where its adhesive powers 
 may be useful. It is also very convenient for making labels, 
 to be attached to bottles and glasses the instant they are 
 required (1303, 1345). 
 
 1119- Paper prepared with a mixture of wax and turpen- 
 tine is also very useful for many of these purposes, especially 
 the labelling of bottles (1345). 
 
 1120. Glue with paper makes a very useful and convenient 
 application. With cloth it makes a strong one, which may be 
 rendered nearly tight by an exterior fold of paper, and quite 
 tight if the joint when dry is brushed over with drying oil, or 
 drying oil and wax (1107). 
 
 1121. Linseed meal or almond paste, well beaten up with 
 water until of an uniform and proper consistence, is an excel- 
 lent lute for cold joints of glass (475), or metal apparatus. 
 It should be applied thickly, and will then adhere well : it will 
 in some hours become a hard mass, and will resist most 
 vapours; but water must not be allowed to run upon it, 
 either within or without the joint. 1 1 will not bear a heat 
 above 600 Fahrenheit. When made up with milk, lime- 
 water, or weak glue, it becomes firm sooner, and forms a 
 harder substance than when water alone is used. 
 
 1122. Caoutchouc. Connectors of this substance have been 
 already referred to and described (449) . Joints may be made 
 tight by means of them, and consequently stiff tubes may be 
 dispensed with, in a great number of instances. These con- 
 
Sect. XVIII.] CEMENTS CAP-CEMENT YELLOW-WAX. 473 
 
 nectors when applied should be tied round the edges with 
 twine, but not be drawn so tightly as to incur any risk of 
 cutting the caoutchouc, for a slight degree of tension is suffi- 
 cient to make the joint secure. When the caoutchouc tubes 
 require slight extension to make them pass over the joints, 
 their own contraction is generally sufficient to make their con- 
 tact with the tube (if of glass) perfectly air tight. 
 
 1123. Cap cement. This is one of the numerous cements 
 which contain resin or wax, and are applied for causing ad- 
 hesion or making close joints at common temperatures. Their 
 principal use is with pneumatic apparatus belonging to the 
 air-pump and the water and mercurial troughs. Cap-cement 
 is used for the attachment of caps to retorts in the manner 
 described (833). It may be formed of 5 parts by weight of 
 resin, 1 part of yellow bees' wax, and 1 part of red ochre or 
 Venetian red in fine powder. The earthy substances should 
 be well dried in an evaporating basin on the sand-bath, at 
 temperatures above 212. The wax and resin should be 
 melted together, the powder stirred in by degrees, and the' 
 heat continued a little above 212, until all frothing ceases and 
 the mixture becomes tranquil. It is then to be cooled, the 
 stirring being continued, until it has become so thick that no 
 probability remains of the separation of the earthy matters by 
 standing. 
 
 1124. Yellow-wax may frequently be made to answer the 
 purposes of a cement. It resists most acid fumes at common 
 temperatures, and hence is often applied not merely for 
 making the joints of apparatus used in operations with acids, 
 but even for coating or lining vessels intended for the re- 
 tention of peculiar vapours and liquids, as those of the com- 
 pounds of fluorine. It will not, however, resist the action 
 long. It is less brittle (though more fusible) if melted with 
 one-eighth its weight of common turpentine. It should be 
 moulded into cylinders or sticks, and thus preserved for use. 
 
 1125. Soft cement, consists of yellow wax melted with its 
 weight of turpentine and a little Venetian red to give it colour. 
 When cold it has the hardness of soap, but by the warmth of 
 the fingers and a little pressure it becomes pliant, and may be 
 moulded into any form required. It is very serviceable in 
 
474 CEMENTS SOFT CEMENT ITS USES. [Sect. XVIII. 
 
 many hasty operations at common temperatures, as making a 
 tube and cork tight into the neck of a flask (484) ; closing the 
 apertures where tubes have passed through vessels which are 
 afterwards to be filled with water ; inclosing deliquescent sub- 
 stances in tubes (973), stopping a sudden leak, &c. In all 
 these cases it requires merely to be moulded into form and 
 pressed upon the joint in a dry state, and will then adhere 
 perfectly. It will not adhere to wood or other porous sub- 
 stances in a moistened state, but in cases of necessity it may 
 be made to adhere to wet metal and glass. The surface of 
 cement to be applied should then be of a convex form at first, 
 that as it meets with and adapts itself to the surface to which 
 it is to adhere, it may thrust the water before it ; more care 
 than is ordinarily required should afterwards be given to press 
 the cement into perfect contact. 
 
 1126. Soft cement is better for joints of apparatus which 
 are liable to be shaken during the operations performed in 
 them than hard cement or lutes, for it allows of a ^degree of 
 motion which would infallibly cause the separation of the hard 
 substance from the glass or metal, and so occasion leakage. It 
 not unfrequently happens that this allowable motion is a cause 
 of safety to the vessels by permitting such slight changes of 
 adjustment as are sufficient to relieve the apparatus from any 
 degree of tension or irregular bearing, which may have oc- 
 curred during the experiment, and which, if not thus allowed 
 for, might endanger the fracture of the weaker parts (854). 
 
 1127. The mouths of bottles which contain gases, mineral 
 waters, or acids, whether corked or stoppered, are frequently 
 covered with cement to render them perfectly tight. In these 
 cases soft cement is very superior to hard cement, or sealing- 
 wax, being much more likely to retain its adhesion to the glass 
 during travelling. The top of the bottle, with the cork or 
 stopper, should be made quite dry, and the cement then ap- 
 plied all over it to a considerable thickness. After being 
 pressed into its place, the whole should be covered with a piece 
 of moistened bladder or cloth, and tightly tied down. When 
 the object is to preserve a corked bottle of water or any other 
 substance having no action upon the soft cement, it is well to 
 melt ajittle of the latter, to dip the cork into it (973), and 
 
Sect. XVIII.] SOFT CEMENT POWDERED GUM. 475 
 
 having previously dried the neck of the bottle within, imme- 
 diately to thrust it into its place, and then to proceed as above. 
 In this way many waters containing carbonic acid, and holding 
 particular substances in solution, may be sent to a consider- 
 able distance with scarcely any change. 
 
 1128. Soft cement is also very useful for taking up small 
 particles, as crystals or fragments of bodies, for the purpose of 
 submitting them to ocular examination. It is easily moulded 
 between the fingers into an acute cone, the fine termination of 
 which being brought into contact with the body, adheres to it 
 by a mere point, with sufficient power to support it, and allow 
 its examination in any position. It is also convenient for 
 effecting the adjustment of any crystal or reflecting body 
 placed upon it, in the desired position ; a circumstance which 
 makes it serviceable in experiments on light or with the re- 
 flective goniometer. 
 
 1129. Powdered gum should be retained in the laboratory, 
 as supplying a ready means of attaching paper labels to bot- 
 tles, minerals, or other articles. A little of the powder stirred 
 up by the finger with a drop of water, if necessary, upon the 
 label or paper itself, is ready for immediate application. Paper 
 which has been covered on one side with a thick solution of 
 gum, and dried, is useful in the same manner as the pasted 
 paper already described (1118), but there are few bodies to 
 which gum adheres so well as paste, and the former almost 
 always separates from glass. The best kind of prepared paper 
 is made, by using a paste formed of equal parts by bulk, of 
 flour and powdered gum, and a small quantity of alum ; these 
 being mixed with sufficient water to make them into a thin 
 cream, are to be heated in an evaporating basin and continually 
 stirred until they boil ; the ebullition is to be continued a few 
 minutes, but evaporation should be prevented as much as pos- 
 sible, lest the paste become too thick. If that happen, a little 
 more water should be added, and the whole well mixed toge- 
 ther. This paste is to be applied to one side of the paper, 
 and allowed to dry as before described (1118). 
 
 1130. When a leak occurs at a luted joint, or at any other 
 part of the apparatus, it is often necessary to search for the 
 exact place of the aperture. If the vapours or gases which 
 
476 LEAKS DISCOVERED STOPPED. [Sect. XVIII. 
 
 issue are acid, the place may be detected by bringing a piece 
 of paper dipped in solution of ammonia towards it ; fumes 
 will be produced. If they are ammoniacal, then a little mu- 
 riatic acid on paper, or a glass rod, will detect the aperture 
 whence the issue. If the vapours are aqueous, the spot may 
 frequently be found, by bringing a cold glass plate or the 
 surface of a bottle towards it, the condensation and dimness on 
 the cold surface leading to the aperture. On other occasions 
 a small taper flame may be brought near, the bias given to the 
 flame, when it comes across the issuing current, or the actual 
 inflammation of the vapours, will show the spot where they 
 find vent. When it can be allowed, that is, where the heat is 
 not great, and the luting will not be injured by a little water, 
 a thick solution of soap-suds, or of gum, or paste, may be 
 washed over the suspected place : a bubble will be blown over 
 the aperture at which the gaseous contents of the apparatus 
 issue forth. 
 
 1131. The leak thus found must be stopped by applying a 
 little soft cement (1125), or fat lute (1106), or lime and white 
 of egg (1110), or paste and paper (1118), according to the 
 nature of the lute originally used, and other circumstances. 
 Many leaks, which can hardly be remedied in any other way, 
 may be stopped by tying a piece of sheet caoutchouc (449) 
 upon them*. 
 
 SECTION XIX. 
 BENDING, BLOWING, AND CUTTING OF GLASS. 
 
 1132. MANY occasions, upon which a knowledge of the me- 
 thods of softening, bending, and blowing of glass by means 
 of a lamp and blowpipe would be useful, have been already 
 mentioned (130, 463, 559, &c.) The attainment of a ready 
 practice on these points, together with that of facility in effec- 
 
 * For further instruction relative to the subject of this section, see Lavoisier's 
 Elements of Chemistry, chap. vi. sect, 5, and Aikin's Chemical Dictionary^ 
 vol. i. p. 273. 
 
Sect. XIX.] GLASS-WORKING BLOW-PIPE TABLE. 477 
 
 tually substituting an apparatus or vessel at hand, for another 
 that is wanting, are, perhaps, of all other experimental acquire- 
 ments, those which render the chemist most independent of 
 large towns and of instrument-makers. 
 
 1133. The apparatus necessary for the most effectual prac- 
 tice of this kind, is the table blow-pipe already described (242), 
 the precautions with regard to the state of the flame, which 
 have been pointed out, being particularly attended to. The 
 methods of working glass with this instrument will be first 
 described, and afterwards the best mode of supplying its de- 
 ficiency, by means of the common spirit-lamp and mouth blow- 
 pipe. The chemist's operations are generally confined to glass 
 in the form of tube or rod ; but though thus limited, they are 
 daily useful, and it is only by practice and the frequent per- 
 formance of such manipulatory processes as those described in 
 Section XVI., that any adequate idea of their great value and 
 service can be obtained. 
 
 1134. Supposing the operator sitting before the table (242), 
 the lamp trimmed and burning, the bellows put in action by 
 the foot, and the flame clear, pointed, and steady, it will be 
 desirable, in the first place, to consider the particular circum- 
 stances requiring his attention whilst raising the middle or the 
 end of a piece of glass tube to a red heat, and also whilst cool- 
 ing it to its first temperature. This is the simplest case re- 
 quiring instruction, and must be performed with facility and 
 readiness, before any further steps be taken. If the tube is 
 to be heated in the middle, its ends may be supported by the 
 fingers of each hand, so that the hands shall be beneath them, 
 with the palms upwards ; and the arms may be rested (till by 
 practice they have acquired steadiness) upon the edge of the 
 table. The part to be heated is to be brought, not into the 
 flame, but into the current of hot air which passes off in the 
 same direction as the flame from it (1142), and the tube is to 
 be turned so as to become heated all round, and also moved a 
 little to the right and left, that the temperature of the neigh- 
 bouring parts may be raised. After a few seconds, when the 
 glass has become hot, it should be brought towards the point 
 of the flame (220, 244), and ultimately into it, being turned 
 round all the time, and also moved laterally, though not to the 
 
478 GLASS TUBE HEATED THICK ANfc THIN. [Sect. XIX. 
 
 same extent as before, that the heat may be generally applied. 
 By the time that the tube (supposed to be about half an inch 
 in diameter, and one-tenth of an inch in thickness) is within the 
 flame, occupying a place about midway between the com- 
 mencement and end of the nearly transparent part (229, 232), 
 it should be of a bright red or yellow heat, to the width of half 
 an inch all round, so as to be perfectly soft at that part ; and 
 the heat should gradually diminish from it on each side, to- 
 wards those parts which are still but little above common tem- 
 peratures. 
 
 1135. The tube is brought at first into the heated air, and 
 not into the flame, because the hasty application of heat en- 
 dangers fracture. Glass suddenly heated breaks, because a 
 part is rendered hot directly in the neighbourhood of a cold 
 part, and expanding, tears the cold and unexpanded part 
 asunder. But when the heat is gradually applied, it has time 
 to diffuse itself over the neighbouring parts, so that no con- 
 tiguous portions have such differences of temperature as to 
 occasion differences of expansion greater than the glass can 
 allow, without separation of continuity. Hence the reason 
 why the heat is directed to be applied gradually ; and hence 
 the reason also why the parts near to the particular spot re- 
 quiring to be heated are also purposely raised in temperature. 
 
 1136. Thin glass, being heated through more rapidly than 
 thick, requires less precaution than the latter : sometimes but 
 little previous warming will be necessary for it, and on other 
 occasions it may be brought directly into the flame. Some 
 tubes are so small and thin that it will be found impossible to 
 break theniv by the most sudden application of the flame ; 
 whilst with large and thick tubes it will be found almost 
 equally impossible to heat them without making them fly to 
 pieces. The precaution adopted must be in proportion to the 
 size and thickness of the tube, and by a little practice will soon 
 be duly appreciated. 
 
 1137. When the end of the tube is to be heated instead 
 of the middle, more care is required, in consequence of the 
 great facility with which cracks commence at an edge. A heat 
 which would cause no danger if applied to the middle of a 
 tube, would instantly cause the extremity to fly to pieces. In 
 
Sect. XIX.] GLASS HEATED DISCOLORATION. 479 
 
 such cases it is best to begin by warming the tube an inch or 
 a little more from the end, and from thence to proceed slowly 
 to the end ; always keeping the temperature of the part first 
 heated rather higher than that of the end, until the glass 
 softens, which will be below a visible red heat in daylight ; 
 after that the end is safe, and the highest heat may be applied 
 there. 
 
 1138. The glass must not be blackened or discoloured 
 during the operation of heating. This is a fault that may 
 happen from either of two circumstances, namely, the incor- 
 poration of charcoal with the glass, or the reduction of the 
 oxide of lead in it. When glass below a read heat is brought 
 into the bright part of the flame *, a coat of charcoal is de- 
 posited, which in many cases does not disappear as the heat 
 rises above redness, because of the incorporation of the char- 
 coal with the melted glass ; and occasionally it even increases in 
 quantity. Being thus brought into contact with the oxide of 
 lead in the glass, that substance is decomposed by the carbo- 
 naceous matter, and the lead being reduced, forms another 
 kind of stain which mingles with the former. When the stain 
 happens by accident, it is removed by bringing the glass to 
 the apex of the flame, that the oxygen of the air may act upon 
 it ; and if the discolouration be superficial, it is soon reduced 
 and disappears. But this process is often inconvenient, be- 
 cause during the time the charcoal is burning away, and the 
 lead becoming oxidized, the glass, which is necessarily in a 
 melted state, is gathering together and thickening, or is con- 
 tracting into inconvenient forms. 
 
 1139. If after the glass has been raised to a full heat with- 
 out any stain, it be brought into the bright, or especially the 
 smoky part of the flame, a part of the oxide of lead is im- 
 mediately reduced and a stain occasioned. This should be 
 immediately rectified and removed as before, but it is far better 
 that it should be altogether avoided. 
 
 1140. The heat produced should not be irregular or patchy, 
 varying with every turn or motion of the glass, but uniform 
 
 * The brightness of the flame depends upon the presence of particles of 
 charcoal ignited in it. See Sir H. Davy on Flame, Quarterly Journal of Science, 
 ii. 124, 
 
480 GLASS -HEATED POWERS OF FLAME. [Sect. XIX. 
 
 all round a certain length of the tube ; the greater the length 
 which by the turning and lateral motions of the tube can be 
 thus retained at a fair uniform red heat, the greater and more 
 efficient is the skill of the operator. To this end it will occa- 
 sionally be found advantageous to incline the tube towards the 
 direction of the flame, and not to hold it directly across. 
 
 1141. After having proceeded thus far successfully, the 
 operator should vary the temperature, and obtain the power 
 of governing it ; sometimes retaining the tube at a low red- 
 heat by carrying it out of the flame ; or raising it to as high 
 a temperature as possible by bringing it into the flame ; or by 
 confining the greatest heat to a narrow ring, or extending it 
 as before mentioned over a broad one. 
 
 1142. By this kind of practice, a knowledge of the heating 
 power of different parts of the flame will be acquired. It will 
 be found greatest within the pale flame just before the point 
 of the bright flame (229), and that part will also heat the 
 greatest quantity of matter. Its power will diminish towards 
 the extremity, though it will still be very considerable and 
 capable of heating a large tube. The current of air which 
 issues from and may be considered as a prolongation of the 
 flame, should also be properly appreciated (234). It has the 
 power of keeping glass at a visible red heat at the distance of 
 two or three inches from the point of the flame, and is of con- 
 stant use in annealing tube and tube apparatus, both in raising 
 and lowering its temperature (1134, 234). 
 
 1143. Besides this examination of the flame in the direction 
 of its length, it should also be investigated laterally, as regards 
 the power it possesses over a piece of tube, placed directly 
 across and through it, compared with that which it exerts when 
 the tube is a little above or below the axis of the cone. 
 
 1144. In this manner every variation produced by ap- 
 proaching the glass in different directions to the hottest part 
 of the flame, may be ascertained and fixed in the mind. The 
 glass worker, instead of varying the temperature of his source 
 of heat, varies the position of his material in relation to it, and 
 thus gains command of all temperatures, up to the highest 
 which the flame can produce. The more perfectly he knows 
 the necessary position, and the more readily he applies his 
 
Sect. XIX.] HEATED GLASS ITS SOFTNESS APPEARANCE. 481 
 
 knowledge and attains the temperature required, the quicker 
 and the better will his operations be performed. 
 
 1145. Besides the difference of heat dependant upon the 
 different parts of the flame in which the glass is placed, much 
 depends upon the size and thickness of the tube itself. It 
 must be a powerful flame, and well managed, that will fully 
 heat an inch in length of the middle of a glass tube two- thirds 
 of an inch in diameter, and the eighth or more of an inch in. 
 thickness. But a tube half an inch in diameter is easily 
 heated ; and when thin, or of much smaller size, care is actu- 
 ally required that it be not brought into the most powerful 
 part of the flame, and become so over heated and soft, as to be 
 unmanageable. Practice alone affords a perfect acquaintance 
 with these points : the size and thickness of tube, the state of 
 the flame itself, and its power in different parts varying almost 
 infinitely. 
 
 1146. The softness of the glass depends upon the tempera- 
 ture to which it is subjected. It begins to soften and bend 
 below a visible red heat, and when in small portions is easily 
 brought to a semi-fluid state. The condition of the glass is 
 judged of as much by the fingers as the eye ; the feeling which 
 the hands appreciate of bending with greater or less facility, or 
 of giving way more or less readily as the ends are pushed or 
 pulled, is a better criterion as to the proper moment of working 
 it than the appearance. Glass, being a transparent substance, 
 does not assume such striking appearances, when ignited to 
 different degrees, as opaque bodies, and its visible red heat is 
 far higher than the visible red heat of metal or charcoal. 
 Hence it is that, if the glass has become stained as above 
 described (1138), those parts will appear red-hot Jong before 
 the glass. Notwithstanding these circumstances, glass when 
 highly heated becomes visibly ignited, and these appearances 
 help, together with the feel, to indicate its state. When of 
 moderate thickness, the glass, in consequence of the oxide of 
 lead that is in it, assumes a greenish yellow tinge when heated ; 
 this occurs before a red heat, and helps with other circum- 
 stances to indicate its state. The experimenter should make 
 himself well acquainted with these indicative appearances. 
 
 1147. When the tube is in a thoroughly heated state, the 
 
 2 I 
 
482 HEATED GLASS HOW SUPPORTED. [Sect. XIX. 
 
 experimenter should bend it ; draw it out so as to render it 
 thinner; and press it up again to increase its thickness. 
 Stopping one end with his finger, and applying his mouth to 
 the other, he should also blow it out and expand it ; and by 
 introducing a smooth piece of thick iron wire into a tube 
 heated at the end, he should observe in what manner it gives 
 way to the pressure, and to what extent it may be moulded 
 (1163). He will find that the glass may be bent as soon 
 as it yields in the hands ; that it must be much hotter before 
 it can be properly drawn out or pressed up again and thick- 
 ened ; and that, generally, the heat must be still higher for 
 blowing and moulding. These comparative but necessary de- 
 grees of softness should be observed and remembered, as also 
 the variations necessary for tubes of different thicknesses ; thin 
 tube is worked generally at lower temperatures than that which 
 is thick. 
 
 1148. The experimenter should also acquire that steadiness 
 yet lightness of hand, and that power of retaining the tube 
 between the fingers, which is necessary to prevent the distor- 
 tion of soft glass. When heating a tube in the middle, it is 
 impossible, whilst all is hard, not to hold it in a straight posi- 
 tion, and any slight irregular strain or pull does no harm. 
 But when the heat has brought the glass into a soft state, it is 
 by no means easy so exactly to turn the tube at both ends 
 alike, and so lightly yet equally to hold them, that the soft 
 part shall retain its cylindrical shape ; being neither twisted, 
 nor bent, nor elongated, nor thrust up. Again, when the end 
 of a tube is heated for an inch or more at once, or when a tube 
 is heated so near the end that it cannot be supported there, but 
 must be sustained from the other end, then the soft glass will 
 tend by its weight to bend downwards. This must be counter- 
 acted by turning round the tube in the hand, so as continually 
 to correct the inclination ; letting the weight of the soft part 
 at one moment rectify the bend it had received the instant 
 before. During this practice it should rather be held with the 
 hot end inclining upwards than downwards, the latter position 
 causing the tendency of the soft piece of glass to draw off and 
 separate from the remainder. 
 
 1149. In these kind of practices is included that of retaining 
 
Sect. XIX.] GLASS HEATED HANDLED COOLED. 
 
 483 
 
 the glass steadily in one particular part of the flame at plea- 
 sure, and not moving it by uncertain motions of the hand from 
 place to place. Very little experience will give a moderate 
 degree of facility in these operations, and will enable a student 
 to make his apparatus in a form adapted for use. Every 
 fresh trial will increase his facility of working, and render his 
 results more perfect. 
 
 1150. Work of this kind should generally be performed at 
 or towards the lower surface of the flame (1143), and almost 
 always be removed out of the flame downwards. By this 
 arrangement the hottest part of the glass is constantly at, or 
 towards, the top of the tube, so that it may be seen ; and 
 consequently the operations whatever they may be, as sealing 
 apertures, or fastening in platina wire, are more conveniently 
 watched. The position of the hottest part of the tube being 
 also constant and known, allows of an advantage in bending 
 or forming the glass, the force necessary being applied in the 
 proper direction with certainty and readiness. 
 
 1151. When the glass has received the required form, it is 
 to be cooled ; this must be effected with some care. It must 
 never be taken directly from the flame and laid on cold bodies, 
 as it is then almost sure to crack. When thin, it is not neces- 
 sary to pay much attention to the annealing, but being brought 
 to the end of the flame or beyond it, and there allowed to fall 
 below a red heat, it may afterwards be laid aside on a tray or 
 across some raised body, as a fragment of tube, that the hot 
 part may be in the air. But if the glass be large or thick, it 
 then requires annealing ; for which purpose it should be car- 
 ried slowly from the hot to the cooler parts of the flame, the 
 appearances and tints being watched, that the temperature 
 may be very gradually lowered; and it should be kept for 
 several minutes in the stream of hot air beyond the flame for 
 the same purpose, being gradually carried to the less heated 
 part of it, and ultimately entirely removed. An instance of 
 the necessity of this kind of annealing has been already pointed 
 out (967). When laid aside it is advisable to cover the 
 cooling glass with a fold or two of paper or cloth, to make the 
 loss of temperature still more gradual. These precautions are 
 the more necessary if the glass varies in thickness, as for exam- 
 
 212 
 
484 GLASS ROD CUT HEATED -FORMED. [Sect. XIX. 
 
 pie, at the junction of one tube with another, or at the end of 
 a tube sealed hermetically ; and they are equally indispensable 
 with the irregularities resulting from the awkward form of a 
 bend, the fusion of wires into glass, or other circumstances. 
 
 1152. The applications of these general directions will be 
 best understood by describing some of the more directly useful 
 operations. One of the simplest of these is that of forming the 
 termination of a piece of glass rod to fit it for use as a stirrer 
 (374). The piece of which it is to be formed is to be cut of 
 a proper length. For this purpose a deep mark is to be made 
 round the rod with the edge of a sharp three-square file, and 
 being then grasped by the two hands placed one on each side 
 of the mark, force is to be applied in a manner similar to that 
 which is adopted in breaking a stick in two, except that in 
 addition the hands are to pull slightly in opposite directions. 
 If the separation be not readily effected, the file-mark must be 
 deepened. Tubes are cut in a similar manner (128, 910) ; 
 such as are small, without difficulty or accident ; larger ones 
 with a little more care. 
 
 1153. When separated by the file, the end of the rod is 
 flat and the edges are sharp. Being heated carefully (1136), 
 because of its thickness, beginning at a little distance from the 
 extremity, it will be found that as soon as the glass has 
 attained a visible heat at the end, the sharp angle at the edge 
 will disappear, yielding to the cohesive force of the particles of 
 glass, which will cause the end to assume a form more or less 
 approaching to roundness. This effect being attained, the rod 
 is to be annealed for a short time, cooled carefully, and is then 
 ready for use. If a conical termination be required (70), 
 then, when the end of the rod is hot and soft, the extremity of 
 a fragment of glass tube should be heated and pressed against 
 it, and will adhere. The rod should then be moved a little, 
 so that the greatest heat may be given at a tenth or twelfth of 
 an inch from the end, and then by withdrawing the fragment, 
 which serves as a handle, the end of the rod will be drawn 
 away with it, leaving the termination of a conical form. When 
 this is obtained, the tail of glass may be separated from what is 
 to be the blunt apex of the cone, by bringing the point of the 
 flame upon it, which causes the thin thread to fuse, and sepa- 
 
Sect. XIX.] GLASS TUBE BENT PRECAUTIONS. 485 
 
 rate, and the portion still remaining on the rod to run together. 
 By retaining the end of the rod in the hot flame, the extre- 
 mity will become more and more rounded ; but when the 
 desired form is acquired, the temperature must be lowered and 
 the glass cooled as before described (1151). 
 
 1154. The operation next in simplicity is bending a tube, 
 requisite for the making of syphons, tube retorts, and in tube 
 operations of all kinds. An unpractised person will effect this 
 most easily with a piece of tube about six or seven inches in 
 length^ half an inch in diameter, and the twelfth or fourteenth 
 of an inch in thickness. Such a piece is easily handled, 
 retains its heat longer than a smaller or thinner tube, and re- 
 quiring more power to bend it, it is for that reason more steady 
 in the hand. Being heated in the manner already described 
 (1134), nothing will be found more easy than to bend it ; but 
 if this be done hastily or inattentively, the bend will be of a 
 bad form ; contracted in its channel ; thin in one part and thick 
 in another ; probably wrinkled and distorted, and then very 
 liable to crack on cooling. 
 
 1155. To avoid these errors, when the glass is uniformly 
 heated for the length of half an inch or more, and to such a 
 degree that it is manifestly soft by the feel, it should be taken 
 out of the flame ; and the two ends being now simply inclined 
 in opposite directions, but without any other tendency by the 
 hand, the glass is to be bent gradually in such a direction that 
 the convex part shall be towards the eye. The operation 
 should be continued until the required degree of curvature or 
 the desired angle formed by the two straight parts is attained, 
 or until the glass from cooling has become too hard to yield ; 
 in the latter case it must be re-heated, and the operation com- 
 pleted. 
 
 1156. The heat in this operation should be nearly uniform 
 all round the glass, that on applying force the parts may give 
 way together, the glass at the convex surface being extended 
 to a certain degree, and drawn out, whilst that at the concave 
 surface is equally but uniformly thickened by its necessary 
 contraction into a smaller space. If the glass be much hotter, 
 and consequently much softer, on one side than the other, 
 weakness or distortion of the bend usually happens, For if 
 
486 GLASS TUBE PRECAUTIONS IN BENDING. [Sect. XIX. 
 
 the hot part be on the convex side, it yields during the opera- 
 tion much more than the stiffer glass on the cooler part, which 
 consequently undergoes but little contraction, whilst on the 
 contrary the soft glass is extended considerably, rendered very 
 thin, and usually assumes a flattened form ; or if the hotter 
 part be on the concave side of the bend, the cooler and convex 
 part will scarcely extend during the operation, the hot glass 
 beneath giving way to the force, and becoming generally thrust 
 up into a sharp fold or into wrinkles ; or if the hotter surface 
 be on one side of the bend, then the glass, yielding more easily 
 on one side than the other, usually acquires an irregular and 
 disturbed form. 
 
 1157. On the whole it is better that the heat should be 
 somewhat greater on the convex than on the concave part, 
 inasmuch as, though it yields rather more than it ought, it is 
 not so readily formed into wrinkles, and also because it cools 
 more rapidly than the concave side. This more rapid degree 
 of refrigeration depends upon the fact, that the glass on the 
 convex side becoming extended and thinner, consequently 
 loses heat faster than the concave part, which, owing to con- 
 traction during the operation, becomes thicker ; this circum- 
 stance may therefore be compensated by a little extra heat at 
 the commencement. 
 
 1158. If the glass be too hot, it gives way so readily 
 during the operation as to assume irregular forms, and some- 
 times, especially in sharp bends, becomes flattened ; the con- 
 vex and concave sides approaching each other, and the lateral 
 portions extending outwards. This particular condition is 
 even useful occasionally, as it prevents the necessity of great 
 extension or contraction of the glass on the convex or concave 
 surfaces ; but an irregular and wrinkled bend should never 
 purposely be allowed, the bore of the tube being preserved 
 nearly as round and free there as elsewhere. If a part be 
 observed on bending to lose its proper form, and to become 
 flattened or wrinkled into folds, from the heat being either 
 too great or irregular, that part should be allowed to cool 
 a little whilst the heat is applied to the neighbouring portions, 
 particularly to such as by contraction on the concave, or 
 expansion on the convex sides, during the continuance of the 
 
Sect. XIX.] BENDING OF GLASS CARE REQUIRED. 487 
 
 operation, are likely to rectify the irregularity of form just 
 commencing. 
 
 1159. Thin and small tube will require much less heat, and 
 generally more care, than that which is thick or large ; but it 
 is the degree of softness which, indicated by the feeling, must 
 principally guide the operator in his proceedings. 
 
 1160. When a considerable bend is to be made, the angle 
 formed by the two arms being very small, as in a syphon for 
 instance, it should not be effected entirely at one particular 
 part of the glass, but a portion having been heated and bent 
 as far as possible, without weakening or distorting the tube or 
 contracting the bore, the neighbouring parts should be heated 
 and the curvature continued until the desired inclination of the 
 two arms is obtained. Small and thick tube may be bent 
 more sharply than large or thin tube, the latter requiring 
 greater extent of curvature for the preservation of the proper 
 form. 
 
 1161. When, during the operation of bending, different 
 parts are to be heated and bent in succession, it is best to 
 begin the operation at one end of that part over which it is to 
 extend, and gradually proceed from it to the other end. By 
 thus proceeding the operator may contrive, when one part is 
 heated and ready to be curved, to remove it sideways from the 
 flame, so as to bring the next portion into the heat, which will 
 then be acquiring temperature whilst the former part is bend- 
 ing, and in consequence of its previous high temperature 
 resulting from mere vicinity, will soon be in a properly heated 
 state. This transition, as it were, of the tube through the 
 flame, must not take place irregularly, but gradually, the 
 heating and bending going on without interruption, and over 
 successive portions of the tube, at the same time. A clear 
 idea of the manner in which this is to be done, and very use- 
 ful first practice, may be easily acquired by using a spirit-lamp 
 flame without a blow- pipe, and drawing a piece of quill 
 tube through it so gradually, that the part in the flame shall 
 be heated red hot before leaving it. It will then be found 
 that by giving lateral pressure on one end of the tube the 
 parts will be bent and curved in succession as they become 
 
488 BENDING OF GLASS GLASS MOULDED. [Sect. XIX. 
 
 heated, and fixed as by their motion onwards they become 
 cooled. 
 
 116*2. When the flexure is required so near the end of a 
 piece of tube as to render it impossible to hold the shorter side 
 with the fingers, the force required must be given by pressing 
 against the end with a piece of wood or another piece of glass 
 tube. But if the bend is to be continued to the very extremity, 
 then wood or glass will not answer the purpose, for the first 
 would burn or soil the tube, and the last melt and adhere to 
 the heated part. 
 
 1163, In such cases cold metal, as a metallic rod, is the best 
 adapted for use, but it should be applied only at the moment 
 when pressure is wanted, and never be retained so long in con- 
 tact with the hot glass as to reduce its temperature below the 
 point of softness ; for as soon as the glass becomes solid the 
 cold metal would crack it. For the same reason, metal should 
 not be used in the cases where wood and glass have just been 
 recommended, as it would probably crack the hot but solid 
 part of the glass. Whenever cold metal is brought into con- 
 tact with glass for the purpose of moulding or working it, the 
 glass should be hot, and not be allowed to cool to its point of 
 hardness. The metal itself should always be cold in such 
 cases, or at least not very hot, otherwise it will adhere to the 
 glass and cause injury ; neither should it be small, like a wire, 
 lest the glass itself should communicate so much heat as to 
 cause its adhesion. If the metal be hot, and the glass below 
 its soft point, they may be brought together without risk of 
 fracture to the glass. 
 
 1164. Quill tube, as has been already remarked, may be 
 bent in the flame of a spirit-lamp. It may also be bent over 
 the glass of an argand lamp in good combustion. Larger 
 tubes may be curved over a charcoal fire, either in the crucible 
 furnace (157), or arranged on a piece of metal plate. Their 
 flexures are large and gradual, not so short and sharp as 
 those effected by the lamp and blow-pipe. Cooper's lamp 
 furnace (710) is a very excellent instrument for softening con- 
 siderable lengths of tubes when the bend required is to be 
 very gradual and extensive. The tube should be continually 
 
Sect. XIX.] TUBES CLOSED. 489 
 
 moved in the flame, both with a lateral and rotatory motion, 
 until uniformly heated to a sufficient degree. 
 
 1165. The next operation to be described is equally useful 
 with the last : it is that of closing the extremities of tubes so 
 as to shut up one end and form those useful vessels (127, 
 910) already often referred to. This operation is most readily 
 performed with a piece of straight tube, open at both ends, 
 and long enough to make two closed tubes. Let it be there- 
 fore supposed that a piece of tube, such as that before men- 
 tioned (1154), is now to be formed into two tubes, each closed 
 at one extremity. 
 
 1166. The piece of tube is first to be heated in the middle ; 
 but in place of endeavouring to extend the heated part as far 
 as possible, it should rather be contracted into a narrow ring 
 (1141). The hands are then to be separated, the glass being- 
 pulled in the direction of its length, when it will be found to 
 elongate, and at the same time contract in diameter at the hot 
 and soft part. Some degree of management in the heat is now 
 required. If it were still to be urged upon the middle of the 
 contraction, and the pulling force also continued, the tube 
 would suddenly be divided into two parts with irregular, long, 
 and pointed terminations. For as the glass is drawn out, and 
 the diameter as well as thickness diminished, the flame acts 
 upon it as if it were a smaller tube ; the smallest part is con- 
 sequently always hottest, it yields most readily to the force 
 applied, and thus the hasty and imperfect result mentioned 
 would be obtained. If on the contrary, to avoid this, the glass 
 were moved so that the flame fell upon and heated the portions 
 at the side, then their softness might be made to surpass that 
 of the contracted part of the tube, and the pulling would 
 merely tend to elongate and contract this part also, and so to 
 reduce the whole of the tube to portions of tube of greater 
 length but smaller diameter. 
 
 1167. It is an effect between these that the operator should 
 produce. As soon as the glass yields to the pull, and in pro- 
 portion as the diameter -diminishes, he should relax the force 
 so as to apportion it to the softness of the glass, and proceed 
 gradually with the operation ; he should at the same time move 
 the glass towards the extremity of the flame, and even out of 
 
490 TUBES CLOSED PROGRESS SUCCESSIVE STATE. [Sect. XIX. 
 
 it, that he may be able to moderate the heat and apply it prin- 
 cipally to a small surface. He should no longer endeavour to 
 keep the two pieces of glass of equal form, but using one as an 
 adjunct, turn all his attention to finishing the extremity of the 
 other, which probably will be that in his left hand, because 
 the piece in his right hand becomes the tool with which he 
 works, and which is thus most adroitly used. Directing there- 
 fore the point of the flame upon what is to be the bottom 
 a of the closed tube, a little above 
 
 the thinnest part, but still not so 
 much above as to render the 
 thicker part the softest, let him 
 carefully retract his right hand, 
 by which operation the narrow 
 part will become more and more 
 attenuated, and finally, when 
 capillary, fuse and separate. The 
 end of the tube will be left closed 
 of a round form, with probably a little knob of glass at the 
 middle of the bottom, whilst the other piece will be drawn out 
 rather irregularly though closed also at its extremity. The 
 accompanying wood -cut illustrates the successive changes in 
 the form and appearance of the tube ; the part to which the 
 greatest heat should be applied, being pointed out by the 
 lines a a a. 
 
 1168. The tube is seldom perfectly finished by this opera- 
 tion. To complete it, the knob of glass at the end, if small, 
 and the whole of the bottom of the tube, should be heated 
 until the glass is soft. Then applying the open end of the 
 tube to the mouth, and propelling air into it with a degree of 
 force proportionate to the heat of the glass, it will yield (1194), 
 the knob expanding more than any other part, because of its 
 higher temperature, and of its continuing for a greater length 
 of time in a soft state. In this manner, by a little address, 
 the knob may be made to disappear, and the bottom of the 
 tube to assume a regular round form (127, 142), and a thick- 
 ness nearly equal in every part (1198). 
 
 1169. If the knob be so large and clumsy in consequence 
 of the partial failure of the first operation, that if heated so as 
 
Sect. XIX,] 
 
 FINISHED THICKENED. 491 
 
 to run up and make part of the bottom of the tube, it would 
 cause the formation of a very thick portion of glass there, then 
 it must be removed. For this purpose it is to be heated, and 
 a piece of waste glass, previously warmed in another part of 
 the flame while held in the right hand, applied to it : then 
 directing the point of the flame above the junction and against 
 the part intended for the bottom of the tube, the glass should 
 be melted, the thick clumsy knob drawn off, and a fresh closing 
 of the tube effected and finished as before. Or if from want 
 of practice the end of the tube be irregular, misshapen, and 
 altogether bad, then after attaching the piece of waste tube, 
 which serves as a tool, the heat is to be applied a little way up 
 the tube, the glass softened in another place as near to the first 
 as possible, and the operation recommenced ; the piece of glass 
 at the end being drawn off and managed by means of the frag- 
 ment of tube which had been attached to it for the occasion. 
 
 1170. If the end of the tube when finished be thin, it should 
 be raised to a red heat, with a little of the neighbouring 
 thicker part, when it will gradually contract and thicken, and 
 it may thus be made of equal strength with the sides of the 
 tube. Its thickness must be judged of by inspection, in the 
 manner formerly described (372). On the contrary, if it be 
 too thick, it may be rendered thinner by being blown out as 
 mentioned above (1168). The precautions requisite in doing 
 so will be immediately described (1194, 1198). 
 
 1171. Having finished one of the tubes to be formed out of 
 the original piece, the other which had been laid down is to be 
 resumed and completed. For this purpose, when held in the 
 left hand, the point of the flame is to be directed as before 
 mentioned upon that part of the contracted termination, which 
 is to form the bottom of the tube, and when soft the tail of glass 
 is to be drawn off in the manner just described for removing 
 a knob (1169). The tube is then to be finished according 
 to, the directions already given (1168). 
 
 1172. When the piece of tube to be operated with is thin, 
 the extent of surface heated at first must be greater, and the 
 operation carried on more carefully, than is necessary with 
 thicker tube. For if a small extent only be heated, and then 
 drawn out quickly, the glass becomes so attenuated, that when 
 
492 THIN TUBES CLOSED THICKENED. [Sect. XIX. 
 
 very hot it will of itself run into holes, or if it remain undi- 
 vided, will form a bottom to the tube, so thin that it will not 
 be safe to trust such a vessel for an experiment, lest a slight con- 
 cussion should break it. In this case, after the tube is partly 
 drawn out and its diameter contracted, the heat should be 
 raised considerably but uniformly round the thin narrow part, 
 and the glass being retained in an undisturbed state, should be 
 allowed to draw together and thicken (1179). When that has 
 taken place to a sufficient degree, it is again to be drawn out, 
 and if a second time it become too thin, it must be thickened 
 as before : in this manner the operation must proceed, until 
 the bottom is closed and completed. 
 
 1173. When a piece of tube is too short to be formed into 
 two tubes, it must be sealed at one extremity an operation 
 often required for other purposes. In these cases the end to 
 be sealed must be heated carefully (1137), the tube being 
 inclined a little with the heated aperture towards the direction 
 of the course of the flame, that the force of the blast may not 
 throw hot air into and along it, and burn the hand at the other 
 extremity ; and in some cases also that the products of the 
 combustion may be prevented from entering the tube and 
 affecting the substances already placed within it (1184). When 
 the end is soft, a piece of waste glass tube is to be held in the 
 right hand, and its extremity used to press the sides of the 
 hot end together, and when three or four places on the edge 
 have been thus made to approach each other, the end of the 
 spare tube is to be attached to them, and the heat being raised 
 a little above the termination, the piece is to be drawn off and 
 the operation proceeded with exactly in the manner already 
 described (1167, 1169). 
 
 1174. When a piece of tube is too short to be held by the 
 fingers during the operation because of the heat, a cork, square 
 or of irregular form, that it may not close the tube perfectly, 
 should be put into the mouth to serve for a handle, by which 
 it may be conveniently held (918) ; even a plug of paper or a 
 piece of wood will answer the same purpose. 
 
 1175. The information given relative to glass-blowing will 
 enable the student to make much of the apparatus already 
 referred to. Tube retorts (934) are made by first closing the 
 
Sect. XIX.] TUBE RETORTS RECEIVERS CAPILLARY TUBES. 493 
 
 end of a piece of tube, and then the parts representing the 
 body and the neck are to be separated by a bend more or less 
 sharp, according to the intended application of the vessel. In 
 the same manner are the tubes necessary for the condensation 
 of gases to be made (962). Syphons (550) are made merely 
 by bending glass tube ; or if their apertures are to be con- 
 tracted, the proceeding is the same as that necessary in the 
 first part of the process for closing a tube (1167), the opera- 
 tion being carried no farther than to lessen the diameter : that 
 done, the glass is to be allowed to cool, and the narrow part 
 is then to be cut by a file (1152). 
 
 1176. If when the glass tube is heated all round and much 
 softened, the parts be pulled asunder quickly, and not in the 
 guarded manner already advised, then instead of a mere con- 
 traction of a small portion of the tube to two-thirds or one- 
 half its first diameter, it will become extended and capillary ; 
 and the two portions of the tube held by the fingers, thus 
 connected, will be found to contract in diameter for the space 
 of half an inch or an inch, gradually becoming capillary. 
 This operation is frequently useful in the preparation of capil- 
 lary tubes for various purposes, as in the contraction and elon- 
 gation of the ends of glass retorts or other similar apparatus 
 (463, 559) ; and in making tube funnels (924), syringes, 
 (560), &c. It should always be performed in the air, and 
 not in the flame of the lamp, unless the operator be very 
 expert : when the glass therefore is heated, it is to be removed 
 from the flame and drawn out. 
 
 1177. The greater the heated portion of glass, the longer 
 will be the tube thus formed. Its length and fineness also 
 increase with the rapidity with which it is drawn, and with the 
 temperature given to it in the first instance. The velocity with 
 which the hands should separate, is most generally useful at the 
 rate of about a foot in a second. The thickness, length, and 
 general character of the capillary tube produced is also consi- 
 derably dependant on the kind of tube out of which it is made : 
 the relation of the diameter to the thickness of the glass will be 
 nearly the same in the tube both before and after it is drawn out. 
 
 1178. When a contracted tube is required too long to be 
 made at once, then having drawn one length, the original tube 
 
494 CAPILLARY TUBES TERMINATIONS FUNNELS. [Sect. XIX. 
 
 is again to be heated so near to the part already drawn, that, 
 when extended, only a little swelling or bulb may intervene 
 between the capillary portions. It is not safe to endeavour to 
 heat the tube so near to the already extended part, as on 
 drawing it out to make one tube with the latter without irre- 
 gularity ; for, owing to its delicacy, the previously extended 
 part will almost certainly give way: no difficulty occurs in 
 afterwards softening and drawing down the small expansions ; 
 for by making use of a little spirit-lamp flame (205), placed 
 under the bulbs, they are soon raised to a red heat, and then 
 by careful management are easily drawn down. 
 
 1179. When the ends of retorts or other tube apparatus 
 are to be thus reduced in diameter (463), they should not be 
 drawn out more than is necessary, but left with sufficient 
 strength to resist the slight mechanical accidents to which they 
 are liable in the course of experiments. The same remark 
 applies to such vessels as the small receivers or retainers re- 
 commended for scarce fluid (928). If the neck of the retort, 
 or tube, to be drawn out be thin, it is for the same reason 
 advantageous to thicken the part before it is extended (1172), 
 for which purpose the glass must be softened in the flame, 
 and retained at a high temperature for some time, and rather 
 thrust together than pulled out ; in this manner the thickness 
 of the glass may be nearly doubled, and consequently the 
 capillary tube resulting from its linear extension rendered 
 stronger. 
 
 1180. When capillary tubes are drawn for air-gauges 
 (1369)? several should be made of different diameters, thick- 
 nesses, and lengths, and the most advantageous afterwards 
 selected. 
 
 1181. The same proceeding, with slight variations, is suf- 
 ficient for the production of several kinds of useful apparatus. 
 A tube funnel (924) is made by elongating a piece of tube in 
 this manner, at about an inch from the end, and then sepa- 
 rating it, leaving the short piece with so much of the capillary 
 tube attached to it as will form a funnel of sufficient length. 
 Tube syringes of various kinds, for the removal of azotane, 
 washing of precipitates, &c. (547, 560), and the tubes recom- 
 mended as being useful in estimating volumes and in mea- 
 
Sect. XIX.] SYRINGES SEALING OF TUBES. 495 
 
 suring (130, 139), are made with equal facility. When the 
 end of a piece of tube is heated and drawn out, a form more 
 or less acute may be given to the termination, which being cut 
 so as to leave an aperture of the proper size, is only to be 
 held for a moment in the flame to soften and obliterate the 
 edges (1153), and a very good syringe body is formed. A 
 little tow wrapped round the end of a wire and moistened, 
 forms an effectual piston, and thus an instrument of great use 
 in numerous operations is quickly made. If it be required 
 that the termination of the syringe should pass off obliquely, 
 it is effected by drawing out the tube in that direction when 
 hot. 
 
 1182. In the same manner the separator delineated (559) is 
 made, by drawing off' the end of a piece of tube so as to form 
 a moderately stout capillary continuation, and then bending 
 this upwards as in the figure. The gas tube, for conveying 
 products into small tube receivers (448, 463), is made by 
 drawing out the end of a tube until of capillary dimensions, 
 and then bending it downwards. 
 
 1183. It is very frequently necessary with tube apparatus 
 to seal apertures hermetically, so as entirely to close the vessel, 
 and make it continuous in every part. This process resembles 
 that by which one end of an open tube is sealed (1173), so far 
 as regards softening the glass, bringing it together, contracting 
 the aperture, and ultimately closing it ; but it differs very 
 much in other circumstances, dependant upon the state of the 
 interior of the vessel. In the open tube the glass is equally 
 pressed on both sides ; but that is rarely the case in the closed 
 tube, a tendency of the contents to pass outwards, or of the 
 air inwards, almost always occurring. 
 
 1184. The simplest case of the kind is, where solid fixed 
 matter is to be confined in a tube for the purpose of preserving 
 it, in the manner already spoken of (974). The included 
 substance then sends off no vapour, and all that is to be 
 guarded against is, the expansion and contraction of the air 
 within by the variations of temperature. Suppose the tube 
 closed at one extremity, and that one-half or two-thirds of it 
 is filled with the substance; care should be taken that the 
 latter does not rise so near to the upper part of the tube as to 
 
496 TUBES SEALED DRAWN OUT CLOSED. [Sect. XIX. 
 
 be affected by the heat, especially if it be an easily fusible or 
 changeable body. The top of the tube when brought towards 
 the flame should be inclined (1173), that the products of the 
 combustion may not enter it ; and the bottom should be in- 
 clined downwards, that the contents may not fall towards the 
 heated part. The upper part, being heated, should be drawn 
 out and contracted, precisely as if it were the end of an open 
 tube that was to be closed, except that the glass generally 
 should be retained as thick (1172) as it will be required when 
 finished, in order that the capillary tube may be of considerable 
 comparative thickness, and that an aperture for the air through 
 
 the middle of it may be preserved 
 the whole time. The wood-cut 
 will illustrate this state of the tube. 
 No difficulty will be found in direct- 
 ing the heat about a, in drawing off the end piece, and in 
 leaving the tube sealed, for the glass will readily coalesce at 
 the moment of separation; but the object is to make this end 
 as strong as any other part of the tube, and of a form similar 
 to that of the opposite extremity ; for effecting this, the fol- 
 lowing explanations and precautions will be found useful. 
 
 1185. Supposing the piece drawn off and the end closed ; 
 the glass is so hot and soft at the moment, that if from an 
 accidental contact of the flame any part of the tube becomes 
 hotter than before, the air within will expand, the glass will 
 be blown out into a thin bubble, which, breaking even by the 
 mere pressure of the atmosphere as the tube cools, will leave a 
 large hole. It will now be more difficult to close the tube 
 than before the extremity was removed, for the sides of the 
 aperture must again be collected together and drawn off, and 
 a capillary neck again formed. 
 
 1186. This may be avoided by purposely heating the upper 
 part of the tube just before sealing it hermetically, so as to 
 expand and expel the air from within; then, removing the 
 flame and applying it to the capillary neck as the general tem- 
 perature of the tube sinks, the piece is to be drawn off, and 
 the aperture sealed, and as the pressure is inwards rather than 
 outwards, the glass will be pressed in the former direction. 
 This is in fact the method to seal the tube strongly, and to 
 
Sect. XIX.] SEALING OF TUBES 'CASUALTIES. 497 
 
 make it of a desirable shape, but it is subject to an accident, 
 which to be avoided must be known. If the glass at the end 
 has been left thin, and it be heated until perfectly soft, the 
 pressure of the external air will frequently force it inwards, 
 sometimes into a decided bubble, or else into various wrinkled 
 and irregular forms, which, when cold, are almost sure to 
 crack in numerous directions. 
 
 1187. These accidents are avoided by making the end of 
 the glass and the capillary neck of considerable comparative 
 thickness, which is done by allowing the glass to gather itself 
 up when in a fluid state (1172, 1179), and also when warming 
 the tube to expel a part of the air, by not raising the tempe- 
 rature too much ; then, upon proceeding to soften the neck 
 and seal the extremity, the flame should be directed rather 
 generally to that end of the tube in such a manner, that, the 
 whole being softened, the apex shall still be retained at the 
 highest temperature. In this way it will be easy by a little 
 practice to make the external pressure effectual in forcing in 
 the end of the glass generally, and causing it to become alto- 
 gether thicker and stronger, instead of having a small portion 
 suddenly blown inwards, and the whole rendered irregular. 
 Or if, by too long a continuance of heat, the air within begins 
 to expand, still, as all the glass at the end is of equal soft- 
 ness, the whole will gradually enlarge outwards; an effect 
 which will be immediately perceived, and the operation may 
 be stopped before any inj ury is occasioned. 
 
 1188. When the tube contains a fluid instead of a solid 
 body, the care required is greater, and must be proportionate 
 to the volatility of the substance. A fixed fluid, if alone, 
 merely requires to be retained in the lower and colder part of 
 the tube, away from the end to be sealed. Sudden motion 
 should be avoided, lest drops be thrown upon the cold part, 
 and cracks be occasioned : during cooling, the tube should 
 also be placed steadily with its heated end uppermost (930). 
 There are particular cases in which great care is necessary to 
 prevent disturbance of the contents of the tube. Such are the 
 experiments upon the condensation of gases (962), in which 
 the strength, uniformity, and annealed state of the end her- 
 metically sealed, are essentially necessary. 
 
 2 K 
 
498 SUBSTANCES CONFINED IN TUBES. [Sect. XIX. 
 
 1189. If the substances to be confined are volatile, but yet 
 like alcohol, ether, chloride of sulphur, &c. have their boiling 
 points not lower than 100 or 150, then additional precautions 
 will be needful : these apply particularly to the moment when 
 the capillary neck is to be finally drawn off and closed, and 
 the end thickened and made strong. The effect of heat upon 
 tubes with such contents, is not only to expand the air within 
 them, but also to increase its bulk, by raising and mixing with 
 it the vapour of the substance. The formation of this vapour, 
 and consequently the tendency of the gaseous matter within to 
 expand, is not simply in proportion to the heat of the end of 
 the glass tube with which the vapour is in contact, but de- 
 pends also upon the heat communicated to the fluid beneath. 
 This effect is produced more slowly than the former, and may, 
 in the hands of an inexperienced person, lead to confusion. The 
 temperature of the glass near the end may be actually falling, 
 and may lead to the expectation of a diminution in bulk of the 
 gaseous or vaporous matter within, and consequently of a 
 pressure from without inwards, whilst at the same time the 
 temperature of the fluid may be rising by contact with the 
 neighbouring hot or warm glass, and may cause an increase in 
 the quantity of vapour given off, and upon the whole a ten- 
 dency of gaseous matter to pass out of the tube ; which not 
 being anticipated would spoil an experiment (930). In these 
 cases the upper part of the glass (1186) should be heated so 
 as to expand the gaseous contents a little, and at the moment 
 the capillary neck is drawn off, and the aperture closed, a 
 piece of moistened bibulous paper should be applied round the 
 part of the tube containing the fluid, and if the substance be 
 very volatile, even a little higher up though not to the heated 
 part of the glass. This will prevent any further elevation of 
 temperature in the fluid, and the end may be safely heated 
 and thickened (1185), in the manner already described for 
 tubes containing solid bodies. 
 
 1190. When the aperture to be sealed is small, and at the 
 end of a capillary tube, as in the vessels described (929, 934, 
 935), nothing more is required than to hold it in the flame of 
 a lamp or candle, when the glass will fuse and coalesce. Or 
 if the end be broken and rather wide, the part softened by 
 
Sect. XIX.] PRECAUTIONS CAPILLARY TERMINATIONS. 
 
 499 
 
 heat should be touched with another piece of glass, 'and 
 be drawn out and sealed as before (1184). In these cases 
 when sealed, the glass is to be removed from the flame, and 
 not suffered to run into a little ball, which would generally 
 break off when cold, or after an interval of three or four days. 
 
 1191. When substances so volatile as to boil almost at 
 common temperatures are to be sealed up, the tubes containing 
 them must be cooled by refrigerating mixtures. This pre- 
 caution has been described as it respects sulphurous acid, and 
 the description will illustrate the process for similar substances 
 (930). The only additional remark here necessary is, that if 
 the fluids are to be preserved as specimens, the capillary neck 
 should be of considerable thickness, and when effectually 
 sealed, whilst the tube is in the frigorific mixture, should not 
 afterwards be altered, nor should any attempt be made to give 
 it more thickness, or a better form. A spirit lamp and mouth 
 blow-pipe is more convenient for softening the capillary necks, 
 and sealing these tubes, than the table blow-pipe. 
 
 1192. When the object is merely to close the ends of capil- 
 lary tubes (929), it is easily effected, the tubes being cooled at 
 the same time. When the fluids are of such volatility as to 
 cause only a feeble stream of vapour from the aperture of the 
 vessel, (and several such may be found amongst the substances 
 held in vapour in oil gas,) the cohesive force of glass is suffi- 
 cient to cause it to run together when softened, and to seal the 
 orifice, even though there be a slight pressure outwards. For 
 this purpose the end of the capillary tube is to be intro- 
 duced into the flame, and being touched with another piece of 
 glass, the extremity is to be drawn off, and at the same time 
 sealed : at the instant of doing this it is to be removed from 
 the flame, that it may cool and solidify, lest the heat of the 
 lamp or hand should increase the tension of the vapour, and 
 cause such pressure outwards as would be sufficient to expand 
 the soft glass. 
 
 1193. The process of sealing tubes hermetically, which 
 j)ave previously been exhausted of air, requires certain pre- 
 cautions to prevent the pressure of the atmosphere from either 
 making an entrance, or forcing in the glass. Suppose it were 
 necessary to enclose some camphor hermetically in a tube 
 
 2 K 2 
 
500 EXHAUSTED TUBES SEALED HERMETICALLY. [Sect. XIX. 
 
 exhausted of air, that certain of its habitudes as to vaporization 
 and crystallization under such circumstances might be ob- 
 served. A tube of sufficient length is to be selected, and being 
 closed at one end, the camphor is to be introduced ; the tube 
 should then be heated at about an inch from the open extre- 
 mity, and should be contracted and thickened in the manner 
 described (1172, 1184), so that the smallest part may be about 
 half an inch in length, about one-twelfth of an inch in internal 
 diameter, and one-third of an inch in external diameter. A 
 retort cap is to be cemented upon the open extremity (834), 
 and a stop-cock attached to it. This being done, the tube is 
 to be connected with the air-pump and exhausted, and the 
 stop -cock being closed, the tube is to be removed from the 
 pump in its exhausted state. The small flame of a spirit-lamp 
 is now to be applied to the middle of the capillary part, so as 
 to heat it gradually all round; as the glass softens the pressure 
 of the atmosphere will make it collapse and become solid, the 
 passage will be obliterated, and the tube will be converted into 
 a rod. This done, the heat is to be applied more immediately 
 to the middle of the solidified part, which, when it has become 
 soft, is to be drawn asunder. No difficulty will be found in 
 doing this, without letting in the smallest portion of air, and 
 if proof of the accuracy of the process be required, it may be 
 obtained to a certain degree by plunging the piece attached to 
 the stop-cock under water, and breaking off the point there ; 
 if the water should enter in such abundance as to fill this piece, 
 it will shew that no common air has entered by the stop-cock, 
 and the appearances will sufficiently indicate whether air has 
 entered or not at the part heated. No attempt should be 
 made to thicken, or in any way bring into form, the sealed end 
 of the exhausted tube ; for the pressure of the air will be 
 almost certain to force in the softened glass, unless the operator 
 be indeed very skilful. 
 
 1194. A more delicate operation than any yet described, 
 and one that requires considerable practice for its performance 
 with even moderate success is, the blowing of bulbs and other 
 expansions, either in the middle or at the end of a tube. 
 Facility will be best obtained by practising with a piece of 
 tube about nine or ten inches in length, one-third of an inch 
 
Sect. XIX.] GLASS BULBS BLOWN- CARE REQUIRED. 501 
 
 in diameter externally, and one-tenth of an inch in internal 
 diameter. The end is first to be closed ; and then about two- 
 thirds of an inch in length of the closed extremity is to be 
 uniformly heated, until so soft as to bend from side to side by 
 its own weight. The aperture is immediately to be placed 
 between the lips, and by means of the mouth (222, &c.), air 
 is to be propelled for the purpose of expanding the soft glass. 
 This must be done quickly but cautiously ; and as soon as the 
 eye, which must be constantly fixed upon the heated end, per- 
 ceives enlargement there, the force exerted by the mouth 
 should be slightly diminished, and the operator should hold 
 himself ready for its instantaneous cessation. For if the 
 power which expands the glass at first be continued in full 
 force, the glass will suddenly burst out into a large irregular 
 thin bubble of no use. This follows as a natural consequence, 
 for every enlargement of the bubble diminishes its thickness, 
 and consequently its resistance, and at the same time increases 
 its internal area, and in that respect increases the power of the 
 air impelled into it ; and if the enlargement take place quickly, 
 so that the glass has not time to cool, it cannot but happen 
 that the bubble should expand to a large size. To avoid this, 
 air should be thrown in from the mouth only (223), and not 
 from the lungs : as the glass expands, the force with which 
 the air is impelled should be diminished ; and the operator 
 should not endeavour to finish the bulb at once, but having 
 succeeded in expanding it to such a size that the internal 
 diameter is five or six times the thickness of the glass, he 
 should heat it again, and complete the bulb at a second 
 operation . 
 
 1195. The glass must never be blown whilst it is in the 
 flame, it being impossible to make it retain an uniform tempe- 
 rature there, but is always to be expanded in the air : as it 
 swells it must be continually turned, and those parts which 
 are thinnest brought to the lowest position ; they are easily 
 recognised by their sudden expansion, by a greater degree of 
 transparency, and a peculiar reflection from them different 
 from that of the neighbouring parts. They are directed to 
 be brought into the lowest situation, because the glass in that 
 position cools most rapidly, and consequently its further ex- 
 
502 TUBES EXPANDED TERMINATED. [Sect. XIX. 
 
 tension is prevented. The operation must be quick to be 
 good, for the temperature of the thin glass is so soon lowered, 
 that it cannot be done at all if not rapidly. The bulb when 
 finished should be round, set straight on the end of the tube, 
 of uniform thickness at the bottom and sides, and without 
 lumps or knots. The size will vary with its thickness and the 
 quantity of glass heated. 
 
 1196. These operations may then be repeated with tubes of 
 different sizes. If their internal diameters are much smaller 
 than that mentioned, as in barometer tubes, the end may be 
 heated until almost solid, and even thrust up into a lump. 
 This being uniformly ignited, should be blown until the air 
 just begins to expand into a small bubble at the end of the 
 bore, and then the temperature of the glass being well raised, 
 it should be blown out into a bulb at once, being turned in the 
 air as before directed during the operation. It will be under- 
 stood from what has been, said (277, 1252), that these bulbs 
 will not serve for thermometers, because of the moisture they 
 receive from the air thrown in by the lungs ; but they are 
 useful in the practice they afford, and for numerous experi- 
 mental purposes. 
 
 1197. Sometimes an expansion is required in the middle of 
 a tube (558, 957), and the operation in general resembles that 
 just described. If the end of the tube be closed, the glass 
 merely requires to be thickened and heated at the part to be 
 blown out, and then expanded by the breath. If it be not 
 closed at either extremity, then the finger or a cork must be 
 applied to one end to close it, and the proper part being heated, 
 the. lips are to be applied to the other end, and the expansion 
 made. 
 
 1198. A little practice of this kind will soon enable the 
 student to remove the knots at the ends of his closed tubes 
 (1168), and make their terminations perfectly round, and 
 uniform in thickness. By similar trials he will succeed per- 
 fectly in forming the little vessels formerly referred to (97), 
 some of which are blown out of small tubes, whilst others may 
 often be made without any blowing at all. For this purpose 
 it is only necessary to take a piece of tube of the proper 
 diameter, or if too large at first it must be drawn down to the 
 
Sect. XIX.] BULBS FOMED TUBES JOINED. 503 
 
 diameter required (1166), and contracting one part into a neck 
 of such width as is necessary to be given to the intended 
 vessel (1167), the flame is afterwards to be removed 
 further down, to fuse the glass, which is to be contracted, 
 drawn out, and closed. In this way the body of the 
 vessel is obtained of any required capacity, according to 
 the length given to the piece of tube forming it ; or by 
 warming the body and then blowing it, it may be ex- 
 panded until of much larger size. The flask is afterwards 
 
 to be separated from the remaining piece of tube, either by 
 
 cutting it with a file (1152), or drawing it off at the lamp to a 
 
 fine termination, if required. 
 
 1199. The bulbs referred to (76, 110) are made in a similar 
 way. A piece of small tube is to be drawn out, closed, and 
 the end rounded. The end of the piece of tube drawn off is to 
 be melted in the lamp, and suddenly applied to the extremity of 
 the tube just closed, which, if at a temperature below the soft 
 point of the glass, will allow of its adhesion in a manner suffi- 
 ciently strong to bear the force required in working and finish- 
 ing the vessel, yet so slight, that a feeble tap or blow will 
 readily cause its separation. So arranged, the glass tube is to 
 be heated a little way from the end, that a sufficient length of it 
 to form the bulb may be drawn away by the attached fragment, 
 and finally hermetically sealed in the manner already described 
 (1190). When cold it is to be tapped against the table ; it 
 will then separate from the waste piece of glass which pre- 
 viously supported it, and will be ready for use. 
 
 1200. Two pieces of tube are sometimes to be melted toge- 
 ther so as to form one, with a continuous bore ; and pieces of 
 the same, or of very different thickness, may, if necessary, be 
 joined. The ends should be straight, and of nearly equal 
 diameter, so as to apply almost accurately against each other. 
 If they are not so at first, the extremity of the larger one 
 should be contracted until they become so. They should be 
 brought into the flame so as to be raised separately, but at the 
 same time to a good heat, that the glass may be quite soft ; 
 and then the ends, being applied to each other, should be 
 pressed together in the flame, until the glass adheres in every 
 
504 WIRES SEALED INTO TUBES. [Sect. XIX. 
 
 part, and runs up into a ring round the tube. The ring 
 should be immediately drawn down again, unless it be perma- 
 nently required, and then by working the glass in the flame, 
 the joint should be brought into a good shape and condition. 
 If, during the operation, the tube contracts, it should be 
 blown out (1197) ; if it become thin, it must be thickened 
 (1172) and pushed up ; if it be thickened too much, it must 
 be pulled out and rendered thinner, the contraction of the 
 diameter occasioned by doing so being rectified by expanding 
 the glass again (1197). The joint, when finished, should not 
 be of imperfect adhesion at any part, or distorted in form, or 
 involve any great irregularity of thickness, for then it will 
 almost certainly fly asunder when cold. Small irregularities 
 may be allowed to remain, and if the glass be well annealed, 
 will do no harm. 
 
 1201. It is of great importance in many experiments to be 
 able to seal a metallic wire into glass, so that the latter shall 
 close round it and adhere to it, in a manner perfectly air-tight 
 and sound. The detonating eudiometer tubes (994), and the 
 tubes for the collection of gas (1046, 1049), during the voltaic 
 decomposition of liquid substances in solution, are common 
 instances of their valuable application. Platina is the only 
 metal which answers well for this purpose, and fortunately it is 
 that which, in consequence of its chemical relations, is the most 
 useful in such situations. The superiority of platina depends 
 upon its infusibility at the temperatures required to work the 
 glass, and on the close agreement of glass and platina, in the 
 rate of their expansion and contraction by changes of tempera- 
 ture. Other metals, as iron, differ much from glass, and when 
 wires of these are inclosed in the most secure manner, they 
 either separate when cold from the glass, by contraction, 
 destroying the continuity all round them, or, if that does not 
 take place, they retain the glass in the immediate neighbour- 
 hood in such a state of tension, that very slight accidents cause 
 it to fly, and cracks to proceed from the wire into the glass in 
 several directions. This rarely happens with platina inclosed 
 in the thickest glass, if the junction has been good, and the 
 glass well softened. 
 
Sect. XIX.] PROGRESS OF THE OPERATION. 505 
 
 2. Suppose a tube like that figured (1050) be required, 
 with a platina wire passing through it, and hermetically sealed 
 into its summit. A piece of tube of the required diameter, 
 thickness, &c., is to be selected, and also a piece of clean 
 platina wire : the tube should be heated at the part where it is 
 to be closed, and should be drawn out so as to form a capillary 
 neck (1172, 1184), the end of the tube and the neck being 
 preserved of considerable comparative thickness, so that no 
 occasion for afterwards increasing it shall exist. The neck 
 should be of such internal diameter as freely to receive the 
 wire, but no more, and, when cold, should be cut with a file, so 
 
 as to leave the proportion repre- 
 ~b sented in the figure attached to the 
 
 tube. The wire is to be intro- 
 U" ^s~ duced through the aperture thus 
 
 opened, and placed in the position 
 
 required when the tube shall be completed. The point of the 
 flame is then to be applied first to a, that the extremity of the 
 aperture may become heated and the wire also, the tempera- 
 ture being kept down to such a point as is sufficient to soften 
 the glass considerably but not to make it run ; and both glass 
 and wire being hot, a very little motion of the latter will cause 
 the edge of the former to adhere to it all round, and make a 
 tight though not a strong joint. This done, the heat must be 
 applied more towards the tube, so as to make the glass and the 
 wire adhere gradually from a to b. This should be done 
 without any twisting or distortion of the glass, and will be 
 found more or less easy according as the end of the tube has 
 been well or ill prepared at first to receive the wire. Finally, 
 all that part by which the wire is surrounded and held should 
 be raised to such a temperature as to make the glass soft and 
 semi-fluid, that no irregularities in form or contraction may 
 remain ; the wire should be arranged so that it passes directly 
 down the axis of the tube, and then the whole must be suffered 
 to cool. It is erroneous in a beginner to make the capillary 
 end of his tube thin, and trust to thickening it after the wire 
 is sealed in by running the glass up. Such sealings are gene- 
 rally unsafe. The end of the tube should first be made of 
 sufficient thickness, and then all that remains to be done is_, to 
 
506 WIRES FIXED IN TUBES TWO. [Sect.XIX. 
 
 soften it, so that it may collapse round and adhere perfectly to 
 the hot wire, in every part of the joint. 
 
 1203. When a tube of this kind is required for voltaic 
 decompositions, having two parallel but insulated wires sealed 
 into its closed extremity (1049), then a piece of platina wire 
 of sufficient length for the two is to be bent in the middle, so 
 that the two parts may be parallel at the distance of the 
 eighth or twelfth of an inch from each other. The extremities 
 are to be fixed into a small piece of cork, which will retain the 
 bent wire so steadily, that it may be worked with as a single 
 piece. That part of the wire which is intended to pass 
 through the end of the tube, and to be fixed in the glass, is to 
 be brought into the flame of the lamp, and a thick filament of 
 glass, or a thin rod being held in the hand, its extremity is to 
 be softened also in the flame, and glass from it worked upon 
 the wires, so as to form a small bead which, lying between 
 them, shall also extend outside of, and inclose them on two of 
 its sides, and when cold serve to tie them together at the dis- 
 tance before arranged. This done, the end of the tube is to 
 be prepared, by drawing it down and contracting it, but only 
 so much, that when the neck is cut off (which should be done 
 closer to the tube than in the former case 1202), the aperture 
 may be so large as to admit the passage of the double wire, 
 but not of the bead of glass upon it. The wire is to be 
 dropped down the inside of the tube, so that its bent end may 
 pass through the aperture, and the glass bead be received and 
 stopped just within it; heat is now to be applied to melt the 
 bead and the end of the glass tube together, and the tempera- 
 ture is to be raised until the cohesion is perfect, and the joint 
 well formed, after which it must be allowed to fall. When 
 the tube is cold, the piece of cork, now within, is to be drawn 
 from the ends of the wire, and the wire itself is to be divided 
 on the exterior, at the bend. It thus forms two insulated por- 
 tions, which may be connected with the poles of a battery, and 
 rendered active in decomposing any solution put into the tube. 
 
 1204. If a wire is to be inserted through and sealed into 
 the side of a tube, that part of the tube through which the 
 wire is to pass is to be softened in the lamp, and the wire 
 pressed against it until it appears in the interior of the tube 
 
Sect. XIX.] WIRES FIXED IN TUBES AT THE SIDES. 507 
 
 it should then be drawn out again in the same direction, and 
 both tube and wire left to cool. The wire will be found 
 coated with glass, which may easily be broken off. The tube 
 will be drawn out at the place forming a conical projection, 
 the end of which, when broken off, will afford a passage to the 
 interior. The wire is then to be put into the aperture, heated, 
 and the glass fused around it : ultimately the wire is to be 
 pushed inwards, until that portion of glass which projected 
 has been returned nearly to its first position. By a little 
 practice this may be done so that the glass shall be in perfect 
 contact with the wire on all sides, and with little disturbance 
 as to its form or position from that which it possessed at first, 
 the wire at the same time having the exact position required. 
 If fears be entertained that, from the removal of glass on the 
 wire, and by breaking off the end of the projection, enough 
 will not remain to confer sufficient strength upon the tube in 
 that part, it will be desirable to put a bead of glass round the 
 wire, in the manner just described for double wires (1203), 
 and when the heat is applied, to work it into contact with the 
 glass of the tube, that the latter may be of sufficient strength. 
 When two wires are required in the same tube, at a certain 
 distance from each other, as is necessary in an eudiometer, the 
 distance is easily regulated by a little previous consideration ; 
 allowance being made for the extent to which the wires will 
 require to be moved, before the operation is finished and they 
 are finally fixed in their places. 
 
 1205. After some practice in softening glass, drawing out 
 and sealing tubes, &c., it will be found easy to extend the art 
 of working this substance by forming it into various shapes. 
 Thus the softened end of a tube may be opened out by the use 
 of a pair of cold scissors or a piece of clean iron (1147), attend- 
 ing to the precautions of temperature before mentioned (1163), 
 and thus small glass funnels, compressed tubes, lipped tubes, 
 &c., may be made with facility. 
 
 1206. When green bottle glass tube is to be worked and 
 submitted to these operations, they will be found more diffi- 
 cult of performance, because of the much higher temperature 
 required for the fusion of this glass. Generally it is only the 
 
508 GLASS TUBES WORKED BY SPIRIT LAMP. [Sect XIX. 
 
 simpler operations that are necessary with green glass, such 
 as bending, closing, or lengthening a tube. These may be 
 performed readily by means of the table blow-pipe ; and as, 
 from the greater strength and infusibility of green glass, it 
 frequently happens that a thinner tube of this substance 
 may be used than of flint glass, a greater facility in the 
 operation is on that account obtained. 
 
 1207. The use of the spirit-lamp in these operations on 
 glass, even when not urged by a blow-pipe, has been noticed 
 more than once. When its powers are increased by the 
 application of the blow-pipe (216, Sec.), it may often be made 
 to perform the work of the table-lamp ; generally not so well, 
 though very usefully; sometimes quite as well; occasionally 
 even better. Small tubes may be bent, closed, drawn out, 
 extended, and worked, in almost any way by its means ; and 
 moderately large tubes, i. e. from one third to half an inch 
 in diameter, may be bent and closed by it. If no other 
 kind of blow-pipe than that for the mouth is at hand, it 
 must be turned to account in the best manner possible. For 
 this purpose the mouth-piece of the blow-pipe may be placed 
 between the lips, and the instrument supported without any 
 help from the hands, being allowed to hang from the mouth 
 with its jet opposite to the flame of the spirit-lamp. The 
 flame may then be urged, whilst both hands remain at liberty 
 for the purpose of moulding and working the glass. The 
 student will at first find it difficult to hold the blow-pipe so 
 steadily in his mouth as to produce a certain and regular 
 flame ; but he may obtain assistance by placing a block of 
 wood, a book, a weight, or a brick upon the table, between 
 himself and the lamp, at such a distance from the latter that 
 the back of the blow-pipe may bear slightly against it. If 
 these steady ing-blocks be formed with a deep wedge-shaped 
 notch in them, or if a block of lead be purposely prepared 
 with such a notch, then this temporary adjustment is much 
 more securely made ; but if there be no notch, the pressure 
 may be easily regulated by the mouth, and will be quite 
 sufficient to render the blow-pipe, and consequently the flame 
 itself, perfectly steady. 
 
Sect. XIX.] 
 
 CUTTING OF GLASS. 509 
 
 1208. Dr. Knight informs me that he has 
 long used a very convenient mouth blow-pipe 
 stand of the form depicted, the spike at the 
 bottom enters a hole in a board two or three 
 inches high, and therefore allows of adjust- 
 ment. The blow-pipe is fixed by a few folds of 
 soft paper in the fork, and so rendered steady. 
 
 1209. The cutting of glass in the laboratory is an operation 
 which is more frequently to be performed with tube and rod 
 than any other form of glass (1152). But occasionally old 
 flasks, retorts, jars, &c., are required to be cut into useful 
 pieces, and several methods have been devised for the purpose. 
 These, though not at all equal in accuracy and security to the 
 methods of the glass-worker, may be performed with such 
 common tools as are to be found almost every where, require 
 but little practice, are frequently efficient in facilitating ex- 
 periments, and highly useful to the student. 
 
 1210. The method of cutting tube or rod by a file has been 
 already described (1152). A cutting diamond will answer 
 the purpose as well as a file, and even a sharp flint may be 
 used upon emergency. When the tube is very large, it is 
 safer to go round the place first with a diamond, and to per- 
 form the operation over a cloth or some other soft substance, 
 lest as the pieces separate they should fall and be broken. 
 
 1211. In all cases in which a diamond is used, it must be 
 remembered that a cut, not a scratch, is required. A scratch 
 by a diamond will rarely give direction to a crack, and is as 
 likely to be crossed by one as followed. A cut, on the con- 
 trary, is a division of the glass, independent of the abrasion, 
 has actually penetrated to some depth*, and is almost certain 
 to be followed by any crack or entire division that may come 
 across or even near to it. A cutting diamond operates well 
 only in one particular position ; which should be found by trial 
 upon a piece of crown glass, and being ascertained should be 
 marked upon the handle, that in any future operation it may 
 always be in the same favourable position relative to the cut 
 that is to be made. The scratching diamond (128, 974) is 
 
 * See Wollaston, Phil, Trans. 1816, p. 265. 
 
510 CUTTING GLASS BY RINGS. [Sect. XIX. 
 
 not fit for cutting, but is intended for distinct uses ; nor should 
 a cutting diamond be injured by employing it in writing and 
 scratching upon glass. 
 
 1212. Old retorts, flasks, globes, and other convex pieces 
 of glass apparatus, are often cut by iron rings into circular 
 pieces, which then answer the purpose of dishes. The rings 
 should be of different diameters, made of wrought iron about 
 the third of an inch in thickness, with a stem attached to them, 
 by which they are fixed into a wooden handle. When made 
 uniformly red-hot, and brought into close contact with the 
 convex surface of a glass retort or flask, a crack generally 
 takes place in a few moments beneath the ring, which occasions 
 the separation of the inner round piece. These pieces are 
 sometimes used as evaporating basins ; but from their great 
 tendency to crack at the edges and gradually break to pieces, 
 are not safe in precise or important experiments. The uses of 
 the rings are much more valuable for the facility with which 
 they cut a flask in half, or by similar operations afford entrance 
 into any other vessel so as to allow of an examination of the 
 interior, and the state of the substances it contains. 
 
 1213. Thin fragments of retorts, flasks, and especially Flo- 
 rence flasks, are very useful for the evaporation of small 
 quantities, but as these vessels are never required to be thus 
 cut up until they are broken, the cracks then existing may be 
 led in advantageous directions more conveniently by other 
 means than by the iron rings. 
 
 1214. Many pieces of glass apparatus which have become 
 useless, such as jars, bottles, globes, and generally those with 
 convex surfaces, may be divided along a particular line by 
 means of a hot iron rod, and thus separated into useful pieces. 
 The operation consists in leading a crack, either made for the 
 purpose or previously existing, according to the required 
 direction. The iron rod may be nearly as thick as tiie little 
 finger, and made tapering at the end for an inch or an inch and 
 a half to a blunt point. The line of division should be decided 
 upon, and even be marked on the glass with pen and ink ; it 
 may pass without impropriety over parts varying in thickness, 
 but should not go suddenly from a thick to a thin part : thus 
 it may be followed with ease round the sides of a jar or bottle, 
 
Sect, XIX.] GLASS DIVIDED BY LEADING A CRACK. 511 
 
 but the crack could scarcely be led down one side of a jar, 
 across the bottom, and up the other side. 
 
 1215. It will rarely occur that a vessel is to be divided in 
 which some previous crack or broken edge does not exist. 
 The iron, being heated to dull redness, is to be brought with 
 its point towards the crack in an opposite direction to it, and the 
 apex is to be laid upon the sound glass just before the crack, 
 the iron rod being at the same time retained at an angle of 
 about 20 or 30 degrees with the as yet uncracked glass 
 beneath. The crack will immediately extend itself to the 
 part of the glass with which the hot iron is in contact ; and by 
 gradually and slowly drawing the latter along the glass before 
 the crack, the division will follow it, and may thus be led in 
 almost any direction. It may, when not carried too near to 
 the edge or to another crack, be made to turn off suddenly at 
 right angles to its former course, or it may be led in gradually 
 winding and curved lines. The crack should at first be led 
 directly towards the line which marks the convenient division, 
 and having reached it, that line is to be pursued until the 
 separation is effected. When the rod has cooled considerably, 
 or even when hot, if thin glass be experimented with, it is 
 often difficult to carry the crack entirely round into the com- 
 mencement or into any other division ; but in such cases the 
 small part which remains undivided easily yields to the slightest 
 mechanical force, the crack being then continued directly into 
 the previously-divided part. 
 
 1216. The rapidity with which a division is effected depends 
 upon the temperature of the rod. It is not desirable to per- 
 form it very quickly, and therefore when very hot, the rod 
 should be held at greater angles with the glass than those 
 mentioned, that the point only may touch it. As the heat 
 diminishes the rod should be more inclined, that the thicker 
 part may be made to approach the glass, and by its heat and 
 effect compensate for the diminished temperature of the point. 
 When still cooler it may be desirable to use the thickest part 
 of the rod instead of the point, laying it down in contact with 
 the glass before the crack and drawing it along, but this can 
 only be done on convex vessels. 
 
 1217. If the direction to be followed lies but a little dis- 
 
512 GLASS DIVIDED CRACK MADE. [Sect. XIX. 
 
 tance from the line of an edge, or a previous division, the 
 operation must be performed more slowly, and with the apex 
 rather than the line of the rod ; for the crack to be led has 
 then a tendency to fly suddenly to the edge by its side. It 
 is not easy by this method to cut nearer to an edge than the 
 third or fourth of an inch. 
 
 1218. If there be no crack to commence with, one must be 
 produced in the following manner. If possible an edge is to 
 be selected, which, being an inch or an inch and a half from 
 the line of division, may have a crack made in it without 
 interfering with the part of the glass intended to be preserved ; 
 if it be a recent edge, i. e. one that has been formed by fracture, 
 rather than one which, existing at first on the piece of appa- 
 ratus, has been fused, it is the more advantageous. The 
 heated iron rod is to be applied to this edge in a direction 
 almost perpendicular to the glass, that the heat may extend to 
 as little distance from the place as possible, and when it has 
 been in contact for a moment, if a division has not spontane- 
 ously occurred, the hot part is to be touched with a moistened 
 finger : a crack will immediately be occasioned, and the smaller 
 the distance to which it runs from the edge the better ; for 
 once commenced, the smallest crack can be led as easily as the 
 largest, and the opportunity of directing it from the commence- 
 ment is secured. If the glass be thick, as that of a bottle or 
 jar, it will usually fly by the heat alone ; if it be thin, as that 
 of a Florence flask, it will generally require the application of 
 moisture after the heat. 
 
 1219. If the crack is to be commenced in the middle of a 
 plane unbroken surface, great care is required, or the fracture 
 will extend to a considerable distance, and probably in a wrong 
 direction. The heated point should be applied to a single 
 spot, and being soon removed, the place should be moistened. 
 It is better to try two or three times unavailingly, than, by 
 heating the glass too much at first, to incur the risk of an 
 extensive fracture. The crack should always be commenced 
 at some distance from the important line of division, that there 
 may be less danger of the first and uncertain separation 
 interfering with or crossing the latter. 
 
 In all divisions of this kind the glass to be cut should 
 
Sect. XIX.] OLD GLASS RENDERED USEFUL. 513 
 
 be supported upon a cloth, that the parts on both sides of the 
 crack may be sustained ; or, when the division approaches its 
 completion, the mere weight of one part may make the crack 
 run in an inconvenient direction. The form of the piece of 
 iron is by no means essential, and a furnace poker, or a pair 
 of tongs, may, in cases of emergency, be used for these pur- 
 poses. It may even be performed with a red hot pointed piece 
 of charcoal, the ignition being heightened by blowing upon it. 
 
 1221. The edges which are exposed when glass is thus 
 divided are very liable to fracture by slight mechanical force, 
 heat, or other causes, much more so indeed than glass of 
 which the edges have been fused or ground. Hence it is fre- 
 quently advantageous either to grind them, which may be done 
 upon a flat stone with a little sharp sand or emery and water 
 (1229) ; or to soften and fuse them, which may be effected 
 either by the table blow-pipe, bringing all parts of the edge in 
 succession into the flame, or by a shallow charcoal fire. When 
 the edges are not thus finished, they should have a sand-stone 
 or a fine file passed over them to remove the linear angles, 
 which, being sharp, are dangerous to the fingers. 
 
 1222. Jars which have been broken at the edges, may by a 
 process of this kind be cut down, and then will long remain 
 useful vessels. Bottles of which the necks or upper parts have 
 been broken may be converted into small jars. Their stoppers 
 should be added to those which already occupy a drawer in 
 the laboratory (25, 1230), and from which the place of an 
 absent one may often be supplied. Broken test glasses may 
 frequently be cut into useful forms ; if but one-half or two- 
 thirds of the cup be removed, the remaining part with the foot 
 will serve for many voltaic decompositions, and frequently as 
 a convenient insulating stand in electrical experiments. If 
 nothing but the foot can be preserved, still there are numerous 
 occasions for its services in the laboratory ; for the body being 
 broken away, and the stem chipped off, which is done by 
 striking it sideways with a file or the edge of an iron spatula, 
 a strong round glass disc remains. Such discs are very con- 
 venient as covers for the mouths of glasses containing precipi- 
 tates or other substances, to exclude dust during the time the 
 experiments are in progress (553). 
 
 2 L 
 
514 GLASS DIVIDED - BY HEAT BY A FILE. [Sect. XIX. 
 
 . In cutting up large pieces of glass by the method 
 described, especially if any importance be attached to the 
 result, it is best to precede the application of the hot iron by 
 going round the part with a diamond. The iron then merely 
 completes what the diamond had begun, and it is seldom that 
 the separation departs from the track thus laid down for it. 
 But the chemist sh6uld never undertake delicate or difficult 
 divisions ; the object of the preceding directions is to enable 
 the economical experimenter to cut up into useful forms old 
 glass, which would otherwise be thrown away as waste. In 
 more important cases he will, of course, transfer it to the 
 hands of an instrument-maker. 
 
 1224. Sometimes it is required that a piece of flat glass, as 
 crown glass, should be broken into two or three smaller pieces. 
 If this be attempted by means of a blow, the glass will usually 
 shiver into many pieces, mostly long, with curved outlines and 
 of very inconvenient forms ; a piece of the desired size or shape 
 being rarely obtained. But by contrivance a piece of such 
 glass may be divided into two parts only, with considerable 
 certainty, the direction of the fracture also being in some 
 degree under government ; and a long slip of glass may be 
 divided into halves or quarters, or a piece of any form cut up 
 into smaller parts without difficulty. Suppose it were required 
 to divide a piece of glass four inches long and two wide, into 
 two nearly equal portions. An angular file (three-square or 
 four-square) is to be placed with one end against an obstacle, 
 as the edge of a table, and the other against the breast, so that 
 by a little pressure it may be supported with one of its edges 
 upwards, and nearly in a horizontal line. The piece of glass 
 is to be held with one end in each hand, and the middle of one 
 of its long sides is to be applied to the edge of the file at that 
 end nearest to the table or support, the glass being inclined 
 a little upwards from the horizontal direction towards the 
 operator. The operator is then to press with a moderate 
 degree of force on the glass, drawing it along the file from 
 one end to the other, and, without taking it off, to turn it as 
 it were over, so as to incline it in the opposite direction, and 
 immediately carry the glass back again with about the same 
 pressure, to its original place on the edge. In this way there is 
 
Sect. XIX-T GLASS DIVIDED BY A FILE BY PRESSURE. 515 
 
 a tendency to notch the glass on the opposite sides of the same 
 edge and place, which is sufficient to originate a fracture there ; 
 and as the glass is returned, it generally divides in the hands 
 by a crack, commencing at the place where it was in contact 
 with the edge of the file, and proceeding directly across 
 between the hands. 
 
 1225. The degree of pressure required is quickly learnt by 
 a little practice on waste pieces of crown glass : it should be 
 insufficient of itself to break the glass, but sufficient when the 
 small fracture is commenced by the file. It is better to make it 
 rather stronger when the glass is returned, than when drawn 
 towards the body ; the former being the most convenient time 
 and position for the fracture to take place in. The direction 
 of the crack is regulated chiefly by the force applied by the 
 hands, being usually across the line of resistance to that force ; 
 and hence the opportunity afforded of giving it a direction by 
 pressing with the hands equally on each side of the line, along 
 which it is desired the crack should pass, at the same time 
 making it commence at the beginning of that line, by placing 
 it on the edge of the file. 
 
 1226. When all other means of directing a crack are absent, 
 it may frequently be done with advantage merely by the 
 pressure of the nail. If a Florence flask be cracked, the 
 division may be extended by putting the thumb over it near 
 the end of the crack, pressing the nail when in contact 
 with the glass, and carrying the thumb forward. The crack 
 will fly before it, extending on this or that side, according 
 to the direction in which the thumb advances, or according 
 as the pressure is on one side or the other. The flask may 
 thus be divided into pieces, much more useful than such as 
 would probably result from crushing or breaking it entirely 
 at random. 
 
 1227. Pieces of glass are reduced at the edges in various 
 ways. The corners may be removed from fragments of plate- 
 glass by running a coarse file with a light and rasping kind of 
 motion against the edges, in a position slightly inclined to the 
 glass. The reduction takes place, not by mere attrition and 
 wearing away, but by the removal of successive chips of glass, 
 each tooth of the file carrying away" a small fragment, per- 
 
 2 L 2 
 

 516 EDGES REMOVED GRINDING OF GLASS. [Sect. XIX. 
 
 haps the eighth or tenth of an inch across ; in fact of a dia- 
 meter equal to the whole thickness of the plate. In this way the 
 large pieces are soon brought into a round form, and serve as 
 plates (1348). In the same manner if, in cutting a thick tube, 
 the aperture should not be level all round, the projecting parts 
 may be removed piecemeal, but more care is required than 
 with flat glass, from the tendency of cracks to form at the edge 
 and fly up the tube. 
 
 1228. The edges of plate-glass may also be removed by a 
 pair of pliers, not by pinching off the superabundance, but by 
 bringing it between the chops of the instrument, holding it 
 lightly there, and then twisting the pliers slightly so as to 
 exert a degree of pressure upon the exterior edge of the glass 
 by one of the sides, whilst the other merely serves as a fulcrum 
 for support to the power. The edge will be found to splinter 
 and crumble away under a force thus applied, and the art of 
 successfully using it is soon learned by practice. This method 
 is not so applicable to the edges of tubes as to straight glass, 
 but it may often be used with crown glass when the file is in- 
 applicable. 
 
 1229. Glass may be ground on almost any flat stone with 
 a coarse grain, by means of a little sharp sand and water, or 
 better still, by emery and water. Thus the ends of the tubes 
 (743, 1221) may be ground level on a piece of Yorkshire or 
 Purbeck stone. The operation is easy in proportion to the 
 smallness and thickness of the tubes. It requires that the 
 glass should be held with a steady hand, and perfectly upright, 
 that the resulting edge may be flat. Larger vessels, as jars, Sec., 
 may be ground in a similar way, but are better trusted to the 
 instrument-maker. 
 
 1230. When a bottle requiring a stopper has been fitted 
 with one from the stopper drawer (25, 1222), it may happen 
 that, though nearly, it is not quite true and tight. In such 
 a case the stopper may be made to fit accurately by being 
 ground with a little sea-sand or coarse emery and water, into 
 the mouth of the bottle, during which operation it should be 
 quickly inserted into and removed from its place and turned 
 at the same time. In this manner the glass is in part worn 
 away and the stopper made tight, but care should be taken 
 
Sect. XX.} 41 CLEANLINESS. 517 
 
 that, during the grinding, the bottle be shifted a little now 
 and then in the hand, that different parts of the neck and the 
 stopper may work against each other at different times, and 
 thus mutually correct the existing inequalities. 
 
 SECTION XX, 
 CLEANLINESS AND CLEANSING. 
 
 1231. MUCH as the chemist may soil his fingers during his 
 experimental occupations, he will soon learn the great im- 
 portance of cleanliness to the success of his experiments. The 
 regular course of his operations causes many kinds of matter 
 to pass in succession through his hands ; and many of the 
 substances which by mixture have exhibited the phenomena 
 they were competent to occasion, and so far answered the 
 purpose of the experiment, then become mere useless dirt. 
 Their dismissal and entire removal, when thus circumstanced, 
 become necessary, that they may not contaminate other bodies ; 
 and is as imperatively required, as was the care previously 
 bestowed to prevent their contamination from extraneous 
 matter. 
 
 1232. It is this" rapid change in the character and relation 
 of the substances with which the chemist works, that makes a 
 constant attention to cleanliness essentially necessary. The 
 very bodies which at one moment are carefully retained in 
 vessels that have previously been cleansed with the most scru- 
 pulous attention, become the next in the situation of so much 
 dirt, from which the vessels must be cleansed as perfectly and 
 carefully, before they can be fit for another experiment, as 
 they were for the reception of the now rejected matter. The 
 results of numerous experiments relative to testing bodies in 
 solution by re-agents, are, in many cases, dependent on the 
 employing of clean vessels. For instance, a portion of water 
 examined in glasses which have been carelessly washed, may 
 occasion a slight precipitate with nitrate of silver or muriate 
 of baryta, and thus seem to contain a sulphate or a muriate, 
 
518 CLEANLINESS REGULATIONS dTO ENSURE IT. [Sect. XX. 
 
 when the cause of the precipitate may be nothing more than 
 portions of salts adhering to the vessels. 
 
 1233. In the same manner the purity of an acid or a test 
 is not unfrequently affected by the state of the bottle contain- 
 ing it, or by the dirty condition of glass rods dipped into it, 
 or of the funnels through which it has been poured or filtered, 
 or of the vessels used in its transference ; and sometimes 
 it is contaminated by laying the stopper of the bottle con- 
 taining it in a dirty place. Nor is it only that kind of dirt or 
 impurity which gives an evident tinge to what it adheres to 
 that is to be avoided, but also numerous colourless substances, 
 as salts, solutions, &c. ; and, in a word, anything which differs 
 from the principal substance itself, and is at the same time 
 liable to be dissolved or mixed with it. 
 
 1234. In consequence of these liabilities, and their inter- 
 ference with experiments, it should be established as a general 
 rule in the laboratory, that no apparatus, nor any vessel, 
 (except such as may be destined to a particular use, and is as 
 convenient when with a little previously adhering matter as 
 if it were clean,) be put away in a dirty state. All vessels or 
 instruments when resorted to should be found fit for the nicest 
 experiment to which they are applicable. Glass rods or 
 stirrers should be preserved in a clean place ; glasses on a 
 clean shelf ; and stoppers when taken out of bottles should be 
 laid upon clean glass surfaces. These attentions and regula- 
 tions will be found always useful, at times essential. They 
 are generally more requisite and influential in minute che- 
 mistry, than in large experiments; and in trains of research, 
 than in the process of the manufacturer. 
 
 1235. As a part of the general system of cleanliness, the 
 walls and ceiling of the laboratory should be lime-washed at 
 intervals, dependant on the nature of the operations performed 
 in it, and the state of the walls. The general light of the 
 place will by this means be increased ; and the surface thus 
 renewed from time to time, more readily absorbs the fetid 
 odours, animal effluvia, and acid fumes, that are occasionally 
 disengaged during chemical operations. The tables and the 
 filtering stands should be cleared and cleaned once a week or 
 a month, according to the use made of them. The shelves 
 
Sect. XX.] CLEANLINESS LABORATORY TROUGHS. 519 
 
 should be periodically dusted, and the bottles upon them 
 wiped. The laboratory drawers should also be cleared and 
 cleaned from time to time, that the stirrers, valves, corks, and 
 other articles in them may be preserved in a proper state for 
 use. All dirty glasses, and the results of experiments when 
 done with and of no further service, should be put together 
 into one particular place, being either a tray upon the table, 
 or a portion of the table appointed for the purpose ; and no 
 substance should be put into this place that is not to be thrown 
 away, nor any glass or apparatus that is not to be cleaned. 
 A little method in these arrangements prevents mistakes and 
 errors; very much facilitates the laboratory operations; and 
 quickly brings every thing into a ready and available condition. 
 
 1236. When the japan or paint of the pneumatic trough is 
 either wearing or pealing away, the trough should be emptied 
 of water, dried , and the surface renewed. The water of the 
 troughs, which are preserved full for constant use, should be 
 changed every fortnight or three weeks, or oftener if any ex- 
 
 'periment has occasioned its contamination more quickly. If 
 alkali, acid, sulphuretted hydrogen, or any extraneous sub- 
 stance likely to exert a chemical action upon, or mixture with 
 gases that may be standing over the trough, find their way 
 into the water, it should immediately be changed. The loose 
 iron trivets (733) for the water trough should be varnished 
 before they are brought into use ; and also again at any future 
 time when rust appears upon them, or if, when put into the 
 water, they impart a yellow tinge. A coat or two of the 
 common varnish, called Brunswick black, is quite sufficient 
 to prevent the contact of the water with the metal, as well as 
 oxidation. A better coat, as being more adhesive, is formed 
 upon the iron, by brushing linseed oil over it when heated 
 just below visible redness ; the heat decomposes the oil, and 
 leaves the iron, when cold, covered with a fine smooth black 
 varnish, adhering very closely, and effectually preserving the 
 metal from contact with the water. 
 
 1237. The sink and its importance have been before briefly 
 noticed (13) : it is essential to an active laboratory. It should 
 be supplied with a pail and a pan, or large vessel, which, being 
 constantly full of water, is to serve in turn both for soaking 
 
520 THE SINK ITS ACCOMPANIMENTS. [Sect. XX. 
 
 and rinsing operations. Several nails should be driven into 
 the wall over the sink, upon which should hang various wires, 
 intended to facilitate the cleansing processes. Six or eight of 
 these should be of copper, about the eighth of an inch in 
 thickness, from twelve to eighteen inches in length, bent into 
 an eye at one end, and having a little tow wrapped round 
 them at the other. The end intended to hold the tow should 
 be roughened, by being struck with an edge, so as to have a 
 few teeth cut in it, or by having a notch or two filed across it ; 
 that the tow may not slip off when it is pushed up and down 
 a tube, or through a narrow aperture. The tow should be 
 twisted round the end in such a manner as to hold by these 
 irregularities. Some of these wires should be quite straight, 
 others curved at the extremity, that they may reach parts 
 unattainable by the straight wire, as the inside of a globe or 
 retort, or that part of a bottle which is close to the neck. 
 
 1238. A similar set of wires of less thickness should be 
 appointed for the purpose of cleaning sharp angles, narrow 
 cavities, and small apparatus, for which the thicker wires 
 would be too large. These are best of iron, being stronger 
 when of equal thickness than those of copper. Some of both 
 these kinds of wires should be retained for use when their tow- 
 terminations are wetted, others for dry tow, and others without 
 any tow at their extremities, that they may be ready for the 
 removal of hard adhering matter. 
 
 1239. Besides these wires, one or two wiping sticks should 
 be provided, for the purpose of drying the inside of long jars, 
 and other apparatus, to which the hand cannot have access. 
 They should be of a tough but light wood, that they may 
 have strength enough to resist considerable force, and yet not 
 endanger the glass by a tap or a slight blow. They should be 
 about two feet in length ; not round, but angular or flat at 
 the end, that the cloth may the less easily slip off; and if the 
 end be thinned away on one side, so as to be wedge-shaped, it 
 is more effectual in applying the cloth with force to the angular 
 space at the bottoms of jars or bottles. 
 
 1240. The necessary supply of dusters, cloths, and tow, 
 should be furnished to the sink, each having its respective 
 place both in the clean nd dirty state. 
 
Sect. XX.] CLEANSING OF VESSELS GLASSES. 521 
 
 1241. Cleansing of Vessels. Glasses. In by far the great- 
 est number of cases glasses are dirtied by moist substances, 
 as precipitates or solutions ; it is then advantageous to cleanse 
 them immediately upon throwing out the contents, and before 
 the dirt can dry or harden. Rinsing will usually remove the 
 whole of the dirt ; or if it adhere, it is but slightly, and imme- 
 diately gives way when touched by a wire with moist tow. If 
 it should resist this application, a similar wire with wet tow, 
 aided by a little of the wood or charcoal ashes, which are 
 always lying at the bottom of some of the furnaces, will gene- 
 rally remove every thing. Sand should not be used for these 
 purposes, as it cuts and roughens the soft flint glass, of which 
 vessels are made in England ; and at the same time that it 
 injures their transparency, it renders them improper for several 
 particular experiments of precipitation. When by any of 
 these methods the dirt has been removed, the glass 4s to be 
 well rinsed in clean water, turned upside down for twelve 
 hours on a side shelf or table to drain, and then wiped. The 
 wiping should be performed with a cloth in each hand, not 
 only because a cloth is more cleanly than the hand, but that if 
 the glass should break the hand may be defended. The cloths 
 should never be in a greasy, resinous or pitchy state ; but so 
 clean, that without communicating any thing they will remove 
 all substances that can be wiped off. Laboratory cloths when 
 clean should be used, first, for wiping glass, then for wiping 
 tables or dirty apparatus, and being once so used, should not 
 be employed for clean glass again until they are washed. 
 Especial care is required in wiping glasses that the inside be 
 thoroughly cleansed in every part, for it is with that part of 
 the vessel that tests and solutions come in contact. 
 
 1242. If the glasses be greasy they should not be washed, 
 but in the first place wiped with tow to remove as much as 
 possible of the grease, and then a dry cloth should be used, 
 until the glass appears clean. Its surface should afterwards 
 be washed with a little strong solution of alkali, applied by 
 means of a wire and tow ; this removes the thin film of grease 
 remaining after the wiping, and the glass may then be rinsed, 
 drained, and wiped, as before directed. A duster should not 
 be used at random for these greasy glasses, lest it should the 
 
522 CLEANSING OF GLASSES TUBES. [Sect. XX. 
 
 next moment be applied to a clean vessel and communicate 
 impurities to it ; but one should be kept apart and appropriated 
 for these purposes. 
 
 1243. If the glass be soiled by resin, turpentine, resinous 
 varnishes, or similar bodies, it should in the first place be 
 washed with a little strong solution of potash, those places 
 where the resin adheres being rubbed by means of a wire and 
 tow, until the alkali has softened the whole, and rendered it 
 soluble in or moveable by water : it is then to be washed, 
 rinsed, and dried, as before. Or, in place of alkali, a little 
 strong sulphuric acid may be used, and is sometimes even 
 more advantageous : being poured into the glass or vessel, the 
 latter should be inclined in various directions, so as to bring 
 the acid into contact with all parts of the foul surface : it will 
 become very black, an^ ^fter a few minutes the resin, &c. wiU 
 wash off, and the glass may be cleaned in the ordinary way. 
 
 1244. Pitch and tar,- when they adhere to glass, may in 
 part be scraped off. A little strong sulphuric acid applied as 
 above, will loosen and separate the remainder. Occasionally a 
 little oil may be used ; being rubbed on the soiled parts, it 
 mixes with and softens these adhesive substances, so that they 
 may be wiped off by tow, and then the glass is to be cleaned 
 from the oil as before described. 
 
 1245. Tubes are cleansed generally in the same manner as 
 glasses. Wires with tow will be found very convenient in dis- 
 placing solid and adhering dirt from their insides. The tubes 
 should be well rinsed twice or thrice, being each time half 
 filled with water, closed by the finger, and then well shaken. 
 They may be turned upside down, and left inclining against 
 each other in a corner to drain ; after some hours they may 
 either be wiped dry within by a cloth and stick, or, what is 
 perhaps more convenient, left with their mouths open to the 
 air until the interior has become dry by evaporation, and then 
 be wiped to remove any dust which may have entered. Tow 
 is not a good substance for the removal of water from glass 
 surfaces, and for tubes it is better to use a long slip of cloth, 
 two or three inches wide. Having introduced a few inches in 
 length of this slip into the tube, the wire or stick is to be in- 
 serted, and the cloth thrust up to the extremity, so as to form 
 
Sect. XX.] CLEANSING OF AIR- JARS BASINS FLASKS. 523 
 
 an accumulation there ; the rest of the tube will then be occu- 
 pied by the wire or stick and a part of the slip of cloth. It 
 will thus be found easy by a very little management, and a 
 rotatory and longitudinal motion of the tube, to wipe every 
 part of the inside clean and dry in an expeditious and perfect 
 manner. 
 
 1246. Long tubes open at both ends, which have become 
 dusty, are' easily wiped by pushing a loose pellet of cloth or 
 tow, up and down them by a long stick : or a piece of string, 
 having a loop at the end into which some tow has been intro- 
 duced, may be used to draw the tow through the tube, and 
 thus to wipe it clean. This is a very useful mode of cleaning 
 out bent tubes open at both ends ; the end of the string may 
 be readily passed through them, by attaching a little piece of 
 wire to it as a weight. The piece of string must be longer 
 than the tube to be wiped, and the portions of tow used at 
 first, should be such as will easily pass the angles ; they may 
 be increased in size by the addition of more tow if necessary. 
 
 1247. Air jars require no further directions for their cleans- 
 ing than is given with respect to glasses (1241). When of 
 such narrow dimensions as not to admit the hand, the insides 
 must be wiped in the same manner as has just been described 
 for tubes (1246). Generally in these cases abundance of 
 cloth should be allowed to enter the vessel before the stick, 
 that the mass thrust up to the extremity may be large, and 
 bear uniformly against the glass over a considerable surface. 
 
 1248. Evaporating basins are ^very easily washed. The 
 soaking tub (1237) is useful for the softening and removing of 
 most substances, which are likely to accumulate in them. 
 Grease, resin, and similar bodies, may be removed by tow and 
 damp ashes, or soft sand, or otherwise by a little strong sul- 
 phuric acid (1243). When all dirt is removed, the basins 
 should be rinsed, turned upside down to drain, and then 
 wiped. It is advisable to clean the stock of evaporating basins 
 belonging to the laboratory once every two or three months, 
 with a little strong solution of alkali, both inside and outside, 
 rejecting at such times those which have become useless. 
 
 1249. Flasks are not so easily cleansed as the vessels al- 
 ready mentioned, from the greater difficulty of access to the 
 
524 * CLEANSING DRYING OF VESSELS WITHIN. [Sect. XX. 
 
 interior ; but the bent wires referred to (1237) will overcome 
 many obstacles. Florence flasks are frequently oily when 
 obtained from the Italian or wine warehouses. They may be 
 readily cleansed by putting a little strong nitric acid into each, 
 and heating it over a lamp or sand bath, after which every 
 thing will wash out with water. Strong sulphuric acid may 
 be used for the same purpose, being brought into contact with 
 every part of the glass, without requiring the application of 
 heat. Either acid is better than solution of alkali. If metallic 
 matter adhere to the inside, a little nitro-muriatic acid intro- 
 duced, and heated on the place, seldom fails of separating and 
 removing the substance. When the impurity is loose or sepa- 
 rable by water, the flasks should be well rinsed and inverted 
 on a filtering-stand (528) or shelf (15), left to drain for half 
 an hour, then well rinsed out with distilled water, and again 
 placed to drain. 
 
 1250. When the impurity within flasks, globes, or similar 
 vessels, adheres mechanically, and is not soluble in water, it 
 may frequently be effectually loosened and removed, by intro- 
 ducing some coarse brown paper torn into fragments about an 
 inch square, with water enough to half fill the vessel, and 
 agitating the whole vigorously. The pieces of paper will rub 
 or break off dirt that has resisted the action of water alone, and 
 most sediments or deposits may be thus removed. The ad- 
 dition of a few wood-ashes increases the effect. 
 
 1251. Upon wiping the exterior of globular vessels, those 
 which are thin, as Florence flasks, require care, lest they be 
 crushed to pieces between the hands. It may be necessary to 
 dry the interior of some of them , but others will not need it. 
 When they are to be dried, they may be left on the retort 
 shelf in the cupboard (14), or on the filtering-stand, with the 
 mouth downwards, until the water within has evaporated; but 
 as this will require some days or weeks, a more rapid method 
 may occasionally be adopted. This is to warm the flask, so 
 as to convert the water within into vapour, and then by intro- 
 ducing one end of a piece of glass tube, whilst the other is held 
 by the hand against the nozzle of a pair of bellows, to blow 
 out the moist air, and replace it by that which is dry. If the 
 first warming be insufficient to convert all the water into 
 
Sect. XX.] CLEANSING FLASKS RETORTS BOTTLES. 525 
 
 vapour, the flask may be heated a second time ; or if the flask 
 be thick, and retain its temperature for some minutes, merely 
 persisting in blowing air through, will gradually evaporate and 
 remove the water from within. 
 
 1252. Instead of using the bellows, the mouth will answer 
 every purpose ; for if, when the flask is hot, the external end 
 of the tube be put between the lips, it will be easy to throw 
 air in from the lungs, which, though it contain moisture, is 
 much drier than that in the flask. When the appearance of 
 liquid within no longer exists, the moist air last introduced 
 from the lungs is easily removed by drawing air out of- the 
 flask, through the tube, into the mouth ; other portions then 
 enter to replace it, and the vessel is left filled with an atmos- 
 phere of ordinary dryness. 
 
 1253. Six or eight Florence and other flasks should be kept 
 ready for use on the filtering-stand ; the mouths of the rest 
 should be covered up with paper to keep the dust out, and be 
 put aside until wanted. In thus guarding the mouth of a 
 flask, retort, tube, or similarly formed apparatus, it is merely 
 necessary to roll a slip of paper round the end, so that it shall 
 project sufficiently beyond the edge, and then to fold or double 
 this projecting part down, in such a manner as to close the 
 mouth, and at the same time prevent the slip from unrolling. 
 
 1254. Retorts may be cleaned according to the directions 
 just given for flasks (1249), but if tubulated they require more 
 care, because of the increased tendency to crack and fly at the 
 junctions. When rinsed they sliould be carefully placed, so 
 that the water which drains may run quite out of the vessel. 
 When warmed for drying (1251), attention must be paid 
 to the tubulature, that it be not suddenly heated or cooled. 
 It is necessary too that drops of water be not allowed to run 
 from a cool upon a hot part, as they might occasion fracture. 
 
 1255. Bottles. The bottles of the laboratory require con- 
 stant attention and cleansing. They are liable to accidents 
 and uses of all kinds, and are soiled by every species of matter 
 in turn. Now and then the stoppers of bottles become fixed 
 (741), in which case means of loosening them, successively 
 increasing in power (but also unfortunately in danger), must 
 be resorted to, until the stopper is removed, or, giving way, 
 
526 STOPPERS LOOSENED REMOVED. [Sect. XX. 
 
 is destroyed. One of the simplest methods when the unaided 
 hands fail, is to tap the stopper alternately on opposite sides, 
 with a piece of wood, as the handle of a bradawl or a chisel, 
 the other part of the tool being held loosely in one hand, whilst 
 the bottle is retained lightly at its lower part in the other. 
 The light alternate concussions on the opposite sides of the 
 stopper are often sufficient to destroy the adhesion between it 
 and the bottle. This is indicated by the sound ; for so long 
 as the adhesion remains perfect, the noise made by the tap is 
 as if the bottle and stopper were but one piece of matter ; but 
 the moment the stopper is loosened, however slightly, the cha- 
 racter of the sound changes, becoming somewhat flatter and 
 heavier, and then a few more taps complete the operation, and 
 the stopper gives way to the hand. Before thus endeavouring 
 to loosen the stopper, the thickness of the neck by which its 
 upper and lower parts are connected should be observed : if 
 that be very small, the force must be carefully applied ; if 
 strong, a little more liberty may be taken with it. If the 
 stopper does not soon give way, this means alone will not be 
 sufficient for its removal. 
 
 1S56. Another method of removing a bottle- stopper is to 
 insert its head into a chink, and then endeavour to turn the 
 bottle with the hands. This kind of force is similar to that 
 exerted by the hand upon the stopper, but is more powerful ; 
 and if the neck of the stopper break, the hand is out of the 
 way of danger. An upright board, such an one as supports 
 the ends of a set of shelves, should be selected in a convenient 
 situation in the laboratory, and a vertical slit cut through it 
 about a foot in length, an inch in width above, but gradually 
 decreasing in size so as to be about the third of an inch at the 
 bottom. The top of the hole may be about the height of the 
 breast. This aperture will in one part or another receive and 
 retain the head of almost any stopper, and prevent it from 
 turning with the bottle. Then by wrapping a cloth about 
 the bottle, and grasping it in both hands, the attempt to turn 
 it round so as to move tlie stopper may be made, with any 
 degree of force which it may be thought safe to exert. If the 
 force be such as to occasion fracture, it will generally occur at 
 the neck of the stopper, twisting the head from the plug. It 
 
Sect. XX.] STOPPERS LOOSENED REMOVED. 527 
 
 is only when the bottle is wide-mouthed, the stopper conse- 
 quently having great surface of adhesion, and the neck of the 
 stopper is also very thick, that there is any risk of the bottle 
 breaking in the hand. But the force employed should never 
 be carried so far as to cause fracture any where ; the attempt, 
 if unavailing with the application of a moderate power, should 
 be desisted from. 
 
 1257. Another and a very successful method of removing 
 a stopper is, to turn the bottle round, when held horizontally 
 over the small flame (199) of a spirit-lamp or candle applied 
 to the neck. The heat should be applied only to the part 
 round the plug of the stopper, and in a few moments, when 
 that has become warm, the stopper should be tapped with 
 the piece of wood as before (1255). The application of 
 the heat expands the neck of the bottle, and rendering it 
 larger, permits the removal of the stopper to be effected by a 
 force previously quite insufficient. As soon as the stopper 
 moves by tapping it is to be taken out, and must not be re- 
 placed until the glass is cold. The application of heat in this 
 manner must be short, and the operation altogether, to be 
 successful, must be a quick one ; for it is obvious that the 
 effect depends upon the difference of temperature between the 
 stopper and the neck, and if the former become heated as well 
 as the latter, no good result can be expected, and the bottle is 
 endangered by the application of heat to no good purpose. 
 
 1258. If, when the neck has thus been warmed, the bottle is x 
 held upright, and struck smartly with the palm of the hand upon 
 the bottom, it will frequently occasion the displacement of the 
 stopper ; and the method is advantageous when the bottle 
 contains fluid ; but precautions must be taken that the stopper 
 do not fall back on to the bottle and break it, or into any other 
 situation to do harm. 
 
 1259* If the contents of the bottle are fluid, it should be 
 held so inclined that they may not become heated ; if they are 
 volatile, this method should be tried very carefully, lest the 
 vapour formed within should burst the bottle. The applica- 
 tion of heat in this way is seldom successful unless immediately 
 so ; and there is always some risk of cracking the neck of the 
 bottle. 
 
528 STOPPERS METHODS OF LOOSENING THEM. [Sect. XX. 
 
 1260. It has occasionally been recommended to apply heat 
 to the neck, not by a flame, but by means of the friction of a 
 long piece of list passed once round the part, and then drawn 
 to and fro. The plan may be occasionally useful, especially 
 where liquids are enclosed, but has its disadvantages. 
 
 1261. It is often advantageous to put a little olive oil round 
 the edge of the stopper at its insertion, allowing it to soak in 
 for a day or two. If this be done before the heat be applied, 
 it frequently penetrates with increased facility at the time of 
 heating ; by oil, heat, and tapping, very obstinate stoppers may 
 be removed. When a stopper has been fixed by a crystalli- 
 zation from solution, water will sometimes set it free, and it is 
 more advantageous in such cases than oil, because it dissolves 
 the cement. When the cementing matter is a metallic oxide 
 or a sub-salt, a little muriatic acid may be useful, if there be 
 no objection to its application, arising from the nature of the 
 substance within. 
 
 1262. The preceding are all quick operations, and one or 
 other of them will generally loosen a tight stopper, and save 
 the bottle with its stopper and contents. If they fail, the fol- 
 lowing method may be tried, which is particularly successful 
 in cases where stoppers are forced inwards by atmospheric 
 pressure, in consequence of internal absorption ; the preceding 
 methods often make such cases worse. A piece of strong 
 twine is to be doubled, and a knot tied so as to form a loop of 
 
 r about four inches in length. The knot is to be brought close 
 to the neck of the stopper, the two ends passed round, so as to 
 meet on the opposite side, and tied there tightly, so as to fasten 
 the string securely round the neck. The two strings are then 
 to be tied together, so as to form a loop on that side the stopper 
 equal in length to the first loop, or about four inches. These 
 loops now serve as handles by which to pull at the stopper ; 
 and, being on opposite sides, permit the force to be applied so 
 as to draw the stopper directly forward out of the neck of the 
 bottle. For this purpose they are to be passed over a fixed 
 bar (if horizontal, so much the more convenient), and are to 
 be placed about 2| or 3 inches apart on the bar, that by 
 directing the pull on the bottle a little on one side or the 
 other, the strain upon the stopper may be equal or nearly so 
 
Sect. XX.] STOPPERS METHODS OF LOOSENING THEM. 529 
 
 on the two sides. A cloth is now to be wrapped about the 
 bottle, the hand being applied round the neck, and the bottle 
 is to be pulled steadily. During the endeavour to separate it 
 from the stopper, the latter must be struck gently on each side 
 with the piece of wood, as before directed (1255). The force 
 with which the bottle is pulled must be increased until the 
 stopper either gives way, or the power has been increased un- 
 availingly to such a degree as to excite fear that the bottle 
 itself may break in the effort. But generally, long before this 
 fear need be entertained, the stopper will leave its place, and 
 the operation will consequently have succeeded. It is neces- 
 sary to be cautious, that as the stopper leaves the neck and 
 falls down suspended only by the string, it shall not swing 
 against anything so hard as to occasion its fracture; this is 
 easily done by putting a cloth or duster to receive it. 
 
 1263. When stoppers become fixed in the necks of jars 
 (741), they are generally removed with great facility by hit- 
 ting them from beneath with the end of a stick, which tends 
 directly to force them out of their places ; few stoppers will 
 resist this advantageous application of mechanical power. 
 The stick should be a solid and rather heavy one, but not 
 so hard as to endanger the glass. The end of the handle of 
 a hammer answers very well for the purpose, the head of the 
 hammer adding to the momentum and steadiness of the blow. 
 
 1264. If the stopper will not give way to any of these 
 methods, then all that can be done is to remove it piecemeal. 
 Large stoppers are often made hollow, to diminish their 
 weight; the heads of these may be broken off, when their 
 plugs are easily penetrated by a pointed file, and thus may be 
 separated without loss of the bottle. But if the stoppers are 
 solid, it is only by grinding that they can be removed ; this is 
 the work of the glass-cutter, and the value of the bottle is 
 seldom equal to the expense and the risk. The bottles of 
 which the stoppers have been successfully broken out, must be 
 refitted with others from the stopper-drawer (25, 1222, 1230). 
 
 1265. All the agents and methods for cleaning glass already 
 referred to, are required occasionally for the cleansing of bottles. 
 The stoppers should be cleaned at the same time ; and when 
 acids or alkalies are applied to the bottles, a little should be 
 
 2 M 
 
530 CLEANSING OF BOTTLES METAL VESSELS. [Sect. XX. 
 
 allowed to flow about the stoppers when in their places, and 
 the latter then worked in the neck for the purpose of rubbing 
 off the impurity, and bringing it more freely into contact with 
 the dissolving or detaching agent. When all foulness is dis- 
 solved or washed away, the bottles should be drained, rinsed 
 in distilled water, drained again, and then wiped; and, if 
 necessary, dried within, by warming and blowing air through 
 them (1251). This must be done with more caution than is 
 necessary for flasks, because of the greater irregularity in 
 thickness and form of these vessels. Finally, the stoppers are 
 to be replaced, a little tallow or yellow wax being put round 
 them in the manner already described (433, 741). 
 
 1266. If the laboratory be in daily use, these washings and 
 cleansings of glass should be performed every evening, the ap- 
 paratus being left to drain during the night, and then wiped 
 on the following morning. Such a practice will be found at 
 least very useful and convenient, and the vessels will be ready 
 for service at all ordinary hours of experiment. The open 
 apparatus, such as glasses, jars, &c. should be put by in their 
 respective places, with their mouths downwards, to exclude 
 dust. 
 
 1267. When oxidized and foul copper, such as wires, plates, 
 &c. are rubbed clean by sand-paper, a subtle cupreous dust is 
 diffused through the air, which is exceedingly unpleasant in its 
 effects upon the mouth and nostrils. It is better in such cases 
 to use a little water with the sand-paper ; the copper is more 
 readily cleaned, and all unpleasant effects are prevented. Foul 
 copper-plates may be cleaned also by putting them into the 
 furnace and heating them to redness for five minutes, with 
 access of air, so as to allow the formation of a coat of oxide 
 upon them, and then plunging them in water. The oxide 
 scales off, or may easily be separated by bending the plate, and 
 leaves the latter clean and metallic. 
 
 1268. When a platina crucible has become tarnished and 
 dirty by use, in consequence of the adhesion of substances, it 
 is perhaps best cleaned by making it red hot in a charcoal fire, 
 and sprinkling over it a powdered mixture of equal parts of 
 borax and salts of tartar, or carbonate of potash *. This flux 
 
 * Wollaston, 
 
Sect. XX.] CRUCIBLES MORTARS MERCURIAL TROUGH. 531 
 
 fuses over the surface of the platina, and dissolves most earthy 
 or metallic impurities, so that when, after ignition for a quarter 
 of an hour, the crucible is thrown into water and left there, the 
 flux dissolves and removes all impurity with it. It is assumed 
 that the crucible has been used fairly, and is soiled only by 
 adhering oxide of iron or other substance. If metal has by 
 any means come in contact with the platina, the ignition will 
 only do harm by making the alloy of the metal and the platina 
 more complete. In such case, if the injury, i. e. the contact of 
 the extraneous metal with the platina be slight, it may be well 
 to dissolve the former by a little nitric acid and heat ; but if 
 heat has been long applied, and the alloy be formed to a con- 
 siderable extent, nothing remains but to use the crucible for 
 the few purposes to which it may yet be applicable until it 
 becomes unserviceable. 
 
 1269. Porcelain and other mortars should be kept in good 
 and clean condition ; dry pulverizations frequently fill the 
 minute irregularities of the inner surfaces with the substance 
 pulverized, so that even after careful washing, portions still 
 remain behind. This may readily be observed with coloured 
 bodies, as oxide of iron, Prussian blue, vegetable substances, 
 &c. A little sand and water put into the mortar and rubbed 
 with the pestle over all the contaminated parts, cleans them and 
 the pestle itself so far, that the affusion of water is sufficient to 
 wash off all impurities. In some cases, sulphuric or nitric acid, 
 or solution of alkali, must be used ; their action is always faci- 
 litated by rubbing a little sharp sand at the same time in the 
 mortar with the pestle. 
 
 1270. There is one apparatus which has not as yet been 
 mentioned in this chapter, but which requires frequent atten- 
 tion relative to its state of cleanliness. This is the mercurial 
 trough (736, 782). It should be covered when out of use, 
 that dirt and dust may not have access. If these be allowed ad- 
 mission they do not merely collect upon the surface of the metal, 
 but by the mechanical motions to which the mass is subjected, 
 are often carried beneath, and are lodged and retained between 
 the mercury and the trough even at the very bottom of the 
 bath. For this reason, when a trough has been exposed to dirt 
 and dust, it is not sufficient to clean, pnly the surface with a 
 
 2M2 
 
532 MERCURIAL TROUGH MERCURY CLEANSED. [Sect. XX. 
 
 card, but the mercury should be poured out, the trough well 
 wiped and cleaned in every part, and the metal restored, after 
 it also has been cleaned and purified. 
 
 1271. The mercury may require to be cleansed both from 
 mechanical and chemical impurities ; and indeed the ordinary 
 operations of the pneumatic trough tend to confer both these 
 contaminations. The processes to be adopted for the removal 
 of extraneous matters must therefore be varied, and several 
 very different in principle have been devised. 
 
 1272. Adhering dirt and dust, as well as the thin films of 
 oxide and other impurities which attach to mercury, may be 
 removed in several ways. A very common method is to fold 
 a piece of paper into a cone, so as to make it nearly tight at 
 the apex, and to pass the mercury through it as through a 
 funnel. The aperture at the bottom may be made larger or 
 smaller by a little management of the paper : when the inward 
 fold is pulled upwards, it increases the aperture below, whilst 
 pulling the outer fold upwards a little, tends to close it. The 
 aperture may also be opened or closed more or less by applying 
 the finger to it. The mercury as it runs through should be 
 received in a glass or other proper vessel, and the last portions 
 reserved in the cone ; they will be found to abound with scum 
 and other impurities, a portion of which might pass out with 
 the metal. It is better to put these latter portions by them- 
 selves, and when they have accumulated, to purify them alto- 
 gether. This method of cleansing mercury is a ready and 
 sufficient one in numerous cases where it is only the adhering 
 dirt that is to be removed. 
 
 1273. Some persons recommend that the mercury should be 
 cleansed from mechanical dirt by being filtered through the 
 pores of a piece of hazel wood by means of atmospheric pres- 
 sure. Others squeeze it through a piece of chamois leather. 
 But when cleaned by any of these methods, a film still gene- 
 rally adheres to its surface ; and the metal when agitated has 
 a scum formed upon it, especially when chemically foul. 
 Much assistance in removing this exterior scum and dirt is 
 gained by pulverizing some loaf sugar, putting it into a bottle 
 with the mercury to be cleansed, and agitating them well toge- 
 ther. The sugar should be damped, which may be done by 
 
Sect. XX.] MERCURY CLEANSED FROM IMPURITIES. 533 
 
 breathing into the bottle two or three times ; by agitation it 
 then adheres to the dirt present, and the mercury, being 
 removed by passing it through a paper funnel, is obtained in a 
 state of great comparative cleanliness, 
 
 1274. The chemical impurities of mercury consist of certain 
 metals, such as lead, tin, zinc, &c. These interfere chemically 
 when the metal is to be used in forming combinations ; and 
 from the rapidity with which they oxidate and produce films 
 on the surface (789), interfere mechanically in its uses in the 
 bath, in certain electro-magnetic experiments, and in the con- 
 struction of thermometers and barometers. Mercury which is 
 chemically impure will soon acquire adhesive films on its sur- 
 face, even when cleared of mechanical impurities, and with a 
 rapidity dependent on the agitation of the metal or extension 
 of its surface. 
 
 1275. The first method of purifying mercury from these 
 metals is by distillation. The operation should be performed 
 in an iron retort, a portion of clean iron and copper filings 
 having been introduced with the mercury, which should be 
 condensed and received in clean water. Although this is an 
 excellent process generally, yet it is by no means unobjection- 
 able, for both zinc and arsenic will pass over, and these metals 
 are not uncommonly introduced in experiments at the mer- 
 curial trough. 
 
 1276. A very useful method of cleaning considerable quan- 
 tities of trough mercury is to put from half an inch to an inch 
 in depth into a large earthenware pan (the pneumatic trough 
 before referred to (732) answers very well for this purpose), 
 and to pour over it sulphuric acid diluted with twice its weight 
 of water. The surface of contact, and consequently of depura- 
 tion, is thus rendered very large. The substances should be 
 left together for a week or two at common temperatures, being 
 frequently agitated. At the end of that time the metal and 
 the acid are to be separated, the latter preserved for a similar 
 operation at some future period, and the former washed, dried, 
 and cleansed mechanically, as already described (1272, &c.) 
 The sulphuric acid acts more readily if a little sulphate of 
 mercury be added to it ; the residue of a process for the pre- 
 paration of sulphurous acid from sulphuric acid and mercury 
 
534 MERCURY PURIFIED BY ACIDS, [Sect. XX. 
 
 may be used for the purpose without further preparation. 
 This residue is not an uncommon one in the laboratory (448), 
 and being put all together into the pan, the mercury, the sul- 
 phuric acid, and the sulphate of mercury present in it, will 
 each be economically and usefully disposed of. 
 
 1277. An acid solution of nitrate of mercury left upon the 
 trough metal in a manner similar to that just described, will 
 also cleanse it to a great extent from other metals. The solu- 
 tion need not be very strong or in large quantity ; a week or 
 two at common temperature is sufficient for .the purpose. The 
 solution when poured off should be reserved apart from other 
 nitrate of mercury, for this particular use ; the impurities which 
 it has received from the metal, and for which it has given up 
 an equivalent portion of mercury, rendering it unfit for any 
 other than very ordinary purposes. 
 
 1278, These chemical cleansings of the trough-mercury are 
 intended to destroy the disposition which exists in impure 
 mercury to form films upon its surface. The films are pro- 
 duced by the oxidation of a very minute portion of the impure 
 metal ; they do not consist of oxide alone, but of metallic 
 matter adhering to it, which being enveloped by the film of 
 oxide, is prevented from coalescing with the fluid metal 
 beneath, and is equally injurious in its effect as if it were 
 really extraneous matter. Whenever the surface of filmy 
 mercury is extended or removed, the film from the neigh- 
 bouring parts rapidly expands over the newly exposed portion, 
 just as a drop of oil extends and expands itself over the surface 
 of water. This may be observed and understood by moving a 
 card over the surface of such mercury from one side to the 
 other : the film will be collected on the one side of the card, 
 and the recent surface on the other will become covered by an 
 extension of that which is on the metal immediately in its 
 neighbourhood. If the operation be repeated, still the renewed 
 surface will be re-covered, and thus a large quantity of film 
 may be collected, which if examined appears to consist for the 
 greater part of metallic mercury. And though after many 
 operations of this kind the surface of the metal will be much 
 cleaner than at first, yet exposure to the air for a while, espe- 
 cially if aided by agitation, will soon bring the surface into its 
 
Sect. XX.] MERCURY PURIFIED FILMS ON IT EFFECT. 535 
 
 first dirty condition, and this will continue so long as the mer- 
 cury contains metallic impurities. 
 
 1279. The manner in which these films interfere with ex- 
 periments made over the mercurial trough, is principally by 
 preventing contact between the metal and the jars or other 
 vessels used (789). If a jar be dipped into the mercury, it 
 does not break through the film and come into contact with 
 the pure metal beneath, but the film expands between the glass 
 and the metal, and from its comparatively solid and rigid 
 nature, entirely prevents that close contact which would occur 
 between pure mercury and the glass. Or if the jar be laid 
 with its side upon the mercury, every particle of the thick and 
 wrinkled film that is included between the glass and the metal, 
 will retain its place upon the sides of the jar, whatever may 
 be the depth or position in which it may afterwards be placed 
 under the surface of the mercury. 
 
 1280. When a jar thus circumstanced contains gas, of which 
 a portion is required to be transferred into another vessel, the 
 consequence is, that, as soon as the jar is so inclined as to cause 
 the gas to approach its edge, the latter escapes (788) ; for 
 instead of passing out in bubbles, and ascending through the 
 metal into the vessel above, it tends to pass up the side of the 
 jar, between the glass and the film, into the air. This is the 
 result of want of continuity, or at least of close contact there ; 
 and though the gravity of the mercury around the gas passing 
 from the edge of a jar, is a force generally sufficient to enable 
 it to overcome and break through the cohesion of mercury 
 when clean, and to occasion it to rise in distinct bubbles through 
 the metal, it is not sufficient to do so when the cohesion of the 
 film is added to that of the metal ; and when, from the inter- 
 ference of the film between the metal and the glass, a passage 
 upwards, although in a somewhat inclined position, is already 
 opened for it. 
 
 1281. In the same manner when the beak of a retort is 
 dipped into such mercury for the purpose of delivering the 
 gas, instead of passing out in bubbles, it will frequently creep 
 round the edge of the glass and ascend between the neck and 
 the mercury into the air (789.) This takes place with greater 
 facility as the mercury is more impure and filmy ; as the incli- 
 nation of the beak approaches to the perpendicular ; and as 
 
536 MERCURY PURIFIED PRIESTLEY'S METHOD. [Sect, XX. 
 
 the gas evolved tends, by its action on the metal or otherwise, 
 to favour the formation of films. Such gases as euchlorine, 
 muriatic acid, ammonia, Sec., are more apt to do this than 
 oxygen, hydrogen, nitrogen, &c. 
 
 1282. Small quantities of mercury, as, for instance, a pound 
 or two, may be purified upon particular occasions by very 
 ready and simple processes. Dr. Priestley's* method is a most 
 excellent one, and highly worthy of attention. So much foul 
 mercury is to be put into a ten or twelve ounce stoppered 
 bottle as will occupy about a fourth part of its capacity, the 
 stopper to be put in, the bottle inverted, and being held in 
 both hands is to be shaken violently, the hand that supports it 
 being generally struck against the thigh. After twenty or 
 thirty strokes the stopper is to be taken out, and the air in the 
 phial changed for fresh air by blowing into it with a pair of 
 bellows. The mercury will soon become black, and a quantity 
 of the upper part will appear as if it were coagulated, so as to 
 be easily separable from the rest ; the phial is then to be in- 
 verted, and the mouth being covered with the finger, all the 
 metal that will flow easily is to be poured out, and the black 
 coagulated part put into a cup by itself; by pressure with the 
 finger this mav easily be separated into running mercury and 
 black powder, the former, with the rest of the metal, is then 
 to be returned to the bottle and agitated as before. This 
 process is to be repeated till no more black matter separates, and 
 it is not a little remarkable that the operator will be at no loss 
 to know when that is the case, because the whole of the mer- 
 cury becomes pure at once ; and Dr. Priestley observes, with 
 regard to a portion of mercury containing lead which had been 
 thus treated, that " whereas, while the lead was in the mer- 
 cury, it felt, as I may say, like soft clay, the moment the lead 
 is separated from it, it begins to rattle as it is shaken, so that 
 any person in the room may perceive when it has been agitated 
 enough." Mercury purposely rendered impure by lead and 
 tin was found to be perfectly purified by this process. 
 
 1283. Another method is, to put the mercury to be cleaned 
 into a bottle, to add a little nitrate of mercury or a small quantity 
 
 * Experiments and Observations on Air, Vol. iv. Sect, xvi. ; or abridged edi- 
 tion, iii. 439. 
 
Sect. XX.] MERCURY PURIFIED PURITY ASCERTAINED. 537 
 
 of diluted nitric acid, to agitate well for a minute or two, then 
 to wash off the soluble parts with any portion of yellow powder 
 formed, and to dry the mercury with a cloth. If any difficulty 
 should occur from the separation of the mercury into an infi- 
 nity of globules, which may proceed so far at last as, with the 
 intervening water, to give the whole a soft solid appearance, it 
 is easily overcome by drying the mercury after it is well 
 washed, in an evaporating basin by heat. As the water eva- 
 porates, the globules of mercury will run together, and the 
 metal will be obtained in its clean and pure state. 
 
 After any of these processes, the adhering dust should be 
 removed by passing the metal through a paper cone or funnel 
 
 . The tests of the purity and cleanliness of mercury 
 are, the absence of all film or powder when a portion is shaken 
 quickly for a moment in a clean tube or bottle ; the freedom of 
 its motions upon the surface when agitated ; the extreme mo- 
 bility of its globules when a little is poured into a clean dish 
 and broken into small parts ; the perfect rotundity of form at 
 the receding edge, when a portion is made to flow from side to 
 side of a glass dish or other clean vessel ; the largeness of the 
 depression which exists, when it is put into a dry bottle, be- 
 tween the sides of the glass and the metal at the surface of the 
 mercury ; and the ready pointing of a small magnetic sewing 
 needle when laid upon its surface out of the magnetic meridian. 
 
 1285. When mercury has been purified and cleansed for 
 very particular experiments, as those relating to the barometer 
 and thermometer, extreme care is required that its surface be 
 not soiled by any portion of dirt from the hands or the vessels 
 used. The smallest quantity of greasy matter, or of deliques- 
 cent, or animal, or vegetable substances soluble in water, is 
 enough to render it improper for these uses : it is rapidly dif- 
 fused by motion over the whole surface of the metal, and even 
 a touch with the finger is sufficient to communicate so much 
 impurity as to render the mercury inapplicable in the con- 
 struction of accurate instruments. 
 
 1286. A glass should always be appointed and kept in one 
 particular place to receive any residual portions of mercury 
 that may be left in an impure state after experiments, or 
 
538 GENERAL RULES. [Sect. XXI. 
 
 gathered from the table in a dirty condition. They are thus 
 saved and accumulated, and when in considerable quantity 
 may be freed from mechanical impurity by washing (348), and 
 then be purified by that one of the methods described which 
 may be most applicable (1274). In this manner a continual 
 saving of metal is effected to a great extent ; the quantity thus 
 returned to the trough in an active laboratory in the course of 
 a year being very considerable. 
 
 SECTION XXI. 
 
 General Rules for young Experimenters. 
 
 1287. BESIDES the numerous directions which occur through- 
 out the preceding pages, there are certain general precepts and 
 rules, the observance of which will be found of great service 
 not only to those who are commencing the practice of experi- 
 mental inquiries in chemistry, but likewise to such as, having 
 made some progress, have indulged themselves in irregular 
 habits. They all relate to method, that great source of facility 
 and readiness which is equally influential in the performance 
 of the most common and the most difficult processes. Such 
 as are given in this section have been proved by long trial: it 
 is not supposed that they include all that are advantageous, but 
 they are all that suggest themselves to the mind of the author 
 as worthy to be classed together for their general usefulness. 
 Those who may add to them will deserve the thanks of the 
 practical chemist. 
 
 1288. A particular and convenient part of the laboratory 
 tables should be appointed for all general operations of experi- 
 ment. It should be considered as a place intended for working 
 only, and should not be encumbered by things carelessly laid 
 upon it : it should be understood that every article placed 
 there by the experimenter is sacred for the time ; that no appa- 
 rently dirty glass or useless bottle is to be removed, nor any 
 arrangement upon it disturbed by others who may be in the 
 laboratory, but that all is to be left until the experimenter him- 
 
Sect. XXL] GENERAL RULES. 539 
 
 self has disposed of them or given special directions to that 
 purport. It is desirable in a long course of experiments that 
 this place should be cleared as much as possible every evening, 
 that it may be ready the next day for further progress, but 
 unless this be done by the experimenter, or under his particular 
 directions, it should be left untouched. 
 
 1289- By the side of this portion of the table should be 
 another, appointed to receive apparatus, bottles, and other 
 articles that are done with. The putting of a thing here should 
 be considered as a direction that it may be cleansed and re- 
 stored to its proper place. The experimenter will do well to 
 disembarrass his part of the table during his pursuits, by 
 moving his dirty glasses, waste precipitates and mixtures, and 
 everything for which he has no further present use, to this 
 place, that they may be taken away. It is convenient that a 
 wooden tray should remain on the spot, which, when filled with 
 dismissed apparatus, may be at once removed towards the sink 
 and replaced by another. 
 
 1290. The laboratory note-book, intended to receive the 
 account of the results of experiments, should always be at hand, 
 as should also pen and ink. All the results worthy of record 
 should be entered at the time the experiments are made, whilst 
 the things themselves are under the eye, and can be re-exa- 
 mined if doubt or difficulty arise. The practice of delaying 
 to note until the end of a train of experiments or to the con- 
 clusion of the day, is a bad one, as it then becomes difficult 
 accurately to remember the succession of events. There is a 
 probability also that some important point which may suggest 
 itself during the writing, cannot then be ascertained by refer- 
 ence to experiment, because of its occurrence to the mind at 
 too late a period. 
 
 1291. The account of the day's experiments should always 
 be prefaced by noting down in the book the day, month, and 
 year ; and if the experiments relate to gaseous manipula- 
 tion, the height of the barometer, and the temperature of the 
 laboratory. 
 
 1292. On commencing the examination of a substance of 
 unknown nature, the experimenter should first proceed to the 
 most general and instructive experiments, and then to those 
 
540 GENERAL RULES. [Sect. XXI. 
 
 which are more particular. He should therefore apply heat to 
 the substance contained in a tube, and remark whether it fuse 
 or volatilize ; he should then heat it in the air upon platina 
 foil, observing whether it will burn or not, whether it will 
 evolve fumes, &c. Afterwards it should be heated in water in 
 a tube, and observed whether it be soluble ; and then trials 
 should be made to ascertain if it be sapid, if it be soluble in 
 alcohol, &c. These general examinations will soon indicate 
 to what class of bodies the substance belongs, and will point 
 out the particular train of investigation it may require ; after 
 which the substance may be dissolved by acids or alkalies, or 
 any other proper solvent, and its properties more minutely 
 ascertained. 
 
 1293. When a substance has been brought into solution, 
 and its relation to various tests and re-agents is to be con- 
 sidered, it will be proper to proceed methodically in examining 
 the different substances eliminated by their action, and not to 
 wander from one to another. The examination of the first 
 product or educt should be completed before proceeding to 
 that of a second, unless indeed it be expected that a particular 
 trial of one will throw light upon the nature of another. Gene- 
 rally speaking, it is best to pursue the precipitates, reserving 
 the remaining solution until these are examined. Thus, if an 
 ore be dissolved in an acid, and the solution be precipitated by 
 potassa, the precipitate should in this method be examined 
 before the remaining solution. If this precipitate require solu- 
 tion in an acid, and precipitation by peculiar tests, the first 
 precipitate it affords should be examined and decided upon, 
 and then the solution containing the remainder resumed, and 
 its nature made out. This done, and consequently the whole 
 of the original precipitate dismissed, the solution which re- 
 mained when it was thrown down by the potassa is to be 
 resumed, and treated with other agents. Perhaps carbonate 
 of ammonia may be applied, and cause a second precipitate 
 from it, which is, as before, to be examined previously to the 
 solution yielding it. 
 
 1294. On other occasions, the solutions may be investigated 
 before the precipitates. This plan, indeed, may be followed 
 generally, and possesses the advantage of supplying the expe- 
 
Sect. XXI.] GENERAL RULES. 541 
 
 rimenter with occupation in the solution whilst his precipitates 
 are washing. The rule intended to be impressed is, that the 
 one or the other of these plans should be adopted as a constant 
 practice ; a deviation from which is to be resorted to only 
 when it is considered as offering peculiar advantages. 
 
 1295. A plan of this kind renders the notes of the experi- 
 ments also more methodical. The different solutions and pre- 
 cipitates may be referred to by letters, as is usual in describing 
 analytical process. Thus, in the instance quoted, the original 
 solution may be called a ; the precipitate by potassa, b ; the 
 remaining solution, c ; the solution of the precipitate, d ; the 
 precipitate from it, e; and the solution with the rest of the 
 precipitate 6, /. The solution c being then resumed, the pre- 
 cipitate by carbonate of ammonia will be g, and the solution 
 remaining, h. 
 
 1296. When the substance to be examined is small in quan- 
 tity and rare, those experiments must be first made that will 
 not prevent the performance of others. The action of heat, of 
 water, and of alcohol, upon a substance may be observed, and 
 still leave it in a proper state for other experiments, as those of 
 solution and precipitation. The same portion of water which 
 has been tested for sulphuric acid by nitrate of baryta, may, 
 after filtration, be tested for muriatic acid by nitrate of silver ; 
 whereas if muriate of baryta had been used in the first place, 
 the second trial would have been impossible. 
 
 1297. New, important, and uncertain or unexpected results, 
 are to be repeated once or twice, that no doubt may exist, at a 
 future period, as to the accuracy of the notes which have been 
 made at the time of observation. 
 
 1298. Upon making a particular experiment, as of heating 
 a substance in some peculiar gas, or the decomposition of a 
 body by voltaic electricity, all the articles that are likely to be 
 wanted should be previously prepared and close at hand, that 
 no hesitation may occur in the performance of the experiment, 
 or the attention be called off from observing the results, by the 
 necessity of supplying some important omission. 
 
 1299. When a long series of experiments with the spirit- 
 lamp is in progress, a candle or lamp continually burning 
 should be at hand. 
 
542 GENERAL RULES. [Sect. XXI. 
 
 1300. On examining a mineral water by precipitants, the 
 glasses used should be placed in a row, each before the preci- 
 pitant which has been added to the water it contains : and 
 they should remain for half an hour, that any ulterior indica- 
 tion of the test may not be overlooked, yet without risk of 
 mistaking one glass for another. 
 
 1301. Every substance or glass that is entirely done with 
 should be dismissed, and placed at once on the tray of dirty 
 articles (1289). 
 
 1302. Besides the working-place (1288), another uncon- 
 nected with the busy part of the laboratory should be ap- 
 pointed, from which nothing is to be moved without the expe- 
 rimenter's direction. There are many occasions on which ex- 
 periments or solutions are to be placed aside for a week or two, 
 to be again resumed. These should be labelled, and put into 
 a place which, from previous appointment, is considered as 
 containing nothing that may be disturbed. In this way the 
 experimenter will often avoid the disagreeable circumstance of 
 finding that what he intended to reserve for future examination 
 has been dismissed to the sink or the dust-hole, A third 
 place of this kind may be appointed in a cupboard, out of the 
 way, for the reception of experiments that require weeks or 
 months for their performance (14) ; or for things that cannot 
 be resumed before long periods have elapsed. 
 
 1303. All products, educts, precipitates, or solutions, that 
 are set aside for some time, should be labelled (1345, 1363), 
 and referred to by their names or marks in the note-book. 
 Thus the precipitates and solutions, before spoken of (1295), 
 should have labels, a, b, c, &c., on the glasses or bottles con- 
 taining them. When the products are new and important, 
 this should be done immediately, that no possibility of mistake 
 from delay may be allowed to occur. The use of gummed or 
 pasted paper (1118, 1345) removes all trouble from this 
 operation. 
 
 1304. Finally, the general rules for cleanliness and order, 
 so often inculcated, are to be attended to. This Section can- 
 not be better closed than by the very excellent observations of 
 Macquer on this subject. He says, <fc A persuasion must 
 exist that arrangement, order, and cleanliness are essentially 
 
Sect. XXI.] 
 
 GENERAL RULES. 543 
 
 necessary in a chemical laboratory. Every vessel and utensil 
 ought to be well cleansed as often as it is used, and put again 
 into its place : labels ought to be attached to all the sub- 
 stances, mixtures, and products of operations which are pre- 
 served in bottles or otherwise ; these should be examined and 
 cleansed from time to time, and the labels renewed when re- 
 quired. These cares, although they seem to be trifling, are 
 notwithstanding the most fatiguing and tedious, but the most 
 important and often the least observed. When a person is 
 keenly engaged, experiments succeed each other quickly ; some 
 seem nearly to decide the matter, and others suggest new ideas; 
 he cannot but proceed to them immediately, and he is led from 
 one to another ; he thinks he shall easily know again the pro- 
 ducts of his first experiments, and therefore he does not take time 
 to put them in order ; he prosecutes with eagerness the expe- 
 riments which he has last thought of, and in the mean time 
 the vessels employed, the glasses and bottles filled, so accumu- 
 late, that he cannot any longer distinguish them, or at least he 
 is uncertain concerning many of his former products. This 
 evil is increased, if a new series of operations succeed, and 
 occupy all the laboratory ; or if he be obliged to quit the 
 place for some time, every thing then goes into confusion. 
 Hence it frequently happens that he loses the fruits of much 
 labour, and that he must throw away almost all the products 
 of his experiments. 
 
 " The only method of avoiding these inconveniences is to 
 employ the cares and attentions above mentioned. It is, in- 
 deed, unpleasant and very difficult continually to stop in the 
 midst of the most interesting researches, and to employ 
 valuable time in cleaning and arranging vessels and attaching 
 labels. These employments are capable of cooling and re- 
 tarding the progress of genius, and are tedious and disgusting; 
 but they are, nevertheless, necessary. Those persons whose 
 fortunes enable them to have an assistant operator, on whose 
 accuracy and intelligence they can depend, avoid many of 
 these disagreeable circumstances ; but they ought, neverthe- 
 less, to attend to the execution of these things. We cannot 
 depend too much on ourselves in these matters, however mi- 
 nute, on account of their consequences. This becomes even 
 
544 USES OF EQUIVALENTS WOLLASTON's SCALE. [Sect. XXII. 
 
 indispensable when the experiments are to be kept secret, 
 at least for a time, which is very common and often necessary 
 in chemistry. 
 
 " When new researches and inquiries are made, the mix- 
 tures, results, and products of all the operations ought to be 
 kept a long time well ticketed and noted (1363, 1364). It 
 frequently happens that at the end of some time these things 
 present very singular phenomena, which would never have 
 been suspected. There are many beautiful discoveries in 
 chemistry which were made in this manner, and certainly a 
 much greater number which have been lost because the pro- 
 ducts have been thrown away too hastily, or because they 
 could not be recognised after the changes which happened to 
 them*." 
 
 SECTION XXII. 
 USES OF EQUIVALENTS WOLLASTON'S SCALE. 
 
 1305. THERE is a small instrument, the invention of Dr. 
 Wollaston, which though not directly concerned in the actual 
 performance of chemical operation, is of great and constant 
 use in the laboratory, either in supplying the information 
 requisite previous to an experiment, or afterwards in interpret- 
 ing and extending its results : it would therefore be improper 
 to pass it by unnoticed in a work the very object of which is to 
 point out to the inexperienced those practices and contrivances 
 which facilitate the acquisition of experimental evidence. The 
 instrument is called a Synoptic Scale of Chemical Equivalents, 
 or more usually Wollaston' s Scale. The paper, by its author, 
 describing the nature of the scale and the manner of ascertain- 
 ing the numbers appropriated to the different substances upon 
 it, is inserted in the Philosophical Transactions for 1814. The 
 scale itself, as purchased of the instrument-maker, consists of 
 a moveable slider with a series of numbers upon it, from 10 to 
 
 * Dictionnaire de Chimie, par Macquer, ii. 486. 
 
Sect. XXII.] DEFINITE NATURE OF COMPOUND BODIES. 545 
 
 320, on each side of which and on the fixed part of the scale, 
 are set down the names of various chemical substances. 
 
 1306. It is not the object of this volume to teach the prin- 
 ciples of chemistry, and they are at no time entered into fur- 
 ther than is necessary to make the student acquainted with 
 so much of the nature of the matter spoken of as is necessary 
 for a clear comprehension. It will be sufficient therefore to 
 state that the scale is founded on three important points, the 
 constancy of composition in chemical compounds ; the equiva- 
 lent power of the quantities that enter into combination, and 
 the properties of a logometric scale of numbers; and to explain 
 briefly how these contribute to the formation of the instrument. 
 
 1307. The same compound body is always of the same com- 
 position ; no variation in the proportion of its elements can by 
 any possibility take place. 48 parts of potassa combine with 
 54 parts of nitric acid to produce 102 parts of nitre ; no me- 
 thod of putting the substances together, as by causing an 
 excess of the one or the other, or abstracting one from a pre- 
 vious state of combination, or allowing other substances to be 
 present, can cause any change in these proportions. Nor is 
 this confined to the numbers 48, 54, and 102, but whatever 
 may be the "quantity of these elements in combination, or of 
 the nitre produced, the proportions will be the same. 
 
 1308. Hence the composition of a substance being once 
 accurately ascertained, it requires no further investigation ; for 
 whenever that substance re-occurs, whatever may be its quan- 
 tity, the proportions of the elements existing in it may be 
 deduced from the former determination ; and whether nitre be 
 produced by combining together pure nitric acid and potassa, 
 or by using nitric acid with carbonate of potassa, or precipitat- 
 ing a nitrate of copper by potassa, or in any other manner, 
 still it will contain the above proportions of potassa and nitric 
 acid : whatever its quantity, yet T 4 ^ parts of it will be potassa, 
 and -f-fa nitric acid. It is but another form of this natural 
 law to say that the same quantity of an element always re- 
 quires the same quantity of another element to form the same 
 resulting compound. 
 
 1309. The second point, or the equivalent power of the 
 quantities which enter into combination, is not so evident as the 
 
 2 N 
 
546 ~ EQUIVALENT PROPORTIONS THEIR NATURE. [Sect. XXII 
 
 former ;' but it is abundantly confirmed by experiment. If a 
 quantity of sulphate of soda in solution be poured into a solu- 
 tion of nitrate of baryta, the latter being in excess, a quantity 
 of sulphate of baryta will precipitate, and nitrate of soda will 
 remain in solution with the excess of nitrate of baryta. So 
 much of the nitrate of baryta will be decomposed as is suffi- 
 cient to supply the necessary quantity of baryta to combine 
 with the whole of the sulphuric acid in the sulphate of soda, 
 and to form sulphate of baryta with it ; but the point now 
 particularly to be observed is, that the quantity of nitric acid 
 which leaves the baryta will be exactly that required to com- 
 bine with the soda separated from the sulphate of soda, to form 
 with it the neutral salt, nitrate of soda ; for the two solutions, 
 after mixture and chemical change, will be found as neutral as 
 before. 
 
 1310. It is evident from the result of this experiment, that 
 the nitric acid is exactly equivalent in combining and saturating 
 power to the sulphuric acid ; for they have both equally 
 neutralized the portion of soda in the solution, and, what is 
 more, they have also both equally neutralized the portion of 
 baryta, which has changed acids during the experiment. Upon 
 very slight consideration it will be perceived too, that the 
 baryta in the sulphate, and the whole of the soda, are similarly 
 circumstanced with respect to each other ; for they have both, 
 during the experiment, exactly neutralized the active portions 
 of the two acids. The excess of nitrate of baryta undergoes 
 no change during the experiment, and is merely considered as 
 present to ensure the total decomposition of the sulphate of 
 soda. If the quantity of dry nitrate of baryta has been 132 
 parts, and the quantity of dry sulphate of soda 72, then the 
 whole of the acids and bases present will have changed places 
 in the manner just described. 
 
 1311. Similar phenomena are presented by all other neutral 
 saline bodies : the reciprocity of saturating power is found to 
 exist as above described whenever chemical change takes place, 
 and is therefore dependant upon no particular body, but 
 belongs to all. Hence a correct notion may be formed of the 
 meaning of the term equivalent as applied to bodies acting 
 chemically. The quantities of substances, which, by combining 
 
Sect. XXII.] CHEMICAL EQUIVALENT WHAT IT IS. 547 
 
 together, saturate each other, are equivalent in their power of 
 combination ; thus 40 parts of sulphuric acid are equivalent to 
 the saturation of 78 parts of baryta. The quantities of two or 
 more substances which combine with and saturate an equal 
 quantity of the same substance, are equivalent to each other in 
 their saturating power ; thus 40 parts of sulphuric acid and 54 
 parts of nitric acid are equivalents, for both are competent to 
 combine with and neutralize 32 parts of soda or 78 parts of 
 baryta (1310); and the latter are equivalents for the same 
 reason. Also the quantities of compound bodies which 
 mutually act upon each other are equivalents, because the 
 same proportional quantities are always necessary and always 
 sufficient. 
 
 1312. The term chemical equivalent may therefore be used 
 to imply that proportion of a body which is necessary to act 
 upon another body, the circumstances of chemical affinity 
 being such as to permit action to take place ; and it has been 
 found that the proportions are the same for one body, what- 
 ever other body it be compared with. So that if a particular 
 number be arbitrarily taken to represent the quantity of any 
 one substance competent to enter into combination, and be called 
 its equivalent, then all the equivalents of other substances may 
 be set down in numbers, those numbers being in the same pro- 
 portion to the first number, that the combining quantities of 
 the bodies they represent are, to the combining quantity of the 
 substance to which that first number belongs. Thus in the 
 change between nitrate of baryta and sulphate of soda (1309), 
 suppose the number 40 to be assumed as the equivalent 
 number of the sulphuric acid present, then 32 will be the 
 equivalent of the soda, for so much is combined with the 40 of 
 sulphuric acid ; and 54 will be the equivalent of the nitric 
 acid, for so much will combine with the 32 of soda, and 78 will 
 be the equivalent of the baryta ; 118 will be the equivalent of 
 the sulphate of baryta, 72 of the sulphate of soda, 132 of the 
 nitrate of baryta, and 86 of the nitrate of soda. 
 
 1313. The determination of these equivalents, or equivalent 
 numbers, is purely a matter of experiment. Any errors which 
 we may adopt with regard to their value, depend entirely 
 upon the errors of our experiments, or our mistaken inter- 
 
 2 N 2 
 
548 L060METRIC LINE OF NUMBERS. [Sect. XXII. 
 
 pretation of them, and not upon a possible change of their real 
 value, under any circumstances. So that once well ascertained, 
 they become a safe and invaluable source of information to the 
 chemist ; which he may refer to and use with the utmost faci- 
 lity, by means of Dr. Wollaston's scale. 
 
 1314. The third point necessary to the scale is the logo- 
 metric line of numbers; or, as it is termed, the common 
 Gunter's line of numbers. It will be found that the numbers 
 are so arranged in this line, that at equal intervals they bear 
 the same proportion to each other. The student will easily 
 observe and understand this, by measuring a few distances 
 upon the scale with a pair of compasses, or even a piece of 
 paper. If his paper extend from 10 to 20, it will also extend 
 from 20 to 40, or from 55 to 110, or from 160 to 320. What- 
 ever number is at the upper edge of the paper will be doubled 
 at the lower. If any other distance be taken, the same effect will 
 be observed. If, for instance, the paper extends from 10 to 
 14, then any other two numbers found at its upper and lower 
 edge will be in the same proportion as these two numbers 10 
 and 14. Thus make the upper number 100, and the lower 
 number will be 140. 
 
 1315. Now, supposing that the paper were cut of such a 
 width that, one of its edges being applied upon the scale to 
 the number representing the equivalent of one body, the other 
 should coincide with the number of the equivalent of a second 
 body ; then upon moving the paper, wherever it was placed 
 over the numbers, those at its upper and lower edges would 
 still represent the corresponding proportional quantities of the 
 two bodies as accurately as at first, because the numbers at 
 equal distances on the scale are proportional to each other. 
 Thus suppose the upper edge were made to coincide with 40 
 and the lower with 78, then the upper edge might be called 
 sulphuric acid, and the lower baryta; and this width once 
 ascertained, the paper wherever applied upon the scale, would 
 shew at its lower edge the quantity of baryta necessary to 
 combine with the quantity of sulphuric acid indicated by its 
 upper edge. 
 
 1316. It is evidently of no consequence whether the paper 
 be moved up and down over the scale, or the line of numbers 
 
Sect. XXII.] SCALE OF EQUIVALENTS HOW CONSTRUCTED. 549 
 
 be moved higher and lower, to bring its different parts to the 
 edges of the paper. And supposing the piece of paper just 
 described to be pasted upon the side of the scale, then by 
 moving the latter any of the numbers might be made to coin- 
 cide with the upper or lower edge at pleasure, and consequently 
 the quantity of sulphuric acid necessary to combine with any 
 quantity of baryta, and vice versa, ascertained by mere adjust- 
 ment and inspection of the scale. Or if, instead of referring to 
 the separate piece of paper, marks were to be made on the side 
 of the scale at 40 and 78, and named sulphuric acid and 
 baryta, the same object would be attained, and the same method 
 of inquiry rendered available. 
 
 1317. Other substances are to be put down upon the scale 
 exactly in the same manner. Thus the scale being adjusted 
 until the number 40 coincides with the sulphuric acid already 
 marked, then sulphate of baryta is to be written at 118, and 
 thus its place is ascertained ; nitrate of baryta at 132 ; soda 
 at 32 ; sulphate of soda at 72 ; and a simi la process is to be 
 adopted with every substance, the number of which has been, 
 ascertained by experiment. The instrument, which in this 
 state merely represents the actual number supplied by experi- 
 ment, will faithfully preserve the proportions thus set down, 
 whatever the variation of the position of the slider may be. It 
 is therefore competent to change all the numerical expressions 
 to any degree required, the knowledge of one only being suffi- 
 cient first by adjustment, and then by inspection to lead to 
 the rest. 
 
 1318. A few illustrations of the powers and uses of this scale 
 will be sufficient to make the student perfect master of its 
 nature and applications. Suppose that in analysing a mineral 
 water, the sulphates in a pint of it have been decomposed by 
 the addition of muriate of baryta, and the resulting sulphate 
 of baryta washed, dried, and weighed: from its quantity may 
 be deduced the exact quantity of sulphuric acid previously ex- 
 isting in the mineral water. Thus, if the sulphate of baryta 
 amount to 43.4 grains, the slider is to be moved until that 
 number is opposite to sulphate of baryta, and then at sulphuric 
 acid will be found the quantity required, namely 14.7 grains. 
 In the same manner the scale will give information of the 
 
550 SCALE OF EQUIVALENTS ITS USE. [Sect. XXII. 
 
 quantity of any substance contained in a given weight of any 
 of its compounds ; these having previously been deduced from 
 experiment, and accurately set down on the scale in the manner 
 just explained (1317, 1307). 
 
 1319. If it be desired to know how much of one substance 
 must be used in an experiment to act upon another, it is evi- 
 dent that the equivalent must be taken, and this may be 
 learned from the scale. Suppose that a pound of sulphate of 
 baryta has been mixed with charcoal, and well heated, to con- 
 vert it into a sulphuret, and that by the addition of nitric acid 
 it is to be converted into nitrate of baryta. The quantity of 
 acid which will probably be required may be learned by bring- 
 ing 100 to sulphate of baryta, and then by looking for the 
 number opposite nitric acid : it will be found to be 46. But 
 this represents the quantity of dry acid ; casting the eye there- 
 fore lower down upon liquid nitric acid of a specific gravity 
 of 1.50, it will be found that 61 Ibs. or a little more, is the 
 equivalent for 100 Ibs., and consequently that 61 hundredth 
 parts, or somewhat above six-tenths of a pound of such acid, 
 will be sufficient for the pound of sulphate of baryta operated 
 with. 
 
 1320. If a certain weight of carbonate of baryta be required 
 in that moist and finely divided state in which it is obtained 
 by precipitation, and in which it cannot be weighed, the accu- 
 racy of the quantity may be ensured by taking the equivalent 
 of dry muriate, or nitrate of baryta, precipitating it by an 
 excess of carbonate of potassa, and then washing off the salts 
 which remain in solution. Suppose 100 grains of the carbonate 
 were required ; by bringing that number to carbonate of baryta, 
 it will be found that the quantity of dry muriate necessary will 
 be 105.8 parts, and the quantity of nitrate 133.4 ; and if the 
 quantity of carbonate of potassa necessary for this purpose be 
 also required, it will be found opposite the name of that sub- 
 stance on the scale, to be little less than 70 parts, so that 5 
 or 10 parts more will ensure a satisfactory excess. 
 
 1321. The second paragraph of Dr. Wollaston's description 
 of this scale may be transcribed, as a further illustration of the 
 powers of the instrument. " If, for instance, the salt under 
 examination be the common blue vitriol, or crystallized sul- 
 
Sect. XXII.] ITS USE ILLUSTRATED. 551 
 
 phate of copper, the first obvious questions are (1) How 
 much sulphuric acid does it contain ? (2) How much oxide 
 of copper ? (3) How much water ? He [the analytic che- 
 mist] may not be satisfied with these first steps in the analysis, 
 but may desire to know further the quantities (4) of sulphur, 
 (5) of copper, (6) of oxygen^ (7) of hydrogen. As means of 
 gaining this information, he naturally considers the quantity 
 of various re-agents that may be employed for discovering the 
 quantity of sulphuric acid (8), how much barytes (9), car- 
 bonate of barytes, or (10) nitrate of barytes, would be requisite 
 for this purpose? (11) How much lead is to be used in the 
 form of (12) nitrate of lead ; and when the precipitate of 
 (13) sulphate of barytes, or (14) sulphate of lead are obtained, 
 it will be necessary that he should also know the proportion 
 which either of them contains of dry sulphuric acid. He 
 may also endeavour to ascertain the same point by means of 
 (15) the quantity of pure potash, or (16) of carbonate of potash 
 requisite for the precipitation of the copper. He might also 
 use (17) zinc, or (18) iron, for the same purpose, and he may 
 wish to know the quantities of (19) sulphate of zinc, or 
 (20) sulphate of iron, that will then remain in the solution." 
 
 1322. All these questions and points are answered by mov- 
 ing the slider until the number expressing the quantity ope- 
 rated with coincides with sulphate of copper crystallized. 
 5, Water. Let it for instance be 100: this being brought 
 opposite crystallized sulphate of copper^ the information rela- 
 tive to all the above points, except the sixth and seventh, is 
 supplied by mere inspection. The sixth may be supplied by 
 subtracting (5) the quantity of copper from (2) the quantity 
 of oxide of copper, or by halving the quantity at 2 oxygen, or 
 taking the third of that at 3 oxygen. The seventh relates to 
 the quantity of hydrogen in the 5 water present in the salt ; 
 this quantity of hydrogen does not come within the line of 
 numbers, but may easily be obtained by doubling the quantity 
 of water, or doubling the quantity of the salt used, which 
 will then bring 10 hydrogen into the scale, and the half 
 of this is to be taken as the quantity in 5 water or in 100 
 grains of the salt. Putting therefore 200 to sulphate of 
 copper, 10 hydrogen is indicated as 17 parts nearly, when 
 
552 SYNOPTIC SCALE. [Sect. XXII. 
 
 of course the half of this, or 8.5 parts, is the quantity in 100 
 grains of the crystallized salt of copper. 
 
 1323. Whenever it thus happens that the number known or 
 the number sought for is out of the scale, then some convenient 
 multiplier of the numbers may be used. The most convenient 
 method is to use the tens or the hundreds as units, or, what is 
 the same thing, to consider for the time that decimal points are 
 inserted between the units and the tens, or between the tens 
 and the hundreds of all the numbers on the scale. Thus if it 
 were required to ascertain how much magnesia and sulphuric 
 acid were contained in a pound of crystallized sulphate of mag- 
 nesia, no 1 exists upon the scale, and of course no fractions or 
 small parts of 1 ; but imagine decimal points between the tens 
 and the hundreds, then ten upon the scale become one-tenth, 
 22 twenty-two hundredths, 100 one, 220 two and two-tenths, 
 and so on. Bringing therefore 100 to crystallize sulphate of 
 magnesia, it represents the 1 pound, and by inspection it will 
 be found that it contains 16 hundredths of a pound of mag- 
 nesia, and 32 J hundredths of a pound of sulphuric acid. 
 
 1324. As another illustration : suppose that the quantity of 
 magnesia in 50 Ibs. of crystallized Epsom salt were required ; 
 upon bringing 50 opposite the name of the salt, the quantity 
 of magnesia will be found smaller than any quantity expressed 
 upon the scale : but all that is necessary to obtain the answer 
 is, to double the quantity of the salt, and then to halve the 
 quantity of magnesia indicated ; in which way it will be found 
 that the 50 Ibs. contain about 8 Ibs. of the earth. 
 
 1325. These Synoptic scales are generally constructed of 
 paper or wood. Those on paper are first laid down accurately 
 upon copper, are then engraved, impressions worked off upon 
 paper, and these impressions pasted upon a wooden frame and 
 slider prepared for them. It is almost impossible that these 
 scales should be accurate, because of the extension and contrac- 
 tion of paper when it is damped, and again dried, and the 
 facility with which it yields to mechanical impressions, and may 
 be stretched when in a moistened state. When the paper is 
 pasted to make it adhere to the wood, it extends considerably 
 in all directions ; and though this extension, as caused merely 
 by ^dampness, would not very much surpass that which had 
 
Sect. XXII.] SCALES OF EQUIVALENTS ERRORS. 553 
 
 taken place in the paper when damped, previous to its receiving 
 the ink from the copper plate, it is seriously increased by the 
 rubbing and other mechanical action employed, both in apply- 
 ing the paste from a brush, and in afterwards bringing the 
 paper into close contact at every part with the wood. These 
 scales should never therefore be considered as accurate when 
 they first come from the instrument-maker. They may be 
 examined by a pair of compasses or a piece of paper, as before 
 described (1314), to ascertain how nearly equal intervals on 
 the scale of numbers accord with equal proportions between 
 the numbers at the extremities of those intervals, and thus the 
 degree of error in them, and the part where it exists to the 
 greatest extent, may be observed : but it will be useless to do 
 so with the view of finding one so accurate as to dispense with 
 calculation in exact analytical experiments. 
 
 Those scales, which are laid down directly upon wood, 
 though not liable to the same sources of error as the paper 
 scales, are still seldom, if ever, so accurate as to compete with 
 calculation. 
 
 1326. The errors just referred to relate to the accuracy of 
 the scale of numbers, and its proportional value in every part. 
 Others relate to the imperfect and inaccurate results of the 
 experiments, by which the numbers representing the equivalent 
 or combining quantities of bodies are obtained. If an inaccu- 
 rate result be mistaken for a correct one, and the proportional 
 number of a body be entered erroneously upon the scale, it is 
 evident that all estimations of substances including that body, 
 which are given by the scale, must involve this original inac- 
 curacy. Whenever therefore a more accurate determination of 
 the number of a body is obtained than was before possessed, 
 its place on the scale should be corrected ; and as the equivalent 
 numbers of substances, previously undetermined, are satisfac- 
 torily ascertained, they should be put upon the scale in their 
 proper situations, as before described (1316, &c.) 
 
 1327. In consequence of the unavoidable errors in the scale 
 of numbers, which, however small, still interfere in the investi- 
 gation of complicated cases and the determination of accurate 
 conclusions, the instrument should only be used in those in- 
 stances where accuracy within a certain degree is sufficient for 
 
554 TABLE OF EQUIVALENTS CALCULATION. [Sect. XXIIr 
 
 the purpose. All nicer results should be obtained by calcula- 
 tion from a table of equivalents : if, for instance, the quantity 
 of sulphuric acid in 64.7 grains of sulphate of baryta were 
 required to two or three places of decimals, it would be better 
 to take the equivalent numbers of sulphate of baryta and sul- 
 phuric acid from such a table, and to say, as the first number 
 is to the second, so is 64.7 to the quantity of sulphuric acid it 
 contains, than to work with the scale. The present determina- 
 tion of the sulphate of baryta is 118, and that of sulphuric acid 
 40, hydrogen being 1 or unity, and as 118 is to 40, so is 64.7 
 to 21,932 very nearly. It will be impossible to ascertain this 
 last number accurately on an ordinary scale, or to observe how 
 far it differs from 22. 
 
 There are numerous tables of equivalents published in dif- 
 ferent chemical works. Whichever may be adopted should be 
 examined from time to time, and the numbers affixed to bodies 
 on it corrected, whenever they are more accurately determined. 
 
 1328. It has been shewn by Gay Lussac and others, that 
 all gases and all volatile substances when in the state of vapour, 
 combine or act chemically in volumes, which have very simple 
 relations to each other. Thus a volume of hydrogen combines 
 with half a volume of oxygen to form a quantity of water, 
 which, if raised into vapour, and corrected for temperature, &c. 
 is equal in bulk to the volume of hydrogen used. A volume 
 of hydrogen combines with a volume of chlorine, to form two 
 volumes of muriatic acid ; and with a volume of the vapour of 
 iodine to form two volumes of hydriodic acid. Three volumes 
 of hydrogen combine with one volume of nitrogen to form two 
 volumes of ammonia ; and half a volume of oxygen, on com- 
 bining with carbon to form carbonic oxide, becomes a whole 
 volume. 
 
 1329. Relations of this simple kind have been found to exist 
 in the case of every volatile body, which has been particularly 
 examined in reference to this point. These volumes once ascer- 
 tained, may be considered in the relation of equivalents, and 
 their proportions are so simple, as to be remembered without 
 the least difficulty : it is therefore highly advantageous, in all 
 tables of chemical equivalents, to place small diagrams by the 
 sides of the substances and their numbers, which may represent 
 
Sect. XXII.] TABLE OF EQUIVALENTS ARRANGEMENT. 555 
 
 the volumes of the equivalents when brought into the state of 
 gas or vapour. For it requires no great power of discernment 
 to perceive that, if bodies combine in definite weights (1307), 
 and also in simple ratios of volumes, these volumes so combining 
 must contain the weights previously found to be definite : for 
 whether two substances which combine to form a third are 
 observed by weight or volume, still they combine only in one 
 proportion. 
 
 1330. So arranged, the table will have an appearance of the 
 following kind : 
 
 Hydrogen 1 .... I I 
 
 Oxygen 8 . . . . CU 
 
 Chlorine ..... 36 .... d 
 
 Iodine 125 .... EH 
 
 Water 9 .... D 
 
 Muriatic acid ... 37 .... I LJ 
 
 Hydriodic acid ... 126 .... I I J 
 
 Ammonia 17 .... LJ I 
 
 and will be found very useful when referred to for gaseous or 
 vaporous substances. The proportions of these volumes are 
 much more easily remembered than the proportions of their 
 equivalent numbers ; which, added to the facility with which 
 the bulks of gases or vapours are ascertained, may often pro- 
 perly induce the chemist to dispense with the determination of 
 weights, and work with volumes only. 
 
 SECTION XXIII. 
 MISCELLANEA. 
 
 1. Uses of Corks. 
 
 1331. THE cork-drawer (25), and some of the uses of corks, 
 have been already referred to, whilst speaking of the facility 
 of their conversion into stands for vessels (67), and handles for 
 hot tubes (918). Their cheapness and general qualities place 
 
556 USES OF CORKS. [Sect, XXIII. 
 
 them in constant requisition in the laboratory. They make 
 excellent wedges at the joints of glass apparatus, or between 
 glass and other substances, yielding in consequence of their 
 elasticity and softness, and adapting themselves to the form of 
 the glass over a considerable surface. 
 
 1332. Their use as stoppers for bottles and jars is very 
 common. When cut from good cork, they may be employed 
 even in closing the apertures of pneumatic apparatus attached 
 to the air-pump ; and notwithstanding that, when so em- 
 ployed, they are subjected to the air's pressure, they will 
 remain perfectly tight for an hour or more, if their surface 
 has been rubbed over with a little soft cement (1127). They 
 are very convenient as stoppers for jars, globes, and other ex- 
 perimental apparatus, because of their ready admission of a 
 sharp point, and other modes of attachment (835, 836). The 
 wires of deflagrating spoons may be passed through them 
 (740). Tubes for voltaic decomposition may be prepared by 
 closing their ends with a cork, through which a wire has been 
 passed (1046). A fine wire passed through a cork will serve 
 to give motion to apparatus within a vessel closed by the latter, 
 without permitting any appreciable portion of air or gas to 
 pass ; and in this manner wire and cork may occasionally be 
 made to supply the place of a sliding rod, passing through an 
 air-tight stuffing-box. Sometimes corks may be strengthened, 
 when used as stoppers, by passing through them a wire attached 
 to a metallic button at the lower surface, and terminated above 
 in a ring or handle, somewhat in the manner of decanter corks. 
 
 1333. Corks being very bad conductors of heat are formed 
 into ready and excellent handles for the support of hot rods and 
 wires, and for the insulation of hot pipes. They serve equally 
 well for the support of cold apparatus ; and three or four corks 
 or bungs make excellent feet to a vessel containing a refrigerating 
 mixture, which is to be preserved in a cold state for as long a 
 time as possible. A long cork makes a ready and good handle 
 for the pole of a powerful voltaic battery (1044), and prevents 
 the unpleasant effects of an accidental discharge of the battery, 
 through the arms of the operator. 
 
 1334. Those which are supplied for laboratory use should 
 be both elastic and compact. When to be used as wedges 
 
Sect. XXIII.] USES OF PAPER. 557 
 
 between glass, or inserted into apertures, they may be softened, 
 either by pressure between the fingers, by rolling them under 
 a weighted board, or by heat. 
 
 2. Uses of Paper. 
 
 1335. Paper will often supply the persevering chemist with 
 a substitute for numerous vessels, when his ardour urges him 
 to pursue a subject under circumstances of great deprivation, 
 as regards his usual means. Good wove and hot-pressed 
 writing-paper is the most desirable, but any that is sized may 
 be made to answer the same purposes. By folding the edges 
 of triangular or square pieces, little vessels may be constructed, 
 which are water-tight, and in which precipitations may be 
 made, and the action of re-agents observed. On such occa- 
 sions, the water or solution should not be put into the paper 
 vessel until the precipitant is ready to be added, and the result 
 should be immediately observed ; the short time which then 
 elapses will not be sufficient to communicate any sensible im- 
 purity to the fluid from the paper. Or if the paper be such as 
 has been imbued with wax, a much longer time may be allowed 
 before any impurity communicated from it to the water need 
 be suspected. Coloured precipitates are observed in such vessels 
 with great advantage. Dr. Paris long since pointed out this 
 use of paper as applicable to the detection of arsenic by nitrate 
 of silver. Even heat may be applied to water in paper vessels ; 
 and though it is not often that the experimenter is likely to be 
 driven to such extremities as to have occasion to resort to such 
 resources, it is proper that he should be acquainted with them. 
 A pint or more of water may be boiled with perfect safety in a 
 paper vessel made out of half a sheet of good cartridge paper, 
 placed over a chemical lamp (212). 
 
 1336. Waxed paper may be purchased of Messrs. Fisher 
 and Toller, of Conduit-street, Bond-street ; or it may be 
 readily made by laying the paper upon a clean hot plate (609,) 
 and rubbing it over with a piece of wax tied up in muslin or 
 cloth. 
 
 1337. The use of paper in forming tubes (246, 272, 842, 
 976) has been already referred to : the elasticity of writing 
 paper is such, that a tube constructed of three or four convo- 
 
558 USES OF PAPER TUBES. [Sect. XXIII. 
 
 ]utions, being tied round with thread or twine, and preserved 
 from rough treatment, may be considered as tight at low pres- 
 sures. It is not intended to say that no gas will pass out of it 
 in any length of time, except at the extremities, but that the 
 quantity is so small that such a tube may be used upon urgent 
 occasions for the conveyance of hot air, carbonic acid gas, or 
 coal gas, or in any other experiment on gases, where exact 
 quantities are not necessary. Those who have suddenly had 
 occasion to collect gas from natural or unanticipated sources, 
 such as the blowers of coal mines, the fissures of the earth, the 
 flues of furnaces, or brewer's fermenting vessels, will fully ap- 
 preciate the use of these and similarly rough but ready instru- 
 ments. 
 
 1338. When the edges of the paper are pasted, the tightness 
 is more permanently ensured. If the whole of one side of the 
 paper be pasted before it be rolled up, the tube will be still 
 tighter and stronger, and being then varnished or covered with 
 a coat of drying oil, will serve for the conveyance of steam and 
 water, as well as of gases. It may be strengthened if there be 
 occasion by passing twine round it (272). Waxed paper (1336) 
 also makes excellent tubes for the conduction of fluids, vapours, 
 
 and gase. 
 
 1339. When the tubes are intended for the conveyance of 
 inflammable gas, they may be made of paper which has pre- 
 viously been washed with a saline solution (976), so as to 
 render it incapable of taking fire and burning with flame. 
 Tubes which are pasted or cemented together, are easily made 
 by folding them upon a round ruler or wooden rod, or upon a 
 wire, a piece of loose paper having been first put upon the 
 ruler or wire, to permit of its ready removal when the tube is 
 finished. 
 
 1340. Round discs of thick writing or cartridge paper, or 
 of card, answer the purposes of glass plates (1348, 1222), 
 for covering glasses at common temperatures, and excluding 
 impurity. 
 
 1341. Waxed paper is very useful when bottles or tubes 
 cannot be obtained, for wrapping up deliquescent or changeable 
 substances, so as to preserve them from water and air. Solid 
 bodies, like crystals, which are to be transported to some dis- 
 
Sect. XXIII.] USES OF PAPER JACKETS STOPPERS 559 
 
 tance, and would be injured by being folded up carelessly in 
 flat paper, may be secured occasionally in little tubes of tah 
 same material, closed by a cork at each end, the tube being 
 tied round with thread or twine upon the cork. 
 
 1342. Paper funnels are of continual service, especially if 
 made of waxed or oiled paper. They may be formed aither 
 by rolling the sheet into a cone, the apex of the cone being 
 in the middle of one of the sides of the paper, as in a grocer's 
 envelope for sugar, or by wrapping up the pieces of paper in 
 the manner of a simple filter (533), and piercing the point. 
 The first kind are the strongest, if the external fold be made 
 fast by a little paste, or a piece of soft cement (1125), and 
 may be made more or less inclined in the side. Fluids, even 
 acids, may be poured through these funnels, especially if of 
 waxed paper : they also serve for filtering funnels ; for con- 
 ducting gas into jars and bottles ; for collecting the gas of 
 stagnant waters ; and for numerous other purposes. 
 
 1343. Similar cones of paper, but of a larger size, are useful 
 for keeping hot or cold materials from exposure to the air 
 (544), to retard their change of temperature. If a glass con- 
 taining a frigorific mixture be applied to freeze a substance 
 inclosed in a tube or wrapped up in foil, the powers of the 
 mixture would diminish much more rapidly by the free contact 
 of the air than by the matter experimented upon ; and in the 
 course of an hour its low temperature and consequent efficacy 
 would probably be gone. But being supported on two or 
 three corks, and covered over by a paper cone, the contact of 
 air and other substances is prevented, and the glass will remain 
 at a very low temperature for many hours. In the same 
 manner paper jackets, or loose sheets of paper, tied round 
 apparatus which are to be retained in a hot (425, 440, 473, 
 706, 941) or a cold (457) state, are very serviceable in pre- 
 venting the diffusion or the reception of heat by the access of 
 air. If an attempt were made on a hot day to freeze the water 
 at one end of a Wollaston's cryophorus by applying a freezing 
 mixture to the other, it would probably fail, because of the 
 rapid transmission of heat to the exposed ball, but if this ball 
 be wrapped up loosely in one or two folds of paper, then the 
 experiment will be sure to succeed. 
 
560 LABELS USES OF COPPER WIRE. [Sect. XXIII. 
 
 1344. Similar small cones of paper held together and finished 
 by folding the edge of the base inwards all round, serve as 
 stoppers to flasks, bottles, tubes, &c., and are often useful in 
 closing the apertures of vessels, especially such as are used for 
 processes of sublimation. 
 
 1345. Paper, on one side of which a coat of gum, paste, or 
 any other cementing matter has been applied which may be 
 brought into an adhesive state by water, has been already 
 referred to as supplying ready labels (1118, 1303). It is 
 equally useful for the instantaneous manner in which it serves 
 to form tubes, funnels, and cones, and to join fractures tempo- 
 rarily, or wheresoever adhesion is suddenly required. 
 
 Paper prepared in a similar way with a mixture of 1 part 
 wax, and 4 parts Venice turpentine, forms excellent extempo- 
 raneous labels, which adhere by the warmth of the hand, may 
 be immediately written upon, and do not peal off. 
 
 1346. Tough paper may even be made to answer the pur- 
 poses of string. A slip of whited brown paper, about two- 
 thirds of an inch in width, being rolled together between the 
 fingers into the resemblance of twine, has considerable strength. 
 Parcels packed up in this manner have arrived safely in this 
 country from China. 
 
 3. Uses of Copper wire. 
 
 1347. Copper wire, when annealed, is, on account of its 
 flexibility, the best kind of wire that can be ordinarily used 
 in the laboratory for binding apparatus together. This service 
 it has to perform very frequently. It is also very useful in 
 forming temporary supports for tapers, tubes, or arranged 
 apparatus ; as also in assisting in the formation of apparatus 
 itself, especially such as is intended for electro-magnetical 
 experiments. It is the best kind of wire for the poles and 
 connections of Voltaic and electric batteries, not only for its 
 flexibility, but also for its high conducting power as respects 
 electricity (1036). When old or useless, it should be wrapped 
 together, or cut into pieces of about an inch in length, and 
 reserved for the purpose of making nitrous gas. Two sizes 
 of copper wire at least will be required in the laboratory ; the 
 one about one-twentieth, and the other one-fifth of an inch in 
 diameter. 
 
Sect. XXIIL] USES OF GLASS PLATES TIN FOIL. 561 
 
 4. Uses of Glass Plates. 
 
 1348. The glass plates mentioned formerly (379, 563, 575, 
 587) are made by clipping fragments of plate glass (1227, 
 1228) into circular discs, from one inch to three or four in 
 diameter, and are applicable to numerous purposes. Being 
 perfectly plane on both surfaces, they are often used to close 
 the apertures of jars (740), of which the tops or ends are 
 ground, and are frequently more convenient than basins for 
 the transference of jars containing gas, especially from shallow- 
 portions of fluid or in confined situations (754) . They serve 
 as covers to glasses and jars ; as vessels for the evaporation 
 and crystallization of small portions of fluids or solutions 
 (575), and as insulators in electrical or electro-chemical ar- 
 rangements. In the latter, drops of the fluids to be decom- 
 posed should be put upon them (1047), or the metallic vessel 
 containing the fluid should be placed on the glass plate. 
 They are often very valuable in testing minute quantities; 
 the smallest quantity of a re-agent may be added to a drop of 
 a solution placed on such a plate, and from the transparency 
 of the plate, and the different positions in which the tested 
 matter may be held, the appearances may be observed to the 
 greatest advantage. 
 
 5. Uses of Leaf and Sheet Metals. 
 
 1349- Tin foil is very useful in the laboratory as a con- 
 ductor of electricity for the purpose of establishing a metallic 
 communication between the different apparatus standing upon 
 it, and for the purpose of forming metallic linings and coat- 
 ings to those which, like the Leyden jar, require them. It 
 may readily be cut with scissors or a knife, and is easily ap- 
 plied by means of paste and rubbing with the hand, as in 
 the case of pasted paper. It is highly useful upon certain 
 occasions of refrigeration, particularly when a solid substance 
 requires immersion in the mixture. The metal leaf should be 
 wrapped so closely round the substance to be frozen, as to 
 prevent the penetration of the frigorific mixture, and being a 
 good conductor of heat, the circumstances are then the most 
 favourable for rapid and great diminution of temperature. It 
 
 2 O 
 
562 LEAD, COPPER, AND ZINC PLATE AND LEAF. [Sect. XXIII. 
 
 is often useful also when wrapped round tubes to darken a 
 certain point, or to cool that part more rapidly. It is a very 
 manageable leaf metal, but should not be handled carelessly, 
 lest it become full of holes, when it is, of course, no longer a 
 water-tight wrapper. 
 
 1350. Lead leaf has similar uses. Sheet lead is of consi- 
 derable service in supplying counterpoises for the balance (39) 
 being readily cut by a knife or scissors. It is of service in 
 heating and cooling bodies by contact ; and from the facility 
 with which it yields under the hammer or pressure, may easily 
 be formed into dishes or basins when those of metal are ne- 
 cessary for particular purposes; or into vessels for freezing, 
 and into other temporary apparatus, when better cannot be 
 had. 
 
 1351. Copperplate is of great service as an electromotor, 
 and, in conjunction with the metal zinc, is of continual use in 
 Voltaic electricity. Slips of it are required also in the labora- 
 tory for the precipitation of certain metals. It is soft when 
 annealed, and is then easily bent into temporary metallic 
 vessels. Copper foil has been already referred to as of the 
 greatest service when wrapped round glass tubes (716), both 
 in strengthening and conducting the heat uniformly over them. 
 It is often used in the same manner, on a smaller scale, with 
 tubes closed at one end and held by the hand. Copper leaf, 
 as it is usually called, is a particular kind of brass, which, 
 being extended very greatly, answers well for observing, in a 
 general manner, the effect of agents upon a metal in a finely 
 divided state. 
 
 1352. Zinc plate and leaf. Zinc, rendered malleable, and 
 rolled out into plate and leaf, is very useful in both forms, 
 Plate or sheet zinc is a powerful electromotor, and with sheet 
 copper, as above mentioned, enters into the construction of 
 Voltaic apparatus. A temporary instrument may be formed 
 in a few minutes with these two metals and a few disks of 
 flannel. Plates of sheet zinc are often required for the preci- 
 pitation of metals. The foil, being thinner than the plate, 
 answers for similar occasions when a smaller quantity of metal 
 than that in the sheet is required, and, being lighter, has on 
 that account partial superiority. From its thinness, also, it is 
 
.Sect. XXIII.] PLATINA FOIL WINDSOR BRICK. 563 
 
 highly advantageous in exhibiting chemical action, mechanical 
 separation being carried in it to a considerable extent. It 
 always comes from the rolling mills covered with a coat of oil, 
 from which it should be freed by washing with a little soap or 
 alkali, before it is used in chemical experiments. 
 
 1353. Platina foil. Many of the services of this substance 
 have already been referred to (204, 236, 1038, 1048, 1051). 
 In all experiments in which it is used to support other sub- 
 stances at high temperatures, the fusible metals, or even their 
 oxides, sulphurets, and other compounds, when mixed with 
 carbonaceous matters, should be kept from contact with it ; 
 for the metal alloying with the platina forms a fusible combi- 
 nation, and the foil is destroyed or rendered impure. It is 
 very useful as an electromotor. A piece of zinc and a piece 
 of platina foil in contact, when put into a solution, will sepa- 
 rate many metals from it if present : the metal passes to the 
 platina, and may afterwards easily be removed. An applica- 
 tion of this kind, made by Dr. Wollaston, has been already 
 referred to (523, 1065). It is not difficult, upon occasions of 
 necessity, so to fold up a piece of platina foil as to make a 
 vessel of it capable of retaining fluids, and in that state it may 
 serve the purpose of a platina crucible so far as to allow the 
 performance of an analysis, which could not otherwise have 
 been effected. 
 
 6. Uses of Soft or Windsor brick. 
 
 1354. This brick is easily cut by a jagged knife or saw into 
 numerous useful forms. It assists by juxtaposition in build- 
 ing up small charcoal furnaces, allowing of the formation of 
 apertures through the brick itself. It is easily shaped into 
 stoppers for furnace apertures (161), or into covers, plugs, and 
 supports for crucibles ; or into wedges, to be applied where 
 necessary about furnaces or rigid apparatus. Its softness, in 
 which it much surpasses ordinary brick or stone, is a consider- 
 able advantage, especially when it is used in contact with glass. 
 These bricks are also. very useful as supports upon the tables 
 for hot apparatus. Furnaces, red-hot crucibles, or heated iron 
 plates may be supported on them very well and steadily, the 
 
 2 O 2 
 
564 CONDUCTION OF HEAT. [Sect. XXlII, 
 
 heat transmitted through the brick being insufficient to do 
 injury (197). They were first brought into notice for these 
 uses I believe by Mr. C. Aikin. 
 
 7. Conduction of heat. 
 
 1355. Heat may frequently be conducted by means of a 
 solid mass of metal, to places into which it could not so con- 
 veniently have been introduced by other means, and the chemist 
 will sometimes find his operations facilitated by such a contri- 
 vance. Sir Everard Home wished to coagulate the blood 
 within an aneurismal tumour without disturbing the tumour or 
 the neighbouring parts. This he effected by passing a needle 
 through the place, and then heating it on the exterior ; the 
 heat conducted to the fluid within was sufficient to cause its 
 coagulation. A similar instance is now very common in the 
 structure of certain lamps ; in which cocoa-nut oil in a reser- 
 voir is preserved in the fluid state by a metallic rod, one end 
 of which enters the oil, whilst the other projects over a flame 
 several inches off. 
 
 1356. In operations with a tube and a spirit lamp, particular 
 parts of the former may be heated and cooled very conveniently 
 by means of the conducting power of metals. The manner in 
 which uniformity of temperature may be insured at the lower 
 part of a tube when heated in the flame, by enveloping it in 
 copper foil, has been already described (1351). If on the 
 contrary it be required to cool a particular portion of the upper 
 part of a tube or other vessel (102), for the purpose of more 
 effectually condensing the vapour at that place, the tube may 
 be wrapped round with metal foil, which is to be placed in con- 
 tact with thicker metal, as sheet lead, or cooled by touching it 
 with wetted paper. The envelope of foil may be moistened 
 and cooled, when, if the glass itself were similarly treated, it 
 would immediately fly to pieces. A heated basin, which, with 
 its contents, requires to be cooled rapidly, may be placed in 
 water, or upon the mercury of the pneumatic trough : the heat 
 will be rapidly abstracted. When the end of a tube in which a 
 substance has been submitted to heat will ultimately require 
 to be broken for examination, it may be cooled and broken at 
 
Sect. XXIIL] CONDUCTION OF HEAT. 565 
 
 the same moment by plunging it whilst hot into the mercury of 
 the trough. 
 
 1357. Bricks, tiles, and other bad conductors, are very use- 
 fully interposed at times between the laboratory table and 
 hot crucible furnaces, to prevent the passage of heat to the 
 former in an injurious degree (197, 388) ; and in many other 
 situations a bad conductor is of service in a similar way, by 
 retaining the heat within its original or intended limits. 
 
 1358. A very useful indication of the conducting power 
 possessed by different substances for heat, is obtained, by put- 
 ting them in contact with the upper lip, or that part of the 
 cheek which is near to the mouth. These places are highly 
 sensible to changes of temperature ; and as the substance which 
 conducts best abstracts the largest quantity of heat in a given 
 time, it will of course feel the coldest, i. e. supposing all the 
 substances are at the same temperature, and several degrees 
 below the temperature of the skin. In this way many differ- 
 ences of conducting power may be observed. Another method 
 is to hold one end or side of a piece of the substance be- 
 tween the fingers, and to apply the other to the flame ; the 
 difference between wires of silver and platina is thus easily dis- 
 tinguished, and also that between various stones, diamond, and 
 glass. The substance which best conducts heat will first feel 
 hot to the fingers. 
 
 8. Uses of reflective and receptive powers. 
 
 1359. Clean polished metallic surfaces receive heat by 
 means of radiation (i. e. from a hot body not in contact with 
 them, but at a distance) with great difficulty ; and if made 
 hot, it is with equal difficulty that they throw off their heat by 
 radiation into space or to other bodies. Hence if a bright 
 metallic vessel be placed before a strong fire, it will receive 
 heat but slowly ; or if it be filled with any hot substance and 
 set in a cool place, it will be a long time before it will become 
 cold by mere radiation. On the contrary, if the surface of the 
 vessel be covered with a thin coat of lamp-black, varnish, 
 paper, or any substance not metallic, its power of receiving 
 and sending off radiant heat is greatly increased. Such a 
 vessel will soon become hot before a fire, or if heated, will soon 
 
566 FURNACES GUARDED RADIATION. [Sect. XXII I 
 
 cool to common temperatures by radiation. These are facts 
 which the student will gain from the most elementary treatises 
 on Chemistry, and may frequently be applied with facility to 
 useful purposes. If a crucible furnace (158) require to be 
 placed so near the sides of the pneumatic trough, or any other 
 piece of apparatus, as to endanger its safety by the heat ra- 
 diating from it, a bright tin plate should be interposed, when 
 the wood work will be perfectly secure (196). But as metallic 
 bodies are excellent conductors of heat, such a shield should 
 not be placed in contact with the hot furnace ; or if it must 
 necessarily bear against and be supported by it, a piece of 
 brick, or tile, or stony matter, should intervene (1357). 
 
 1360. When it is necessary to prevent change of tempera- 
 ture in a very hot or very cold substance for a long time to- 
 gether, it may be placed with advantage in a clean metallic 
 vessel, the radiation or the reception of heat by the surface 
 being thus prevented. The contact of air which would carry 
 off or communicate heat by conduction is to be retarded by 
 paper cones (544, 1343), or by flannel wrappers. Clean tin 
 foil is often useful in thus supplying a metallic cover. If, for 
 instance, part of the neck of a retort were to be preserved in a 
 hot state, in order that the vapours may be prevented from 
 condensing too soon, the object would often be attainable by a 
 wrapper of tin foil when the application of flannel, paper, or 
 other means, might be inconvenient or inadequate. 
 
 1361. If whilst heating a flask over a chemical lamp (212, 
 386) the sides of the vessel have become blackened by the 
 smokiness of the flame, the deposition should be immediately 
 removed, for otherwise, by its radiating power, it causes con- 
 siderable dispersion of the heat which has been previously 
 communicated by the lamp. 
 
 1362. On the contrary, when the object, in place of pre- 
 serving the temperature constant, is to bring it rapidly up or 
 down to that of the neighbouring bodies, the vessels should be 
 covered with a surface that will radiate or receive heat with 
 facility. On such occasions metallic vessels, such as canisters, 
 tubes, the envelopes of foil applied to the necks of retorts, &c. 
 should be blackened or closely coated with a good radiator of 
 heat. 
 
Sect. XXIII.] WRITING ON GLASS INK FOR GLASS. 567 
 
 9. Writing on Glass. 
 
 1363. When, in the progress of active and earnest experi- 
 mental inquiry, various bottles, jars, glasses, &c. containing 
 different products and preparations, require to be marked or 
 labelled (1304), it is advantageous that this be done with as 
 little interruption to the general course of the thoughts and 
 occupations as possible. It is often therefore convenient to 
 write upon the glass of the vessel with a common pen and ink, 
 with the intention of substituting a proper label afterwards. 
 There is no difficulty in writing with great distinctness upon 
 glass provided it be wiped perfectly dry, the last rub being 
 given with a clean part of the cloth, and also with a slow mo- 
 tion to remove any electricity that may have been excited on 
 the surface of warm or very dry glass by the previous quick 
 action. The pen should contain plenty of ink, the letters be 
 large and written quickly, and the pen held nearly perpen- 
 dicular to the glass. Jars containing particular gases over the 
 pneumatic trough, or bottles of gas required for temporary 
 purposes, may be sufficiently distinguished by such inscrip- 
 tions. 
 
 1364. If it be required that the writing should remain for 
 some time, and should resist the action of the damp vapours or 
 acid fumes that are continually afloat in the laboratory, it is 
 convenient to prepare an ink by diluting black varnish, such 
 as Brunswick black, with its bulk of oil of turpentine, and 
 keeping the mixture, with a pen, in a bottle for this particular 
 purpose. For certain stock-bottles, and jars or bottles of gas 
 which are put by in damp or unaired places, this method of 
 labelling surpasses paper and ink. The writing soon dries, 
 and, though pale, it is very distinct and legible. If in the 
 course of five or ten minutes, or after any greater lapse of 
 time, a little lamp-black be rubbed over it with cotton or tow, 
 the writing immediately becomes as black as that of common 
 ink, and then will resist rubbing or wiping with either wet or 
 dry cloths for a long time. 
 
 10. Smelling by a Tube. 
 
 1365. It is desirable, in certain experiments, to increase in 
 
568 SMELLING BY A TUBE. [Sect. XXIII. 
 
 every possible way the means of perceiving whether a substance 
 possesses odour : whether, for instance, ammonia, when reduced 
 to very low temperatures, affects the olfactory nerves or not. 
 At such times a tube six or seven inches long, applied in the 
 following manner, is of great use. One extremity is to be put 
 into the vessel containing the substance, and placed in contact 
 with it ; the other extremity is to be applied to one of the 
 nostrils, the other being closed, and then air is to be inhaled 
 through the tube. This air will pass by the substance before 
 it enters the nostril, and if it affords any odour, it may then 
 be perceived. In this manner substances inclosed within ves- 
 sels, or at the bottom of tubes which are subjected to very low 
 temperatures, may be examined ; but when thus operating, the 
 end of the tube must be allowed to become as cold as the sub- 
 stance, before it is placed in contact with it. 
 
 11. Engraving on glass. 
 
 1366. This is an amusing and sometimes a useful experi- 
 ment, arid, as involving also a little serviceable practical mani- 
 pulation, is worthy of description. Suppose the object be to 
 engrave a design on a piece of flat glass ; common crown glass 
 will be found the best for the purpose, and a pane of this 
 substance should be procured, of such dimensions that a circle 
 may be described upon it large enough to include the intended 
 drawing. The glass is then to be warmed over a spirit-lamp, 
 sand-bath, or other convenient source of heat, and rubbed with 
 yellow bees'-wax ; this will melt, and by using such a quantity 
 of it as will flow readily upon the glass when hot, a uniform 
 coat may be applied. If when cold it prove to be not quite 
 uniform, still if every part of the surface to be engraved be 
 perfectly covered, it will suffice. The design is then to be 
 traced upon the waxed side with a coarse point, every mark 
 being made to penetrate the wax. The point may be that of 
 a knife, or a piece of wire, or a brad-awl ; if made flat at the 
 end in one direction, but round in another, st> as to resemble 
 a minute round- edged chisel, no difficulty will be found in 
 making lines through the wax, finer or coarser, according to 
 the relative position of the edge or end of the tool and the 
 line which it is describing. If the design be previously drawn 
 
Sect. XXIII.] ENGRAVING ON GLASS. 569 
 
 upon paper with ink, it may be easily seen and traced through 
 the wax. 
 
 1367. An evaporating basin, either of earthenware or metal 
 (369, 1350), is to be selected of a diameter that will include 
 the whole of the design when the glass plate is inverted over 
 its mouth. Coarsely-bruised fluor spar, in quantity equal to 
 about two ounces for a pint basin, is to be put into the basin 
 with a sufficient quantity of strong oil of vitriol to make it into 
 a thin paste ; the two substances are to be stirred together 
 with a wire, and the waxed plate put over the mouth of the 
 basin with the design downwards. A very moderate heat is 
 then to be applied to the bottom of the basin, which is best 
 done by means of the sand-bath ; it soon causes the evolution 
 of fumes in abundance from the mixture, but should never be 
 allowed to increase so as to melt the wax on any part of the 
 glass ; a temperature of 100 to 140 is sufficient. The basin 
 and its contents, being warmed, should be removed to a cooler 
 part of the sand-bath, and left for half an hour. The etching 
 is known to proceed well, when, upon raising one edge of the 
 plate, vapours are visible within. At the end of the half hour 
 the glass plate should be rinced with water to wash off the ad- 
 hering acid, and the wax removed either by scraping it with 
 the edge of a flat case-knife, or otherwise. The design will 
 generally be found perfectly engraved upon the glass, and 
 may be rendered still more evident by lightly rubbing over it 
 a little finely-powdered vermilion with a ball of cotton. 
 
 1368. If the glass to be etched or engraved be so formed as 
 not to close the mouth of a basin or capsule, it must be waxed 
 all over, which may be done by dipping it into the melted 
 substance ; and after the design is drawn upon it, it must be 
 put with the mixture of fluor spar and sulphuric acid into a 
 vessel sufficiently long and deep to include the whole of the 
 glass to be etched. The mixture of fluor spar and sulphuric 
 acid is to be placed at the bottom, and the glass supported 
 over it upon corks or wires, or suspended so as to be out of 
 contact with the mixture. The vessel is then to be covered 
 over, that the vapours which arise may be retained and sur- 
 round the glass on every side. Evaporating basins, metallic 
 dishes, or other metallic vessels, not having sufficient depth, 
 
570 SMALL AIR GAUGES TUBES GRADUATED. [Sect. XXIII. 
 
 may be made to answer the purpose by a paper cap or cone 
 (1343) put over the edge rather tightly : the upper part of 
 such a cone serves the purpose of a chamber for the reception 
 of the glass to be engraved, and the vapours that are to act 
 upon it. 
 
 12. Small Air-gauges. 
 
 1369. The air-gauges by which the pressure of the vapour 
 of liquefied gases (962) were measured, may be made in the fol- 
 lowing manner. Some capillary tubes must be drawn (1176), 
 not of equal diameter throughout, but much smaller at one 
 extremity than the other. Their lengths may be from 8 to 
 12 inches ; each tube being formed as it were of two or three 
 portions, successively diminishing in size from one end to the 
 other, so that a volume of mercury at the narrow end shall 
 occupy a length, eight or ten times greater than at the wider 
 end. Many of these tubes being drawn, those are to be 
 selected for further preparation in which the proportions of the 
 different parts are such as to make them most advantageously 
 applicable, 
 
 1370. The selected tubes should be graduated into parts of 
 equal capacity in the following manner. The widest extremity 
 of the tube to be graduated, which is open at both ends, is to 
 be dipped into mercury, and, when a portion of the metal has 
 entered, raised into a horizontal position. The mercury may 
 easily be brought to any required part of the tube by inclining 
 it one way or the other, and at the same time slightly tapping 
 the hand retaining it ; either surface of the included column 
 of metal may thus be made to coincide accurately with any 
 given mark on the glass. The mercury, being brought into 
 the narrow part of the tube, will be very much extended in 
 length, and so much should be allowed to run out as to leave a 
 portion not more than an inch in extent, which is to be reserved 
 in the tube and considered as the measure of each degree upon 
 the scale of the gauge to be formed. Being moved in the man- 
 ner above described a little way towards the wider part of the 
 tube, search is to be made for that portion of the narrow part 
 which, being nearly of equal diameter, or rather of equal capa- 
 city for an inch or an inch and a half in length, is also nearest 
 
Sect. XXIIL] SMALL AIR GAUGES TUBES GRADUATED. 571 
 
 to the wider part. This place in the tube, if it exist, will be 
 easily found, for the mercury will not undergo any change in 
 length in different parts of it. So soon as a portion of the 
 narrow part of the tube of the required regularity has been 
 discovered, the column of mercury is to be brought to the 
 middle of it, and the tube marked with ink (1363) at the 
 places where it coincides with the ends of the cylinder of metal ; 
 thus the first degree will be fixed. Other degrees must then 
 be marked off in a direction towards the wider part of the 
 tube; the column of mercury being removed forwards for 
 each degree until its posterior surface coincides with the mark 
 which has previously been made at its anterior extremity ; 
 the latter in this new situation will point out the place where 
 the mark for a new degree is to be made. 
 
 1371. On proceeding from the narrow part of the tube to 
 the wider, the included portion of mercury will soon become 
 very much shortened, and increased in diameter. When its 
 length is less than one half what it was at first, it must no 
 longer be used as a measure ; but being returned towards the 
 narrow part of the tube, may be employed to mark off equal 
 spaces or degrees beyond the first, these degrees being only for 
 a temporary purpose and extending to the end of the tube. 
 This mercury is then to be thrown out, and a fresh portion 
 taken in and adjusted in the manner already described, until 
 it is equal in bulk to two or three, or even four degrees. It is 
 then to be used to divide the wider part of the gauge-tube, 
 and an account is to be preserved of the value of these degrees 
 on a piece of paper marked with the same intervals, and at the 
 same time as the tube. The paper scale is easily made, by 
 laying the gauge-tube upon it, and making lines coincident 
 with the degrees upon the gauge. 
 
 1372. By this mode the tube will be divided into a number 
 of equal or proportionate parts. So much of the mercury may 
 then be rejected, as to leave a quantity sufficient to form a 
 column in the wide part about one-third or one-half of an inch 
 in length. The end of the column towards the narrow part of 
 the tube is to be made to coincide with one of the graduations 
 on the wide part, so that a certain number of degrees, 20 or 
 30 for instance, may be included between it and the extremity 
 
572 SMALL AIR GAUGES CLOSED COMPLETED. [Sect. XXIII. 
 
 of the first degree (1370) marked down on the narrow part of 
 the tube. Now, by employing a small spirit-lamp flame it 
 will be easy to draw off and seal the narrow part of the tube 
 at the extreme end of the first degree, or rather, a little further 
 towards the end than the exact spot. This may be done by 
 heating so small a proportion of the tube, or of the air within, 
 that it may be considered as an unimportant quantity when 
 compared with the whole bulk of air in the gauge. Even this 
 may be in part compensated for, by sealing the tube a little 
 beyond the extremity of the first degree, and, when sealed, 
 applying the heat so far up the tube as to fuse the glass to- 
 gether exactly to the mark indicating the degree. Supposing 
 for a moment that by this method a little too much air, as, for 
 instance, a quantity equal to the twentieth part of a degree, has 
 been included, it is only a four hundredth or a six hundredth 
 part of the whole of the air in the gauge, which is of no conse- 
 quence. But it is of essential importance that the glass should 
 afterwards be made to coalesce to the line of the first degree, 
 that the scale may accurately commence from that line, and 
 that the divisions reckoned from it may be equal. 
 
 1373. When the gauge has been so far advanced, the glass 
 should generally be softened at the distance of about an inch 
 on the outside of the little column of mercury and drawn off 
 (1167), a small hole only being left at the extremity, for the 
 entrance of the air which is to press upon the mercury. 
 
 1374. These gauges are to be introduced into the tubes 
 in which the compression of the gases is to be effected (962). 
 The gas tubes should be formed of greater length than for 
 cases of simple condensation, and bent twice instead of once, 
 so as to form three straight portions separated by two angles, 
 the gauge being in one of the long limbs. If, during the 
 lapse of time, the graduation of the gauge disappear, still the 
 paper scale being preserved, may be placed on the outside of 
 the tube, and its termination made to coincide with the end of 
 the gauge ; in which position it will indicate the compression 
 with sufficient accuracy. 
 
 1375. The compression is estimated of course in the same 
 manner as by other similar gauges. If there are at first thirty 
 degrees included between the mercury and the closed end of 
 
Sect. XXIII.] SCREENS AND MASKS FOR THE EYES. 573 
 
 the gauge, and in the course of an experiment the metal is 
 forced up to the fifteenth degree, then the pressure exerted is 
 equal to two atmospheres ; if it stands at the third degree, it is 
 equal to ten atmospheres ; if at the end of one degree, it is equal 
 to thirty atmospheres. In consequence of the great length 
 of the first degree, it is easy by such a gauge to read off to 
 above a hundred atmospheres ; Marriotte's law, as supported 
 by the late experiments of Oersted, and the French philoso- 
 phers, being considered as correct. These gauges, however 
 thin; are perfectly safe, being subjected to the same pressure 
 within and without ; and for that reason no inaccuracy result- 
 ing from unequal pressure is likely to rise. 
 
 1376. Such gauges are of similar use in the repetition of 
 M. Cagniard de la Tour^s experiments; and in many others, 
 where gases or vapours are subjected to pressure, either by 
 mechanical or chemical means. 
 
 13. Screens and Masks for the eyes and face. 
 
 1377. It is worse than thoughtless to neglect the proper 
 means of preserving the eyes, when experiments on dangerous 
 or explosive substances, as chloride of nitrogen, or on gases 
 under great pressure in glass vessels, are in progress; and 
 hence the use and necessity of masks in the laboratory. A 
 very excellent mask for the defence of the eyes and face, may 
 be made of a piece of wire gauze, sufficiently large to cover 
 the visage. It may be attached at the upper edge to a spring 
 band, which, passing round the head, will retain it in its place. 
 This mask is flexible, consequently not liable to be shattered 
 like one of glass, and is free from the inconvenience of pro- 
 ducing dimness, which is often occasioned by masks of glass, 
 owing to the condensation of moisture from the breath. But 
 it is objectionable for all experiments which require close obser- 
 vation, because of the interference of the wire gauze with per- 
 fect distinctness of vision ; and as it allows the passage of 
 fluids through its meshes, it is inefficient in explosive experi- 
 ments, made with corrosive liquids, as for instance, those upon 
 the chloride of nitrogen by acids. 
 
 1378. An excellent mask may be formed of a piece of plate 
 or even crown glass, guarded on the side towards the eyes with 
 
574 SILVERING GLASS. [Sect. XXIII. 
 
 a sheet of mica, both being bored at their upper edges, and 
 made fast to a piece of wood which, being curved and attached 
 to a band, will admit of adaptation to, and support from, the 
 head. The glass, if broken by an explosion, is prevented from 
 doing harm to the eyes or face by the mica, and the latter 
 being flexible and tough, is not likely to be shattered to 
 pieces. Mica alone would scarcely answer the purpose, unless 
 of such thickness as would colour the transmitted light, when 
 it occasions a dimness before the eyes ; for there is not much 
 of this mineral found which, being large and thick, is yet so 
 clear as to allow the passage of light through it as freely as 
 through glass. Mica too, undefended by glass, would soon 
 become rough and dull from scratches and slight injuries. A 
 mask of glass and mica need not descend far below the eyes, 
 for all beneath the nostrils to the chin may be defended by 
 wire gauze, and thus dimness from the moisture of the breath 
 will be avoided. 
 
 1379. A pair of spectacles, with side as well as front glasses, 
 afford sufficient protection in many experiments ; the glasses 
 should be large and of thick plate glass. The spectacles 
 should fit close to the eye-brows and cheek bones, and the 
 eyes being thus secured, the rest of the face may incur the 
 risks of the hands and other parts of the body. 
 
 14. Silvering Glass. 
 
 1380. The advantage of being able to silver a small surface 
 of glass for experiments on light having been experienced, it 
 is assumed that the student may have occasion to perform the 
 same operation : and as regards the manner in which he may 
 coat one side of a glass plate (1348) with a bright metallic 
 surface, and thus convert it occasionally into a reflector, he 
 will find no difficulty by proceeding according to the following 
 directions. Having prepared the glass, a piece of clean smooth 
 tin foil, free from holes (1349), is to be cut to the same size, 
 and laid upon a couple of sheets of filtering (529) or blotting 
 paper, folded into quarters. A little mercury is to be placed 
 on the foil, and rubbed over it with a hare's foot, or with a 
 ball of cotton slightly greased with tallow, until the whole of 
 the upper surface of the leaf be amalgamated and bright. 
 
Sect. XXIII.] PHOSPHORESCENCE ITS PRODUCTION. 575 
 
 More mercury is then to be added, until the quantity is such 
 as to float over the tin foil. A piece of clean writing paper, 
 with smooth edges, is to be laid upon the mercury, and then 
 the glass surface, previously well cleaned, is to be applied to 
 the paper. The paper is to be drawn out from between the 
 mercury and the glass, whilst a slight but steady pressure is to 
 be applied to the latter. As the paper recedes, it carries all 
 air and dirt with it from between the glass and the metal, 
 which come into perfect contact. 
 
 1381. The mirror is now made, and maybe used for an ex- 
 periment ; but there is still much more mercury present than is 
 required to make the definite and hard amalgam of tin consti- 
 tuting the usual reflecting surface. If it be desired to remove 
 this excess, the newly-formed mirror must be put on its edge 
 for some days, when the superabundance of fluid metal will drain 
 to the bottom ; or it may be put under the pressure of a flat 
 board, in a slightly-inclined position, arid loaded with weights. 
 
 1382. The mercury used for silvering should be free from 
 other metals ; and such as has been used in the manner above 
 described should be kept apart from the rest of the laboratory 
 stock, because of the tin it may contain, or, before being added 
 to it, should be purified in some of the methods described 
 (1282, &c.) 
 
 15. Phosphorescence. 
 
 1383. There are many substances which, when heated, be- 
 come more or less luminous ; but in numerous cases, the light 
 evolved is so feeble as to require the most favourable circum- 
 stances to render it visible. A usual and very good method 
 of producing the effect in ordinary cases, is to heat a thick 
 plate of iron to a temperature at which it is barely visible in 
 the dark, to place it on a brick, and, after carrying it into a 
 dark place, to sprinkle upon it the substances to be tried. It 
 is better to heat the iron more at one part than another, so 
 that when the former is just visible, the latter, being at an 
 inferior temperature, is not sensible to the sight ; trials may 
 then be made on both parts with the same substance. A sub- 
 stance often emits so little light as not to yield any appearances 
 on the part of the iron visibly hot, while it is distinctly phos- 
 
576 PHOSPHORESCENCE HOW OBSERVED. [Sect. XXIII. 
 
 phorescent on the other part, where there is no light to blend 
 with that evolved. 
 
 1384. The substance should not be altogether in fine pow- 
 der : it is better to experiment with a mixture of coarse and 
 fine parts. If the fine particles or the mixture does not seem 
 to become phosphorescent, a few small fragments should be 
 tried, unmixed with smaller portions. Their form becomes 
 faintly visible, and may be distinguished on the black iron, 
 when the light of an indiscriminate and general sprinkling 
 cannot be certainly ascertained. Occasionally a fragment is 
 more advantageous, because of the different temperatures of 
 its parts at different moments, a faint light appearing to pass 
 gradually over it as its parts acquire the necessary temperature. 
 
 1385. It is usually better to place the substance at once upon 
 a hot body, from which it may quickly receive the heat it may 
 require, than upon platina foil or in a crucible, and to heat 
 both it and the vessel at the same time. The operation is then 
 slower, because of the larger mass to be heated ; and the eye 
 in certain cases becomes accustomed, to such a degree, to the 
 gradual change of light, as not to notice it. The quicker the 
 phosphorescence occurs, the more distinctly is it recognised. 
 The eye should not be directed towards luminous or enlight- 
 ened bodies immediately previous to the observation, but 
 towards darkness, that it may be rendered more sensible to 
 the impression of light. 
 
 1386. Dr. Brewster, in giving an account of some experi- 
 ments by which he recognised this property in so many bodies 
 as to nearly quadruple the number previously known to be 
 phosphorescent, says, " I never reduced the body to powder, 
 but always placed a fragment of it upon a thick mass of hot 
 iron, carried into a dark room, When the phosphorescence 
 was not readily perceived by this method, I took a pistol- 
 barrel, and, having shut up the touch-hole, I introduced the 
 mineral into the breech, and placed the bottom of the barrel 
 in the fire. Before a red heat was produced, phosphorescence 
 was distinctly seen by looking into the barrel, which I some- 
 times did through a plate of glass, to keep the heated air from 
 the eye, and sometimes through a small telescope, adjusted to 
 distinct vision at the bottom of the barrel. At other times the 
 
Sect. XXIII.] SOLAR RAYS MAGNETISM. 577 
 
 mineral was not introduced into the barrel till it was taken out 
 of the fire, and till the red heat had entirely disappeared*." 
 
 16. Uses of Solar Radiant Matter. 
 
 1387. The rays of the sun, when concentrated in a focus, 
 have not imfrequently been used in heating bodies placed in, 
 the middle of glass vessels, to which heat could not otherwise 
 be communicated. Thus the Florentine Academicians and 
 Sir Humphry Davy heated the diamond in oxygen gas. 
 
 1388. Their influence in occasioning chemical change in a 
 manner unlike that of any other agent, is such as to make their 
 application in the laboratory highly important (6) ; and it is to 
 be regretted that chemists generally are not more in the habit 
 of trying their powers over bodies which as yet have not been 
 submitted to them. Chloro-carbonic acid is always formed by 
 their means, so also is one of the hydriodides of carbon ; and 
 the chlorides of carbon cannot be produced in any other way 
 so advantageously as by their assistance : chlorine will de- 
 compose water when exposed to them, which it can scarcely do 
 without their aid ; and having these strong evidences of a pe- 
 culiar and very effectual power, there is no reason why we 
 should not hope to find, that even solid bodies exposed to solar 
 light when in contact with gases and vapours, and also with 
 fluids, exert an action quite independent of the powers of 
 heat, and adequate to the production of new results. 
 
 17. Magnetism. 
 
 1389. Though magnetism may be thought to form no part 
 of chemical science, yet, from its extraordinary development 
 by electricity, and its equally extraordinary residence in some 
 of the metals, it cannot but press upon the attention of the 
 chemist. The present notice will principally relate to the use 
 of the magnetic needle as a test of the presence of magnetism 
 in minerals or substances containing iron, or of its development 
 by electro-chemical arrangements. 
 
 1390. When a magnetic needle of the ordinary kind is used, 
 
 * Edinburgh Philosophical Journal, i, 385. 
 
 2 P 
 
578 MAGNETIC POWER TESTED FOR. [Sect. XXIII. 
 
 its point of suspension should be very fine and delicate, that no 
 serious retardation of its motion may be occasioned by friction ; 
 and the agate, glass, or other cap which supports the needle, 
 should be clean and smooth within. The magnetic state of the 
 needle may be judged of from the freedom and readiness with 
 which it vibrates when disturbed from its natural position. It 
 may be appreciated also by dipping the points into iron filings : 
 the brush of filings sustained should be considerable, and quite 
 at the end of the needle ; no part towards the middle of the 
 needle ought to shew attractive powers sufficient to lift up any 
 particles of the iron. 
 
 1391. When the needle is used as a test of the magnetic 
 powers of a body, as an ore of iron, or other mineral, it should 
 be allowed to take its state of rest, when the body should be 
 approximated to one side of either extremity or pole: the 
 attraction or disturbance of the needle will indicate the mag- 
 netic state of the substance, and the magnetism may be consi- 
 dered of a strength proportionate to the distance to which the 
 substance attracts the needle, or that at which it first acts. 
 
 1392. If the magnetism be very weak, its effects may be 
 rendered more evident by the following management. Suppose 
 the substance to be a piece of iron ore applied on the right side 
 of the pole, and capable of deflecting the needle only a very 
 small distance from its original position : if the substance 
 be removed sideways, and the needle allowed to return, it 
 will, if freely suspended, pass beyond its position of rest to a 
 distance on the left side, nearly equal to that to which it had 
 been deflected on the right side of the magnetic meridian, and 
 will regain its state of rest only after several oscillations. But 
 in place of allowing it thus to regain its state of rest after it 
 has swung to the left side, and is in the act of returning to the 
 right by the attraction of the earth, and the mere momentum 
 of its parts, the iron ore should be again brought near to it on 
 the same side, to conjoin its attractive force with the forces 
 before mentioned, and thus to draw it as far as possible towards 
 the right side. The ore is then to be withdrawn from the 
 needle as before, and when the latter has passed to the 
 left side, is to be again applied whilst it is returning to the 
 right; this is to be done repeatedly, the oscillations of the 
 
Sect. XXIIIJ MAGNETISMOBSERVED HAUY's METHOD. 579 
 
 needle in one direction being favoured by superadding the 
 attractive powers of the ore each time. This will be found 
 very easy of performance by an alternate movement of the 
 hand to and from the pole of the needle on the right side; the 
 object being to hold the ore as near to the pole as possible, 
 while the latter is passing from left to right, and to remove it 
 so as to leave the needle quite uninfluenced by it, as the same 
 pole moves from right to left. In this manner a new impulse 
 is added to the pole or needle at each oscillation, the amplitude 
 becomes gradually increased, and deflections, which at first 
 were scarcely visible, become extended to a very considerable 
 degree. 
 
 1393. If it be a weak repulsive power that is thus to be 
 rendered evident, the substance tried must be made to follow 
 the pole closely as it recedes, and is to be withdrawn to a 
 distance as it returns in the oscillation: but it is better in 
 such a case to use the attractive force of the substance on the 
 other pole ; for no mistake can arise as to any tendency of the 
 substance to draw the pole, through the mere motion of the 
 air, though such a mistake might occur as to repulsion, the 
 effect supposed to be repulsion, being nothing more than 
 motion communicated mechanically through the air by the 
 approximated body, driving, as it were, the air and needle 
 before it. 
 
 1394. M. Haiiy has instructed us that, under the combined 
 influence of the earth and a magnetic bar, a needle may be 
 made a much more delicate test of the presence of small mag- 
 netic attractions, than when under the earth's influence alone. 
 The power which is required to deflect a needle from its 
 natural position is least when the deflection is smallest, and 
 greatest when the deflection is 90. It increases therefore 
 from to 90, and then decreases again ; but the increase is in 
 a decreasing ratio, and the decrease in an increasing ratio, so 
 that it requires a much greater magnetic force to move it from 
 to 10, than to move it from 80 to 90. 
 
 1395. To take advantage of this circumstance, the needle 
 is to be allowed to acquire a state of rest when under the 
 earth's influence only ; then if the south pole of a bar magnet 
 be approached towards the south pole of the needle, the bar 
 
 2P2 
 
580 MAGNETISM OF A BAR. [Sect. XXIII. 
 
 being in a line with the needle, a repulsion will take place, and 
 the needle will deviate until the repelling power of the bar and 
 the attractive force of the earth on it are equal to each other. 
 This may have brought the needle to an angle of 30 with the 
 magnetic meridian, but by approximating the bar the effect 
 may be increased, and the angle rendered greater. In this 
 way the distance of the bar is to be diminished, until the 
 needle is very nearly at right angles with its first direction, 
 and will scarcely, retain that position, but on the slightest 
 further degree of motion pass through another quarter of a 
 revolution, or even more. It is thus placed in the most 
 favourable position as a test of magnetism ; for an attractive 
 power, many times smaller than that which would sensibly 
 deflect it, when in the magnetic meridian, will now be suffi- 
 cient to make it pass through the few remaining degrees to 90, 
 and then entirely invert its position. 
 
 1396. When a bar of iron is examined for magnetism by 
 the needle, the method is, to observe whether both ends attract 
 both poles at all distances, or whether in any case a repulsion 
 on either pole can be observed. This repulsion is a proof of 
 magnetism in the bar, but in such cases it is necessary to hold 
 the bar in a horizontal position, and perpendicular to the 
 direction of the needle ; for in any other position a bar of soft 
 iron without previous magnetism, will seem to be magnetic and 
 to possess poles, solely in consequence of its relative position 
 to the earth and needle. Whilst in a plane perpendicular 
 to the dip of the needle, it will not shew this effect, but when 
 out of that plane the end below acts as a north pole to the 
 needle, and the end above as a south pole. Although it has 
 just been said that when in such a plane it shews no effect of 
 this kind, the assertion is not strictly true ; for such a plane 
 being considered as passing through the thickness of the bar, 
 all that is above will seem to have the one effect on the needle, 
 and all that is below the other ; but the power is so slight in 
 a bar having this position, as to be scarcely perceptible under 
 ordinary circumstances. 
 
 1397. An iron bar may also be examined for magnetism by 
 bringing it near fine iron filings ; if it have poles they will 
 attract the filings, but the test is not so delicate as the needle. 
 
Sect. XXIIL] 
 
 MAGNETIC NEEDLES. 581 
 
 Iron filings afford ready indications of the power of bar 
 magnets ; the bulk of the brush taken up being in proportion 
 to the attractive power of the bar. 
 
 1398. Small temporary and very delicate magnetic needles 
 may be made by magnetising a common sewing needle, and 
 then either floating it upon water on a small piece of cork, or 
 suspending it by a single fibre of silk. For this latter pur- 
 pose a small ball of soft cement (1125) is to be attached to 
 each end of a piece of the fibre, about a foot or two in length. 
 One of these being pressed against any convenient place from 
 which the needle may be suspended, will adhere with a force 
 quite sufficient to support the needle. The latter, having pre- 
 viously been magnetised, is to be pressed against the other ball 
 of cement, and adjusted until it balances in a horizontal posi- 
 tion. Being left to itself it will take its natural position in 
 the magnetic meridian, and during suspension will be more 
 delicate, and more readily obey impulses exerted upon it, than 
 a needle supported on a point. 
 
 1399. The needles are easily magnetised in the usual way 
 by an ordinary magnet. If such be not at hand, a steel bar 
 may be rendered powerfully magnetic, as Mr. Scoresby has 
 shewn, by placing it in the magnetic dip, i.e. with one end 
 pointing about 24 \ degrees west of north, and downwards, so 
 as to make an angle of 72^ degrees with the horizon. When 
 the bar is held in this position, with one end on a large kitchen 
 poker in the same position, and the other end struck three or 
 four times with a heavy hammer, it will become a good magnet, 
 and quite sufficient for the preparation of small magnetic 
 needles. 
 
582 EXPERIMENTAL, PRACTICES. [Sect. XXIV. 
 
 SECTION XXIV. 
 
 A COURSE OF INDUCTIVE AND INSTRUCTIVE 
 PRACTICES. 
 
 THE Chemical student must not expect that, by reading this 
 book, he will .find himself ready and expert in the application 
 of the various methods and contrivances which it describes. 
 No valuable experimental knowledge can be obtained at so 
 cheap a rate. Practice is essential to that facility, without 
 which nothing dependant upon the hands can be done well. 
 With the view therefore of expediting the acquirement of the 
 necessary habits, the present Section will contain a number of 
 practices, arranged either as single experiments, or in sets ; the 
 performance of which, whilst it will confer considerable experi- 
 mental readiness, will convey instruction relative to numerous 
 important points of chemical science, and teach the applications 
 and powers of the contrivances described, when they are 
 afterwards to be applied in trains of new and original research. 
 All the experiments are accompanied by references to the pre- 
 vious paragraphs of the book, that the information necessary 
 for their successful performance may be found at the moment 
 it is wanted : and thus, at the same time that the instruction 
 given directs the practical manipulation, it is itself illustrated 
 and rendered more forcible by the performance of the experi- 
 ment. 
 
 II. Balance, Weighing fyc. 
 
 [1.] Observe the equality and readiness of oscillation in the 
 balance (43) when the scales are empty, and also when they 
 are equally loaded with, first, a fourth, and then one half of 
 what they ought to carry (44). Remark the difference, if 
 any, in the time of the oscillation when the pans are empty 
 and when they are loaded. 
 
 [2,] Load the balance with the full weight it is intended to 
 carry, then observe whether it sets or not (44). If it set, 
 diminish the weights in the scale, until the charge with which 
 it first begins to set be ascertained. 
 
Sect. XXIV.] BALANCE WEIGHING. 583 
 
 [3.] Try the different weights of the balance against each 
 other (49) in various ways. 
 
 [4.] Examine the old brass weights belonging to the balance, 
 by counterpoising them with new and accurate weights (49) ; 
 during the trial put all the weights to be tried on one side, and 
 the ascertained weights on the other (59). 
 
 [5.] Counterpoise the balance by weights equal to about 
 one half of what it should carry (33) ; and when in equilibrium, 
 change the weights from pan to pan, and observe whether the 
 balance still remains equipoised (48, 59). 
 
 [6.] Weigh two pieces of solid substance together (52, 56), 
 to the hundredth of a grain ; then weigh the two separately, 
 and observe whether the sum of their weights make the first 
 weight. 
 
 [7.] Balance two pieces of writing paper in the pans (61) 
 by as few cuts with the scissors as possible. Put these papers 
 successively into the same pan ; weigh 300 grains of sand into 
 each (62, 59), and then ascertain whether the weighed portions 
 equipoise each other. 
 
 [8.] Counterpoise a piece of smooth writing paper (61), 
 weigh 50 grains of magnesia on it (62) ; then pour off the 
 magnesia, and ascertain whether the portion which adheres to 
 the paper has rendered it sensibly heavier. Do the same with 
 a fine heavy powder, as carbonate of baryta. In this way an 
 idea of the quantity of powder which will adhere to paper may 
 be acquired. 
 
 [9.] Weigh 49.7 grains of carbonate of lime in fine powder 
 (61, 62), weigh a second portion of 49.7 grains, then put 
 them together, and try if they weigh accurately 99-4 grains ; 
 if not, ascertain whether the rest of the weight is on the 
 paper, or what has occasioned the apparent inconsistency in 
 the results. 
 
 [10.] Weigh a piece of glass or metal of about 400 or 500 
 grains (52), cool it well (454, 1349), then hold it for a few 
 minutes in a glass containing a little water at the bottom, but 
 so as not to touch the fluid ; afterwards ascertain if the weight 
 of the cold body has been increased by moisture condensed 
 upon its surface. 
 
 [11.] Counterpoise a cold platina crucible (64), make it 
 
584 BALANCE WEIGHING. [Sect. XXIV. 
 
 hot, and putting it into the pan in that state, observe the 
 quantity by which the weight appears to be diminished (58). 
 
 [12.] Counterpoise a tube supported on a cork (64, 67), 
 then accurately weigh a hundred grains of water into the 
 tube (69), taking particular care that none pass to the out- 
 side. 
 
 [13.] Counterpoise a glass (64), and weigh 127 grains of 
 mercury into it (130, 131). 
 
 [14.] Counterpoise a bulb or little flask, supported on a 
 cork ring (64, 67), weigh into it 150 grains of strong sulphuric 
 acid (69), adjusting the quantity by a rod (70). 
 
 [15.] Counterpoise a little evaporating basin or capsule (64), 
 and weigh into it 130 grains of Venice turpentine in a cleanly 
 manner (70), adjusting the quantity by the tip of a wire or 
 rod. 
 
 [16.] Counterpoise a small glass (64), weigh 300 grains of 
 water into it (69) ; fuse some chloride of calcium in an earthen 
 crucible to dissipate all the water (642, 669, 670), pour it upon 
 a cold metallic or stone surface, and as soon as it is solid break 
 it into pieces and introduce two or three fragments, together 
 exceeding 100 grains in weight, into the water, before the 
 chloride can have increased in weight, by absorbing moisture 
 from the air (72). Ascertain the increase of weight; then stir 
 up the solution carefully with a glass rod until it is perfectly 
 uniform (514), and afterwards remove so much of it (69, 71) 
 as to leave exactly 100 grains of chloride of calcium behind, 
 i.e. if 110 grains of the compound have been added, making 
 410 grains of solution, remove an eleventh part of it, by which 
 10 grains of the chloride will be withdrawn, and 100 grains 
 left for analysis, or for experiments. 
 
 [17.] Balance a green glass tube closed at one extremity 
 (64, 66), weigh into it 60 grains of crystallized muriate of 
 baryta in a dry state (51), heat the tube so as to drive off the 
 water and fuse the muriate (707) ; when cold, re- weigh it, and 
 ascertain the diminution occasioned by the dissipation of water 
 (59). It should equal 8.71 grains. Ascertain how many 
 proportions of water this accords with, either by the scale of 
 equivalents (1318), or by calculation (1327). 
 
 [18.] Weigh two or three portions of solid matter by a 
 
Sect. XXIV.] MEASURES MEASURING. 585 
 
 Black's balance (112), or an unadjusted instrument, applying 
 the weights and the substances on the same side (59) ; then 
 compare the weights so obtained with such as may be obtained 
 by weighing the same portions of matter in a good balance. 
 
 [19-] Weigh a glass flask (65), or a tube (66), attaching it 
 by a wire to the bottom of the pan. 
 
 [20.] Take the specific gravity of a smooth solid body, as a 
 piece of glass (81, 85). Take also the specific gravity of a 
 piece of solid matter in the rough state, for example, a frag- 
 ment of zinc or antimony (85). 
 
 [21.] Ascertain the specific gravity of alcohol, of ether, of 
 sulphuric acid, and of water, by the bottle (92). 
 
 [22.] Make a number of small weights (116) ; ascertain 
 their truth by trying them against correct weights (49). 
 
 [23.] Make a Black's balance (112) ; compare its results 
 with those obtained by a good balance (59, &c.) 
 
 [24.] Take the specific gravity of water and beer by the 
 hydrometer (103), and compare the results with those obtained 
 by the bottle and balance (93). 
 
 III. Measures. Measuring, 8fc. 
 
 [25.] Measure out a pint of water (120, 121), avoiding the 
 formation of bubbles near the graduation. Whilst measuring 
 out the fluid pour it slowly into the vessel, that the exact 
 quantity may be observed and ascertained at once. 
 
 [26.] Pour a quantity of water into an ungraduated glass 
 or jar; then measure it (120, 121); afterwards pour mercury 
 into the first vessel, to the same height (121), and measure it 
 by a graduated vessel (118), to verify the first result. 
 
 [27-] Counterpoise a graduated measure in the balance 
 (64) ; pour a certain measure of distilled water into it, four 
 ounces for instance (118), then weigh it (67), and ascertain 
 whether the weight is what it ought to be, or 1750 grains, at 
 the temperature of 62 F. (117). Remove the first portion 
 of water, and measure in the same quantity a second time 
 (120). See if its weight be the same as the weight of the 
 first, or to what extent it differs. It ought to be the same ; 
 and the nearer the results approach in weight, the more reason 
 
586 MANAGEMENT OP HEAT. [Sect. XXIV. 
 
 has the operator to be satisfied with the accuracy of his eye 
 and habit of measuring. 
 
 [28.] Measure half a cubical inch of mercury (121, 135), 
 and then ascertain its weight (126). 
 
 [29.] Mark a line down a glass tube (129). Make a mark 
 across it with a file (132), beginning either at the line, or 
 extending on both sides at pleasure; divide a space about 
 an inch in length, first into two, then four, and then eight 
 equal parts by the eye (143) ; ascertain the accuracy or inac- 
 curacy of these divisions, by weighing mercury into them 
 (126). Practise also the division by the eye into three, five, 
 and ten parts. 
 
 [30.] Graduate a tube into tenths of a cubical inch by 
 weighing water into it (65, 127, 71, 126, 129, &c.) 
 
 [81.] Graduate a tube into hundredths of a cubical inch by 
 weighing mercury into it (65, 126, 129, &c.) 
 
 IV. Management of Heat. 
 
 [32.] Convert a blue pot or large earthenware crucible into 
 a furnace (157, Sec.) Then put some chalk into an earthen- 
 ware crucible (642), and by heating it in this furnace (670), 
 convert it into quick lime. Try whether it has become quick 
 lime, for which purpose put a small piece into water, and add 
 muriatic acid ; no effervescence should occur (366). 
 
 [33.] Heat some zinc in a Hessian crucible in the same fur- 
 nace (158), until it burn freely upon agitation and exposure 
 to air. 
 
 [34.] Boil some water in a Florence flask (383), on the 
 furnace sand-bath (173) ; observe the temperature of the 
 steam that passes off (279, 286), and also of the water. In- 
 troduce some iron-filings into the flask, and again observe 
 the temperature of the steam and of the water beneath (441). 
 
 [35.] Diffuse 1 oz. of starch through a pint of cold water, 
 allow it to settle (549), pour off a little of the water, and 
 evaporate it to dryness (591); observe if any thing remain; 
 then heat the mixture of starch and water (380, &c.) and ob- 
 serve the solution of the starch ; allow the fluid to stand 
 twelve hours, then decant a portion (550), and evaporate it 
 
Sect. XXIV.] MANAGEMENT OF HEAT. 587 
 
 to dryness (599) by a bath of water covered with oil, and 
 observe how much starch is left, and in what state. 
 
 [36.] Heat a little starch in a tube (910, 935) to 500 by 
 means of a metallic bath (264), allow it to cool, and then upon 
 adding water it will dissolve without heat : on evaporating the 
 solution in a basin over a chemical lamp (590, 212), the same 
 results as in the former experiment will be obtained. 
 
 [37.] Evaporate a portion of the above solution of starch to 
 dryness by a steam heat (271, 274). 
 
 [38.] Evaporate a quarter of a pint of mineral water to 
 dryness over a chemical lamp (592, 212) ; add a drop of water 
 to the residue, and observe whether it be alkaline by turmeric 
 paper (624). All the deep well-waters of London yield 
 alkaline matter. 
 
 [39.] Heat a piece of wood on platina foil (135$, 204) by 
 the spirit-lamp (199) ; observe the odour, the production of 
 flame, the carbonaceous residue, and its combustion by a con- 
 tinuance of the heat. Heat also a piece of isinglass or cheese 
 in the same manner ; remark the fetid ammoniacal smell, the 
 flame, the fusion, the difference between its coal and the former, 
 and the greater difficulty of incineration. 
 
 [40.] Fuse a mixture of equal parts of the carbonates of 
 potash and soda in a platina crucible (653) by the heat of a 
 spirit-lamp and jacket (206, 666, 667), afterwards, if possible, 
 fuse some common salt in the same manner. . 
 
 [41.] Attain the highest possible ignition of a platina wire 
 by a spirit-lamp or candle (199, 230) and the mouth blow- 
 pipe (216). Try the same experiment with platina foil (204), 
 holding the foil vertically, or directing the flame from below 
 upwards, or from above downwards (231, 233) upon the 
 metal ; observe the circumstances of the most intense heat 
 (235). 
 
 [42.] Endeavour to fuse the extremities of a film of asbes- 
 tus by the mouth blow-pipe and a candle (216, 230, 232). 
 
 [43.] Melt first 20 and then 30 grains of bi-carbonate of 
 soda in a platina-foil crucible (1353), until they fuse freely, 
 and become fluid dry carbonate of soda, using the mouth blow- 
 pipe and spirit-lamp for the purpose (233). If this be found 
 too difficult at first, use a mixture of two parts bi-carbonate of 
 soda, and one part bi-carbonate of potassa. 
 
588 COMMINUTION. [Sect, XXIV. 
 
 [44.] Melt a globule of tin on charcoal (232) by the mouth 
 blow-pipe and a candle (227, 230), keeping it perfectly me- 
 tallic and bright for one or two minutes together. 
 
 [45.] Heat a globule of antimony on charcoal (240) by the 
 mouth blow-pipe and candle-flame (230, 232) ; when hot 
 remove it from the flame, and still forcibly urging a stream of 
 air upon it, observe how it continues to burn until nearly the 
 whole is consumed. 
 
 [46.] Heat a globule of antimony as just described, then 
 drop it from a height of five or six feet, upon a sheet of paper, 
 and observe its brilliant combustion, and the trains of oxide it 
 leaves on the paper. Heat another globule, and when in full 
 combustion throw it through the air against a wall ; remark 
 its combustion in the air before and after it is broken. 
 
 [47.] Heat a small platina crucible (653) red hot, by a 
 lamp (233) and mouth blow-pipe (235). 
 
 [48.] Make a spirit-lamp according to Mr. Phillip's method 
 (208), and complete the apparatus by making a temporary 
 blow-pipe from a piece of glass tube (221). 
 
 [49.] Fuse platina on charcoal (240) by means of the oxy- 
 alcohol blow-pipe (251). Burn a cast-iron sparable in the 
 same manner. 
 
 [50.] Compare two thermometers at high and low tempe- 
 ratures (281, 286). 
 
 [51.] Cool a thermometer in ice and water (453, 454), 
 quickly wipe it, and then immerse it in a jar of water at com- 
 mon temperature, to ascertain the heat ; and observe the time 
 required (287). Again, cool the thermometer, and wiping it 
 quickly as before, ascertain the temperature of the air above 
 the water, and noticing the time required, remark how much 
 longer it is than in the first experiment. Hence learn to be 
 cautious with respect to the time allowed for a thermometer to 
 acquire its proper temperature in different situations (286). 
 
 V. Comminution. 
 
 [52.] Break a flint in the hand, supporting it upon a cloth 
 or glove (315). Break a small pebble on the anvil (316). 
 
 [53.] Heat flints red hot, and quench them in water 
 then reduce a portion to an impalpable powder (323, 330). 
 
Sect. XXIV.] 
 
 COMMINUTION. 589 
 
 [54.] Break a piece of flint glass in a mortar (315) ; reduce 
 it to small fragments or a coarse powder (321) ; then pulverize 
 a small portion very finely (323, 330) ; afterwards place it 
 on turmeric paper, and moistening it render the alkali evident 
 (624)*. 
 
 [55.] Rub a piece of white marble of about 400 grains in 
 weight into an impalpable powder (329, 330) ; reduce half as 
 much muriate of ammonia also to fine powder (319, 323) ; 
 mix the two well together (32 5), for experiment 99. 
 
 [56.] Make an intimate mixture (327) of equal parts by 
 weight of muriate of ammonia and quicklime ; observe the 
 ammonia evolved even at common temperatures (624, 626) ; 
 then use it in experiment 211. 
 
 [57.] Break and pulverize some charcoal (332) for experi- 
 ments 174, 181, 183. 
 
 [58.] Pulverize a brittle metallic ore, as sulphuret of copper, 
 or of lead, or native oxide of iron (321, 323), and weigh 100 
 grains (61) for analysis. 
 
 [59.] Before using the common salt of experiment 40, 
 pulverize it (340) to prevent decrepitation. 
 
 [60.] Weigh 200 grains of white marble in lumps (52) ; 
 pulverize it very finely (323, 330) ; then collect it together 
 (334), and again weigh it (61), and ascertain how much is lost 
 by dispersion or adhesion to the mortar. The loss ought to 
 be very small. 
 
 [61.] Pulverize (332, 321, 323) and levigate (344) a piece 
 of felspar or slate, so as to obtain an uniformly fine powder. 
 
 [62.] Rub and wash crude platina (344, 348), for the pur- 
 pose of separating the black particles from those which are 
 bright and metallic. 
 
 [63.] Dissolve a silver coin in nitric acid (373, 380), dilute 
 the solution, and precipitate the metal in a finely divided state 
 (356), by a plate of copper. 
 
 [64.] Dissolve the washed platina of experiment 62 in 
 iritro-muriatic acid (373, 383), made by mixing five mea- 
 sures of strong muriatic acid, one measure of strong nitric 
 acid, and three measures of water together, precipitate the 
 solution by muriate of ammonia (509), wash and dry the 
 * AQ experiment due to Mr. Griffiths. Quar. Jour. xx. p. 259. 
 
590 SOLUTION DIGESTION INFUSION. [Sect. XXIV. 
 
 precipitate (553, 539, 601), then decompose a part of it by 
 heat (670) in an earthenware crucible (642), so as to produce 
 platina in a spongy state (356). Test its state of division by 
 throwing a jet of hydrogen upon it (820) ; although perfectly 
 cold it will become hot, causing the ignition of the gas : the 
 readiness with which this will take place will depend on the 
 sponginess and lightness of the platina. 
 
 [65.] Granulate some zinc (351), that it may be ready for 
 the preparation of hydrogen gas in future experiments. If 
 the heat of the fused zinc be moderate, the resulting pieces of 
 metal will be thicker than if the heat be much higher. Granu- 
 late some thus raised to a high heat and almost ready to burn, 
 the metal will be almost in films ; dry it (590), and then break 
 it down in a mortar (315, 321), for the purpose of preparing 
 carbonic oxide gas in future experiments. 
 
 VI. Solution. Digestion. Infusion. 
 
 [66.] Examine the solubility of crystals of sulphate of pot- 
 assa, sulphate of soda, borax, and sugar (361). The first is 
 difficultly soluble: observe the effects in all, and note the 
 absence of similar effects when an insoluble substance is im- 
 mersed in the fluid. 
 
 [67.] Examine corrosive sublimate as to its solubility in 
 water (361) ; then dissolve some common salt or muriate of 
 ammonia in the water, and again examine the solubility of the 
 corrosive sublimate (361) ; the difference occasioned by the 
 salt will be very considerable. 
 
 [68.] Make a saturated solution of nitre in water without 
 heat (375) by trituration in a mortar. Then to each pint add 
 about four ounces of crystallized nitre, dissolve it by the 
 application of heat (369, 381), and set the solution aside to 
 crystallize, as in experiment 127. 
 
 [69.] Disssolve common salt in common water in a tube, 
 for the purpose of obtaining evidence that air is expelled 
 during the solution (366). 
 
 [70.] Mix together nearly equal quantities of sugar, marble, 
 and sand, in a mortar (327). Take about an ounce of the 
 mixture, and, by means of cold water, dissolve out the sugar 
 
Sect. XXIV.] SOLUTION DIGESTION INFUSION. 591 
 
 (368, 374) ; collect the washed residue (539), which need not 
 be dried, and subject it to the action of diluted muriatic acid, 
 to dissolve the carbonate of lime (372, 409) ; and having re- 
 moved the solution formed by washing (540, &c.), nothing 
 but the sand will remain. A separation and imperfect ana- 
 lysis of the mixture will thus be made. 
 
 [71.] Dissolve a crystallized and clean carbonate of baryta 
 in pure muriatic acid in an evaporating basin (381, 409), con- 
 taining excess of the carbonate, so that the solution shall be 
 neutral (624) ; pour off the solution formed (397), and add 
 fresh acid; proceed in this manner until the carbonate be 
 nearly all dissolved; filter the solution (536), pour it into a 
 clean bottle by a rod (398) or funnel (436), and preserve it 
 for use as a test. 
 
 [72.] Boil a few fragments of gum mastic in a tube with 
 alcohol (405) under pressure (99, 919). When this solution 
 is diluted with more alcohol, so as to diminish the quantity of 
 mastic to 70 grains in half a pint, it forms an excellent wash, as 
 Mr. Hatchett has shewn, for fixing chalk and pencil drawings. 
 
 [73.] Weigh one hundred grains of pure dry white marble 
 in small fragments (5.2, 61), put them into a Florence flask 
 (395, 435), with two or three ounce measures of water. Put 
 about one-half or two-thirds of an ounce measure of strong 
 muriatic acid into a test glass, and adding its bulk of water, 
 stir them well together : then counterpoise (64, 65) the test- 
 glass and the Florence flask with their contents, putting both 
 into the scale at once, the flask on the glass. This done, pour 
 the diluted acid into the flask (399), using no funnel, rod, or 
 other means, but taking care that no acid escape down the 
 outside of the vessel. It is not requisite that all should be 
 poured out of the glass, but that none should be lost to these 
 vessels. Attend to the effervescence, that no liquid be thrown 
 off (396) : when all the solid matter is dissolved, expel the 
 atmosphere of carbonic acid by blowing in air through a tube, 
 and again weigh the vessels, observing the loss of weight due 
 to the expulsion of the carbonic acid (59). It should be 44 
 grains. Leave it a night and observe the difference, if any, 
 next morning. 
 
 [74.] Dissolve pulverized sulphuret of iron (323) in nitro- 
 
592 SOLUTION DIGESTION INFUSION. [Sect. XXIV. 
 
 muriatic acid (409, 414), under a hood (391, Sec.), that the 
 fumes may be carried away. When dissolved, examine small 
 portions of the solution (400, 505) by ammonia, to shew the 
 presence of oxide of iron, and by the muriate of baryta, of expe- 
 riment 71, to shew the sulphuric acid formed during the action. 
 
 [75.] After observing the precipitation of the oxide of iron 
 from the above solution by ammonia, take another portion of 
 the solution, add tartaric acid to it (412), and then, on adding 
 the ammonia, it will be found that no precipitate will take 
 place. 
 
 [76.] Put a solution of chromate of potassa into a flask, and 
 add a portion of sulphuric acid ; the colour will be very much 
 deepened and rendered almost red ; add a little alcohol and 
 apply heat (416, 386), when on a sudden the colour will 
 change to green. Upon examination it will be found that the 
 chromic acid has lost oxygen, has become chromic oxide, and 
 has formed a sulphate with the acid present. 
 
 [77.] Dissolve caustic lime in water in a close vessel (372), 
 evaporate a certain volume of the solution to dryness (596), 
 and note the quantity of earth left. Then make a similar 
 solution of lime in a vessel with water, containing one half its 
 weight of white sugar (412) ; take the same volume of this 
 solution as before, evaporate to dryness, and burn off the sugar 
 (653, 666) in a crucible ; ascertain the weight of lime left, 
 and observe how much it surpasses the former quantity, in 
 consequence of the solubility conferred by the sugar. 
 
 [78.] Digest some pale Peruvian bark in four times its 
 weight of water (369, 417) ; after the infusion has stood some 
 time pour off the clear part (397), and when cold, test it by 
 tincture of galls and by carbonate of potassa (506). The 
 precipitate will be proportionate to the quantity of cinchona in 
 the bark. 
 
 [79.] Make a strong infusion (419) of bruised nut galls, 
 and set it aside in covered jars (566) for a month or two 
 (1302) ; at the end of that time a quantity of crystalline 
 matter will be observed at the bottom of the fluid, which may 
 be collected (549), purified by crystallization, &c. (563, 564), 
 and will be nearly pure gallic acid. 
 
 [80.] Pour water or a solution by means of a rod (397) 
 
Sect. XXIV.] DISTILLATION SUBLIMATION. 593 
 
 without spilling. Pour out exactly one ounce measure of 
 muriatic acid in the same way (120, 398), so steadily as to 
 make the fluid coincide with the mark on the measure at once, 
 and without addition or abstraction. Add this acid carefully 
 to the carbonate of baryta in experiment 71, washing out the 
 last portions from the measure by water (402). In this way 
 acquire the facility of apportioning exact quantities, and of 
 adding every particle of them to other substances when re- 
 quired. 
 
 VII. Distillation, Sublimation, <^c. 
 
 [81.] Distil common water in a metal still (424), or in a 
 glass retort (428, 438), condensing, if requisite, by a funnel 
 and paper (465), or using a globe of sufficient capacity (447) 
 to condense all the vapour. Apply the heat of a lamp (212, 
 386), or hot air (269), or a small charcoal fire (158, 386). 
 
 [82.] Distil half a pint of wine in a glass retort (465), until 
 three-fourths of the fluid has passed over. Change the re- 
 ceiver or flask (467) when about an eighth has been distilled, 
 for the purpose of keeping apart the first strong spirit. In- 
 troduce a few slips of platina foil, and a piece or two of cork 
 (441), to facilitate the formation of vapour. Use any of the 
 sources of heat mentioned in the last experiment. 
 
 [83.] Distil nitric acid from nitre and sulphuric acid in a 
 glass retort (475). Introduce the acid in a neat manner 
 (436) ; apply heat by means of a sand-bath (176) ; and con- 
 dense in the manner already described (476). 
 
 [84.] Distil dry nitrate of lead in a glass retort (463) by 
 the heat of a crucible furnace (386), condense the products in 
 small dry flasks (461), tubes (929), or bottles (461), cooled 
 by a refrigerating mixture (454). Nitrous acid will pass over 
 and be procured in the fluid state. 
 
 [85.] Rectify some sulphuric acid in a glass retort (429, 
 439) over a sand-bath (176), or crucible furnace (158). Use 
 platina foil to facilitate the evolution of vapour (444). Con- 
 dense the vapour in a flask (447), supported in the open air 
 (483), and not purposely cooled by ice or freezing mixtures. 
 
 [86.] Put two ounces of acetate of potash into a retort 
 (435), with its weight of strong sulphuric acid ; distil, using a 
 
 2 Q 
 
594 mSTILLATIQN SUBLIMATION. [Sect. XXIV. 
 
 flask as a receiver (446), containing one ounce of diluted 
 water. Heat the retort by a chemical lamp (212), and cool 
 the flask by a basin of water (447). A solution of pure 
 acetic acid will be obtained. 
 
 [87,] Pistil sulphurous acid as already described (448). 
 Heat the retort by a chemical lamp (812) ; cool the little tube 
 receivers (929) in a well prepared refrigerating mixture (454), 
 and ultimately seal them up (1191), 
 
 [88.] Distil a portion of muriatic acid from common salt, 
 mixed with nearly its weight of sulphuric acid, previously 
 diluted with an equal weight of water (475). Apply heat by 
 a sand-bath or low charcoal fire (163), and use the tube of 
 safety (478) to prevent absorption. Receive the products into 
 vessels containing a little water. Test the acid, which will 
 thus be prepared, by muriate of baryta (506), to ascertain 
 whether any sulphuric acid has passed over or not, 
 
 [89-] Distil a little isinglass or horn, or even slips of leather, 
 in a small coated glass retort (489) by a crucible furnace fire 
 (490). Receive the products in successive portions, using 
 glass flasks as condensers (446), employing a little water at 
 first in them to dissolve the ammonia formed. Observe 
 the production of water, ammonia, fetid gas, tar, and empy- 
 reumatic matter ; heat the retort to redness (490), so that 
 when cold and broken, the charcoal within may be well 
 formed. Remark its peculiar appearances, its cellular state, 
 its lustre, great hardness, &c. and its difficult incineration in 
 the air (204). 
 
 [90,] Mix the finely-divided zinc of experiment 65 with 
 thrice its weight of powdered marble (323), and heat the 
 mixture in an iron (493) or an earthenware retort (491), for 
 the production of carbonic oxide (experiment 215) ; a dull 
 red heat will be required, and may be obtained either by 
 means of the table-furnace (494) or the crucible-furnace, ac- 
 cording to the size of the retort (490). The gas, if inflamed 
 as it issues from the mouth of the retort, will burn with a fine 
 blue colour. 
 
 [91.] Prepare phosphorus according to the direction con- 
 tained in elementary works ; or make chloride of antimony, 
 distilling in coated glass retorts (489, 490). 
 
Sect. XXIV.] DISTILLATION SUBLIMATION. 595 
 
 [92.] Put some ether into a tube, close the mouth of the 
 tube by the finger (766, 99), and heat the ether until it is 
 ready to boil upon opening the aperture (919, 921) ; remove 
 the tube from the heat, and displace the finger so as to allow 
 ebullition, until the temperature is so low as to occasion its 
 cessation ; then suddenly drop in a chip of dry wood (444), 
 and remark how powerfully the ebullition is renewed by it. 
 
 [93.] Make a freezing mixture of ice and salt (454), put it 
 into a glass, and ascertain whether its temperature is, as it 
 ought to be, at Fahrenheit (286). Put a little water into a 
 thin glass tube (910), and stir the mixture by means of it 
 (454, 457). The water will be frozen solid in the course of 
 two or three minutes. 
 
 [94.] Introduce a little metallic arsenic into a tube (495, 
 910), apply the heat of a spirit-lamp (199), and sublime the 
 metal so as to form bright metallic films or crusts of crystals at 
 pleasure (935) ; observe the temperature at which it sublimes, 
 and the degree of rapidity with which it condenses on parts 
 more or less heated. Sublime it up and down the tube, so as 
 to obtain command of it, and the power of condensing it in 
 this or that part of the tube at pleasure (937) . 
 
 [95.] Introduce some naphthaline into a large flask or globe 
 (495), place it on a warm part of the sand-bath (171), and 
 allow it to sublime slowly ; close the mouth of the vessel with 
 paper (1253). When a sufficient quantity has sublimed, re- 
 move the vessel carefully on one side till all is cold, then shake 
 out the crystals and examine the beauty of their forms. 
 
 [96.] Sublime iodine in the same manner (495), both quickly 
 and slowly ; observe the beauty of the forms obtained in the 
 latter case. 
 
 [97.] Put a portion of calomel into a Florence flask (495), 
 and sublime it into the upper part by placing the bottom in 
 sand (497) on a hot part of the bath (171) ; nearly a red 
 heat is required. When sublimed allow the vessel to cool : 
 cut it by an iron ring (1212), and examine the sublimed 
 mass. 
 
 [98.] Sublime a little indigo in the manner described (499). 
 It will be obtained in very minute but beautiful crystals. 
 
 [99.] Take the mixture made in experiment 55, put it into 
 
 2 Q 2 
 
596 PRECIPITATION. [Sect. XXIV. 
 
 a Florence flask, and sublime it by a sand-bath or chemical 
 lamp (386). Incline the flask and pass its neck through a 
 cork (468) into a cool receiver (495), or into the end of a wide 
 tube that may be cooled by the air (497), or if necessary by 
 water (468). Carbonate of ammonia will be obtained. 
 
 VIII. Precipitation. 
 
 [100.] Neutralize the solution left by experiment 73 with 
 ammonia (629), adding a slight excess of the alkali, then add 
 carbonate of ammonia until all the lime be precipitated (513) ; 
 collect it together (521), wash it (553), dry it (554, 601), and 
 weigh it. It should be exactly 100 grains, or the quantity at 
 first dissolved. 
 
 [101.] Select a marie or a lias limestone, pulverize it (323), 
 weigh a given quantity (61), act upon it by diluted muriatic 
 or acetic acid at ordinary temperature (375) until all effer- 
 vescence cease ; wash off (553) and preserve the solution as 
 well as the insoluble portion; dry the latter (601), and weigh 
 it (64, 52). Precipitate the solution by ammonia and car- 
 bonate of ammonia (521) as above, and having washed (553) 
 the carbonate of lime formed, dry and weigh it (64, 682, &c.) 
 Its quantity is the same as the quantity of carbonate of lime in 
 the marie, and with the quantity of residue should make up 
 the whole weight of the marie used. An analysis of the marie 
 will thus be effected. 
 
 [102.] Precipitate a portion of muriate of baryta in solution 
 by sulphate of soda (509, 513, 518), wash the precipitate 
 well (540), dry it and heat it red hot (666) in a platina cru- 
 cible. 
 
 [103.] Weigh out 50 grains (51) of crystallized muriate of 
 baryta, dissolve it in distilled water (368), precipitate the acid 
 by nitrate of silver (513, 517), and after separating all the 
 soluble matter from the insoluble by repeated washing (553), 
 dry (602) and weigh the latter, which is chloride of silver ; it 
 ought to amount to 58.87 grains (1318). Then proceed to 
 precipitate the soluble portion by sulphate of soda (513, 518) 
 to separate the baryta as a sulphate; wash (553, 555), dry, 
 and heat this substance to redness (666), then weigh it (51, 
 682) : it ought to be 47.42 grains (1318). 
 
Sect. XXIV.] PRECIPITATION. 597 
 
 [104.] Dissolve a silver coin (372, 380), precipitate the silver 
 by adding a solution of common salt (513, 517), wash and 
 dry the pure chloride of silver thus formed, and use it here- 
 after in experiment 180, for the preparation of pure silver. 
 
 [105.] Precipitate the muriates from a mineral water by adding 
 solution of nitrate of silver (517, 514), wash, dry, and weigh 
 the precipitate (51, 64), and estimate the quantity of muriatic 
 acid present in a given quantity of the water by referring to the 
 scale of equivalents (1318). 
 
 [106.] Take a portion of the ferruginous solution of experi- 
 ment 74, or any other solution of iron, and throw down the 
 oxide of iron by ammonia (509, 629) ; wash, dry, heat to 
 redness (670), and weigh the oxide obtained. If the iron in 
 the solution be not in the state of peroxide, first render it so 
 (414) by a little nitric acid and heat. 
 
 [107.] Take a small portion of the same ferruginous solution, 
 and precipitate it by the ferro-prussiate of potassa (509, 519). 
 A blue precipitate will be obtained, which is then to be re- 
 peatedly washed (553) . As long as much of the soluble matter 
 remains, the washing water and the precipitate will easily 
 separate (519), but as the washing approaches completion it 
 will be found that the pure water added dissolves the blue pre- 
 cipitate. Remark this effect, and then add a little pure muriatic 
 acid (555) ; this will immediately cause as complete a separation 
 of the prussian blue as before, and the washing fluid will 
 become nearly colourless. 
 
 [108.] Dissolve 100 grains of crystallized sulphate of copper 
 in water (375) , immerse a clean plate of soft iron to precipitate 
 the copper in the metallic state (522) ; when the precipitation 
 is completed collect the metal, wash, dry, and weigh it [553, 
 602, 51) ; its weight should be 25.6 grains. Then dissolve it 
 carefully in nitric acid. Precipitate the solution by excess of 
 caustic potassa, applying heat at the same time (516), till the 
 precipitate becomes a dense black powder. Then wash and 
 dry it, and heat it to 300 or 400 (264), afterwards weigh it ; 
 it ought to equal 32 grains (1321). 
 
 [109.] Test a weak solution of potassa by muriate of pla- 
 tina (506). 
 
 [110.] Examine the distilled water of the laboratory by 
 
598 FILTRATION DECANTATION- WASHING. [Sfect. XXIV 
 
 various precipitating tests. Previously evaporate three or four 
 pints to half a pint (594, 597) , to render any salts that may be 
 present more sensible to the action of the reagents. 
 
 IX. Filtration, Decantation, Washing. 
 
 [Ill,] Burn 400 grains of the filtering paper in use in the 
 laboratory (530), and ascertain the quantity by weight of the 
 ashes left (531); Wash them Well with Water (542), dry the 
 insoluble portion (609), and ascertain its amount. 
 
 [112.] Pass a quarter of a pint of distilled water several 
 times in succession through the same double filter of paper 
 (537) so as to wash out every thing soluble (542) ; evaporate 
 the water to a fourth of its bulk (591 ) 3 then test it for different 
 substances^ the presence of which has been suspected in the 
 paper, as sulphates, muriates* &c. (504). 
 
 [113.] Filter some foul or turbid water through a folded 
 filter (534j 536), remarking that it pass through perfectly 
 clear. 
 
 [114.] Filter a turbid solution (539), as that obtained from 
 the marie or lias limestone iri experiment 101, washing out all 
 the soluble matter from the filter (542). 
 
 [115.] Separate a precipitate of oxide of iron by filtration, 
 experiment 106, or one of sulphate of baryta, experiment 102, 
 (540), washing it in the filter until the water that will pass 
 in the first case contains no trace of muriatic acid (504) or 
 other soluble matter, and in the second case no trace of sul- 
 phuric acid resulting from the excess of sulphate of soda 
 used (506). 
 
 [116.] Wash carbonate of lime precipitated as in experiment 
 101* or in any other way (521 )* until all traces of soluble 
 matter are removed (540), stirring up the carbonate by the 
 bottle (541, 402) or the washer (547). 
 
 [117.] Dissolve four ounces of crystallized Glauber's salt 
 in two ounces of water by heat (680) in a flask, filter the 
 solution whilst hot (544) to avoid crystallization in the pores 
 of the paper, and cover the whole up with a glass vessel or 
 paper cover (1343). 
 
 [118.] Filter a portion of heated hog's lard or talloW through 
 paper (544). 
 
Sect. XXIV.] FILTRATION *DECANTATION WASHING. 
 
 599 
 
 [119.] Mix up equal measures of oil and water; separate 
 these bodies one from the other by filtration of the water [543] 
 through a wet paper filter. 
 
 [120.] Dissolve five grains of carbonate of baryta by means 
 of a little muriatic acid in a small evaporating dish (369), pass 
 the solution through a small filter without a funnel (546), test 
 for the baryta on a glass plate (1348), using but little of the 
 solution. Precipitate the rest by carbonate of ammonia in a 
 tube (910), separate the carbonate on a small paper filter 
 (546), wash it on the filter by the dropping bottle till pure 
 (404, 547), then dry it (609), and ascertain with how small a 
 loss the whole has been effected (51, 59). 
 
 [121.] Dilute an ounce of port wine with three ounces of 
 water; set aside a small quantity of it and boil the rest (386) 
 with an ounce of animal charcoal (61) for ten minutes, filter it 
 (539, 543), and by comparing the colour with that of the 
 reserved portion, observe how powerfully the charcoal has 
 acted in removing it. 
 
 [122.] Collect some charcoal ashes from the crucible furnace 
 (158), and lixiviate them (420). Examine the solution for 
 alkali (624) and other substances. 
 
 [123.] Precipitate a solution of two ounces of alum in water 
 by carbonate of potassa (504, 629) ; wash the precipitate in 
 much water (553), mixing it up well with a tube (514) ; when 
 settled, decant off the fluid (397, 550), and wash the preci- 
 pitate again (553) ; when subsidence has taken place, remove 
 the fluid by a syphon (550), and thus proceed till no trace of 
 alkali or sulphuric acid exist in the washing fluid. 
 
 [124.] Put water, oil, and mercury into the same glass. 
 Separate them by the funnel (557) as accurately as possible, 
 receiving them into different vessels. 
 
 [125.] Mix a little oil of turpentine and water together in a 
 tube (910), then separate them by the little vessel before 
 described (559). 
 
 [126.] Put some globules of mercury at the bottom of 
 some water or sulphuric acid ; remove them by means of the 
 mouth and a pointed tube (558), or by the use of a little glass 
 syringe (560), and transfer them in a clean dry state into a 
 separate vessel. In the same manner remove a few drops of 
 water from the bottom of some oil. 
 
600 CRYSTALLIZATION. [Sect. XXIV. 
 
 X. Crystallization. 
 
 [127.] Make a solution of crude or common nitre on the 
 sand-bath, exp. 68, of such strength as to crystallize when 
 cold (379) ; filter it (544) ; then set it aside in a deep basin 
 (564) to crystallize slowly. 
 
 [128.] In the same manner crystallize warm solutions of 
 alum, and of Glauber's salt (564), previously trying the pro- 
 per strength of the solutions on a glass plate (379) , cover the 
 solutions with paper cones (1343) or flannel. 
 
 [129.] Crystallize acetate of lead (563) by cooling a hot 
 solution. 
 
 [130.] Crystallize muriate of soda (565) by the slow evapo- 
 ration of a cold saturated solution (378). 
 
 [131.] Prepare a solution of alum for crystallization by 
 diminution of temperature (378, 563) ; hang a thread across 
 it, or leave in it a glass rod with a thread wound round it, and 
 observe the greater tendency to deposition on the one sub- 
 stance than the other. 
 
 [132.] Dissolve a little sulphate of magnesia in water in a 
 capsule (575) ; evaporate drops of it slowly on a glass plate 
 (1348), and examine the crystals (575, 580). Do the same 
 with alum, nitre, Glauber's salt, phosphate of soda, and com- 
 mon salt ; and observe with what facility the crystals of these 
 salts may be obtained from small quantities of solutions, and 
 examined, so as to determine their characters and the nature 
 of the substances crystallized. 
 
 [133.] Transform several small crystals of sulphate of nickel 
 into a large one (570). 
 
 [134.] Crystallize sulphur, bismuth, or lead (578) in a cru- 
 cible, by fusion, and partial solidification. 
 
 [135.] Crystallize naphthaline by sublimation in a globe or 
 flask (579). 
 
 XI. Evaporation. Desiccation. 
 
 [136.] Evaporate a solution of common salt gradually to 
 dryness (583, 565), covering the vessel containing it with 
 paper (566) to keep out the dirt. 
 
Sect. XXIV.] EVAPORATION DESICCATION, 601 
 
 [137.] Evaporate a solution of sulphate of copper, so that it 
 shall crystallize on cooling (379, 564), make it thus give suc- 
 cessive crops of crystals by successive processes, till all the salt 
 is separated. 
 
 [138.] Procure some spring water, as the deep well water 
 of London ; evaporate a portion to dryness, in a basin (369), 
 on the sand-bath (598, 381) or otherwise (590), and then test 
 the residue by a little water and turmeric paper for free alkali 
 (624), or by other agents for the detection of other sub- 
 stances. 
 
 [139.] Evaporate some of the same water by boiling it away 
 in a Florence flask (594), until reduced to a very small quan- 
 tity; then test the remaining portion (504). 
 
 [1 40.] Evaporate a part of the same water in a platina cru- 
 cible (597), and heat the residue (666), to ascertain whether 
 it be changeable by such treatment or not. 
 
 [141.] Evaporate an infusion of a vegetable substance to 
 dryness (419), so as to obtain the extract uninjured by heat 
 (599). 
 
 [142.] Dissolve an impure carbonate of baryta in muriatic 
 acid added until in slight excess (369, 624) ; evaporate the 
 solution to dryness (596), to dissipate the excess of acid, 
 stirring the product when it becomes thick or solid (592), to 
 prevent its dispersion. 
 
 [143.] Heat crystallized Glauber's salts in a basin (601) to 
 drive off' all the water (602), and reduce the substance to an 
 anhydrous state. Stir the melted salts with a rod, until they 
 become nearly solid (592), and then rub them with a pestle, 
 that all parts may be pulverized and dry (592). 
 
 [144.] Evaporate the moisture from washed carbonate of 
 lime (521), in a basin (369), covering the substance with 
 another basin (596), during the operation, to keep out the 
 dirt. Test the dryness of the carbonate by a cold glass plate 
 (602). 
 
 [145.] Dry a little pulverized black oxide of manganese on 
 the sand-bath (173), or over a lamp (212) : test the dryness 
 by a glass plate (602). 
 
 [146.] Evaporate a solution of sugar in water (375), by 
 Leslie's process (583), until it be as dry as possible. 
 
602 COLOURED TESTS NEUTRALIZATION. [Sect. XXIV. 
 
 [147.] Freeze Water by evaporation by means of Leslie's 
 process (583). 
 
 [148.] Dry a part of the vegetable solution of exp. 141, 
 by sulphuric acid or other bodies (589) under a receiver, no 
 exhaustion being made. 
 
 [149.] Dry a filter and its contained precipitate, as that of 
 exp. 101, on a tin plate (609) over a larrip or sand-bath. 
 
 [150.] Dissolve 2 grains of carbonate of soda in water in a 
 watch glass (400) ; add excess of muriatic acid, evaporate to 
 dryness (603) ; re-dissolve and re-evaporate, so as to obtain 
 small Well-formed crystals in the glass (568) ; observe their 
 forms (580), which will be those of chloride of sodium 01* 
 common salt. 
 
 [151.] Dry some precipitates on filters (542)$ in a box (608) 
 or air jar, into which heated air is thrown from a lamp (270) 
 or by some other arrangement (269) * 
 
 [152.] Drain the crystals of exp. 127 or 128, in a funnel 
 (613), aiding the desiccation by a current of air (614). 
 
 XII. Coloured Tests. Neutralization. 
 
 [153.] Dilute 10 grains (67, 51) of strong sulphuric acid 
 until it will scarcely affect litmus paper (624), comparing it 
 with water (625) ; observe and estimate the quantity of water 
 required for the dilution. Then heating a little of the diluted 
 acid in a basin or tube, remark how much further the dilution 
 may be carried, and yet the acidity remain sensible. Leave 
 little pieces of litmus paper in the liquor for this purpose (627). 
 
 [154.] Try the effects of different acids (615) on the blue 
 test solution (616.) 
 
 [155.] Try alkalies and carbonated alkalies on turmeric 
 (624) or reddened litmus paper (626) ; remark how little of 
 these substances produces a sensible effect. Try lime and 
 baryta water in the same manner, but notice the restoration of 
 the colour on the turmeric paper as the earth becomes car- 
 bonated by contact of the air. 
 
 [156.] Test the air of the laboratory for acid fumes by lit- 
 mus paper (619, 623). 
 
 [157.] Try the effect of boracic acid on turmeric paper 
 
Sect. XXIV.] COLOURED TESTS NEUTRALIZATION. 603 
 
 (630), and afterwards the effects of other aeids on the same 
 places. Try the effect of a mixture of boracic acid and other 
 acids upon turmeric paper (630), and compare it with the 
 effects of the pure acids. 
 
 [158.] Test ammonia, either in solution or in vapour, by 
 turmeric paper (622, 624), and observe the transient effect 
 produced by this alkali, 
 
 [159.] Heat a piece of isinglass in a small tube (910, 954) j 
 and test the vapours given off at the mouth of the tube by 
 turmeric paper, for ammonia (622) . 
 
 [160.] Reilder a portion of diluted sulphuric acid neutral 
 by the addition of a solution of carbonate of potassa, ap- 
 plying heat during the operation (628), and ascertaining the 
 state of the solution by litmus and turmeric papers (624, 6&5). 
 
 [161.] Dilute some sulphuric acid to a given strength (633). 
 
 [162.] Lixiviate half a pound of wood or charcoal ashes 
 (157, 420), and ascertain by the diluted sulphuric acid (633) 
 and alkalimeter tube (632) how much alkali they contain 
 (634). 
 
 [163.] Try an impure alkali, as barilla or kelp, in the same 
 manner (634, 638). 
 
 [164.] Precipitate a solution of the persulphate of iron by 
 carbonate of ammonia in an evaporating basin (369), applying 
 heat and adding the alkali only to neutralization (628, 629). 
 Then examine the solution, and it will be found that all the 
 iron will have been separated (504). 
 
 [165.] Make a solution of the common ore of manganese 
 in dilute sulphuric acid (380) ; filter (539) ; add a little nitric 
 acid, and apply heat (414) to peroxidize the iron that has 
 been dissolved ; then gradually add solution of carbonate of 
 ammonia to the hot solution (628), until the latter is neutral 
 (624, 625) ; by this process all the iron will be precipitated, 
 but all the manganese remain in solution. 
 
 [166.] Try the strength of a diluted pure acetic acid or a 
 specimen of distilled vinegar by a piece of marble (639). 
 
 [167.] Ascertain the strength of diluted muriatic acid by 
 a similar process (640), and also of diluted nitric acid (640), 
 applying heat in all these cases to expedite the action (628), 
 and to render the point of neutralization distinct (624). 
 
604 CRUCIBLE OPERATIONS. [Sect. XXIV. 
 
 XIII. Crucible Operations. 
 
 [168.] Heat some flints to redness in a Hessian crucible 
 (646, 670), and quench them in water (332), to prepare them 
 for pulverization. 
 
 [169.] Convert some carbonate of lime into quick lime in 
 an earthenware crucible (642), by means of a crucible furnace 
 (158, 670), and flue (165). 
 
 [170.] Fuse a portion of lead in an earthenware crucible 
 [648, 662], heated in a crucible furnace (670). After con- 
 cluding that experiment fuse a portion of copper in another 
 crucible in the same furnace (670, 165) : and ultimately, 
 if possible, a portion of cast-iron in a third crucible, raising 
 the heat for this purpose to the highest degree (671, 168). 
 Remark the difference of temperature required for these ope- 
 rations, and also the powers of the furnace when assisted by 
 the flue (165), &c. 
 
 [171.] Fuse 400 grains of copper in an earthenware crucible 
 (643) heated in the crucible furnace (158, 670), and cover the 
 metal with a few pieces of charcoal (683) . When well melted, 
 add 100 grains of zinc in fragments, and mix it with the 
 copper, either by one of the pieces of charcoal or an iron rod 
 (683). The result will be brass, and may either be poured 
 into a mould, or be allowed to cool in the crucible. 
 
 [172.] Fuse a portion of steel in an earthenware crucible 
 (643) in the blast furnace (184, 673), being careful to keep 
 the carbonaceous matter from contact with the steel (674, &c.) 
 
 [173.] Fuse a portion of pure iron, as horse- shoe nails, in 
 the same manner in the blast-furnace (679). When the cru- 
 cible is cold, examine the button of iron by nitric acid, to 
 ascertain the absence of carbonaceous matter; for this pur- 
 pose the surface of the button must be brightened on one 
 part, and a drop of dilute nitric acid placed on the spot. 
 Being wiped off a few minutes afterwards, it should leave 
 no black stain, but the metallic iron should appear pure and 
 untarnished. 
 
 [174.] Mix two ounces of red-lead with about two drams of 
 pulverized charcoal, one ounce of common salt, and a little 
 borax (685, 691) ; heat the mixture in a Hessian crucible (643, 
 
Sect. XXIV.] CRUCIBLE OPERATIONS. 605 
 
 670) in the crucible furnace (158), that the lead may be re- 
 duced. If the experiment be properly performed, metallic 
 lead, equivalent to the red-lead used, will be obtained at the 
 bottom of the crucible. 
 
 [175.] Pulverize a native oxide of tin (323), mix it with 
 one-eighth its weight of pulverized charcoal (332) and half its 
 weight of borax (691), put the mixture into a crucible with 
 a few pieces of charcoal over it, and heat it (669, 670) to re- 
 duce the metal. The tin will ultimately be obtained at the 
 bottom of the crucible. 
 
 [176.] Melt carbonate of soda in a platina crucible (653, 
 662) in the crucible furnace (158, 670). Afterwards melt 
 green glass in the platina crucible in the same furnace (670). 
 
 [177.] Melt borax in the platina crucible over a large spirit- 
 lamp (205, 666), or oil-lamp (212, 667). 
 
 [178.] Mix together three parts by weight of bi-carbonate of 
 potash, and one part of pulverized flints, see experiment 168 ; 
 fuse the mixture in a platina crucible (653, 662), by means 
 of the crucible furnace (670) ; pour out the result upon a 
 clean cold stone or a metallic surface, and dissolve it in water. 
 
 [179-] Carefully melt a mixture of caustic alkali and sili- 
 ceous matter in a silver crucible (656), using the crucible fur- 
 nace (158,670). 
 
 [180.] Take the silver obtained by reducing the chloride of 
 exp. 104, by means of zinc and a little sulphuric acid, and fuse 
 it in a Hessian crucible with a little carbonated alkali (686). 
 
 [181.] Mix an ounce of oxide of copper with one-twelfth 
 its weight of pulverized charcoal (332, 696), adding oil enough 
 to make the whole into a paste (697) ; put it into a crucible 
 with an ounce of borax, and ignite it in a wind-furnace (669), 
 or a crucible furnace if it can be made to afford sufficient heat 
 (168, 670). The oxide will be reduced, and a button of 
 metallic copper obtained. 
 
 [182.] Line a crucible with charcoal (652) ; place some 
 oxide of copper in it (696) ; then add more charcoal, and close 
 it with a cover nearly tight (676). Apply a temperature 
 sufficient to melt copper for half an hour ; the metal will be 
 reduced. If the heat has not been sufficient to melt the copper, 
 still it will be found perfectly reduced and adhering together 
 in one mass. 
 
606 FURNACE TUBE OPERATIONS. [Sect. XXIV. 
 
 [183.] Introduce some dry pulverized (323) oxide of iron, 
 as, for instance, clean scales, into a crucible lined in a similar 
 manner (652) ; cover and heat it for an hour at a high tempe- 
 rature (673) ; the oxide will be reduced throughout, and leave 
 the iron in a spongy and extremely divided state*. If a por- 
 tion of this iron be cut off in thin layers by a knife, heaped 
 up and lighted at one corner, it will burn like tinder. 
 
 [184.] Put some sulphate of potash into a similar crucible 
 (652) ; place some charcoal over it, and then lute on a cover 
 (676) ; heat the crucible highly for an hour, after which take 
 it out of the furnace and allow it to cool ; when cold, the 
 sulphate will be found converted into a pure sulphuret of 
 potassium f. 
 
 [185.] Take the oxide of iron separated in experiment 106, 
 and when washed, and also dried as much as possible by the 
 heat of the bath or a hot plate (171, 609), introduce it into a 
 platina crucible (653), and raise the temperature to dull red- 
 ness over the chemical or spirit-lamp (666) to dissipate the last 
 portions of water. If the crucible be large, or the lamp alone 
 ineffectual, use the jacket (667) for the purpose of increasing 
 the power. 
 
 [186.] Put 50 grains of dry hydrate of lime into a counter- 
 poised platina crucible (653, 682) ; carefully heat the crucible 
 and its contents to redness for a quarter of an hour (667) ; 
 then weigh and ascertain the loss (51 , 682) : again heat for 
 five minutes, to ascertain whether any further loss will be 
 occasioned (58, 59> 682). In this manner the water may be 
 driven off, and the composition of the hydrate of lime ascer- 
 tained. The loss should be 12.16 grains. 
 
 XIV. Furnace Tube Operations. 
 
 [187.] Send steam (706, 704) through an iron tube (700) 
 containing iron turpings (721), heated to redness (699) in a 
 furnace. The water will be decomposed, arid a mixture of 
 hydrogen gas and steam evolved, or even gas alone if the ope- 
 ration be slow ; this may be burnt at the end of the tube, or 
 received in jars pver a pneumatic trough (704, 746), 
 
 * JJerthier, Annales de Chimie, xxvii, 24. f Journal des Mines, vii. 421. 
 
Sect, XXIV.] FURNACE TUBE OPERATIONS. 607 
 
 [188.] Decompose ammonia by passing it through a red-hot 
 iron tube (719, 700). The ammonia may be liberated from 
 a retort containing the usual mixture of quick lime and sal 
 ammoniac ; and the gases evolved may be received into jars 
 (748, 751) over the pneumatic trough. The ammonia will 
 in this manner be resolved into a mixture of three parts by 
 volume of hydrogen, and one part of nitrogen, which upon 
 trial will be found to be combustible. 
 
 [189.] Pass ammonia in the same manner over black oxide 
 of manganese (784) heated to redness in a tube either of iron 
 (700), glass, or earthenware (703). The vapours, if thrown 
 into a globe or large flask, will be found to produce red fumes, 
 from the presence of nitrous acid; the alkali being decom- 
 posed in this experiment and occasioning the production of an 
 acid body. 
 
 [190.] Pass oil through an iron tube heated to redness 
 (700, 708) in a furnace. The fluid will be decomposed, and 
 a quantity of oil gas produced which will burn at the farther 
 end of the tube with a brilliant flame, or may be received and 
 preserved in jars (746) over water. 
 
 [191.] Decompose alcohol (706) by passing its vapour gra- 
 dually through a glass tube (703) containing rock crystals 
 (718), heated by the lamp (710) ; collect the gas (746), and 
 observe its combustibility and other properties. Ether may be 
 decomposed in the same manner : the deposition of carbon 
 will be far more abundant than when alcohol is employed. 
 
 [192.] When chlorine is passed over crystals of metallic 
 titanium in a glass tube heated by the lamp (710) combina- 
 tion takes place^ and a chloride of titanium is deposited in the 
 cool part of the tube (727).* 
 
 [193.] In the same manner chlorine passed over arsenical 
 ores combines with the arsenic, sulphur, and other substances 
 present, and carries them onwards (727). For a complicated 
 out excellent process of this kind, see Berzelius, on the Ana- 
 lysis of Arsenical Ore '(*. 
 
 [194.] Put peroxide of manganese into a green glass tube 
 (703), apply heat by m/eans of Cooper's lamp (710), and then 
 
 * Mr. Georges. Annales of Philosophy, N. S. 
 t Annales de Chimie, xvii. p. 113. 
 
608 FURNACE TUBE OPERATIONS. [Sect. XXIV. 
 
 pass hydrogen over it (724). The peroxide will become pro- 
 toxide, and the manner in which the change proceeds will be 
 observed through the glass. 
 
 [195.] Send naphthaline (698) through a tube heated to 
 redness by the ordinary oil-lamp (709), that the effect of heat 
 upon the substance may be observed. 
 
 [196.] Select a green glass tube about one-third of an inch 
 in diameter (703), and counterpoise it (65). Introduce some 
 pure baryta in fragments, so as loosely to occupy the length of 
 six inches (718, 725) ; weigh it, and ascertain the quantity of 
 earth introduced (52). Then heat the tube and its contents 
 to dull redness, either by Cooper's lamp-furnace (710), or any 
 oiher convenient means (707), and pass oxygen (704) over 
 the earth, until, from the abundance which issues at the open 
 extremity of the tube (725), it is evident that no more will be 
 absorbed. Allow the tube to cool (58), closing the extremities 
 (960, 1253) to prevent the free access of air. Then weigh it 
 again (59), and ascertain how much oxygen has been absorbed 
 to convert the baryta introduced into peroxide of barium. 
 
 [197.] Make a similar experiment with lime, except that 
 instead of oxygen, pass chlorine over the earth (727). It 
 will be found, if the gases be collected (746), that oxygen is 
 evolved during the experiment, the lime being decomposed, 
 and its metallic base, calcium, combined with the chlorine to 
 form a chloride. The quantity of oxygen set free may be 
 ascertained by collecting all the gas (750), and absorbing the 
 excess of chlorine. The quantity of lime experimented with 
 may be ascertained also, as well as the quantity of chloride of 
 calcium produced (65, 59), and in this manner the composi- 
 tion of the oxide and the chloride of calcium may be ascer- 
 tained, not only as to the elements they contain, but as to their 
 actual quantities. 
 
 [198.] By putting some spongy platina into a glass tube 
 (703), and heating it over an oil (212, 709) or spirit-lamp 
 (205), and then passing mixtures of gases through the tube, 
 the power of the platina (720) to facilitate chemical changes 
 may be easily observed. Thus a mixture of carbonic oxide 
 and oxygen is readily converted into carbonic acid at com- 
 paratively low temperatures and without explosion. 
 
Sect. XXIV.] PNEUMATIC MANIPULATION. 609 
 
 XV. Pneumatic Manipulation. 
 
 [199-] Put about one ounce of granulated zinc (351) into a 
 pint retort (428, 435) ; dilute half an ounce (118) by measure 
 of oil of vitriol, with four or five measured ounces of water, 
 add the mixture to the zinc in the retort (436), and collect the 
 gas evolved (746) in jars (739), over the pneumatic water 
 trough (729). When two or three jars of gas (751) have 
 been received, remove the' retort, and proceed to manipulate 
 with the gas. Transfer (759) a portion from one of the jars 
 into a lipped glass (368, 760), then transfer a little from the 
 glass (761, 765) into a tube (743), using a funnel (766) for 
 the purpose, and filling the tube for about two inches in length 
 with gas; close the end of the tube by the finger (766), and 
 then apply a lighted taper to the gas (950) to prove its 
 combustible nature. Refill the tube with water (762), and 
 transfer a second portion of gas into it from the glass (765), 
 not using the funnel but the fingers only (763). Transfer a 
 part of the gas from this tube to a smaller (764), not using a 
 funnel but the fingers, as already directed. 
 
 [200.] Fill a transfer jar (742) with water (755) over the 
 trough, and decant some of the hydrogen gas from the jars 
 into it (759) ; depress the transfer jar in the water of the 
 trough (755), so as to cause a jet of gas to issue at the aper- 
 ture of the stop-cock (827) as soon as the latter is opened ; do 
 this gradually, and apply a light to the issuing jet of hydro- 
 gen, so as to inflame it and shew its combustibility. 
 
 [201.] Fill a small jar or a large glass (368) with water at 
 the trough (751) and throw part of the remaining hydrogen 
 gas into it (759), until the jar or glass is full. Raise it 
 carefully from the water into the air, still keeping the mouth 
 horizontal and downwards. It will be found that after the 
 lapse of a minute nearly, still a light applied to the air in the 
 glass will cause slight explosion, from the ignition of the 
 hydrogen gas- remaining in it. Refill the jar or glass in the 
 trough with hydrogen (759), cover its mouth with a glass 
 plate (739, 1348), set the glass upright, mouth upwards, and 
 then remove the plate. If after the lapse of two or three 
 seconds only, a light be applied to the contents of the glass, no 
 
 2 R 
 
610 PNEUMATIC MANIPULATION. [Sect. XXIV. 
 
 inflammation will take place, the hydrogen gas having now 
 escaped, in consequence of its lightness, and the position of 
 the vessel. 
 
 [202.] Put some fragments of marble (315) into a gas bottle 
 (746), and pour upon them muriatic acid, diluted with thrice 
 its bulk of water ; carbonic acid gas will be evolved, which 
 is to be received in jars (739) over the water trough (729). 
 Transfer a portion of it (760) into a small jar (739), filling 
 the latter and then closing its mouth with a glass plate (754, 
 1348) ; take it out of the trough and set it upright, with the 
 mouth upwards. Remove the plate and apply a lighted taper 
 to the gas ; the taper will be extinguished as soon as it de- 
 scends in the jar below the level of the edge. Leave the jar 
 thus open for a minute or two, the air about it being undis- 
 turbed, and then on applying the taper, it will be observed to 
 be extinguished as readily as before. Such is the weight of 
 this gas, that after four or five minutes, still enough will be 
 left in the jar to extinguish the taper. 
 
 [203.] Refill the jar with carbonic acid gas over the trough 
 from the portion originally received (751, 759) ; put a lighted 
 taper fastened to a wire at the bottom of a similar jar standing 
 on the table and containing air ; it will burn freely ; bring the 
 mouth of the jar containing the carbonic acid gas to the mouth 
 of that inclosing the taper, and pour the carbonic acid gas into 
 the latter jar ; the gas will descend and extinguish the flame 
 as effectually as so much water. Remove the taper and test 
 the presence of the gas by another method, namely, by lime 
 water, for which purpose pour a little lime water into the jar 
 and agitate it, it will immediately become turbid from the for- 
 mation of carbonate of lime. In doing this do not bring the 
 mouth of the lime water bottle near the jar containing the car- 
 bonic acid, but pour the lime water required into a glass, and 
 from that into the jar; otherwise all the lime water in the 
 bottle will become turbid, from a little carbonic acid gas thus 
 introduced. 
 
 [204.] Transfer a portion of carbonic acid gas at the water 
 trough into a tube (762), of a size that may be closed by the 
 finger (766), then quickly introduce a piece of potassa through 
 the water into the tube ; close the tube by the finger, and 
 
Sect. XXIV.] PNEUMATIC MANIPULATION. 611 
 
 shake it to dissolve the potassa ; then open its aperture by re- 
 moving the finger under water, observe the absorption of the 
 gas by the alkaline solution ; the whole of the carbonic acid 
 gas will be absorbed, and thus its purity may be ascertained. 
 
 [205.] Mix one volume of good alcohol with two volumes 
 of oil of vitriol carefully (436), because of the heat liberated. 
 Distil the mixture in a glass retort (386), applying the heat 
 of an oil lamp (212, 386), and receive the gas into jars over 
 water (751) ; it will be olefiant gas, and should burn with a 
 brilliant flame. Receive small portions into tubes (743), and 
 observe whether it burns with a bright flame when lighted 
 (950, 749) ; do not collect the gas to be preserved until that 
 be the case. During the progress of the operation, test the 
 gas that is passing over in the same manner, and when its 
 flame decreases in brightness, preserve that which is after- 
 wards collected apart, as inferior and impure. Allow the gas 
 to stand over water (751, 753), or agitate it with water to 
 wash out the sulphurous acid. Transfer a jar filled with it 
 into an evaporating basin (753), and add some quick-lime to 
 the water in which it stands, for the purpose of more effectually 
 separating the carbonic and sulphurous acid gases. 
 
 [206.] Half fill a tall cylindrical jar (739) with chlorine 
 (732) over the pneumatic trough (751), and then throw up an 
 equal volume of the olefiant gas. Immediately transfer the 
 jar into a large basin (369, 753), and observe the gradual 
 combination and disappearance of the gaseous fluids, and the 
 production of a liquid in drops, insoluble in water, and so 
 heavy as to fall through it ; the liquid will communicate a 
 very aromatic sweet taste to it, and is itself powerfully sweet 
 and sapid. Into a similar jar (739) throw chlorine, until it 
 be two- thirds full, and fill the remaining third with olefiant 
 gas. Close the mouth of the jar with a glass plate (1348), 
 remove it from the trough, invert it two or three times (857), 
 to mix the contents, and removing the plate, immediately 
 apply a light to the mouth of the vessel ; the gases will com- 
 bine with inflammation, the flame slowly passing through the 
 jar, and rendering it opaque from the great quantity of carbon 
 suddenly evolved. 
 
 [207.] Burn a jet of olefiant gas from the stop-cock of a 
 
 2 R 2 
 
612 PNEUMATIC MANIPULATION. [Sect. XXIV. 
 
 transfer jar (742, 755) in the manner described in experiment 
 200, and remark the brilliancy and beauty of the flame. Pass 
 a bladder full of it (820) through a heated glass tube, as in 
 the practices of Section XIV. and observe both the deposition 
 of carbon in the tube (723), and the diminished intensity of 
 the flame produced by the gas, after the operation. 
 
 [208.] Put some fragments of sal ammoniac into a small dry 
 gas bottle (746), retort (429), or flask (372, 746), and add 
 strong sulphuric acid ; muriatic acid gas will be evolved. 
 Receive it into jars (739, 783), over the mercurial trough 
 (736, 782), applying the heat of a spirit-lamp to the retort 
 if necessary (199, 439), and shaking the vessel to break the 
 bubbles. When several jars are filled with the gas, close the 
 mouth of one of them by a plate, and place it upright with 
 the mouth upwards, on the table (739, 783). Remove the 
 disc, and observe the fumes produced by the gas in the air, 
 and the heat which becomes sensible when the finger is dipped 
 into the gas. Apply a lighted taper, and observe its instant 
 extinction. Pour a little water into the jar, remark the in- 
 crease of fumes within, and by a little agitation their final 
 absorption. Test the acidity of the solution by litmus paper 
 (624, 617) or cabbage liquor (616), and test the acidity of the 
 fumes also by litmus paper (626) . 
 
 [209.] Transfer a little tube full of water into another jar 
 of the gas as it stands over the mercury (782) ; observe the 
 immediate absorption, and ultimately the entire disappearance 
 of the gas. Remove the jar from the trough by means of a 
 flat plate (739, 783), and examine the solution (624, Sec.) ; it 
 will be found to be the same substance as ordinary solution of 
 muriatic acid. 
 
 [210.] Transfer a portion of the muriatic acid gas into a 
 tube (743) under the mercury (787, 794), then close the 
 mouth of the tube by the finger (766), transfer it into an 
 evaporating basin containing water (732), remove the finger, 
 and observe how instantaneously the gas is absorbed by the 
 water. 
 
 [211.] Make a mixture to evolve ammonia, as in experi- 
 ment 56. Put it into a small retort (429, 438) ; heat it by 
 the large spirit-lamp (205), and receive the amrnoniacal gas 
 
Sect. XXIV.] PNEUMATIC MANIPULATION. 613 
 
 which will be liberated into jars (739) over the mercurial 
 trough (736). Throw up a little water into a jar of the gas, 
 and observe its solubility, and the alkaline nature (624) of the 
 solution produced. Take two jars, one containing ammoniacal 
 gas, and the other muriatic acid gas of the last experiment, 
 observe their volumes in the jars (798), and then pass up the 
 ammoniacal gas gradually into the muriatic acid gas (787) ; 
 dense fumes will be produced, and condensation will take place. 
 By degrees the whole of one of the gases will disappear with 
 an equal volume of the other, and in their places will remain a 
 solid muriate of ammonia. Estimate the quantities of the two 
 gases used (798), and practically verify the statement just 
 made, that equal volumes of the two condense each other. 
 
 [212.] Make muriatic acid gas (826) and ammoniacal gas 
 (825), and receive them in clean dry bottles (824) without 
 the aid of a mercurial trough. 
 
 [213.] Make chlorine in a glass retort (428), from a mix- 
 ture of eight parts of salt with three parts of black oxide of 
 manganese, to which has been added six parts of sulphuric 
 acid, diluted with four times its bulk of water, and allowed to 
 become cold. Heat the retort gradually by an oil-lamp (212), 
 removing the lamp if the evolution of gas become quiek^ or 
 the mixture froths over into the neck of the retort. Receive 
 the gas when good into stoppered bottles (824) , in a trough 
 containing warm water (732) j close the bottles well (824), 
 and preserve them inverted in a dark place, with their stop- 
 pers and necks immersed in water. To test the goodness of 
 the chlorine, fill a tube with water, and receive a few bubbles 
 of the gas into it, then remove the tube to a trough containing 
 cold water, agitate it with the gas (766), and observe whether 
 the absorption be entire ; any residue is impurity. This trial 
 should be repeated until not more than a fourteenth part re- 
 mains unabsorbed, and then the chlorine may be received. 
 
 [214.] Make an aqueous solution of the gas contained in 
 one of these bottles (824, 856). Then remark its bleaching 
 powers as shewn upon a little finely-divided indigo, or upon 
 writing or printed calicoes, &c. 
 
 [215.] Make some carbonic oxide, as in experiment 90; 
 receive it into jars over water (748, 758). Wash it well over 
 
614 PNEUMATIC MANIPULATION. [Sect. XXIV 
 
 water, or lime and water, as in experiment 205 with olefiant 
 gas, or even over alkaline solutions. Mix (759, 857) a portion 
 of the pure gas with half its volume of oxygen in a glass (368, 
 505) ; transfer a little of the mixture into a tube (761), and 
 applying a taper to it, examine its combustibility ; it will be 
 found to explode. Transfer a small quantity of the mixture 
 into a detonating tube (994) , pass the electric spark through 
 jt (986, 993) ; explosion will take place, and the bulk of the 
 gas will be diminished. By agitation the remaining gas will 
 now be absorbed ; or if a little piece of potassa be introduced 
 and agitated with it, the effect will proceed more rapidly, the 
 resulting gas being carbonic acid. 
 
 [216.] Transfer a portion of the detonating mixture into a 
 dry tube, over mercury (792, 794), and from that transfer a 
 small quantity into a dry eudiometer tube, also over mercury 
 (994). Observe the volume of gas to be detonated (798), 
 and when the explosion has taken place (997), again remark 
 the volume ; the diminution will be found equal to one-third 
 of the original bulk. Throw up a tube full of lime-water into 
 the eudiometer : the opacity thereby occasioned, and the con- 
 densation of the gas, will sufficiently prove that carbonic acid 
 gas has been the result. 
 
 [217.] Make a little oxygen in a tube retort (924) from 
 chlorate of potassa, by the heat of a large spirit-lamp (205), 
 and receive the gas in tubes (127) and phials over water, con- 
 tained in an evaporating basin (946). Try portions of this 
 oxygen in the tubes (766). Introduce a glowing taper, or the 
 ignited end of a splinter of wood, into a tube containing some 
 of it, and observe the increased combustion at the moment. 
 Twist together five or six folds of steel harpsichord wire, fasten 
 a little piece of wood to one end of the bundle, light it and 
 then plunge it into the oxygen gas contained in one of the 
 phials. The steel wire will burn brilliantly. 
 
 [218.] Transfer a little of the oxygen of the preceding ex- 
 periment into a dry tube (792, 793) over mercury, or make a 
 little oxygen from the tube retort (924) directly into dry 
 tubes or jars, over the mercurial trough (737). Mix a portion 
 of it with twice its volume of dry hydrogen, transfer a part of 
 the mixture into a dry eudiometer tube (994), using Pepys's 
 
Sect. XXIV.] PNEUMATIC MANIPULATION. 615 
 
 instrument for the purpose (794), and detonate it by the elec- 
 tric spark (986). If pure, the gases will entirely disappear, 
 and only a minute quantity of water will remain. 
 
 [219-] Make some nitric oxide gas in a glass retort, by 
 acting on copper clippings, with a mixture of two parts water 
 and one part nitric acid. The action, which is often tardy at 
 first, very frequently increases on a sudden and becomes 
 powerful ; hence attention and watchfulness is required. The 
 gas should be received into glasses (743) or jars (739) over 
 water, and after standing an hour or two, will be sufficiently 
 washed from acid fumes. Mix a portion of this gas in a glass 
 (743, 759), with some of the oxygen of experiment 217. Ob- 
 serve the deep orange colour produced, and the rapid disap- 
 pearance of the gases in consequence of the solubility of the 
 product in the water. 
 
 [220.] Measure equal volumes of common air and nitric 
 oxide (776), mix them together in a tube (127) over water, 
 and observe the diminution (780). 
 
 [221.] Mix equal volumes of dry air and hydrogen over 
 mercury (798), introduce a portion of the mixture into a tube, 
 and observe its detonation by the application of a lighted 
 taper. Introduce a portion of the mixture into an eudiometer 
 tube (994), observe its volume accurately (800), detonate it 
 by the electric spark (994), and then remark the diminution 
 in bulk (800). One third of the diminution will be the quan- 
 tity of oxygen existing in the common air used, the latter 
 amounting to half the bulk of the mixture detonated. 
 
 [222.] Take any one of the jars of the preceding experi- 
 ments containing gas standing over water, and measure the 
 gas in it (772). In doing this be careful to level the surfaces 
 accurately (769), to mark the place of the gas before transfer- 
 ring it (767), and to verify the measurement (770) in the 
 manner described. Note also the temperature and pressure 
 (780, 773). Then measure a given quantity of gas into a 
 graduated jar, or up to a certain mark in a jar (774), adjusting 
 the quantity accurately (775). Measure out also a given 
 number of parts into a graduated tube (127), as eight or ten 
 (779) ; carefully adjusting the quantity by the use of the 
 finger (775). Make use of a standard measure (776) in mix- 
 
616 PNEUMATIC MANIPULATION. [Sect. XXIV. 
 
 ing together two parts of hydrogen with one of oxygen by 
 volume, for experiments like those of 221 . 
 
 [223.] Transfer the remaining oxygen, chlorine, hydrogen, 
 or any other valuable gas of the preceding experiments that 
 may be unused, into bottles (760), being careful to close their 
 mouths accurately with stoppers (824). 
 
 [224.] Measure half a cubical inch, or any small quantity 
 of oxygen, hydrogen, or common air, in a tube (127) over 
 mercury (798) ; then transfer the tube to a basin of water 
 (766), allow the mercury to escape, and again observe the 
 volume of gas now that it stands over water (769), the level 
 being in both cases attended to (767). In this way the effect 
 produced by the different curvatures of mercury and water in 
 the tube (135) may be valued and appreciated. 
 
 [225.] Cement a cap, tightly (833) upon the mouth of a 
 clean dry retort (429) attach a stop- cock (827), and by an 
 air-pump (838, 858) or syringe (861) examine whether the 
 arrangement be air-tight. Exhaust the retort (858, 866), 
 attach it to a graduated transferring jar (742, 836), containing 
 common air, and allowing the air to enter (869), observe how 
 much is required to fill the retort. Exhaust the retort again 
 (858), and attaching it to a graduated transfer jar (742) con- 
 taining nitric oxide (experiment 219), allow so much to enter 
 (869) as is equal to two-thirds of its capacity ; then remove 
 and attach it to another graduated transfer jar (742), contain- 
 ing oxygen, open the stop-cock, and allow so much to enter 
 (869) as is equivalent to one-third in bulk of the contents of 
 the retort: then close the stop-cock. The two gases will 
 combine, and form a deep red gaseous product, which is 
 nitrous acid, but great condensation will at the same time occur. 
 To measure the extent to which this proceeds, allow the vessel 
 to cool, that the heat evolved may not tend to expand the 
 gases, and then attach it to a graduated transfer jar (742), 
 containing hydrogen or nitrogen, or some gas dissimilar to 
 those which have been used. Open the communication (869), 
 and observe how much gas will enter to fill the retort, at a 
 pressure equal to that of the atmosphere (767, 773). This 
 quantity will be nearly one-half the capacity of the vessel. 
 Then upon dipping the stop-cock into water, opening it, and 
 
Sect. XXIV.] PNEUMATIC MANIPULATION. 6J7 
 
 cooling the retort slightly (447), water will enter ; and dis- 
 solving the red gaseous nitrous acid, will shew by the quantity 
 of unabsorbed air or gas left, how much of the mixed contents 
 of the flask were soluble in that fluid. 
 
 [226.] Fix a cap and stop-cock upon a retort as before 
 (833), introduce a little litharge, and exhaust the air from the 
 vessel (858). Afterwards, fill it with muriatic acid gas (869) 
 from a transfer jar over mercury (742,, 782, 809) ; leave the 
 communication open, and heat the litharge (866) ; the latter" 
 will change colour and water will appear, and after some time 
 the gas will be observed to rise in the receiver beneath, to a 
 considerable degree, partly in consequence of the actual de- 
 composition of a portion of the gas by the elements of the oxide 
 of lead with the consequent formation of water, and partly of 
 the absorption of gas by the water so produced. 
 
 [227.] Fill a transfer jar (742) with water, over the trough, 
 by the mouth (755). Put some copper leaf (352, 1351) into 
 a capped retort (833, 866), attach a stop-cock to it, and 
 exhaust the air from within (869) ; screw^ the retort upon the 
 transfer jar, and then pass chlorine (759) which has been 
 stored and set aside in bottles (824), into the latter, in sufficient 
 quantities to fill the retort. Admit the chlorine to the metal 
 leaf (871) ; the latter will instantly inflame and become con- 
 verted into a metallic chloride. 
 
 [228.] Partly fill a gas-holder (811) with oxygen (748), or 
 in the absence of oxygen, with air. Fill a transfer jar or a 
 glass with the gas, at the trough on the top of the instrument 
 (813). Exhaust a flask (868), and fill it from the gas-holder 
 (869, 813). Fill a bladder with the gas from the holder 
 (813). Attach a flexible tube (841) and a blow-pipe jet 
 (219) to the stop-cock (815), and throw a stream of the gas 
 upon burning charcoal (251). If the gas be oxygen, and the 
 metals be silver, lead, iron, copper, or tin, they may easily be 
 burned in this manner with brilliant phenomena. In the same 
 way oxygen may be sent through the tube in the baryta 
 experiment 196; caoutchouc connecting pieces (449) being 
 used at the different junctions. 
 
 Now transfer the gas in the bladder (820) into the gas- 
 holder again (814), and removing the transfer jar above 
 
618 TUBE CHEMISTRY. [Sect. XXIV. 
 
 mentioned into a deep trough (753), transfer the gas in it 
 first into a bladder, and then back into the gas-holder (814). 
 
 [229.] Fill a gas-holder with coal or oil gas, see experi- 
 ment 190 (811), and then screwing on a jet (815), burn it 
 gradually, as in the applications of such gases to artificial 
 illumination. 
 
 [230.] Compress the oxygen contained in the air-holder 
 (813, 815), experiment 228, into a caoutchouc bottle (822), by 
 means of a syringe (858). Then use the latter with a spirit- 
 lamp as an oxygen blow-pipe (252) . 
 
 [231.] Send muriatic acid gas, or ammoniacal gas through a 
 series of Woulfe's bottles containing water (844), to form a 
 solution (856); use a safety tube (847), and connect the joints 
 where necessary by caoutchouc connecters (451). 
 
 [232.] Weigh a portion of air, of carbonic acid, and of 
 oxygen (887), attending to the points particularized (892, &c.) 
 
 [233.] Dry carbonic acid gas over muriate of lime (897) at 
 the mercurial trough. 
 
 XVI. Tube Chemistry. 
 
 [234.] Test a mineral water (506, 913) or a solution, as that 
 of experiment 74, in tubes (911), standing in corks (67) or 
 glasses (368), or in a rack (911). Use the dropping bottle 
 (402) and glass stirrers (912). 
 
 [235.] Dissolve a small silver coin in nitric acid in a tube 
 (915) ; examine a part of the solution for copper in another 
 tube (911) ; precipitate a part of the remaining solution in 
 a third tube, by a piece of copper wire, and wash (914) 
 and dry the silver precipitated. Then precipitate the re- 
 mainder of the solution in a fourth tube, by a solution of 
 common salt, and wash the precipitate well (912) in the tube 
 itself. 
 
 [236.] Heat a little pulverized sulphuret of antimony in 
 muriatic acid, using a bent tube of the form represented in 
 Sect. XVI., for the purpose (922) ; examine the gas evolved at 
 the mouth of the tube (954) by a taper flame, by acetate of lead 
 on a strip of paper, by smell, &c. (950), it will be found to 
 be sulphuretted hydrogen. Return the muriatic acid which 
 
Sect. XXIV.] TUBE CHEMISTRY. 619 
 
 will distil over (922), upon the sulphuret, once or twice in 
 succession. At last pour the solution ^'over the sulphuret 
 forward into the angle (922), and ultimately pour a little of it 
 into water, examine the effect, and observe whether a white 
 precipitate be produced. 
 
 [2B7-] Distil some oil of turpentine from a tube retort (924) 
 into a tube receiver or phial (925), or use the open bent tube 
 receiver, described (926), cooling the angular part by water 
 (927) or ice (454). 
 
 [238.] Distil a piece of wax in the tube figured (928), cool 
 the first receiving angle (927), and collect the liquid products 
 there ; at the same time immerse the open extremity of the tube 
 in water in a basin (928), and collect the gas evolved in tubes 
 (946). Examine it as to inflammability, &c. 
 
 [239-] Heat some copper or iron pyrites in a green glass 
 tube (935) to redness. Receive the sulphur which sublimes 
 into a plain or a bent tube (938). Heat a portion of the same 
 pyrites in an open tube (939), and observe by the smell and 
 appearance whether sulphur burns off or not. 
 
 [240.] Sublime a small quantity of crude naphthaline from 
 a plain tube, into a bent tube receiver (938). 
 
 [241.] Put a minute quantity of metallic arsenic into a plain 
 tube (935), closed at one end ; sublime it to different parts of 
 the tube by the heat of a spirit lamp (199), and observe the 
 metallic, crystalline, and other appearances of the film of sub- 
 limed metal ; continue this sublimation to and fro until the 
 arsenic has become oxidized, and then remark the crystalline 
 appearance, transparency, whiteness, and volatility of the new 
 substance formed. 
 
 [242.] Put a small piece of common paper, about half an 
 inch square, into a tube (910) closed at one end ; warm the part 
 inclosing the paper (918), keeping the other part cold (936), 
 and observe the dew which will appear on the cold part, and 
 which proves the presence of moisture in the paper. 
 
 [243.] Repeat experiment 39, in open inclined tubes (939), 
 for the purpose of observing the production of acid and alkali 
 (624, 626) at the upper apertures. 
 
 [244.] Put some per-oxide of iron into a tube (910), ex- 
 amine i^ and remark that it is not magnetic (1391) ', add a 
 
620 TUBE CHEMISTRY. [Sect. XXIV. 
 
 little naphthaline, and heat the oxide to redness in its (940) 
 vapour ; after a short time examine it again by the magnetic 
 needle (1393) > when it will be found highly magnetic. 
 
 [245.] Evaporate a solution containing silver, or any other 
 requiring the dissipation of excess of acid (592), in a bent 
 tube evaporator (943), then add water, and apply a slight de- 
 gree of heat to dissolve all that is soluble. 
 
 [246.] Make a little oxygen gas in a tube retort (924) from 
 chlorate of potassa, and receive it in tubes (910) immersed in a 
 basin of water (946). Examine the gas by a splinter of wood, 
 with a spark of fire at the extremity (766) ; ascertain how 
 small a bubble of oxygen may be thus tried with readiness and 
 certainty. Make a little hydrogen into tubes at the same 
 trough (946), and try in a similar manner with how small a 
 quantity its power of inflaming may be certainly ascertained. 
 Then mix two volumes of the hydrogen with one volume of 
 the oxygen (763), and remark with how minute a bubble the 
 explosive power of the mixture may be observed in a tube. 
 
 [247.] Make a little muriatic acid gas (736) in a tube retort 
 (924) , and receive it into the mercurial receiver described (950) ; 
 use it in small successive portions in the manner directed, 
 for the purpose of ascertaining the general properties of the 
 gas. 
 
 [248.] Make a little oxygen in the bottom of a tube (954), 
 and try its powers in the tube itself. Prepare a little sul- 
 phurous acid gas in the same manner (954), and observe its 
 powers of extinguishing flame, of reddening and then bleach- 
 ing litmus paper (617), its odour, &c., at the mouth of the 
 tube. Put a few pieces of zinc, and a little muriatic acid into 
 such a tube, and examine the gas as it passes off. It will 
 prove to be hydrogen. 
 
 Prepare euchlorine also in the bottoms of tubes, and repeat 
 all the experiments and observations with it, described (955). 
 
 [249.] Decompose oxalic acid by sulphuric acid in the bent 
 tube, described (958). Test the combustibility and other 
 properties of the gas evolved, upon successive portions at the 
 mouth of the tube (950). The gas is a mixture of carbonic 
 acid and carbonic oxide. 
 
 [250.] Generate muriatic acid gas in a phial, with a cork 
 
Sect. XXIV.] TUBE CHEMISTRY. 621 
 
 and tube (484), pass the gas over water in a tube, Woulfe's 
 apparatus (959) and examine the solution formed. It will 
 be found to be powerfully acid (624) , precipitating nitrate of 
 silver (912), dissolving carbonate of lime (915), and indeed 
 being a pure solution of muriatic acid. 
 
 [251.] Condense a gas into a liquid in the manner described 
 p. 411, &c. Experiment with sulphurous acid gas (970), or 
 cyanogen (962), as being those substances which incur the 
 least risk. 
 
 [252.] When upon any occasion a comparatively rare fluid 
 product, as chloride of phosphorus, for instance, has been 
 obtained in a pure state, confine it in a retaining tube (929) . 
 Observe its action upon water or upon litmus paper, in the 
 air (624), dispensing the small portions necessary from the 
 beak of the tube, then sealing up the remainder (929). Seal 
 up a specimen of the good chloride of phosphorus permanently 
 (974, 1189) for preservation. 
 
 [253.] Decompose a certain weight (52) of chlorate of pot- 
 assa in a green glass tube (703, 910), by a heat (935) sufficient 
 to drive off all that is readily volatile, and all the oxygen. 
 Then again weigh the tube and its contents (59), and ascer- 
 tain the loss of weight. This will be the weight of the oxygen 
 which existed in the salt that has thus been decomposed and 
 analyzed. The residue will be chloride of potassium. 
 
 [254.] Put tartrate of lead into a green glass tube (703, 
 910), contract the extremity, but do not close it (1184), heat 
 the tartrate gradually, so as to decompose it in succession, 
 beginning at the end nearest the aperture (710). In this 
 way dissipate all that is volatile. A black powder will remain, 
 which will inflame the moment it is poured out into the air, 
 and burn for some time. By sealing up the contracted aper- 
 ture of the tube whilst it is still hot (1190), the powder may 
 be preserved for any period of time without injury. 
 
 [255.] Heat a solution to 212 in a tube, by means of a 
 water-bath formed by another tube (259), shorter and wider 
 than the first. 
 
 [256.] Freeze a little water in a tube (910), by a piece of 
 ice and some salt (454). 
 
622 ELECTRICITY. [Sect. XXIV. 
 
 XVII. Electricity. 
 
 [257.] Excite a glass rod (1021) by silk, with a little amal- 
 gam spread upon it (981). Observe its effect when brought 
 near to the face, or its power over an electrometer (1012). 
 Excite a stick of wax or resin (1021), by friction with flannel 
 (1014), and remark its influence upon the electrometer (1022), 
 and other light bodies. 
 
 [258.] Experiment with a Bennet's electrometer (1012), 
 first diverging the leaves by brushing the cap lightly with 
 warm flannel, and then determining the kind of electricity 
 produced (1021). Diverge the leaves by the rapid evapora- 
 tion of water, and ascertain the kind of electricity developed. 
 Occasion divergence by contact of excited bodies (1013, 1020), 
 and also by approximation (1014, 1020) ; and in each case 
 determine the kind of electricity which has produced the 
 effect (1021). Insulate the substances whose electricity is to 
 be examined, upon stick-lac or resin (1077), or silk (1078). . 
 
 [259.] Excite an electrical machine (979), warming it care- 
 fully (980). Approach the knuckles of the hand to the 
 cylinder or plate, and observe the brushes and sparks of 
 electricity which dart about them and the machine (982) when 
 the latter is in good order. Put the prime conductor (983) 
 into its place, and then take sparks from it to the hand, or a 
 metallic ball. Warm a Leyden jar, charge and discharge 
 it (990). Remark for how long a period the charge can be 
 retained by the jar (991). 
 
 [260.] Pass the charge of the Leyden jar through the eudio- 
 meter wires (988) ; pass it also through thin wires so as to 
 ignite them. Detonate an explosive mixture of gases (997), 
 in the eudiometer tube over water (994), and also over mer- 
 cury. Insulate the jar when required on a plate of wax, glass, 
 or mica (1074) . 
 
 [261.] Make a small electrophorus (1007, 1011), excite it 
 (1009), observe the sparks given by it to the knuckle, charge 
 a warmed Leyden jar (990) by it (1010), and use the jar to 
 detonate a mixture of gases (997) in the eudiometer tube (999). 
 
 [262.] Charge a voltaic battery (1025), and bring it into an 
 
Sect. XXIV.] ELECTRICITY. 623 
 
 efficient state (1026) ; try the discharge between its poles by 
 charcoal points (1030), and observe the intensity of the light 
 produced. Ignite some fine wires by discharging the electri- 
 city through them (1073). Immerse the poles in water con- 
 tained in a glass (1037 9 1046), and remark the decomposition 
 which takes place. Decompose saline solutions contained in 
 tubes (1046), using platina foil to extend the surface of con- 
 tact (1038). Collect the gases (1049) evolved during the 
 decomposition of water, and examine them (950) as to their 
 qualities and nature ; that at the positive pole will be oxygen, 
 that at the negative pole hydrogen (1050). Remark the 
 double quantity of hydrogen produced in the experiment as 
 compared to the oxygen evolved. 
 
 [263.] Observe the magnetic properties of a wire (1040) 
 connecting the poles of the battery just referred to (1035). 
 Place a magnetic needle under and over the wire, and remark 
 the influence of the wire upon it (1079). Dip a part of the 
 connecting wire into iron filings, they will be attracted in rings, 
 as it were, surrounding every part of the wire, and not in a 
 particular part only, as is the case with a common magnet. 
 Twist the wire which connects the poles into a helix, then 
 place a thick needle or a small bar of steel in this helix for a mo- 
 ment, break the voltaic communication (1040), remove the steel 
 bar, and observe how suddenly it has been rendered a magnet. 
 
 [264.] Take a piece of zinc and a piece of silver, and observe 
 their peculiar electric effect upon the tongue (1066) ; their 
 effect also upon frogs, fish, worms, or other small animals. 
 Remark the power of the two metals, when, being in contact, 
 they are immersed in a weak acid (1062). Ascertain by the 
 tongue the power of a fragment of metal, and another of glass 
 or stone (1066), with respect to the conduction of electricity. 
 
 [265.] Make a little voltaic battery of halfpence or discs of 
 copper, with pieces of zinc (1059), and flannel moistened in 
 dilute acid (1026). Discharge it through charcoal (1030); 
 try the conducting power of different specimens of charcoal j 
 heat fine platina wire red hot (1073), decompose water and 
 saline solutions by it (10'49), and show the magnetic influence 
 which a wire connecting its extremities (1040) has over a mag- 
 netic needle (1079). 
 
624 LUTES CEMENTS. [Sect, XXIV. 
 
 [266.] Precipitate a portion of copper from a solution of 
 the sulphate in a platina crucible (1065, 523) , by Dr. Wollas- 
 ton's method ; wash the copper precipitated on the platina, and 
 afterwards dissolve it from the vessel by a little pure nitric acid 
 
 XVIII. Lutes. Cements. 
 
 [267.] Lute a glass retort (489, 1084) with a coating of 
 uniform thickness (1087), attending carefully to the drying 
 (1088), and bringing it ultimately into a state fit for use. 
 
 [268.] Make a comparatively moist lute (1090), some straw 
 chaff, or other similar substance (1092) having been mixed 
 with it (1093). Coat a phial with it uniformly (1087), that 
 when dry it may be ready for the preparation of pyrophorus. 
 
 [269.] Coat an earthenware (699) or a glass tube (703) 
 with stiff lute (1084), and surround it with a band of canvass 
 (1094). 
 
 [270.] Fix one crucible firmly in another (648) by lute, then 
 fix the double crucible upon a third as a stand (673, 1101.) 
 
 [271.] Cement a bent tube to the neck of a Florence flask 
 (373, 484), by Parker's cement (1107), or plaster of Paris 
 (1108). A flask of this kind is competent to the preparation 
 of carbonic oxide over a crucible furnace fire (158). A mass 
 of the cement should in the first place be put round the tube 
 and left to harden ; this being cut into a conical form, and 
 ground slightly, will, with very little management, close the 
 mouth of a Florence flask accurately, and thus form a useful 
 gas bottle (746). 
 
 [272.] Make a tight joint between a retort and a receiver 
 (475) with bladder and string (1116), or with a fat lute 
 (1106), or with paste and paper (1117). 
 
 [273.] Connect apertures in tubular arrangements by means 
 of caoutchouc connecters (448, 1122). 
 
 [274.] Examine the bottles containing solutions of muriatic 
 acid and ammonia, to ascertain whether the stoppers are tight 
 or leaky (1130). Examine the gas holder, exp. 228, as to 
 the existence of leaks about the body (810) or the pipes con- 
 nected with it (1130). 
 
Sect. XXIV.] BLOWING AND CUTTING OF GLASS. 625 
 
 XIX. Blowing and cutting of Glass. 
 
 [275.] Bend a piece of glass tube into a syphon (1154). 
 
 [276.] Make some tubes (1165) closed at one end (910) ; 
 expand the open extremity of one or two into a flanch (1147) \ 
 contract the apertures of others by scissors, so as to form a 
 neck (1163) ; bend some of them into tube retorts (924, 1175). 
 
 [277.] Close one of the open extremities of a short piece of 
 tube (1173). 
 
 [278.] Soften the middle of a piece of tube (1134), and 
 thicken it into a ring (1200), then draw it out into a contracted 
 neck (1175). 
 
 [279-] Make a tube funnel (1176, 924) and a tube syringe 
 (547, 1181.) 
 
 [280,] Blow some glass into frost (1194). Blow a Jbulb at 
 the end of a piece of tube (1194, 1196). Expand the angle 
 of a tube retort (924, 1197) in the particular direction before 
 explained (956), that it may answer the purpose of a tem- 
 porary retort and receiver for gases. Make a separator (558, 
 1197). Make a few candle crackers (1199). 
 
 [281.] Join two pieces of tube together (1200). Seal a 
 platina wire into a tube (1201) for the purposes of electrical 
 decomposition (1046). Make a small detonating eudiometer 
 (994), and then graduate it (127). 
 
 [282.] Use quill tubes (910, 1207) with a common spirit- 
 lamp (199) and the mouth blow-pipe (218). With these 
 make some closed tubes (910, 1165) ; some small tube retorts 
 (1175), expanding the bulb or body of a few (1194), so as 
 to make them more capacious ; some tube receivers (929) and 
 other useful apparatus ; performing the same operations in the 
 small way, which have been directed upon a larger scale. 
 
 [283.] Seal up some water hermetically in a tube (1188, 
 1184), not leaving more than half an inch between the surface 
 of the water and the extremity last closed. In the same man- 
 ner seal up some ether in a tube hermetically (1189), leaving 
 about li inches between the fluid and the extremity to be 
 sealed, and make the glass thick and strong (1185). Practise 
 the same operation by sealing up some fragments of sulphur in 
 
 2 s 
 
626 CLEANLINESS AND CLEANSING. [Sect. XXIV. 
 
 a tube (1184). The operation may be considered as well 
 done when the end is made smooth and strong, without melt- 
 ing the included sulphur at a distance of li or 11 inches. 
 
 [284.] Seal up some water hermetically in a tube exhausted 
 of air (1193). 
 
 [285.] Cut a piece of tube about twelve inches long into 
 two (1152) ; make each of these into two tubes closed at one 
 end, one about 4 and the other 2 inches long (1166). Take 
 a piece of tube with a fractured and irregular termination, and 
 cut it off straight and level (1152) within half an inch of the 
 extremity, or else make the termination nearly straight by 
 rasping off (1227) the irregularities. 
 
 [286.] Before dismissing broken apparatus to the waste 
 glass box, collect them on a tray, and then cut up old retorts, 
 flasks, or glasses, into dishes, by iron rings (1212) or a hot 
 iron rod (1214) ; cut off the tops of fractured Florence flasks 
 (1212), and make the lower part into basins, and convert old 
 jars or bottles into shorter jars (1222) by the hot iron (1214). 
 
 [287.] Take every opportunity of becoming expert in loos- 
 ening (1255) and removing glass stoppers which have become 
 fixed in the bottles (741) ; in cutting pieces of crown glass 
 into useful forms (1227, &c.) by means of a file (1224), and 
 in crushing the edges of fragments (1227, &c.), so as to bring 
 them into serviceable shape. 
 
 XX. Cleanliness and Cleansing. 
 
 [288.] The practice corresponding to this division of the 
 volume will be abundantly dictated by the wants which will 
 occur the instant the student commences his progress in expe- 
 rimental chemistry. It will be well, however, that he should 
 try to dry the insides of a retort, a flask, and a bottle, which 
 have been washed clean, and observe how effectually and 
 readily he may do it by the methods described (1251,102). 
 He should grease or wax a stopper (433, 741) with the pre- 
 cautions given, and minutely observe the degree of resistance 
 and kind of feeling occasioned when it is properly lubricated 
 (433). 
 
 [289.] A portion of foul mercury should be rendered pure 
 and clean by Dr. Priestley's method (1282). Another por- 
 
Sect. XXIV.] MISCELLANEA. 627 
 
 tion bv nitrate of mercury (1283), and some that is dusty and 
 foul should be cleaned by sugar and agitation (1273, &c.) 
 
 XXII. Uses of the Scale of Equivalents, fyc. 
 
 [290.] Ascertain by the scale (1305) the quantity of nitric 
 acid required to dissolve 473 grains of carbonate of lime 
 (1319), and the quantity of crystallized carbonate of potassa 
 (1320) required to precipitate the resulting nitrate. 
 
 [291.] Tell by the scale how much sulphuric acid is con- 
 tained in the sulphate of baryta of experiment 102. 
 
 [292.] Ascertain how much muriatic acid and baryta 
 (1318) are indicated in the chloride of silver and sulphate of 
 baryta of experiment 103. 
 
 [293.] Observe by the scale how much metallic copper and 
 oxide of copper (1321) may be expected in experiment 108. 
 
 [294.] Ascertain the composition of 250 grains of crystal- 
 lized sulphate of magnesia as to its earth, acid, and water 
 (1323) ; and also as to the sulphur, oxygen, and hydrogen, in 
 the acid and water of the salt (1321). 
 
 [295.] Ascertain by the scale (1321) the points expressed 
 p. 551, relative to 300 grains of sulphate of copper. 
 
 [296.] What quantities of lime, baryta, strontia, magnesia, 
 potassa, and soda, will neutralize 320 grains of dry sulphuric 
 acid (1315, 1318), and what quantities of their carbonates 
 will produce the same effect ? 
 
 [297.] Ascertain all these points by calculation from a table 
 of equivalents (1327), and observe if the results agree with 
 the conclusions arrived at by means of the scale (1310). 
 
 XXIII. Miscellanea. 
 
 [298.] Make some hydrogen from a few pieces of zinc and 
 a little dilute sulphuric acid, in an oiled paper vessel (1335) ; 
 conduct it through paper tubes (1337) into a trough made of 
 a soup plate or a basin (732), and receive it into oiled paper 
 tubes (1337, 1339), which will answer the purpose of jars (946). 
 In these test its inflammability, and observe its other qualities, 
 and remark with how simple an apparatus these and many 
 other sucfl experiments can be made. Attach the edges of 
 
 2 S 2 
 
628 MISCELLANEA. [Sect. XXIV. 
 
 oiled paper vessels which are to be air and water tight for a 
 time, by a little soft cement (1342, 1125). 
 
 [299.] Heat the interior of a steam-bath (271), by steam 
 generated in a kettle (272), and conducted from its spout by 
 oiled paper tubes (1338). Even the bath itself may be made 
 of a few pieces of wire or stick, and oiled or wax paper. 
 
 [300.] Test a weak mixed solution of sulphate of copper 
 and muriate of lime in paper vessels (1335), for all the proxi- 
 mate elements. 
 
 [301.] Pour a few drops of a weak solution of phosphate 
 of potassa or soda upon one part of a sheet of white paper, 
 and a few drops of a weak solution of arsenite of potassa upon 
 another part of the same paper (1335). Draw a piece of 
 nitrate of silver through the two portions, pressing on the 
 paper at the same time, and observe the differences in charac- 
 ter between the two precipitates. 
 
 [302.] Boil half a pint of water in a paper vessel (1335). 
 
 [303.] Make (563) and crystallize a solution of alum (564) 
 in oiled or waxed paper vessels (1335) ; separate the more 
 perfect crystals, and preserve them in paper tubes (1341). 
 
 [304.] Heat a little white arsenic on platina foil (1353) by 
 a small spirit-lamp flame (199, 205). Then heat a portion 
 on the foil, but with a large flame (205), and incline the foil 
 that the hydrogen of the flame may mix with the vapours of 
 arsenic; or heat the arsenic on a hot coal. Observe the differ- 
 ence in the odour occasioned in these two cases : the odour 
 when developed is dependent upon the reduction of part of 
 the white arsenic to the metallic state. 
 
 [305.] Draw out a small capillary tube (1176), examine its 
 bore by a small quantity of mercury ; graduate it (1370) and 
 make it into an air-gauge (1369). 
 
 [306.] Retain a platina wire in a state of ignition in the 
 vapour of ether, over a small portion of that fluid in a glass. 
 
 [307.] Sublime (935) a little cinnabar in a tube (910) not 
 more than 1J inches in length (1333). 
 
 -[308.] Sublime some naphthaline from one tube (938) into 
 a long open tube fixed to the smaller by a perforated cork 
 (1331, 465). 
 
 [309-] Put a fragment of camphor at the bottom of a tube 
 
Sect. XXIV.] MISCELLANEA. 629 
 
 two feet long, observe its odour by means of another tube 
 (1365). 
 
 [310.] Try the phosphorescence of fluor spar, and different 
 kinds of carbonate of lime (1383). 
 
 [311.] Mix equal volumes of hydrogen and chlorine over 
 water ; transfer portions of the mixture into glass tubes 
 (910, 946), using paper funnels (1342), if there be occasion 
 for such convenience ; then expose these mixtures to sun light 
 (6, 1387), and observe the explosion which immediately takes 
 place. 
 
 [312.] Observe the effect of solar light and day light upon 
 nitrate of silver and chloride of silver (6, 1388) spread upon 
 paper. Make Mr. Wedgwood's experiment, using magic 
 lantern glasses for the purpose. 
 
 [313.] Make a magnet (1399). Make a magnetic needle 
 (1399), suspending it in any convenient way (1398). Try 
 a piece of Elba iron ore by this needle (1391), reiterating the 
 approximations, or adopting Hauy's method (1394). 
 
 [314.] Write legibly on a glass tube with a scratching dia- 
 mond (974), the tube being from one half to one quarter of an 
 inch in diameter. 
 
 [315.] Cut a crucible, or stopper, with its cover and a sup- 
 port, out of soft Windsor brick (1354), and make some box- 
 wood charcoal in it (1033). 
 
 [316.] Evaporate a mineral water to one-eighth its original 
 bulk (594), and then test it on glass plates (1348). Crys- 
 tallize a solution of nitre on a glass plate (565, 1348) ; also 
 a solution of salt, and examine the forms of the crystals 
 (580). 
 
 [317.] Freeze a little water in a cup of tin foil (1349), by 
 a mixture of ice and salt. 
 
 [318.] Etch on glass by fluoric acid (1366), using a leaden 
 dish (1367, 1350), for the mixture of acid and fluor spar. 
 
 [319.] Make a single electrical circuit (1352, 1062) ; ob- 
 serve its effect in deflecting and otherwise influencing the 
 magnetic needle. 
 
 [320.] Precipitate a solution of acetate of lead by zinc foil 
 (1352) ; test the solution for lead in paper vessels (1335), 
 that the completion of the precipitation may be ascertained. 
 
630 MISCELLANEA. [Sect. XXIV. 
 
 Burn filaments of zinc foil (1352) in the flame of a 
 ]amp or candle. 
 
 [322.] Fuse a little piece of lead on platina foil (1353), and 
 remark the instant liquefaction of the foil in consequence of 
 the formation of an alloy (662). Even sulphuret of lead will, 
 on trial, be found to have a similar action. Heat a little 
 chloride of silver, or a little oxide of iron on the foil to white- 
 ness ; no harm will result (1353). 
 
 [323.] Distinguish wires of silver and platina by their power 
 of conducting heat (1358) . 
 
 [324.] Sublime a little calomel in a tube (935) enveloping 
 the tube about half way from the bottom (1351) so as to pre- 
 serve the heat (716), and prevent condensation on that space; 
 ultimately crack the end of the tube in mercury (1356). 
 
 [325.] Place a board within twq or three inches of a hot 
 furnace; protect one half of it by a plate of tin (1359), and 
 observe the difference between that and the other half. 
 
INDEX. 
 
 Acetic acid, strength of, ascertained, 276 
 Acid for alkalimetry, 273, 275 
 
 voltaic trough, 439 
 Acidimitery, 279 
 Acids, their uses as solvents, 185 
 
 strengths ascertained, 277 
 tested for, 269 
 filters for, 241 
 Adjustment of liquids, 42 
 Aerometer, Hall's, 375 
 Aikirfs furnace, 94 
 
 Air exhausted from vessels, 365, 367 
 weighed, 375 
 hot, a heating agent, 128 
 
 procured, 128 
 chamber, warm, 262 
 furnace, 93 
 guages, 494, 570 
 holder, 344 
 jars, 312 
 
 tuhe, 403 
 cleansed, 523 
 pump, 363 
 
 examined, 364 
 preserved, 23, 366 
 exhaustion by, 364, 367 
 evaporation under, 255 
 thermometer, 140 
 Alcohol, its use as a solvent, 184 
 fuel, 101, 105 
 its flame, 101 
 decomposed in tubes, 305 
 bath, 128 
 
 thermometer, 135, 137 
 Alembic, 221 
 Alkalies tested for, 269 
 
 strength ascertained, 273, 276 
 Alkalimeter acid, 273, 274 
 
 tube, 272 
 
 Alkalimetry, 272, 276, 603 
 Alkaline solvents, 180 
 
 earths decomposed in tubes, 
 
 307. 608 
 
 Alloys made, 292 
 Almond paste, 472 
 
 Amalgam applied to silk, 421 
 Ammoniacal gas collected in bottles, 350 
 prepared and experimented 
 
 with, 612 
 
 Analysis, pulverisation for, 156 
 Annealing of glass, 483 
 Apertures closed temporarily, 411 
 Apparatus room, its use, 23 
 Aqueous solutions crystallized, 247 
 Argand's lamp, 105 
 
 double wicked, 106 
 
 Bags for gas, 348 
 Balance, 25, 582 
 
 Blacks delicate, 63 
 Ritchie's delicate, 64 
 substitute for, 63 
 varieties of, 26, 47 
 its theory, 29 
 
 indications, 30, 50 
 examination, 28, 31 
 setting. 31 
 preservation, 23 
 Barometer observed, 327 
 Barometric pressure, 373 
 Basins, earthenware, 167, 318 
 
 examined, 167 
 glass, 168,510 
 evaporating, 167 
 metallic, 168 
 sublimations in, 222 
 in the sand-bath, 173 
 cleansed, 523 
 covered with paper, 252 
 Baths, alcoholic, 128 
 mercurial, 126 
 metal. 127 
 sand, 91, 123, 173 
 solution, 126 
 steam, 129 
 water, 123 
 Battery, electric, 429 
 
 voltaic, 439 (see Voltaic pile) 
 Bellows, 95, 96 
 Bending of glass, 476, 482, 485 
 
632 
 
 INDEX. 
 
 Bennefs electrometer, 433 
 Black lead crucibles, 278 
 
 flux, 293 
 
 Black's balance, 63 
 Bladder for joints, 471 
 Bladders for gases, 348 
 Blast furnace, 94, 287 
 
 its operation, 289 
 Blocks, adjusting, 19 
 Blowing of glass, 476, 482, 501, 625 
 Blow-pipe, 107 
 
 use of, 110, 587 
 
 its powers, 112, 114, 117 
 
 temperature of flame, 114 
 
 action of mouth, 110, 112 
 
 its theory, 115 
 
 jet, 108 
 
 lamp, 112 
 
 supports, 116 
 
 charcoal, 117 
 Black's, 108 
 Clarke's, 123 
 common, 108 
 glass, 109 
 Gurney's, 123 
 Leeson's, 122 
 Marcet's, 121 
 oxygen, 121, 347 
 oxy-hydrogen, 122 
 temporary, 109, 120, 508 
 Wollaston's, 108 
 table, 19,118,477 
 its place, 19 
 how used, 119 
 Blue pots, 278 
 
 Boiling under pressure in tubes, 57, 389 
 Book Laboratory note, 23, 539 
 Boracic acid on turmeric paper, 271 
 Borax, 294 
 Bottles for gases, 350 
 
 specific gravity, 53 
 their stoppers loosened, 526 
 caoutchouc, 349 
 cleansed, 525, 530 
 dried, 524, 525 
 Box-wood charcoal, 442 
 Breaking of bodies, 148, 150 
 Brick, soft, or Windsor, 563 
 Bricks, their uses, 20, 563 
 Broken glass cut up, 510, 512 
 Brunswick black varnish, 519 
 Bulbs of glass blown, 501 
 
 filled with liquid, 56 
 
 for specific gravity, 62, 503 
 
 Camp hor pulverised, 155 
 Canvas, its use over lute, 296, 466 
 Caoutchouc connectors, 202, 357, 472 
 gas bottles, 349 
 sheet, 202,353,357,476 
 
 Cap cement, 473 
 Capillary tubes, 493 
 
 graduated, 570 
 Caps for retorts, 354 
 
 attached, 354, 370, 616 
 their place supplied, 355 
 Capsules, metallic, 103, 168 
 
 sublimations in, 222 
 Carbonate of lime precipitated, 229 
 Carbonic acid gas prepared and experi- 
 mented with, 61 
 oxide prepared and experimented 
 
 with, 6 13 
 Cards, use of, 156 
 Cavendish's gas transferor, 335 
 Cement, iron, 471 
 
 Parker's, 469 
 Roman, 469 
 soft, 254, 473 
 yellow wax, 473 
 for caps, 473 
 powdered gum, 475 
 Cements, 461,473, 624 
 Chalk-stone, drying, 264 
 Charcoal, 99, 117 
 
 pulverized, 155 
 
 its reducing powers, 295 
 
 for blow-pipes, 117 
 
 voltaic experiments, 442 
 crucibles, 280 
 
 Charge for voltaic troughs, 439 
 Charging of a battery, 440 
 flasks, 178 
 retorts, 196 
 Chemical action, deceptive appearance of, 
 
 166 
 
 equivalent, 547 
 Chemistry, tube, 386, 618 
 Chloride of silver precipitated, 228 
 Chlorine gas collected, 310, 613 
 
 prepared and experimented with, 
 
 613 
 
 preserved, 350 
 solution of, made, 362J 
 Cleanliness, 517, 626 
 
 regulations for, 518, 530, 539 
 Cleansing, 517, 626 
 flux, 531 
 wires, 520 
 of air jars, 523 
 bottles, 525, 529 
 copper, 530 
 crucibles, platina, 530 
 evaporating basins, 523 
 flasks, 523 
 glasses, 521 
 mercurial trough, 531 
 mercury, 532 
 mortars, 531 
 retorts, 532 
 
INDEX. 
 
 633 
 
 Cleansing tubes, 522 
 
 Closing of tubes, 489, 495, 499 
 
 Coal, 98 
 
 Coated vessels, 462, 465 
 
 Coating of retorts, flasks, and crucibles, 
 
 462 
 
 how performed, 462, 466 
 to sustain a high temperature, 
 
 462 
 
 to prevent passage of air, 468 
 dried, 464 
 repaired, 464 
 strengthened, 465 
 supported iu the fire, 219, 467 
 contraction of, in the fire, 466, 
 
 467 
 Cocks, gas, 351 
 
 examined, 352 
 tightness of, 356 
 Coke, 98 
 
 Staffordshire, 98 
 Collars, 353 
 Collection of gas, 316 
 Coloured tests, 266, 602 
 fluids, 266 
 papers, 267 
 precautions, 271 
 Combination of bodies influenced, 304 
 
 effected in tubes, 306 
 Comminution, 144, 588 
 Compound bodies, their definite nature, 
 
 545 
 
 Compression of gases, 369, 570 
 Condensation, in distillation, 192, 201, 
 
 205 
 
 on retort neck, 209 
 of gases in tubes,41 ], 415, 
 
 570 
 
 precautions, 413 
 of cyanogen, 411 
 muriatic acid, 416 
 sulphurous acid, 415 
 Conduction, of electricity, indications. 
 456 
 
 Rousseau's 
 
 test, 458 
 heat applied, 564 
 Con e, heating, 174, 176, 198 
 Connecting pieces, 356 
 Connection of tubes, 298 
 
 pneumatic apparatus, 351 
 Connectors, 35 G 
 
 of caoutchouc, 202. 203, 357, 
 
 472 
 
 Contact, voltaic, 445 
 Cooling mixtures made and used, 205 
 Copper, cleansed, 530 
 divided, 162 
 
 foil cases to tubes, 303, 562 
 leaf, 562 
 
 Copper plate, its uses, 562 
 
 pneumatic trough, 309 
 precipitated, 230 
 wire, uses of, 560 
 Cork handles to tubes, 389, 492 
 Corks, uses of, 21, 42, 209, 389, 555 
 Cornish crucibles, 278, 279 
 Correction of gas volume, 371 
 
 for moisture, 376 
 pressure, 373 
 temperature, 372 
 Cotton syphon, 244 
 Counterpoising, 28, 39, 583 
 Course of inductive and instructive prac- 
 tices, 582 
 Covering of vessels, 243, 260 
 
 with paper, 249 
 Covers of glass, 243, 513 
 of paper, 249 
 to crucibles, 288 
 filters, 239 
 glasses, 243 
 Crack in glass directed, 511, 515 
 
 stopped, 422 
 Cream of tartar, 293 
 Crown glass divided, 514 
 Crucible covers, 285, 288 
 furnace, 84, 286 
 made, 84 
 arranged, 86 
 used, 286 
 jacket, 285 
 operations, 277, 291, 604 
 
 precautions, 290 
 shelter, 290 
 stoppers, 280 
 supports, 284, 287 
 Crucibles, 84, 277 
 
 appropriated, 283 
 heated, 2 84 
 
 by furnaces, 286 
 by lamps, 103, 284 
 
 and blow- 
 pipe, 114,284 
 and jacket, 
 
 285 
 
 sublimation in, 222 
 black lead, 278 
 cleansed, 530 
 coated, 462 
 Cornish, 278, 279 
 charcoal, 280 
 double, 279 
 earthen, 277, 284 
 English, 277 
 gold, 282 
 Hessian, 278, 279 
 iron, 282 
 lined, 284 
 platina, 281, 284 
 
634 
 
 INDEX. 
 
 Crucibles, platina, cleansed, 530 
 silver, 281 
 temporary, 283 
 Wedgwood's, 278 
 Crude tartar, 293 
 Crystallization, 246, 600 
 
 indications of, 252 
 influenced, 251 
 how effected, 247 
 its usefulness, 246 
 of metals, 253 
 in water, 247 
 
 alcohol, 250 
 by cooling, 248, 249 
 evaporation, 248 
 fusion, 247, 253 
 sublimation, 254 
 Crystallizing point, 247 
 Crystals, formed, 248 
 dissected, 252 
 dried, 265 
 examined. 252, 254 
 large, 249 
 
 many converted into one, 250 
 appearances influenced, 251 
 Cubic inch bottles, 69 
 
 measures, 69 
 
 Cupboards, their arrangememt, 17 
 Cutting diamond, 509 
 
 of glass rod or tube, 484, 509 
 crown glass, 509, 514 
 glass by diamond, 509, 514 
 hot iron, 517, 514 
 rings, 510 
 old glass, 510, 513 
 Cyanogen condensed, 411 
 
 Danielfs dissection of crystals, 252 
 
 pyrometer, 143 
 Decantation, 241, 598 
 
 washing by, 243 
 
 of gas from jars, 320 
 
 from tubes, 322 
 Decoction, 189 
 Decomposition, voltaic, 448 {see Voltaic 
 
 decomposition) 
 in tubes, 305 
 
 influenced, 304 
 
 Decrepitation prevented, 157, 292 
 Definite nature of compound bodies, 545 
 Deflagrating jars, 312 
 Degrees of the thermometer, 1 33 
 Deoxygenation of oxides, 295, 306 
 
 metallic solutions, 188 
 Desiccating tubes for gases, 378 
 Desiccation, 258, 601 
 
 in close vessels, 256 
 tubes, 400 
 of crystals, 265 
 gases, 378 
 
 Desiccation of organic matter, 261 
 
 powders, 261 
 
 Desiccators, 255, 258, 378 
 Detonation of gases, proportions to be 
 used, 427 
 
 by electric spark, 422 
 precautions, 
 
 423, 426 
 electrophorus 
 spark, 432 
 Leyden jar, 
 
 425 
 Diamond, cutting, 509 
 
 scratching, 70, 418 
 pulverized, 157 
 Differential thermometer, 142 
 Digestion, 170, 590 
 
 in tubes, 389 
 
 Discharger, electrical, 425, 430 
 Discoloration of glass removed, 479 
 Dishes for gas jars, 314 
 Dissection of crystals, 252 
 Dissolution, 164 
 Distillation, 191, 392, 593 
 ordinary, 192 
 at high temperatures, 218 
 products of, 200 
 in close vessels, 209, 397 
 dry vessels, 214 
 flasks, 217 
 retorts, 198, 217 
 iron retorts, 220 
 tubes, 389, 392 
 vacuo, 397 
 facilitated, 199, 218 
 of nitric acid, 213 
 
 sulphurous acid, 202, 207 
 wine, 209 
 
 Distilled water important, 21, 179 
 Division of glass, 509 
 
 matter, 144, 588 
 
 its use, 144, 170 
 metals, 161 
 silica, 161 
 Drawers, their appropriation, 21 
 
 cleanliness, 519 
 Dropping bottle, 182, 240, 387 
 Drying chamber, 262 
 stone, 264 
 of flasks, bottles, and retorts, 
 
 524 
 
 gases, 378 
 Dry ness of powders examined, 262 
 
 Earthenware crucibles, 277, 284 
 retorts, 219 
 tubes, 296 
 Earths, alkaline, soluble in sugar, 186 
 decomposed in tubes, 
 307, 608 
 
INDEX. 
 
 635 
 
 Ebullition irregular prevented, 199 
 
 under pressure in tubes, 389 
 Edges of glass removed, 484, 516 
 Effervescence guarded against, 179 
 Egg and lime lute, 470 
 Electric discharge, intensity exalted, 423 
 passed through wires, 
 
 425 
 
 spark, its uses, 422 
 Electrical battery, 429 
 
 communications, 424, 429 
 discharger, 425, 430 
 insulation, 459 
 jar, 424 
 
 examined, 424 
 
 charged by electrophorus, 
 
 432 
 
 substitute for, 430 
 machine excited, 420 
 
 action examined, 421 
 preserved, 23, 422 
 warmed, 420 
 Electricity, 419 
 
 practices in, 621 
 voltaic, 439 
 
 conducting power for, exa- 
 mined, 456 
 Electro-magnetic arrangements, 447, 454, 
 
 461 
 Electrometer, nature of its divergencies, 
 
 434, 437 
 
 affected by contact of ex- 
 cited bodies, 
 439 
 vicinity of do. 
 
 435 
 its indications interpreted, 
 
 437 
 electricity examined by it, 
 
 437 ' 
 
 Bennet's, 433 
 Henly's, how used, 429 
 Singer's, 434 
 Electrophorus, made, 431 
 excited, 432 
 its powers, 433 
 English crucibles, 277 
 Engraving on glass, 568 
 Equivalent proportions, 547 
 Equivalents, their nature, 546 
 chemical, 547 
 synoptic scale of, 544 
 table of, 554 
 Escape of gases from mercury, 333, 
 
 535 
 
 Euchlorine prepared in tube retort, 404 
 Eudiometer* detonation of gases in, 422, 
 
 425 
 
 management of, 426, 428 
 wires, 423 
 
 Eudiometer, wires fixed in, 507 
 
 Ure's, 428 
 Eupyrion, 22 
 Evaporating basins, 167 
 
 cleansed, 523 
 
 Evaporation, 248, 255, 402, 587, 610 
 minute, 262 
 at common temperatures, 
 
 248, 255 
 by currents, 258, 262, 402 
 
 heat, 258, 402 
 for analysis, 258 
 in basins, 258 
 
 close vessels, 255, 257, 
 
 260 
 
 open vessels, 258 
 platina crucible, 260 
 tubes, 402 
 the air pump, 255 
 
 hot air chamber, 262 
 of destructible matter, 261 
 to dryness, 258, 402 
 Exhausted tubes sealed, 499 
 
 vessels, 366 
 
 Exhaustion of air, 365, 367 
 Expansion of gas by heat, 372 
 
 moisture, 376 
 
 Experiments, a course of, 582 
 Explosion in tubes guarded against, 404 
 
 Fahrenheit's scale, 134 
 Face, masks for the, 573 
 Fat lute, 469 
 Feathers, uses of, 238 
 Feeding tube for retort, 216 
 Ferro-prussiate of iron precipitated, 232 
 Files, marking on glass with, 70 
 metals divided by, 162 
 to cut glass, 386 
 Films of mercury, 534 
 
 their influence, 333, 
 
 535 
 Filtering paper, 232 
 
 stands, 16, 231 
 
 Filters, their substance, 230, 232 
 charged. 236 
 dried, 263 
 folded, 233 
 large, 241 
 made, 233 
 moistened, 238 
 plain, 233, 236 
 small, 239 
 strengthened, 236 
 supported, 233, 236 
 for acids, 241 
 Fillration, 230, 236, 598 
 
 precautions, 238, 239 
 hot, 239 
 washing by, 237 
 
636 
 
 INDEX. 
 
 Flame, its heat, 101, 102, 114, 480 
 Flasks, their use in solution, 172 
 
 distillation, 196, 217 
 powders introduced into, 178 
 their place supplied by tubes. 
 
 388 
 used as receivers, 201, 210 
 
 retorts, 217 
 boiling in, 173, 176 
 evaporation in, 260 
 effervescence in, 179 
 cleansed, 523 
 closed, 525 
 coated, 462 
 dried within, 524 
 heated, 174, 176 
 supported, 175 
 flint glass, 168, 224 
 Florence, 169, 221, 224, 260, 523 
 Flint-glass (flux), 294 
 Flints, pulverized, 155 
 Florence flasks, 169, 224, 260, 367, 525 
 Flues, their arrangement, 13, 177 
 connecting, 88, 177 
 temporary, 88 
 Fluids, decanted, 241 
 
 heated in tubes, 56 
 introduced into bulbs, 56 
 separated, 244, 599 
 mixed in tubes, 387 
 Flux, alkaline, 293 
 argol, 293 
 black, 293 
 borax, 294 
 cleansing, 530 
 crude tartar, 293 
 cream of tartar, 293 
 flint glass, 294 
 green glass, 294 
 nitre, 294 
 sal enixum, 294 
 white, 293 
 Fluxes, 292 
 
 applied, 295 
 
 Foil, copper casing to tubes, 303, 562 
 platina, 103, 563 
 tin, 561 
 
 Frigorific mixtures made and used, 205 
 Fuel, 20, 86, 98 
 
 alcohol, 101, 103 
 charcoal, 99 
 coal, 98 
 coke, 98 
 gas, 107 
 oil, 105 
 Funnels, 181, 231 
 
 of tube, 392, 495 
 
 paper, 559 
 
 for filtration, 231,233 
 gas, 3 14, 322 
 
 Funnels, for pouring, 197 
 powders, 181 
 
 Furnace, ast, 94, 95, 287 
 Aikin's, 94 
 powerful, 95, 287 
 crucible, 84, 175, 219, 286, 299 
 powers of, 88 
 increased, 86 
 flue, 87 
 fuel, 86 
 grate, 85 
 Knight's, 93 
 portable, 84 
 table, 15, 89, 220, 286 
 
 its construction, 89 
 tube, 300 
 wind, 88, 93 
 rings, 92 
 stoppers, 86 
 
 tube operations, 296, 606 
 Furnaces, 15, 83, 286 
 
 their situations, 100, 176 
 protections from, 100, 176 
 Fusible lutes, 468 
 Fusion, of alloys, 292 
 
 metals, 292, 604 
 crystallization by, 253 
 
 Gas bags, 349 
 bladders, 348 
 bottles, 315 
 
 bottles of caoutchouc, 349 
 dishes, 314 
 
 funnels, 314, 322, 324 
 glasses, 314, 323, 403 
 holder, its construction, 344 
 
 uses, 345, 617 
 jars, mercurial, 312, 332 
 plain, 312, 403 
 stoppered, 312 
 transfer, 3 13 
 cleansed, 523 
 lamps, 107 
 measures, 67, 329 
 
 Cavendish's, 329 
 transferrer, Cavendish's, 335 
 Hare's, 81, 338 
 Pepys's, 336 
 tubes, 314, 324, 357, 403 
 
 generating, 406, 409 
 Gaseous manipulation, 308, 403 
 
 tube, 393, 403 
 
 Gases, bodies exposed to, 366, 369 
 bottles for, 350 
 escape from over mercury, 333, 
 
 535 
 expansion of, by moisture, 376 
 
 heat, 372 
 
 measures for, 69, 329 
 management of, 308, 609 
 
INDEX. 
 
 637 
 
 Gases, pressure upon, 327, 339, 570 
 quantities of, adjusted, 328 
 temperature of, 331 
 transmission of, 314 
 their volumes, 555 
 bottled, 321, 350 
 collected over mercury, 331, 333, 
 
 water, 315, 393, G09 
 entirely or pure, 316 
 in a gasometer, 341 
 an airholder, 345 
 bottles, 350 
 jars, 317 
 
 from voltaic decomposi- 
 tion, 448 
 
 compressed, 369, 572 
 condensed in tubes, 411, 415, 570 
 precautions, 
 411, 415 
 
 conducted through tubes, 357, 418 
 corrected, 371 
 
 for moisture, 376 
 temperature, 372 
 pressure, 373 
 decanted, 320 
 
 into bottles, 321 
 
 decomposed by voltaic heat, 459 
 detonated in an eudiometer, 422, 
 
 424, 426 
 by electric spark, 422, 
 
 432 
 dissolved, 358, 362 
 
 in tubes, 410 
 dried, 378 
 
 by tubes, 379' 
 
 sulphuric acid, 379, 381 
 evolved, 315, 609 
 examined in generating tubes, 406 
 
 mercurial receiver, 404 
 heated in tubes, 304 
 measured over mercury, 338 
 
 water, 324 
 
 in jars, 325, 327, 338 
 tubes, 326, 328, 329," 
 
 333 
 
 corrections for, 328 
 mixed, 363 
 retained, 317, 340 
 transferred over mercury, 333, 
 
 335, 612 
 water, 320, 346, 
 
 609 
 from jars, 320 
 
 tubes, 322 
 into exhausted vessels, 
 
 367 
 
 by dishes, 314, 318 
 weighed, 375 
 
 Thomson's method, 382 
 
 Gasometer, its construction, 340 
 
 use, 341 
 adjusted, 342 
 examined, 342 
 mercurial; 343 
 General rules for young experimenters, 
 
 538 
 
 Generating gas tubes, 406, 408, 409 
 Glass, a bad insulator, 460 
 engraving upon, 568 
 writing upon, 70, 418, 567 
 stains upon removed, 479 
 green, its advantages, 223 
 
 worked, 507 
 crown, cut, 514 
 bulbs blown, 500, 503 
 covers, 513 
 (flux), 294 
 masks, 573 
 plates, 314, 561 
 rods, 169, 484 
 rods, cut, 484 
 stirrers, 172, 484 
 stoppers, 195, 313, 513 
 ground, 516 
 
 loosened, 313, 525, 529 
 syphon made, 485 
 syringes, 245, 495 
 tubes, 298, 386, 489 
 bent, 482, 485 
 closed, 489, 492, 495 
 cut, 484, 509 
 fracture of, by heat. 478, 
 
 488 
 
 heated, 300, 303 
 joined, 503 
 made, 489, 502 
 sealed, 489, 492, 495 
 strength of, 370 
 wires sealed into, 504 
 annealed, 483 
 bending of, 476, 481, 485 
 blowing of, 476, 482, 501 
 broken, cut up, 510, 513 
 cooled, 483 
 cutting of, 476, 484, 509 
 
 by diamond, 509 
 hot iron, 510 
 rings, 510 
 discoloured, 485 
 divided, 509 
 drawn out, 499 
 edges removed, 484, 516 
 grinding of, 516 
 heating of, 477 
 moulded, 482, 488 
 rasped into form, 515 
 silvered, 574 
 softened, 481 
 worked, 476, 634 
 
638 
 
 INDEX. 
 
 Glasses, laboratory, 170, 224, 313 
 
 cleanliness of, 518 
 cleansed, 521 
 Glauber's apparatus, 358 
 Glue, with paper or cloth for a junction, 
 
 472 
 
 Gold crucible, 282 
 divided, 163 
 
 Graduation of capillary tubes, 570 
 jars, 80 
 
 triple, 80 
 
 thermometers, 133, 139 
 tubes, 70 
 
 by measuring, 76 
 weighing, 70 
 the eye, 79 
 minute, 79 
 
 Granulation of metals, 161 
 Grate, furnace, 85 
 Grease removed from glass, 521 
 Green glass tube, 507 
 Grinding of glass, 516 
 
 stoppers, 516 
 
 Guages for condensed air, 494, 570 
 Gum, powdered, 481 
 Gunter's line of numbers, 555 
 
 Hallos aerometer, 375 
 
 Hancock's caoutchouc, 202 
 
 Handles of paper for tubes, 389 
 
 Hare's measurer, 81, 338 
 
 Hauy's test of magnetism, 579 
 
 Heat, sources and management of, 83, 
 
 284, 459, 586 
 
 retained, 130, 132, 213, 239 
 increases chemical action, 1 72 
 
 solubility, 167, 170 
 of flame, 102 
 
 blow-pipe flame, 1 1 4, 480 
 voltaic discharge, 459 
 applied to flasks, &c. 172 
 
 retorts, 198, 219 
 its careful application to glass, 
 
 172, 176 
 conduction of, 564 
 
 tested, 565 
 
 reception of (uses), 565 
 reflection of (uses), 565 
 its transmission pi'evented, 206, 
 
 213,239 
 
 Henly's electrometer, how used, 429 
 Hessian crucibles, 278, 2/9 
 Hood, vapour, 16, 177 
 
 portable, 177 
 Hot air, a heating agent, 128 
 
 procured, 128 
 Hydrogen gas, prepared and experimented 
 
 upon, 609 
 Hydrometer, 59 
 
 verified, 61 
 
 Hydrometer, precautions in its use, 59 
 Hygrometric power of powders, 157 
 
 Ignition, appearance of, 142 
 of bodies, 291 
 
 in vapours, 400 
 India-rubber, or caoutchouc connectors, 
 
 202, 357, 472 
 bottles, sheets, &c., 202, 
 
 349, 357, 476 
 Indigo sublimed, 222 
 Inductive practices, a course of, 582 
 Infusion, 192, 590 
 Ink for writing upon glass, 567 
 Insolubility, indications of, 165 
 Insulation, electrical, 459 
 Iron, its influence in decompositions, 305 
 its magnetism examined, 580 
 cement, 471 
 retorts, 220 
 tubes, 297 
 
 Jackets to crucible, 288 
 Jar, Leyden, 424 
 
 examined, 425 
 substitute for, 430 
 Jars for gases, 312 
 
 precipitation, 167, 224 
 solutions, 167 
 capped, 313 
 cleansed, 523 
 deflagrating, 312 
 graduated, 80, 325 
 plain, 312, 332 
 filled, 317 
 stoppered, 312 
 transfer, 313 
 
 filled, 319, 332 
 their stoppers loosened, 529 
 Jet of the blow-pipe, 108 
 Joining of glass tubes, 503 
 Joints luted, 462, 467 
 Junctions rendered tight by luting, 467 
 hot, rendered tight, 469 
 secured by soft cement, 474 
 of apparatus, 210, 212, 214, 358 
 tubes, 202, 298 
 
 Kerr's generating gas tube, 408 
 
 fMboratory,iis arrangement, 11 
 
 cleanliness, 518 
 Lamination of metals, 1 64 
 Lamp furnace, Cooper's, 300 
 Lamps, 101 
 
 Argand, 105, 175, 198,300 
 double wicked, 106 
 chemical, 105 
 gas, 107 
 
 oil, 105,175,198, 300 
 trimmed, 106 
 
INDEX. 
 
 639 
 
 Lamps, spirit, 101, 284 
 
 its heat, 102 
 large, 103, 284 
 Phillips', 104 
 for blow-pipe, 112 
 Lead, leaf and sheet, its uses, 562 
 precipitated, 230 
 white (lute), 471 
 Leaf metals, uses of, 561 
 copper. 562 
 zinc, 562 
 
 Leaks in lutings discovered, 475 
 Leeson's blow-pipe, 1 22 
 Leslie's specific gravity apparatus, 52 
 Leydcn jar, 424 
 
 charged from the electro- 
 
 phorus, 432 
 examined, 425 
 substitute for, 430 
 Lime, carbonate of, precipitated, 229 
 
 lutes with egg, &c. 470 
 Line of numbers, Gunter's, 548 
 Linseed meal, 472 
 Liquids, adjusted, 42, 181 
 
 heated in tubes, 57, 389 
 
 introduced into bulbs, 56 
 
 measures for, 66 
 
 measured, 68 
 
 poured, 179, 197 
 
 transferred, 181 
 
 their specific gravity ascertained, 
 
 Do 
 
 volatile, weighed, 45 
 weighed, 41 
 Litmus paper, 267 
 
 preserved, 269 
 used, 269 
 
 Lixiviation, 189, 243 
 Loosening of stoppers, 525 
 Lute, prepared, 462, 467 
 applied, 463 
 
 its contraction in the fire, 466 
 Luted vessels dried, 464 
 
 repaired, 464 
 their liabilities, 465 
 
 in the fire, 
 
 466 
 supported in the fire, 219, 
 
 467 
 Lutes, 461, 624 
 
 almond paste, 472 
 
 bladder, 471 
 
 caoutchouc, 472 
 
 caustic lime and white of egg, 470 
 
 fat lute, 469 
 
 fusible lutes, 468 
 
 iron cement, 471 
 
 linseed meal, 472 
 
 paper and paste, 471 
 
 Parker's cement, 469 
 
 Lutes, plaster of Paris, 469 
 
 Stout-bridge clay, 462, 468 
 white lead, 471 
 Willis's lute, 468 
 Windsor loam, 468 
 Luting, 462, 465, 467, 624 
 of joints, 467 
 
 leaks in, discovered, 
 
 475 
 guarded by canvass, 466 
 
 Maceration, 189 
 Magnetic needles, 578 
 
 made, 581 
 Magnetism, 5/7 
 
 its presence ascertained, 578 
 Magnets made, 581 
 Management of gases, 308 
 
 heat, 83, 586 
 Manipulation, its importance, 3 
 
 pneumatic, 308, 609 
 Marcel's blow-pipe, 121 
 Marking of tubes, 70, 72, 418 
 Masks for the face, 573 
 Masses broken, 148 
 Measurement of gases, 324, 338, 615 
 
 liquids, 66, 68 
 Measures, 66, 68, 585 
 
 for gases, 69, 329 
 liquids, 66, 68, 81 
 mercury, 76, 77 
 graduation of, 67 
 tables of, 82 
 cubic inch, 69 
 pint, 67 
 graduated, 70 
 verified, 68, 70 
 Measuring, 68, 324 . 
 
 practices, 585, 615 
 Mercurial bath, 126 
 
 gasometer, 342 
 thermometer, 127, 132, 137 
 trough. 16, 311,331,404 
 
 its jars, 312, 332, 339 
 cleansed, 531 
 dispensed with, 405 
 tube receiver, 404 
 Mercury, weight of, 69 
 
 its influence, 331 
 
 333 
 its films, 75, 534 
 
 their effect, 333, 535 
 cleansed, 532 
 purified, 533, 537 
 surface observed, 74 
 weight adjusted, 71, 76 
 Metal baths, 127 
 tubes, 297 
 
 heated, 299, 303 
 Metallic crucibles, 281, 283 
 
640 
 
 INDEX. 
 
 Metats, broken, 150 
 
 comminuted, 161, 589 
 granulated, 161, 590 
 leaf, their uses, 569 
 precipitated, 229, 45S 
 reduced, 295 
 sheet, their uses, 561 
 Method, rules relating to, 538 
 Mineral water evaporated, 260 
 
 secured by soft cement, 474 
 Mirrors made, 574 
 Mixture effected in a filter, 237 
 in a mortar, 153 
 by sieves, 158 
 in tubes, 387 
 of fluids, 227 
 gases, 363 
 refrigerating, 205 
 Mortars, 19, 145 
 
 their material, 145 
 form, 146 
 uses, 148, 589 
 bodies broken in, 148 
 
 pulverised in, 151 
 dissolved in, 170 
 agate, 147 
 iron, 145 
 
 its uses, 145 
 porcelain, 145 
 
 examined, 146 
 porphyry, 147 
 for diamonds, 157 
 cleansed, 531 
 Muriatic acid, its use as a solvent, 185 
 
 gas collected in bottles, 351 
 condensed, 416 
 dissolved, 359 
 prepared and experi- 
 mented with, 612 
 
 Naphthaline, purified in tubes, 387 
 Needles, magnetic, 461, 578, 581 
 Neutral precipitations, 270 
 Neutralization, 270, 602 
 Nitre (flux), 294 
 Nitric acid distilled, 213 
 
 its use as a solvent, 185 
 Nitric oxide gas, prepared and experi- 
 mented with, 615 
 Noottfs apparatus, 362 
 Note book, laboratory, 23, 539 
 
 Oil as fuel, 105 
 
 lamps, 105, 175 
 Oiled silk, its use, 349, 366 
 Oil* filtered, 239 
 Olejiant gas, prepared and experimented 
 
 with, 611 
 Oxides deoxygenated, 295 
 
 reduced in tubes, 306 
 
 Oxy -alcohol blow-pipe, 121, 347 
 Oxy-hydrogen blow-pipe, 122 
 Oxygen prepared in tube retorts, 403, 614 
 OxygenationQi metallic solutions, 187 
 
 Paper, uses of, 38, 129, 557, 628 
 and paste for joints, 471 
 vessels covered with. 249, 559 
 cones and covers, 239, 249, 559 
 filtering, 232 
 funnels, 559 
 
 handles for hot tubes, 388, 492 
 litmus, 267 
 pasted, 472, 558,560 
 string, 560 
 tubes, 357, 558, 628 
 turmeric, 268 
 vessels, 557, 628 
 waxed, 557, 558 
 Parker's cement, 469 
 Paste and paper for junctions, 471 
 Pasted paper, 472 
 Pepyf gas-holder, 344 
 
 gas transferrer, 336 
 mercurial gasometer, 342 
 Pestle, its form, 146 
 use, 149, 152 
 
 Phosphorescence observed, 575 
 Phosphorus bottle, 22 
 Phillips' precipitating glasses, 167, 224 
 
 spirit-lamp, 104 
 
 Pile voltaic, 439 (see Voltaic pile) 
 Pint measures, 67 
 
 for steam, 129, 558 
 469 
 
 rendered air tight, 469 
 Plate copper, 562 
 
 zinc, 562 
 
 Plates of glass, 252, 257, 314, 561 
 Platina, influence of on combination, 305 
 cleansed, 530 
 divided, 163 
 capsules, 281 
 crucibles, 281, 283 
 
 cleansed. 530 
 foil, 102, 563 
 spatulas, 39, 159, 231 
 spongy, 163 
 tubes, 297 
 
 heated, 303 
 
 wires sealed into tubes, 504 
 Pneumatic manipulation, 308, 403, 609 
 
 in tubes, 393, 
 
 403,619 
 
 apparatus connected, 351 
 jars, 312, 403 
 joints, tightness of, 356 
 trough, 309,403, 519 
 
 manipulation of, (see 
 Gases) 
 
 Pipes of paper fc 
 Plaster of Paris, 
 
INDEX. 
 
 641 
 
 Pneumatic trough, material of, 309, 519 
 mercurial, 311 
 
 cleansed, 531 
 level of water in, 310, 320 
 small, 313, 318, 403 
 Poles voltaic, 444, (see Voltaic poles) 
 Porosity of earthenware prevented, 296. 
 
 468 
 Pouring without loss, 179, 241 
 
 hyrod, 180, 236 
 Powders dried, 261 
 
 fine and coarse separated, 158 
 hygrometric, 157 
 introduced into flasks, 178 
 mixed, 158 
 separated, 158 
 transferred, 39, 156, 178 
 washed, 158 
 weighed, 38, 178 
 fineness judged of, 154 
 their specific gravity ascer. 
 
 tained, 52 
 
 Practices, a course of, 582 
 Precipitant, 224 
 
 quantity required, 225, 227 
 Precipitating glasses, 224 
 Precipitates, 224 
 
 collected, 240, 265 
 dried, 243, 263, 264 
 in tubes, 402 
 filtered, 240 
 washed, 237, 243 
 Precipitation, 223, 387, 596 
 
 effected, 225, 227 
 
 facilitated, 228 
 
 in tubes, 387 
 
 neutral, 271 
 
 precise, 225 
 
 precautions, 228 
 
 rules relating to, 540 
 
 tests of, 224 
 
 vessels required for, 224 
 
 voltaic (Wollaston's), 230, 
 
 456 
 
 of carbonate of lime, 229 
 chloride of silver, 228 
 ferro-prussiate of potassa, 
 
 metals, 229 
 
 sulphate of baryta, 229 
 Preservation of bodies in tubes, 417, 496 
 Pressure on gases, 327 
 
 corrections for, 373 
 Production of gas, 315 
 Promoters of vaporization, 199 
 Proportional numbers, 547 
 Proportions, equivalent, 546 
 Prussian blue precipitated, 229 
 Pulverization, coarse, 151 
 fine, 152 
 
 Pulverization, fine, appreciated, 154 
 for analysis, 156 
 precautions, 155, 157 
 Purification of mercury, 533 
 Puffy, 469 
 
 Pyroligneous ether, 105 
 Pyrometer, Daniell's, 143 
 
 Wedgwood's, 143 
 
 Quill feathers, uses of, 237 
 tube, 386 
 
 bent, 488 
 worked, 488, 508 
 
 Rack for tubes, 19, 386 
 
 Rays of the sun, their power, 14, 577 
 
 Receivers for condensation, 201, 208 
 
 volatile products, 207 
 tube, 392, 393, 403, 493 
 
 for sublimation, 399 
 mercurial tube, 404 
 Reception of hejtt, 565 
 Rectification in tubes, 395 
 Reduction of metals by charcoal, 295 
 
 oxides in tubes, 306 
 Refrigerating mixture made, 205 
 
 guarded, 206 
 
 Refrigeration, cautions in applying, 214 
 in distillation, 192, 201, 
 
 206, 210, 218 
 in tube sublimations, 398 
 on retort neck, 200 
 Reflection of heat, uses of, 565 
 Regulations as to cleanliness, 517, 530 
 Removal of stoppers, 525, 529 
 Residual charge of a battery, 429 
 Resin removed from glass, 521 
 Retention of heat, 130, 132, 213, 239, 
 Retort caps, 354 
 
 affixed, 354, 370 
 their place supplied, 355 
 stands, 175 
 Retorts, 193, 219, 392, 402 
 
 broken useful, 222, 510 
 gas evolved from, 315 
 for exhaustion, 194, 366 
 glass, 193 
 
 their form, 194, 36 G 
 thickness, 194 
 coated, 219,462 
 
 heated, 219 
 necks elongated, 208 
 earthenware, 219 
 
 luted, 220 
 iron, 220 
 
 tube, 392, 403, 493 
 tubulated and plain, 195 
 capped. 354 
 charged, 196, 197 
 cleansed, 525 
 
 2 T 
 
642 
 
 INDEX. 
 
 Retorts, coated, 219, 462, 465 
 
 supported in the fire, 219, 
 
 467 
 
 dried, 524, 525 
 heated, 198 
 Rings listed, use of, 43 
 
 furnace, 92 
 
 Rock crystal, surface of in tubes, 304 
 Rod, glass, cut, 484, 509 
 Rods, glass, 169,484 
 
 their use in pouring, 180 
 transference of liquids by, 181 
 Roman cement, 469 
 Rules for young experimenters, 538 
 
 relative to cleanliness, 517, 530, 539 
 precipitates and testing, 
 540 
 
 Safety tube, 215 
 
 of Hassenfratz, 360 
 
 Welter, 215 
 Sal enixum, 294 
 
 Salts, favour voltaic decomposition, 452 
 Sand, kind required, 20, 92 
 Sowd-bath, 91, 123, 173 
 Sand-pot, 92, 221, 222 
 Saturation, indication of, 171 
 Scale of chemical equivalents, 544, 627 
 its construction, 
 
 548 
 
 use, 549 
 errors, 553 
 
 Scales of thermometers, comparative, 133 
 Scratching diamond, 70, 418 
 Screens for the face, 573 
 Sealing of tubes, 489 
 
 hermetically, 394, 495 
 Selection of solvents, 183 
 Separation of fluids, 244, 599 
 powders, 158 
 
 precipitates, 230, 241, 598 
 by crystallization, 246, 251 
 Separators, 245, 495 
 Sheet lead, its use, 562 
 metals, vises of, 561 
 caoutchouc, 202, 357 
 Shelves, their arrangement, 18 
 Sieve, 158 
 
 mixtures, 158 
 Si/ting, 158 
 Silica divided, 161 
 Silk, insulations, precautions, 461 
 
 valve, 366 
 Silver basins, 171 
 divided, 162 
 crucible, 281 
 precipitated, 230 
 Silvering glass, 574 
 Singers' electrometer, 433 
 Sink, its arrangements, 17 
 
 Sink, its accompaniments, 519 
 Smelling through a tube, 567 
 Soft brick, 563 
 
 cement, 254, 473 
 
 mineral waters confined by, 
 
 474 
 
 Softness "of hot glass, 481 
 Solar radiant matter, its powers, 14, 577 
 Solid bodies, their specific gravity deter- 
 mined, 47, 52 
 
 Solubility affected by presence of sub- 
 stances, 186 
 
 conferred by tartaric acid, 186 
 increased by heat, 167 
 indication of, 164 
 Solution, 163, 590 
 
 its uses, 164 
 
 vessels required for, 167, 388 
 in a mortar, 170 
 acids, 185 
 alcohol, 183 
 alkalies, 186 
 water, 164 
 by heat, 171, 388 
 of carbonates, 179 
 chlorine, 362 
 gases, 358, 362 
 
 in tubes, 410 
 muriatic acid gas, 358 
 organic substances, 188 
 on a small scale. 181,388 
 of two kinds, 164 
 baths, 125 
 Solutions, boiling points of, 126 
 
 saturated, obtained, 171 
 metallic, 187 
 deoxygenised, 188 
 oxygenised, 187 
 
 Solvents, their selection, 183, 250 
 Spatulas, 39, 156,231 
 Specific gravity ascertained, 47 
 bottles, 53 
 bulbs, 56, 61 
 of liquids, 53, 59 
 porous bodies, 51 
 powders, 51 
 solids, 47 
 
 Spikes, their places and use, 19 
 Spirit-lump, 101 
 
 large, 103, 104, 285 
 Phillips's, 104 
 its heat, 102, 284 
 
 Standards of measurement, 67, 79, 82 
 Stands for retorts and flasks, 1 75 
 Steam, its heating powers, 129 
 apparatus, 130 
 bath, 130 
 boiler, 132 
 chamber, 131 
 Still, 93, 191 
 
ISOEX. 
 
 G43 
 
 Slirrcrs, glass, 169, 484 
 Stones, breaking of, 143 
 Stop-cocks, 35l!, 354 
 collars of, 
 
 examined, . 356 
 tightness of, 356 
 Stoppers , furnace, 86 
 
 glass, 195, 218, 313, 513 
 ground, 516 
 examined, 195 
 loosened, 526, 529 
 Stourbridge, clay lute, 279, 462, 468 
 Strength of glass tubes, 374 
 Strinn^ paper, 560 
 Sublimation, 194, 220, 397, 593 
 
 vessels required for, 221 
 in tubes, 397 
 of indigo, 222 
 Subliming tubes, 397 
 Substances, broken, 148 
 heated, 291 
 
 in lamp flame, 102 
 preserved in tubes, 417, 495 
 Sulphate of baryta precipitated, 229 
 Sulphuric acid a desiccator, 255, 381 
 
 distilled, 200 
 
 . exactly precipitated, 225 
 gas dried over, 381 
 its use as a solvent, 185 
 Sulphurous acid condensed in tubes, 415 
 distilled, 202, 394 
 receivers for, 394 
 Supports for apparatus, 217 
 
 crucibles, 2S6, 288 
 blow-pipe experiments, 1 1 6 
 Surface for decomposition extended in 
 
 tubes, 304 
 Synoptic scale of equivalents. 544, 553, 
 
 627 (see Scale) 
 Syphon, 241 
 
 made, 493 
 of cotton, 244 
 its use, 242 
 decantation by, 242 
 Syringe, its use, 363, 369 
 examined, 364 
 tube, 246, 494 
 
 Table blow-pipe, 118,477 
 
 how used, 118 
 furnace, 15, 89, 286 
 of boiling points of solutions, 126 
 chemical equivalents, 554 
 measures, 82 
 weights, 66 
 Tables, laboratory, 16 
 Tar removed from glass, 522 
 Tart uric acid, solubility conferred by, 
 
 186 
 Taste as an indication of solubility, 165 
 
 Temperature estimated, 133, 143 
 of gases, 327 
 gas corrected for, 372 
 Temporary blow-pipe, 109, 1 19, 508 
 
 line, 87 
 Test glasses, 224 
 
 cleanliness of, 518 
 cleansed, 520 
 papers, 267, 602 
 
 their indications, 269, 271 
 
 use, 270 
 preserved, 269 
 solutions, 266, 276, 602 
 tubes, 386 
 Testing, 224, 387 
 Tests, coloured, 26 6, 602 
 Thermometers, 132 
 
 temperature observed by, 
 
 127, 135, 138, 588 
 air, 140 
 alcohol, 137 
 chambered, 139 
 changes of, 136 
 compared, 135 
 differential, 142 
 errors of, 138 
 graduation of, 134, 139 
 mercurial, 127, 133, 137 
 examined, 133 
 its indications, 137 
 observed, 140 
 open and closed, 137 
 Tightness of pneumatic joints, 356 
 Tin foil, its uses, 561 
 Tobacco pipe used as a crucible, 283 
 Tongs, 93, 291 
 Tools, laboratory, 20 
 7<>ztf,itstises, 520, 523 
 
 wrapped round glass, 404 
 Transfer ya, 313 
 
 filled, 319 
 Transference of gas, 318, 320, 367 
 
 over mercury, 333, 
 335 
 
 water, 31 8, 320 
 from jars, 320 
 
 tubes, 322 
 into exhausted ves- 
 sels, 367 
 of liquids, 179, 181 
 
 powders, 39 
 Transferred, gas, 336 
 Trivets for troughs, 310, 519 
 Trough, mercurial, 311, 332, 404 
 
 its place, 16 
 
 pneumatic, 308, 403, 51 9 
 its place, 19 
 manipulation at (see 
 
 Gases) 
 
 varieties of, 309, 403 
 2 T 2 
 
644 
 
 INDKX. 
 
 Trough, pneumatic, mercurial, 311, 404 
 
 its waters changed, 519 
 Tube combinations, 306, 607 
 decompositions, 305, 607 
 operations (furnace), 296, 606 
 chemistry, 181,386, 618 
 practices, 618 
 condensation, 398 
 desiccation, 400 
 digestion, 389 
 distillation, 391 
 
 gaseous, 393, 403 
 in vacuo, 397 
 
 ebullition, under pressure, 389 
 gases collected, 403, 620 
 condensed, 411 
 dissolved, 410 
 examined, 405 
 ignition in vapours, 400 
 pneumatic manipulation, 403 
 precipitation, 387 
 preservation of substance, 417 
 rectification, 395 
 chemistry, separation, 387 
 solution, 388 
 sublimation, 397 
 testing, 387 
 washing, 387 
 apparatus, 386 
 
 for distillation, 391 
 air jars, 403 
 evaporators, 402 
 feeding, 216 
 funnel, 392, 493, 494 
 handles, 388 
 
 Kerr's generating gas, 408 
 lamp-furnace, 300 
 pneumatic apparatus, 403, 620 
 quill, 386 
 rack, 19, 387 
 retort, 392, 403, 404 
 receivers, 392, 393, 403, 493 
 supported, 393 
 mercurial, 404 
 of safety, Hassenfratz's, 360 
 
 Welter's, 21 5 
 separator, 245, 495 
 stand, 387 
 syphons, 241, 493 
 syringes, 240, 245, 495 
 test-glasses, 386 
 water-bath, 125 
 Woulfe's apparatus, 410 
 Tubes, caoutchouc (flexible), 203, 357 
 copper, 208 
 earthenware, 296 
 glass, 298, 386 
 
 strength of, 370, 411 
 cut, 484, 509 
 heated, 300, 302, 477 
 
 Tubes, glass, cased with foil, 303, 562 
 green glass, 293 
 iron, 297 
 metallic, 297 
 
 heated, 303 
 paper, 357, 418, 557 
 plutina, 297 
 plumbago, 297 
 bent, 482, 485 
 cleansed, 522 
 closed, 386 
 
 by the finger, 323 
 temporarily, 411 
 coated or luted, 296, 465 
 connected, 298 
 
 contracted, 208, 393, 494, 496 
 cut, 481, 509 
 graduated, 70 
 heated, 87, 299, 477 
 
 in the middle, 477, 485, 489 
 at the ends, 478, 488 
 supported, 388 
 marked, 70, 72 
 made, 489, 492, 502 
 sealed, 489, 494 
 
 hermetically, 495 
 strength of, 370 
 supported, 297 
 weighed, 41 . 
 for gases, 314, 357 
 digestion, 388 
 
 voltaic decompositions, 448, 505 
 uses of, as bottles, 417 
 in mixing, 227 
 substances preserved in, 417 
 liquids heated in them under 
 
 pressure, 57, 389 
 their contents mixed, 387 
 transference of gas in, 322 
 capillary made, 493 
 wires sealed into, 504 
 generating, 406, 408, 410 
 
 gases examined in, 
 
 406 
 
 Tubulated retorts, 195 
 Turmeric paper prepared, 268 
 uses, 269 
 precautions, 271 
 Turpentine removed from glass, 522 
 
 Urc ? s eudiometer, 428 
 
 steam apparatus, 130 
 Uses of copper wire, 560 
 
 corks, 555 
 
 glass plates, 561 
 
 leaf and sheet metals, 561, 629 
 
 paper, 557, 628 
 
 reflective and receptive powers, 565 
 
 Windsor brick, 563 
 
EX. 
 
 645 
 
 Valve silk, 366 
 Vaporization promoted, 1 9') 
 
 crystals obtained by, 254 
 Vapour liood, 15, 177 
 Vapours, bodies heated in, 400 
 conveyed away, 177 
 decomposed in tubes, 305, 400 
 heated in tubes, 299, 304, 400 
 ignited in simple tubes, 400 
 their volumes, 555 
 Varnish for trivets, 519 
 Ventilation of the laboratory, 14 
 Vessels of paper, 557 
 covered, 260 
 
 with paper, 249 
 exhausted of air, 366 
 
 precautions, 367 
 graduated, 70 
 luted or coated, 462 
 Volatile bodies confined, 394 
 distilled, 202 
 Voltaic contact, 446 
 
 communication, 443, 446, 454 
 decomposition, 444, 448, 451 
 of fluids, 448 
 favoured, 452 
 gases, 459 
 
 in glass capsules, 449 
 tubes, 448 
 separate vessels, 451 
 tubes for, 505 
 gases collected, 448 
 interfering circum- 
 stances, 451 
 
 precipitation, Wollaston's, 230, 456 
 battery, 439 
 discharge through charcoal, 441 
 
 heat of, 459 
 
 pair of plates arranged, 455 
 pile, 439, 623 
 
 arrangement of, 454 
 
 its parts connected, 443, 454 
 
 constructed quickly, 453 
 
 small, 454 
 
 temporary, 453 
 
 Wollaston's, 455 
 
 charge for, 439 
 
 put into action, 439 
 
 examined, 440 
 
 its decomposing powers applied, 
 
 raised at intervals, 453 
 poles of, 444, 454 
 
 their nature and extent, 444 
 
 454 
 
 handled, 447 
 
 quantity and intensity, 45 I 
 polos, -144 
 
 distance from each other, 445, 
 451 
 
 Voltaic poles, their material, 445 
 
 surface, 445, 448, 449 
 thickness, 444, 448 
 troughs connected, 443, 454 
 Volume of gas observed, 325, 330 
 corrected, 371 
 
 for moisture, 376 
 pressure, 373 
 temperature, 372 
 Volumes of gases, 555 
 
 Warm air chamber, 262 
 Washers, 353 
 Washing bottle, 240 
 
 by decantation, 243, 598 
 of powders, 158, 598 
 
 precipitates, 237, 243, 598 
 Water distilled, important, 21, 179 
 its use as a solvent, 164 
 decomposed in tubes by heat, 305 
 evaporated in tubes, 402 
 weight of, 68, 82 
 baths, 123 
 
 uses of, 124 
 arrangement of, 124 
 trough, pneumatic, 19, 308, 519 
 Wax, yellow, 473 
 Waxed paper, 557, 558 
 Wedgwood's basins, 167 
 
 crucibles, 278, 280 
 pyrometer, 143 
 
 Weighing, operations of, 34, 37, 50, 65, 
 582 
 
 practices, 582 
 
 effect of the air's buoyancy, 46 
 of changeable substances, 44 
 fluids, 41 
 gases, 375, 382 
 heated substances, 37 
 pieces, 34 
 powders, 38, 291 
 tubes, 41 
 volatile fluids, 45 
 in vessels, 41 , 79 
 Weight of measures of mercury, 69 
 
 water, 67, 69 
 
 Weights^ examination of, 33 
 handled, 35, 36 
 required, 26 
 small, 27, 63, 66 
 substitutes for, 65 
 table of, 66 
 
 Welters safety tube, 215 
 While flux, 293 
 
 lead (lute), 471 
 Willis's lute, 468' 
 Wind furnace, 88, 93 
 JJ'itntoH.'.'i of the laboratory, 14 
 11-hnlmr brick, 563 
 
 loam (lute), 468 
 
646 
 
 Wine distilled, 209 
 Wiping sticks, 520 
 Wire, copper, uses of, 560 
 Wires amalgamated, 446 
 
 of the eudiometer, 423 
 
 sealed into tubes, 505 
 
 eudiometer tubes, 507 
 
 for cleansing, 520 
 Wollastorfs scale, 544, 627 (see Scale of 
 
 equivalents) 
 Wooden blocks, 19 
 
 INDEX. 
 
 Working of glass, 477 
 
 JFo/7wtub, 192 
 
 m :.;<>* bottles, 214, 358 
 
 replaced by tube, 410 
 Writing upon glus:,, 71, 418, 567 
 
 Yellow wax, 473 
 
 Zinc foil, 562 
 
 plate, 453, 562 
 pulverized, 155 
 
 THE END, 
 
 IOM ON ; 1'r'uiU'd-by WILLIAM CLOWES, Stamford- street 
 
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