r REESE LIBRARY UNIVERSITY OF CALIFORNIA. '^%vi'/V>\ /tc&ssL inm\>er0it tutorial Series GENERAL EDITOR WILLIAM BRIGGS, M.A., LL.B., F.C.S., F.R.A.S. THE TUTORIAL CHEMISTRY. TUniverditc tutorial Series THE TUTORIAL CHEMISTRY. PAET I. NON-METALS. BY G. H. BAILEY, D.Sc. LOND., PH.D. HEIDELBERG, LECTURER IN CHEMISTRY IN THE VICTORIA UNIVERSITY. EDITED BY WILLIAM BRIGGS, M.A., F.C.S., RRA.S., PRINCIPAL OF UNIVERSITY CORRESPONDENCE COLLEGE. LONDON : W. B. CLIVE, UNIVERSITY CORRESPONDENCE COLLEGE PRESS. WAREHOUSE : 13 BOOKSELLERS Row, STRAND, W.C. ERRATA. Pair*' 8, line 3 from bottom for "corona" road "chromosph<>7'< " :5 ^ 7 "(5)" "(4)" ,. 48, ,,16 from top ,, "weight" ,, "weights" M 2, 9 -, "ferrous" "nickel" 63, ,, 1 ,, " be collected" ,, "not I.-- collected' 1 ,,118, on margin ,, "8ft." ,, "18ft." ..206, line 1 ., "22-32" ,, "22-24" ,, ,. .. 2 from top ,, "22-32" ,, "22-24" M M n * ,, "1-428" "1-423" ,,211, ,, 15 from bottom ,, "25" ,, "2*5" ..220, Answer to Example 6 ,, "129-17" "129-7" 27 "4-123" "4-626" 32 ,, "61-023" "61023" 35 "14-39" "14-16." PREFACE. Ix writing this small treatise, it has been the aim of the author to furnish a systematic outline of chemistry so far as it relates to the non-metals. At the outset especially, experiment, observation, and inference should go hand in hand ; details of experimental methods are therefore given, which, under the guidance of the teacher, will be found sufficient to admit of the book being also used as a companion in the laboratory. In the view that it is unwise at the earlier stages to overburden the student with chemical theory, the full force of which he is not in a position to grasp, there has been no attempt to do more than establish the fundamental principles. The text has been further lightened by throwing aside a great deal of purely physical matter which it has been the fashion to incorporate in text-books of chemistry. The ac- quaintance with the principles of light, heat, and electricity, necessary as they may be to the chemist, is surely better gained from a good elementary text-book of physics. PREFACE. The subject of " Chemical Physics," which during recent years has extended so largely and presented such a fascina- tion for the chemist, has been chiefly reserved for the part on the metals, where it will be more fully treated. To Mr. W. H. Hurtley, B.Sc., both author and editor have to express their thanks for his many valuable sugges- tions, and for help in seeing this little work through the press, especially in connection with the diagrams. tnsrr CONTENTS. CHAPTER I. PAGE DEFINITION AND AIMS OF CHEMISTRY ... 1 CHAPTER II. THE NATURE OF CHEMICAL REACTION 10 CHAPTER III. HYDROGEN AND THE HALOID ACIDS ... ... ... 22 CHAPTER IV. PHYSICAL PROPERTIES OF GASES 36 CHAPTER V. COMPOUNDS OF HYDROGEN WITH OXYGEN AND SULPHUR 51 CHAPTER VI. PROPERTIES OF WATER NATURAL WATERS ... ... 66 CHAPTER VII. THE HALOGENS: TH^IR OXIDES AND OXY- ACIDS ... 79 CHAPTER VIII. OXYGEN AND OZONE ... 92 Vlll CONTENTS CHAPTER IX. PAGE SULPHUR AND SULPHUR DIOXIDE ... ... 103 CHAPTER X. SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM ... 114 CHAPTER XI. NITROGEN THE ATMOSPHERE AMMONIA ... 128 CHAPTER XII. OXIDES AND OXY-ACIDS OF NITROGEN 142 CHAPTER XIII. PHOSPHORUS ... ... ... ... ... ... 152 CHAPTER XIV. CARBON AND THE HYDROCARBONS ... ... ... 163 CHAPTER XV. FUELS COMBUSTION 176 CHAPTER XVI. OXIDES OF CARBON CARBON BISULPHIDE ... 184 CHAPTER XVII. SILICON AND BORON .193 CHAPTER XVIII. CHEMICAL CALCULATIONS ... ... ,. ... 201 ANSWERS TO QUESTIONS ... ... ... ... 219 OF UNIVERSITY J TEXT-BOOK OF CHEMISTRY. CHAPTER I. DEFINITION AND AIMS OF CHEMISTRY. The dawn of chemistry. From very early times the con- stitution of matter lias been a subject of interest to man. The first investigators were satisfied with observations almost entirely confined to the colour, hardness, or other physical properties of the mineral substances which they found around them ; arid when- ever they succeeded in bringing about any transformation of these substances, the process by which the change was accom- plished received little attention. Thus iron, copper, and a few other metals were obtained, but by empirical methods. Substances chemically identical, such as water and steam, were regarded as essentially different, whilst other substances for instance, ice and quartz though composed of entirely different materials, were, in consequence of their simi- larity in appearance, regarded as being forms of the same substance. B TEXT-BOOK OP CHEMISTRY. In the investigation of natural phenomena it is always necessary in the first place to perform experiments. Experiments carefully planned were, however, almost unknown in the beginnings of chemistry, and even when performed, the deductions drawn were too often falsified through placing a too great reliance on what, judging by the appearance, the resultant body might be. Tims Geber, by adding mercury to lead, obtained a silver-white solid which he regarded as being tin, which indeed it resembles. Experimental inquiry. Solid progress in the knowledge of chemistry has been achieved only after the performance of a vast number of experiments, each experiment being rigidly followed up by others, and the conclusion only accepted when the evidence accumulated from every possible source places it beyond dispute. As an instance of the methods followed in the chemical in- vestigation of matter, let us take cylinders (A) containing oxygen, and (B) containing carbonic acid gas. So far as we can see they are similar, but if we perform varied experiments we shall learn something of the chemical differences between the gases. Exp. 1. Pour clear lime-water into each ; in A no change is observed, in B the lime-water becomes turbid. Exp. 2. Place a lighted taper in each ; in A the taper continues to burn, and burns even more brightly than it does in air ; in B the taper is extinguished. Further experiments may be performed, and the observations classified. In this way we arrive at a knowledge of the properties of the gases in question, and are able to recognize them with certainty whenever we may meet with them. So, too, mineral substances ; they are usually of a complex nature, and before the chemist can arrive at a knowledge of their constituents they must be decomposed and the more elementary parts examined. Marble when strongly heated gives off a gas which may be recognized as carbon dioxide, and the residue falls readily to powder, especially when moistened, and shows all the characteristic properties of lime. Thus, when we have further satisfied ourselves that these are the only products of the 4e- DEFINITION AND AIMS OF CHEMISTRY. 3 composition, and that no part of them lias been derived from Surrounding media, we are justified in making the statement marble consists of lime and carbon dioxide. If we now act upon the lime with carbon dioxide, we are able to reproduce a body having all the essential characters of marble. We have in this way convinced ourselves by two independent processes that lime and carbon dioxide are the constituents of marble. The former method of procedure is known as the method of analysis, and the second that of synthesis. The formation of rust when iron is exposed to moist air, and the reproduction of iron when rust is heated in contact with charcoal ; the decomposition of water by a current of electricity, and the formation of water when hydrogen and oxygen are exploded together; these and similar changes are calculated to throw light on the chemical composition of rust and water. Elements and compounds. It is by decomposing known substances whenever that is possible, and by building them up again from their constituents, that the chemist arrives at a know- ledge of the composition of matter. When the process of decomposition has been carried as far as it can be, we arrive at products which no process can split up into portions which show different chemical properties from the original. We regard the products thus obtained as elements. By the chemical com- bination of elements together we obtain compounds. Physical and chemical properties of matter. When we look deeper into phenomena such as these, and discuss the con- stitution and properties of matter, we cross the threshold not only of Chemistry, but also of Physics, and we must therefore define the. properties which directly concern the chemist. And in general we may take it that those properties such as elasticity, weight, cohesion, regarded as belonging to matter irrespective of its differences of composition, and those changes which affect the form of matter without altering its composition, are essentially physical in their nature. Wherever a difference of composition is brought about, and the properties are no longer common to matter but are dependent on composition, we are dealing with chemical phenomena. Thus a fragment of iodine is reduced to a powder, but however minute 4 TEXT-BOOK OF CHEMISTRY. the particles so obtained may be they are still iodine, and what- ever reactions or chemical changes we may subject them to they will behave as iodine. So if we heat the iodine it is transformed into vapour differing altogether in appearance and in physical properties from solid iodine, but still retaining all the chemical characteristics of iodine, and indeed on cooling, the vapour con- denses again to a solid, having the same physical characters as the original substance. But if we bring a small piece of phosphorus into contact with the iodine, heat is evolved, and a substance is produced differing altogether in its properties from either iodine or phosphorus. A chemical change has been brought about. Or again, if we consider the case of a gaseous body, hydrogen. If it is heated, it expands in the same degree as all perfect gases, whatever their composition may be ; it diffuses according to a fixed law independent of composition : these are physical pro- perties. But if we burn it, water vapour is produced, arid this differs from hydrogen in density ; it is not inflammable, it con- denses readily to liquid water: we have indeed effected a chemical change. Definition of chemistry. Summing up we may say, then, that the objects of the chemist are (1) To decompose complex matter (compounds) into simpler forms, so long as the resulting bodies show properties differing chemically from the original substance, the ultimate products of such decomposition (elements) being no longer capable of further resolution by any known method. (2) To ascertain by means of experiment the properties of elements and compounds, so far as they are associated with differences of chemical composition, and to study the manner in which they react upon one another. (3) By means of the analytical method employed in (1), and by the synthetical method in (2), to trace the steps in the trans- formations which take place, so as to express the relations which exist between a compound body and its constituents. (4) To study the nature of the attraction by which the different constituents of a compound body are held together in chemical combination, and the conditions which influence this attraction. DEFINITION AND AIMS OF CHEMISTRY. 5 General methods employed in bringing about chemical change. When a substance is heated, the changes first observed are usually physical in their nature. The substance expands, or it undergoes an alteration from the solid to the liquid condition, or from the liquid to the gaseous. Such changes betoken a passage to a state in which the particles of the body become more free to move ; or in other words, the cohesion of the particles is diminished. As the temperature is raised, even the chemical attraction which has previously held together the different chemical constituents of the body is wholly or in part overcome, and the body is decomposed. Given a sufficiently high tempera- ture, most compound bodies undergo decomposition. Secondly, substances which conduct electricity may often be readily resolved into their more elementary parts by means of the electric current. Thirdly, the simpler constituents of a body may be liberated by the intimate contact of another chemical substance-, the reaction being facilitated by heat. Chemical symbols. The description of the composition of a body, and of the changes which it undergoes under different circumstances, is of so frequent occurrence in chemistry that it has been found convenient to use abbreviated forms or symbols to indicate the ultimate elements of which all known substances are composed. The symbols employed to designate them usually consist of the initial letter or significant letters of the name of the element. The number of bodies at the present time recognized as elements is about seventy. Improved methods and appliances are however constantly being brought into use ; also discoveries in other branches of science are the means of presenting matter to us in new forms and of placing more powerful agencies at the disposal of the chemist. Substances which we now believe to be elements may thus be proved to be compounds, while other bodies, of which we now think the exact composition has been ascertained, may probably be found to contain elements hitherto unrecognized. The following list shows the symbols used, and also the atomic weights of the more common elements TEXT-BOOK OF CHEMISTRY. THE SYMBOLS AND ATOMIC WEIGHTS OF THE MORE COMMON ELEMENTS. Hydrogen ... H 1-00 Carbon ... C 11-97 Nitrogen ... N ... 14-01 Oxygen ... O 15-96 Fluorine ... F ... 19-06 Sodium ... Na (Natrium) ... ... 23-00 Magnesium ... Mg ... 23-94 Aluminium ... Al ... 27-04 Silicon ... ... Si ... 28-00 Phosphorus ... P ... 30-96 Sulphur ... S ... 31-98 Chlorine ... Cl ... 35-37 Potassium ... K(Kalium) ... ... 39-03 Calcium ... Ca ... 39-91 Chromium ... Cr ... 52-45 Manganese ... Mn ... 54-80 Iron ... Fe (Ferrum) ... ... 55-88 Cobalt ... ... Co ... 58-60 Nickel ... ... Ni ... 58-60 Copper... Cu (Cuprum) ... ... 63-18 Zinc ... Zn ... 65-10 Arsenic ... As ... 74-90 Bromine ... Br ... 79-76 Strontium ... Sr ... 87-30 Silver ... ... Ag (Argentum) ... 107-66 Cadmium ... Cd ... 111-70 Tin ... ... Sn (Starmimi) ... ... 118-80 Antimony ... Sb (Stibium) ... ... 119-60 Iodine ... ... I ... 126-54 Barium ... Ba ... 136-90 Mercury . . . Hg (Hydrargyrum) ... 199-80 Lead ... ... Pb (Plumbum)... ... 206-40 Bismuth Bi ... 207-30 DEFINITION AND AIMS OF CHEMISTRY. 7 The symbol is, then, the abbreviation for the name of an element. But it signifies more than this, for whenever two or more symbols are used in regard to chemical transformations, they imply not only the elements by name, but also definite weights of the elements, bearing the same relation to one another as the atomic weights, and a number placed in juxta- position to the symbol indicates a multiple of these weights. Thus Hg and I 2 imply that the mercury and the iodine are to be taken in the proportions 199'8 and (126'5 x 2). Formulae. When two or more symbols are placed in im- mediate juxtaposition, it is implied that the elements represented are in a state of combination in the relative quantities indicated. Thus HgI 2 stands for a compound of mercury and iodine, the red iodide of mercury, and H 2 for a compound of hydrogen and oxygen, water. Equations. The sign + placed between two or more elements or compounds indicates that the bodies in question are brought together under such conditions that they may react upon one another; and the sign =, that when they have so reacted, the resulting products are those placed to the right-hand side of the sign =. Thus Hg + I 2 = HgI 2 indicates that when mercury and iodine are brought together in such a condition that they act upon one another in the chemical sense, they form the red iodide of mercury indicated by HgI 2 ; and further, that the quantities which take part in the reaction, and which go to form the compound HgI 2 , are in the relative proportion already spoken of. Distribution of the elements. We are acquainted with a comparatively small part of the earth's crust, but we may arrive at an approximate idea of its composition by analyzing such samples of the granitic or other rocks as may be taken to typically represent the composition of the whole. An estimate of the masses of the earth, air, and water, together with the consideration of 880 such analyses of typical rocks, shows that three-fourths of the whole is made up of oxygen and silicon. The quantities of the more commonly occurring elements de- duced in this way are given below TEXT-BOOK OF CHEMISTRY. Oxygen 49-98 per cent. Silicon 25-30 n Aluminium ... 7-26 Iron 5-08 Calcium 3-51 5) Magnesium ... 2-50 ;> Sodium 2-28 n Potassium ... 2-23 j> Hydrogen 0-94 )j These are all elements of low atomic weight, the elements of high atomic weight occurring either in very small quantities and in particular localities, or being almost entirely confined to the igneous rocks. There is also a marked tendency for elements and compounds (as minerals) of a like chemical character to associate themselves together. For instance, minerals containing nickel usually con- tain cobalt and frequently iron ; cadmium is always associated with zinc; the platinum metals, platinum, palladium, iridium, rhodium, osmium, and ruthenium, are always found together, and so in many other cases. An examination of the sun, stars, nebulae, etc., by means of the spectroscope, has shown that in these bodies there exist the same elements as are found in the earth. Some have not yet been detected, and there is evidence of the existence of one or two bodies 1 that are new to us ; but iu general we have no reason to regard the composition of the heavenly bodies as essentially different from that of the earth. 1 Quite recently it has been found that Helium, one of the bodies which had already been observed to exist in the corona of the sun, occurs in the gases extracted from certain minerals by heating them in vacuo. No evidence of its existence in the earth had previously been obtained. DEFINITION AND AIMS OF CHEMISTRY. aUESTIONS. CHAPTER I. 1. What is limestone, and how is it converted into lime? 2. The composition of a body may be determined. by analysis or by synthesis; explain these terms, and give examples in illustration of your answer. 3. How would you show by an experiment that rust contains iron ? Under what circumstances does iron become covered with rust ? 4. Define the terms element and compound. Why do we regard oxygen as an element and water as a compound ? 5. What properties of matter do you define as physical properties, and what as chemical properties? 6. State in separate paragraphs (ft) the physical, (/>) the chemical properties of any element or compound you choose. 7. What are the principal agencies by which chemical decom- position is effected ? 8. Give the precise meaning to be attached to the symbols H, C0 2 , H 2 0, Hgl, HgI 2 . 9. What elements form the essential constituents of (ft) lime- stone, (6) sandstone, (c) water, (d) air? 10. How may we arrive at an estimate of the relative amounts of the elements occurring in the earth's crust ? UNIVERSITY CHAPTER II. THE NATURE OF CHEMICAL REACTION. WHEN two or more bodies react upon one another, it is desirable to conduct an inquiry not only into the qualitative nature of the change, but also by weighing and measuring to determine the quantities of the materials which have taken part in or resulted from it. The former of these steps involves a knowledge of the properties of the reacting bodies, and a determination of those resulting from the reaction ; the latter is effected by the process of estimating the amount of each of the bodies concerned with the aid of the balance. The necessity for adopting both these courses of procedure will be evident when we have considered the matter in greater detail. For the present we shall, as a prelude to such consideration, follow the changes which take place as actually observed in some simple instances. Exp. 3. Having weighed out 15'8 grammes of mercury and 10 grammes of iodine, rub them intimately together in a mortar, 1 it will be observed that the mercury, and at the same time the iodine, both gradually lose their characteristic appearance, and in place of them we have a powder every particle of which is green and amorphous. The product shows none of the characteristic properties of either mercury or iodine. 1 The operation is facilitated by adding a few drops of alcohol, also smaller quantities of the substances may be" used, provided the same proportion is 10 THE NATURE OF CHEMICAL REACTION. 11 Exp. 4. Add a further quantity of 10 grammes of iodine, and bring this into intimate contact with the green powder, and it will be transformed into a red powder, the iodine as such disappearing. In this case also all the particles of the red powder will be found to possess the same character. Exp. 5. Again add 10 grammes of iodine, and perform a similar operation. On carefully examining the resulting substance, we shall be able now to discern two kinds of particles, and by gently warming, or by solution in alcohol, the whole of the iodine added in this experiment may be extracted, whilst in the case of the givijn or red powder, it is no longer possible to extract the iodine by such means. In the tirst two experiments the mercury and the iodine have undergone a process quite different from any ordinary admixture, since they no longer exist in the free condition, and they are held together by a force different in character from ordinary cohesion. The phenomena are those which accompany cheiuico.l, combination, and the mercury and iodine are bound together in the compounds formed, by chemical attraction. In this, as in all other chemical reactions tli at we are acquainted with, it is necessary that the substances between which the re- action takes place shall be brought into intimate contact, and we learn therefore that before chemical reaction can take place tJiere must be contact between the particles. Chemical attraction is therefore unlike gravitation or magnetism, for these forces can be exerted over measurable distance. Had we- taken, in the first experiment, a smaller quantity of iodine relatively to the mercury, we should have had some of the mercury remaining uncombined, just as iodine remained un- combined in Exp. 5. We might have proceeded by trial to determine what proportions of the mercury and iodine must be used in order to form the green or the red powder respectively, without excess of mercury or of iodine. Had we done so, we should have arrived at numbers bearing the same relation to one another as the quantities actually employed in Exps. 3 and 4. We learn, therefore, that T58 grammes of mercury combine with 1 gramme of iodine to form the green substance, and with 2 grammes to form the red 12 TEXT-BOOK OF CHEMISTRY. substance, and that chemical combination takes place in these proportions. But on examination, the relation 1-58 : 1 will be found pro- portional to the atomic weights of mercury and iodine, and we may therefore represent the chemical reaction which has taken place, thus Hg + I = Hgl ; and the result of the second experiment may be expressed Hgl + 1 = HgI 2 ; and of the third HgI 2 + I = Hgl 2 + I, no change having taken place. We have then, above, an instance of chemical combination by contact alone. It is, Innvever, much more usual to find tliat chemical action is not set up until the reacting bodies are brought into much more intimate contact than is possible by mechanical admixture. Thus, it is promoted by heat, which brings the particles of the reacting bodies into a more mobile condition, and even vaporizes them ; or by solution, which acts similarly. In cither case a very much greater freedom of the particles is effected, and this brings about more intimate contact, and assists chemical reaction in a very remarkable degree. To illustrate this, and to afford a further example of chemical change by combination of elements, we shall consider the behaviour of iron and sulphur. Exp. 6. Mix together 17 '5 grammes of iron filings and 10 grammes of flowers of sulphur ; a greenish-looking powder results, but both the iron and the sulphur can be seen in it by means of a magnifying-glass ; moreover, a magnet will extract the particles of iron, and the sulphur will remain, both unchanged mere contact does not suffice to bring about chemical combination in this case, and even if we were to dissolve the sulphur in bisul- phide of carbon, the iron would still remain unacted upon. But if we gently heat the mixture of iron and sulphur, a reaction takes place, and instead of the original substances we have a dark brown mass formed, from which neither the iron can be extracted by a magnet, nor the sulphur be dissolved by bisulphide of carbon. THE NATURE OF CHEMICAL REACTION. 13 Chemical combination has taken place between the iron and sulphur in the proportions of the atomic weights of these elements, and sulphide of iron has been formed. The chemical change may be expressed by the equation Fe + S = FeS. A second type of reaction is that in which a compound sub- stance is decomposed into simpler constituents. To illustrate this we may examine the action of heat on the red oxide of mercury. Exp. 7. Heat a small quantity of red oxide of mercury in a test- tube ; it will, if pure, slowly disappear, and there will be formed a bright metallic mirror on the sides of the tube. The mirror readily yields silver- white liquid globules, answering in all re- spects to mercury, whilst in the tube it may be found that the air has been replaced by a gas which supports combustion even more strongly than air. A glowing splinter placed in the tube will bur.st into a flame. The gas in the tube is oxygen, and the red powder has been resolved into mercury and oxygen. If we should further deter- mine the weight of the oxide of mercury taken, and that of the mercury left, we should find that the composition of the oxide of mercury, that is, the relation between the amount of mercury and oxygen it contained, is constant. The third type of chemical change is that which takes place when the substances entering into the reaction are complex, and the reaction consists in a mutual exchange of constituents between the bodies. This is termed double decomposition. Exp. 8. Place in a test-tube some of the sulphide of iron produced in Exp. 6, and add a little dilute sulphuric acid. A gas is evolved, having au odour of rotten eggs. Soon the evolution of gas ceases, even though some of the sulphide of iron remain. The liquid has changed its character, aud is now no longer capable of acting on sulphide of iron. Allow any particles to settle, and when the liquid is quite clear pour it off into a porcelain basin, aud evaporate it nearly to dryness ; on cool- ing, pale green crystals will separate out. By adding more sulphuric acid the whole of the sulphide of iron may be dis- solved, and more of the green crystals obtained. 14 TKXT-BOOK OP CHEMISTRY. The reacting bodies, sulphide of iron and sulphuric acid, have been transformed into a gaseous body and the green crystals. An examination of the products shows that the hydrogen of the sulphuric acid and the iron of the sulphide of iron have mutually replaced each other, giving rise to the gas (sulphuretted hydrogen SH 2 ), and the green crystals (sulphate of iron). And if we determine the relative quantities of the substances concerned in the reaction, we shall find that they are such as to be represented by the equation FeS + H 2 S0 4 = FeS0 4 + H 2 S. Ferrous Sulphate Indestructibility of matter. In the experiments with mercury and iodine, we have seen that though the mercury and iodine have disappeared as such, there has been formed a new body, an iodide of mercury, and by means of the balance we may satisfy ourselves that the weight of the iodide of mercury is exactly the same as the combined weight of the mercury and iodine used to produce it. And so it will be in the case of the sulphide of iron. But in the case of the oxide of mercury in Exp. 7, the proof will be more difficult to carry out. The oxide of mercury and the mercury resulting from its decomposition we may arrange to weigh with an approach to accuracy, but the oxygen which is given off is not so easily dealt with. It must be collected in such a way that there shall be no loss, and when this is done it must be weighed. Both these operations call for considerable experimental ability ; when, however, they are successfully per- formed we find, as in the previous cases, that the total weight of the mercury and oxygen is exactly that of the oxide of mercury which has been decomposed. And whatever chemical changes we submit to the test of the balance, the conclusion is the same : there is no exception. We are therefore convinced by such results that matter may be transformed, but cannot be destroyed. The familiar operations of combustion at first sight seem opposed to this statement, but it is merely that the products of combustion are chiefly gaseous, and thus, unless special means are adopted, they escape recognition. We have indeed solid TIIK XATU11E OF (.'HKMICAL REACTION. 15 fin-'l reacting with gaseous oxygen, with the production of gaseous ctirbon dioxide and water. This will be more fully appreciated when we have considered the nature of combustion. Transformations of Energy. Up to this point we have learnt that when chemical action is set up there is a rearrange- ment of the chemical constituents of the bodies which take part in the reaction. Such a view, however, overlooks altogether the energy which is always associated with chemical change. Thus heat is usually evolved or absorbed in a chemical change. Let us therefore make some observations on the heat evolved during chemical combination. Exp. 9. Place in a beaker 100 grammes of freshly-burnt lime broken into pieces about the size of a hazel-nut ; pour a litre of cold water (noting its temperature) over it, stirring after a few moments, when the lime has fallen to powder, with a glass rod. The lime enters into combination with some of the water^and In at is evolved, as may be seen by taking the temperature with a thermometer. A rise of temperature approaching 30 C. will be noted, and this notwithstanding that some of the heat is dissipated by radiation during the experiment. This large amount of heat is due to the combination of the lime with the water to form a new compound, viz. slaked lime, a substance met with in solution in lime-water. But we must not assume that all the heat evolved when sub- stances react upon one another is due to the chemical changes which occur. Frequently, changes of physical condition take place alongside chemical changes, and must be taken account of if we desire to estimate the heat arising from chemical action. Tin-, following experiments with sulphuric acid and water will afford a striking example of this. Exp. 10. Measure out 50 cubic centimetres of concentrated sul- phuric acid and 300 cubic centimetres of water. The tempera- ture 1 of the liquids should be noted. Pour the water into a beaker, and then add the sulphuric acid, and stir them well 1 It is convenient to have both at the same temperature, which may be effected either by cooling them to zero in ice, or by allowing them to stand for some hours in the same room. The former is best for experiment 11 and the latter for experiment 10. 16 TEXT-BOOK OF CHEMISTRY. together with a glass rod. Again note the temperature, and it will be found to have risen about 40 C. Exp. 11. Measure out 50 cubic centimetres of concentrated sul- phuric acid, and weigh out in a beaker 300 grammes (1 grammo water = 1 cubic centimetre) of snow or finely-powdered ice. Pour the acid into the snow and stir well. The snow will be observed to melt rapidly, and on taking the temperature of the mixture it will be found that instead of the considerable rise of temperature which occurred in the previous experiment, we have a lowering of temperature approaching eighteen degrees Centi- grade ; that is to say, with sulphuric acid previously cooled to zero the final temperature will approach - 18 C. An excellent freezing mixture may indeed be made by mixing sulphuric acid and snow. Now Low are we to account for the great difference between the results of these two experiments ? The sulphuric acid in the latter experiment combines with the water, and the heat evolved in consequence of the combination is just as great as it was in the former. On comparing the experiments, the only difference we note is that in one case liquid water is used and in the other solid water (snow), and the heat absorbed in the fusion of the snow must be held accountable for the variation of 58 C. between the two records. Again, when a gramme of hydrogen is burnt in oxygen, the heat arising from the combustion is sufficient to raise the tem- perature of a litre of water a little more than 34 C. About five-sixths of this heat is due to the transformation of chemical energy in the process of combination into heat, the remainder coming from the condensation of the steam formed during the combustion. Water may be decomposed again into its elements by means of a current of electricity, and affords an interesting example of the transformation of energy. In the course of the decom- position electrical energy is being transformed into chemical energy. If we inquire into the source of the electrical energy, we shall find that it is generated by dissolving the zinc of the cells of the battery in sulphuric acid a transformation of chemical energy into electrical energy. THE NATURE OF CIIKMU'AL REACTION 17 So that here we have an instance of the transformation of chemical into electrical energy, which is transformed again into chemical energy when the water is decomposed. Or again, if we connect up the poles of the battery by means of a thin platinum wire, this will become heated, the electrical energy being trans- formed into heat during its passage along the wire. Conservation of energy. Just as the balance has proved that there is no destruction of matter, so a measurement of the energy concerned in various operations has shown that it is im- possible to destroy energy. "The total energy of any body or system of bodies is a quantity which can neither be increased nor diminished by any mutual action of these bodies, though it may be transformed into any of the forms of which energy is susceptible." Energy may be denned as the capacity for doing work. Steam has a greater capacity for doing work than water, and when steam is converted into water there is apparently a loss of energy, but really only a transformation of part of the energy into the heat which accompanies the condensation of steam to water. Chemical attraction. Such transformations of energy take place in every chemical reaction. The intrinsic energy of hydrogen in the free state is greater than that of the water vapour to which it gives rise when burnt, by the amount of energy (chemical attraction) exerted between hydrogen and oxygen in the process of combination, thus heat is evolved. Freshly-burnt lime when moistened with water becomes hot, and the heat is due to the transformation of the energy of chemical attraction exerted between the lime and water. Similar trans- formations, which are quite manifest, accompany the burning of iron in oxygen, the combustion of coal, etc. Chemical reactions are in general accompanied by an evolution of heat, and the same reaction gives rise (other conditions being the same) to the same amount of heat. It is generally true that the greater the amount of heat generated, the greater is the attraction between the bodies, and the greater the stability of the resulting compound. And it might be thought that the heat evolved is an accurate measure of the chemical attraction exerted ; we must, however, bear in mind that every chemical change is c 18 TEXT-BOOK OF CHEMISTRY. accompanied by changes of physical condition, which are also accountable for part of the heat evolved during chemical reaction. In the large majority of cases it may be accepted that the heat evolved when two substances combine with one another is some measure of the chemical attraction or affinity exerted between them, but an accurate estimate of chemical attraction cannot be obtained till the heat arising from changes of physical condition is measured. Law of Definite and Multiple Proportions. We must now call attention to one other point of great importance, the proportions in which elements combine toyeUn.'r. We have noticed that in the case of the green iodide of mercury, the sulphide of iron, or the oxide of mercury, the proportions in which the mercury and iodine or the iron and sulphur or the mercury and oxygen unite are expressed by numbers which are definite and invariable. If w be the weight of iodine taken, 1'58 w will always be the weight of the mercury which combines with it to form the green iodide of mercury; so if w 1 be the weight of the sulphur in iron sulphide, 1'75 tc? 1 will be the weight of the iron ; and whatever chemical compound is examined, the relative proportions of its constituents are fixed and invariable. This is the law of definite proportions. In addition to this, we notice that the amount of iodine required to form the red iodide of mercury is exactly twice that required to convert the same amount of mercury into the green iodide, a fact which finds expression shortly in the formulae for the two iodides, viz. Hgl, HgI 2 . We have found 1 '58 grms. of Hg combine with 1 grm. of I to form mercurous iodide. 1'58 ,, ,, ,, ,, 2 ,, ,, mercuric iodide. Kelative proportion of iodine combining with the same weight of mercury is 1 : 2. So 12 grms. of C combine with 16 grms. of to form carbonic oxide. 12 ,, ,, ,, ,, 32 ,, ,, ,. carbon dioxide. Relative proportion of oxygen combining with the same weight of carbon is 1 : 2. 32 grms. of sulphur combine with 32 grms. of to form sulphur dioxide. 32 ,, ,, 48 ,, ,, ,, sulphur trioxidf. THE NATURE OF CHEMICAL REACTION. 19 Relative proportion of oxygen combining with the same weight of sulphur is 2 : 3. 14 gnus, of nitrogen combine with 8 grins, of to form nitrous oxide. 14 ,, ,, ,, ,, 16 ,, ,, ,, nitric oxide. 14 ,, ,, ,, ,, 24 ,, ,, ,, nitrogen trioxide. 14 ,, ,, ,, ,, 32 ,, ,, ,, nitrogen peroxide. 14 ,, ,, ,, ,, 40 ,, ,, ,, nitrogen pentoxide. Relative proportion of oxygen combining with the same weight of nitrogen is 1 : 2 : 3 : 4 : 5. These and all other cases may be summed tip in the following statement, which is known as the law of multiple proportions. When one element combines with another in more than one Proportion, these proportions bear a ratio to one another which may be expressed by small whole numbers. If we mix together two liquids like water and sulphuric acid, or two solids such as carbon and sulphur, we may do this in any proportion whatever, and the differences between the relative proportions of the two constituents may be made as small as we please. The number of mixtures that maybe made from the two liquids or the solids, each differing from the other in composition, may be indefinitely large. But if now we seek to combine two substances together, we shall find a marked difference ; 12 parts by weight of carbon may combine with 32 parts by weight of sulphur and no less than this. If more sulphur than this can be induced to combine, the amount will not be indefinitely small or large, as was the case with the mixing operation ; it will be again 32 parts more by weight, that is 12 parts by weight of carbon to 64 parts by weight of sulphur. The amount of sulphur which enters into combination with the same weight of carbon increases not gradu- ally but by steps, each step implying the addition of 32 parts of sulphur per 12 parts of carbon. And if we examine the whole series of chemical compounds which contain sulphur we shall find that combination is invariably a step by step process. We have therefore for each element a mass of matter (the rela- tive weights of which we know, e. g. II = 1, C = 12, = 16, S = 32, etc.), very small it may be, but not indefinitely small, ^ 01 n ^> UNIV.T 20 TEXT-BOOK OF CHEMISTRY. and each act of combination involves the attachment of one or more of these masses and never any fractional part thereof. We may now state Dalton's Atomic Theory thus (1) Matter is capable of division up to a certain point only, the ultimate particles being- called atoms. In the case of the same substance the atoms are all alike, but in the case of different substances the atoms differ in weight and chemical properties. (2) When chemical combination takes place between two substances, it does so between their component atoms. From this it will be seen that if A n be used to denote n atoms of the element A, and B n n atoms of the element B, all the com- pounds which these two elements can form will be included in the table, A 3 B 1 etc. and it is plain that any two compounds in this list must obey the law of multiple proportions : which is thus accounted for by the theory. The absolute weight of the atoms is unknown, but the relative weight can be determined, and adopting hydrogen as unity the values relative to 'hydrogen for all other elements are known as the atomic weights. The smallest mass of sulphur which can enter into combination, the atom, is 32 times as heavy as the smallest mass of hydrogen which can enter into combination. TltK NATURE OF CHEMICAL KEACTlOX. aUESTIONS. CHAPTER II. 1. How \vould you convert the green iodide of mercury into the red iodide ? 2. IIo\v would you ascertain whether a sample of red iodide of mercury contained any free iodine? 3. You are given (a) a compound of mercury and iodine, (b) a mixture of mercury and iodine containing precisely the same amount of each of these elements as the compound; what differences would be observable between the two? 4. State the phenomena which are usually to be observed whilst chemical combination is taking place. 5. In what respects does chemical attraction differ from gravita- tion and from magnetism ? 6. Two elements (solids) are brought into contact, but without undergoing combination ; what means would you employ in order to induce them to combine ? 7. Why is a substance usually more ready to take part in chemical reaction when it is in the form of vapour rather than in the solid condition? 8. Explain in words the precise meaning of the expression Fe + S = FeS. 9. What is meant by combination, decomposition, double decom- position? Give examples of each. 10. What is the nature of the evidence which leads us to conclude that matter is indestructible? 11. What is the nature of the evidence which leads us to conclude that energy is indestructible ? 12. Give an instance of the transformation of (a) chemical energy into heat, (6) electrical energy into heat, (c) electrical energy into chemical energy. 13. What changes other than chemical may give rise to the evolution of heat? 14. Explain what is meant by the Conservation of Energy. CHAPTER III. HYDROGEN AND THE HALOID ACIDS. HYDROGEN. Occurrence. Hydrogen occurs in the free state as an incandescent gas in the sun, but in the earth it is always found in combination with other elements. Water is a compound of hydrogen and oxygen, H 2 ; many oils consist of hydrogen and carbon, and these elements, together with oxygen, form the chief constituents of animal and vegetable tissue, and of organic compounds in general. Hydrogen is usually prepared by the decomposition of water, or of compounds into which water enters as a constituent. Direct decomposition of water. This may be effected either at a high temperature, or by means of a current of electricity. By passing steam through a porcelain tube heated to at least 1000 C., Grove was able to show that a part of it underwent decomposition into hj'drogen and oxygen. But by means of the following arrangement water may be decomposed into the elements hydrogen and oxygen, and these gases may be collected in the proportions in which they exist in water. Exp. 12. The apparatus shown in Fig. 1 is of glass except the wires bearing strips of foil fused into each limb of the U-tube near the bend : these are of platinum, and are called the elec- trodes. The apparatus is filled up to the bulb with water con- taining a little sulphuric acid, 1 and each electrode is connected 1 Water is practically a non-conductor of electricity, and a little sulphuric acid must be added to it to enable the electric current to pass ; indeed we may regard the decomposition as being that of dilute sulphuric acid. 522 JIYDIMMJKN AND TIIK HALOID ACIDS. by a copper wire with a pole of a battery of four Bunscu's or Groves's cells. As soon as the connection is made, gas is seen to rise from the electrodes, and to collect in the tubes. The vol- ume of gas col- lected in one tube will be observed to be twice as great (or rather more, owing to the greater solu- bility of oxygen in water) as that in the other, and on examination it will be found that this gas is inflammable, and shows the pro- perties of hydro- gen, whilst the other will prove to be oxygen. Decomposition of water by the action of certain i m. i. elements. The al- kali metals (K, Na, Li, etc.), and also those of the alkaline earths (Ba, Sr, Ca), decompose water at ordinary temperatures. Only half the hydrogen of the water is liberated in this case, the reaction being represented by the following equation 2Na + 2II 2 = 2NaOH + II 2 . Caustic soda (NaOH) is formed and dissolves in the water, imparting to it a soapy feeling, and rendering it alkaline, as may be shown by pouring red litmus into the liquid. 24 TEXT-BOOK OF CHEMISTRY. Iron, zinc, magnesium, and even carbon, at moderately high temperatures, decompose water. Thus, by passing steam over red-hot iron, the oxygen of the steam combines with the iron, and hydrogen is set free, and may be collected as in Exp. 14. 3 Fe + 4 H 2 - Fe 3 4 + 4 II 2 . Magnetic oxide of iron. Steam passed over red-hot coke forms what is known as water-gas, which contains a large proportion of hydrogen ; oxygen compounds of carbon are formed, however, at the same time, and, being gaseous, pass over with the hydrogen. This method would therefore not be suitable for obtaining pure hydrogen. Fluorine decomposes water at ordinary temperatures with great readiness, and chlorine does so in presence of sunlight. 2 F 2 + 2 H 9 = 4 II F + 2 (ozone is formed here). 2 C1 2 + 2 H 2 = 4 HC1 + 2 . Exp. 13. Small pieces of sodium the size of a pea are thrown upon the surface of distilled water. Hydrogen is given off, and if each piece of metal is held under the mouth of a cylinder of water, by using a gauze net as shown in the diagram, the collected and FIG. 2. ' examined. We learn therefore that water may be decomposed (1) by heat; (2) by a current of electricity ; (3) by some elements which possess a great affinity for oxygen liberating hydrogen ; and others which possess a great affinity for hydrogen liberating oxygen : for example, sodium and chlorine respectively. HYDROGEN AND THE HALOID ACIDS. 25 Action of metals on dilute acids as a means of preparing hydrogen. When hydrogen is required in quantity and of a moderate degree of purity, it is best prepared in this way, zinc and dilute sulphuric acid being convenient reagents for the purpose; some other metals, such as iron or magnesium, may however be employed, and hydrochloric acid may be substituted for sulphuric acid. Indeed, as a general ride, acids, when acted upon by metals, liberate hydrogen as the primary product. Exp. 14. Introduce into a twelve-ounce flask, fitted with safety funnel and delivery-tube as shown in the figure, 10 grammes of zinc, and add 180 c.c. of dilute sulphuric acid. 1 Bubbles of gas will be observed to rise at the zinc, and the gas passing out of the delivery-tube may be collected in strong glass cylinders as shown. FIG. 3. Five cylinders of the gas may be obtained and reserved for an experimental investigation of the properties of hydrogen. When the action has ceased, the clear liquid from, the flask may be poured into a porcelain basin, and evaporated until it has been reduced to about 20 c.c. in bulk. On allowing this liquid to cool, crystals of a white salt will be observed to separate out ; the zinc has displaced the hydrogen of the sulphuric acid and formed sulphate of zinc. Zn + H a S0 4 = ZnS0 4 + H 2 . 1 Prepared by previously mixing the concentrated acid with eight times its volume of water. 26 TEXT-BOOK OF CHEMISTRY. Properties of hydrogen. Exp. 15. Take the cylinder of gas first collected, and holding it mouth downwards, apply a light the hydrogen will bum instantaneously throughout the vessel with explosion, owing to its being intimately mixed with air carried over from the flask in which the hydrogen was generated. The second cylinder, treated in the same way, will probably be found to burn quietly, as it contains very little air. Notice that the hydrogen only burns in this instance where it has access to air, namely, at the mouth of the cylinder ; also that a lighted taper pushed up into the cylinder whilst the hydrogen is burning will be extinguished. "We see, therefore, that hydrogen burns Avhere it comes into contact with the air, but will not support the combustion of a taper. Exp, 16. Take a dry cylinder, similar to those used for collecting the gas, and holding it mouth downwards transfer the hydrogen from one of the cylinders into it by pouring upwards. The hydrogen will rise in the dry cylinder and displace the air from it. Now apply a light to the mouth of this cylinder and there will be a slight explosion, owing to a small admixture of air during the transference, whilst the gas will burn and moisture appear on the sides of the cylinder. We learn from this experiment that hydrogen is lighter than air, and that when it burns water is formed. The burning consists in the combination of hydrogen with the oxygen of the air. As by heat or electricity we are able to decompose water, and ascertain by an analytical method that it is composed of hydrogen and oxygen, so in this experiment we have synthesized water from the elements hydrogen and oxygen. Compounds of hydrogen with the halogens. Fluorine, chlorine, bromine, and iodine constitute a group of elements bearing very considerable resemblance to one another in their chemical characters. The chemical affinity of these elements for hydrogen and for metals shows a gradation from fluorine to iodine in the order given above, decreasing with the increase of atomic weight. Tims, if we consider the stability of the com- pounds of these elements with hydrogen, we find that whilst AND THE HALOID ACIDS. 2? hydrofluoric acid may be strongly heated without decomposition, liydriodic acid is decomposed almost completely by exposure to light, or by heating to dull redness. Also, fluorine combines with hydrogen directly under all cir- cumstances, and will, as we have seen, even decompose water at ordinary temperatures by reason of its great affinity for hydrogen. Chlorine, however, only combines with hydrogen under the stimulus of heat or light, and the direct combination with bromine and iodine is effected with difficulty. It is worthy of remark that their affinity for oxygen, on the contrary, increases with the increase of atomic weight, so that fluorine has not under any circumstances been induced to combine with oxygen ; it is indeed the only element which forms no compound with oxygen. Having thus considered the general relations of the halogen dements to hydrogen, we shall proceed to describe the methods by which the hydrogen compounds are prepared, and the proper- tics of these bodies. PREPARATION AND PROPERTIES OF HYDRO- FLUORIC ACID, HF. This gas is obtained when a fluoride is gently heated with concentrated sulphuric acid ; calcium fluoride (fluorspar) is generally used in its preparation, a platinum or leaden retort being used, since glass is rapidly acted upon by the gas. The equation representing the reaction is CaF 2 + H 2 S0 4 = CaS0 4 + 2 HF Calcium fluoride. Sulphuric acid. Calcium sulphate. Hydrofluoric acid. The pure acid is obtained by heating hydrogen potassium fluoride, KIIF 2 , in a platinum retort with a delivery tube and receiver both of platinum and both kept cool by a freezing mixture : KHF 2 = HF + KF Hydrofluoric acid at ordinary temperatures is a highly corrosive gas, which fumes in moist air, and may be condensed to the liquid form in a freezing mixture ; this liquid boils at 19 C. The gas at ordinary temperatures has a density of 20, corresponding to the formula H 2 F 2 , but on gently warming, its density diminishes rapidly, and approaches the value 10, corresponding to the 28 TEXT-BOOK OF CHEMISTRY. formula HF. It is readily soluble in water, giving an acid reaction (see end of chapter), and the aqueous .solution may conveniently be used for demonstrating its properties. An examination of the elementary properties of the gas may be made without actually collecting the gas. The powdered fluorspar is gently warmed in a small leaden dish, with so much sulphuric acid as will make it into a thin paste. The fumes of the gas must not be inhaled, nor should the acid in any form be allowed to come in contact with the lingers. Exp. 17. Coat a watch-glass with a thin layer of bees- wax, scratch on it some device, and expose to the fumes rising from the dish. The surface of the glass, where the wax has been removed, will be acted upon, the silica of the glass being converted into the volatile silicon tetrafluoride, thus Si0 2 + 4 HF = SiF 4 + 2 H 2 0. Hydrofluoric acid attacks most metals and oxides with the formation of fluorides. The acid fluorides of the alkali metals like hydrogen potassium fluoride (KHF 2 ) should be noticed, because the other halogen acids do not form such salts. It may be remarked also, that when hydrogen fluoride is quite free from water it does not attack glass : similarly perfectly dry hydrogen chloride does not attack sodium. THE PREPARATION OF HYDROCHLORIC ACID GAS, HC1. Hydrochloric acid gas is most conveniently pre- pared by the action of concentrated sulphuric acid on common salt (sodium chloride) 1 ; on gently heating the mixture the following reaction takes place NaCl + H 2 S0 4 XaIIS0 4 + HC1. Sodium chloride. Sodium hydrogen sulphate. and when a higher temperature is employed the sodium hydrogen sulphate reacts further NaCl + NaHS0 4 = , Na 2 S0 4 + IIC'l. Sodium sulphate. The two stages of this reaction may be summed up together thus, regarding only the ultimate products 2 NaCl + H 2 S0 4 = Na 2 S0 4 + 2 HC1. 1 All chlorides, except those of silver ;tnd mercury, yield hydrochloric acid when treated with sulphuric acid. HYDROGEN AND THE HALOID ACIDS. 29 The preparation is carried out in a flask fitted with safety funnel and delivery-tube, as shown in the figure. In consequence of the FIG. 4. great solubility of the gas in water, it must be collected over mercury or in dry cylinders by displacement of air. Properties of the gas. Exp. 18. Pass the gas rapidly through a few cubic centimetres of water ; it will be found to dissolve very freely in the wati-r, yielding a strongly acid solution. The concentrated hydrochloric acid used as a reagent is a saturated solution prepared in this way, and contains about 40 to 45 per cent, by weight of hydro- chloric acid. This experiment shows the very great solubility of hydrochloric acid gas in water. This may also be effectually exhibited by the following device. 30 TEXT-BOOK OF CHEMISTRY. Exp. 19. Fill a large dry flask, of at least two or three litres content, with hydrochloric acid gas by displacement. Fit it with an india-rubber cork, through which passes a tube with stop-cock, and drawn out into a jet as shown. Dip the extreme end of the tube into water and open the stop-cock. Under these con- ditions the gas at first only comes into contact with the water very slowly by a process of dif- fusion, and it is desirable to bring about contact with a larger surface of water by cooling the flask ; this may be done by pouring a few drops of ether over its surface. When the jet once comes into play the water continues to rise into the flask until all the hydro- chloric acid is absorbed. Water at C. absorbs 503 times its volume of the gas. Hydrochloric acid is a colourless gas which fumes in moist air, and has a strongly irritant action on the mucous membrane. A weak aqueous solution of the gas when boiled under normal pressure becomes stronger, until it contains 20'24 per cent, of the gas, and a stronger solution than this, when boiled, grows weaker, and ultimately falls to 20'24 per cent, strength. A solution of this strength distils unchanged at 110 and 760 m.m. Dry hydrochloric acid gas may be condensed under a pressure of 40 atmospheres at zero, forming a colourless liquid. It is a remarkable fact that whilst the aqueous solution of the gas readily acts upon metals, oxides, carbonates, etc., the anhydrous gas and the liquefied acid are much less active. Liquefied hydrochloric FIG. 5. HYDROGEN AND THE HALOID ACIDS. 31 acid is indeed entirely without action upon iron, zinc, magnesium, and many other metals, and will not even decompose anhydrous carbonates. The preparation of hydrobromic and hydriodic acids. These compounds are best prepared by the action of water upon the phosphorus compounds of bromine and iodine. Phosphorus combines directly with bromine and iodine, forming PBr 6 and PI 5 respectively. These compounds are immediately acted upon by water thus PBr 5 + 4 H 2 = H 3 P0 4 + 5 HBr. Phosphorus penta-bromide. Phosphoric acid. Hydrobromic acid. PI 5 + 4 H 2 = H 3 P0 4 + 5 HI. Hydriodic acid. It is not necessary to previously prepare the penta-bromide or penta-iodide of phosphorus, for if amorphous phosphorus and water are introduced into a flask, and bromine or iodine are added wry 34 TEXT-BOOK OF CHEMISTRY. Summing up, we have as methods for the preparation of the haloid salts (1) Direct combination of elements with the halogens. (2) Solution of the metal, the oxide, hydrate, or carbonate in the acid. (3) The addition of the acid or a soluble haloid salt -to a solution of a salt of the metal with the production of an insoluble, or slightly soluble, haloid salt. The nature of haloid acids and salts. In the same sense that we regard the haloid salts as compounds of F, Cl, Br, or I with the metals, we may look upon the haloid acids as compounds of these elements with hydrogen. All acids contain hydrogen, and may be regarded as hydrogen salts in which the hydrogen is replaceable by metals to form what are ordinarily termed " salts " ; they are usually sour to the taste and often corrosive. They all possess the property of turning a solution of the vegetable colouring matter, litmus, red, and a body which exhibits this property is said to have an acid reaction to litmus. Tests for the halogen acids and their salts. 1. A solution of silver nitrate, AgN0 3 , when added to a solution of a halogen acid or haloid salt, gives with Hydrochloric acid, a white curdy precipitate of silver chloride AgCl, soluble in ammonia, insoluble in nitric acid. Jffydrobromic acid, a pale yellow precipitate of silver bromide, AgBr, soluble in strong ammonia, insoluble in nitric acid. Hydriodic acid, a yellow precipitate of silver iodide, Agl, insoluble in ammonia and nitric acid. 2. Free HC1, HBr, or HI, heated with manganese dioxide, or their salts, heated with manganese dioxide and sulphuric acid, evolve chlorine, bromine, and iodine respectively, and these elements are easily recognized by their colour, smell, and bleaching action. 3. Chlorine water (which must not be in excess) added to a bromide or iodide liberates bromine or iodine, and on shaking the liquid with carbon bisulphide, the bromine imparts to it a red colour and the iodine a violet colour. HYDROGEN AND THE HALOID ACIDS. 35 QUESTIONS. CHAPTER III. 1. Name some natural substances which contain hydrogen as an essential constituent. Is hydrogen known to occur in the free state ? 2. How may water be decomposed without the application of chemical re-agents ? 3. Show by a synthetical method that two volumes of hydrogen combine with one volume of oxygen to form water. 4. What elements decompose water (a) at ordinary temperature with the liberation of hydro- gen ; (6) at ordinary temperature with the liberation of oxygen ; (c) at red heat? Give equations showing the nature of the reaction in each case. 5. If you desire to obtain hydrogen in as pure a condititm as possible, what method would you adopt ? 6. If you desire to prepare moderately pure hydrogen in large quantities, what method would you adopt ? 7. Write down equations showing the action of iron and mag- nesium respectively on dilute sulphuric acid. 8. Devise three experiments suitable for illustrating in a striking manner the extreme lightness of hydrogen. 9. What is the action of concentrated sulphuric acid on calcium fluoride, on calcium chloride, and on potassium iodide ? 10. Explain the action of hydrofluoric acid in etching glass. 11. Give the properties of hydrochloric acid gas, and show in what respects this gas differs from hydriodic acid. 12. State briefly the general method of preparing chlorides from metals, oxides, and carbonates respectively, giving equa- tions. 13. How may hydrobromic acid be obtained ? If it should contain free bromine, how would you remove this? 14. State the changes which take place when very concentrated and very dilute hydrochloric acid are respectively boiled for some time in an open vessel. CHAPTER IV. PHYSICAL PROPERTIES OF GASES. ALTHOUGH some of the earlier philosophers regarded air as a fluid, it was not till the seventeenth century that any definite proof of this was given. Nor was it till late in the eighteenth century that (with the exception of air, hydrogen and carbon dioxide) gases were distinguished from one another as different chemical substances. At the present day, and especially amongst the non-metals and their compounds, we are acquainted with a large number of bodies which exist under ordinary atmospheric conditions in the form of gas. The examination of the properties of gases, and of the part which they play in chemical reaction, cannot be carried out without a knowledge of their physical properties. We purpose then to show how the weight of a gas may be determined, having regard to the allowances to be made for temperature and pressure. The General Property of Weight of Gases. This may be shown in the following way Exp. 24. Suspend two similar beakers of about 5 litres content, ono of them in an inverted position, at the ends of the arms of a rough balance and counterpoise them. ISTow pass hydrogen into the inverted beaker by means of a tube held as far up the beaker as possible, but without coming into contact with it, and gradually lowering the tube towards the mouth of the beaker. The hydrogen PHYSICAL PROPERTIES OF GASES. 37 will accumulate in the upper part of the beaker and gradually fill it to the mouth, pressing out the air before it. The arm of the balance will at the same time be deflected, and the beaker in question will rise. Add small weights till the arm becomes horizontal again. If the beakers are of the size prescribed above, about 6 grammes will be necessary for this. If we continue to pass the gas after this, the equilibrium of the balance will not be disturbed, but on withdrawing the tube the arm bearing the inverted beaker will soon begin to fall again, showing that it is now gaining weight. This is due to the dilFusion of the hydrogen out of the beaker and its replacement by air, and it will be seen how gradual such a process is. We have seen then by this rough experiment that when 5 litres of air are replaced by 5 litres of hydrogen, a loss of weight occurs equal to about 6 grammes, which represents that a litre of hydrogen is approximately 1'2 grammes lighter than a litre of air. Exp. 25. When the whole of the hydrogen has been cleared t>ut of the inverted beaker and replaced by air, pass carbon dioxide down- wards into the other beaker, and note that it is depressed, show- ing that whilst hydrogen is mnoh lighter than air, carbon dioxide is licaricr than air. The weight required to restore equilibrium in this case will be found to be approximately 3 grammes. To determine the weight of gases more accurately ; suspend from the arms of a delicate chemical balance two globes fitted with stop-cocks, and having a content of about 500 c.c. In order to eliminate corrections for buoyancy of the air the two globes should be as nearly as possible similar. Exhaust one of. the globes carefully at the air-pump, and then close the stop-cock. Now attach it at one arm of the balance, and the other globe filled with dry air at the other arm, and note the weight to be added in order to bring it into equipoise. This will be the weight of 500 c.c. of air, say 0'618 gramme at the temperature and pressure prevailing at the time, say 9 C. and 750 m.m. pressure. Now attach the vacuous globe to a supply of dry hydrogen and again equipoise. Instead of 0'618 gramme we find only 0*575, and we have the data necessary to determine (1) The relative density of hydrogen and air. 38 TEXT-BOOK OF CHEMISTRY, (2) The weight of a litre of hydrogen or air. For the present we only know that one litre of air and of hydrogen at 9 C; and 750 m.m. pressure weigh respectively 1'236 grammes and 0'086 gramme. ~\Ve shall now consider the effect of temperature and of pressure on the volume and density of a gas. Relation of Volume of Gases to Temperature. Exp. 26. Take one of the globes previously mentioned, and plunge it (with the stop-cock open) in a bath of water cooled down to C. by the addition of fragments of ice. "When it has remained some minutes, and the air in it has been reduced to zero, close the stop-cock and carefully dry the outside of the globe. The other globe is to be heated to 100 C. by steam or boiling water, the stop-cock is then closed, and the globe dried. Attach both to the balance, and the latter will be found to be considerably lighter than the other. The air in the globe owing to expansion has been partly expelled from the globe. The expansion which a gas undergoes is a constant, and inde- pendent of the chemical composition of the gas. Dalton found the expansion to be -^-g part of its volume at ^f for each incitement o/l G. in temperature. Tin's is, however, more usually known as the Law of Charles. Stated in another form we have 273 vols. of gas at C. become 274 vols. at 1 C. ,, 5, .. 275 ,, 2 C. 276 3 C., and so on; also 272 ,,-lC. 971 9 P 55 5) 5) llt - 11 11 * ** 270 ,,-3C. Now the absolute zero of temperature is - 273 C., and convert- ing the temperatures stated above into degrees absolute by the addition of 273, we see that the volume of the gas will be At 270 absolute, 270 volumes 271 271 272 272 273 273 & c ., that is the volume of a gas is directly proportional to its absolute temperature. PHYSICAL PROPERTIES OF GASES. Relation of volume of Gases to the pressure to which they are subjected. An experimental investigation of this may be made by using the simple apparatus here described. A B C is a bent glass tube of even diameter, one limb of which is made at least 8 feet long, and the other, provided with a tap at the extremity, is 40 inches. A side tube is provided at B, for running off mercury from the longer limb. It is not necessary to graduate the tubes throughout, but the following points may be marked on the shorter limb (1) a point 4 inches from C. (2) a point 6 inches from C. (3) a point 12 inches from C. (4) a point 24 inches from C. (5) a point 39 inches from C. And on the longer limb (6) a point 63 inches higher than the level of (5). (7) a point 95 inches higher than the level of (5). Open the tap and pour in mercury to the level (3), then close the tap, and al- low mercury to run off till it falls to level of (5). The pressure to which the gas is subjected is now that of the atmosphere (say 30 inches of mercury, minus the column of mercury in the shorter limb that stands above the point (5), i. e. 15 inches of mercury). The length of the tube occupied by the gas is now 24 inches instead of 12 inches at the outset. The 40 TEXT-BOOK OF CHEMIST11Y. pressure on the gas originally to that exerted now is in the ratio 30 : 15, or 2 : 1, and the volume of the gas (the tube being of even diameter throughout) is in the ratio 12 : 24, or 1 : 2. Now pour in mercury till it reaches the level of (6) in the longer limb, and we shall find that in the shorter limb it will then stand at level (2). Tbe length of the tube occupied by the gas is now 6 inches, or the volume is in the ratio 1 : 2 of that which it originally occupied. The pressure is 60 : 30, or 2 : 1. Finally pour in more mercury till the level (7) is reached in the longer limb, and we find that in the shorter limb it will stand at level (1). The length of the tube occupied by the gas is now 4 inches, or the volume is in the ratio 1 : 3 of that which it origin- ally occupied. The pressure is 90 : 30 or 3 : 1. That is, placing the respective ratios of pressures and volumes side by side we have Pressure increased, 1 : 2. Volume decreases, 2 : 1 decreased, 2:1. increases, 1 : 2 Q.I 1 . Q ,, ,, tJ . -L. ,, ,, A . O, or when the temperature remains constant the volume oci-ujtied />// a gas is inversely as the pressure. This is known as the law of Boyle from the fact that he first gave definite experimental proof of its truth in 1662. In France and Germany it is often called Marietta's Law, Mariotte being credited with the independent discovery of the law fourteen years later than Boyle. It may be expressed shortly by the formula P. V = a constant. P. being the pressure, and V. the volume occupied by the gas under that pressure. If the volume is taken as unity under a pressure of 1 atmo- sphere, the law may be stated thus P. V = 1. The above description is only true for a perfect gas under moderate pressure and temperature. No perfect gas exists in reality : hydrogen, nitrogen, and a few other gases behave at ordinary temperatures and pressures nearly like a perfect gas, but at very low temperatures or high pressures even these no longer agree strictly with the laws as stated. It is found indeed that all gases when placed under certain extreme conditions of PHYSICAL PROPERTIES OF CASKS. 4 L temperature and pressure, behave abnormally, and ultimately pass into the liquid state, and it is only when they are far removed from this liquid state (i. e. at temperatures and pressures such that they are far above the boiling-point of the liquid) that they obey Charles' and Boyle's laws. Some gases such as sulphur dioxide and carbon dioxide liquefy much more readily than others, for instance the former gas liquefies at ordinary atmospheric pressures, even at - 10 C., and it will be seen by reference to the following tables that they form exceptions. The expansion co-efficient for air under standard pressure is .,!.., or 0*003666 for 1 degree centigrade, but Amagat found for sulphur dioxide between and 10 it is 0*004233 10 20 0-004005 at 50 0-003846 100 0-003757 200 0-003G95 As an instance of the behaviour of a readily condensible gas under high pressure, we may give the results of Andrews relating to carbon dioxide. This gas was exposed at a constant temperature to the pres- sures (in atmospheres) given in the table, with the result that the volume decreased with increasing pressure more rapidly than is required by the expression P. V = 1, so that P. V in all cases was smaller than 1. For P = 12-01 P. V = 0-951 = 17-09 P. V = 0-918 = 24-81 P. V = 0-858 = 34-49 P. V = 0-767 Liquefaction of gases. By a combination of high pressure and low temperature every gas can be liquefied. The following table gives the temperatures and pressures at which some of the commoner gases become liquids Carbon dioxide at - 80 C. and 1 atmosphere pressure, or at - 20 C. 23 or at + 20 C. 58 Sulphur dioxide at - 10 C. 1 or at + 10 C. 2-3 or at + 30 C. 5'3 42 TEXT-BOOK OF CHEMISTRY. Nitrogen at - 193 C. and 1 atmosphere pressure or at - 160 C. 14 or at - 146 C. 52 Air at - 191 C. 1 or at - 140 C. 39 Ethylene at - 103 C. 1 . A gas cannot always be liquefied by pressure alone. There is in fact a temperature peculiar to every gas above which the gas cannot be liquefied by any pressure whatever. Thus Andrews has shown that at temperatures above 31 C. it was impossible to liquefy carbon dioxide by pressure. This temperature is called the critical temperature of the gas, so that the critical temperature of carbon dioxide is 31 C. The pressure which a gas exerts at its critical temperature is called the critical pressure. The following table gives these two con- stants for a number of gases- Critical temperature. Critical pressure. Nitrogen - 146 C. 33 atmospheres. Oxygen - 119 C. 50 Nitric oxide - 93 C. 71 Marsh gas - 100 C. 50 Carbon monoxide - 140 C. 39 - It will be noticed that the five gases in the table have very low critical temperatures ; these gases and hydrogen were until recently called permanent gases, because until 1879 all attempts to liquefy them had failed owing to the temperatures employed being above the critical point. Hydrogen has the lowest critical temperature of all gases, 1 and it has only recently been liquefied by Olszewsld. Various methods have been employed in liquefying gases. Faraday was able to liquefy a large number of gases by means of their own pressure in glass tubes. To liquefy chlorine in this way the yellow crystals of chlorine hydrate, C1 2 8 H 2 0. are brought into a glass tube of about 1 c.m. in diameter, and closed at one end. The tube is then bent at right angles at about its middle point and sealed. If now the sealed end be placed in a 1 The newly-discovered gas helium has resisted liquefaction even under con- ditions which were found sufficient to bring about the liquefaction of hydrogen. PHYSICAL PROPERTIES OF GASES. 43 freezing mixture, whilst the other end containing tlio hydrate is gently wanned, a comparatively large volume of chlorine is liberated, and the pressure of the accumulated gas together with the low temperature employed is sufficient to bring about its liquefaction. If silver chloride be saturated with ammonia gas, it forms the compound 2 AgCl. 3 NH 3 , and this body treated in the same way evolves ammonia in such a quantity as to liquefy by its own pressure. With many gases a much lower temperature is required than can bo obtained by using an ordinary freezing mixture. Pictet liquefied oxygen by submitting it to very high pressure in a copper tube at - 120 C. This low temperature was obtained by Kurrounding the copper tube with liquid carbon dioxide, and 1hcn causing this to boil with great rapidity by exhausting the vessel in which it was contained. Recent experimenters employ liquid ethylene in place of carbon dioxide, and in this Avay a temperature of 200 C. may be obtained. The Metric System of Weights and Measures. Before proceeding to further detail in regard to the relative density of gases, it will be well to adopt certain units of mass and volume, and the metric system has been found convenient for all operations in which weighing and measuring are concerned. The unit of length in this system is the metre, which is equiva- lent to 39-37 inches. The unit of volume is that of a cube whose side is ^ of a metre, equivalent to very nearly one-sixteenth of a cubic inch, and the unit of weight is the weight of this volume of water, tho temperature being that at which water has its maximum density, viz. 4 C. This weight is termed the gramme, and is equivalent to 15-432 grains. The prefix l-ilo indicates the multiple 1000, thus 1 kilogramme = 1000 grammes = 15432 grains = abt. 2*2 Ibs. The prefixes deci, centi, and mull respectively indicate the fractional parts iV? T^SI an d nnnr- 1 decimetre = T V metre = 3'937 inches. 1 centimetre = TOTT ?? = 0'3937 1 millimetre = T75 W *= 0-03937 44 TEXT-BOOK OF CHEMISTRY, One inch is thus slightly more than 25 millimetres. 1 decigramme = T V gramme = 1*5432 grains. 1 centigramme = T J 7 = 0-15432 1 milligramme = ToW = 0*015432 A measure of volume very frequently employed is the litre, which is the volume occupied by a kilogramme of water ; it is therefore equivalent to a cubic decimetre, or, in English measure, 61-027 cubic inches. Whenever the specific gravity of a liquid or solid is spoken of, water is used as the standard of comparison ; thus, if we say that sulphuric acid has a specific gravity of 1*84, we imply that it is 1-84 times as heavy as water, and hence one cubic centimetre of such acid will weigh 1*84 grammes. Hydrogen is in like manner employed as the standard by which to express the density (or better, specific gravity) of gases. One litre of hydrogen at standard temperature and pressure (i. e. C. and 760 m.rn. mercury) weighs 0-0899 gramme, and when we say that nitrogen has a density of 14, we mean that it is 14 times as heavy as hydrogen ; one litre of it should therefore weigh (0*0899 x 14) grammes. In calculations bearing upon the weight and volume of gases, it is convenient to bear in mind the volume occupied (at C. and 760 m.m.) by a gramme of hydrogen ; this is, of course, -litres, or 11-12 litres. 0-0899 The volume occupied by 1 gramme 6f nitrogen is . 0*0899 x 14 litres, and by 14 grammes of nitrogen ,^7^ - litres, that is V* VO7t/ X JL4: again 11*12 litres. And in general, the volume occupied by x grammes of an elementary gas, when x is the atomic weight of the element, is 11-12 litres. It must be added that sometimes air is taken as the standard of density ; air is 14*383 times as heavy as hydrogen, and one litre of air at standard temperature and pressure weighs 1-293 grammes. Combining 1 volumes and relative density of gases. Shortly after Dalton had enunciated his atomic theory, Gay PHYSICAL PKOPERTIES OF GASES. 45 Lussac announced the discovery of the Law of Combination of Gases by volume, which may be stated thus Wlien fjases combine together they do so in volumes which bear a xintjde ratio to one another and to that of the product. The relative volumes which do so combine are also found to be represented by small numbers. Thus actual experiment shows that 2 vo'.s. of hydrogen and 1 vol. of oxygen combine to form 2 vols. of water vapour. 1 vol. of hydrogen and 1 vol. of chlorine combine to form 2 vols. of hydrochloric acid gas. 2 vols. of carbon monoxide and 1 vol. of oxygen combine to form 2 vols. of carbon dioxide. 1 vol. of nitrogen and 3 vols. of hydrogen combine to form 2 vols. of ammonia, that is* 1 vol. of water vapour is formed from/ 1 , vo1 ' v 2 , oxygen. 1 ,, hydrochloric acid ,, ,, - 1 " t hydrogen and chlorine, lioxide ' A " .carbon monoxide and , oxygen. , hydrogen and , nitrogen. * Hence if it is assumed that equal volumes of gases contain the same number of atoms or ultimate particles, we see that an ultimate particle of water must contain one ultimate particle of hydrogen, and half an ultimate particle of oxygen. Now according to Dalton's Atomic Theory, the ultimate particle of a body is indivisible, and such a statement as the foregoing cannot be accepted. Avogadro however had drawn a distinction between two kinds of ultimate particles, viz. atoms and molecules, and we shall see that by the adoption of his views, the Atomic- Theory and Gay Lussac's generalization may be brought into harmony. An atom is the smallest particle of an element which can enter into, or be expelled from chemical combination. (See p. 19.) A molecule is the smallest particle of any substance which can exist in the free state. 46 TEXT-BOOK OF CHEMISTRY. It will be clear that the smallest particle of a compound which can exist is the molecule ; in the case of elements we have reason to believe that the molecule consists in some cases of single atoms, in others of aggregates of two or more atoms. Having distinguished between atoms and molecules, Avogadro set forward a hypothesis of the greatest importance, viz. That equal volumes of all gases at the same temperature, 53'0 2 I* Icdine at 1500 C. ... 63-3 126-5 126 5 1 Sulphur at 500' C. ... 96-0 32-0 192-0 6 S 6 Sulphur at 1000 C. ... 32-0 32-0 64-0 2 S 2 Ozone ... 240 16-0 48-0 3 3 Phosphorus ... 62-0 31-0 124-0 4 r 4 Arsenic ... . ... 159-8 74-9 299-6 4 As 4 PHYSICAL PROPERTIES OF GASES. 49 Since the common gaseous elements have a vapour density equal to their atomic weight they are generally regarded as having a normal vapour density. In other cases the vapour density is said to be abnormal, and instances of both conditions will be found in the above table. All gaseous substances, whether they be elements or compounds, exist in the free state as molecules, and whenever an element or compound is expressed by means of symbols, this must be borne in mind. 1 molecule of hydrogen is H 2 molecular weight 2-0 1 ammonia is NH 3 17-0 1 water vapour is H 2 18'0 1 hydrochloric acid gas is HC1 36*4 We see from the remarks that have been made, that a very definite meaning is attached to the numbers placed alongside the symbols which represent elements or compounds. In writing equations to express chemical reactions regarchnust therefore be paid to the state in which the bodies concerned exist. If in the solid condition, the molecular structure is usually undefined, and a mere empirical statement of the quantity of the " reagent" employed must be made. 6 S 3 S 2 and S 6 all represent 192 parts by weight of sulphur. The first is the form used for expressing a certain weight of solid sulphur, the second expresses the same weight of sulphur in the form of vapour at 1000 C., and the third the sulphur in the form of vapour at 500 C. So H 2 + = H 2 and KC10 8 = KC1 + 3 would be incorrect, since in the first equation free oxygen is employed, and we have learnt that in this state there are two atoms in the molecule, and in the second equation 3 would indicate that ozone was the gas resulting from the decomposition of KC10 3 : this is not the case. The correct forms of expression would be obtained by doubling the formulae 2 H 2 + 2 = 2 H 2 and 2 KC10 3 = 2 KC1 + 3 2 . E 50 TEXT-BOOK OF CHEMISTRY. QUESTIONS. CHAPTER IV. 1. What gases were known to the earlier chemists ? 2. Describe an experiment showing that air has weight. 3. How would you determine the density of air as compared with hydrogen ? 4. A gas under a pressure of 890 m.m. of mercury occupies 240 c.c., what volume would it occupy under standard pressure (760 m.m.) ? 5. The volume of a gas at C. was found to be 240 c.c., what volume would it occupy at 10 C., at - 10 C., at 100 C., and at - 100 C., the pressure remaining constant? 6. A litre of gas is collected at C. and 760 m.m. pressure, what volume would it occupy at 10 C. and 780 m.m. pressure ? 7. Given that a metre is 39'37 inches, calculate the number of cubic inches in a litre, and determine in the same measure the equivalent of 150 c.c. 8. A liquid has a specific gravity of 1-45, find the \veight in grammes of 100 c.c. of it, and also the volume of it that will just weigh 100 grammes. 9. If a litre of hydrogen weighs 00899 grin,, find the number of litres of it that will weigh 1 grm., and also the volume occupied by a gramme of oxygen. 10. What is meant by the vapour density of a body ? 11. Enunciate the hypothesis of Avogadro and state the evidence in favour of its acceptance. 12. Give instances of the elements whose vapour density is abnormal. How are these cases reconciled with Avogadro's hypothesis ? 13. Taking the molecular weight of hydrogen as unit, write down the molecular weight of the following bodies in the gaseous condition: nitrogen, phosphorus, arsenic, ozone, bromine, carbon bisulphide, and ethylene. 14. Correct the equations K + H 9 = KOH + H, S0 2 +0 =S0 3 , NaCl + H 2 S0 4 = Na 2 S0 4 + HC1, H 2 O + C1 2 =2 HC1 + O. CHAPTER V. COMPOUNDS OF HYDROGEN WITH OXYGEN AND SULPHUR. WATER. When pure, water is a clear and tasteless liquid ; under ordinary circumstances it may be regarded as colourless, but in reality it has a faintly bluish tinge, which is perceptible when white light is passed through a stratum of about 20 feet in thickness. It freezes at zero Centigrade, and boils under normal atmospheric pressure at 100 C. ; leaving no residue on evaporation. It is chiefly remarkable for its solvent properties, and there are few chemical substances which are not dissolved to some extent by water. The chemical composition of water. It is easily demonstrated (see Exp. 27) that water is composed of hydrogen and oxygen, but this simple experiment gives us no information as to the proportions in which the hydrogen and oxygen combine ; it will be necessary to proceed to quantitative determinations, which may be either by volume or by weight. If the determination by weight alone were made we could, knowing the relative density of hydrogen and oxygen, deduce the composition by volume, and vice versd. 51 TEXT-BOOK OF CHEMISTRY. Exp. 27. The fact that water is composed of hydrogen and oxygen may be shown by burning hydrogen in oxygen or air, and condensing the pro- ducts of the com- bustion by holding a cool glass vessel over the flame. Moisture may be seen to form on the sides of the vessel, and in a little while this will run to- gether into drops which will be found to show the proper- ties of water. Not only hydrogen, but also bodies which contain hydrogen, such as coal gas and paraffin, when burnt give rise to the formation of water vapour, and hence the condensation of moisture often ob- served on the win- dows of a room. FIG. 8. By such means it is established that water consists of hydrogen and oxygen. Further experiments are, however, necessary before we are able to say in what proportions the hydrogen and oxygen occur. In Chapter III. it has already been shown that water may be decomposed by heat, by the electric current, and by the action of certain elements. These processes are all based upon the decomposition of water, and they indicate that the hydrogen obtained from the decomposition of water is twice the volume of the oxygen contained in it. The volumetric composition of water may, however, be determined with much greater accuracy by a synthetical process. HYIWOGKN' WITH OXYGEN 7 AND SULPHUR. OO Composition of water by volume. The method employed at the present day, which we owe to Bunsen, is similar in principle to that employed by Cavendish in 1781, but capable of greater accuracy, and is moreover applicable to gases in general. A tube of even bore, about 700 millimetres in length, is used. FIG. 9. This is furnished with platinum wires to enable the gases to be 54: TEXT-BOOK OF CHEMISTRY. "sparked," and millimetre divisions are etched on the tube. The "eudiometer," as such a tube is called, is first calibrated so that its relative volume down to any given graduation is known. It is then moistened on the inside with a few drops of water, filled with mercury and inverted in a trough containing mercury. Pure oxygen sufficient to occupy about- one-tenth of the volume of the eudiometer is now passed in, and the exact level of the mercury in the eudiometer and in the trough is read. Hydrogen is then added equal to about six or seven times the volume of the oxygen, and the levels of the mercury again read. The temperature and pressure existing at the time must also be noted. The eudiometer is now closed by pressing it down firmly on an india-rubber cushion at the bottom of the trough, and the spark is passed. Under these circumstances the whole of the oxygen enters into combination with hydrogen, and as the water which forms con- denses, a partial vacuum is formed inside the tube, and on gently raising it from the cushion the mercury is seen to rise. After allowing sufficient time for the gas to regain the temperature of the room (much heat having been generated by the combination which has taken place) the levels of the mercury in the eudiometer and trough are again read. We have now the whole of the data necessary for ascertaining the relative volumes of hydrogen and oxygen which have united to form water. The volumes occupied by the gases are all re- duced so as to represent standard conditions, and correction is made for the tension of aqueous vapour. 1 When this has been done, let us suppose Oxygen taken occupied 12 volumes. Hydrogen added 80 Eesidual hydrogen 56 1 If a tube closed at one end and open at the other, and about one metre in length, be completely filled with mercury and inverted over a vessel containing mercury, the mercury will fall in the tube until the difference in level between the mercury in the trough and in the tube is about 7 in. in. If a few drops of water are now allowed to rise through the mercury into the vacuous space above it. part of the water will be vaporized and cause a depression of the mer- cury in the tube. This is because the water vapour exerts a pressure. This pres- sure is called the tension of aqueous vapour, and has a particular value at each particular temperature. Hence, in the case in point, the pressure on the gas will be the total pressure as calculated from the levels, less the tension of aqueous vapour. HYDROGEN WITH OXYGEN AND SULPHUR. 55 It is evident that 12 volumes of oxygen have entered into com- bination with 24 volumes of hydrogen to form water. If we arrange to surround the eudiometer with a steam-jacket, so as to prevent the condensation of the water, we shall be able to ascertain that the volume of the water vapour produced is ex- actly that of the hydrogen it contains. We may summarize these faets in the statement Two volumes of hydrogen combine with one volume of oxygen to form two volumes of water vapour or steam. Cavendish in 1781 was the first to ascertain the composition of water. He introduced a mixture of two volumes of hydrogen and one of oxygen into a strong glass vessel fitted with two wires, which passed into the inside of the vessel so as nearly to touch one another. The electric spark was passed by means of the wires, and the gases exploded. By repeating the experi- ment many times, he was able to show that oxygen combines with twice its volume of hydrogen, and that the liquid resulting from the combination was water, Composition of water by weight. Many oxides, such as those of lead, copper, iron, etc., when heated in a current of hydrogen give up their oxygen, and are " reduced," as it is termed, to the metallic condition. In this reduction the oxygen combines with hydrogen with the production of water. If, then, we can ascertain (1) the weight of the water formed, and (2) the weight of the oxygen which has gone to form it, we shall have by difference the weight of the hydrogen contained in the water, and thus a full synthesis of water by weight. Very careful ex- periments have been performed in this way, using oxide of copper (CuO) as the medium for the supply of the oxygen. The equation expressing the reaction is CuO + H 2 = Cu + H 2 0. Our requirements for the performance of the synthesis are (1) Pure hydrogen. (2) A known weight of oxide of copper. (3) A means of collecting and weighing the whole of the water produced. Dumas and Stas, in 1843, performed the synthesis of water in this way with extreme care, and the requirements above- mentioned were attained in the following manner. The hydrogen, 56 TEXT-BOOK OF CHEMISTRY. prepared by the action of zinc on sulphuric acid, was purified by passing it through nitrate of lead, sulphate of silver, and caustic potash, and then carefully drying it by passing it over phosphorus pentoxide. The oxide of copper was placed in a bulb A, the weight of both being determined. The greater part of the water con- densed in the bulb B, and the rest was absorbed ip U tubes containing solid caustic potash C and phosphorus pentoxide D. FIG. 10, Weighings before and after the experiment show (.) The loss of weight of the oxide of copper, that is, the amount of oxygen used ; (6) The gain in weight of the second bulb B and the U tubes succeeding it, that is, the amount of water formed. As the combined result of nineteen determinations, they found that the amount of oxygen used was 840-161 grammes and the amount of water formed 945 '439 grammes. Water consists, therefore, of 840'161 grammes of oxygen and 105*278 ,, hydrogen ; or one part by weight of hydrogen combines with 7'98 parts of oxygen to form water. HYDROGEN WITH OXYGEN AND SULPHUR. 57 Water of crystallization. Many salts, when they are allowed to crystallize from solution, contain water, which is associated with them in definite proportions, and it cannot be regarded otherwise than as water in combination with the salt. There is, however, very little stability in the combination ; for instance, copper sulphate crystallizes with the composition CuS0 4 . 5 H 2 0. At 100 C. 4 H 2 is set free, and the remaining molecule of water requires a temperature of 240 C. to liberate it. Alum crystallizes with 24 H 2 0, 10 H 2 separate at 100 C., a further 9 H 2 at 120 C., and nearly the whole of the remainder at 280 C. In some cases, indeed, such as crystallized sodium car- bonate or washing soda, Na 2 C0 3 . 10 H 2 0, the salt loses water or effloresces at ordinary temperatures in a dry atmosphere. The amount of water of crystallization which attaches itself to a salt varies according to the temperature at which the crystals form. Thus, from a solution of sodium sulphate, crystals of Na 2 S0 4 . 7 H 2 can be obtained at temperatures below 2^ or crystals of Na 2 S0 4 . 10 H 2 (Glauber's salt) at temperatures below 34: while above 34 crystals of Na 2 S0 4 are obtained. Epsom salts MgS0 4 . 7 H 2 furnishes another example giving MgS0 4 . 6 1U>. Frequently, salts which at ordinary temperatures separate from solution in the anhydrous condition, possess water of crystal- lization when crystallized at low temperatures. Thus if a con- centrated solution of common salt be allowed to stand at ordinary temperatures crystals of NaCl are obtained, but at - 10 C. crystals of NaCl. 2 H 2 0, and at - 23 C. crystals of NaCl. 10 H 2 separate: compounds like the two last are called cryohydrates. Hydrates or hydroxides. These possess a higher degree of stability, and in some cases are not decomposed even at very high temperatures. Thus, from caustic soda, which we may regard as Na 2 0. H 2 0, we cannot separate the water at all by heat, nor is it possible to do so in the case of caustic potash. Lime (CaO), when moistened with water, forms CaO. H 2 or Ca(OH) 2 , with the evolution of much heat, and the water is only separated again at a dull red heat. Similarly, S0 3 + H 2 form the very stable body sulphuric acid, H 2 S0 4 , which may be regarded as the hydrate of sulphur trioxide, and P 2 5 + 3 II 2 forms 2 H 3 P0 4 , phosphoric acid. 58 TEXT-BOOK OF CHEMISTRY. HYDROGEN PEROXIDE. Hydrogen occurs in combin- ation with oxygen, not only in the proportion represented by H 2 (as water), but also in that represented by H 2 2 (hydrogen dioxide or peroxide), which contains twice as much oxygen, in relation to hydrogen, as water does. This substance has been found in very small quantities in rain and snow, and also in the water formed by the combustion of hydrogen. It is a very unstable body, and readily undergoes decomposition into water and oxygen ; it bleaches vegetable colours, and is a powerful oxidizing agent, as sho\vn in the following equations PbS + 4 H 2 2 = PbS0 4 + 4 H 2 Lead sulphide. Lead sulphate. H 2 S + H 2 2 = S + 2 H 3 Sulphuretted hydrogen. CaO + H 2 2 = Ca0 2 + H 2 Calcium oxide. Calcium dioxide. In each case one atom of oxygen readily separates from hydrogen peroxide and performs the oxidation, leaving water as the residue. Thus, with lead sulphide we have 4 H,0 2 = 4 H 2 + 2 2 and PbS + 2 2 = PbS0 4 . Ordinary oxygen is, however, not nearly so active as the oxygen directly derived from hydrogen peroxide, and it is very probable that this greater activity is due to the liberation of oxygen in the atomic condition, so that the reaction would be 4H 2 2 = 4(H 2 + 0) and PbS + 40 = PbS0 4 . This is the more likely since, in presence of hydrogen peroxide certain oxides are deprived of oxygen ; thus Ag 2 + H 2 2 = 9, Ag + H 2 + 2 . In such cases there is a single atom of oxygen feebly attached in both compounds, and these are readily liberated and combine to form the molecule of oxygen Ag 2 1.04-0 |OH 2 . Hydrogen peroxide c;m be preserved in dilute solution, and is so prepared by the action of dilute acids on barium peroxide H 2 S0 4 =* BaS0 4 + H 2 2 . HYDROGEN WITH OXYGEN AND SULPHUR. 59 Exp. 28. Add 10 c.c. of concentrated sulphuric acid to 200 c.c. of water, and allow the mixture to stand till it becomes quite cold ; now add little by little, with constant stirring, about 30 grammes of barium peroxide. Allow to settle, and decant off the clear liquid. It is a dilute solution of hydrogen peroxide, and the following experiments may be performed with it (1) To some of the liquid add potassium iodide, iodine will be liberated, and the solution become brown 2 KI + H,0 2 = 2 KOH + I 3 . (2) Make a dark stain of sulphide of lead on filter paper by first moistening it with a solution of a lead salt, say the acetate, and then exposing this to sulphuretted hydrogen. Steep the paper in a little of the hydrogen peroxide solution and it will become white, the black sulphide of lead having been transformed into the white sulphate, as shown in the equation given above. (3) Add silver nitrate to some of the solution, and then caustic soda ; a black precipitate of hydrated oxide of silver Will be formed, and this in contact with the hydrogen peroxide will undergo decomposition in the manner already described ; the effervescence of gas which is seen to occur may be shown to be due to oxygen. Compounds of Hydrogen with Sulphur. Hydrogen combines with sulphur in the same proportions that it combines with oxygen, forming sulphuretted hydrogen (H 2 S) and hydrogen disulphide or persulphidc (H 2 S 2 ). SULPHURETTED HYDROGEN. This is a gaseous body occurring in solution in certain mineral waters, and formed during the putrefaction of animal and vegetable matters which contain sulphur. It is a colourless gas with a disagreeable odour, and is poisonous if inhaled in quantity. It burns in a free supply of oxygen or air, forming water vapour and sulphur dioxide, whilst in a limited supply of air free sulphur is formed. Water at C. and 760 nun. pressure dissolves 4'37 times its volume of the gas, and at 20, 2 - 9 times its volume, the solution possessing the characteristic smell of the gas, and having a faintly acid reaction. The gas is decomposed by heat, the hydrogen it contains being set free, whilst in presence of many metals the sulphur combines with the metal. 60 TEXT-BOOK OF CHEMISTRY. Composition of Sulphuretted Hydrogen. Sulphuretted hydrogen when heated either alone or in contact with metallic tin yields its own volume of hydrogen, that is, the hydrogen set free occupies (under the same conditions of temperature and pressure) the same volume as the sulphuretted hydrogen from which it has been obtained. Now according to Avogadro's hypothesis (p. 46) equal volumes of gases under like conditions of temperature and pressure con- tain the same number of molecules. Hence one 'molecule of sul- phuretted hydrogen yields and contains one molecule of hydrogen. As yet we have not determined the number of atoms of sulphur in the gas. Call this number for the present x, and so H 2 S;e on decomposition = H 2 + S^. We have a ready means of ascertaining the relation of the sulphur to the sulphuretted hydrogen by comparing its density with that of hydrogen and determining the molecular weight of the gas ; this we find to be 34, and so Molecular weight of sulphuretted hydrogen ... 34 ,, hydrogen contained in it ... 2 Weight of sulphur in the molecule by difference ... 32 But 32 is the atomic weight of sulphur, hence the molecule of sulphuretted hydrogen contains one atom of sulphur the value of x is 1, and the equation given above becomes H 2 S on decomposition = H 2 + S, and the composition of the gas is represented by the formula H 2 S. The decomposition of sulphuretted hydrogen by metallic tin is represented by the equation 2 H 2 S + Sn = 2 H 2 + SnS 2) its combustion in excess of air or oxygen by 2 H 2 S + 3 2 = 2 H 2 + 2 S0 2 , and in a limited supply of air or oxygen by 2H 2 S + 2 = 2H 2 + 2S. The following equations represent the reaction of the gas with sulphur dioxide and chlorine respectively S0 2 + 2 H 2 S = 2 H 2 + 3 S, C1 2 + H 2 S =2 HC1 + S, and thus explain the action of these gases in deodorizing the atmosphere of a room contaminated with sulphuretted hydrogen. HYDROGEN WITH OXYGEN AND SULPHUR. 61 Preparation of the gas. Place iu a small flask ferrous sulphide, and fit the flask with a two-holed cork, through which pass a thistle funnel and delivery-tube, and connect with a flask containing a little water to retain impurities carried over. The whole arrangement is shown in the figure. When the gas is 4^ required, pour about 50 c.c. of dilute sulphuric acid down the thistle funnel. The reaction is FeS + IJ 2 S0 4 = FeS0 4 + H 2 S. Ferrous sulphide usually contains free iron, and the sulphur- etted hydrogen prepared from it is thus contaminated with hydrogen Fe + H 2 S0 4 = FeS0 4 + H 2 . The gas may be obtained in a purer condition by the action, aided by heat, of concentrated hydrochloric acid on sulphide of antimony according to the equation Sb 2 S 3 6 HC1 2 SbCK 3 ILS. Antimony trichloride. Exp. 29. Make a solution of the gas in water, and dip in it a blue litmus paper, it will be slightly reddened. Note the odour of the solution. Pour a few c.c. of it into neutral solutions of copper sulphate, lead nitrate, nickel sulphate, . zinc sulphate, calcium chloride, sodium chloride. The following results will be noticed 62 TEXT-BOOK OF CHEMISTRY. With copper sulphate, a dark brown precipitate of cupric sulphide i CuS0 4 + H 2 S = CuS + H 2 S0 4 . Cupric sulphide. With lead nitrate, a dark brown precipitate of lead sulphide : Pb(X0 3 ) 2 + H. 2 S = PbS + 2HX0 8 . Lead sulphide. With nickel sulphate, a dark brown precipitate of nickel sulphide: NiS0 4 '+ H 2 S = NiS + H 2 S0 4 . Ferrous sulphide. With zinc sulphate, a white precipitate of zinc sulphide : ZnS0 4 + H 2 S ZnS + H 2 S0 4 . Zinc sulphide. Iii the case of calcium chloride and sodium chloride there will be no precipitate, owing to the fact that the sulphides of calcium and sodium are readily soluble in water. Now add some hydrochloric acid to the tubes containing the precipitates, and the sulphides of nickel and zinc will be found to dissolve, whilst those of copper and lead will remain. By such a method we may prepare many of the sulphides of the metals, and we shall find them divisible into the following classes (1) Sulphides insoluble in water and dilute mineral acids. (2) Sulphides which are insoluble in water, but soluble in dilute mineral acids. (3) Sulphides which are soluble even in water* The precipitate may be separated by filtration from the solu- tion which remains, and it is possible in this way to separate any member or members of one of these classes from those of another class. Many of the sulphides may also be prepared by mixing the metal (preferably in a finely divided condition or in filings) intimately with excess of powdered sulphur and heating in a porcelain crucible until the portion of sulphur over and above that which will enter into combination with the metal is vola- tilized. Access of air or of gases which may act upon the sulphide is to be avoided. Exp. 30. Sulphuretted hydrogen is, as we have seen, very soluble in water, and it attacks mercury ; also, owing to its offensive nature, and to the fact that it is only slightly heavier than air, it should HYDROGEN WITH OXYGEN AND SULPHUR. 63 be collected by displacement of air. We may, however, collect it over hot water, the solubility of gases being in general smaller the higher the temperature of the solvent. Having obtained a cylinder of the gas by collecting in this way, apply a lighted tapur to the mouth, and note that the gas burns with a pale blue flame, and that a gas (S0 2 ) is formed which has the suffocating odour of burning sulphur 2 H 2 S + 3 2 = 2 S0 2 + 2 H 2 0. There is usually a slight deposit of sulphur on the sides of the vessel due to the cooling of the gas, and the difficulty of access of air in sufficient quantity to ensure complete combustion. If the taper be passed within the cylinder in which the gas is burning, it will be extinguished, showing that sulphuretted hydrogen, like hydrogen, burns in air (or oxygen), but does not support the combustion of a taper. Exp. 31. Detach the preparation flask, and fit it with a tube about 20 centimetres long, and drawn out to a fine jet. The gas may be lighted at the jet when all the air is expelled, and the presence of water in products of combustion may be shown by holding a cool glass vessel over the flame. Also, by depressing the lid of a porcelain crucible into the flame, a deposit of sulphur may be obtained. Now heat the tube some distance away from the orifice with a Bunsen burner or spirit-lamp, and the gas will be decomposed by the heat, and a deposit of sulphur will form a little beyond the point where the heat is applied. Finally, extinguish the flame, and allow the gas to impinge on a piece of filter-paper moistened with nitrate (or acetate) of lead, a dark stain will be produced owing to the formation of sulphide of lead ; by this test the presence of sulphuretted hydrogen may be detected even when present in very small quantities. Tests for Sulphides. (1) Warm the substance with dilute sulphuric acid ; most sulphides are decomposed with the evolution of sulphuretted hydrogen, e. g. ZnS + H 2 S0 4 ZnS0 4 + H 2 S. Zinc sulphide. Zinc sulphate. The sulphuretted hydrogen may be detected by its odour or by its action on paper moistened with a solution of acetate of lead, Pb (C 2 H/) 2 ) 2 . G4 TEXT- BOOK OF CHEMISTRY. (2) Mix a little of a dry sulphide with sodium carbonate arid heat strongly on charcoal with the blowpipe flame. Sulphide of sodium is formed, and may be recognized by the fact that when a little of the product is placed on a silver coin and moistened, a brown stain is produced. All sulphides react in this waj*. HYDROGEN BISULPHIDE, H,S,. This is an oily liquid which separates out when a saturated solution of 'sulphide of calcium is gradually poured (stirring constantly) into a large ex- cess of hydrochloric acid, diluted with twice its volume of water; sulphur is likewise liberated CaS 5 + 2 HC1 = CaCl 2 + 3 S + H 2 S 2 . This liquid bears considerable resemblance to hydrogen peroxide in its chemical properties. It forms persulphides corresponding in character to the peroxides, and acts as a bleaching agent. It is very unstable, and on gentle heating readily breaks up into sulphuretted hydrogen and sulphur, jus-t as hydrogen peroxide breaks up into water and oxygen. HYDROGEN WITH OXYGEN AND SULP1IU aUESTIONS.-CHAPTER V. 1. Write down in separate parngraphs (a} the physical, (6) tlie cliemical properties of water. 2. Under what circumstances does hydrogen combine with oxygen to form water ? 3. Make a list of those properties of water which you regard as being absolutely characteristic of that body. 4. Give briefly two methods by which it may be shown that water is composed of hydrogen and oxygen in the propor- tions of two volumes of the former to one of the latter. 5. Pure hydrogen is pns.sed over heated oxide of copper, and the water which forms is collected ; if the loss in weight of the oxide of copper be 4*20 grammes, and the weight of the water obtained 4'73 grammes, determine the amount ot hydrogen and oxygen in 100 grammes of water. G. How is hydrogen peroxide prepared? Give equations. 7. Define, with examples, what is meant by water of crystallization. 8. It lias been said that hydrogen peroxide behaves both as an oxidizing and a reducing agent ; explain this statement, and illustrate your remarks by references to reactions. 9. In what proportions does hydrogen combine with sulphur? Is there any analogy between the compounds so formed and those of hydrogen with oxygen ? 10. What is the effect of heating (a) hydrogen peroxide, (6) sulphuretted hydrogen, (c) steam ? 11. How would you show (a) that sulphuretted hydrogen contains hydrogen and sulphur, (6) that it contains these elements in the proportions represented by the formula H 2 S ? 12. What is the action of sulphuretted hydrogen on acid solutions of (a) silver nitrate, (6) copper sulphate, (c) lead nitmte V Give equations showing the changes which take place. 13. How is sulphuretted hydrogen collected ? 14. What products are obtained by burning sulphuretted hydrogen (a) in a limited supply of air, (I) in excess of air ? CHAPTER VI. PROPERTIES OF WATER NATURAL WATERS. Physical properties of water. Water occurs not only in the liquid form, but also in the solid form, as ice or snow, and in the gaseous form, as water vapour or steam. Below C. it takes the solid form, and above 100 C., at standard pressure, 1 it passes into steam ; but at lower temperatures, however, water evaporates slowly into the air, and even in the solid con- dition, as snow and ice, evaporation goes on, though still more slowly. Water possesses a high specific heat, and is adopted as the unit with which other bodies are compared ; ice has the specific heat 0*5, and steam 0'48. Changes of volume of water at different tempera- tures. When ice melts, the water which it forms is smaller in volume by nearly 10 per cent, than the ice from which it is formed. Also, as the temperature rises from to 4 C. a further contraction, amounting however only to about T ^ per cent., occurs. 1 For further information concerning the tension of water-vapour and the boiling-point of water consult text-books on physics. CO PROPERTIES OF WATER NATURAL WATERS. 67 At 4 C. water has its maximum density (and hence smallest volume), and above this it expands again as the temperature rises, until at 100 C. it occupies a volume rather over 4 per cent, greater than that at its maximum density. Water vapour has T^-nr the density of liquid water, and the volume of steam at 100 is nearly 1,700 time's that of the water from which it is formed. Latent heat of ice and of steam. When heat is imparted to ice it melts, but the thermometer continues to record C. nntil the whole of the ice is melted, and when water is boiled the temperature of the water remains at 100 C., until it is wholly transformed into steam ; moreover, the steam resulting also shows the temperature of 100 C. Although heat is being continually imparted to the ice or water, as the case may be, the thermometer records no increment of temperature. This heat is termed latent, for although it is undoubtedly communicated to the ice or water, it is unrecognized by the thermometer. The following ex- periments will afford convincing evidence on this point. Exp. 32. 1 Mix 100 c.c. of water at 0C. with 100 c.c. of water at 80 C., stir quickly together, and the temperature of the resulting 200 c.c. of water will be found to be 40 C. (or rather less, in point of fact, owing to radiation of heat during the experiment). Now mix 100 grammes of snow or powdered ice with 100 c.c. of water at 80 C. ; the snow will just all melt, and the result will be 200 c.c. of water at C. In order to compare the results of these two experiments, we must adopt a unit of heat ; this is defined as that amount of heat which will raise one gramme of water 1 C. in temperature, and it is termed a calorie. Since in the former experiment we have as an end result 200 grammes of water at 40 C., and in the latter 200 grammes at C., there is a difference of 8,000 calories in the results as recorded by the thermometer. This amount represents the latent heat of fusion of 100 grammes of water in the solid state (snow), and for one gramme the value would be 80. That is to say, that as much heat is needed to melt one gramme of ice or snow as would raise one gramme of water from C. to 80 C. (See also Exps. 10 and 11, Chap. II.) 1 A simple form of calorimeter for this and similar experiments may be made of thin brass or copper standing on cork supports. 68 TEXT-BOOK OF CHEMISTRY. This property is not peculiar to water, for, as a rule, when a change of physical condition occurs in any substance by the passage from the solid to the liquid state, similar phenomena can be observed. Frequent instances of it occur when salts, such as ammonium nitrate, calcium chloride, etc., are dissolved in water. When the change takes place in the inverse manner, i. e. the passage from liquid to solid state, heat is given out equal in amount to that which, in the former case, had been rendered latent, and indeed the latent heat of steam is most readily ascer- tained by determining in this way the heat given out on the condensation of steam. Exp. 33. By means of the arrangement shown in the figure pass steam into a vessel containing litre ( kilogramme) of water at C. until the temperature indicated by the thermometer just rises to 100 C. FIG. 12. Now weigh the vessel again and let the increase in weight be a? grammes. This represents the amount of steam at 100 C, that PROPERTIES OF WATKtt NATURAL WATERS. 60 has been condensed to water at 100C. But the litre of water originally at C. has now been raised to 100 C., an increment of 25,000 units of heat due entirely to the condensation of these grammes of steam. The heat given out during the condensation of one gramme of steam is therefore 25,000 latent heat of steam. x Supposing, as the result of an experiment, the actual increase was found to be 47^ grammes, then a number approximating as nearly to 536, the value generally accepted, as is to be expected from a rough experiment uncor- rected for radiation, or for heat taken up by the calorimeter itself. 1 Similarly, the conversion of other liquids into vapour is accom- panied by a large absorption of heat ; a few drops of ether placed on the band quickly evaporate and give rise to a sensation of great cold, the heat requisite for the transformation into vapour being abstracted from the hand. And in general, whenever a change occurs in which the particles partake of a freer motion, heat really does disappear as beat, it lining converted into energy of motion which is communicated to the particles. So when the reverse change occurs, the energy of motion is converted back again into heat and reappears as such. Freezing mixtures. By dissolving a quantity of many salts snob as ammonium nitrate or potassium iodide in water, a con- siderable depression of temperature may be obtained, but the freezing mixture most commonly employed is a mixture of common salt and snow or powdered ice, by whicli a temperature as low ns - 23 C. may be reached. The cooling is due to the fact that snow and salt when mixed, rapidly pass into the liquid condition, a change which we have seen is accompanied by an absorption of beat. The heat so 1 Such an experiment will serve to convey a general idea of the meaning of the term " latent heat." The student is referred to treatises on Physics for a more detailed statement. 70 TEXT-BOOK OF CHEMISTRY. absorbed in the passage from the solid to the liquid state is abstracted from the mixture, arid hence the depression of temperature. Any depression below - 23 C. would result in the separation of the solid cryohydrate NaCl. 10 H 2 (see page 57) with an evolution of heat which would counteract the cooling. The limit of temperature that can be attained by the use of salt and snow is therefore - 23 C. "Water as a solvent. Most of the solid substances and gases which we meet with in chemical operations dissolve to an ap- preciable extent in water ; some liquids, such as alcohol and sulphuric acid, associate themselves with water in all proportions; whilst others, such as oils, if shaken up with water separate ag-iin, being taken up by the water either only to a slight extent or not at all. Solubility of solids. The extent to which solid substances are soluble in water under similar circumstances varies according to the nature of the substance. Minerals, such as coal, limestone, quartz, and some chemical compounds, such as sulphate of lime, oxide of lead, sulphide of iron, are only very slightly soluble, whilst others, e. g. nearly all chlorides and nitrates, are freely soluble. In any case, however, there is a limit to the amount of solid matter which can be dis- solved, and when water has taken up as much as it will, we have what is known as a saturated solution. The quantity of a substance required to form a saturated solution is usually greater the higher the temperature, though there is no simple general relation between the temperature and the amount dissolved. Th 3 solubility in parts per 100 of water is given for a few substances in the following table 0C. 2G 6 C. 60 C. 100 C. Potassium nitrate ... 13'3 31'2 85'0 246'0 Sodium chloride ... 35'5 36'0 37'0 39 -6 Potassium chlorate ... 3'3 8'0 19'0 58'0 Sodium chlorate ... 81-9 99*0 136'0 232 '6 Mercuric chloride ... 5'7 7'4 11-3 54*0 Potassium sulphate... 8'3 12-5 17'0 26'0 PROPERTIES OF WATER NATURAL WATERS. 71 Solubility of gases. There is no general connection between tin 1 solubility of gases and their chemical composition. Some ibises, such as nitrogen, hydrogen, and carbon monoxide, are very slightly soluble, whilst others, such as ammonia, sulphur dioxide, and hydrochloric acid, are very freely soluble in water. The solu- bility, instead of increasing with the temperature, decreases, though in no simple relation. One volume of water at the temperatures stated, and under 760 m.rn. pressure, dissolves the volumes of the respective gases given in the following table C. 10 C. 20 C. Nitrogen 0-020 0-016 0'014 Oxygen 0'041 0'033 0-028 Hydrogen 0-019 0'019 0-019 ('.-irbt.n dioxide- 1-799 1-185 0'901 Sulphuretted hydrogen ... 4'371 3'586 2 905 As instances of much more soluble gases we may take- Sulphur dioxide 79-8 56-6 3S 7 ? Hydrochloric arid ... ;"<>:',<) 475'0 444'0 Ammonia 1049'6 812-8 654'0 The influence of pressure on the solubility of gases. The volume of a gas which dissolves in water is directly pro- portional to the pressure (Henry's Law). Thus water at C. dissolves of carbon dioxide At 1 atmosphere pressure 1*8 times its volume. 2 atmospheres ,, 3*6 ,, A 7-9 55 * n j> ,, 2 atmosphere ,, 0'9 ,, 55 3 5) 55 \) V }i ,, )) Soda-water is water charged with carbon dioxide under a pressure of about 4 atmospheres, and so long as this pressure on the surface of the water is maintained this volume of gas will be retained, but directly the pressure is released an effervescence is observed, and gas escapes from the liquid in proportion to the diminution of pressure. 72 TEXT-BOOK OF CHEMISTRY. Solution of mixed gases. At C. and standard pressure a litre of water shaken up with oxygen will dissolve 41 c.c. of the gas. If, however, we mix another gas, say nitrogen, with the oxygen, a smaller volume of oxygen will be found to dissolve, a volume indeed, proportional to the pressure of the oxygen alone (Dalton's Law of Partial Pressures). In the same way the nitrcgen will no longer dissolve to the extent of 20 c.c. (see table), but to a smaller extent, in proportion to the pressure due to the nitrogen alone. For mixed gases, therefore, solution takes place in accordance with (a) the solubility of the gas in question, (6) the pressure exerted by it independently of any other gas or gases that may be present in the mixture. Let us consider the important case of the solution of air (taken as 79 volumes of nitrogen and 21 of oxygen) in water The oxygen dissolved by a litre of water from air will, accord- ing to this law, be not 41 c.c. but - , or 8'6 c.c. per litre. 1UO The nitrogen dissolved will be, not 20 c.c., but , or 15-8 c.c. per litre. So that in consequence of its greater solubility the proportion of oxygen to nitrogen dissolved in water is 8'6 : 15 - 8, and is there- fore 35 per cent, of the whole. Air expelled from solution in water by boiling or by exposure to a vacuum is, then, much richer in oxygen than ordinary air. So taking 0'04 as the normal percentage of carbon dioxide in air, tliis gas will be dissolved, not to the extent of 1,799 c.c. to the litre, but 1,799 ) 100 and from this we ascertain that the air dissolved in water is over 70 times as rich in carbon dioxide as the original air taken. Natural waters. The water which evaporates from Hie surface of sea and land, and passes as water vapour into the air, is the purest form of natural water, and it retains its purity unt'l it begins to fall as drops from the rain cloud. Rain water. When this is collected at the surface of the earth PROPERTIES OF WATER NATURAL WATERS. 73 it has passed through a considerable stratum of air, and dissolved in its passage not only gases normally occurring in the atmo- sphere, but also such impurities as are found there. Even then the solid matter contained in it does not amount normally to more than 3 or 4 parts per 100,000. In the neighbourhood of towns the impurities taken up are more numerous and in larger quantity; also near the sea, and especially during high winds, much sodium chloride is found in rain water. River water. The composition of this water will of course depend on the nature of the surface and of the strata over which the water passes. For instance, a considerable part of the drainage area of the Thames consists of chalk, and its water contains about 30 parts of dissolved matter in 100,000, two- thirds of this consisting of calcium carbonate and sulphate, whilst tho Dee in Scotland, passing over the older strata (prin- cipally slate and sandstone), contains only 5'6 parts of dissolved matter per 100,000, one-fourth of this being calcium salts. Since the water which passes into rivers collects from the surface of the soil, it contains also much more organic matter and carbon dioxide than rain water, arising from contact with plants and decaying vegetable matter. Spring water. The water of springs is rnin water which has percolated through soil and rocks. The composition of spring waters varies very considerably, according to the depth from which the water rises, and the nature of the strata which it lias traversed. In some cases the amount of dissolved matter is very large, and such springs, especially when they have a saline taste or medicinal properties, are known as mineral springs. The springs of Bath and Harrogate contain magnesia and sulphuretted hydrogen, and are known as magnesia and sulphur waters ; a spring near Wooclhall Spa contains free iodine ; many springs contain iron, and are known as chalybeate waters. Mineral springs which rise from great depths are frequently hot, some having a temperature of nearly 100 C. ; this is especially the case in volcanic regions, where the earth's temperature rises more rapidly with increase in depth below the surface. Spring water is bright and sparkling, since it is more fully 74 TEXT-BOOK OF CHEMISTRY. charged with gases than either rain or river water, and contains less organic matter, this being removed in its passage through beds of sofl or gravel. The composition of some typical waters is given in the table further down. Sea water. The matters dissolved or suspended in river or spring water are carried to the sea and remain there, since the water vapour rising from the sea consists of practically pure water. So that notwithstanding the removal of large quantities of these impurities by settling out or by the action of organisms, sea water is still the most impure form of natural water, and owing to the large amount of matter in solution its specific gravity is on the average 1'03. In those land-locked seas which receive much river water the impurities are of course in smaller quantity, but in the open ocean the residue obtained on evaporating 100,000 parts of sea water amounts to about 3,600 parts, of which nearly four-fifths is sodium chloride, the rest being chiefly calcium and magnesium sulphate and mag- nesium chloride. The peculiar taste of sea water is due to the presence of these salts. In the following table details are given of the composition of some typical natural waters, the solids in parts per 100,000, the gases in cubic centimetres per litre COMPOSITION OF SOME NATURAL WATERS. SOLIDS. GASES. Total Residue. Calcium Salts. Magne- sium Batts. Sodium Chlor- ide. Organic Matter. X. 0. (<>,,. Rain Water 3-4 nil. nil. 0-5 I'd 13-1 64 River Water (Thames) _".* 20 1-8 _'; 3-4 15'0 7'4 River Watei (Dee) 9-6 1-4 0-5 i-o 2-2 Spring Water Mineral Water (Bath) 20 236 137 23 j-o 34 Traces Traces 15-8 4-0 w, 2-0 1-0 Sea Water 3,500 140 530 2,650 Traces 12'1 6"0 17-U Chemically pure water may be obtained by distillation, the water being boiled and the steam which is given off condensed. On .1 1'ROPERTIES OE WATER NATURAL WATERS. 75 small scale the apparatus shown (Fig. 1)3) may be used. The waier is boiled in a flask connected with a condenser, through which a continual stream of cold water passes for the purpose of condensing the steam. FKJ. 13. A small quantity of volatile organic matter may be carried over during a first distillation, and soluble matter from the glass condenser and receiver may be present: but on adding a few drops of potassium permanganate solution, and distilling again in platinum apparatus, very pure water is obtained. Drinking water. When water is to be used for drinking purposes, it is of the highest importance that it should be clear and colourless, and as free as possible from organic impurity arising from sewage contamination, or contact with decaying animal or vegetable matter. Dissolved salts, such as ordinarily occur in natural waters, are of less moment than organic impurity, and even such minute quaniities as O3 or 0*4 per 100,000 may be injurious. The taste of drinking wat T is also an important factor, and whilst distilled water and rain water are flat and insipid, owing to the smaller quantity of dissolved gases which they contain, spring water has a characteristic freshness which renders it most palatable. Hardness of water. It is a matter of common experience that the sensation felt when washing the hands differs with waters from different sources. With rain water or the waters derived 76 TEXT-BOOK OF CHEMISTRY. from sandstone areas a lather quickly forms, whilst with cal- careous waters there is a sense of harshness, and a good deal of soap is required to produce a lather ; we notice further that in the latter case a scum is formed which floats on the surface of the water. Waters that readily form a lather are known as soft waters, whilst those which do not are called hard waters. Hard waters contain much dissolved matter, and especially salts of lime or magnesia, which are the chief cause of the hardness. The cleansing action of soap is due to the alkali and fatty acids which it contains, and no lather begins to be produced or in other words no soap is available for cleansing until the whole of the lime or magnesia in the water has entered into combination with the fatty acids to form the scum of which we have spoken. The hardness of any sample of water is indeed measured by adding a standard soap solution little by little to a knoAvn volume of the water until a lather is formed ; the more soap solution required to effect this,. the harder is the water. The softening of water. Carbonate of lime is insoluble in pure water, but readily dissolves in water containing carbon dioxide. Natural waters, especially when they have passed through a layer of peat, become highly charged with carbon dioxide, and if in this condition they come into contact with lime- stone (this being essentially calcium carbonate) they take up calcium carbonate and are rendered hard. Exp. 34. To a few cubic centimetres of lime water add four or five times the volume of distilled water, and pass a stream of carbon dioxide through the clear liquid. At first a turbidity is produced, owing to the formation of calcium carbonate CaO + C0 2 = CaC0 3 . Continue to pass the gas and the liquid will become quite clear again, because we have now carbon dioxide in solution in the water. Divide the clear liquid into two portions, and boil one portion for a little time ; to the other add a volume of lime water equal to that originally taken. In each case the turbidity first noticed will be reproduced, since in each case we have got rid of the excess of carbon dioxide ; in the first case we expelled the excess of carbon dioxide by heat, in the second we added sufficient lime to combine with it and form calcium carbonate. PROPERTIES OF WATER NATURAL WATERS. 77 We may, then, precipitate the calcium carbonate and get rid of the hardness due to this cause, (a) by boiling- the water, (6) by adding to it the proper amount of lime (Clark's process), and after allowing- the precipitate to settle the w.-iter will he found to yield a lather with less soap than before : it has become softer. Hardness due to calcium and magnesium carbonates can be removed in this way, and is termed temporary hardness. The hardness due to sulphates and chlorides of lime, magnesia, etc., cannot, however, be got rid of by boiling, and is known as j><'r>naneiit hardness. Boiling water in a kettle or steam boiler therefore makes it softer, and the "fur" which forms on the vessel is chiefly calcium carbonate which has been precipitated during the process. QUESTIONS. CHAPTER VI. 1. Trace the changes in volume that occur when heat is applied to a mass of ice until it melts and passes into vapour. 2. What do you understand by the term " latent heat" ? Under what circumstances does heat become latent, and what becomes of the heat thus rendered latent ? 3. What is meant by " specific heat " ? The specific heat of air is 0'24 ; find how much the temperature of a cubic metre of air will be raised by the heat given off during the cooling of 100 kilogrammes of water from 25 C. to 20 C. 4. A kilogramme of water at C. is intimately mixed with a kilogramme of mercury at 100 C., until both acquire the same temperature ; the specific heat of mercury being 0'033, find the increase in temperature of the water. 5. How much ice at C. will a kilogramme of mercury at 100 C. just suffice to melt ? 6. How many units of heat are required to raise the temperature (a) of 100 grammes of water 10 C. ; (6) mercury 10 C. ; and to convert 100 grammes of water at C. into steam at 100 C. ? 78 TEXT-BOOK OF CHEMISTRY. %. 7. When is a solution said to bo saturated? What amount of potassium nitrate (see table, p. 70) would be required to form a saturated solution in 150 c.c. of water, (a) at zero, (6) at 50 C. ? 8. What volume of C0 2 will dissolve in 250 c.c. of water under standard pressure, (a) at zero, (6) at 20 C., an,d what at these temperatures when the pressure is that of 76 rn.m. of mercury, and when it is three atmospheres ? 9. A mixture of C0 2 and oxygen containing 95 per cent, by volume of the former gas is shaken up with 500 c.c. of water at standard temperature and pressure ; what volume of each gas will be dissolved ? 10. In what respects does a typical sample of rain water differ from the water of the Thames ? 11. How does it come about that sea water contains more matter in solution than river water ? 12. What are the essential qualities of good drinking water? 13. Why is more soap required to produce a permanent lather with hard water than with soft water ? 14. State the constituents to which the temporary and permanent hardness of water are respectively due. 15. Explain the circumstances under which the addition of lime- water renders a water soft, and state why it does so. 16. How can calcium carbonate be made to dissolve freely in water, and how may the calcium carbonate be precipitated out of such water again without the addition of chemical reagents ? CHAPTER VII. THE HALOGENS : THEIR OXIDES AND OXY- ACIDS. A COMPARISON of the physical and chemical properties of the four elements, fluorine, chlorine, bromine, and iodine, and ofUieir compounds, readily lead one to regard these elements as forming a natural group. And this not so much from the closeness of the resemblance as from the fact that there is a gradual transition in properties which proceeds always in the same order, viz. in the order of tln-ir atomic weights. A general survey of the group will illus- trate this. Physical properties of these elements. Fluorine is a gas which does not condense to a liquid even when cooled down to -95C.; it possesses a very faint greenish-yellow colour; chlorine is much more readily condensible, and has a distinct greenish colour; bromine is a reddish-brown liquid boiling at 59 C. and solidifying at 7 C., whilst iodine is a black crystalline solid which boils at 184 C., its vapour being of a beautiful violet colour. In the gaseous condition these elements have a very irritant action on the mucous membrane which is most marked in the case of fluorine and chlorine, and least so with iodine. They have an odour resembling that of seaweed if they are in a largely diluted condition. 79 80 TEXT-BOOK OF CHEMISTRY. Their solubility in water follows the order of their atomic weight ; chlorine, the most soluble (fluorine decomposes water), dissolving in about half its volume of water, bromine to the extent of three parts in 100 of water, whilst iodine is only very slightly soluble in water, but dissolves readily in alcohol, ether, bisulphide of carbon, or in a solution of potassium iodide. When chlorine is passed into water to saturation at C., yellow crystals having the composition C1 2 . 8 H 2 separate out. On warming these crystals they readily decompose with the evolu- tion of chlorine. Bromine under similar circumstances forms crystals having the composition Br 2 . 10 H 2 0. General Chemical Properties. Whilst the tendency to combine with oxygen increases as we pass from fluorine to iodine, the affinity for hydrogen and the metals decreases. Fluorine forms no compound with oxygen, chlorine can only be made to combine indirectly and forms unstable oxides, iodine however is directly oxidized by nitric acid, and its oxide is much more stable. Hydrogen, on the other hand, combines directly even in the dark with fluorine and at very low temperatures, but with chlorine the combination only takes place on heating or under the stimulus of rays of light of great chemical activity, and bromine and iodine are induced to combine with hydrogen with much greater difficulty. Moreover, the stability of the products of such action, HF, HC1, HBr, HI, shows a falling off in the order named. The interaction of the halogens and water is instructive. Fluorine decomposes water immediately at ordinary temperatures, and with considerable energy, giving rise to the formation of ozone. Chlorine acts at ordinary temperatures only in presence of sunlight, and bromine and iodine are without action. FLUORINE. The isolation of a substance which even at ordinary temperatures decomposes water and other compounds, and attacks solid substances with great readiness, cannot but be attended with difficulty, and it was not till 1887 that fluorine was obtained in the free state. Moissan accomplished this by the elec- trolysis of liquid hydrofluoric acid perfectly free from moisture. Liquid hydrofluoric acid is however a non-conductor of electricity, and it was necessary to add to it potassium hydrogen fluoride THE HALOGENS : THEIR OXIDES AND OXY-ACIDS. 81 (KIIF 2 ) to enable it to conduct the current. The apparatus used in the decomposition consists of a platinum U tube. This tube, which is shown in the figure, is provided with side tubes to lead off the hydrogen which is evolved at the negative pole, and the fluorine from the positive pole. FIG. 14. The negative pole consists of platinum, and the positive pole of an alloy of platinum and iridium, which is less rapidly acted upon by fluorine than any other metal, and these are fitted into the U tube by means of fluor-spar stoppers, which close the end of the U tube gas-tight. Liquid hydrofluoric acid, being a very volatile substance at ordinary temperatures, the apparatus is kept at - 23 C. Fluorine acts with great energy on mercury, sodium, potassium, and magnesium, etc., and less violently on such metals as copper, silver, platinum. Bromine, iodine, carbon, sulphur, silicon, o 82 TEXT-BOOK OF CHEMISTRY. phosphorus, and arsenic likewise combine immediately with the production of flame at ordinary temperatures, fluorides of those elements being formed. Not only water, but the haloid acids. also sulphur dioxide, sulphuretted hydrogen, ammonia, and even silica, are decomposed at once. In fluorine we have then the most active chemical substance known. Manufacture of Bromine and Iodine. Bromine is obtained from the liquors which remain after the extraction of potassium and magnesium chlorides from carnallite (KC1. MgCl 2 . 6 H 2 0) as carried out at Stassfurt. These liquors, containing about 0'25 per cent, of bromine, as magnesium bromide, are first heated and then acted upon by chlorine and steam. The bromine is liberated according to the equation MgBr 2 + C1 2 = MgCl 2 + Br 2 , and escapes as vapour which is condensed by being caused to traverse a worm immersed in cold water. The bromine obtained in this way usually contains chloride of bromine, and this is decomposed by agitation with ferrous or potassium bromide, the bromide being further purified by re-distillation. Iodine. The most important source of iodine at present is the crude sodium nitrate (caliche) of Chili and Peru. It occurs in this body as sodium iodate NaI0 3 . On treating the mineral with water and crystallizing, the bulk of the sodium nitrate separates, and the sodium iodate being much more soluble remains in the mother liquor. This mother liquor is treated with sodium hydrogen sulphite solution which reacts upon it and precipitates the iodine 2 NaI0 3 + 5 NaHS0 3 = 3 NaHS0 4 + 2 Na 2 S0 4 + I 2 + H 2 0. The iodine is allowed to settle out, and then washed and pressed into cakes, being finally resublimed at as low a temperature as possible. In Scotland, iodine is extracted from deep-sea weed, which contains from about 27 to O47 per cent, of iodine. The best process in use for obtaining this iodine is the following The weed, which must after collecting be kept dry until used, is boiled with sodium carbonate and filtered : the filtrate is treated with hydrochloric acid and again filtered, the filtrate in this case being neutralized with caustic soda, evaporated to dryness, and THE HALOGENS : THEIR OXIDES AND OXY-ACIDS. 83 carbonized, The two filtrations have separated two organic bodies resembling cellulose and albumen respectively, and which have found several useful applications. The carbonized residue is treated with warm water, and evaporated until all the less soluble salts (chiefly potassium sulphate and chloride) have crystallized out. The mother liquor is treated with a small quantity of sulphuric acid to decompose sulphides and sulphites. It is then distilled with manganese dioxide and sulphuric acid, the former being added in small quantities at a time. Iodine distils over and is purified by resublimiiig. In the laboratory, sodium chloride, bromide and iodide may respectively be used as sources of the halogens. These when treated with manganese dioxide and sulphuric acid give the following reaction, 11 standing for chlorine, bromine or iodine 2 Xall + 3 1L,S0 4 + Mn0 2 = 2 NaHS0 4 + MnS0 4 + 2 H 2 + R 2 . More usually in preparing chlorine, concentrated hydrochloric acid is substituted for the common salt and sulphuric acid, the reaction being Mn0 = MnCI C1 2 . 4 HCl + The reaction may be performed in a flask fitted with a s;ifety funnel simi- lar to that used in preparing hydro- chloric acid (see p. 20) ; very gentle heat is required. In the preparation of bromine and iodine a small glass retort such as is shown in the accompanying figure is more con- venient, the bro- mine and iodine FlG> 15 ' condensing either in the neck of the retort or in a small receiver which is kept cool by means of a stream of water. 84 TEXT-BOOK OF CHEMISTRY. Exp. 35. Pass chlorine for some minutes through about 50 c.c. of water, and to about 20 c.c. of this add a solution of sulphuretted hydrogen ; hydrochloric acid is formed, the liquid becoming turbid owing to the separation of sulphur, according to the equation C1 2 + H 2 S = 2 HC1 + S. On passing sulphuretted hydrogen into water in which iodine or bromine are suspended a similar reaction takes place, and this is a convenient method for preparing solutions of hydriodic and hydrobromic acids. Exp. 36. Fill a Cowper's tube with chlorine water (see figure), and expose to direct sunlight ; bubbles of gas will be seen to rise in the liquid. When sufficient gas has collected it may be tested with a glowing splinter, and will be found to be oxygen. The change which has taken place is repre- sented by the equation 2 C1 2 + 2 H 2 = 4 HC1 + 2 . Chlorine is soluble in water and acts upon mercury, it is therefore collected by downward displacement, and four jars of it may be obtained in this way, using precautions to avoid inhaling the gas. Exp. 37. Introduce a lighted jet of hydrogen into a jar of chlorine. It continues to burn with the production of fumes of hydrochloric acid, which may be made more visible by bringing a drop of ammonia liquor to the mouth of the jar. Exp. 38. In the same manner burn coal gas in chlorine ; it will be seen that the flame becomes duller and more smoky. Hydrochloric acid is produced as in the previous experiment from the hydrogen in the coal gas, and the smokiness of the flame is due to the separation from the coal gas of carbon with which the chlorine does not unite. Exp. 39. Into a third jar of chlorine bring a piece of phosphorus on a deflagrating spoon and without the application of heat ; presently the phosphorus will ignite and burn feebly with the formation of THE HALOGENS : THEIR OXIDES AND OXY-ACIDS. 85 phosphorus trichloride 2 P + 3 C1 2 = 2 PC1 3 . Bromine and iodine unite with phosphorus directly with the pro- duction of tribromide and triiodide of phosphorus ; it is how- ever desirable in the case of the bromine to reduce the violence of the action by the addition to the bromine of three times its volume of bisulphide of carbon. Antimony, copper and some other metals in a finely divided condition also ignite when plunged into chlorine, and readily combine with bromine and iodine when brought into intimate contact with them. Exp. 40. Heat a piece of sodium in a deflagrating spoon until it lakes fire, and then plunge it into a jar of chlorine; the sodium burns brilliantly, uniting with the chlorine to form sodium chloride. The bleaching- of vegetable colouring matters. Chlorine and to a slight extent bromine possess the property of depriving the leaves of plants, flowers and vegetable dyes of their colour. In the absence of moisture no such action however takes place, the bleaching being due to the oxidation of the colouring matter by nascent oxygen resulting from the interaction of chlorine and water. Certain oxidizing agents which likewise furnish nascent oxygen, notably hydrogen peroxide, have a similar action. Exp. 41. Place a piece of cloth dyed with turkey-red in a stoppered jar of dry chlorine, 1 and leave it some minutes ; no decolonization will occur, but on moistening the cloth it will be bleached. The composition of hydrochloric acid. Hydrochloric acid may be decomposed by the electric current, but owing to the fact that chlorine dissolves in the liquid to a considerable extent, no satisfactory proof of the composition of hydrochloric acid can be arrived at in this way. If, however, the decomposition be allowed to go on until the liquid is saturated with chlorine, the gases hydrogen and chlorine are given off in the proportions in which they exist in hydrochloric acid. An elegant proof of the com- position of hydrochloric acid is furnished by the following course of procedure. 1 Dried by passing it through concentrated sulphuric acid. 86 TEXT-BOOK OF CHEMISTRY. The gases hydrogen and chlorine resulting from the decom- position of hydrochloric acid as described above are passed through thin glass bulbs kept in the dark until all the air is displaced, the bulbs are then sealed off. 1 Exp. 42. Bring the drawn-out point of one of the bulbs (protected from the action of the light) under a solution of potassium iodide and break it off. The liquid will gradually rise in the bulb, assuming a dark brown colour due to the liberation of iodine by the chlorine present. 2 KI + CLj - 2 KC1 + I,, and the whole of the chlorine will be taken up. The hydrogen remaining will be found to occupy just half the volume of the bulb. Hydrochloric acid consists therefore of equal volumes of hydrogen and chlorine. Exp. 43. Expose a second bulb to diffused daylight for some hours. The hydrogen and chlorine will slowly combine to form hydro- chloric acid. If the point of tbe bulb bo now broken oil' under mercury, the gas will be found to occupy the same volume as it did before combination took place, but when dipped into water the hydrochloric acid gas will be absorbed readily, and the water will fill the bulb. From these experiments we learn that one volume of hydrogen combines with one volume of chlorine to form two volumes of hydrochloric acid gas. OXIDES AND OXY- ACIDS OF CHLORINE. Only two oxides of chlorine (C1 2 and C10 2 ) are known, and these are very unstable bodies, and readily undergo decomposition with explosion. Chlorine monoxide, C1 2 O, is prepared by the action of dry chlorine on well-cooled arid freshly precipitated mercuric oxide. HgO + 2 C1 2 = HgCl 2 + CJ 2 0. Chlorine peroxide, C10 2 , is obtained by the action of sulphuric acid on potassium chlorate. The sulphuric acid, of which a large excess is taken, must be kept cool in a freezing mixture and the potassium chlorate added little by little ; on gently heating, C10 2 is given off as a yellow gas. Eucldoriite, which is obtained on warming potassium chlorate with concentrated hydrochloric acid, consists of a mixture of this gas with chlorine. 1 The student is not recommended to attempt to prepare these bulbs. THE HALOGENS : THEIR OXIDES AND OXY-ACID3. 87 Three oxy-acids of chlorine are known Ilypochlorous acid HC10. Chloric acid IIC10 3 . Perchloric acid HC10 4 . Hypochlorous acid, HC10, is a very unstable body, and only known in dilute solution. The free acid is a powerful bleaching agent. Ilypochlorous acid may be prepared- (1) By shaking up together precipitated mercuric oxide and chlorine water. We have seen that in the absence of water C1 2 is formed. (2) By distilling a solution of a hypochlorite with very dilute nitric acid. Hypoclilorites may be prepared by the action of chlorine on caustic alkalies when kept quite cool 2NaOII + C1 2 = NaCl + NaCIO + H 2 Sodium hypochlorite. The most important derivative of this acid is bleaching powder, obtained by passing chlorine over dry calcium hydrate. ^Mineral acids or even carbon dioxide act on the hypochlorites and liberate chlorine, and it is for use in this way that bleaching powder is produced on a large scale. Chloric acid, HC1O 3 . The acid has not been obtained anhydrous, the strongest chloric acid containing more than half its weight of water. In this form it is a syrupy liquid which readily decomposes by heat or in presence of oxidizable sub- stances. It is obtained by adding dilute sulphuric acid to a solution of barium chlorate in just sufficient quantity to combine with the whole of the barium. Ba(C10 3 ) 2 + H 2 S0 4 = BaS0 4 + 2 HC10 3 . The rltltirnlcis are all soluble in water. The alkaline chlorates are prepared by the action of chlorine on hot concentrated solutions of caustic alkalies, the reaction taking the form 6KOII + 3C1 2 - KC10 3 + 5KC1 + 3 H 2 0. Potassium chlorate. The chlorate being much more insoluble, can be readily separated from the chloride by crystallization. Perchloric Acid, HC1O 4 . Prepared by distilling potassium perchlorate in a small retort with concentrated sulphuric acid. KC10 4 + H,S0 4 = KIIS0 4 + HC10 4 . 88 TEXT-BOOK OF CHEMISTRY. It is a heavy oily liquid which fumes in air, and although possessed of considerable stability in the pure condition, it readily decomposes in the presence of organic matter. It is a very powerful oxidizing agent, and detonates strongly when dropped on to dry charcoal ; it sets fire to paper when brought into contact with it. The pet-chlorates are soluble in water and are more stable than the chlorates. They are distinguished from the chlorates by yielding no euchlorine when warmed with hydrochloric acid. When potassium chlorate is fused and the heat continued till the mass becomes pasty, potassium perchlorate is formed, the change which has taken place being 2 KC10 3 = KC10 4 + KC1 + 2 . The perchlorate, being more insoluble than the chloride, may be obtained by dissolving the mass in water and allowing the perchlorate to crystallize out. If the chlorate be strongly heated for some time the whole of the oxygen is given off and the chloride remains as a residue 2 KC10 3 ^ 2 KC1 + 3 2 . Oxy-acids of bromine. Xo oxides of bromine are known, and of the oxy-acids only the hypobromous acid, HBrO, and the bromic acid, HBr0 3 , have been prepared. These are prepared by methods resembling those used for the corresponding chlorine compounds, with which they also agree in their general properties. Oxides and oxy-acids of iodine. Only one oxide of iodine, the pentoxide, J 2 5 , known with certainty, whilst of the oxy- acids, iodic acid, -HT0 3 , and periodic arid) HI0 4 , have been obtained. Iodine pentoxide is a white crystalline powder obtained by heating iodic acid to 180 C. 2 HI0 3 = I 2 5 + H 2 0. At 300 C. it is decomposed into iodine and oxygen. Iodic acid. Concentrated nitric acid lias no action on chlorine, but when heated with iodine, iodic acid is formed. It is also produced when chlorine is passed into water in which iodine is suspended 5 C1 2 + 6 H a O + 2 I = 2 HI0 3 + 10 HC1. THE HALOGENS : TIi::iR OXIDES AND OXY-ACIDS. 89 It is soluble in water, and is a powerful oxidizing agent. The iodates, like the chlorates, readily part with oxygen on heating, leaving iodides. They are formed by the action of caustic alkalies on iodine, the reaction either in the hot or cold solution taking a similar course to that which occurs with chlorine in the hot solution 6 KOH + 3 I 2 = KI0 3 + 5 KI + 3 H 2 0. Periodic acid, HIO 4 . If perchloric acid be acted upon by iodine, periodic acid is formed and chlorine liberated 2 IIC10 4 + I 2 = 2 HI0 4 + C1 2 . Periodates of the alkalies may be prepared by the action of chlorine on the iodate, other periodates by double decomposition of these with soluble salts of the metals. Barium period ate is a body of great stability, and may be obtained by heating barium iodate to redness. Nomenclature of compounds. Compounds may be divided into two classes, those composed of two dements (called " binary " compounds), and those composed of three or more elements. Binary compounds. These may be designated according to the number of atoms of the elements they contain, the number bring usually stated only for the more negative element, the termination of the name being idc. H 2 2 hydrogen dioxicZe. I 2 6 iodine pentoxide. PC1 3 phosphorus trichloride. PC1 6 ,, pentachloiide. Where only two compounds of the same elements exist, the termination otis may be applied to the one with the smaller pro- portion of the negative element (the " lower" oxide, iodide, etc.), and the termination ic to the other. Hgl mercurons iodide. HgI 2 mercuric iodide. Cu 2 cuproiis oxide. CuO cupric oxide. Oxides, which when dissolved in water form acids, are termed " anhydrides," and these, together with the acids they give rise to, receive the terminations ous and ic in the same sense as the oxides. 90 TEXT-BOOK OF CHEMISTRY. N 2 3 nitrons anhydride or nitrogen trioxide. HN0 2 nitrous acid. N 2 5 nitric anhydride or nitrogen pentoxidc. HN0 3 nitric acid. C0 2 carbonic anhydride or carbon dioxide. H 2 C0 3 carbonic acid. Salts take the termination ite or ate according as they are derived from ous or ic acids respectively. H 2 S0 3 sulphurous acid Na 2 S0 3 sodium sulphite. H 2 S0 4 sulphuric acid Na 2 S0 4 sulphate. HS0 4 jjetadlphttric acid Na S0 4 persulphate. Where more than two compounds of the same elements exist, further discrimination is necessary, and the prefix hypo is applied to the lowest and per to the highest. HC10 hypochlorous acid KC10 potassium hypochlorite. HC10 2 chlorous acid KC10 2 ,, chlorite. HC10 3 chloric acid KC10 3 ,, chlorate. HC10 4 perchloric acid KC10 4 perchiorafe. THE HALOGENS : THEIR OXIDES AND OXY-ACIDS. 91 QUESTIONS. CHAPTER VII. 1. Draw up in tabular form a comparison between the halogen elements with regard to (a) their colour, ([) their solubility in water, (c) their action on water, (f tiro yases is inversely as the square root of their densities. Thus the densities of H and are 1 : 16. The square root of these densities is 1 : 4. Hydrogen therefore diffuses through a porous membrane fonr times as fast as oxygen. The comparative rate of diffusion of ozonized oxygen and chlorine has been measured, and the results indicate that Rats of diffusion of Cl : Rate of diffusion of ozone approxi- mately : : 5 : 6. Thus density of Cl : density of ozone approximately as G 2 : 5 2 , or36:25. The actual density of chlorine is 35*4, and hence we must conclude that the actual density of ozone is in agreement with the value based on the acceptance of 3 as representing a molecule of ozone, and occupying the space of a molecule of hydrogen, H 2 . 102 TEXT- BOOK OF CHEMISTRY. QUESTIONS. CHAPTER VIII. 1. How was oxygen first isolated? Mention any oxides which will give up oxygen when they are heated. 2. State how baryta may be used as a means of obtaining oxygen from the atmosphere. 3. Give instances of the formation of oxides by the action of oxygen on elementary substances, (a) where such action takes place at ordinary temperatures, (6) where heat must be applied in order to start the reaction. 4. What takes place when the products of combustion of carbon, sulphur, phosphorus, and sodium are respectively brought into contact with water ? 5. What is an oxide ? Give instances of oxides of the metals which are soluble in water, and of oxides which are insoluble in water. 6. How do acid-forming oxides (anhydrides) differ from basic oxides? What is usually the effect of bringing together solutions of these two classes of oxides ? 7. Given metallic magnesium and sulphuric acid, how would you prepare a specimen of Epsom salts (MgS0 4 . 7 H a O) ? 8. Give examples showing that the same oxide may at one time function as the acidic constituent of a salt, and at another time as the basic constituent. 9. How do the peroxides differ (a) in composition, (6) in their chemical deportment, from ordinary oxides ? 10. Give two methods by which ozone may be produced. 11. How may ozonized oxygen be distinguished from ordinary oxygen (a) without the application of reagents, (6) by means of chemical tests ? 12. What experiments tend to show that ozone is a more active oxidizing agent than oxygen ? 13. The molecule of 0x3' gen being represented by 2 , that of ozone is found to be 3 ; how has this been established ? 14. State the law of diffusion of gases. It is found that 10 c.c. of oxygen diffuse through a porous plug in one minute; what volume of l)3'drogen, marsh gas, sulphur dioxide, and ozone respectively will diffuse under the same conditions ? CHAPTER IX. SULPHUR AND SULPHUR DIOXIDE. Occurrence of sulphur. Sulphur is one of the comparatively few elements which occurs in quantity in the uncombined con- dition. In Europe it is found in the neighbourhood of active or extinct volcanoes in Italy, Sicily, Iceland, etc., being- usually associated with mineral matter. In combination with hydrogen it is found as sulphuretted hydrogen in certain mineral springs, and with metals as mineral sulphides, such as iron pyrites, FeS 2 ; galena, PbS ; zinc blende, ZnS ; and cinnabar, HgS. Sulphates of lime (gypsum) and barium (heavy spar) also occur in some localities in considerable quantity. We see then that sulphur either free or in combination is widely distributed. Extraction of sulphur. Sulphur melts at 115 C., and in the molten condition can be run off from the earthy impurities and obtained in a state of moderate purity. It boils at 440 C., giving off brownish-red vapours which readily condense again on cooling, and the further purification of the sulphur may be effected by distillation in an iron retort, the vapours being passed into a brick chamber where they condense. (Fig. 18.) At the out- set when the chamber is cool the product obtained is a fine powder, called " flowers of sulphur," for just as water vapour at temperatures below zero (the melting-point of ice) condense in the form of snow, so in the case of sulphur there is formed by rapid cooling finely divided sulphur. 103 104 TEXT-BOOK OF CHEMISTRY. When the temperature of the chamber rises above the melting- point of sulphur (115 C.), the product of the condensation is liquid sulphur, and this is run off into moulds where it is cast into sticks known familiarly as u brimstone." FIG. 18. Sulphur is largely used in the arts for the production of matches, gunpowder, sulphuric acid, and as a source of sulphurous acid for bleaching wool, straw, and silk. Physical changes of sulphur under the action of heat. Exp. 51. Put about 30 grammes of sulphur in a wide test-tube, and heat it as evenly as possible in the flame of a Bunsen burner. At 115 C. it will be seen to melt, and at a slightly higher tempera- ture it forms a limpid liquid of a pale yellow colour. As it gets hotter the liquid grows more viscid and darker in colour, this stage occurring between 120 C. and 250 C. Above 250 C. it again becomes more mobile, and at 440 C. it boils and gives off a brownish-red vapour whose density is 96 times that of hydrogen SULPHUR AND SULPHUR DIOXIDE. 105 (the molecule, S 6 , see p. 48), and when this vapour is heated to 1000 C. its density is only 32 times that of hydrogen (the mole- cule, S 2 , see p. 48). Pour some of the sulphur at about 350 C. in a thin stream into a beaker of water, and note the production of plastic sulphur. Allotropic modifications of sulphur. Some elements, notably sulphur, carbon, and phosphorus, show different properties, according to the particular treatment to which they have been subjected, and the conditions under which they have passed into the solid form. The differences observed are chiefly of a physical nature, relating to specific gravity, hardness, melting-point, solu- bility, and the like, but accompanying these there are variations in chemical behaviour towards reagents. The varieties of form which show such differences of physical character, or of chemical behaviour, are termed allotropic modifications. Sulphur exists in the crystalline form, showing two allotropic modifications. (1) Octahedral sulphur. (2) Prismatic sulphur. It exists also in the plastic form, a third allotropic modification obtained by suddenly cooling the molten sulphur, when at the temperature of about 350 C. it p;isses from the condition of a viscid liquid to the more mobile form. Amorphous sulphur, often, called "milk of sulphur,'' is perfectly white arid quite insoluble in bisulphide of carbon. This constitutes a fourth allotropic modification of sulphur. Octahedral sulphur. Sulphur is found naturally in rhombic pyramids resembling octahedra, and it is in this form that it separates out from solvents, such as bisulphide of carbon, on slow evaporation. The specific gravity of rhombic sulphur is 2'045. Prismatic Sulphur. Sulphur in this form is no longer rhombic, but monoclinic ; it is also of lower specific gravity, T93, and melts at 120 instead of 115, and when left at the ordinary temperature for some time, breaks up and passes into the more stable rhombic form, as, indeed, all the modifications tend to do. Exp. 52. Melt about 500 grammes of sulphur in a clay crucible, and allow it to cool until a crust forms at the surface ; the crust is then pierced and the still liquid portion poured out. Beneath the crust will be found long prismatic needles of sulphur. 106 TEXT-BOOK OF CHEMISTRY. Plastic sulphur. Whilst in the crystalline form sulphur is brittle, in this condition, as the name implies, it can be moulded with the fingers, or drawn out into long flexible threads. Unlike the modifications previously described, it is only partially soluble in bisulphide of carbon. On standing, it slowly hardens and passes into the ordinary form of sulphur. Amorphous sulphur. This modification, as the name implies, is devoid of any definite structure, and consists of an impalpable powder, the particles of which are often so small that they pass through filter paper. It has a lower specific gravity (1-82) than prismatic sulphur, arid is insoluble in bisulphide of carbon. Exp. 53. Make a moderately concentrated solution of sodium thio- sulphate, or of an alkaline sulphide (e.g. solution of ammonium sulphide), and add a fe\v drops of hydrochloric acid. The solu- tion becomes turbid, and a white precipitate of "milk of sul- phur " is produced. Na 2 S 2 3 + 2 HC1 = 2 NaCl + S + S0 2 + H 2 0. Sulphur combines with many elements when heated with them. Thus it burns in oxygen at about 400 C., and it combines with carbon at a red heat, forming carbon disulphide CS 2 : while chlorine and hydrogen passed into boiling sulphur give sulphur monochloride S 2 C1 2 , and sulphuretted hydrogen respectively. Many metals combine with sulphur when heated with it ; for example iron (see Exp. 6), silver forming silver sulphide Ag 2 S, and copper forming cuprous sulphide Cu 2 S. Exp. 54. Heat sulphur to the boiling-point and until the upper part of the tube is filled with its vapour, and then plunge into it thin sheet copper, or Dutch metal ; the metal glows, and enters into combination with the sulphur to form sulphide of copper. "Alkali-waste," the residue from the soda-ash manufacture (see vol. ii.) contains much calcium sulphide, and sulphur is recovered from it. The waste is suspended in water and acted upon by carbon dioxide, when sulphuretted hydrogen is given off CaS + C0 2 + H 2 = CaC0 3 + H 2 S. Tliis gas is then burnt with just sufficient air to combine with the hydrogen and the sulphur set free 2 H.,S + CXj = 2 H 3 + 2 S SULPHUR AND SULPHUR DIOXIDE. 107 Chlorides of Sulphur. AVhen perfectly dry chlorine is brought into contact with sulphur vapour by being passed over sulphur heated in a retort, combination takes place, with the formation of chloride of sulphur, S-jCL. This is condensed in a receiver fitted to the mouth of the retort and kept cool by water. Fio. 19. Chloride of sulphur is a brownish-yellow liquid which boils at 144 C., fumes in moist air, and is decomposed by water; it is used as a solvent for sulphur. When chlorine is passed into chloride of sulphur kept cool in ice, dichloride of sulphur, SC1 2 , is formed, and if the tempera- ture be kept sufficiently low ( 22 C.) a further addition of chlorine takes place, and tetrachloride of sulphur, SC1 4 , is obtained. The dichloride and tetrachloride are both liquids which on heating readily give up chlorine, leaving behind S 2 C1 2 . Thionyl chloride, SOC1 ; . Chlorine monoxide, CI 2 0, combines directly with sulphur (dissolved in chloride of sulphur), forming SOC'g, which is also formed by the action of dry sulphur dioxide on PC1 5 (p. 161). Thionyl chloride is a colourless liquid which boils at 78 C., and in presence of water is decomposed thus + H 2 = S0 2 + 2 HC1. 108 TEXT-BOOK OF CHEMISTRY. SULPHUR DIOXIDE, S0 2 . When sulphur burns in air or oxygen, sulphur dioxide is formed, and for purposes in which admixture with nitrogen or the excess of oxygen is of no moment, the gas may be prepared by this method. On the manufacturing scale indeed sulphur dioxide is sometimes so obtained, though more usually a sulphide containing a large proportion of sulphur such as iron pyrites, FeS 2 , is employed (see p. 116). Preparation of sulphur dioxide. When the gas is required in a tolerably pure condition the following method is applicable Exp. 55. About 20 grammes of metallic copper are placed in an eight-ounce flask provided with a thistle funnel and delivery tube, and 50 c.c. of concentrated sulphuric acid are poured down the funnel. The flask is then heated on a sandbath, moderating the heat so soon as the action commences. The reaction which takes place is a complex one, but consists essentially in the reduction of the sulphuric acid by copper. Mercury, charcoal, or sulphur may be substituted for copper, but in the case of charcoal the gas which passes off is mixed with carbon dioxide C + 2 H 2 S0 4 = C0 2 + 2 H 2 + 2 S0 2 . With sulphur the reaction is S + 2 H 2 S0 4 = 2 H 2 + 3 S0 2 , sulphur dioxide being formed both from the sulphur itself and from the sulphuric acid used. It remains to be added tli.it all sulphites when treated with a mineral acid yield sulphur dioxide Na 2 S0 3 + 2 H 2 S0 4 = 2 NaHS0 4 + H 2 + S0 2 . Sodium sulphite. Sodium hydrogen sulphate. Sulphur dioxide being very soluble in water cannot be collected over this liquid, mercury may however be used, but as it is more than twice as heavy as air it may be conveniently collected by displacement of air. Several jars may be filled with it, and its properties demonstrated by the experiments given below. Properties. Sulphur dioxide is a heavy colourless gas having a suffocating odour. At 760 m.m. pressure water at zero dissolves 80 times its volume of the gas, and at 10 C. 56 times its volume, the solution having acid reaction. Sulphur dioxide condenses to a liquid under ordinary atmospheric pressure at 8 C., and under 2 atmospheres pressure at C. It can SULPHUR AND SULPHUR DIOXIDE. 109 therefore be obtained in the liquid form by passing the gas into a vessel surrounded by a freezing mixture of ice and salt. Exp. 56. Put a lighted taper into a jar of the gas, it will be extinguished, nor will the gas itself burn. Metallic potassium when previously ignited will however burn at the expense of the oxygen in this gas. Exp. 57. Show the great solubility of the gas by the method used in experiment 19 (page 30), or by passing the gas through 10 c.c. of water until a saturated solution is obtained. Note the acid properties of the solution, and that it possesses the odour of the gas. As oxidizing agents are those which readily transfer oxygen to other substances which are thereby subjected to oxidation, so reducing agents are those which take away oxygen and effect reduction. Sulphur dioxide is a typical reducing agent; its powers as an antiseptic and as a medium for bleaching silk, straw and wool being due to its affinity for oxygen. Chlorine bleaches in consequence of its bringing about the oxidation of the colouring matter ; sulphur dioxide bleaches, on the contrary, in consequence of its reducing action. The one liberates oxygen, from water CI 2 + H 2 = 2HC1 +0 Nascent oxygen. the other liberates hydrogen H 2 S0 3 + H 2 = H 2 S0 4 + H 2 Sulphurous acid. Sulphuric acid. Exp. 58. Rose-leaves thrown into a solution of sulphur dioxide are bleached, the colouring matter however is not destroyed as when chlorine is used, and the colour may even be restored again by adding a few drops of strong sulphuric acid, or by exposure to air' for some time. Exp. 59. Liberate iodine from potassium iodide by adding a. few drops of chlorine water ; now add sulphurous acid, and the brown colour of the iodine will disappear. 2 KI + Clo = 2 KC1 + I 2 . I 2 + H 2 + H 2 S0 3 = H 2 S0 4 + 2 HI. 110 TEXT-BOOK OF CHEMISTRY. The sulphurous acid reduces water, and is itself oxidized to sul- phuric acid, whilst the hydrogen which is liberated combines with the iodine to form hydriodic acid. A similar reaction takes place with chlorine water. Exp. 60. To a solution of potassium chromate add sulphurous acid, the yellow colour of the chromate will change to green owing to the reduction of Cr0 3 to O 2 3 , the salts of the former being red or yellow, whilst those of the latter are green. This change from yellow to green affords a means of testing for the presence of sulphur dioxide either in the gaseous state or in solution. Composition of sulphur dioxide. This may be determined by synthesis. By means of the arrangement shown (Fig. '20), a fragment of sulphur may be burnt in oxygen. The sulphur is fused on to thin platinum wire, and ignited by pass- ing an electric current along the wire by which the wire is heated. The apparatus and the oxy- gen used in the experi- ment must be free from moisture. The gas in the globe at first expands owing to the heat of com- bustion, and forces the mercury up the further limb, but on cooling it returns to its original volume. It is seen there- fore that during the combination of sulphur and cxygen to form sulphur dioxide no alteration in volume occurs, that is to say w.lpliur dioxide contains its oivn volume of oxygen. It follows then from Avogadro's hypothesis that one molecule of sulphur dioxide must contain one molecule of oxygen. Further, since the molecular weight of the gas as found by experiment is 64, the FIG. 20. SULPHUR AND SULPHUR DIOXIDE. Ill composition, according to the method given under sulphuretted hydrogen (see page GO), must be represented by the formula S( )._,. Sulphuryl chloride, S(XC1 2 .~ This body is obtained by the direct combination of sulphur dioxide and chlorine in presence of sunlight, or by heating chlorsulplionic acid, S0 3 IK '], in a sealed tube to 200 C, 2 SO OI1 SO Cl 4- SO OI1 2 b0 3 Cl 90 a cl + bO, OH Chlorsulphonic Sulphuryl Sulphuric acid. chloride. acid. It is a fuming liquid which boils at 70 J (J. and readily decom- poses when brought into contact with water S0 2 C1 2 + 2 H 2 = 2 HC1 + H 2 $0 4 . It acts upon alcohols and amines, replacing hydrogen by the group SOjjCI, and eliminating hydrochloric acid C 2 TI,,OH + SO a Cl 2 = (UI 5 0. S0 2 C1 + HC1 Ethyl alcohol. CH,01[ , son JCII 2 OH CH 2 OH ~ 5 2 U 2 - |CH 2 0. S0 2 C1 Ethylono alcohol. ( CII 3 ( CH 3 N < C1L + S0 2 C1 2 = N { CH 3 + HC1 ( II (S0 2 C1 Dimethylamiiie. Sulphurous acid and sulphites. We have seen that sulphur dioxide dissolves readily in water, forming an acid, H 2 S0 3 . We may regard this as a salt of hydrogen (see page 123), or as formed by the union of water with sulphurous anhydride, S0 2 . In acids which have been previously treated such as HF, HC1, HC10 3 , we have only had one atom of hydrogen replaceable by metals, and these are termed monobasic acids. In sulphurous acid we have two atoms of hydrogen so replaceable, affording an example of a (// ; ^.s/e acid ; in phosphoric acid, H 3 P0 4 , we have a tribasic acid. Sulphurous acid being dibasic forms two series of salts called sulphites, one in which both the hydrogen atoms are replaced, such as Na 2 S0 3 , K 2 S0 3 , CaS0 3 , and these are termed normal sulphites, or sometimes, because they are usually neutral to litmus, neutral sulphites. The second series of salts are those in which only one hydrogen atom is replaced by a metal, such as NaHSOg, , ^y UNIVEKSITY 112 TEXT-BOOK OF CHEMISTRY. KHS0 3 , CaH 2 (S0 3 ) 2 , the acid sulphites ; NaHS0 3 is, for instance, called acid sulphite of soda, or bisulphite of soda, or regarding sulphurous acid as a hydrogen suit, it may be termed sodium hydrogen sulphite. They may be prepared by passing S0 2 into solutions containing the basic hydroxide or carbonate. Exp. 61. Take 50 c.c. of a solution of caustic soda, and pass sulphur dioxide into it till it is saturated with the gas. On allowing the solution to evaporate at ordinary temperatures (it decomposes when heated), or. on adding alcohol to it, the acid salt, sodium hydrogen sulphite, separates out NaOH + S0 2 = XaHSOg. If we add a second 50 c.c. of the same solution of caustic soda we shall then obtain on evaporation or treatment with alcohol the normal salt NaOH + NaHS0 3 = N^SOg + H 2 0. In a similar way, substituting caustic potash instead of soda, the sulphites of potash may be prepared. The normal sulphites of all other metals excepting the alkalies are insoluble in water, and may be obtained as precipitates by the addition of a soluble salt of the metal to a solution of an alkaline sulphite. CaCI 2 + Na 2 S0 3 = CaS0 3 + 2 NaCl. Sulphites slowly take up oxygen from the air, passing into sul- phates, and all sulphites are decomposed by acids with evolution of S0 2 . SULPHUR AND SULPHUR DIOXIDE. 113 QUESTIONS. CHAPTER IX. 1. How is sulphur separated from the mineral matter with which it is cissociated in the native condition ? 2. Under what conditions are "flowers " of sulphur and " milk " of sulphur formed ? 3. Describe the physical changes through which sulphur passes when it is heated in the absence of air. 4. Explain what you understand by " allotropic modification." Is ozone an allotropic modification of oxygen ? 5. Tabulate the properties of the different allotropic modifications of sulphur so as to bring out the differences between them. 6. What is the action of hydrochloric acid on sodium thiosulphate, on calcium sulphide, and on ferrous sulphide? 7. What is the action of sulphur vapour on heated copper, iron, oxygen, hydrogen, and chlorine respectively? Give equa- tions representing the changes which occur. 8. Describe how sulphur dioxide is prepared on the laboratory scale and how it is collected. 9. State the physical properties of sulphur dioxide. What volume of the gas will dissolve in 100 c.c. of water at 10 C. under normal pressure ? 10. Explain the bleaching action of sulphur dioxide, and show in what respects it differs from that of chlorine. 11. What is the effect of passing chlorine into a solution of sulphur dioxide in water? Give equations. 12. A little chlorine is passed into a solution of potassium iodide, and then afterwards sulphur dioxide is passed in ; state the changes which take place and give equations representing them. 13. "Sulphur dioxide contains its own volume of oxygen." Explain the meaning of this statement, and show how you would prove the truth of it by experiment. 14. What is sulphuryl chloride? Give two methods by which it is obtained, and show by meaus of equations the action of water on S0 2 C1 2 and S0 3 HC1 respectively. 15. Describe the preparation of the normal and acid sulphites of soda ; what is the action of sulphuric acid on them ? I CHAPTER X. SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. Sulphur trioxide, SO 3 . This body occurs in small quantity with the sulphur dioxide formed during the combustion of sulphur or iron pyrites. Preparation. Sulphur dioxide and oxygen are passed over platinum sponge, obtained by igniting the double chloride of ammonium and platinum. The gases must be dry, and the platinum sponge gently heated, and there then appear at the exit, dense white fumes, which if passed into a cool dry receiver condense to white silky needles of sulphur trioxide. A second method which is employed in the production of sulphur trioxide in large quantities is based on the decomposition of ferrous sulphate, FeS0 4 . 7 H 2 0. This body, when heated, first loses most of its water of crystallization. The partially dehydrated salt more strongly heated is decomposed thus 2 FeS0 4 - Fe 2 3 + S0 2 + S0 3 . The water which still remains attached to the salt, however, com- bines with some of the S0 3 forming sulphuric acid, H 2 S0 4 , and this takes. up another molecule of S0 3 forming H 2 S 2 7 H 2 + S0 3 = H 2 S0 4 and H 2 S0 4 + S0 3 ='H 2 S 2 7 . The acid thus produced is known as Nordhausen sulphuric acid ; it differs from ordinary sulphuric acid, in that it fumes when exposed to moist air, and is often termed fuming sulphuric acid- This liquid which condenses from the distillation of 114 SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 115 partially dehydrated ferrous sulphate, when removed from the receiver and heated, yields the S0 3 which it has taken up, leaving behind sulphuric acid. By distilling- with a powerful dehydrating agent, such as phos- phorus pentoxide, the elements of water may even be removed from sulphuric acid itself, and this affords a third method whereby S0 3 may be obtained P 2 5 + H 2 S0 4 = 2 HP0 3 + S0 3 . Properties of sulphur trioxide. At ordinary temperatures sulphur trioxide forms white transparent needles, which melt at 15 C., and boil at 46 C. ; at a red heat it breaks up into sulphur dioxide and oxygen. It combines very eagerly with water, evclving much heat, and in contact with water it gives a hissing sound like that of the quenching of hot iron. Sulphuric acid is thereby formed ; it is of interest to add that it enters into direct combination with certain oxides, such as baryta, BaO, with the production of barium sulphate, BaS0 4 . Chlorsulphonic acid, SO,HC1. This interesting body is obtained by direct combination of dry hydrochloric acid gas and sulphur trioxide, or by the action of phosphorus pentachloride, PC1 3 , on sulphuric acid S0 3 + HC1 = SO.OHCl S0 2 (OII) 2 + PC1 G S0 2 OHC1 + POC1 3 + HCI, Phosphorus oxychloride. The first method of production may be conveniently carried out by passing dry hydrochloric acid gas into Nordhausen sul- phuric acid ; the chlorsulphonic acid boils at 153 C.. and may be readily separated by distillation. Like S0 2 C1 2 it decomposes in presence of water SOg.OH.Cl + H 2 = S0 2 (OH) 2 + HCI. A similar reaction takes place with the alcohols C 2 H 5 OH + S0 2 .OH.C1 = S0 2 .OH.OC 2 H 6 + HCI. Ethyl alcohol. Chlorsulphonates of the alkalies are formed by the direct union of S0 3 and a chloride, or by the action of chlorsulphonic acid on the chloride KC1 + S0 3 ~ S0 3 .OK.C1 KC1 + SOgOHCl S0 8 ,OK,C1 + HCI, 116 TEXT-BOOK OF CHEMISTRY. SULPHURIC ACID, OR OIL OF VITRIOL, H 2 S0 4 . We have seen that under certain circumstances sulphur dioxide com- bines with oxygen to form sulphur trioxide, and that this in presence of water gives sulphuric acid. The oxidation of sul- phurous acid to sulphuric acid also takes place slowly when its aqueous solution is exposed to air at ordinary temperatures. Such methods are, however, not suitable for the production of large quantities 1 of sulphuric ucid as an article of commerce. The oxidation of sulphurous acid is effectually performed by the intervention of the oxides of nitrogen, and on the large scale sulphur dioxide, oxygen (supplied in the form of air) and steam are brought together, and these in presence of oxides of nitrogen form sulphuric acid. The sulphur dioxide in works where a very pure acid is made is obtained by burning brimstone, but in the very large majority of cases iron pyrites is used as the source of the gas. This is burnt in a series of "kilns," and the heat arising from the com- bustion is sufficient to render the operation continuous, fresh charges being added from time to time. 2 Fe S 2 + 11 = FegOg + 4 S0 2 . The nitric acid from which the oxides of nitrogen are derived is prepared by the action of concentrated sulphuric acid on Chili saltpetre, NaN0 3 NaN0 3 + H 2 S0 4 = NaHS0 4 + HXO ? ; the acid fumes are carried into the flues along which the sulphur dioxide and air pass, and there intermingle with these gases. The air is drawn in through the pyrites burners or kilns, the draught being maintained by means of a chimney, and by adjustment of the doors of the kilns so as to admit the quantity of air which experience has shown to be necessary. The st earn is supplied from low pressure boilers, and introduced into the "chambers" in such a way as to become intimately associated with the other products. The reaction ending in the production of sulphuric acid does not take place under the circumstances very rapidly, and it is necessary to provide for a lengthened period of contact between i Over a million tons of oil of vitriol are produced in Great Britain alone in the course of a year. SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 117 the various bodies which take part in it. The gases are led into a series of larg'i chambers where they meet with the steam. These are usually three in number, and have a total capacity of 100,000 to 150,000 cubie feet, the relation of the sulphur burnt to the capacity of the chamber being- such that the average time occupied by the gas in traversing the chambers is something like three hours. The walls and floor of the chambers are constructed of sheet-lead supported on a wooden framework, lead being a metal which is scarcely attacked at all by sulphuric acid of the strength produced in the chambers. The chambers are kept cool enough to serve as condensers, so that the acid collects on the floor, and is drawn off periodically. The recovery of the oxides of nitrogen. In practice, the higher oxides of nitrogen are carried forward in the chambers, and would escape at the exit. To avoid this waste, advantage is taken of the fact that they are absorbed by concentrated sul- phuric acid. The exit gases from the chambers are therefore passed through a tower (known as the fay-I/itssac tower), packed with coke, down which concentrated sulphuric acid constantly trickles. The oxides of nitrogen taken up in this way are dis- charged again if the acid be diluted, since they are practically insoluble in dilute sulphuric acid. In order therefore to render these absorbed gases again available in the production of sulphuric acid, the acid which has traversed the Gay-Lussac tower is pumped up to the top of a Glover tower placed at the entrance of the chambers. This tower is packed with flints and coke, and the nitrated acid is diluted as it runs down by being mixed witli the weaker "chamber acid." The oxides of nitrogen which have been absorbed in the Gay-Lussac tower are thus discharged within the Glover tower, and there mix with the gases which are passing from the pyrites burners to the chambers, the Glover tower being phieed between the. pyrites burners and the chambers. The Glover tower performs the further function of cooling the gases before they enter the chambers, and in addition to this, a considerable amount of sulphuric acid is actually formed in the Glover tower itself. The acid which escapes from the Glover is strong (80 per cent.), and has a temperature of 120 to 130. 118 TEXT-BOOK Of CHEMISTRY. SULPHUR TRIOXIDK, SKLKXTOL AXP TELLURIUM. 119 Details relating to Sulphuric Acid plant. Fig. 21. (1) Pyrites burners. These are shown partly in section, so as to indicate the charge and the common flue into which the gas passes. There are 24 burners, a second row of 12 being placed back to back with those shown. The various doors on the front of the burners serve for charging- the ore, stirring the charge when necessary, and finally for removing the burnt ore which has fallen into the ashpit underneath. (2) The Glover tower. This is packed with flints, through which trickle from the tanks above (a) strong nitrated acid, which has been previously used to absorb nitrous fumes in the Gay-Lussac tower (6), weak chamber acid. When the two acids mix, nitrous fumes are freely liberated within the tower, and thus it supplements the nitre-pots in providing the nitrous fumes necessary for the process. (3) The Gay-Lussac tower. This is packed with coke, and the strong acid (sp. gr. 178) which is supplied from the tank above, passes over the coke and absorbs any nitrous fumes in the exit gases from the chambers. The course taken by the gases. The sulphur dioxide and air (in excess) pass along the common flue A B from the pyrites burners over the nitre-pots, and then along the pipe C, through the Glover tower. At D they pass in at the front of chamber No. 1, and thence from the back at E to the back of chamber No. 2, entering this at F by the pipe E F. Similarly by G II from the front of chamber No. 2 to the front of No. 3, and from the back of this to the base of the Gay-Lussac tower by K L. Having traversed the Gay-Lussac tower the exit gas finally passes off to the chimney by the outlet at the upper part of the tower. The steam is blown in at the ends of the chambers in such a way as to travel always in the direction of the draught, that is to folloAv the same course as that taken by the gases. Each chamber is 25 ft. wide, 20 ft. high, and 100 ft. long, and they are seen in the figure in transverse section, so that the direction of the length would be perpendicular to the plane of the paper. 120 TEXT-BOOK OF CHEMISTRY. The functions of the various parts of the sulphuric acid plant may be summed up thus The Chambers (1) bring about a prolonged contact between the reacting bodies. (2) Condense the sulphuric acid which collects as the chamber acid (sp. gr. 1*6, containing nearly 70 per cent. H 2 S0 4 ) on the floor of the chamber. The Gay-Lussac Tower absorbs the oxides of nitrogen in the exit gases from the chamber. The Glover Tower (1) effects discharge of oxides of nitrogen from the nitrated acid produced in Gay-Lussac tower. (2) Cools the gases from the pyrites burners, the heat so absorbed concentrating the acid to sp. gr. 1'75, or 80 per cent. (3) Assists in the actual production of sulphuric acid. At a higher degree of concentration sulphuric acid rapidly attacks lead, and if stronger acid is needed, the concentration is effected by boiling it in glass or platinum stills, when -very weak acid passes over, and the acid remaining in the still rises in strength till it contains 95 to 98 per cent. H 2 S0 4 . Acid containing 100 per cent H 2 S0 4 cannot be obtained by distillation alone. It is prepared by adding sulphur trioxide to the 98 per cent, acid, and then on freezing, crystals of pure H 2 SC) 4 , melting at 10 C., separate out. Properties of sulphuric acid. The pure concentrated arid is a thick oily liquid (sp. gr. 1'84), from whence it derives the name, o-tt of vitriol. It boils at 338 C., with partial decomposition, so that when the acid containing 100 per cent. H 2 S0 4 is distilled the residue becomes weaker, until it reaches a strength of about 96 per cent. H 2 S0 4 , at which it remains constant. It is highly corrosive, charring wood and many organic sub- stances even at the ordinary temperature. This is largely owing to the great avidity with which it takes up water. Wood con- sists mainly of cellulose, a compound of carbon, and hydrogen and oxygen in the proportions in which they are contained in water: the acid therefore abstracts water, leaving a mass of carbon. The concentrated acid is frequently used for drying the ordinary gases. Its affinity for water is likewise shown by the large amount of heat evolved when the two liquids are mixed. SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 121 Laboratory representation of the Sulphuric Acid Manufacture. The formation of Sulphuric acid may be represented in the laboratory by taking a large ilask (5 litres) and fitting it with a cork provided with live holes through which pass tubes de- livering (1) Sulphur dioxide (for preparation see p. 108), (2) Nitric oxide ( p. 148), (3) Steam, (4) Oxygen from a gasholder ; while the fifth hole is provided with a tube opening into the air. The arrangement is shown in the figure. FIG. 22. Pass some sulphur dioxide, nitric oxide, steam, and oxygen into the ilask, then shut off the sle;im supply; crysf.-ds of nitro- sulphonic acid (lead chamber crystals) may be seen to form. On clearing the flask of red fumes by a current of oxygen, and then passing in more steam, these crystals will dissolve with the evolution of red fumes. After allowing the reaction to go on for some minutes, the liquid condensed in the flask may be tested for sulphuric acid (see p. 123). 122 TEXT-BOOK OF CHEMISTRY. The theory of the Sulphuric Acid Manufacture. As we Lave seen (p. 116), sulphur dioxide under the action of air and moisture is transformed into sulphuric acid, but the change takes place very slowly, and the sulphuric acid obtained is extremely dilute. In presence of certain substances, notably the higher oxides of nitrogen as in the sulphuric acid chambers, the con- version is more rapid : but much difference of opinion exists as to the actual changes which take place, and even as to the particular oxides of nitrogen which take part in the reaction. The older theory, originally suggested by Berzelius, regards the nitric oxide (NO) as the body which brings about the formation of the sulphuric acid. This it does by taking up oxygen from the air and forming nitrogen peroxide (N0 2 ), which in its turn oxidizes the sulphur dioxide, and in presence of steam forms sul- phuric acid, being itself reduced again to nitric oxide, the alternate oxidation and reduction going on indefinitely : (1) N0 2 + S0 2 + H 2 = NO + H 2 S0 4 . (2) 2 NO + 2 =2 N0 2 It is however observed that if the chambers are insufficiently supplied with steam, white crystals ("lead chamber crystals") are formed, consisting of nitrosul phonic acid, S0 2 OHN0 2 . Ac- cording to the above theory the formation of nitrosulphonic acid is not essential to the process, and does not occur in chambers working normally. The theory more recently proposed by Lunge on the other hand assumes nitrogen trioxide 1 to be the true intermediary in the formation of sulphuric acid, and nitrosulphonic acid to be continually formed in the chambers and decomposed again by the excess of steam according to the equations (3) 2 HN0 3 + 2 S0 2 + H 2 = 2 H 2 S0 4 + N 2 3 . (4) N 9 3 4- 0, + 2 S0 2 + H 2 = 2 S0 2 OHXO.,. (5) 2 S0 2 OHN0 2 + H 2 = N 2 3 + 2 H 2 S0 4 . Under some conditions, and especially where the gases are just entering the chambers and sulphur dioxide is in large excess, it is however admitted that nitric oxide plays a prominent part. With this exception Lunge's theory is not inconsistent with the observations recorded in actual working on the large scale. 1 The theory holds if N 2 3 be regarded as a mixture of X0 2 and NO (see p. 147). SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 123 The sulphates. Concentrated sulphuric acid in presence of metals frequently undergoes partial reduction, sulphur dioxide being evolved (see p. 108), but with basic oxides it reacts with great energy and forms a series of salts called the sulphates. The sulphates of lead, calcium, barium, and strontium arc in- soluble or only slightly soluble in water, the rest being readily soluble. Sulphuric acid like sulphurous acid forms two classes of sulphates, the normal sulphates such as Na 2 S0 4 . CaS0 4 , and the acid sulphates such as NaHS0 4 , either one or the other being form* d according to whether the base or the acid are in excess. Test for Sulphates.- Exp. 62. Add barium nitrate to a solution which contains either sulphuric acid or a sulphate in presence of hydrochloric acid : a white precipitate is formed consisting of sulphate of barium. This is the only common barium salt which is insoluble in water and acids, and the formation of the precipitate is therefore characteristic, and may be taken as a sure indication of the presence of sulphuric acid either in the free state or in combination. The replacement of hydrogen by other elements. If we regard the acids as salts of hydrogen, and other salts as formed by replacing hydrogen, the most cursory inspection of the formulae of a series of salts will show that the elements differ in respect of the number of atoms of hydrogen which they replace. For instance, we have written above Na 2 S0 4 and CaS0 4 ; in the former each atom of hydrogen in H 2 S0 4 is replaced by one atom of sodium, in the latter one atom of calcium replaces two atoms of hydrogen. Extending the examination we have Type. Salts. H 2 S0 4 > 4 ,^so 4 ,Kso 4 >, H 2 S0 4 CuS0 4 , MgS0 4 , CaS0 4 , ZnS0 4 , BaS0 4 . H 2 S0 4 ) H 2 S01 ( AlSCV A > or A1 2 3 S0 4 . 124 TEXT-BOOK OF CHEMISTRY. From this table we see that (1) One atom of Na or K replaces one atom of H. (2) Cu, Mg, Ca, &c., replaces tico atoms of H. (3) Al replaces three atoms of H. A similar examination of other series of salts, such as the phosphates or carbonates, will lead to like conclusions. Moreover it may be shown by actual experiment that 23 l grins, of Xa or 39 grms. of K will liberate from water one gramme of hydrogen ; 63'2 grms. of Cu or 24 grms. of Mg - , etc., will liberate two grammes of hydrogen ; 27 grammes of Al will liberate three grammes of hydrogen. If we inquire what weight of these metals will liberate equivalent weights of hydrogen, the values obtained with sodium and potassium will be proportional to the atomic weight, with Cu, Mg, etc., proportional to half the atomic weight, with Al proportional to one-third the atomic weight. Numbers in such relations to the atomic weight are termed equivalent iveiyhts, and the equivalent weights of Na and K are 23 and 39 respectively, in other words atomic weight is identical with the equivalent weight ; these elements are therefore termed monovalent. The equivalent weights of Cu, Mg, etc., are 31 '6, 12, &c., and the atomic weight is double the equivalent weight ; these elements are therefore termed divalent. The equivalent weight of Al is 9, and the atomic weight is threefold the equivalent weight ; Al is therefore termed trivalent. Regarding the acids as salts of hydrogen, we may derive the formulae of the metallic salts by replacing hydrogen according to the equivalency of the metal in question ; thus Nitric acid, HN0 3 Nitrates, KN0 3 , Cu(N0 3 ) 2 ,Al 2 (N0 3 ) 6 . Carbonic acid, H 2 C0 3 Carbonates, K 9 C0 3 , KHC0 3 , CuC0 3 , Phosphoric acid, H 3 P0 4 Phosphates, lv,r<> 4 , I\,riP0 4 , KH 2 PO 4 , Ca 3 (P0 4 ) 2 , All'Op It must be added that certain metals, such as Cu, Fe, Ilg, Bi, form two series of salts in which they show different valcm-y. For instance, in FeS0 4 (ferrous sulphate), or FeCU (ferrous 1 These numbers being the atomic weights of the respective elements. SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 125 chloride), etc., the Fe replaces t\oo atoms of hydrogen, whilst in' Fe 2 3 S0 4 (ferric sulphate), or Fe 2 CJ (ferric chloride), Fe replaces three atoms of hydrogen ; and in the same way we have mercuroris salts such as HgCl, HgN0 3 , etc., and mercuric salts HgCI 2 , Hg(X0 3 ).,, etc. The valency of the more common metals as derived from the hydrogen they replace is as follows M<>norlen(. K, Na, Ag, Hg(ous), Cu(ons). Divalent. Ba, Sr, Ca, Mg, Zn, Cd, Co, Ni, Pb, Hg(ic), Cu(ic), Fe(ous), Mn(ous), Sn(ous). Trimlent. Al, Cr, Fe(ic), As(ous), Sb(ous), Bi(ous). Tetravalent. Sn(ic). In like manner an inspection of the more stable compounds of elements with hydrogen will show that the number of atoms of hydrogen which enter into combination with one atom of different elements shows like variations. Thus we have IIF, HC1, HBr, III. H 2 0, H 2 S. H 3 N, H 3 P. H 4 C, IJ 4 Si. From which we gather that F, Cl, Br and I are monovalent, and S (in H 2 S) are divalent, N and P are trivalent, and C and Si are tetravalent. Accepting that oxygen is divalent, we may examine the oxides Na 2 0, K 2 0, C1 2 0, N 2 0. CnO, MgO, CaO, Zno, BaO, PbO, FeO. A1 2 3 , N 2 3 . C0 2 , S0 2 , Si0 2 . NA, PA, IA S0 3 . We conclude that in these compounds, Na, K, Cl and N (in N 2 0) are monovalent; Cu, Mg, Cn, etc., are divalent; Al, N (in N 2 3 ) are trivalent; C, S (in S0 2 ) and Si are tetravalent; N (in N 2 5 ), P (in P 2 5 ), I (in I 2 5 ) are pentavalent ; S (in S0 3 ) is beiavalent We might go further, and ask in what manner the constituents of a compound are arranged within the molecule. 126 TEXT-BOOK OF CHEMISTRY. Such an inquiry would afford a fuller insight into the valency of the elements, and enable us to offer some explanation of anomalies that appear under the method of replacement with regard to certain compounds. It would, however, involve a deeper knowledge of chemical physics than can be assumed at this stage. We shall therefore content ourselves with a general statement relating to the valency of the non-metallic elements, deferring the consideration of exceptional cases, CO, NO, etc. Monovalent. Hydrogen, fluorine, chlorine, bromine, iodine. Divalent. Oxygen, sulphur (in H 2 S, SC1 2 , etc.). Trivalent. Boron, phosphorus (in PC1 3 , etc.), nitrogen (in NH 3 , N 2 3 , etc.). Tetravalent. Carbon, silicon, sulphur (in S0 2 , SCI 4 , etc.). Peatavcdent. Phosphorus (in PC1 5 , P 2 5 , etc.), nitrogen (in N 2 5 , etc.). Hexavalent. Sulphur (in S0 3 , etc.). It will be observed that nitrogen and phosphorus maybe either trivalent, or pentavalent whilst sulphur may be divalent, tetra- valent or hexavalent; the halogen elements in such compounds as ICI 3 , HI0 4 have probably a higher valency. In general. ;in element which is hexavalent may, in some of its compounds, be tetravalent or divalent, and one which is pentavalent may be trivalent or monovalerit. Selenium and Tellurium. Selenium and tellurium are rare elements, the former occurring along with iron pyrites in a few localities, and the latter along with gold, silver, and bismuth. Selenium is a red amorphous body which, like sulphur, exists in several allotropic modifications, whilst tellurium has a grey metallic appearance. Both elements form gaseous compounds, H 2 Se, H 2 Te, corresponding to sulphuretted hydrogen. They are prepared by a similar reaction, and precipitate selenides and tellurides from solutions of the salts of most metals. They likewise burn in air forming dioxides, Se0 2 , TeO.,, find tellurium on further oxidation yields a tri oxide, Te0 3 . The dioxides dissolve in water forming acids corresponding to sul- phurous acid, which on oxidation give selenic acid, H 2 Se0 4 , and telluric acid, H 2 Te0 4 , which form salts like the sulphates. They form di and tetrachlorides and bromides by direct union, SULPHUR TRIOXIDE, SELENIUM, AND TELLURIUM. 127 QUESTIONS. CHAPTER X. 1. Under what circumstances does sulphur dioxide combine directly with oxygen ? What is the action of heat on FeS0 4 , 7H 2 ? '.">. How may sulphur trioxide be obtained from (a) Nordhausen sulphuric acid ; (6) ordinary sulphuric acid? 4. Describe how sulphur dioxide becomes transformed into sul- phuric acid on the large scale ; give equations. 5. Describe the general construction and the functions of the lead chambers used m the manufacture of sulphuric acid. 6. How is sulphur dioxide obtained for the manufacture of sulphuric acid, and what means are employed to ensure, its being mixed with the proper quantify of air? 7. What is the part played by the Glover tower in the produc- tion of sulphuric acid ? 8. How are the oxides of nitrogen, which are found in excess towards the exit of the chambers, recovered ? 9. What is "chamber" acid, arid how is concentrated acid obtained from this ? 10. Write down the formulae of the normal sulphates of copper, potassium, lead, iron, and aluminium. 11. Give a method of testing for the presence of a soluble sul- phate, and show how you would distinguish whether an aqueous solution contained (a) free sulphuric acid only, (6) a normal sulphate, (c) a mixture of the two. 12. What is meant by the " equivalent " of metal ? State the relation between the equivalent weight and the atomic weight of the elements sodium, calcium, iron, mag- nesium, aluminium. 13. Write down the names and formulae of the phosphates and carbonates of sodium, calcium, and magnesium. 14. Compare the properties of the elements selenium and tellurium with those of sulphur. CHAPTER XL NITROGEN THE ATMOSPHERE AMMONIA. NITROGEN is the first member of a group of elements, nitrogen, phosphorus, arsenic, antimony, and bismuth, which either in themselves or their compounds exhibit considerable analogy to one another. The first two members only are usually classed with the non-metals. The elements forming this group show a transition in physical properties as the atomic weight increases, nitrogen being gaseous at the ordinary temperature, whilst phosphorus is solid but easily vapourized, the other members being more difficult to volatilize. Speaking more particularly with regard to nitrogen and phos- phorus, it will be seen by a reference to the following pages that they resemble one another (1) in forming hydrides of similar composition NH 3 , PH 3 , both of which combine directly with haloid acids yielding the ammonium and phosphonium salts (see p. 155). (2) in forming a characteristic series of oxides some of which yield powerful acids. Occurrence. Nitrogen occurs mixed with oxygen in the atmosphere, of which it forms nearly four-fifths the volume. Alihongh it does not enter to any large extent into the composition of animal and vegetable tissues, it is, notwithstanding, a very constant and essential constituent of such tissues. The nitrogen of plants is obtained chiefly through the medium of the NITROGEN THE ATMOSPHERE AMMONIA. 129 soil, in which small quantities of nitric acid, nitrates, and ammonium salts always occur. Animals cannot assimilate nitrogen directly, and derive their supply from the plants. Recently, the investigations of Ramsay and Rayleigh have established the existence of a new gas in the atmosphere. This gas has been named argon, and it remains associated with the nitrogen after the oxygen has been removed, constituting nearly 1 per cent, of the air ; it is exceedingly inert, and is only separated from the nitrogen with great difficulty. Preparation. Air may be deprived of oxygen either by burning phosphorus in it or by passing it over red-hot copper, the oxygen combining to form phosphorus pentoxide and cupric oxide respectively. Exp. 63. Float a small porcelain crucible containing red phosphorus on water, and place a large bell-jar with a narrow neck (Fig. 23) over it, and so that the depth of the water is about one-third tho 130 TEXT-BOOK OF CHEMISTRY. height of the bell-jar. Now ignite the phosphorus by touch- ing it with a hot wire, and close the bell-jar by means of a cork or stopper. The phosphorus will burn brightly at first, and the heat evolved will expand the gas and depress the water inside the jar. After a little time the combustion will cease, and the water ultimately rise further than its original level. The fine white powder which is formed during the combustion, consisting of phosphorus pentoxide, will gradually settle down and dissolve in the water. "When the water has ceased to rise within the jar, pour more water into the vessel in which it stands until the levels inside and outside are the same. The gas has diminished in volume and altered in character. It will be found to extinguish a lighted taper, and to be quite inert towards chemical reagents. "When air is deprived of its oxygen, the residual gas which we have now in the jar is nitrogen. A second method of preparation consists in heating ammonium nitrite, which breaks up into water vapour and nitrogen. NH 4 N0 2 ^ N 2 + 2 H 2 0. A third method is to act on concentrated solution of ammonia (taking care to keep a large excess of ammonia present throughout the experiment) with chlorine 8 NH 3 + 3 C1 2 = N 2 + 6 NH 4 C1. This reaction may be represented in two stages 2 NH 3 + 3 C1 2 = N 2 + 6 HC1 6 NH 3 + 6 HC1 = 6 NH 4 C1. If the ammonia be not kept in excess the reaction is NH 3 + 3 C1 2 = NC1 3 + 3 HC1, the nitrogen trichloride being a heavy liquid which is liable to explode in a very dangerous manner. Properties of nitrogen. Nitrogen is a colourless, tasteless gas, which is unable to support life or combustion. Nitrogen does not combine with oxygen under ordinary conditions ; but it may be made to do so by means of an alternating current of electricity, when the higher oxides of nitrogen are formed. It is somewhat lighter than air, and condenses to the liquid form at 193 C. ; it is slightly soluble in water, less so than oxygen (see p. 71). It combines directly only with some few metals, such as magnesium, titanium, and iron, and on the whole is characterized by its great inertness. NITROGEN THE ATMOSPHEKE AMMONIA. 131 THE ATMOSPHERE. The gaseous envelope which sur- rounds the earth is chiefly composed of nitrogen and oxygen. With these are associated water vapour, carbon dioxide, ammonia, and other gases, the amounts of which vary according to circum- stances. From whatever locality the air has been obtained, the relative proportions of nitrogen and oxygen show only slight variations, as the following results show. Percentage of Oxygen by Volume. 72 analyses in different parts of Europe (mean) 20'95 17 the Polar Seas ' ' 20-90 3 at elevation of 15,000 ft. or over 20'94 The determination of the composition of the atmo- sphere. If a known volume of air, from which the impurities have been removed, be introduced into a eudiometer and exploded with about twice its volume of hydrogen (see p. 54), two volumes of hydrogen combine with one volume of oxygen to form water vapour, which condenses, and thus one-third the diminution in volume represents the volume of oxygen present. The difference between this and the original volume of air taken is the volume of nitrogen. An approximate determination of the composition by volume may be made in the following way, Exp. 64. Take aglass tube about 700 m.m. high and!5 m.m. diameter closed at one end, and of as even bore as possible. Invert this, filled with air, over water, note the volume of the air, and pass up into it a piece of phosphorus attached to a stout copper wire. The phosphorus will slowly combine with the oxygen of the air, and the water will rise in the tube. Allow it to stand in a shaded place until the water ceases to rise. Now remove the phosphorus, and adjust the level of the water to the same height inside and outside the tube, and note the volume of residual nitrogen. The volume (correction may have to be made for variation of temperature and pressure during the experiment) occupied by the original air and the residual nitrogen may be ascertained with tolerable accuracy by seeing what volume of water is required to fill the tube to the two levels noted. The composition of air by weight may be ascertained by passing the air over red-hot copper, with which the oxygen 132 TEXT-BOOK OF CHEMISTRY. combines to form copper ox- ide. The air is previously freed from carbon dioxide and moisture, by being- passed over potash and con- centrated sulphuric acid. The apparatus rtsedis shown in Fig. 24 ; it consists es- sentially of a large glass globe, to which is attached a tube containing metallic copper, and heated in a fur- nace. The globe is first ren- dered vacuous by means of a good air-pump, the stop- cock is closed, and the globe carefully weighed. The tube containing the copper is then rendered vacuous, closed and weighed. The copper having been heated to redness, the stop-cock is opened sufficiently to allow a slow current of purified air to pass through the tube and into the glass globe. On the way, it is deprived of its oxygen, and if the ex- periment has been carefully conducted, only nitrogen passes into the globe. After the apparatus has quite cooled, the globe is again weighed, and the increment gives the weight of the ni- trogen. The tube is also weighed again, and the increase there shows the NITROGEN THE ATMOSPHERE AMMONIA. 133 weight of the oxygen, together with a little nitrogen which remains in the tube. On exhausting and weighing again, the decrease in weight is added to the increase in weight of the globe to obtain the total nitrogen. The oxygen is given by the difference of the two weighings of the exhausted tube. A series of such determinations gave the composition by weight of air as Nitrogen 76'995 Oxygen 23-005 Water vapour in air. The amount of water vapour varies with the temperature and the degree of saturation of the air, for the higher the temperature of the air, the more moisture will it take up before it is saturated. The average amount is some- what under 1 per cent, by volume, but in warm, moist climates may approach 4 per cent. It may be measured by observations on the dew-point (see text-books on physics), or by passing a known volume of air over calcium chloride contained in U tab and noting the increase in weight of the tubes. The amount of water vapour which the air can contain may be estimated by the fact that 1 cubic mile of air saturated at 35 would deposit, if cooled to 0, 140,000 tons of rain. But while the air is seldom completely saturated, it never contains less than TtV of the possible amount. Carbon dioxide in air. The amount of this gas in air varies considerably, according to the locality from which the sample of air is taken. In country air there are from three to four volumes of C0 2 in 10,000, but in towns the amount is larger, and may reach seven or eight volumes. In badly- ventilated dwellings even ten-fold the normal amount of carbon dioxide may occur. The determination of carbon dioxide is a matter of importance, espe- cially in the case of indoor air, since it serves to show the efficiency of ventilation. The presence of carbon dioxide in air may be shown by exposing lime-water in a shallow dish ; the lime-water is soon covered with a thin pellicle, owing to the formation of calcium carbonate or chalk, which is insoluble in water CaO + C0 2 = CaC0 3 . Baryta water may, by Pettenkofer's method, be used as a 134 TEXT-BOOK OP CHEMISTRY. means of determining the amount of carbon dioxide in air. A solution of baryta (which is alkaline) of known strength is shaken up with a measured quantity of air, say 10 litres ; part of the baryta is converted into barium carbonate (a neutral body), whilst part remains unaltered. The amount of alkali (the baryta) is now smaller by reason of the conversion of part of it into carbonate by the carbon dioxide. The more carbon dioxide is present, the greater will be the amount of baryta converted into barium carbonate, and the greater will be the difference between the amount of alkali originally taken and that remaining afterwards. By ascertaining the amount of oxalic acid required to neutralize the original baryta water, and that required to neutralize the residual liquid, the quantity of carbon dioxide in the 10 litres of air may be ascertained. Other impurities in air. The remaining impurities, such as suspended dust and carbon, ammonia, sulphur compounds, hydrochloric acid and chlorides, occur in much smaller and more variable quantities. During thunderstorms oxides of nitrogen are formed, and these give rise to nitrous and nitric acid ; ozone is also probably produced under such circumstances. The ammonin, carbon (soot), and sulphur compounds occur in larger quantity in the vicinity of towns, from the combustion of coal, or where decaying refuse is found. The hydrochloric acid and chlorides come for the most part from manufacturing operations, though it is significant that, especially during high wind, the air in the neighbourhood of the sea contains much more sodium chloride than is usual. The relation of animal and plant life to air. By breath- ing on a cool glass surface, and by expelling air from the lungs through lime-water, it is easy to demonstrate that expired air contains large quantities of moisture and carbon dioxide. Indeed the expired air from man contains usually over 4 per cent, of carbon dioxide, that is, over one hundred times as much as normal air. The agencies at work in producing carbon dioxide are (1) Eespiration of animals and plants. (2) Combustion of fuel. (3) Decay of organic matter. (4) Subterranean causes. NlTliOGEN THE ATMOSPHERE AMMONIA. 13& Faraday calculated that nearly five million tons of carbon dioxide were contributed daily to the atmosphere by these processes. Under such a contribution the air would slowly get more and more charged with carbon dioxide, and the percentage of oxygen diminish. There are, however, processes constantly in operation which act in the opposite direction. (1) In the process of assimilation in plants, the green colouring mutter (chlorophyll), in presence of direct or diffused sunlight, effects the decomposition of carbon dioxide and liberates oxygen. (2) Carbon dioxide being moderately soluble in water is carried down by rain, and is also taken up by surface waters and sea water. The precise extent to which the loss and gain counteract one another is difficult to estimate, but that plant life is an important factor is shown by actual observations on the living plant, and by the variations in the amount of carbon dioxide in air in the neighbourhood of forests in the daytime, when the foltage is exposed to the sun's rays, as compared with night, when assimilation is checked and only respiration goes on. Is air a compound or a mixture of nitrogen and oxygen ? We have seen that a chemical compound shows the following characters (1) It possesses a definite composition (see p. 18). (2) The weights of the elements composing it are in proportion to the atomic weights, or in some simple multiple proportion of the atomic weights e. g. Hgl, HgT 2 , H 2 0, etc. (see p. 12). (3) The compound shows distinctive physical and chemical properties, the individual properties of the constituent elements being more or less completely concealed (see p. 10). (4) When combination takes place, heat is usually evolved (see p. 17). (5) When gases combine to form a gaseous compound there is always a condensation to two volumes, whatever the volumes of the constituent gases may be, thus 2 vols. hydrogen + 1 vol. of oxygen form 2 vols. water vapour. 3 ,, ,, +1 }> nitrogen ammonia. (See p. 45.) (6) The simple solution of a gas in water does not affect its 136 TEXT-BOOK OF CHEMISTRY. chemical composition ; for instance, if we dissolve ammonia or carbon dioxide in water, arid then, by boiling the solution, expel the gas again, it will be found to be unaltered in character or composition. Now let us apply these tests to air. (1) The composition of air varies very little under different circumstances, but even such small variations as are found in its composition do not occur in the case of chemical compounds. (2) If we divide the relative proportions by weight of nitrogen and oxygen in the air by the atomic weights of nitrogen and oxygen, we shall see whether any simple multiple relation is shown. 76-995 Nitrogen ^ = 5 '499 ; 23-005 xygen 16W = 1>441 ; And 5-499 : 1-441 : : 3'82 : 1. That is, to be even approximately in agreement with the results of analysis we should have to assume a compound N 19 5 . The same result may be arrived at by considering the volume relations of nitrogen and oxygen in air. (3), (4), and (5) Nitrogen and oxygen retain their characters with slight modification in air, and a mixture of the two gases in the proper proportions shows precisely the same characters in all respects as air. No heat is evolved when they are brought together, nor does any contraction in volume take place. (6) We have seen (p. 72) that when air is shaken up with water, a greater proportion of oxygen dissolves than nitrogen, owing to the greater degree of solubility of oxygen, so that whilst in the air originally taken, one volume of oxygen is associated with approximately four volumes of nitrogen, air dissolved in water consists of one volume of oxygen associated with two volumes of nitrogen. On all these grounds, therefore, we must admit that air is simply a mixture of nitrogen and oxygen. Fogs are caused by condensation of water vapour induced by dust. That dust is the cause of fog formation is proved by the fact that in filtered air fogs cannot form. Analysis of the deposit NITROGEN THE ATMOSPHERE AMMONIA. 137 left after a fog showed it to consist of carbon, hydrocarbons, sulphuric acid, iron and its oxides, and silica. During a fog, too, the amount of carbon dioxide increases enormously and reaches from three to five times the normal amount. AMMONIA, NH 3 . Ammonia or its compounds exist in small quantities in air and in natural waters, being produced either from oxides of nitrogen formed in the air, or by the action of bacteria from refuse matters in the soil. Whenever animal or vegetable products containing nitrogen are strongly heated in closed retorts (air being excluded), and especially when they are heated with lime or other alkalies, ammonia is given off. In this way large quantities of ammonia are obtained during the distillation of coal (which contains about 1^ per cent, of nitrogen), the coal gas being cooled and then washed, by which means any ammonia is separated and obtained in solution. The further distillation of the liquid so obtained with lime, sets free the ammonia, which if passed into aqueous hydrochloric acid, forms ammonium chloride or sal ammoniac. NH 3 + HC1 = NH 4 C1. Ammonium chloride. The distillation of animal refuse, horns, or hoofs with lime likewise affords ammonia, and '' spirits of hartshorn " is a name by which a solution of ammonia is known. Preparation. In the laboratory it is usually prepared by heating together a mixture of two parts of lime and one part of ammonium chloride. Both must be in a state of line powder, intimately mixed, and as dry as possible. The mixture is heated in a dry flask, and the gas collected over mercury or by upward displacement, being much lighter than air ; it cannot be collected over water owing to its very great solubility. If it is to be dried, the ordinary desiccating agents for gases cannot be used, since sulphuric acid combines with it with great readiness, and calcium chloride absorbs it; a layer of lime or fragments of caustic soda may, however, be used. Properties. Ammonia is a colourless gas, having a very pungent but not disagreeable odour if diluted with much air ; in the pure condition it is injurious when breathed in quantity. At - 34 C. at ordinary pressure, and at C. under a pressure of 138 TEXT-BOOK of CHEMISTRY. seven atmospheres, dry ammonia condenses to the liquid form (see below, Carre's apparatus). Exp. 65. Fill a litre flask by displacement with dry ammonia, and show its solubility in the same way as already described (p. 30). Water at C. dissolves 1,050 times its volume of the gas, and at 15 C. 727 volumes. The aqueous solution is 'lighter than water, and in its most concentrated form has the specific gravity 0-884 ; it contains 36 per cent, by weight of the gas. The gas may be entirely expelled by boiling the solution. Ammonia neither burns readily in air nor supports combustion, but a mixture of warm ammonia and oxygen burns with a greenish-yellow flame. Exp. 66. Gently warm a strong solution of ammonia in a wide- mouthed eight-ounce flask, and bubble oxygen gas through the solution at the same time. A mixture of ammonia and oxygen will pass out at the open mouth of the flask, and will burn when a light is applied to it. Metallic oxides which are reduced in hydrogen also undergo reduction when heated in ammonia gas, the hydrogen of the ammonia combines with the oxygen of the oxide to form water, and nitrogen is set free. Ammonia combines directly with acids to form ammonium salts; this can be well shown with hydrochloric acid gas. Exp. 67. Fill two similar jars by displacement with ammonia and hydrochloric acid gas respectively, and cover the mouth of each jar with a glass plate. Now bring them mouth to mouth and withdraw the glass plates. The gases as they come into contact will combine, forming a fine white powder, which remains for some time diffused throughout the jars. This body is ammonium chloride, NH 4 C1. NH 3 + HC1 = NH 4 C1. 2 vols. 2 vols. Ammonium sulphate, (NH 4 ) 2 S0 4 , ammonium nitrate, NH 4 X0 3 , and other salts may be obtained by neutralizing a solution of ammonia with the respective acids, and then evaporating to dryness on a water-bath. Liquefaction of ammonia by pressure. If ammonia gas be generated in quantity, and the receiver into which it passes be a closed vessel much smaller than the volume of the gas gener- NITROGEN- THK ATMOSPHERE AMMONIA. 139 ated, it will be compressed and ultimately condense by its own pressure to tbe liquid form. This is indeed tlie method of Faraday (see p. 42), and a simple form of apparatus in which this principle is made use of is that of Carre (Fig 25). It consists essentially of a strong 1 iron cylinder containing con- centrated ammonia solution, as shown at A in the figure ; this com- municates with a receiver B, of relatively small volume, by means of the tube C. When A is surrounded by hot water, ammonia gas is given off freely and accumulates in the apparatus in such quantity that it condenses in the receiver C, which has been surrounded by cold water. If we now reverse the arrangement and surround A with cold water, the liquid ammonia will boil very rapidly and pass back as gas into A, and this rapid transformation of liquid into gas will bring about a considerable depression of temperature in B. This vessel is provided with a space D, into which water may be introduced and frozen. By various applications of this principle, liquid ammonia is used on a large scale for obtaining Ion- temperatures. 140 TEXT-BOOK OF CHEMISTRY. Composition of ammonia. The composition of ammonia may be determined by passing the gas through a red-hot tube containing copper oxide. The hydrogen is transformed into water, which may be collected and weighed in the manner already described (p. 56), and the volume of nitrogen which passes forward may also be ascertained. 3 CuO + 2 NH 3 = 3 Cu + 3 H,0 + N 2 .' The volume of hydrogen may be readily calculated from the weight of water obtained. A second method depends on the fact that when electric sparks are passed through gaseous ammonia it is slowly decomposed into its constituents. Dry ammonia is passed into a eudiometer over mercury, and its volume accurately measured. The sparks are then passed until no further increase in volume occurs ; it will be found to be just double its original volume. If now excess of oxygen be passed into the eudiometer and the spark passed, the hydrogen will combine with it and form water, which condenses, leaving nitrogen and the excess of oxygen added, two-thirds the diminution being the volume of hydrogen. This method is not very accurate owing to the fact that some of the nitrogen combines with oxygen, forming oxides of nitrogen. By the electrolysis of ammonia it may however be shown that the volume of nitrogen it contains is one-third that of the hydro- gen. The experiment is performed in the following manner. A saturated solution of common salt is prepared, and to this is added about one-tenth of its volume of strong ammonia. The solution is now introduced into a voltameter similar to that figured on page 23, but fitted with carbon electrodes and submitted to the action of the current from six Bunsen cells. Nitrogen collects in one tube and hydrogen in the other, and the volumes will be found to be in the proportion 1 : 3. Teds for Ammonia. Ammonia may be recognized by its smell, action on litmus, and by giving dense white fumes of ammonium chloride when brought in contact with hydrochloric acid gas. With Nessler's solution (see Vol. II.) ammonia gives a characteristic brownish colouration or precipitate, according to the amount of ammonia present. NITROGEN THE ATMOSPHERE AMMONIA. 141 QUESTIONS. -CHAPTER XL 1. Describe a method by which nitrogen may be obtained from air by removal of oxygen. 2. Give two methods for the preparation of nitrogen from ammonia or ammonium salts. 3. State the chief physical and chemical properties of nitrogen. 4. A mixture of 25 c.c. of air and 50 c.c. of hydrogen is exploded in a eudiometer, and the volume of the residual gas is found to be 6O3 c.c. ; find the percentage of oxygen in the air. 5. The percentage composition of air by weight being 76'995 nitrogen, 23*005 oxygen, find the composition by volume. 6. A litre of dry air is passed over heated copper and the increase in the weight of the copper found to be 0'297 gramme, find the percentage by weight of oxygen in the air. (1 litre of air weighs T293 gramme.) 7. How would you show that air contains carbon dioxide, and what means would you adopt for ascertaining the amount of carbon dioxide in air ? 8. How do the following impurities originate in air : carbon dioxide, sodium chloride, ammonia, sulphurous acid? 9. What agencies are at work which tend to remove such impurities as carbon dioxide and ammonia from the air ? 10. In what respects does a mixture of two gases, such as nitrogen and oxygen, differ in its behaviour from a compound of the two gases when shaken up in contact with water ? 11. What indications are usually shown that two gases which you have brought together have entered into combination ? 12. Give a general method by which ammonia may be obtained from nitrogenous animal or vegetable substances. 13. How would you prepare and collect dry ammonia ? 14. How can it be shown that ammonia contains hydrogen ? 15. What experiments would you make to show that the composi- tion of ammonia is rightly expressed by the formula NH 3 ? 16. Under what circumstances do nitrogen and hydrogen enter into combination, and under what circumstances is the com- pound so formed decomposed again without the intervention of chemical reagents ? CHAPTER XII. OXIDES AND OXY-ACIDS OF NITROGEN. IN the following table is given a list of these compounds Nitrous oxide, N 2 0, Hyponitrous acid, HNO, Nitric oxide, NO. Nitrogen trioxide, N 2 3 , Nitrous acid, HN0 2 . or nitrous anhydride. Nitrogen peroxide, N 2 4 . Nitrogen pentoxide, N 2 5 , Nitric acid, HX0 3 . or nitric anhydride^ Occurrence. The higher oxides are formed in small quantity when the electric discharge takes place in a mixture of nitrogen and oxygen These oxides, or nitrous and nitric acid formed from them, therefore occur in the atmosphere and in rain water ; waters contaminated by the drainage of surface soil, or by decay- ing nitrogenous organic matter, also contain similar products. In all such cases, owing to the difficulty of bringing about direct combination of nitrogen and oxygen, they are present in very minute quantities. Nitric acid or the nitrates being in all cases the source from which the oxides of nitrogen are derived, we shall treat these first. 142 OXIDES AND OXY-ACIDS OF NITROGEN. 143 NITRIC ACID, HN0 3 . Preparation.- Nitric acid, being a volatile acid, is expelled from nitrates by tbe ciction of less volatile acids, such as concentrated sulphuric acid (or silica), arid this reaction is made use of in its preparation, nitrate of potash or soda being usually employed. Exp. 68. Introduce 20 grammes of potassium nitrate into a stop- pered retort, and as much concentrated sulphuric acid as will just cover it. Apply a moderate heat, and presently the vapour of nitric acid will pass over and condense in the neck of the retort. The liquid may be collected in a small flask slipped over the mouth of the retort, and kept cool by means of a stream of cold water, or a wet cloth. When about 10 c.c. have been distilled over, or so soon as whitish fumes of sulphuric acid begin to appear, the experiment should be stopped. KX0 3 + H 2 S0 4 = KHS0 4 + HN0 3 . Potassium nitrate. Acid potassium sulphate. On the large scale, the native Chili saltpetre, NaN0 3 , is em- ployed, being a cheaper material, and the distillation is performed in large iron cylinders, the condensation of the acid taking place in a series of stoneware bottles. Economy can also be effected in regard to the amount of sulphuric acid used, since it is prac- ticable to work at a temperature sufficiently high to leave as the residue the normal sulphate of sodium, and hence the reaction is 2NaN0 3 + H 2 S0 4 = Na 2 S0 4 + 2 HN0 3 . Sodium nitrate. Sodium sulphate. Properties of the acid. The pure acid is a colourless, fuming liquid, of specific gravity 1'53, boiling at 86 C. It is highly cor- rosive, and by contact, instantly stains the skin yellow, more prolonged exposure giving rise to serious wounds. Dry straw and woody fibre are charred or even set fire to by contact with it. It mixes with water in all proportions, and if the dilute solution be concentrated in air at atmospheric pressure it becomes stronger until 68 per cent, of acid is present; it then distils unchanged. It is chiefly characterized by its powerful oxidizing action, carbon, sulphur, and tin being transformed readily into C0 2 , II.,S() 4 , and Sn0 2 respectively; whilst turpentine, when mixed with it, inflames. When it is remembered how readily nitric acid breaks up (e. g. by passing its vapour through a red-hot tube) 144 TEXT-BOOK OF CHEMISTRY. into water, oxides of nitrogen, and oxygen, the powerful oxidizing action of nitric acid will be understood. Most metals are dissolved by it with the evolution of red fumes, the nitrate of the metal, or, in some cases, the oxide being formed. The reactions which take place are complex, and vary according to the conditions under which the experiment is performed and the strength of the acid used. The more important examples are expressed by the equations below Sn + 4 HN0 3 = Sn0 2 + 2 N 2 4 + 2 H 2 0. 4 Ag + 6 HN0 3 = 4 AgN0 8 + N 2 3 + 3 H 2 0. 3 Cu + 8 HN0 3 = 3 Cu(N0 3 ) 2 + 2 NO +4 H 2 0. 4 Zn +10 HN0 3 - 4 Zn(N0 3 ) 2 + N 2 + 5 H 2 0. Regarding nitric acid as composed of water (H 2 0) and nitric an- hydride (N 2 5 ), we see that with the different metals in the order taken, the extent of the reduction of the N 2 5 increases : thus Sn reduces 2 N 2 5 to 2 N 2 4 and forms Sn0 2 4Ag N,0 6 toN,0 8 2Ag 2 3 Cu N 2 5 to N 2 2 (2 NO) ,, 3 CuO. 4 Zn N 2 5 to N 2 4 ZnO. The three last oxides combine with sufficient N 2 5 to form nitrates, the water being eliminated. The so-called "noble" metals, such as gold and platinum, are not acted upon by it, but readily dissolve in a mixture of hydro- chloric and nitric acids, 1 which has for this reason been termed aqim regia. Exp. 69. To a few cubic centimetres of dilute nitric acid in a porce- lain basin add fragments of lead, digesting on a water- bath, until the acid is saturated, and no more of the metal will dissolve. Evaporate the clear liquid to dryness, and a white salt, nitrate of lead, remains. Exp. 70. Dilute 5 c.c. of nitric acid with an equal bulk of water, and add a little litmus solution, which will become of a bright red colour. Now add ammonia solution little by little until the last drop turns the litmus blue, and concentrate the liquid to a point at which, when a drop of it is allowed to cool on the end of a glass rod, it crystallizes. On standing, crystals of ammonium nitrate will be obtained. i Aqua regia is usually made by mixing nitric acid with four times its volume of hydrochloric ac-id. OXIDES AND OXY-ACIDS OF NITROGEN. 145 The nitrates. These salts may be looked upon as nitric acid in which the hydrogen of the acid is replaced by a metal, thus IINO S KN0 3 NaN0 3 NH 4 NO S AgN0 3 . HN0 3 } Pb ( N 3)2 Cu(N0 3 ) 2 Ca(N0 3 ) 2 Ba(N0 3 ) 2 . They are all soluble in water. The nitrates of the alkalies are the most stable, and those of the heavy metals the least stable. When strongly heated all undergo decomposition with the evolution of nitric acid or the products of decomposition of nitric acid, viz. oxides of nitrogen and oxygen, and exert a powerful oxidizing action on substances which may be mixed with them. Exp. 71. Heat a few grammes of potassium nitrate in a test-tube until it fuses, and then drop into it one or two fragments of dry charcoal. The charcoal will ignite and burn with violence, being oxidized by the nitrate to C0 2 . Exp. 72. Repeat the experiment, introducing a few small shavings of lead ; the lead will be oxidized at the expense of the nitrate and transformed into a yellowish powder of oxide of lead. Tests for nitrates. (1) Nitrates when heated with sulphuric acid or silica give off nitric acid fumes, often accompanied by red fumes of the higher oxides of nitrogen. (2) Mix a solution of a nitrate with strong sulphuric acid, and add copper turnings ; on warming red fumes will be given off. (3) (The most sensitive test). Mix a cold solution of a nitrate with a cold, strong solution of ferrous sulphate, and pour gently down the side of the tube strong sulphuric acid : the latter sinks to the bottom, and a dark ring forms above it. The sulphuric acid liberates nitric acid from the nitrate, and the ferrous sulphate reduces the nitric acid to nitric oxide, which combines with more ferrous sulphate to form the dark-coloured solution. THE OXIDES OF NITROGEN. NITROGEN PENTOXIDE, N 2 O 5 This is a white crystal- line solid obtained by the action of a powerful dehydrating agent, s-icli as phosphorus pentoxide, on nitric acid, cooled by means of a freezing mixture. When the oxide is brought into contact with water it enters into combination with great energy, repro- L 146 TEXT-BOOK OF CHEMlSTfcV. ducing nitric acid H 2 + N 2 5 = 2 HN0 3 . On this evidence nitrogen pentoxide is to be looked upon as the anhydride of nitric acid. It is an unstable body and under- goes decomposition with explosive violence, when heated. NITROGEN TETBOXIDE or PEROXIDE, N 2 O 4 . This oxide is formed, together with X 2 3 , on the direct combination of nitric oxide, NO, with oxygen, and the condensation of the red fumes by means of a freezing mixture 2 NO + 2 = N 2 4 . It may also be prepared by heating lead nitrate 2 Pb(N0 3 ) 2 - 2 PbO + 2 N 2 4 + 2 . Exp. 73. Introduce 10 grammes of finely-powdered lead nitrate into a retort of "hard" glass (see Fig. 26) connected with a U tube surrounded by a freezing mixture (pounded ice or snow FIG. 26. and salt) and heat strongly. lied fumes are given off and condense to a colourless liquid, N 2 4 . Remove the freezing mixture and note that as the temperature rises the liquid darkens in colour, and at ordinary temperatures is orange yellow. o\li>i> AND OXY-ACIDS OF N1TIIOGEN. At about 27 C. it boils and gives off a vapour which also grows darker in tint as the temperature rises. These changes are accompanied by a partial dissociation of the gas into NO.,, and at 135 C. the whole of the gas has passed into this form. Thus at low temperatures ( - 9C.) nitrogen peroxide has the composition NoO.,, and at 135 C. the composition N0 2 , and at intermediate temperatures it exists partly in the one form, partly in the other. Bodies which burn in oxygen, and generate a Sufficiently high temperature to decompose this gas, will burn in it. Nitrogen peroxide is decomposed by water, giving nitrous and nitric acids at low temperatures N 2 4 + H 2 = HN0 2 + HN0 3 ; and nitric acid and nitric oxide at high temperatures 3 N0 2 + H 2 = 2 HN0 3 + NO. The gas also attacks many metals, such as mercury and copper. NITROGEN TRIOXIDE, N a 3 . This oxide is obtained when a nitrite is decomposed by sulphuric acid 2 KN0 2 + H 2 S0 4 = K 2 S0 4 + N 2 3 + H 2 ; or by passing nitric oxide into liquid N 2 4 at C. In the gaseous condition it is very probable that it consists merely of a mixture of nitrogen tetroxide and nitric oxide. At low temperatures, however, it condenses to a blue liquid, and in this form it may be regarded as a definite oxide. It sho\vs great activity as an oxidi/ing agent, and some metals on which nitric acid has little or no action dissolve readily when N./), is dissolved in the acid. Being the anhydride of nitrous acid, it combines with water to form this acid N 2 3 + H 2 = 2 HNOo. Nitrous acid is, ho\vever, also very unstable, and has not been prepared in a pure condition, as it readily decomposes, yielding nitric acid and nitric oxide as the chief products. The nitrites. These salts, like the nitrates, are all soluble in water, but may be distinguished from the nitrates by giving off red fumes when warmed with a dilute mineral acid. The more stable nitrates when strongly heated, alone or with metallic lead, yield nitrites 2 KN0 3 by heat = 2 KNO, + 2 . 148 TEXT-BOOK OF CHEMISTRY. Potassium nitrate was indeed many years ago commonly employed for the preparation of oxygen. Tests for nitrites. (1) The evolution of red fumes (oxides of nitrogen) when warmed with dilute sulphuric acid. (2) The formation of a dark ring at the surface of contact when a solution of ferrous sulphate is poured upon a solution of a nitrite, and this without the addition of sulphuric acid. (3) The liberation of iodine from potassium iodide, and the decolourization of potassium permanganate solution in presence of acetic acid. NITRIC OXIDE, NO. Preparation. A few 7 grammes of copper turnings are introduced into an 8-ounce flask provided with a thistle funnel and delivery-tube, and about 50 c.c. of a mixture of equal parts of nitric acid and water. In a few moments gas begins to be evolved without the application of heat, and red fumes appear in the flask. These red fumes are formed by the action of the nitric oxide on the oxygen contained in the flask; -after a time the colour disappears as they are displaced, and the gas may then be collected. The reaction which takes place is 3 Cu + 8 HN0 3 = 3 Cu(N0 3 ) 2 + 2 NO + 4 H 2 ; essentially it is 3 Cu + 2 HN0 3 = 3 CuO + 2 NO + H 2 0, and the CuO with the excess of nitric acid becomes Cu(N0 3 ) 2 . The gas is not very soluble in water (water dissolves about T^th its volume under ordinary conditions), and it may be collected over water. It dissolves in a cold solution of ferrous sulphate (as FeS0 4 .NO), and is expelled in a very pure condition from such a solution on warming it. Properties of nitric oxide. It is a colourless gas which by mere admixture with oxygen combines with it, giving rise to red fumes of the higher oxides of nitrogen. NO + O = N0 2 . It is very difficult to liquefy, requiring a pressure of 104 atmospheres at -11C. ; the liquid boils at -93C. It is a tolerably stable body, and is only decomposed at a red heat. Exp. 74. Expose a jar of the gas to air, and observe the red fumes. OXIDES AND OXY-ACIDS OF NITROGEN. 149 Exp. 75. Pass oxygen into a jar of the gas standing over water little by little, allowing an interval to elapse between each addition. Red fumes will be formed, and these will dissolve in the water, which gradually rises in the jar. If the gas is pure and the oxygen be added in the proper proportion, the water will rise to completely fill the jar. A dilute solution of nitrous acid is thus formed, and may be shown to liberate iodine from potassium iodide, or to decolourize permanganate of potash. Exp. 76. The flame of phosphorus, if feebly burning, will be extin- guished in the gas, whilst if already fully ignited it will continue to burn brightly. The temperature at which the gas is decom- posed being about 600 C., this seems to indicate that combustion is only supported when the temperature is sufficient to decompose the gas, the oxygen which is liberated being the supporter of the combustion. Composition of nitric oxide. When iron is heated in nitric oxide it combines with the oxygen and sets free the nitrogen. The gas first expands by the heat, and the iron when it burns takes up the oxygen from the nitric oxide. On the completion of the reaction only nitrogen remains, and this gas will be found to occupy half the volume of the original gas. Hence one mole- cule of nitric oxide contains one atom of nitrogen, and its formula will be NjOx. To determine the value of x we must ascertain the density of nitric oxide compared with hydrogen. It will be found to be fifteen times as heavy as hydrogen, and since the hydrogen molecule, H 2 , weighs 2, the molecule of nitric oxide must weigh 30. that is, the molecule consists of NO. NITROUS OXIDE, N 2 0. This gas is familiarly known as " laughing g ; i$," because when breathed in small quantity it produces a feeling of exhilaration. Inhaled in larger quantities it is an anaesthetic, and renders the subject insensible to pain, and is for this reason employed in dentistry. Preparation. It has already been pointed out (p. 144) that when nitric acid (dilute) is acted upon by zinc, nitrous oxide is formed. It is more usual, however, to prepare it by heating ammonium nitrate, the decomposition being represented by the equation NH 4 N0 3 = N 2 + 2 H 2 0. Introduce about 30 grammes of dry ammonium nitrate into a 150 TEXT-BOOK OF CHEMISTRY. 4-ounce flask and heat gently, and just so as to bring about a steady and not too rapid evolution of the gas. The delivery- tube should be wider than usual, as the salt is liable to be carried over and stop up the tube ; also stop the experiment when about two-thirds of the salt has been decomposed or an explosion may ensue. Cold water dissolves about its* own volume of the gas ; it may, however, be collected over hot water. Properties of nitrous oxide. ^It is a colourless gas with an agreeable odour and taste. It condenses at 15 C. under a pressure of 40 atmospheres to a liquid which boils at - 92 C. under ordinary pressure. One hundred volumes of water dissolve 130 volumes of the gas at C., 92 at 10 C., and 67 at 20 C. It is easily decomposed by heat, and supports combustion as readily as oxygen. Exp. 77. Plunge a glowing taper into a jar of nitrous oxide, and it will burst into a flame just as it does in oxygen. Sulphur and phosphorus also burn in the gas with almost as much vigour as in oxygen, though if only feebly ignited they may be extin- guished. To distinguish it from oxygen, pass nitric oxide into ajar of the gas no red fumes will appear. Composition of nitrous oxide. The composition of the gas may be determined by the combustion of potassium in it, and by an estimation of its density, the proof corre- sponding with that al- ready given in previous cases. The potassium may be heated in the gas as shown in Fig. 27. It will be found to con- tain its own volume of nitrogen 2 X,6 = 2 N 2 2 . ^ ii^ -- ^^-^ff^ 4 volumes. 4 volumes. Fio. 27. Or it may be mixed with excess of hydrogen, and exploded in a eudiometer, when the reaction is = H 8 OXIDES AND OXY-ACIDS OF NJTROfJKY. 151 QUESTIONS. CHAPTER XII. 1. How do you account for the occurrence of oxides of nitrogen, and the oxy-acids or salts of these, in the air and in tho soil? 2. What is the effect of heating lead nitrate alone, and what when it is heated along with concentrated sulphuric acid ? 3. How is nitric acid prepared on the large scale? 4. In what respects does nitric acid differ from sulphuric acid? 5. Give striking experiments calculated to illustrate in regard to nitric acid, (a) its powerful oxidizing action ; (6) solvent action. C. How would you prepare nitrates of lead and potassium, and obtain them in the form of crystals ? 7. Explain the term L1 anhydride," and give instances of anhy- drides. What is the action of phosphorus pcntoxide on nitric acid ? 8. How is tho tetroxido of nitrogen obtained? Under what circumstances are you justified in regarding it as N 2 4 , and when as N0 2 ? 9. Describe the preparation of nitrogen trioxide in the liquid form. 10. By what chemical reactions may nitrites be distinguished from nitrates ? 11. Express by means of equations the action of copper, cupric oxide, lead oxide, and tin respectively on nitric acid. 12. What are the properties of nitric oxide, and how may it be distinguished from nitrous oxide? 13. Demonstrate that the chemical formula of nitric oxide is NO. 14. Give two methods for the preparation of nitrous oxide. 1.0. State the physical properties of nitrous oxide, and say how you would distinguish by chemical tests nitrous oxide from oxygen. In what respects docs it resemble oxygen ? CHAPTER XIII. PHOSPHORUS. Occurrence. Phosphate of lime, Ca 3 (P0 4 ) 2 , the principal source of phosphorus, forms the essential constituent of the mineral apatite, and of bone-ash. The former occurs in the older formations of the earth's crust as Chlorapatite, 3 Ca 3 (P0 4 ) 2 . CaCl 2 ; and Fluorapatite, 3 Ca 3 (P0 4 ) 2 . CaF 2 1 Bone-ash is obtained by the dry distillation of bones. In small quantities phosphates are very widely distributed, all fertile soils contain a small percentage, and they are always found in plants, being, like nitrogen, essential to plant-life. Preparation of phosphorus. The first step in the prepara- tion of phosphorus from bone-ash consists in treating it with sulphuric acid, whereby a double decomposition takes place Ca 3 (P0 4 ) 2 + 3 H 2 S0 4 - 3 CaS0 4 + 2 H 3 P0 4 . When the decomposition is complete, the product is filtered through a bed of cinders ; the calcium sulphate remains on the filter, and the phosphoric acid passes through. The liquid is then concentrated, mixed with charcoal, and further heated almost to dryness, the phosphoric acid losing water and being converted into metaphosphoric acid H 3 P0 4 = HP0 3 + H 2 0. Finally, the granular product is heated to full redness in clay retorts placed horizontally in series over a fire, when the following reaction takes place 2 HP0 3 + 6 C = H 2 + 6 CO + 2 P. Luted into the mouth of each retort is an iron pipe, bent at right angles and dipping into water ; the vapour of phosphorus is thus led into the water, and there condensed out of contact 152 PHOSPHORUS. 153 with air. The temperature of the water is high enough to keep the phosphorus in the liquid state, and it can be run off or ladled out from time to t ; me. It is further refined by re-melting in water, and filtering through chamois leather or canvas to remove suspended matter, and then finally cast into sticks. Properties of phosphorus. The phosphorus so obtained is a yellowish, translucent solid which can be readily cut with a knife. It has a specific gravity of 1*82, it melts at 43 C., and boils at 269 C. It is insoluble in water, but readily dissolves in bisulphide of carbon. It is kept under water, since when ex- posed to air it slowly oxidizes, and even at 34 C. ignites and burns with great brilliancy. It combines also at ordinary temperatures with fluorine, chlorine, bromine, iodine, and sulphur, and in the finely-divided condition with oxygen, with the evolution of light and heat. Phosphorus may be obtained in two other allotropic modifica- tions, the red or amorphous phosphorus, and the crystalline form (rhombohedra). 154 TEXT-BOOK OF CHEMISTRY. Amorphous phosphorus is, according to its method of pre- paration, a reddish-brown powder or a close-textured mass showing conchoidal fracture. This form is prepared on the large scale by heating ordinary phosphorus at 250 C. in cast- iron pots from which the air is excluded, and removing the unconverted phosphorus which remains, by boiling the finely- divided product with caustic soda solution. On a small' scale in the laboratory it may readily be obtained by heating ordinary phosphorus in an atmosphere of nitrogen or carbon dioxide. The amorphous phosphorus differs very considerably in its properties from that already described. It has a higher specific gravity (2'14), and is insoluble in bisulphide of carbon. It undergoes no change in air at ordinary temperatures, and may be freely handled without danger ; it combines with oxygen, the halogens, and sulphur at much higher temperatures than ordinary phosphorus. Unlike ordinary phosphorus, it is not poisonous. Lucifer matches are tipped with a mixture of phosphorus and certain substances, such as lead dioxide and potassium nitrate, which readily part with oxygen. " Safety" matches contain no phosphorus, being tipped with a mixture of antimony sulphide (Sb 2 S 3 ), the sulphur being the inflammable body, and potassium chlorate; in this case the match is ignited by rubbing it on a prepared surface of red phosphorus and powdered glass. In either case the heat requisite to promote chemical action and to ignite the phosphorus is generated by friction on a rough surface. Crystalline phosphorus is obtained by heating phosphorus in a sealed tube along with metallic lead and allowing it to cool, subsequently removing the lead by dissolving it in dilute nitric acid. Hydrides of Phosphorus. Phosphorus forms three hydrides Gaseous phosphoretted hydrogen or phosphine PH 3 . Liquid phosphoretted hydrogen ... ... ... l^H^ Solid phosphoretted hydrogen IV^- PHOSPHORUS TR-IHYDRIDE, PH 3 . This gas, which is the analogue of ammonia, is obtained by heating phosphorus in a flask with a solution of caustic soda. As obtained in this way it is mixed with small quantities of the liquid and solid PHOSPHORUS. 155 hydrides which render it spontaneously inflammable in air, the air is therefore, previous to heating, displaced from the apparatus by hydrogen, and the end of the delivery tube must dip under water as shown (Fig. 29). The reaction which takes place is FIG. 29. PIT,. 4 P + 3 NaOII + 3 H 2 = 3 NaH 2 P0 2 + Sodium hypophosphito. It is also formed when phosphide of calcium (obtained by heating together lime and phosphorus in a closed crucible) is brought into contact with water. Properties of PH ;! . It is a colourless gas which condenses only when cooled to 90 C. It is very slightly soluble in water, and possesses a penetrating garlic-like odour which is evident even with very small quantities of the gas ; it is very poisonous. If free from other hydrides, it is not inflammable in air at ordinary temperatures ; heat decomposes the gas into its elements more readily than the corresponding nitrogen compound, NH 3 . Just as ammonia combines directly with the haloid acids HC1, II Br, etc., to form ammonium chloride, ammonium bromide, etc., so phosphorus trihydride forms similar compounds. The com- bination with hydriodic acid to form phosphonium iodide PH 3 + HI = PH 4 I takes place very readily. This body may be used as a source of 156 TEXT- BOOK OF CHEMISTRY. pure PH 3 by acting upon it with potash or soda, the reaction being analogous to that employed in the preparation of ammonia PH 4 I + NaOH = PH 3 + Nal + H 2 0. NH 4 C1 + NaOH = NH 3 + NaCl + H 2 0. The Oxides and Oxy-acids of Phosphorus. Oxides. Corresponding Acids. P 2 (not known in free state) PA (PA) Hypophosphorous acid, H 3 P0 2 or 3 H 2 0. P/). Phosphorous acid, H 3 P0 3 or 3 H 2 0. P 2 3 . Hypophosphoric acid, H 4 P 2 6 or 2 H 2 0. P 2 4 . Orthophosphoric acid, H 3 P0 4 or 3 H 2 0. P 2 5 . Pyrophosphoric acid, H 4 P 2 7 or 2 H 2 0. P 2 5 . Metaphosphoric acid, HP0 3 or H 2 0. P 2 5 - The more important are the phosphorous oxide and the phos- phorus pentoxide, and the acids derived from them, and we shall confine our attention to these. Phosphorous oxide, P 4 O C . Phosphorous oxide or anhydride is obtained when phosphorus is exposed to oxidation in air at ordinary temperatures, or when it is burnt in a limited supply of air. This may be effected by placing a small piece of dry phosphorus in a tube drawn out so as to form a fine orifice, the other end of the tube being connected with an aspirator. The phosphorus is gently warmed, and then a slow stream of dry air is drawn through the tube. The phosphorous oxide collects in the tube as a white powder, which on exposure to moist air ignites, forming the higher oxide P 2 5 . Phosphorous acid, H 3 PO 3 , is prepared by the action of excess of water on phosphorus trichloride PC1 3 + 3 H 2 = H 3 P0 3 + 3 HC1. The hydrochloric acid is easily volatilized by heating the product on a water-bath, phosphorous acid remaining. It is a reducing agent, as it readily takes up oxygen, and is transformed into ordinary phosphoric acid, H 3 P0 4 . PHOSPHORUS. 157 PHOSPHORUS PENTOXIDE, P 2 O ;V Whenever phos- phorus is burnt in an excess of dry oxygen or air this oxide is formed. The operation may be performed in a glass bolt-head with two side tubes, through one of which passes air dried over fused calcium chloride, and through the other the fumes are aspirated, a bottle being placed between the aspirator and the side tube to intercept the phosphorus pentoxide (Fig. 30). A FIG. 30. small piece of phosphorus carefully dried between filter paper is introduced through the neck of the bolt-head into a small basin attached as shown, and then successively other pieces, until sufficient of the oxide has been prepared. After the first piece has been ignited by touching it with a hot wire, the basin will be hot enough to start the combustion of the subsequent portions as they are dropped into it. The pentoxide so obtained always contains phosphorous oxide, from which it may be freed by pass- ing it in the gaseous form along with oxygen over gently heated finely divided platinum. Compare preparation of sulphur trioxide. Properties of P 2 O.,. The oxide is an amorphous white powder, which when left in contact with moist air gradually absorbs moisture and deliquesces. When thrown into water it combines with it with a hissing noise, and forms rnetaphosphoric acid, HP0 3 . P 2 6 + H 2 = 2 HP0 3 . 158 TEXT-BOOK OF CHEMISTKV. Its great affinity for water renders it a valuable agent for completely drying gases, whilst in contact with acids it frequently deprives them of water, forming anhydrides H,S0 4 + P 2 5 = 2 HP0 3 + S0 3 . 2 HN0 3 + P.,0- - '2 HP0 3 + X,0 5 . Similarly it chars wood, paper, and many organic suhstances by its dehydrating action. ORDINARY PHOSPHORIC ACID, or Orthophosphoric Acid, H 3 P0 4 . This acid is prepared by the action of nitric acid on ordinary phosphorus, or by boiling for some time a solution of metaphosphoric acid. Exp. 78. Introduce a few pieces (say 10 grammes) of phosphorus into a large retort, and pour upon it 150 c.c. of a mixture of one part of nitric acid to two parts of water. Heat cautiously, and presently red fumes of oxides of nitrogen will be evolved by the reduction of the nitric acid 4 P + 10 HN0 3 + H 2 = 4 H 3 P0 4 -f 5 X 2 3 . The heating is continued in such a manner as to keep the liquid about its boiling-point, but so that as little as possible distils over. When the phosphorus has all disappeared, and red fumes are no longer generated, the acid is distilled over until that remaining has a syrupy consistency, more reel fumes being evolved at this stage through the oxidation of some phosphorous acid. Finally, the thick liquid is transferred to a porcelain dish and evaporated so long as strongly acid fumes (HX0 3 ) are given off. As trichloride of phosphorus when treated with excess of water yields phosphorous acid, so the pentachloride, by similar treatment, gives ordinary phosphoric acid PC1 5 -f 4 H,0 = H 3 P0 4 + 5 HC1. Phosphoric acid, when sufficiently concentrated, crystallizes on standing; it is a tribasic acid, each of the atoms of hydrogen being replaceable by a metal. The phosphates. The phosphates of the alkalies, sodium, potassium, and ammonium, are soluble in water, and are obtained by the addition in solution of the alkaline hydrates to phosphoric acid. The amount of the alkali added may be sufficient to " OF THK UNIVERSITY 1-lloSl'lfOllUS. replace one, two, or three atoms of the hydrogen, thus NaOH 4- H 3 P0 4 = NaH 2 P0 4 + H 2 0. 40 98 2 NaOH + H 3 P0 4 = Na 2 HP0 4 + 2 H 2 0. 80 '98 3 NaOH + H 3 P0 4 = Na 3 P0 4 + 3 II,(). 120 98 The numbers underneath show the combining proportions of caustic soda and phosphoric acid required to form such salts. That is to say, if to 98 grammes of phosphoric acid there be added 40 grammes of caustic soda and the solution evaporated the salt NaII a P0 4 will be obtained ; if 80 grammes, then the salt formed will he N;i.JIl'( ) 4 , and if 120 grammes, the salt Na 3 P0 4 will be formed. The salt in which the whole of the hydrogen is rephiced is known as the normal salt, and we have here an instance of a normal salt which is not neutral in its reaction with litmus but alkaline. NaH 2 P0 4 , Sodium dihydrogen phosphate acid reaction. Na 2 HP0 4 , Disodium hydrogen phosphate slightly alkaline. Na 3 P0 4 , Normal sodium phosphate distinctly alkaline. In "microcosmic salt" part of the hydrogen is replaced by sodium and part by ammonium, Na.NH 4 .HP0 4 . The normal phosphates of the alkaline earths (Ba, Sr, Ca) and of Mg, Pb, Ag, and indeed of all the other metals, are insoluble in water, but soluble in dilute mineral acids. They may be pre- pared by adding a soluble salt of the metal in question to an aqueous solution of an alkaline phosphate 2 Na 3 P0 4 + 3 CaC! 2 = Cn 3 (P0 4 ) 2 + 6 NaCl. Xa 3 P0 4 + 3 AgN0 3 = Ar 3 P0 4 + 3 NaN0 3 . Tests for phosphates. (1) Ferric chloride gives, even in pivsoiice of acetic acid, a yellowish-white precipitate of ferric phosphate. (Arseiiutcs also give a yellowish-white precipitate.) (2) Silver nitrate gives a pale yellow precipitate of silver phosphate. (Arsenates give a brick-red precipitate.) (3) Excess of ammonium molybdate in the presence of nitric acid gives a bright yellow precipitate of phospho-molybdate of ammonium even in the cold, but more rapidly on warming. (The arsenates give a similar precipitate only on warming.) 160 TEXT-BOOK OF CHEMISTRY. (4) The presence of phosphorus may always be detected by heating a little of the powdered substance along with magnesium filings in a narrow tube and then moistening the product with water. Phosphoretted hydrogen is given off, and may be recog- nized by its characteristic odour. Pyrophosphoric acid. H 4 P 2 O 7 , is obtained by heating ordinary phosphoric acid to 300 C. 2 H 3 P0 4 - H 4 P 2 7 + H 2 0. As with the phosphates, the salts of the alkali metals are soluble in water, those of the other metals being insoluble in water but soluble in dilute mineral acids. Tests for pyrophosphates. (1) Silver nitrate gives a white precipitate of the pyrophosphate, thus distinguishing it from the phosphate. (2) Pyrophosphoric a.-id does not coagulate albumen. Metaphosphoric acid, HPO 3 , is obtained when ortho- or Pyrophosphoric acid or their ammonium salts are strongly heated H 3 P0 4 = HP0 3 + H 2 0. Like the pyrophosphates they give a white precipitate with silver nitrate, but metaphosphoric acid is distinguished by the fact that. it coagulates albumen. Compounds of phosphorus with the halogens. By direct union of phosphorus with these elements, bodies of the type PX 3 and PX 5 are farmed, and by the action of moisture on PC1 5 and PBr 5 , the oxychlorides POC1 3 , and oxy bromides POBr 3 , respectively, are formed. Chlorides of Phosphorus, PC1 3 and PC1 5 . When phosphorus burns in dry chlorine, phosphorus trichloride, PC1 3 , is formed as a colourless fluid whose boiling-point is 73 C., and if excess of chlorine be present the trichloride is gradually transformed into the pentachloride, PC1 5 . This is a yellowish solid substance which passes directly into vapour at 168 C., without melting, undergoing partial decomposition into PC1 3 and C1 2 . In presence of moisture, PCI- slowly changes into a fuming liquid, phosphorus oxychloride, POC1 3 PCL + H 9 = POOL + 2 HC1. PHOSPHORUS- 161 Phosphorus trichloride under similar circumstances forms phos- phorous acid PC1 * 3 H0 H 3 P0 3 + 3 HC1. This tendency to combine with oxygen and liberate chlorine renders these chlorides valuable reagents for substituting chlorine for oxygen or hydroxyl (Oil), in this latter case eliminating HCI. The following equations represent some of the more im- portant reactions illustrating this so 80s so b S0 3 S0 2 (OH j OH (OR PC1 S = POC1 3 + S0 2 . PC1 6 = POC1 3 + SOCI; PC1 5 = POC1 3 + S0 2 , PC1 5 = POC! 3 + S0 2 CIj PCI, = POOL + CVHr, ' OH C1 + HCI. + HCI. HCI. PC1 6 = POClg PCL = POC1, 1IC1 C 2 H 5 OH Ethyl alcohol. C,II 3 0. OH + Acetic acid. CH 3 CHO + Aldehyde. By the action of an excess of water on phosphorus pentachloride orthophosphoric acid is formed, the whole of the chlorine being eliminated as hydrochloric acid PC1 6 + 4 H 2 = H 3 P0 4 + 5 HCI. Ethyl chloride. + tyi 3 o. ci + Acctyl chloride. + CH 3 CHC1., Ethylidene chloride. 162 TEXT-BOOK OF CHEMISTRY. QUESTIONS. CHAPTER XIII. 1. What is the effect of heating chlorapatite and fluorapatite respectively with concentrated sulphuric acid ?, 2. How is phosphorus extracted from phosphoric acid ? 3. Write down in parallel columns the physical properties of ordinary and red phosphorus. 4. What differences are there in chemical behaviour between ordinary and red phosphorus ? 5. Why does a match ignite when rubbed on a rougli surface ? What chemical action takes place during the ignition ? 6. To what is the spontaneous^ignition of phosphorus trihydride due, and how may the hydride be prepared so as not to ignite spontaneously ? 7. Express by equations the action of phosphorus on chlorine, iodine, caustic potash, and nitric acid. 8. Compare the trihydride of phosphorus with the trihydride of nitrogen. 9. How is phosphorous oxide prepared, and how may it be converted into the pentoxide ? 10. How may phosphorus pentoxide be obtained in quantity and converted into metaphosphoric and phosphoric acid ? 11. What is the action of water on the trichloride and on the pentachloride of phosphorus ? Give equations. 12. What is meant by saying that orthophosphoric acid is a tribasic acid ? Write down the names and formulas of a few phosphates that are soluble in water. 13. By what chemical tests may phosphates be distinguished from arsenates and from pyrophosphates ? 14. How is the trichloride of phosphorus prepared, and by what means may it be converted into the pentachloride ? CHAPTER XIV. CARBON AND THE HYDROCARBONS. OAUBON is the first member of a group consisting of the elements carbon, silicon, titanium, zirconium, and tliorium, of which the first two members alone come under consideration amongst the non-metals. They show a considerable resemblance to one another in their physical and chemical properties. ~~ Comparing together more particularly carbon and silicon we observe that (1) The elements themselves are very infusible. (2) They exist in allotropic modifications of similar character. (3) They form oxides of great stability and also gaseous hydrides, C1I 4 and SiH 4 , the farmer of these being a stable body, whilst the latter undergoes decomposition very readily. (4) Carbon and silicon both combine directly with fluorine to form CF 4 and SiF 4 respectively. With the other halogen elements they do not combine directly, but volatile liquid tetrachlorides CC1 4 and SiCl 4 are obtained indirectly. Occurrence Carbon is found in nature in a state of com- parative purity as diamond and graphite, the latter known as mineral plumbago, from which black-lead pencils are made. These forms do not, however, occur in any very considerable quantity, and the sources from which the large supplies of carbon are obtained are coal and vegetable matter. The tissue of plants is very constant in composition, and disregarding the moisture and the mineral ash left after com- bustion, amounting usually to about 1 per cent., dried tvood is found to consist of 163 164 TEXT-BOOK OF CHEMISTRY. Carbon 50 per cent. Hydrogen 6 Oxygen and nitrogen ... ... 44 ., "Where plants undergo decay and form thick accumulations of peat) the relative proportion of the carbon increases, and the following may be taken as the average composition of peat, leaving out of account moisture and mineral matter Carbon ... ... ... ... 58 per cent. Hydrogen ... ... ... ... 5 ,, Oxygen and nitrogen 37 In deposits of peat and the remains of vegetation which have lain for long periods of time this process of parting with the more volatile constituents and consequent increase in the proportion of carbon goes on, and instead of peat we have a much denser product known as brown coal or lignite, in which the structure of the vegetation composing it can, however, still be observed. Lignite varies greatly in composition, especially in regard to the amount of moisture and ash. Excluding these, it contains on the average Carbon 66 per cent. Hydrogen 5 Oxygen and nitrogen 29 ,, In the older formations of the earth's crust there are large deposits of coal, which have resulted from long-continued action similar to the foregoing. The seams of coal usually occur at some depth, and are overlaid by other strata. The vegetable tissue from which coal is derived has thus been subjected to immense pressure and to increased temperature, and under these agencies, acting over long periods of time, the changes already noticed in the passage from woody tissue to lignite have been still farther accentuated. Coal is darker in colour, denser, and more brittle ; as to composition, the following numbers may be compared with those given for wood, peat, and lignite Bituminous CoaL Anthracite. Carbon ... ... ... 84 per cent. 94 per cent. Hydrogen 5 3 Oxygen and nitrogen ... 11 3 CARBON AND THE HYDROCARBONS. 165 Over 150 million tons of coal are brought to the surface in the United Kingdom annually. In many localities, especially in South Russia and the United States, there are large deposits of petroleum a mixture of various oils, but all composed of carbon and hydrogen, and hence termed hydrocarbons. And when we add the very extensive series of carbon com- pounds which have been prepared in the laboratory from coal and petroleum, and the products, such as starch, sugar, turpen- tine, albumen, stearin, etc., elaborated by plants and animals, we are in a position to appreciate the immense importance of the element carbon. The study of such bodies is indeed set apart as a special branch of the science, and known as Organic Chemistry, or the Chemistry of the Carbon Compounds. Finally, carbon occurs in combination with oxygen as carbon dioxide in the air, and in vast deposits of limestone and dolomite. The carbon dioxide in air, being less than 4 volumes in 10,000, might be regarded as insignificant, but the mass of the^atmo- sphere is such that at this computation there must be very nearly a billion tons of carbon in it. Allotropic forms of carbon. (1) Diamond is the crystal- line form of carbon ; it is found in South Africa and Brazil, usually as octahedra or cubes, or as some modifications of these. Its value is due to its great hardness and brilliancy of lustre, and to the fact that it does not oxidize or undergo change even in presence of corrosive substances. It is the densest form of carbon, having a specific gravity of about 3'5, and is also the most difficult to ignite in oxygen. It is therefore not to be wondered at that the composition of diamond remained unknown until the time of Lavoisier, although it had been previously observed that diamond could be burnt and left no appreciable residue. Lavoisier about a century ago, by means of a burning glass, ignited diamond in air enclosed over mercury, and found that when it burnt, the gas which was formed turned lime-water milky and was carbon dioxide. Dumas, later, showed that carbon dioxide was the only product obtained when diamond is burnt in oxygen, and that every 12 parts by weight of diamond yielded 44 parts of carbon dioxide, according to the equation 166 TEXT-BOOK OF CHEMISTRY. C + 2 = C0 2 . 12 32 44 Diamond consists, therefore (with the exception of a minute quantity of ash) of pure carbon. (2) Graphite. This also occurs naturally, being found usually in the older crystalline rocks. Cast-iron contains plates of this form of carbon, which can be seen at a freshly-fractured surface, and masses of it accumulate at the base of blast furnaces. It is a soft, dark-grey substance, with a metallic lustre, and possesses a much lower specific gravity (2'2) than diamond. Graphite (and also amorphous carbon) is acted upon when gently heated with a mixture of potassium chlorate and nitric acid, whilst diamond is imattacked. (3) Amorphous carbon is familiar to us as charcoal, lamp- black, or animal charcoal, which, however, are usually more or less impure forms of carbon. The former may be obtained by strongly heating wood or organic bodies in vessels from which air is excluded, or by the action of dehydrating substances such as concentrated sulphuric acid. Exp. 79. Heat a few pieces of wood in a hard glass tube over the flame of a Bimsen burner. Volatile vapours are at first given off and burn at the mouth of the tube, and when these are no longer to be seen, throw out the contents of the tube into water. The black charred pioduct is wood charcoal, and though its specific gravity is 1*8 or thereabouts, it will float on water in consequence of the large amount of air contained within its pores. A special form of charcoal is manufactured by charring wood by means of superheated steam. Exp. 80. Make about 100 grammes of sugar into a thick syrup by dissolving it in a small quantity of hot water, and place it in a deep glass cylinder, then pour in about 100 c.c. of concentrated sulphuric acid. Presently the liquid will blacken and froth considerably, and a mass of black charcoal much more bulky than the sugar originally taken will be formed. "VTash this thoroughly with water till free from acid, and there remains carbon in a granular, amorphous condition. By drying this, and then heating it in a stream of chlorine to remove hydrogen or other gases, a very pure specimen of carbon is obtained. CARBON AND THE HYDROCARBONS. 167 Animal charcoal is prepared by charring bones in closed iron retorts, and consists of a mixture of very porous charcoal and the mineral constituents of bone (chiefly phosphate of lime). It is used for decolourizing raw sugar, as it has the property of removing many colouring matters. Exp. 81. Shake up "with animal charcoal a hot solution of indigo or litmus for a few moments and then pour it on a filter, the filtrate will be colourless. That tho colouring matter is removed by the animal charcoal and not by the filter, may be shown by pouring a similar .solution which has not been treated by aninnl hear coalt hrough a filter paper, Lamp-black may be made by burning resin or turpentine, and bringing a cool surface, e.g. the under-side of a porcelain basin lilled with cold water, into the llame. In this form, after treat- ment with chlorine, a particularly pure and finely-divided -form of carbon is prepared. In whatever form it occurs, carbon is infusible at the highest temperatures attainable ; it is also a very bad conductor of heat or electricity. It cannot be considered an element of great chemical activity, since at ordinary or moderate temperatures it does not combine directly with any of the elements except fluorine, and even at high temperatures there are comparatively few elements with which it shows a disposition to unite. At high temperatures, however, it combines directly with oxygen, forming carbon monoxide or carbon dioxide ; with sulphur to form carbon disulphide, and with hydrogen to form acetylene (C 2 H 2 ). Two very characteristic properties are (1) its power of absorbing gases manifested by the amorphous form ; (2) its ajtivity as a reducing agent. If the air be removed from the pores of wood charcoal by exposure to a vacuum, and this body be then introduced into an atmosphere of ammonia or carbon dioxide, etc., a volume of gas will be taken up many times greater than that of the charcoal, the gas therefore undergoing condensation, and some heat being evolved in consequence. Cocoa-nut charcoal, under favourable conditions, was found to absorb of 168 TEXT-BOOK OF CHEMISTRY. Ammonia 172 times its volume. Hydrochloric acid ... 165 Nitrous oxide ... 99 ,, ,, Carbon dioxide ... 97 It is this power of absorbing gases to which charcoal owes its efficacy as a medium for disinfecting purposes, .the gaseous products of putrefaction being taken up within its pores : and gases like sulphuretted hydrogen are oxidized by absorbed oxygen. We have already had an example of a gaseous reducing agent in hydrogen, which, owing to its affinity for oxygen, reduces many oxides to the metallic condition. And in sulphurous acid or phosphorous acid we have instances of liquids as reducing agents, their activity being due to the ease with which they undergo oxidation to sulphuric acid and phosphoric acid respectively. In carbon we have a solid reducing agent which finds very frequent employment in operations conducted at high temperatures, the carbon under such conditions being oxidized to carbon monoxide or dioxide at the expense of the oxygen contained in the bodies with which it is mixed. Tims, most metallurgical operations involving a reduction of oxides to the metal, are carried out with the use of carbon in the form of coke or coal which is oxidized to CO or C0 2 in the process. Exp. 82. Make an intimate mixture of about a gramme of finely- powdered oxide of lead (litharge) with about one-tenth its weight of charcoal, and heat to redness in a hard glass tube or porcelain crucible for five minutes. Now throw some of the powder into a mortar with a little water and rub it up, using pressure, with the pestle, and then wash away the charcoal by means of a stream of water. Pellets or plates of metallic lead will be obtained 2 PbO + C = 2 Pb + C0 2 Similarly, oxide of copper or bismuth may be reduced, and metallic copper or bismuth obtained from them. The reduction of iron ores, or oxide of zinc or tin, are examples of similar reductions carried out on the large scale. CARBON AND THE HYDROCARBONS. 169 Hydrocarbons. These are compounds consisting of carbon and hydrogen alone. The direct combination of carbon and hydrogen in the laboratory can only be effected with difficulty (acetylene, C 2 H 2 , being formed), and yet the number of known hydrocarbons is exceedingly great. They vary in physical and chemical character according to their composition, and according to the arrangement of the ultimate particles of carbon and hydrogen of which they are composed. Hydrocarbons containing a small number of atoms of carbon and hydrogen are usually gaseous, such as marsh gas, riI 4 , ethylene or olefiant gas, C 2 H 4 , acetylene, C 2 H 2 ; and those whose composition is more complex are at ordinary temperatures liquid, such as pentane, C 5 H 12 , benzene, ^ (i ll, ; , turpentine, C 10 H 1( . ; or solid, such tis naphthalene, C 10 H 8 , anthracene, C 14 H 10 . The hydrocarbons may be arranged in series in accordance with the relative numbers of atoms of carbon and hydrogen which they contain (1) The Marsh Get a >SV/V.s (or Paraffins), the first member of which is marsh gas, CH 4 , and succeeding members C 2 H C , C 3 H 8 , and so on, the general expression for the relation of carbon to hydrogen being C n II 2 ,, + 2 . (2) The JSthylene .Series (or defines), the first member of which is ethylene, C 2 H 4 , and succeeding members C 3 H 6 , C 4 H 8 , and so on, the general expression for the relation of carbon to hydrogen being C u H 2n . (3) The Acetylene Series, the first member of which is acetylene^ C 2 II 2 , and succeeding members C 3 H 4 , C 4 H , and so on, the general expression for the relation of carbon to hydrogen being C n II 2n - 2 . (4) Hydrocarbons having the general formula C n H 2n - 4 and C n H 2n _ 6 , and others having still smaller proportions of hydrogen, are known, a familiar example of the C n H 2n - series being biMixene, C 6 H , the first member of this series. At this stage we shall only take into consideration the three hydrocarbons, marsh gas, ethylene, and acetylene. MARSH GAS, CH 4 . This gas is so called because it is frequently generated in marshes or pools where vegetable matter 170 TEXT- BOOK OF CHEMISTRY. is in course of decay. The "blowers" in coal-mines discharge large quantities of this gas, which from its inflammable nature is termed " fire-damp," and it is also formed in the destructive distillation of wood or coal, coal gas containing usually about 35 per cent, of marsh gas. Preparation. About 30 grammes of sodium acetate is intimately mixed with 100 grammes of soda-lime (lime to which caustic soda lias been added), and dried at a gentle heat. The charge is then introduced into a flask of hard glass and heated strongly, the reaction which ensues being represented by the equation + NaOH = Na 2 C0 3 + CH 4 . The gas may be collected over water. Properties. Marsh gas or methane is a colourless and odourless gas, which at zero is condensed to the liquid form under a pressure of 140 atmospheres. It is only slightly soluble in water, 100 volumes of which at zero dissolve 5'5 volumes of the gas. It burns with a pale blue non-luminous flame, forming carbon dioxide and water vapour CH 4 + 2 2 = C0 2 + 2 H 2 0. With oxygen or air within certain limits it forms an explosive mixture, and the explosions occurring in coal-mines are usually due to the firing of such a mixture. With the halogen elements it forms compounds in which part or even the whole of the hydrogen is replaced atom for atom by these elements. The composition of marsh gas may be determined by exploding a known volume (say 30 c.c.) with an excess of oxygen (120 c.c.) in a eudiometer ; the carbon and hydrogen unite with oxygen to form carbon dioxide and water vapour respectively. No diminu- tion in volume will occur if the experiment be performed at 100 C., that is, so long as the water remains in the form of vapour ; but when the water condenses, a diminution of 60 c.c. will be recorded. Carbon dioxide and the excess of oxygen remain, and the amount of the former may be found by absorbing it with caustic potash ; this will give a reduction of 30 c.c., the oxygen excess being 60 c.c. Expressing this shortly we have CARBON AND THE HYDROCARBONS. 171 2 vols. marsh gas -f 8 vols. oxygen = 4 vols. water vapour + 2 vols. carbon dioxide + 4 vols. oxygen. No\v water vapour contains its own volume of hydrogen, and two volumes of marsh gas therefore consist of four volumes of hydrogen, and that amount of carbon which is contained in two volumes of carbon dioxide. This would give as the composition CH 4 , or some multiple of this. We iintl, by weighing, that the density of marsh gas as com- pared with hydrogen is 8, so that its molecular weight must be 16: and thus the formula of marsh gas is CII 4 . Marsh gas, as ordinarily prepared, is frequently contaminated with hydrogen or with other hydrocarbons. ETHYLENE or Olefiant Gas, C 2 H 4 , occurs as one of the products of the destructive distillation of coal, and the luminosity of the coal gas flame is largely owing to the presence of this gas. Preparation. Mix together 200 c.c. of sulphuric acid and 50c.c. of water, and cautiously add 50 c.c. of alcohol. Pour into a- wide- mouthed flask of about a litre capacity, fitted with a cork through which pass (1) a rather wide delivery-tube, (2) a thermometer, (3) a thistle tube dipping into the liquid. Heat until the temperature rises to 165 C., and keep as near this as possible. If the alcohol 172 TEXT-BOOK OF CHEMISTRY. is impure a good deal of frothing occurs, which is, however, less troublesome if sand has been introduced into the flask. The gas should be passed through wash-bottles containing a solution of caustic soda, and collected over water, but the first three or four cylinders of it should be rejected, as they contain a very explosive mixture of ethylene and the air displaced from, the flask and wash-bottles. Properties. Ethylene is a colourless gas which is freely soluble in alcohol, but in water it is even less soluble than marsh gas, 100 volumes of water dissolving about 2^ volumes of the gas at C. It is more easily condensed to the liquid form than marsh gas, requiring a pressure of 43 atmospheres at C. ; the liquid boils at- 103 C. It burns with a luminous flame, which is smoky unless the gas is diluted with hydrogen or marsh gas. It combines directly with chlorine to form C 2 H 4 C1 2 , an oily liquid, and it is for this reason often called olefiant gas. Mixed with oxygen it explodes much more powerfully than marsh gas, and great care must be exercised in dealing with mixtures of ethylene with air or oxygen. The composition of ethylene is established by a similar method to that employed in the case of marsh gas. Coal gas. When coal is heated in retorts from which air is excluded, the chief products formed are (1) Tarry matters and condensible oils. (2) Ammonia. (3) Coal gas. (4) Small quantities of carbon dioxide, and of sulphur com- pounds such as CS 2 , H 2 S. A ton of coal yields about 10,000 cubic feet of coal gas, the composition of which varies according to the kind of coal used and the method of preparation. The following may be taken as representing its general composition Hydrogen 50 per cent. \ Marsh gas 35 > Diluent gases. Carbon monoxide ... 5 ) Ethylene and other) defines | 6 Light-giving gases. Oxygen, nitrogen, etc. 4 CARBON AND THE HYDROCARBONS. 173 The tar and condensible oils are removed by cooling- the gas, the ammonia by passing it through "scrubbers,'* where it is brought into intimate contact with water, and the C0 2 and sulphur compounds by passing it over lime. Oxide of iron is frequently used instead of lime for the removal of sulphur compounds. ACETYLENE, C 2 H 2 , occurs in small quantity in coal gas, and is formed when coal gas is burnt with an insufficient supply of air, or the flame is cooled by impinging on a cold surface. Carbon and hydrogen unite directly to form acetylene when a powerful electric discharge is passed between carbon poles in an atmosphere of hydrogen. Exp. 83. Fit into an ordinary lamp chimney a cork through which ]t.-i>so.s a short piece of straight wide tubing, and a second narrow piece bent at right angles as shown in Fig. 32, and connected with the supply of coal gas. Close the aperture at the top of the chimney, and allow the gas to escape by the straight tube until the air is displaced, then light it at the lower extremity of this tube and uncover the aperture at the top of the chimney. The flame will then pass up the tube and attach itself to the inner opening where the air and coal gas meet, the flame area being 174 TEXT-BOOK OF CHEMISTRY. air and the surrounding atmosphere being coal gas. The gas escaping at the top of the chimney may be ignited, and here we shall have a flame of coal gas burning in air as in combustion under ordinary circumstances. In the flame burning in coal gas at the base of the chimney much acetylene is formed, and if a glass tube be passed through the upper flame and gas be aspirated from, the inside of the lamp glass it \vill be found to contain acetylene. An ammoniacal solution of cuprous chloride x absorbs acetylene with the formation of a brown powder, cuprous acety- lide, a body which in the dry condition detonates violently by friction or if heated. If this body be prepared by aspirating the gas as above through such a solution, then pure acetylene may be liberated from the moist cuprous acetylide by acting on it with hydrochloric acid. Acetylene is a colourless gas which possesses the disagreeable odour observed when a Bnnsen lamp burns at the base ; it is poisonous. Water dissolves its own volume of the gas at ordinary temperatures, and it may be condensed to a liquid under a pres- sure of 48 atmospheres. It burns with a luminous smoky flame, and forms explosive mixtures with air or oxygen. 1 Boil oxide of copper and metallic copper with concentrated hydrochloric acid for some time, decant off the clear liquid, and add ammonia until the solution remains permanently blue. dAHliON AND THE HYDROCARBONS. 175 QUESTIONS. CHAPTER XIV. 1 Show in tabular form the percentage of carbon and hydrogen in (a) wood, (6) peat, (c) lignite, (d) bituminous coal, (e) anthracite. 2. Taking the atmospheric pressure as 15 Ibs. on the square inch, calculate the weight of carbon in a column of the air whoso base is a square mile, the carbon dioxide present being O'OG per cent, by weight. 3. Compare the densities of diamond, graphite, and amorphous carbon. What do you regard as a full and sufficient proof that each of these bodies consists of the same element? 4. What is animal charcoal, arid how is it prepared? 5. State the conditions under which carbon monoxide is formed when oxygen is passed over carbon. What is the effect of passing steam over white-hot carbon? G. What is a reducing agent? Give examples of solid liquid and gaseous reducing agents, illustrating your answer by equations showing the chemical changes which take place during reduction. 7. How would you show by experiment that a hydrocarbon contains carbon and hydrogen, and that it consists entirely of these elements ? 8. Where is marsh gas found to occur naturally, and how is it usually prepared in the laboratory? 9. How may marsh gas be distinguished from ethylene ? 10. What are the chief gaseous products formed during the destructive distillation of coal ? 11. Describe with equations the chemical changes which take place when ethylene is burnt in air arid in chlorine. 12. Under what circumstances is acetylene formed during com- bustion of hydrocarbons ? Can you suggest any means of determining the amount of acetylene in a mixture of hydrogen and acetylene? 13. How may acetylene be obtained in the pure condition? CHAPTER XV. FUELS - COMBUSTION. WHENEVER carbon, hydrogen, or bodies containing carbon and hydrogen burn, they combine with the oxygen of the air, the carbon to form carbon monoxide or dioxide, and the hydrogen to form water, and the amount of heat accompanying the change is perfectly definite and constant. If a gramme of pure carbon be burnt to carbon dioxide, the heat given out will be sufficient to raise the temperature of 8,080 c.c. of water one degree Centigrade. The heat requisite to raise one gramme (i. e. 1 c.c.) of water one degree Centigrade being adopted as the unit for measurement of heat (the calorie or thermal unit), we say that the heat of combustion of one gramme of carbon is 8,080 thermal units. So, in like manner, the com- bustion of a gramme of hydrogen is found to give rise to the evolution of 34,200 thermal units of heat. Hydrogen, therefore, on combustion gives out more than four times the amount of heat as compared with the same weight of carbon. Bituminous coal consists chiefly of carbon, but as it contains some hydrogen, it should give out more heat on combustion than the same weight of carbon, and it would do so except that it contains usually 15 to 20 per cent, of oxygen, sulphur, nitrogen, and mineral ash, which are practically unproductive of heat. In anthracite, however, these constituents amount to little more than 5 per cent, and the heat of combustion of this kind of coal is greater than that of bituminous coal. Petroleum, consisting entirely of carbon and hydrogen, and containing much more hydrogen than coal, actually does give out more heat than the same weight of carbon. Fuel being employed for heating purposes, the amount of heat 176 FUELS COMBUSTION. 177 generated in its combustion is of primary importance, and the following table shows at a glance the comparative value of different substances which are applicable as fuels Hydrogen ... 34,200 thermal units per gramme consumed. Petroleum ... 12,000 Coal ... 7,500 to 8,500 Carbon ... 8.080 Wood ... about 3,000 Flame. Whenever a gas or vapour is brought into an atmosphere with which it can react chemically, and the heat generated is sufficient to bring about incandescence of the particles, flame is produced. The heat is generated and the incandescence effected in the region where the reaction is carried on, that is, at the surface where contact occurs between the two gases, as is seen when a jar of hydrogen burns mouth down- wards. When we speak of liydrogen or coal gas as being com- bustible gases, and of air as being the supporter of combustion, we imply that hydrogen or coal gas, when once ignited, burn in air. And in flames under ordinary circumstances this is the case ; if, however, we were to lead a stream of air from a jet into an atmosphere of coal gas, the flame would attach itself to the jet, and might be described as air burning in coal gas. This is already apparent in reference to Exp. 83 (p. 173). In either case the flame marks the surface of contact between the air and coal gas, and is the region where the chemical changes take place which transform the hydrogen and carbon in the coal gas into water and carbon dioxide as ultimate products. Where the gases are intimately mixed and then ignited, the burning takes place with great rapidity, and explosion of a more or less violent nature ensues, but where a regular supply of the combustible product impinges upon the atmosphere in which it burns, a more or less steady flame is the result, the particular form of which is determined by the nature of the jet and the shaping influence of air-currents. In any case before flame can be produced at all, the tempera- ture of the combustible body must first reach a certa : n limit known as the point of ignition. This temperature varies with different bodies ; the vapour of carbon bisulphide may t 178 TEXT-BOOK OF CHEMISTRY. FIG. 33. ignited by a glass rod heated only to 150 C., whilst with hydrogen or coal gas a dull red heat (600 C.) is insufficient. Conversely, a flame is extinguished if its temperature is by any means reduced below the point of ignition of the vapours consumed in it (see Exp. 88). Exp. 84. Hold a piece of wire gauze (about 30 meshes to the inch) horizontally over a Bunsen burner and about an inch above the orifice (Fig. 33). Turn on the gas and light it on the upper side of the gauze, the flame will not be com- municated to the stream of gas on the under-side of the gauze. Much heat is carried off by the gauze, and the part of the flame in contact with the gauze where it meets the upward current of gas, is so far cooled in consequence of this that its temperature falls below the point of ignition of the gas. Exp. 85. Make a piece of the wire-gauze into a cylindrical roll and place a candle within it. Now direct the flame of a Bunsen burner against the outer surface of the gauze ; the wax may be melted, but the candle cannot be lighted unless the gauze is heated to redness. The reason for this will be gathered from the explanation given in the previous experiment. The Davy Lamp (Fig. 34) is such an arrangement, in which an oil lamp is shut in by a layer of gauze, and even if such a lamp be entirely surrounded with inflam- mable gas, this will not become ignited, although the inflammable gas which passes through the gauze may burn inside it and fill FIG. 34. FUELS COMBUSTION. 179 the space above the oil lamp with flame. If, however, the gauze becomes strongly heated, or if the flame should be mechanically driven through the meshes, communication with the inflammable atmosphere outside may be established and ignition will then take place. The candle flame. The inflammable matter in a candle is the wax or tallow, consisting essentially of carbon and hydrogen. This is melted round the wick, which becomes charged and serves as a still from which the vapours of hydrocarbons are supplied into the area immediately surrounding it. That such an area exists containing combustible vapours may easily be shown. Exp. 86. Depress a sheet of stout paper quickly into a candle flame to the level of the top of the wick, and hold it steadily there for about a second. On withdrawing it, a ring of sooty deposit will be seen, and within it a clear space. Secondly, take a glass syphon tube, as shown in Fig. 35, and bring the shorter FIG. 35. limb into the centre of the flame ; presently yellowish-brown vapours will be seen to pass down the tube and issue at the other end. These vapours will be found to be inflammable, and may be burnt at the exit of the tube. We can thus distinguish in the candle flame 180 TEXT-BOOK OF CHEMISTRY. (1) A central zone surrounding the wick and containing hydro- carbon vapours the zone of no combustion (A in Fig. 35). (2) A luminous zone or mantle surrounding the dark central zone, in which the hydrocarbons are in the process of combus- tion. The light emitted by the candle proceeds from this mantle, which contains white-hot particles of carbon and, the products of the incomplete combustion of the hydrocarbon vapours (BC in Fig. 35). There is also, external to this, (3) A non-luminous zone in which more intimate contact with the air is effected and the combustion is completed, the products formed consisting of carbon dioxide and aqueous vapour. Under ordinary circumstances this zone is not easily seen, but by sprink- ling a little finely-powdered common salt over the flame it will flash out as a golden-yellow fringe, the colour of which is due to the salt. The operations which take place in the three zones may be Bummed up in the order of their occurrence as (1) the vapour- ization of hydrocarbons, (2) the partial combustion of the vapours produced, with the evolution of heat, whereby the carbon particles become white-hot and luminous ; the access of air at this stage being insufficient for complete combustion ; (3) the com- pletion of combustion owing to admixture with an excess of air, producing great heat but little light. The phenomena of flame are dependent on the nature of the hydrocarbons supplied, on the heat generated within the flame, and on the air-supply. A few experiments will easily show us that modification of the conditions has considerable influence on the nature of flame. Exp. 87. Introduce the nozzle of a blowpipe into the dark central zone of a candle, and direct a current of air into that area. By so doing we bring a supply of air into the heart of the flame sufficient to secure complete combustion, and we do it in such a manner that it becomes intimately mixed witli the hydrocarbons. The conditions necessary for the production of a luminous zone are no longer present, and in the resulting flame, the " blowpipe flame," we have two zones only, and in both the luminosity is feeble. The inner zone (see Fig. 36) contains excess of hydrocarbon over air, and the outer zone contains excess of air over hydro- carbon. FUELS COMBUSTION. 181 Similar phenomena are to be observed in the non-luminous flame of a Bunsen burner. Here the air is admitted by the holes at the base of the burner, and intermingles with the gas supplied from a small jet at the same level, so that the flame is the result of the combustion of an intimate mixture of gas and air, just as in the case of the blowpipe flame. Exp. 88. Make a short coil of stout copper wire by giving it half-a- dozen turns round a piece of glass rod about 5 m.m. in diameter, and so that only a small space is left between one coil and the next. Bring the coil into the upper part of the luminous zone of a candle flame ; the flame will become smoky : if it be quickly depressed to the level of the wick, the flame loses its luminosity, and indeed may be extinguished altogether. Copper, being a good conductor and radiator, carries off heat and lowers the temperature to such an extent that the particles no longer maintain the white heat which imparts the luminosity to the flame, and the com- bustion is rendered so incomplete that carbonaceous matters escape combustion and pass off as smoke. Indeed the vapours may in this way be cooled down below their point of ignition, and the flame is then extinguished altogether. Oxidizing and reducing flames. The foregoing paragraphs show that heated hydrocarbon vapours have the power of com- bining Avith oxygen in the gaseous condition to form carbon monoxide or dioxide and water vapour. They have also the power of abstracting oxygen from many solid oxides or bodies containing oxygen. This property may readily be shown either by means of the flame of a Bunsen burner or of the blowpipe. Exp. 89. Partially close the holes at the base of the Bunsen burner until there appears a well-defined luminous tip (A in Fig. 37) within the flame. Now introduce within the luminous area a small amount of barium sulphate on a loop of thin platinum wire, and hold it steadily there for two or three minutes. The substance will be found to have changed in character, for whilst the barium sulphate originally taken is unacted upon by hydrochloric acid, the resulting body when moistened with dilute hydrochloric acid evolves an odour of sulphuretted hydrogen. The sulphate of barium (BaS0 4 ) has been deprived of its oxygen, and has become barium sulphide (BaS) ; this on treatment with dilute TEXT-BOOK OF CHEMISTRY. hydrochloric acid is transformed into the soluble chloride of barium with the evolution of H 2 S BaS + 2 HC1 = BaCl 2 + H 2 S. Similarly, oxide of lead or copper may be reduced to metallic lead or copper when brought into the inner flame of the blow- pipe (Fig. 36). In whatever part of a flame the hydrocarbons predominate and the supply of oxygen is limited, such a reducing action prevails. And wherever in a flame the supply of oxygen is in excess of that required to consume the hydrocarbons, as in the outer zone of the candle or the Bunsen burner or the blowpipe flame, an oxidizing action is experienced. This may be shown by bringing metallic tin or other metals into the outer margin of the Buusen flame. The accompanying diagram (Fig. 37) illustrates the structure of the Bunsen flame with especial regard to the oxidizing and reducing areas, and to the temperature of the different parts of the flame. Fio. 36. In Fig. 37 A is reducing area BCD is oxidizing area B low temperature oxidizing area Chigh FIG. 37. ii I:LS COMBUSTION. 183 QUESTIONS. CHAPTER XV. 1. Describe the chemical changes \vl\icli lake place during the combustion of coal in a furnace. 2. What is the unit adopted for the measurement of heat ? What volume of water may bo raised from 10 C. to 50 C. by the heat derived from the combustion of 10 grammes of hydrogen and 10 grammes of carbon respectively ? 3. What are the chief differences between lignite and peat, and between anthracitic and bituminous coal ? Why does a pound of petroleum give out more heat during combustion than a pound of coal ? 4. What conditions must be fulfilled in order that flame may be produced from coal, petroleum, and coal gas respectively? 5. Under what conditions is combustion accompanied by explosion ? Three mixtures of coal gas and air are made and a light applied to each ; one does not ignite at all, the second explodes, and the third burns quietly with a luminous flame. Explain these phenomena. 6. Sketch the flame of a candle showing the boundaries of the different zones of combustion. 7. Mention the chief constituents in the different zones of a candle flame. 8. In what respects does the blowpipe flame differ from the flame of a candle ? 9. What is meant by the temperature of ignition of a gas ? Explain the principle of the Davy lamp. 10. Give a diagram of the Bunsen flame, and indicate on it (a) the reducing area ; (b) the oxidizing area ; (c) the high temperature oxidizing area; ((/) the low temperature oxidi/iug area. 11. How may calcium sulphate be reduced to calcium sulphide (rt) in the blowpipe flame ; (6) in the Bunsen flame ? CHAPTER XVI. OXIDES OF CARBON CARBON BISULPHIDE. CARBON MONOXIDE, CO, occurs in small quantity in chimney gases, especially where the air-supply during combustion is not in sufficiently large excess ; it is also formed during the dry distillation of wood, coal, and such organic bodies. The gases from blast or other furnaces in which an excess of carbon is present, and in which a reducing operation is being performed, consist largely of carbon monoxide. Preparation. The gas is usually prepared on the small scale in the laboratory by the action of concentrated sulphuric acid on oxalic acid, an equal volume of carbon dioxide being given off at the same time. Exp. 90. About 20 grammes of crystallized oxalic acid is put into an 8-ounce flask provided with thistle funnel and delivery-tube, and as much concentrated sulphuric acid as to cover it. Heat is applied steadily until effervescence sets in, and then moderated so as to secure a regular and not too rapid evolution of the gas. Collect over water, avoiding any escape of the gas, as it is very poisonous. The reaction which takes place is COOH 1 + H 2 S 4 = C0 + c 2 + H 2 + H 2 S0 4 . The sulphuric acid removes the elements of water from the oxalic acid without itself undergoing any chemical change. Exp. 91. Pour lime-water into ajar of the gas, and shake up ; the lime-water will become turbid owing to the formation of calcium carbonate : CaO + C0 2 = CaC0 3 . The presence of carbon dioxide is thus indicated. i After the experiment has been performed, it is well to bum the gas rather than to let it escape directly into the air. 184 OXIDES OF CARBON CARBON BISULPHIDE. 185 Exp. 92. Pour a few cubic centimetres of caustic soda iiito a jar of the gas and shake up well, the carbon dioxide will combine with the caustic soda, forming sodium carbonate 2 NaOH + C0 2 = Na 2 C0 3 + H 2 0. Bring the mouth of the jar under water, the water will rise, and it will be seen that about half the volume of the gas is left. This is the carbon monoxide. Transfer some of this gas to a smaller vessel by decanting it over water, and shake up with lime-water ; no turbidity will be produced, the carbon dioxide having been removed. Now apply a light to the gas ; it will burn with a beautiful blue lambent flame. "When the combustion is finished, again shake up the vessel, and marked turbidity will then be produced, showing that carbon dioxide has again appeared. The carbon monoxide has united with oxygen during the process of combustion, with the formation of carbon dioxide 2 CO + 2 = 2 C0 2 . It may also be noticed that carbon monoxide does not itself support combustion, for if whilst it is burning the lighted taper be plunged into the vessel, the flame will be extinguished. Exp. 93. Remove the carbon dioxide from a second jar of the col- lected gas, and then decant into the jar sufficient air to fill the vessel. We have now a mixture of equal volumes of carbon monoxide and air, and if after allowing the gases to stand for two or three minutes to mix properly, the mouth of the jar be held towards the flame of a Bunsen burner, it will be seen that carbon monoxide and air form an explosive mixture. If it be desired to separate the carbon dioxide from the monoxide before collecting the gas this may be done by passing the gases evolved during its preparation through two wash-bottles containing caustic soda solution, as shown in Fig. 31. Carbon monoxide may, however, be prepared free from the dioxide by gently warming a mixture of sodium formate and sulphuric acid COONa + H 2 SO * = NaHSO * + H 2 + C0 > 186 TEXT-BOOK OF CHEMISTRY. or by heating roughly-powdered potassium ferrocyanide with concentrated l sulphuric acid. An interesting method whereby carbon monoxide may be obtained in large quantities, though in an impure condition, is to pass carbon dioxide over red-hot charcoal. The charcoal may con- veniently be heated in an iron pipe by means of a combustion furnace, and the carbon dioxide evolved in a gentle stream by the action of hydrochloric acid on marble C0 2 + C = 2 CO. The carbon monoxide is either collected or burnt at a jet attached to the exit of the tube. This method of formation may be observed in a coke or red- hot cinder fire, on the surface of which the blue flames of the burning gas may be seen. The air passing in at the base of the fire at the lower part of the grate unites with carbon, forming carbon dioxide, and this as it passes over the mass of red-hot carbon in the upper part of the grate is transformed into carbon monoxide. " Generator" gas, used in some manufacturing oper- ations, consists largely of carbon monoxide, and is obtained by passing air over a high column of red-hot coke or anthracite. Properties. Carbon monoxide is a colourless, tasteless gas of a very poisonous nature. It is only very slightly soluble in water, 100 volumes of water at ordinary temperatures dissolving less than three volumes of the gas. It is also A'ery difficult to con- dense, the liquid boiling under atmospheric pressure at -190C. Under ordinary circumstances, carbon monoxide burns in air, or may be exploded with oxygen in a eudiometer, forming carbon dioxide. But when the gases fire perfectly dried by exposing them for a lengthened period to phosphorus pentoxide, sparks may be passed through the mixture without combination taking place. In this connection it may be mentioned also that bodies like carbon, sulphur, and phosphorus will not burn in oxygen or air if moisture be entirely removed. Owing to the readiness with which carbon monoxide combines with oxygen, it is a powerful reducing agent. It also combines directly with the vapour of sulphur, forming caibonyl sulphide (COS), and in sunlight with chlorine, forming carbonyl chloride (COC1 2 ), also known as phosgene gas. 1 Dilute sulphuric acid gives rise to the formation of hydrocyanic acid (HCN). OXIDES OP CAfeBON CABBON BISULPHIDE. 187 The composition of carbon monoxide may be ascertained by exploding the gas in a eudiometer along with oxygen. It will be found that 100 volumes of CO and 100 volumes of oxygen after explosion show a contraction to 150 volumes, and on absorbing the carbon dioxide formed, by means of potash, 50 volumes of oxygen will remain. Thus 100 volumes of carbon monoxide have united with 50 volumes of oxygen to form 100 volumes of carbon dioxide, according to the equation 2 CO + 2 = 2 C0 2 4 vols. 4 vols. Carbon monoxide is fourteen times as heavy as hydrogen, and therefore the molecule of hydrogen being 2, that of carbon mon- oxide is 28. Its composition is therefore represented by the for- mula CO. CARBON" DIOXIDE, CO.,. This gas is of more frequent occurrence than carbon monoxide. Its presence in air and water has already been mentioned, and also the part it plays in.. the animal and vegetable kingdoms. It is given off in large quantities from lime-kilns, in which the limestone (CaC0 3 ) is decomposed by heat into quicklime (CaO) and carbon dioxide. Processes of fermentation and putrefaction give rise to the gas. Whenever an explosion of firedamp occurs in coal-mines carbon dioxide is formed in large quantities, and constitutes what the miners call the after-damp or choke-damp. Preparation. Carbon dioxide is usually prepared by the action of dilute hydrochloric acid on marble (CaC0 3 ). No heat is re- quired, and the operation may be carried out in a flask or Wonlff's bottle fitted with delivery-tube, the reaction being CaC0 3 + 2 HC1 = CaCl 2 + C0 2 + II 2 0. Although somewhat soluble in water, the gas is usually collected over water ; being, however, much heavier than air, it may be collected by downward displacement. All carbonates, when treated with dilute hydrochloric acid, liberate carbon dioxide; many, such as limestone, liberate it when heated. We have already seen that carbon dioxide is formed when carbon or compounds containing it are burnt in excess of air. If carbon compounds are heated to redness with oxide of copper, the whole of the carbon is transformed into carbon dioxide, and it 188 TEXT-BOOK OF CHEMISTRY. is in this way that the amount of carbon in such compounds is estimated. Exp. 94. Fill a large heaker of three or four litres capacity by downward displacement with carbon dioxide which lias been bubbled through water to remove hydrochloric acid, and plunge a taper into the gas ; it will be immediately extinguished. Xo\v detach a soap-bubble charged with air into the beaker, and it will be found to float on the surface of the heavier carbon dioxide. The density and other properties of the gas may further be illustrated by pouring it over a lighted candle, and thus ex- tinguishing it, or by ladling out the gas with a smaller beaker, and showing the presence of carbon dioxide in the beaker by its extinguishing a taper. Exp. 95. Insert burning magnesium ribbon into another beaker of carbon dioxide ; the combustion will continue at the expense of the oxygen in the carbon dioxide, and particles of carbon which are liberated will be observed on rinsing out the beaker with water. Carbon dioxide is a compound of great stability, but it may be decomposed by certain metals, such as magnesium or potassium, which have a considerable affinity for oxygen. Exp. 96. Pass a stream of carbon dioxide through a few cubic centimetres of water to which some drops of litmus solution have been added, and note that the litmus assumes a claret tinge ; contrast this with the effect of adding litmus to water containing a little hydrochloric or sulphuric acid. Notice also that by boiling, the carbon dioxide is expelled, and the litmus assumes its original colour. A solution of carbon dioxide in water is therefore very unstable, and possessed of a feebly acid character. Exp. 97. Pass the expired air from the lungs, or carbon dioxide (washed) from marble, through a slightly alkaline pink solution of phenol-phthalein ; the pink liquid becomes colourless. This change from a pink to a colourless solution may be used as a means of indicating the presence of carbon dioxide. Properties of carbon dioxide. Carbon dioxide is a colour- less gas with a very faintly acid taste. It is about H times as heavy as air ; water at 15 C. dissolves about its own volume of the gas, at C. 100 volumes of water dissolves 180 volumes of the gas. As with other gases, the amount dissolved increases directly as the pressure under which solution takes place, and OXIDES OF CARBON 0. \RRON BISULPHIDE. 189 soda-water being water charged with the gas under about four atmospheres pressure contains about four times its volume of the gas. Under a pressure of 36 atmospheres at C. it con- denses to the liquid form, and in this form it is prepared on a tolerably large scale and stored in steel cylinders. If the nozzle of one of these cylinders be opened, the pressure being released, the liquid is rapidly transformed into gas. The amount of heat absorbed by the passage from the liquid to the gaseous condition is considerable, and the issuing gas becomes so far cooled that a part of the gas condenses again even to the solid form. Solid carbon dioxide is a white, snow-like substance which passes only comparatively slowly into the gaseous condition again. The depression of temperature by its passage from tire solid to the gaseous condition is such that mercury can be readily cooled down to 40 C. and obtained as a solid body. Carbon dioxide, as will appear from the previous experiments, is in general a non -supporter of combustion or of animal life. It is decomposed by the green colouring-matter of plants in presence of sunlight, carbon being assimilated and oxygen set free in the process. The composition of carbon dioxide may be shown by a method similar to that employed in the case of sulphur dioxide. Thus when carbon is burnt in oxygen no change of volume occurs, and carbon dioxide is therefore said to contain its own volume of oxvgen. Moreover, if a known weight of diamond, a very pure form of carbon, be burnt in oxygen, and the c-irbon dioxide formed be weighed, the relation between the weight of carbon taken and that of carbon dioxide obtained will be found to be 12 : 44, or 12 parts by weight of carbon unite with 32 parts by weight of oxygen. On this evidence the formula for carbon dioxide must be C0 2 , or some multiple of this. But as the molecular weight of carbon dioxide is 44, the composition is that represented by the formula C0 2 . The carbonates. We have seen in a previous paragraph that a solution of carbon dioxide in water shows a feebly acid reaction. For this reason, and from a consideration of the salts known as the carbonates, carbon dioxide is to be regarded as the anhydride of carbonic acid, and the composition of the acid, although never isolated, may be taken as H 2 C0 3 . 190 TEXT-BOOK OF CHEMISTRY. Carbonic acid has two atoms of hydrogen replaceable by metals, and is therefore a dibasic acid. In the acid carbonates or bicarbonates only half the hydrogen is so replaced, thus KHC0 3 is bicarbonate of potash, and NaHC0 3 is bicarbonate of soda. In the normal carbonates the whole of the hydrogen is replaced, as with K 2 C0 3 , potassium carbonate, and Xa.,C0 3 , sodium carbonate. Exp. 98. Pass carbon dioxide to saturation into a solution of caustic soda, and then evaporate down to dryness on a water- bath. A residue will be obtained consisting of the monohydrated normal carbonate of soda, XaoC0 3 . H 2 0. Dissolve as much ,is possible of this in hot water and allow to cool, crystals of Na 2 C0 3 . 10 H 2 will be formed. This is the product known as " soda crystals," and used as washing soda. Very gently warm a quantity of this salt, or preferably the Na 2 C0 3 . H 2 in an atmosphere of carbon dioxide ; it will take up C0 2 and be transformed into the bicarbonate, NaHC0 3 Na 2 C0 3 . H 2 + C0 2 = 2 NaHC0 3 . Exp. 99. Heat in a porcelain basin over the Bunsen flame a few grammes of dry bicarbonate of soda ; carbon dioxide will be given off, and the normal carbonate again reproduced 2 NaHC0 3 = Xa. 2 C0 3 + C0 2 + H 2 0. The carbonates and bicarbonates of the alkalies are obtained by means of such reactions ; they are soluble in water, whilst the carbonates of other metals are insoluble in water but soluble with decomposition in acids CaC0 3 + 2 HC1 = CaCl 2 + C0 2 + H 2 0. Some bicarbonates, e. g. CaH 2 (C0 3 ) 2 , are soluble in water (see p. 76). The carbonates that are insoluble in water may be obtained (1) by the addition of alkaline carbonates to a soluble salt of the metal Na 2 C0 3 + BaCI 2 = BaC0 3 + 2 NaCl ; (2) by passing carbon dioxide into a solution of the hydrate CaH 2 2 + C0 2 = CaCCy + H 2 0. Weak bases such as alumina, oxide of silver, and oxide of 1 Excess of CO-2 transforms this into the soluble bicarbonate " H 2 + C0 2 = CaHo(C0 3 > 2 . OXIDES OF CARBON CARBON BISULPHIDE. 191 mercury either form no carbonates or very unstable ones, and the normal carbonates of the alkalies are the only ones which withstand a high temperature without decomposition. Test for carbonates. Add dilute hydrochloric acid to the solid carbonate, or an aqueous solution of a carbonate in a test- tube. An effervescence will be observed, and on decanting the gas downwards into a second tube containing lime-water, and shaking up, a turbidity will be produced in the lime-water owing to the formation of calcium carbonate. Carbon bisulphide, CS 2 , occurs in traces in coal gas, and is formed in quantity when sulphur vapour is passed over red-hot charcoal. It is a colourless liquid, which refracts light strongly ; it is very volatile, boiling at 4G C. and giving off a very inflam- mable vapour. When pure it has a sweetish, ethereal smell, but usually the impurities which it contains render it very disagree- able. One of its most remarkable properties is its solvent action ; india-rubber, fats, and some of the non-metallic elements such as phosphorus, sulphur, and iodine, which are otherwise difficult to obtain in solution, are readily dissolved by bisulphide of carbon. In consequence of its high refractive power for light, it is frequently employed as a means of producing a spectrum, the liquid being introduced into a hollow glass prism. CS 2 is the analogue in composition of C0 2 and thiocarbonic acid (H 2 CS 3 ), the analogue of carbonic acid (H 2 C0 3 ) is known ; moreover, recently, CS corresponding to CO has been discovered. Thus a number of bodies are known containing sulphur in place of oxygen, and resembling one another in their chemical properties. QUESTIONS. CHAPTER XVI. 1. Mention some conditions under which carbon monoxide is produced during the combustion of fuel on the large scale. 2. You desire to collect a specimen of CO as free as possible from air or C0 2 , using oxalic acid as the source of the gas ; how would you proceed ? 3. How may CO be transformed into C0 2 and C0 2 into CO ? 192 TEXT-BOOK OF CHEMISTRY. 4. What experiments would you perform in order to distinguish between () CO and C0 2 ; (6) C0 2 and a mixture of CO and C0 2 containing large excess of C0 2 ; (c) CO and a mixture of CO and C0 2 containing large excess of CO ? 5. What is the action of sulphuric acid on potassium formate? Give the equation. 6. What is the action of dilute and of concentrated sulphuric acid on potassium ferrocyanide ? 7. What is "generator gas," and how is it made ? How would you show that it contains (a) CO, (6) C0 2 , (c) H ? 8. It has been shown that chemical action undergoes modifi- cation when the reacting substances are perfectly dried ; give instances of this. 9. How would you prove that carbon monoxide has the compo- sition indicated by the formula CO ? 10. Describe the reactions which take place when sodium bicar- bonate (NaHC0 3 ) and lead carbonate (PbC0 3 ) are respect- ively subjected to the action of heat, and when they are brought into contact with dilute nitric acid. 11. Give two methods by which it may be shown that sugar contains carbon. 12. Write down in separate columns (a) the physical, (6) the chemical properties of carbon dioxide. 13. Give two methods for the decomposition of carbon dioxide. 14. How may it be demonstrated that carbon dioxide has the formula C0 2 ? 15. Are there any grounds for the assumption that H 2 C0 3 represents the composition of carbonic acid? 16. How are carbonates in general formed ? Given metallic zinc, lime, and caustic potash, how would you prepare specimens of zinc carbonate, calcium carbonate, and potas- sium carbonate ? 17. What are the characteristic properties of bisulphide of carbon ? What are the products formed, and their relative volumes, when this body is burnt in oxygen ? CHAPTER XVIT. SILICON AND BORON, Occurrence. Silicon, occurring in combination with oxygen as silica (Si0 2 ), is widely distributed, and forms the predominant constituent of many minerals and rocks. Quartz, agate, and kieselguhr (a finely-divided siliceous material of organic origin) are essentially pure silica, whilst sandstone must be regarded as silica associated with varying quantities of oxide of iron, or alumina. Shale or clay consists of silica and alumina in more or less definite proportions, and a large body of mineral silicates of common occurrence, such as felspar, serpentine, steatite, are very rich in silica. The element silicon is not found in the free state, and is not easy to isolate from its compounds, so that although it constitutes nearly one-fourth of the mass of the earth's crust (see Chap. I., p. 8) it is yet a substance rarely met with even in the laboratory. Preparation and properties of silicon. Silicon is obtained by the action of sodium, potassium, or aluminium on silicon tetrachloride (SiCl 4 ), or on potassium silico-fluoride (K 2 SiF 6 ), in an atmosphere of hydrogen, or under such other conditions as to exclude oxidation SiCl 4 + 4 K = 4 KC1 + Si. K 2 SiF fl + 4 K = 6 KF + Si. The residue is washed free from the potassium salts, which are readily soluble in water, and the silicon remains usually as a brown, amorphous powder. A crystalline modification of silicon is also obtained under certain conditions, and has in its colour and lustre a considerable resemblance to graphite. Silicon also resembles carbon in that it can be burnt in oxygen (to form the dioxide, silica) and at 103 O 194 TEXT-BOOK OF CHEMISTRY. ordinary temperatures fluorine is the only element which com- bines with it directly. Acids (except HF) have no action upon it. Silicon hydride, SiH 4 . By heating together metallic sodium and potassium silicofluoride (after the manner requisite to obtain silicon) in presence of anhydrous magnesium chloride, an alloy of magnesium and silicon is obtained. This, on treatment with hydrochloric acid, forms the hydride, SiH 4 , a gaseous body, analogous to marsh gas, CH 4 . This compound is not very stable, and decomposes at a red heat into amorphous silicon and hydro- gen. In presence of oxygen or chlorine it takes fire spontaneously, forming silica and silicon tetrachloride respectively. Silicon fluoride, SiF 4 , is obtained by the direct union of silicon and fluorine at the ordinary temperature, or by the action of hydrofluoric acid on silica or a silicate Si0 2 + 4 HF = SiF 4 + 2 H 2 0. Exp. 100. Make an intimate mixture of about 10 grammes of silica or fine white sand with twice its weight of calcium fluoride or finely-powdered fluorspar, and introduce it into a dry 8-ounce flask, with enough concjntrated sulphuric acid to form a tliin paste. Fit a cork and delivery-tube (Fig. 38), FIG. 38. SILICON AND BORON. 195 bent twice at right angles ; on gently heating, .silicon fluoride will be given off. If the gas bo passed into water (50 c.c.), gelatinous silica separates out and a solution of hydroiluosilicic acid is formed 3 SiF 4 + 4 H. 2 = H 4 Si0 4 + 2 H 9 SiF 6 . In order to prevent the delivery-tube becoming stopped by the gelatinous silica, a little mercury is poured into the cylinder and the delivery-tube arranged so that it just dips below the surface of this. Pour off some of the clear liquid after the gas has been passed for some minutes, and show its acid reaction by means of litmus paper. Add potassium carbonate and carbon dioxide is given off with effervescence, whilst a fine white powder will separate out, consisting of potassium silico- fluoride, K 2 SiF 6 , one of the most insoluble of the salts of potassium. The gelatinous silica may be washed by decantation. To do this, pour off the clear liquid as completely as possible, then fill the cylinder with water, and after allowing time to settle, decant off the clear liquid, repeating the operation several times. Silicon fluoride is a colourless gas which fumes in moist air, and has an irritant effect on the mucous membrane, even more pronounced than that of hydrochloric acid. As is evident from the previous experiment, it is decomposed by water. Silicon chloride, SiCl 4 , is a fuming liquid obtained either like the fluoride, by the direct union of silicon and chlorine, or by heating an intimate mixture of silica and carbon in a current of chlorine ; SiQ 2 + 2 C + 2 C1 2 = SiCl 4 + 2 CO. With water it forms gelatinous silica and hydrochloric acid SiC! 4 + 4 II 2 = H 4 Si0 4 + 4 HC1. Silica, SiO 2 . This is the only known oxide of silicon. It occurs in the crystalline form as quartz and tridymite, and in the amorphous form as opal, flint, and agate. It may also be prepared from certain mineral silicates, or silicates of the alkalies, by treat- ing them with hydrochloric acid. It separates at first in the gelatinous form containing water, and if this gelatinous silica be heated the water is expelled, and anhydrous silica remains. In the anhydrous condition, or in the mineral form, silica is unattacked by acids, with the exception of hydrofluoric acid ; it 196 TEXT-BOOK OF CHEMISTRY. can, however, be brought into solution again by fusion with alkaline carbonates. Exp. 101. Mix thoroughly together silica and about four times its weight of potassium carbonate, and heat in a platinum crucible over the flame of a Bunsen burner. Presently the mass swells up and evolves large quantities of carbon dioxide K 2 C0 3 + Si0 2 = K 2 Si0 3 + C0 2 . Potassium Silicate. After heating for about half-an-hour, allow to cool, and extract with water, filtering off any insoluble matter (unattacked silica) which remains. The solution contains potassium silicate, together with potassium carbonate, which has been used in excess. Add strong hydrochloric acid to the solution until a marked acid reaction is obtained. If the solution be sufficiently concentrated, a flocculent precipitate of silica will be obtained. If, however, the solution be dilute, no immediate precipitate is obtained, though one may separate on standing or by boiling. From such a solution a soluble form of silica may be prepared. Exp. 102. The solution contains potassium chloride, free hydro- chloric acid, and silica. Make a shallow dish by binding parch- ment paper over a hoop of tin or gutta-percha, float this on a considerable body of water (Fig. 39), and pour the liquid into it. The potassium chloride and hydrochloric acid will slowly pass through the membrane and diffuse into the water, while tlio silica will remain behind in solution in the dish. FIG. 39. Sugar, salt, and such bodies behave like potassium chloride, and readily pass through such a membrane, whilst white of egg, caramel, and the like, only do so extremely slowly. The former, from the fact that they are mostly crystallizable bodies, have SILICON AND BORON. 197 been termed crystalloids, and the latter, from their gelatinous and amorphous nature, colloids. Silica is a colloid, and by means of this experiment it may be separated from such substances as common salt and potassium chloride, and obtained in solution. Under these circumstauces we obtain silica in a form in which it is soluble in water. There is, however, a third modification intermediate between these two, for when silica is freshly precipitated in the cold, it may be rcdissolved by the addition of dilute hydrochloric acid. On standing, and more rapidly when boiled, this form becomes much less soluble, and ultimately passes into the insoluble variety. To sum up we have (1) Mineral silica (crystalline or amorphous) and anhydrous silica insoluble in and unattached by the ordinary acids, with the exception of hydrofluoric acid. (2) Gelatinous silica, soluble in dilute acids. (3) Dialyzed silica, soluble in water. Gelatinous silica when dried at the ordinary temperature retains water, .and has approximately the composition Si0 2 , 2 H 2 0, or H 4 Si0 4 . The silicates. These salts are chiefly interesting from the fact that they are largely represented in the mineral kingdom ; the following list indicates some of those of more common occurrence (1) Silicates of magnesium. Olivine, Mg a Si0 4 , or 2 MgO. Si0 2 . Talc, Mg 3 H 2 Si 4 Oi 2 , or 3 MgO. H 2 0. 4 Si0 2 . Serpentine, Mg 3 Si,0 T , or 3 MgO. 2 S;0 2 . (2) The Felspars. Orthoclase, K 2 Al 2 Si lc , or K 2 0. A1 2 3 . 6 Si0 2 . Albite, Na 2 Al 2 Si 6 1G , or Na 2 0. A1 2 3 . 6 Si0 2 . Anorthite, CaAl 2 S 2 8 , or CaO. A1 2 3 . 2 Si0 2 . and the decomposition product of the felspars Kaolin, H 2 Al 2 Si 2 8 , or H 2 0. A1 2 3 . 2 Si0 2 . A glance at this list is sufficient to show that the composition of the silicates is often very complex. With the exception of those of the alkalies they are all practically insoluble in water, 198 TEXT-BOOK OF CHEMISTRY. and for the most part they can only be brought into solution either by treatment with hydrofluoric acid or by fusion with alkaline carbonates. BORON. Occurrence. Boron is chiefly derived from native borax (Xa 2 B 4 7 . 10 H 2 0), obtained by the condensation of steam issuing from the ground in certain parts of Tuscany. It is also found in combination with lime as calcium borate, the mineral borocalcite, CaB 4 7 . 4 H 2 0, and as boracite, 2 Mg 3 B 8 15 . MgCl 2 . Boron is obtained by reducing its oxide, B 2 3 , by means of sodium, potassium, or magnesium B 2 3 + 6 Na = 3 Na 2 + 2 B. It is thus prepared in the amorphous condition as a brown powder, which is very difficult to fuse and not readily oxidized. Like other non-metals, it is a bad conductor of electricity. When mixed with aluminium, exposed to a white heat and allowed to cool, the crystalline form of boron is obtained, the aluminium being removed by treatment with caustic soda. Pre- pared in this way it is, however, always associated with small quantities of carbon and aluminium. Boron hydride, BH 3 , is a gaseous body which burns with a green-mantled flame, and is decomposed into its elements at a red heat. In order to obtain it, magnesium boride, Mg 3 B 2 , is first prepared by heating together magnesium and boric acid, and this is then treated with hydrochloric acid. It has, however, not been obtained in a state of purity, being always associated with free hydrogen. Boron trichloride, BC1 3 . Amorphous boron combines directly without the application of heat with chlorine. The trichloride may also be prepared by a method similar to that used for silicon tetrachloride, viz. by passing chlorine over an intimate mixture of the trioxide with carbon at a high temperature B 2 3 + 3 C + 3 C) 2 = 2 BC1 3 + 3 CO. It is a colourless liquid which fumes in air, and is readily decomposed by water, forming the trioxide and hydrochloric acid 2 BC1 3 + 3 H 2 = B 2 3 + 6 HC1. SILICON AND BOROX. 199 In the anhydrous condition it is, however, very stable, and may even be distilled in contact with sodium without decomposition. Fluorine combines energetically at ordinary temperatures with boron, and bromine can also be made to combine directly with it, forming the trifluoride and tribromide respectively. Nitrogen also combines directly with it, forming the nitride, BN. Boron trioxide, B.^. This and the boric acid and borates derived from it are the most important of the boron compounds. The oxide is formed when boron is burnt in air, but is usually prepared by heating boric acid 2 H 3 B0 3 = B 2 3 + 3 H 2 0. Water is driven off and there remains a glassy-looking mass which when powdered combines slowly with water, forming boric acid (H 3 B0 3 ) again. Boric acid and the borates. Boric acid is a very weak acid which, like carbonic acid, gives with litmus a wine-red colour quite distinct from the bright red resulting from such acids as hydrochloric and sulphuric. If concentrated hydrochloric acid be added to a strong hot solution of borax (Nti 2 B 4 7 ) the acid is set free and separates out in thin lamina} Na 2 B 4 7 + 2 HC1 + 5 H 2 = 4 H 3 B0 3 + 2 Nad. The borates, with the exception of those of the alkalies, are only slightly soluble in water. When mixed with concentrated sulphuric acid and gently heated at the border of the Bunsen flame they impart a green colour to it, owing to the volatilization of free boric acid. A similar colouration is also obtained when alcohol is added to such a mixture and ignited. These properties may be used as the means of detecting the presence of borates. When borax is fused on a platinum wire along with small quantities of chromium, cobalt, copper, manganese, or other compounds, characteristic colours are imparted to it. 200 TEXT-BOOK OF CHEMISTRY. aUESTIONS. CHAPTER XVII. 1. Mention any natural forms of silica either in the free state or in combination. 2. How is silicon obtained, and with what elements does it combine directly? 3. Compare the allotropic forms of carbon, silicon, and boron. 4. How is the hydride of silicon prepared, and what is the effect of heating it (a) in absence of air, (6) in presence of air ? 5. Describe two methods by which the fluoride of silicon may be obtained. What is the action of hydrofluoric acid on glass ? 6. Under what circumstances is gelatinous silica obtained, and how may it be converted into the anhydrous form of silica ? 7. How may a solution of silica be prepared and separated from any sodium chloride which may be associated with it? 8. Give a general description of the silicates, pointing out any characteristic properties which they possess. 9. In what minerals does boron occur, and how may boric acid be obtained from these minerals ? 10. Describe the preparation of the hydride of boron. 11. How is the oxide of boron obtained from boric acid, and boron from the oxide of boron ? 12. Give the general character of the borates, and show how you would detect the presence of a borate. CHAPTER XV1II/} CHEMICAL CALCULATIONS. I. The relations between weight and volume of gases. WE have seen (Chapter I\ r .) that the densities of gases are proportional to their molecular weights. In order to express the weight of any gas it is convenient to remember as the basis of calculation that 1 litre of hydrogen o.t the standard temperature (0 C.) and pressure (760 m.m. of mercury") is 0'0899 grammes, or that 11-12 litres of hydrogen weigh one gramme". If then we desire to ascertain the weight of any other gas under like conditions, we commence by expressing in chemical symbols the molecule of the gas thus The molecule of hydrogen is expressed by H 2 (2) nitrogen oxygen chlorine ozone phosphorus water vapour hydrochloric acid carbon dioxide nitric oxide sulphur dioxide sulphuretted ) 2 CI 2 hydrogen (28) (32) (71) (48) P 4 (124) H 2 0(18) IIC1 (36-5) C0 2 (44) NO (30) S0 2 (64) H 2 S (34) ammona and so on. NH 3 (17) '201 202 TEXT-BOOK OF CHEMISTRY. The relative weights are, then, those stated in parenthesis after the symbol in the above list, as derived from the respective atomic weights. Thus the weight of a litre of nitrogen is 14 times that of a litre of hydrogen or (O0899 x 14) grammes ; a litre of carbon dioxide weighs (0-0899 x 22) grammes ; a litre of sulphuretted hydrogen weighs (0'0899 x 17) grammes. The alternative method of expressing the same facts is perhaps more readily applied in chemical calculations, viz. that 11*12 litres of hydrogen weigh 1 gramme or 22'24 litres (usually stated as 22-4) of hydrogen weigh 2 grammes, the same number of grammes as that used for expressing the molecular weight. In this form the statement is quite general, that the molecular weight being m, 22 '24 litres of any gas whatever weigh m grammes. 22-24 litres of nitrogen weigh 28 grammes, 22-24 oxygen 32 22-24 chlorine 71 22-24 sulphur dioxide 64 ,, 22-24 ,, ammonia 17 It is convenient to remember both forms of the expression, as one or the other is more readily adapted for the purpose of cal- culation according to the terms which are given. For instance, if it be desired to calculate the weight of a certain volume of a gas, the former expression lends itself more readily for the purpose as in the following example (1) Required the weight of 100 c.c. of carbon dioxide at C. and 760 m.m. pressure 1000 c.c. (1 litre) of hydrogen weigh 0'0899 grammes. carbon dioxide 1-9778 100 cubic centimetres of 0-19778 Should the weight of the gas be given, and its volume is to be determined, the second form of expression is more easily applied. (2) Required the volume occupied by 0*5 gramme of ammonia at C. and 760 m,m. pressure 17 grammes of ammonia occupy 22-24 litres, n 1 1-308 0-5 0-654 CHEMICAL CALCULATIONS. 203 It is useful also to bear in mind that air is 14'435 times as heavy as hydrogen, since frequently the densities of vapours as actually determined by experiment are stated in terms of air as unit. Thus the density of sulphur dioxide is 'found by experiment to be 2-247, air being the unit. The density compared with hydrogen is therefore 2-247 x 14'435, or 32'43, a value agreeing well with that deduced from the accepted composition of this gas. II. Correction for temperature and pressure. We shall first consider the influence of variations of temper' it! m-e on the volume of a gas, and consequently on the weight of a given volume. We have seen (Chap. IV.) that a gas at C. expands ?fu- of its volume for each increment of one degree Centigrade in temper- ature. The more general form of expression, viz. that the volume of the gas is proportional to the absolute temperature (see p. 38), will be found the most useful, as a few examples will show. In order to make the calculation it is in the first place necessary to convert the temperatures as ordinarily stated into absolute temperatures. (3) A litre of gas is measured at C. ; what volume will it occupy at - 20 C., and what at 50 C. ? C. = 273 absolute. - 20 C. = 253 + 50 C. = 323 oro Volume required is at - 20 C. 1 litre x ^ = 926' 8 c.c. 2 1 o + 50 C. 1 litre x |?| = 1183-2 c.c. (4) The volume of a gas measured at 10 C. is found to be 150 c.c. ; what volume would it occupy at the standard temper- ature (0 C.) ? 10 C. = 283 absolute. 970 Volume required is at C. 150 x ~ | = 144-7 c.c. Zoo (5) The volume of a gas measured at 15 C. is found to be 204 TEXT-BOOK OF CHEMISTRY. 250 c.c. ; what volume would it occupy at - 15 C. and at 57 C. respectively ? 15 C. = 288 absolute. - 15 C. = 258 + 57'C. = 330 Volume required at - 15 C. = 250 x ?| = 224-0 c.c. + 57 C. = 250 x !|? = 286-5 c.c. Zoo And now let us consider the effect of variation in pressure. According to Boyle's Law (see p. 40), the volume of a gas is inversely proportional to the pressure to which it is subjected jj^hen the temperature is constant. ^ (6) A gas measured at standard atmospheric pressure (760 rn.m.) %j found to occupy 1'5 litres; what volume will it occupy at ^ 1,000 m.m. and at 100 m.m. pressure ^ * t, ^ Ef quired volume at l ; OdUm,ra. is 1,500 x ^jj^ = 1,140 c.c. 100 m.m. is 1,500 x ~ = 11,400 c.c. (7) The volume of a gas at 500 m.m. pressure is found to be 250 c.c. ; what would it measure under 5 atmospheres pressure ? 5 atmospheres = (760 x 5) m.m. = 3,800 m.m. r\c\c\ Required volume at 5 atmos. = 250 x ' - = 32-9 c.c. o,oOO Finally, an example is given of the allowance for both temperature and pressure in the same expression. (8) A gas occupies 190 c.c. at 13 C. and 740 m.m. pressure ; what volume would it occupy at standard temperature and pressure (0C. and 760 m.m.), and what at - 130 C. and 780 m.m. pressure ? 13 C. = 286 absolute. C, = 273 973 v 7J.O Volume at C. and 760 m.m. = 190 x ^| ^ ^ ^ 176-6 c.c. - 130 C. = 143 absolute. Volume at - 130 C. aiid 780 m.m. = 190 x J - ^ = 90 "1 c.c. Zoo x /oU CHEMICAL CALCULATIONS. 205 III. The relation between weight and volume of liquids and solids. The specific gravity of liquids is expressed in terms of pure water at 15 C. as unit. The following table shows that the specific gravity of water varies at different temperatures, water at 4 being taken as 1. Specific gravity of water at = 0-99987 . 2 = 0-99997 4 = 1-00000 10 = 0-99975 15 = 0-99916 20 = 0-99826 25 = 0-99712 j In ascertaining the density of a liquid by comparison with water it is more convenient to make the determination at ordinary temperatures, and hence it is usual to adopt the specific gravity of water at 15 C. as the basis of comparison. \Yhen we say that the specific gravity of a liquid is T8 we mean that it is heavier than water in the proportion 1*8 : 1 ; if therefore 1 c.c. of water weighs 1 gramme, 1 c.c. of such a liquid will weigh 1-8 grammes. 1 The following examples will show how specific gravity of liquids enters into chemical problems. (9) What is the weight of 100 c.c. of sulphuric acid of sp. gr. 1-84? 100 c.c. of water weigh 100 grammes. ,, sulphuric acid of the ) . . (j> Io4 ., density given ; (10) Hydrochloric acid of sp. gr. 1112 contains 21 per cent.. by weight of gaseous hydrochloric acid ; find the volume of hydrochloric acid gas in 10 c.c. of such acid. By the method used in the previous problem 10 c.c. of hydro- chloric acid will weigh 11-12 grammes. 11*12 x 21 - = 2-3352 grammes, the weight of gaseous hydro- IvU chloric acid contained in it. 1 This is not strictly accurate, since the gramme is the weight of 1 c.c. of water at 4 C. The correction, however, is only made in case a very exact expression is desired, and for ordinary purposes it is omitted. In any case the actual weight may be obtained by multiplying the result by 0'99916. OF THK UNIVEi 206 TEXT-BOOK OF CHEMISTRY. 36'5 grammes of HC1. occupy 22 '32 litres ; 22 - 32 x 2'3352 2*3352 grammes occupy ^-^ - " litres; ' = 1-428 litres. The relation between weight and volume of solids, like that of liquids, is expressed in terms of water as unit. Thus, diamond is 3'5 times as heavy as water, and its sp. gr. is 3'5, the sp. gr. of graphite is 2 2, of mercury 13'6. The weight of these bodies that occupy the same volume as 1 gramme of water (that is, 1 c.c.) is 3'5, 2*2, and 13'6 respectively. This relation is seldom necessary in chemical calculations. IV. Calculation of the percentage composition of a body. When the chemical composition of a body is expressed by symbols, the proportions of the respective elements contained in it are the weights of the elements as determined from the table of atomic weights. HC1 indicates a compound formed by the union of 1 part by weight of hydrogen with 35*5 parts by weight of chlorine. H 2 indicates a compound formed by the union of 2 parts by weight of hydrogen with 16 parts by weight of oxygen. C0 2 indicates a compound formed by the union of 12 parts by weight of carbon with 32 (i.e. 2 x 16) parts by weight of oxygen. P 2 5 indicates a compound formed by the union of 62 (i.e. 2 x 31) parts by weight of phosphorus with 80 (i.e. 5x16) parts by weight of oxygen. H 3 P0 4 indicates a compound formed by the union of 3 parts by weight of hydrogen, 31 parts by weight of phosphorus, and 64 (i. e. 4 x 16) parts by weight of oxygen. 36*5 parts by weight of HC1 contain 1 pt. of H and 35 '5 pts. of Cl. 18 H 2 2 HandlG 0. 44 C0 2 ,, 12 C and 32 0. 142 PA ., 62 P and 80 0. 98 HgPC^ 3 H, 31 of P and 64 of 0. The percentage composition is merely the statement of the relative weights of each of the constituents in 100 parts of the compound. CHEMICAL CALCULATIONS. 207 Thus, if 18 parts by weight of water contain 2 parts of hydrogen and 16 parts of oxygen, then 100 parts of water will contain 2 _ x ; 10 2 parts of H, i.e. 1M1 ; lo and- 1 ! 0,*.c. 88-88; and this represents the percentage composition of water. (11) Find the percentage composition of potassium chlorate, KC10 3 - K = 39-1 Cl = 35-5 3 = 48>0 122-6 Percentage amount of K ?JLi*19? = 31-89 7< lAZ'o Cl= 5 ^.^ 28-95 . _ 48 x m m 100^0 (12) Find the percentage amount of water of crystallization in FeS0 4 .7H 2 0. Fe = 56 S = 32 4 = 64 7 H 2 =126 278 278 parts of FeS0 4 .7 H 2 contain 126 parts of water. Percentage of water = i??*i?? = 45-32.^0 Zio The question which even more frequently arises in practice is the converse one, the determination of the formula of a substance from the results of analysis of the substance. We have seen already that the relative composition by weight of a body is obtained by taking the atomic weight of each constituent, and where more than one atom of any constituent is present, then the multiple of that according to the number of atoms. 208 TEXT-BOOK OF CHEMISTRY. E.g., for COC1 2 Atomic No. of TJ i 4- Percentage weight. atoms. llct " composition. C 12 1 12 12-12 16 1 16 16-16 C1 2 35-5 2 71 71-72 We now reverse the process, and desire to determine the relative number of atoms of each element, having given the composition by weight of a body as deduced from its analysis S = 23-7 per cent. = 23-7 Cl = 52-6 Let n, n', n" be the number of atoms of S, 0, and Cl respectively, the atomic weights being 32, 16, and 35'5, we have the relative weights of each of the constituents 32 n, 16 n', and 35 '5 n". These values are proportional to the weights as represented by the percentage composition, viz. 23-7, 23-7, 52-6. Thus 32 n oc 23'7 and n is proportional to 0-74. 16 n' <* 23-7 n' 1-48. 35-5 n" <* 52-6 n" 1-48. The simplest proportion in whole numbers is 1:2:2, and the formula on this assumption is S0 2 C1 2 . This, then, is the empirical formula as deduced solely from the consideration of the results of the analysis. It is quite consistent with such a calculation that the formula should be S 2 4 C1 4 , or S 3 6 C1 6 , or any such multiple. Which of these is to be finally accepted can only be decided after a determination of the vapour density of the body, or of its chemical constitution and character, and this would be the constitutional formula of the body. To determine the empirical formula of a body, we therefore divide the results of analysis by the respective atomic weights, and the numbers so obtained are proportional to the number of atoms. CHEMICAL CALCULATIONS. 209 (13) The percentage composition of a compound is found to be II = 5-88 and = 94-12 : find its formula. In this case n and n i being in proportion to the number of atoms of hydrogen and oxygen respectively nU = 5-88, and H being 1, n = 5'88. w t O = 94-12, and being 16, Wj = 5-88. The body therefore consists of an equal number of atoms of II and 0, and the simplest formula would be HO. Chemical considerations, however, compel us to accept a multiple of this, viz. H 2 2 , as the formula of hydrogen peroxide, the substance whose composition had been ascertained. (14) Find the formula of a substance having the composition Mg = 9-76. S = 13-01. = 26-01. Water of crystallization = 51-22. 9'76 Mg gives - = 0'406 as proportional number. 26-01 -jg- = 1-626 H 2 y_| 2 = 2-846 From these numbers we deduce as the simplest whole numbers bearing the same relation to one another 1:1:4:7, and the simplest formula for the body is MgS0 4 .7 H 2 0. V. Application to chemical problems. We have now considered the fundamental calculations which enter into chemical problems, and a few examples will be given to show how these bear upon questions involving chemical decom- position and interchange. (15) What weight of caustic soda (NaOH) will be needed to just neutralize 10 c.c. of dilute sulphuric acid (sp. gr. 1'155) con- taining 21 per cent, of H 2 S0 4 ? p 210 TEXT-BOOK OF CHEMISTRY. In all cases where a chemical reaction is concerned, involving considerations of weight or volume, it is well to state the reaction in the form of an equation at the outset 2 NaOH + H 2 S0 4 = Na 2 S0 4 + 2 H 2 0. Sodium Sulphate. From this we see that 2 NaOH neutralize H 2 S0 4 , the respective weight relations being 2 (23 + 16 + 1) and (2 + 32 + 64) or 80 : 98. 80 parts by weight of caustic soda serve to neutralize 98 parts by weight of sulphuric acid. Now determine the actual weight of sulphuric acid that is to be neutralized 10 c.c. of the dilute sulphuric acid (sp. gr. 1-155) weigh 11-55 gnus. 21 percent, of this is H 2 S0 4 , i.e. H 'f * 21 = 2-4255 grammes. 100 Required amount of caustic soda is 2 ' 425X 8 or 1'98 grammes. (16) What volume of oxygen collected at standard temperature and pressure (0 and 760 m.m.) is given off on heating 10 grammes of mercuric oxide ? 2HgO = 2Hg + 0*. First determine the weight of oxygen from the above equation, which shows that 432 parts of mercuric oxide yield 32 parts of oxygen, or, in simpler numbers, 27 parts yield 2 parts of oxygen. 2x10 10 grammes therefore yield - , or 0'74 grammes. Now 32 grammes of oxygen occupy at standard temperature and pressure 22*24 litres, and the volume of oxygen corresponding to this weight is 0-74 x 22-24 _ 5U cubic centimetreg> o2 (17) What weight of sulphur must be burnt so as to yield 1 litre of sulphur dioxide at standard temperature and pressure? S + 2 = S0 2 . Here we start from a known volume of gas and must work back ! to the weight in terms of which the result is to be expressed. CHEMICAL CALCULATIONS. 211 22'24 litres of S0 2 weigh 64 grammes. 1 litre of S0 2 weighs -f~ or 2'8G7 grammes. Also 64 grammes of S0 2 contain 32 grammes of S, suid 2-877 : , S0 2 1-4385 S. 1-4385 gramme of sulphur will therefore be required to produce 1 litre of S0 2 . Such a calculation may, however, be shortened by the consider- ation that as 32 grammes of sulphur, according to the equation, yield 64 grammes or 22'24 litres of S0 2 , 39 ^ ^- grammes will yield 1 Ktre of S0 2 . The next example will be rendered more complex by intro- ducing conditions of temperature and pressure differing from the standard. No further difficulty is really involved, except that the correction for temperature and pressure must be made. (18) 2 J litres of nitrous oxide have been collected at 39 3 C. and 741 m.m. pressure; what weight of ammonium nitrate has been decomposed in order to supply the gas ? First eliminate the irregularity introduced by the temperature and pressure, by determining what Volume the gas would have occupied had it been collected at standard temperature and pressure. This will be Now according to the equation NH 4 NO ? N 2 + 2II/). Ammonium Nitrate. Nitrous Oxide. 80 grammes of ammonium nitrate yield 44 grammes (or 22'24 litres) of nitrous oxide, and hence >>.^ y grammes, or 7'673 grammes, of ammonium nitrate have been decomposed. (19) One gramme of Water is () converted into steam at 100 C., (6) decomposed by means of sodium and the hydrogen collected at 13 C. ; what volume will each occupy, the barometer at the time standing at 750 m.m. ? First, let us consider the case of the steam. This being water 212 TEXT-BOOK OF CHEMISTRY. vapour has, at standard temperature and pressure, a density such that, as previously shown, 18 grammes is the weight of 22*24 litres. 22'24 Thus 1 gramme occupies or 1'235 litres. lo At 100 C. and 750 m.m. pressure this occupies Secondly, as to the hydrogen, the decomposition is represented by the equation 2 Xa + 2 H 2 = 2 NaOH + H 2 ; from which we S2e that 36 grammes of water yield 2 grammes of hydrogen, and therefore 1 gramme of water yields T V gramme of hydrogen. The volume of hydrogen at standard temperature and pressure is thus or 0'62 litre. Corrected so as to represent the lo volume at 13 C. and 750 m.m. pressure this becomes The whcle of the more important elements entering into the treatment of chemical problems have now been discussed, and it only remains to add some examples in further illustration of their application to chemical reactions. (20) 10 grammes of mercury are heated with excess of concen- trated sulphuric acid and the sulphur dioxide formed is collected at 15 C. and 765 m.m. pressure ; what volume does it occupy? Here, as in most cases, it is best to commence by a statement of the reaction which takes place. Hg + 2H 2 S0 4 = HgS0 4 + 2H 2 + S0 2 . Mercuric Sulphate. 200 grammes of mercury give 64 grammes of S0 2 , or 200 22-24 litres of S0 2 . 10 M12 at standard temperature and pressure. Volume at 15 C. and 765 m.m. pressure is then ' CHEMICAL CALCULATIONS. 213 (21) 25 c.c. of marsh gas (CH 4 ) are mixed with 500 c.c. of air and exploded in a eudiometer ; what volume of gas should there be (a) before the removal of the carbon dioxide formed, (b) after the absorption of the carbon dioxide by means of caustic potash ? The temperature and pressure may be assumed to bo the same when each of the readings of volume were taken. The chemical reaction which takes place is CH 4 + 2 2 = C0 2 + 2 H 2 0, 2 vols. 4 vols. 2 vols. the nitrogen of the air taking no part in the combustion. It is further manifest on inspection that the 2 volumes of marsh gas and 4 volumes of oxygen, before explosion, give rise to 2 volumes of carbon dioxide, the space occupied by the water being negligible. Thus 6 volumes are reduced to 2, and the diminution is 4 volumes. But the marsh gas occupies 25 c.c., and is represented by 2 volumes. The diminution in volume is therefore 50 c.c., and the 525 c.c. of mixed gases originally present in the eudiometer have been reduced to 475 c.c. Similarly the C0 2 occupies the same volume as the marsh gas from which it was obtained, and is thus 25 c.c., and if this be removed there will remain 450 c.c. of gas in the eudiometer. The result is that the residual gas (a) before removal of C0 2 is 475 c.c. (6) after 450 c.c. (22) 10 c.c. of liquid carbon bisulphide (sp. gr. 2'63) are burnt in oxygen ; find the volume of the resulting gases measured at standard temperature and pressure. We must first ascertain the weight of the carbon bisulphide. Its sp. gr. being 2 '63, the 10 c.c. will weigh 26*3 grammes. The chemical change during combustion is represented in the equation CS 2 + 3 2 = C0 2 + 2 S0 2 . 76 grammes of CS 2 yield 44 grammes or 22'24 litres CO.,. 128 44-48 S0 2 . ,, G6-72 litres of C0 2 and S0 2 together. 214 TEXT-BOOK OF CHEMISTRY. 26-3 grammes of CS 2 yield 66 '' 2 * 2 ?j = 2 3-09 litres, (23) Considering air as a mixture of 79 per cent, by volume of nitrogen with 21 per cent, by volume of oxygen, find the density of air compared with hydrogen. Also find the density of the vapour of carbon bisulphide compared with air. 79 vols. of nitrogen are as heavy as 79 x 14, orl.lOGvols. of II. 21 oxygen 21 x 16, or_J536 100 air 1,442 Density of air is 14' 42. * Density of the vapour of bisulphide of carbon is -a or 38, compared with H. 38 Compared with air it is therefore , . , . 2*635. r 14-42 Atomic weights to be used in the following calculations. Hydrogen, 1. Chlorine, 35*5. Carbon, 12. Potassium, 39. Nitrogen, 14. Calcium, 40. Oxygen, 16. Iron, 56. Sodium, 23. Bromine, 80. Magnesium, 24. Silver, 107-6. Phosphorus, 31. Antimony, 119-6. Sulphur, 32. Mercury,* 200. Load, 206-4. ] Actual density at normal composition is taken as 14 - 435. CHEMICAL CALCULATIONS. 215 OTESTIONS. CHAPTER XYITT. 1. The volume of a permanent gas at C. is 3 litres ; at wli.it temperature would it occupy 4 litres, the pressure remaining unaltered ? 2. T\vo samples of gas occupy the same volume, but one is at - 20 C., and the other at 20 C. ; what is their relative volume when both are at C. ? o. The volume of a gas at 13 C. is 100 c.c. ; find its volume at - 130 C., at - 13 C., and at 130 C. 4. A gas under standard atmospheric pressure measures 209 c.c. ; what volume will it occupy under a pressure of^-, J, 2, and 5-| atmospheres respectively ? 5. What volume will half a litre of gas measured at 750 m.m. pressure occupy when subjected to a pressure of 850 rn.m. of mercury ? 0. A rectangular vessel 10 c.m. long, 5 c.m. wide, and 3'5 c.m. deep, is filled with gas at 100 C. and 770 m.m. pressure; what volume will the gas occupy at standard temperature and pressure ? 7. A sample of gas is collected in a eudiometer, and it is found that the level of the mercury in the eudiometer is 257 m.m. above that of the trough, also the height of the barometer at tho time is 745 m.m. ; under what pressure is the gas? 8. A sample of gas is collected at standard temperature and pressure, and the pressure is then doubled, and the temper- ature gradually rnised until the volume of the gas is the same as it was originally ; at what temperature does this occur ? 216 TEXT-BOOK OF CHEMISTRY. 9, Under how many atmospheres pressure will steam have the same density as water (1 c.c. weighs one gramme), if the contraction takes place in accordance with Boyle's law, and the temperature remains at 600 C. ? 10. If the temperature remains at zero, at what pressure will hydrogen have a density equal to 0'62 of that of water, this being the density found by Dewar for hydrogenium ? 11. One cubic centimetre of bromine (density 3 '2) is transformed into vapour at 78 C. ; determine the volume occupied by the vapour. 12. The sp. gr. of pure nitric acid being 1'522 ; find the weight of 100 c.c. of it, arid the volume that you must take to weigh 100 grammes. 13. What volume of such acid will be required to just neutralize 100 grammes of caustic potash (KOH), and what weight of potassium nitrate is formed ? 14. Calculate the percentage composition of calcium carbonate ; what percentage of carbon dioxide does it contain ? 15. Chlorine forms with water a solid hydrate, having the com- position C1 2 . 10 H 2 ; calculate the percentage of hydrogen, chlorine, and oxygen contained in this body. 16. Find the empirical formula of a compound consisting of 46 '66 per cent, of iron and 53 '33 per cent, of sulphur. 17. An oxide of iron contains 72 - 3 per cent, of iron ; determine its empirical formula. 18. Determine the simplest formula for a salt having the follow- ing percentage composition Sodium, 29-36. Phosphorus, 2638. Oxygen, 44-26. loom 19. A solution of caustic soda having the sp. gr. 1;32 contains 28*8 per cent, of NaOH ; what weight of sulphuric acid is required to be just sufficient to neutralize a litre of such a solution ? 20. What volume of sulphuretted hydrogen at 13 n C. and 798 m.m. pressure is required to effect the complete precipita- tion of one gramme of corrosive sublimate, HgC!.,? CHEMICAL CALCULATIONS. 217 21. What weight of pure antimony sulphide, Sb 2 S 3 , should yield a litre of sulphuretted hydrogen collected at 10 C. and 7GO m.m. pressure ? '2'2. Determine the volume of chlorine required to convert 10 grammes of phosphorus into the pentachloride. 23. A gramme of common salt is dissolved in water and excess of silver nitrate solution is added ; what weight of silver chloride should be precipitated ? 24. Calculate (a) the volume, (b) the weight, of carbon dioxide in the air of a room 6 metres long, 4 metres wide, and 3 metres high, if there is 1 volume of this gas present per 1,000 volumes of the air. 25. Dumas determined the relative amounts of nitrogen and oxygen in air by passing it over heated copper. He found Weight of tube and copper before experiment, 120 grms. after 12M5 ,, globe when exhausted ... ... 852 ,, and nitrogen ... ... 855'85 From these numbers calculate the percentage composi- tion of air by weight, and deduce its percentage composition by volume. 26. Dumas determined the composition of water synthetically by passing hydrogen over heated copper oxide, and found Weight of tube and copper oxide before experiment, 334*598 grs. > 5 after 314'236 ,, ,, ,, drying tubes before experiment ... 426 '358 } , after ... 449'263 Calculate the percentage composition of water by weight. 27. Ten grammes of steam are passed over red-hot iron ; what volume of hydrogen at 26 C. and 741 m.m. pressure will be obtained if one-third of the steam undergoes decom- position ? 28. Fifteen cubic centimetres of ammonia are completely decom- posed by electric sparks, and then 40 c.c. of oxygen are added and the mixed gases exploded ; state the gases present and the volume of each (a) just before exploding, (6) after exploding. 218 TEXT-BOOK OF CHEMISTRY. 23. A mixture of 10 litres of oxygen with one litre of carbon dioxide is shaken up with 100 c.c. of water ; determine the volume of each gas that will be dissolved the barometer at the time standing at 760 m.m. and the thermometer at zero. 30. Make the same determination with a mixture of one litre of oxygen and 10 litres of carbon dioxide. 31. A litre of sea- water (sp. gr. 1'03) is evaporated to dryness, and found to leave as residue 36'4 grammes of salts ; find the percentage of solid matter in the sea-water. 32. Given that a metre is equivalent to 39*37 inches, calculate the number of cubic inches in a litre, and the number of litres in a cubic foot. 33. Determine the percentage of carbon in cane-sugar (C 12 H 22 O n ) and the volume of carbon dioxide that results from the combustion of 0'2 gramme of sugar. 34. A mixture of 20 c.c. of ethylene and 200 c.c. of oxygen is exploded in a eudiometer ; what volume of gas remains after the explosion, and what volume when the carbon dioxide is subsequently removed by absorption with potash ? 35. What quantity of crystallized oxalic acid (C 2 H 2 4 . 2 H 2 0), heated with excess of sulphuric acid, will yield 5 litres of gas at standard temperature and pressure ? / 3G. If 50 c.c. of sulphuretted hydrogen be mixed with excess of chlorine, what volume of hydrochloric acid will be formed, and what weight of sulphur liberated ? f 37. A gramme of a substance containing carbon is heated with lead oxide, and found to form 10 grammes of metallic lead ; what percentage of carbon was present ? \J 38. What weight of iron must be dissolved in dilute sulphuric acid in order to yield sufficient hydrogen to till a balloon having a capacity of 100 cubic metres ? \J 39. Ten grammes of carbon are burnt in 1,000 litres of air (taken as consisting of 79 vols. of N and 21 of 0) at 15 C. and 700 m.rn. pressure ; find the percentage of nitrogen, oxy- gen, and carbon dioxide in the air after the combustion is complete. CHEMICAL CALCULATIONS. 219 ANSWERS TO OTESTIONS. Chap. iv. 4. 281 c.c. 5. 248-8 c.c., 231'2 c.c., 327'9 c.c., 1521 c.c. ", 6. 1010 c.c. 7. 61023 cubic inches. 9153-4 ,, 8. 145 grms. 68-96 c.c. 9. 11-12 litres. ,, 700 c.c. 13. 14, 62, 149-8, 23'8, 79'8, 38, 14. 14. 2 K + 2 H 2 = 2 KOH + H 2 . 2 S0 2 + 2 = 2 S0 3 . 2 NaCl + H 2 S0 4 = Na 2 S0 4 + 2 HC1. 2 H 2 + 2 C1 2 - 4 HC1 + 2 . Chap. v. -5. 11-205 of hydrogen. 88-795 of oxygen. Chap. vi. 3. 1'61 C. 4. 1'65C. ,, 5. 41 '3 grms. 6. 1000, 33, 63600. 7. 19-95, 127-5. 8. 449-75 44-975 1349*25 225-25 22-525 67575 ,, 9. 44-975 of C0 2 and 19-475 of 0. Chap. viii. 14. Hydrogen 40 c.c. Marsh gas 14 14 c.c. Sulphur dioxide 7 '07 c. c. Ozone 8'16 c.c. Chap. ix. 9. 5660 c.c. Chap. xi. 4. 19 -6. 5. 20-78, 79-22. 6. 22-97. Chap. xiv. 2. 3794 tons. Chap. xv. 2. 8550 c.c., 2020 c.c. Chap. xvi. 17. C0 2 and S0 2 in the proportions 1 : 2 by volume. 220 TEXT-BOOK OF CHEMISTRY ANSWERS TO CHEMICAL CALCULATIONS IN CHAPTER XVIII. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15 16. 17. 18. 19. 20. 21, 22. 23. 91. 293 : 253. ' 50 c.c., 90-9 c.c., 140-9 c.c. 2090 c.c., 418 c.c., 104-5 c.c., 38 c.c. 441 c.c. 129-17 c.c. 488 m.m. 273 C. 3,951 atmospheres. 6,894 atmospheres. 571-9 c.c. 152-2 grammes ; 65'7 c.c. 73-9 c.c. ; 180-4 grammes. Ca = 40 per cent. C = 12 O =48 44 per cent. H = 7-97 per cent. Cl = 28-28 = 63-75 FeS 2 . Fe 3 4 . Na 6 P 4 13 . 465*7 grammes. 81-9 c.c. 4 '847 grammes. 17-93 litres. 2 -446 grammes. 24. 72 litres ; 142-4 grammes. 25. Oxygen, 23 ; Oxygen, 20'7. Nitrogen, 77; Nitrogen, 79*3. 26. Hydrogen, 11-1. Oxygen, 88'9. 27. 4-123 litres. 28. (a) N = 7-5 c.c. H = 22-5 c.c. = 40-0 c.c. (6) N = 7-5 c.c. = 28-75 c.c. 29. Oxygen = 3'73 c.c. Carbon dioxide = 16'36 c.c. 30. Oxygen = 0-37 c.c. Carbon dioxide = 163"6 c.c. 31. 3-534 per cent. 32. 61-023 ; 28-317. 33. 42-1 per cent. 157 litre. 34. 180 c.c. ; 140 c.c. 35. 14-39 grammes. 36. 100 c.c. ; 0-0719 gramme. 37. 29 per cent, 38. 251'8 kilogrammes. 39. Nitrogen, 79.00 per cent. Oxygen, 19'2 Carbon dioxide i ,] 1 ' INDEX A. PAGE Acetylene 173 Acid, definition of 34 Acid oxides 96, 98 Acid salts ill, 123 Agate 193, 195 Air is a mixture of gases ... 135 Alkaline reaction 96 Allotropic forms. Carbon... 165 ,, ,, Phosphorus 153 ,, ,, Sulphur 105 Ammonia, preparation and properties 137 , liquefaction of ... 138 , composition of ... 140 , tests for 140 Amorphous boron 198 carbon 166 phosphorus 154 silicon 193 sulphur 106 Analysis 3 Anthracene 169 Apatite 152 Aqua regia 144 Argon 129 Atmosphere, determination of composition 131 ., , water vapour in 133 } C0 2 in 133 Atom 19, 45 Atomic theory (Dalton's) ... 20 Atomic weight, definition of 47 ,, ,, , table of 6 Avogadro's hypothesis 46 B. PAGE Basic oxides 96, 98 Basicity of acids Ill Benzene 169 Binary compounds 89 Bleaching 85, 109 Blowpipe flame 180 Boracite 198 Borax .7... 198 Boric acid and berates 199 Borocalcite 198 Boron 198 hydride 198 trichloride 198 ,, trioxide 199 Boyle's Law 40 Bromic acid 88 Bromine, physical properties 79 ,, , chemical ,, 80 ,, , manufacture of ... 82 Bunsen flame 182 C. Candle flame 179 Carbon, allot ropic forms of 165 ,, , occurrence 163 ,, , properties of 167 ,, , reducing power of... 168 Carbon bisulphide 191 Carbon dioxide, amount in air 1 33 ,, ,, , preparation 187 ,, .. , properties... 188 Carbon monoxide, prepara- tion... 184 ,, , properties 186 222 IXDEX. Carbonates 189 , tests for 191 Carnallite 82 Carre's apparatus 139 Chalybeate waters 73 Chamber acid 117 Charles, law of 38 \ Chemical action, methods employed 5 ,, ,, , nature of 10 ,, attraction 11, 17 , , combination in defi- nite proportions 18 ,, combination in mul- tiple proportions 19 j ,, properties of mat- ter 3 ,, symbols 5, 6 Chemistry, definition of 4 Chlorapatite 152 Chlorates 87 Chloric acid 87 Chlorides of phosphorus 1 60 ,-, ,, sulphur 107 Chlorine preparation 83 ,, properties, chemi- cal 80, 84, 85 ,j properties, physical 79 Chlorine hydrate 42 ,, monoxide 86 ,, peroxide 86 Chlorsulphonic acid 115 Cinnabar 103 Clark's process for softening water , 77 Clay 193 Coal gas 172 Combining volumes of gases 45 Combustion 177 Composition of ammonia ... 140 ,, ,, carbon di- oxide 189 ,, ,, cajbon mon- oxide 187 ,, ,, hydrochloric acid gas... 85 ,, sulpjiur di- oxide ,.110 Composition of sulphuretted hydrogen 60 , 5 ,, nitric oxide 149 , } ,. nitrous oxide 150 ,, .. Mater 51 Compounds 3 Conservation of energy 17 Constitutional formulas 208 Critical pressure 42 ,, temperature 42 Cryohydrates 57 Crystalline phosphorus 154 Crystalloid and colloid 197 D. Dalton's Atomic Theory 20 Dalton's Law of Partial Pressures 72 Davy lamp 178- Decomposition of water 22 Definite proportions (law of ) 18. Density of gases 44, 46 Diamond 165 Dichloride of sulphur 107 Diffusion of gases 101 Distillation 75 Distribution of elements ...7,8 Double decomposition 13 Drinking water 75 Dumas' and Stas' experi- ments on composition of water " E. Efflorescence 57 Element Empirical formula 208 Energy of chemical action. . . 15 Equations 7 Equivalent weights of ele- ments 124 Ethylene 171 Euchlorine 86 F. Felspars 197 Flame 177 INDEX. 223 r.\r;i: Flint H).-) Flowers of sulphur 1 08 Fluorapatite 1 ,YJ Fluorine, isolation of SO ,, , chemical proper- ties 80, 81, 82 . physical properties 79 Fogs 1 130 Formula' 7, 'JOS Freezing mixtures (59 Fuol* 170 G. Galena 103 Gaseous diffusion 101 Gases, density of 44, 40 , , , relation of volume to pressure 39 ,, , relation of volume to temperature 38 ,, , relation of volume to weight 201 ,, , weight of 30 Graphite 100 H. Halogens, chemical proper- ties 80 ,5 , physical proper- ties 79 Haloid acids, tests for 34 ,, ,, , salts of 32 Hardness of water 75, 77 Helium 8, 42 Henry's Law 71 Hydrates or hydroxides... 57, 9(5 Hydriodic acid 31, 84 Hydrobromic acid 31, 84 Hydrocarbons 109 Hydrochloric acid 28, 84 ,, . composi- tion of 85 Hydrofluoric acid 27 1 1 ydrogen, combination with halogens 20 ,, , preparation 22 ,, , properties 20 Hydrogen disulphide 04 ,,. peroxide ,18 sulphide 59 Hypobromous acid 88 Hypochlorous acid 87 I. Ignition point 177 Indestructibility of matter. . . 14 Influence of pressure on solu- bility 71 lodates 89" lodic acid . 88 Iodine, chemical properties 80 ,, , physical 79 ,, , preparation 82 Iodine pentoxide 88 Iron pyrites 103 K. Kaolin T.7.. 197 Kieselguhr 193 Kinetic theory of gases 47 Lampblack 107 Latent heat (>7 Law of Boyle and Mariotte 40 ,, Charles 38 ,, combination of gases by volume 45 ,, definite proportions 18 of Henry 71 multiple proportions ... 19 partial pressures (Dal- ton's) 72 Lignite 104 Liquefaction of gases 41 M. Manufacture of bromine and iodine 82 ,, ,, sulphuric acid 110 Mariotte's Law 40 Marsh gas 109 Metaphosphates, tests for... 100 Metaphosphoric acid 100 224 INDEX, PAGE Metric system 43 Microcosmic salt 159 Mineral springs 73 Molecular formula 48 weight 46 Molecule 45 Multiple proportions, law of 19 N. Naphthalene 169 Natural waters 72 ,, composition of 74 Nature of chemical action... 10 Nitrates, tests for 145 Nitric acid 143 Nitric oxide, preparation and properties 148 ,, ,, , composition... 149 Nitrites 148 Nitrous oxide, preparation ... 149 ,, ,, ,propertiesand composition 150 Nitrogen, occurrence 128 ,, , preparation 129 ,, , properties 130 Nitrogen pentoxide 145 ,, tetroxide or per- oxide 146 ,, trioxide 147 "Noble" metals 144 Nomenclature of compounds 89 Normal salts Ill, 123 0. Octahedral sulphur 105 Olefiantgas 171 Olefines 169 Olivine 197 Opal 195 Orthophosphoric acid 158 Oxides 96 ,, , tests for ; 98 Oxides of carbon 184 Oxides and oxyacids of chlorine 86 Oxides and oxyacids of ni- trogen 142 PAGE Oxides and oxyacids of phos- phorus 156 Oxides and oxyacids of sul- phur 108, 111, 114, 116 Oxidising agents 1 09 ,, flame 181 Oxyacids of bromine 88 ,, ,, iodine 88 Oxygen, occurrence 92 , , . , preparation 93 ,, , properties 94 , , compounds w i t h hydrogen... 51, 58 Ozone 99 ,, , preparation of ozon- ised oxygen 99 ,, , molecular formula of 101 P. Paraffins 169 Pentane , 169 Pentoxide of iodine 88 Percentage composition, cal- culation of 206 Perchlorates 88 Perchloric acid 87 Periodates 89 Periodic acid 88, 89 Peroxides 98 Petroleum 165 Plastic sulphur 106 Phosphates 158 ,, , tests for 159 Phosphonium iodide 155 Phosphoric acid 158 Phosphorous acid 1 56 Phosphorous oxide 156 Phosphorus, amorphous 154 , , , crystalline 154 ,, , occurrence and preparation... 152 ,, , properties 153 Phosphorus trihydride 154 Phosphorus trichloride 160 ,, pentachloride . . . 160 Phosphorus pentoxide 157 Physical properties of gases 36 ,, matter 3 INDEX. PACK Pressure, influence on solu- bility of gases 71 "Prismatic sulphur 105 I'yrolusile 93 I \\Tophosphates, tests for... 160 Pyrophosphoric acid 160 Quartz Q. 193 It. 1\uin water 72 Reducing agents 109 Reducing flune 181 Relation of volume of gases to pressure 39, 204 Relation of volume of gases to temperature 38, 203 Relation between volume and weight 206 Relative density of gases... 44 Replacement of hydrogen of ;iu acid by metals 123 River water 73 Salts of haloid acids 32 ,, ,, ,, , tests for 34 Salts, formation of 97 Sandstone 193 Saturated solution 70 Sea water 74 Selenium 126 Serpentine 197 Shale 192 Silica 195 ,, , soluble modification of 197 Silicates 197 Silicon 193 ,, chloride 195 ,, fluoride 194 ,, hydride 194 Softening of water 76 Solubility of gases, in water 71 ,, ,, ,, , influence of pressure on 71 Solubility of solids in water 70 Solution of mixed gases I'l Spring water 73 Stas' (and Dumas') experi- ments on composition of water 55 Steatite 193 Sulphates, tests for 123 Sulphides 62 Sulphur, allotropic forms of 105 , amorphous 106 , octahedral 105 , plastic 106 , prismatic 105 , action of heat on... 104 , occurrence and ex- traction 103 Sulphur, chlorides of 107 ,, , compounds with hydrogen 59 Sulphur dioxide , 108 ,, ,, , composition of 110 Sulphur trioxide, preparation 1 14 ,, ,, , properties 115 Sulphuretted hydrogen 59 Sulphuretted hydrogen, com- position of 60 Sulphuretted hydrogen, pre- paration of 61 Sulphuric acid, manufac- ture of 116 Sulphuric acid, properties of 120 , theory of manufacture 122 Sulphurous acid Ill Sulphuryl chloride Ill Symbols, chemical 5 Synthesis 3 T. Talc 197 Tellurium 126 Tetrachloride of sulphur ... 107 Theory of manufacture of sulphuric acid 122 Thionyl chloride 107 Tridymite 195 Turpentine 169 226 INDEX. V.. PAGE Valency of element s 1 23 Vitriol, oilof 116 Volume of gases, relation to pressure 39 ',, ,, , correction for pressure 204 ,. .. ,, , relation to temperature 38 ,, ,, ,, , correction for temper- ature ... 203 Volume of liquids and solids, with relation to weight ... 205 Volume, combining, of gases 45 w. Water, composition of 51 ,, , determination by volume 53 ); , determination by weight 55 PAGE Water, properties of GO Water of crystallisation 57 Water as a solvent 70 Water vapour in air 133 Water, chalybeate 73 Water, drinking . % 75 Water, mineral 73 Water, natural, composi- tion of 74 Water, rain 7 '2 Water, river 73 Water, sea 74 Water, hardness of 7-"> Water gas 24 Weight of gases 3(3 Weight of liquids and solids, relation to volume 205 Z. Zinc blende .. .. U3 THE END. Richard Clay & Sons, Limited, London & Bungay. Select Xist of Boohs IN THE 1flni\>ersit\> {Tutorial Series PUBLISHED AT THE UNIVERSITY CORRESPONDENCE COLLEGE PRESS (W. B. CLIVE, 13 BOOKSELLERS BOW, LONDON, W.C.) CONTENTS. PAGE LATIN AND GREEK CLASSICS 3-5 LATIN AND GREEK GRAMMARS, ETC. 6 ROMAN AND GREEK HISTORY 7 FRENCH 8 ENGLISH HISTORY 8 ENGLISH LANGUAGE AND LITERATURE 9 ENGLISH CLASSICS 10 MENTAL AND MORAL SCIENCE 11 MATHEMATICS AND MECHANICS 12, 13 CHEMISTRY 14 BIOLOGY 14 PHYSICS AND GENERAL ELEMENTARY SCIENCE. . . .15 DIRECTORIES THE UNIVERSITY CORRESPONDENT . .16 THE ORGANIZED SCIENCE SERIES 16 A List of Books for London University Students, classified for the various Examinations, List of Books for the Cambridge and Oxfora Locals and the College of Preceptors Examinations, and also the Complete Catalogue of the University Tutorial Series, may be had post free on application to W. B. CLIVE, University Corre- spondence College Press Warehouse, 13 Booksellers Row, Strand, W.C. OCT., 1898. THE UNIVERSITY TUTORIAL SERIES. < \amvereit\> tutorial Series General Editor: WILLIAM BRIGGS, M.A., LL.B., F.C.S., F.R.A.S. Cfasical Editor: B. J. HAYES, M.A. The object of the UNIVERSITY TUTORIAL SERIES is to provide candidates for examinations and learners generally with text-books which shall convey in the simplest form sound instruction in accord- ance with the latest results of scholarship and scientific research. Important points are fully and clearly treated, and care has been taken not to introduce details which are likely to perplex the be- ginner. The Publisher will be happy to entertain applications from School- masters for specimen copies of any of the books mentioned in this List, SOME PRESS OPINIONS, " ' The University Tutorial Series' should prove most useful to students generally." Westminster Review. " ' The University Tutorial Series ' . . a businesslike undertaking which has all the prestige of success." Spectator. " Turned out in a workmanlike way by competent scholars." Saturday Review. "This series has proved serviceable to many, and is now well-known for its accuracy in teaching elementary principles, and the thoroughness of the aid which it supplies." Educational Review. " This series is successful in hitting its mark and supplying much help to students in places where a guiding hand is sorely needed." Journal of Education. " The more we see of these excellent manuals the more highly do we think of them." Schoolmaster. " The text-books in this series are well suited to the object for which they are so carefully prepared." Young Man. " This excellent and widely appreciated series." Freeman's Journal. " Clearness and thoroughness characterize this series of classics, which will be found eminently useful." Educational Times. " Tie evident care, the clearly conceived plan, the genuine scholarship, and the general excellence of the productions in the series give them high claims to com- mendation." Educational News. " This useful series of text-books." Nature. "Has done excellent work in promoting higher education." Morning Post. " It may justly be said that any books published in this series are admirably adapted for the needs of the large class of students for whom they are intended." Cambridge Review. THE UNIVERSITY TUTORIAL SERIES. 3 Xatin ant) <5reefc Classics. (See also page 4.) The following are among the editions of LATIN and GREEK CLASSICS contained in the UNIVERSITY TUTORIAL SERIES, and are 011 the following plan: A short INTRODUCTION gives an account of the Author and his chief works, the circumstances under which he wrote, and his style, dialect, and metre, where these call for notice. The TEXT is based on the latest and best editions, and is clearly printed in large type. The distinctive feature of the NOTES is the omission of parallel passages and controversial discussions of difficulties, and stress is laid on all the important points of grammar and subject-matter. Information as to persons and places mentioned is grouped together in a HISTORICAL AND GEOGRAPHICAL INDEX; by this means the expense of procuring a Classical Dictionary is rendered unnecessary. The standard of proficiency which the learner is assumed to possess varies in this series according as the classic dealt with is usually read by beginners or by those who have already made considerable progress. A complete list is given overleaf. Casar. Gallic War, Book I. By A. H. ALLCROFT, M.A. Oxon., and F. G. PLAISTOWE, M.A. Camb. Is. 6d. "A clearly printed text, a good introduction, an excellent set of notes, and a 'historical and geographical index, make up a very good edition at a very . Th Tutorial History of Borne. (To 14 A.D.) By A. H. ALLCROFT, M. A. Oxon., and W.F. MASOM, M.A. Lond. With Maps. 38. 6d. " It is well and clearly written." Saturday Rerieic. A Longer History of Borne. In Five Volumes, each containing a Chapter on the Literature of the Period : I. History of Borne, 287-202 B.C. : The Struggle for Empire. By W. F. MASOM, M.A. Lond. 3s. 6d. II. History of Borne, 202-133 B.C. : Rome under the Oligarchs. By A. H. ALLCROFT, M.A. Oxon., and W. F. MASOM, M'.A. Lond. 3s. 6d. III. History of Borne, 133-78 B.C. : The Decline of the Oligarchy. By W. F. MASOM, M.A. Lond. 3s. 6d. ' This volume gives a vigorous and carefully studied picture of the men and of the time." Spectator. IV. History of Borne, 78-31 B.C. : The Making of the Monarchy. By A. H. ALLCROFT, M.A. Oxon. 3s. 6d. "Well and accurately written." Yorkshire Post. V. History of Borne, 31 B.C. to 96 A.D. : The Early Principate. By A. H. ALLCROFT, M.A. Oxon., and J. H. HAYDON, M.A. Cnmb. and Lond. Second Edition. 3s. 6d. " Written in a clear and direct style. Its authors show a thorough acquaintance with their authorities, and have also used the works of modern historians to good Affect." Journal of Education. History of Borne, 390-202 B.C. By W. F. MASOM, M.A. Lond., and W. J. WOODHOUSE. M.A. Oxon. 4s. 6d. 'A good specimen of a well-told historical narrative." Westminster Review. A History of Greece. In Six Volumes, each containing a Chapter on the Literature of the Period : I. Early Grecian History. (To 495 B.C.) By A. H. Ar.LCKOFT, M.A. Oxon.. and W. F. MASOM, M.A" Lond. 3s. 6d. "For those who require a knowledge of the period no better book could be recommended." Educational Times. II. History of Greece, 495 to 431 B.C.: The Making of Athens. By A. H. ALLCROFT, M.A. Oxon. 3s. 6d. III. History of Greece, 431-404 B.C. : The Pelopormesian War. By A. H. ALLCROFT, M.A. Oxon. 3s 6d. IV. History of Greece, 404-362 B.C. : Sparu. and Thebes. Hy A. H. ALLCROFT, M.A. Oxon. 3s. 6d V. History of Greece, 371-323 B.C. : The Decline of Hellas. By A. H. Al.LCROFT, M.A. Oxon. 3s. 6d. VI. History of Sicily, 490-289 B.C. By A. II. ALLCKOFT. M.A. Oxon., and W. F. MASOM, M.A. Lond. 3s. (id. 41 We can bear high testimony to its merits." Schoolmaster. THE UNIVERSITY TUTORIAL SERIES. ffrencb. The Tutorial French Accidence. By ERNEST WEEKLEY, M.A. Lond., Professor of French, University College, Nottingham. With EXERCISES, and a Chapter on Elementary Syntax. 3s. 6d. " The essentials of the accidence of the French Language are skilfully exhibited in carefully condensed synoptic sections." Educational Neirn. "A most practical and able compilation." Public Opinion. The Tutorial French Syntax. By ERNEST WEEKLEY, M.A. Lond., and A. J. WYATT, M.A. Lond. & Camb. With Exercises. 3s. 6d. " It is a decidedly good book and should have a ready sale." Guardian. ' Mr. "Weekley has produced a clear, full, and careful Grammar in the ' Tutorial Trench Accidence,' and the companion volume of ' Syntax,' by himself and Mr. Wyatt, is worthy of it." Saturday Review. The Tutorial French Grammar. Containing the Accidence and the Syntax in One Volume. 4s. 6d. The Preceptors' French Course. By ERNEST WEEKLEY, M.A. Lond. 2s. 6d. French Prose Composition. By ERNEST WEEKLEY, M.A. 3s. 6d. 'The arrangement is lucid, the rules clearly expressed, the suggestions really helpful, and the examples carefully chosen." Educational Times. The Preceptors' French Reader. By ERNEST WEEKLEY, M.A. Lond. With Notes and Vocabulary. Second Edition. Is. 6d. "A very useful first reader with good vocabulary and sensible notes." School- master. French Prose Reader. Edited by S. BARLET^ B. es Sc., Examiner in French to the College of Preceptors, and W. F. MASOM, M.A Lond. With VOCABULARY. Third Edition. 2s. 6d. " Admirably chosen extracts. They are so selected as to be thoroughly interesting and at the same time thoroughly illustrative of all that is best in French literature " School Board Chronicle. Advanced French Reader: Containing passages in prose and verse representative of all the modern Authors. Edited by S. BARLET, B. es Sc., Examiner in French to the College of Preceptors, and AV. F. MASOM, M.A. Lond. Second Edition. 3s. 6d. "Chosen from a large range of good modern authors, the book provides excellent practice in 'Unseens.' " Schoolmaster. Higher French Reader. Edited by ERNEST WEEKLEY, M.A. 3s. 6d. " The passages are well chosen, interesting in themselves, and representative of the best contemporary stylists." Journal of Education. The Intermediate Text-Book of English History : a Longer History of England. By C. S. FEARENSIDE, M.A. Oxon., and A. JOHNSON EVANS, M.A. Camb., B.A. Lond. With Maps & Plans. VOL. I., to 1485 (In preparation.} VOL. III., 1603 to 1714. 4s. 6d. VOL. II., 1485 to 1603. 4s. 6d. VOL. IV., 1714 to 1837. 4s. 6d. " The results of extensive reading seem to have been photographed upon a small plate, so that nothing of the effect of the larger scene is lost." Teachers 1 Monthly. " It is lively ; it is exact ; the style is vigorous and has plenty of swing ; the facts are numerous, but well balanced and admirably arranged." Education. THE UNIVERSITY TUTORIAL SERIES. language anJ> literature* The English Language : Its History and Structure. By W. H. Low, M.A. Lond. With TEST QUESTIONS. Fourth Edition. 3s. 6d. CONTENTS : The Relation of English to other Languages Survey of the Chief Changes that have taken place in the Language Sources of our Vocabulary The Alphabet and the Sounds of English Grimm's Law Gradation and Mutation Trans- position, Assimilation, Addition and Disappearance of Sounds in English Introductory Remarks on Grammar The Parts of Speech, etc. Syntax Parsing and Analysis Metre 320 Test Questions. " A clear workmanlike history of the English language done on sound principles." Saturday Hcricir. "The author deals very fully with the source and growth of the language. The parts of speech are dealt with historically as well as grammatically. The work is scholarly and accurate." Schoolmaster. " The history of the language and etymology are both well and fully treated." Teacher^ Monthly. "Aptly and cleverly written." Teachers' Aid. "The arrangement of the book is devised in the manner most suited to the student's convenience, and most calculated to impress his memory." Lyceum. " It is in the best sense a scientific treatise. There is not a superfluous sentence." Educational Neu-s. The Preceptors' English Grammar. With numerous Exercises. By ARNOLD WALL. M.A. Lond. [In preparation.. The Intermediate Text-Book of English Literature. By W. H. Low, M.A. Lond., and A. J. WYATT, M.A. Lond. and Camb. PART I. (to 1660), 3s. 6d. ; PART II. (1660-1832), 3s. 6d. [Part II. in the press. Also: VOLUME II., 1558 to 1660. By W. H. Low. 3s. 6d. VOLUME III., 1660 to 1798. By W. H. Low. 3s. 6d. " Really judicious in the selection of the details given." Saturday Review. "Designed on a thoroughly sound principle. Facts, dates, and representative quotations are plentiful. The critical extracts are judiciously chosen, and Mr. Low's own writing is clear, effective for its purpose, and evidently the result of thorough knowledge and a very considerable ability to choose between good and bad." National Observer. "It affords another example of the author's comprehensive grasp of his subject, combined with a true teacher's power of using such judicious condensation that the more salient points are brought clearly into view." teachers' Monthly. "Mr. Low has succeeded in giving a very readable and lucid account of the literature of the time." Literary World. " Mr. Low's book forms a serviceable student's digest of an important period in our liter iture." Schoolmaster. "The style is terse and pointed. The representative quotations are aptly and judiciously chosen. The criticisms are well grounded, clearly expressed and modestly presented." Morning Post. 10 THE UNIVERSITY TUTORIAL SERIES. (Classics. Addison. Essays on Milton, Notes on. By W. H. Low, M.A. 2s. Chaucer. Prologue, Knight's Tale. With INTRODUCTION and NOTES by A. J. WYATT, M.A. Lond. and Camb., and a Glossary by S. J. EVANS, M.A. Lond. 2s. 6d. "The notes are of real value." Educational Review. Quite up to date. The Glossary is excellent." Morning Pout. Chaucer. Man of Lawes Tale, with the PROLOGUE to the CANTER- BURY TALES. Edited by A. J. WYATT, M.A. Lond. and Camb., with a GLOSSARY by J. MALINS, M.A. Lond. 2s. 6d. Dryden. Essay on Dramatic Poesy. Edited by W. H. Low, M.A. Lond. TEXT and NOTES. 3s. 6d. Goldsmith. Poems. Edited by AUSTIN DOBSON. 2s. 6d. net. Langland. Piers Plowman. Prologue and Passua I. -VII., Text B. Edited by J. F. DAVIS, D.Lit, M.A. Lond., Assistant Examiner at the University of London. 4s. 6d. Milton. Paradise Eegained. Edited by A. J. WYATT, M.A. 2s. 6d. "The notes are concise and to the point." Cambridge Review. Milton. Samson Agonistes. Edited by A. J. WYATT, M.A. 2s. 6d. " A capital Introduction. The notes are excellent." Educational Timet. Milton. Sonnets. Edited by W. F. MASOM, M.A. Lond. Is. 6d. Shakespeare. With INTRODUCTION and NOTES, by Prof. W. J. ROLFE, D.Litt., in 40 volumes. 2s. each. A descriptive catalogue, containing Prof. Bolfe's Hints to Teachers and Students of Shakespeare, can be obtained on application. Merchant of Venice Winter's Tale Tempest King John Midsummer Night'* Richard II. Dream Henry IV. Part I. As You Like It Henry IV. Part U. Much Ado About Nothing Henry V. Twelfth Night ! Henry VI. Parti. Comedy of Errors Henry VI. Part U. Merry Wives of Windsor Henry VI. Part m. Love's Labour's Lost Richard ILL Two Gentlemen of Verona j Henry VLLT. The Taming of the Shrew Romeo and Juliet th Hamlet King Lear Cymbeline Julius Caesar Coriolanus Antony and Cleopatra Timon of Athena Troilus and Cressida Pericles The Two Noble Kinsmen Titus Andronicus Venus and Adonis Sonnets All' s Well that Ends Well ! Macbeth Measure for Measure Othello This edition is recommended by Professor Dowden, Dr. Abbott, and Dr. Furnivall. Shakespeare. Henry VIII. Edited by W. H. Low, M.A. Lond. 2s. Spenser. Faerie Queene, Book I. Edited with INTRODUCTION. NOTES, and GLOSSARY, by W. H. HILL, M.A. Lond. 2s. 6d. THE UNIVERSITY TUTORIAL SERIES. \\ flDental anb flDoral Science. Ethics, Manual of. By J. S. MACKENZIE, M.A., Professor of Logic and Philosophy in the University College of South Wale* ;trui Monmouthshire, formerly Fellow of Trinity College, Cambridge, Examiner in the Universities of Cambridge and Aberdeen. Third Edition, revised, enlarged, and partly rewritten. 6s. 6d. " In writing this book Mr. Mackenzie has produced an earnest and striking con- tribution to the ethical literature of the time." Mind. "This excellent manual." International Journal of Ethics. 'Mr. Mackenzie maybe congratulated on having presented a thoroughly good and helpful guide to this attractive, yet elusive and difficult, subject. ' ' Schoolmaster. " It is a most admirable student's manual." Teacher's Monthly. " Mr. Mackenzie's book is as nearly perfect as it could be. It covers the whole Held, and for perspicuity and thoroughness leaves nothing to be desired. The pupil who masters it will find himself equipped with a sound grasp of the subject such a.* no one book with which we are acquainted has hitherto been equal to supplying. Not the least recommendation is the really interesting style of the work." Literary World. ' ' Written with lucidity and an obvious mastery of the whole bearing of the sub j ect. ' " Standard. " No one can doubt either the author's talent or his information. The ground of ethical science is covered by his treatment completely, sensibly, and in many respects brilliantly." Manchester Guardian. " For a practical aid to the student it is very admirably adapted. It is able, clear, and acute. The arrangement of the book is excellent. Netccastle Daily Chronicle. Logic, A Manual of. By J. WELTON, M.A. Lond. and Camb. 2 vols. Vol. I., Second Edition, 8s. 6d. ; Vol. II., 6s. 6d. This book embraces all those portions of the subject which are usually read, and renders unnecessary the purchase of the numerous books hitherto used. The relative importance of the sections is denoted by variety of type, and a minimum course of reading is thus indicated. Vol. I. contains the whole of Deductive Logic, except Fallacies). which are treated, with Inductive Fallacies, in Vol. II. " A clear and compendious summary of the views of various thinkers on important and doubtful points." Journal of Education. "A very good book . . . not likely to be superseded for a long time to come." Educational Review. "Unusually complete and reliable. The arrangement of divisions and subdivision, is excellent." Schoolmaster. "The manual may be safely recommended." Educational Time*. "Undoubtedly excellent." Board Teacher. Psychology, A Mannal of. By G. F. STOUT, M.A., Fellow of St. John's College, Cambridge, Lecturer on Comparative Psychology in the University of Aberdeen. Two Vols., 4s. 6d. each. [/ the />?v.v.v 12 THE UNIVERSITY TUTORIAL SERIES. flDatbematics anb flDecbanics. Books marked (%) are in the Organized Science Series. Algebra, A Middle. By WILLIAM BRIGGS, M.A., LL.B., F.R.A.S., and G. H. BRYAN, Sc.D., M.A., F.R.S. Based on the Algebra of Radhakrishnan. 3s. 6d. Algebra, The Tutorial. By the same Authors. Part I. ELEMENTARY COURSE. [/ preparation. Part II. ADVANCED COURSE. 6s. 6d. [/? the press. Astronomy, Elementary Mathematical. By C. W. C. BARLOW, M.A., Lond. and Camb.. B.Sc. Lond., and Gr. H. BRYAN, Sc.D., M.A., F.R.S., Fellow of St. Peter's College, Cambridge. Second Edition, with ANSWERS. 6s. 6d. " Probably within the limits of the volume no better description of the methods by which the marvellous structure of scientific astronomy has been built up could have been given." Athenceum. " Sure to find favour with students of astronomy." Nature. Coordinate Geometry: The Right Line and Circle. By WILLIAM BRIGGS, M.A., LL.B., F.R.A.S., and G. H. BRYAN, Sc.D., M.A., F.R.S. Third Edition. 3s. 6d. " It is thoroughly sound throughout, and indeed deals with some difficult points with a clearness and accuracy that has not, we believe, been surpassed." Education. "Thoroughly practical and helpful." Schoolmaster. " The arrangement of matter and the copious explanations it would be hard to surpass. It is the best, book we have seen on the subject." Board Teacher. Coordinate Geometry, Worked Examples in : A Graduated Course on the Right Line and Circle. Second Edition. 2s. 6d. Dynamics, Text-Book of. By WILLIAM BRIGGS, M.A., F.C.S., F.R.A.S., and G. H. BRYAN, Sc.D., M.A., F.R.S. 2s. 6d. " The treatment is conspicuous for its clearness and conciseness." Nature. Euclid. Books I. -IV. By RUPERT DKAKIN, M.A. Lond. and Oxon., Headmaster of Stourbridge Grammar School. 2s. 6d. Also separately: Books I., II., Is. "The book is clearly printed, the demonstrations are well arranged, and the diagrams, by the judicious use of thin and thick lines, are rendered more intelligible." Saturday Review. " An admirable school Edition." Speaker. Geometry of Similar Figures and the Plane. (Euclid VI. and XI.) With numerous Deductions worked and unworked. By C. W. C. BARLOW, M.A., B.Sc., andG. H. BRYAN, Sc.D., F.R.S" 2s. 6d. Hydrostatics, An Elementary Text-Book of. By WILLIAM BRIGGS, M.A., F.C.S., F.R.A.S., and G. H. BRYAN, Sc.D., F.R.S. Second Edition. 2s. " The work is thoroughly sound. The hand of the practical teacher is manifest throughout." Educational Review. THE UNIVERSITY TUTORIAL SERIES. 13- flDatbematics anfc /Ifcecbanics -continued ; Mathematics, Second Stage. Edited by WILLIAM BRIGGS, M.A., LL.B., F.C.S., F.R.A.S. 3s. 6d. i Mechanics, Advanced. With the Questions of the last eleven years- set at the advanced examination of the Science and Art Department. By WM. BRIGGS, M.A., LL.B., F.R.A.S., and G. H. BRYAN, Sc.D., F.R.S. Vol. I. DYNAMICS. 3s. 6d. Vol. II. STATICS. 3s. 6d. Vols. I. and II. deal respectively with those portions of Dynamics and Static* which are required for the Science and Art Second (Advanced) Stage Examination, in Theoretical Mechanics. Mechanics, An Elementary Text-Book of. By the same authors. Second Edition. 3s. 6d. " A most useful and helpful manual." Educational Review. ^Mechanics (of Solids), First Stage. By F. ROSENBERG, M.A., B.Sc. Second Edition. 2s. " The work of a practical teacher." Educational Review. Mechanics, The Preceptors'. By F. ROSENBERG, M.A., B.Sc. 2s. 6d. ;Mechanics of Fluids, First Stage. By G. H, BRYAN, Sc.D., F.R.S., and F. ROSENBERG, M.A., B.Sc. 2s. Mechanics and Hydrostatics, Worked Examples in: A Graduated Course on the London Matriculation 'Syllabus. Third Editioti, Revised and Enlarged. Is. 6d. Mensuration of the Simpler Figures. By WILLIAM BRIGGS, M.A.,. F.C.S., F.R.A.S., and T. W. EDMONDSON, M.A. Camb., B.A. Lond. Second Edition. 2s. 6d. Mensuration and Spherical Geometry: Being Mensuration of the Simpler Figures and the Geometrical Properties of the Sphere. Specially intended for London Inter. Arts and Science. By the same authors. Second Edition. 3s. 6d. "The book comes from the hands of experts; we can think of nothing better qualified to enable the student to master this branch of the syllabus, and to promote a correct style in his mathematical manipulations." Schoolmaster. Statics, The Tutorial. By WILLIAM BRIGGS, M.A., LL.B., F.R.A.S., and G. H. BRYAN, Sc.D., M.A., F.R.S. 3s. 6d. Trigonometry, The Tutorial. By WILLIAM BRIGGS, M.A., LL.B., F.K.A.S.. rind G. H. BRYAN, Sc.D., M.A., F.R.S. 3s. 6d. "An eminently satisfactory text-book, which might well be substituted as an elementary course for those at present in use." Gunrtlian. " Good as the works of these authors usually are, we think this one of their best." Education. Trigonometry, Synopsis of Elementary. By WILLIAM BRIGGS, M.A., LL.B., F.R.A.S. Interleaved. Is. 6d. U THE UNIVERSITY TUTORIAL SERIES. Chemistry Books marked (+) are in the Organized Science Series. Analysis of a Simple Salt. With a Selection of Model Analyses, and TABLES OF ANALYSIS (on linen). By the same Authors. Fourth Edition. 2s. 6d. TABLES OF ANALYSIS (separately). 6d. "The selection of model analyses is an excellent feature." Educational Times. Chemistry, The Tutorial. By G. H. BAILEY, D.Sc. Lond., Ph.D. Heidelberg, Lecturer in Chemistry at Victoria University. Edited by WILLIAM BRIGGS, M.A., F.C.S. PART I., NON-METALS. 3s. 6d. PART II., METALS. 3s. 6d. " "We can unhesitatingly recommend it for the higher forms of Secondary and other schools." Education. " A good text-book. The treatment is thorough and clear, and the experiments are good and well arranged." School Guardian. jChemistry, First Stage Inorganic. By G. H. BATLEY, D.Sc. 2s. "A valuable and comprehensive book for young students." Secondary Education. ^Chemistry, First Stage Practical Inorganic. By F. BEDDOW, D.Sc., Ph.D. Is. Carbon Compounds, An Introduction to. By R. H. ADIE, M.A., B.Sc 2s. 6d. [In the Press. Chemistry, Synopsis of Non-Metallic. With an Appendix on Calcu- lations. By WILLIAM BRIGGS, M.A., LL.B., F.C.S. New and Revised Edition, Interleaved. Is. 6d. " Arranged in a very clear and handy form." Journal of Education. Chemical Analysis, Qualitative and Quantitative. By WILLIAM BRIGGS, M.A., LL.B., F.C.S., and R. W. STEWART. D.Sc. Lond. 3s. 6d. Metals and their Compounds. By G. H. BAILEY, D.Sc., Ph.D. Is. 6d. Biology Biology, Text Book of. By H. G. WELLS, B.Sc. Lond., F.Z.S., F.C.P. PT. I., Vertebrates. 6s. 6d. ; Pr. II., Invertebrates and Plants. 6s. 6d. Zoology, Text-Book of. By H. G. WELLS, B.Sc. Lond., F.Z.S., F.C.P. Enlarged and Revised by A. M.DAVIES, B.Sc. Lond. 6s.6d. " The information appears to be well up to date. Students will find this work of the greatest service to them." Westminster Review. Botany, Text-Book of. By J. M LOWSON, M.A., B.Sc. 6s. 6d. THE UNIVERSITY TUTORIAL SERIES. 15 Jlook* marked () are in the Organized Science Seriet. By R. W. STEWART, D.Sc. Lond. Heat and Light, Elementary Tezt-Book of. Third Edition. 3s. 6d. " It will be found an admirable text-book." Educational Newt. Heat, Elementary Tezt-Book of. 2s. JHeat, Advanced. (For the Advanced Stage of the Science and Art Department.) 3s. 6d. Light, Elementary Tezt-Book of. 2s. ^Magnetism and Electricity, First Stage. By R. H. JUDE, M.A., D.Sc. 2s. Physiography, First Stage. By A. M. DA VIES, B.Sc. 2s. +Sound, Light, and Heat, First Stage. By JOHN DON, M.A., B.Sc. 2s. Sound, Elementary Tezt-Book of. By JOHN DON, M. A., B.Sc. Is. 6d. THE TUTOBIAL PHYSICS. By E. CATCHPOOL, B.Sc. Lond., First Class Honourman. Vol. I. Sound, Tezt-Book of. Second Edition. 3s. 6d. By R. W. STEWART, D.Sc. Lond. Vol. II. Heat, Tezt-Book of. Third Edition. 3s. 6d. Vol. III. Light, Tezt-Book of. Third Edition. 3s. 6d. Vol. IV. Magnetism & Electricity, Tezt-Book of. Third Edition. 3s. 6d. "The author writes as a well-informed teacher, and that is equivalent to saying that he writes clearly and accurately. There are numerous books on acoustics, but few cover exactly the same ground as this, or are more suitable introductions to a serious study of the subject. ' Nature. "Clear, concise, well-arranged and well-illustrated, and, as far as we have tested, accurate." Journal of Education. "Distinguished by accurate scientific knowledge and lucid explanations." Educational Tune a. " It is thoroughly well done." Schoolmatter. "The author has been very successful in making portions of the work not ordinarily regarded as elementary appear to be so by his simple exposition of them." Teachers' Monthly. Properties of Matter: an Introduction to the Tutorial Physics. By E. CATCHPOOL, B.Sc. [/n preparation. GENERAL ELEMENTAET SCIENCE. General Elementary Science. Edited by WILLIAM BRIGGS, M.A., LL.B., F.C.S. Second Edition. 3s. 6d. " The book u decidedly above the average of this class of work. The Mechanics is sound, and the experimental part of the Chemistry is decidedly good."- - Guardian. " We can confidently recommend this book." Journal of Education. " Extremely well adapted for its purpose." Education. rctanisefc Science Series Adapted to the Requirements of the Science and Art Department. FOR THE ELEMENTARY STAGE. 2s. each Vol. First Stage Mechanics (Solids . By F. ROSENBERG, M.A., B.Sc. First Stage Mechanics of Fluids. By G. H. BRYAN, Sc.D., F.R.S., and F. ROSENBERG, M.A., B.Sc. First Stage Sound, Light, and Heat. By JOHN DON, M.A., B.Sc. First Stage Inorganic Chemistry (Theoretical). By G. H. BAILEY, D.Sc. First Stage Physiography. By A. M. DAVIES, B.Sc. First Stage Magnetism and Electricity. By R. H. JUDB, D.Sc. First Stage Inorganic Chemistry (Practical). Is. Practical Organic Chemistry. By GEORGE GEORGE, F.C.S. Is. 6d. FOR THE ADVANCED STAGE. 3s. 6d. each Vol. Second Stage Mathematics. Edited by WILLIAM BRIGGS, M.A., F.C.S. Advanced Mechanics (Solids). By WILLIAM BRIGGS, M.A., F.C.S., F.R.A.S., and G. H. BRYAN, Sc.D., M.A., F.R.S. Part I. DYNAMICS. Part II. STATICS. Advanced Heat. By R. W. STEWART, D.Sc. Lend. The following books are in course of preparation : For THE ELEMENTARY STAGE First Stage Mathematics, First Stage Physio- logy, First Stage Botany. For THE ADVANCED STAGE Advanced Magnetism and Electricity, Advanced Inorganic Chemistry (Theo- retical), Advanced Inorganic Chemistry (Practical), Organic Chemistry (Practical). TIbe *Clni\>ersit Gorresponfcent AND UNIVERSITY CORRESPONDENCE COLLEGE MAGAZINE, Issued every Saturday. Price Id., by Post l|d. ; Half-yearly Subscription. 3s ; Yearly Subscription, 5s. 6d. Examination Directories* Matriculation Directory, with Full Answers to the Examination Papers. (jYo. XXI'. will be published during the fortnight following the Exmninaton of Jan., 1899). Nos. VI., VII., IX., XI. XXI. XXIII., XXIV. Is. each, net. Intermediate Arts Directory, with Full Answers to the Examination Papers (except in Special Subjects for the Year). Nos. II. (1889) to VI. (1893), 2s. 6d. each, net. Inter. Science and Prelim. Sci. Directory, with Full Answers to the Examination Papers. Nos. I. to IV. (1890-3), 2s. 6d. each, net. B.A. Directory, with Full Answers to the Examination Papers (except in Special Subjects for the Year.) Nos. I. III., 1889-91 . 2s. 6d. each, net. No. IV., 1893 (with Full Answers to the Papers in Latin, Greek, and Pure Mathematics). 2s. 6d. net. YB H058