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AN EXPERIMENTAL COURSE 
 
 OF 
 
 CHEMISTRY 
 
 FOR AGRICULTURAL STUDENTS 
 
Digitized by the Internet Archive 
 
 in 2008 with funding from 
 
 Microsoft Corporation 
 
 http://www.archive.org/details/experimentalcourOOdymorich 
 
General Editor: Professor R. MELDOLA, F.R.S. 
 
 AN EXPERIMENTAL COURSE 
 
 OF 
 
 CHEMISTRY 
 
 FOR AGRICULTURAL STUDENTS 
 
 BY 
 
 T. S. DYMOND, F.I.C. 
 
 LATELY PRINCIPAL LECTURER IN THE AGRICULTURAL DEPARTMENT 
 COUNTY TECHNICAL LABORATORIES, CHELMSFORD 
 
 ;FlfVH : IMPXESSION 
 
 LONDON 
 
 EDWARD ARNOLD 
 
 41 AND 43 MADDOX STREET, BOND STREET, W. 
 

EDITOR'S PREFACE 
 
 In the present state of scientific education, or, more correctly 
 speaking, education in science, in this country, the instructor 
 is frequently called upon to face the problem of teaching a 
 particular science to students engaged or about to be engaged 
 in some special industry. The problem is confessedly a 
 difficult one to deal with practically, and many diverse views 
 are held respecting its feasibility, or even the desirability of 
 attempting its solution. The diversity of opinion no doubt 
 represents the differences in the mode of treatment to which 
 the various branches of science lend themselves. To the 
 majority of educationists it is evident that instruction in 
 science is, as a mental discipline, of a very high order of 
 importance, quite apart from any technical knowledge in 
 relation to any special industry. More particularly does this 
 apply in the case of those occupied in productive industries 
 of all kinds, whether manufacturing or agricultural, in the 
 widest meaning of the term. 
 
 Starting with the very reasonable assumption that those 
 who are concerned with agriculture should know, at least, 
 something of the general principles of chemical science, the 
 question presents itself to all who are interested in the welfare 
 of agriculture — How and When is such instruction to be given ? 
 The elementary schools, especially in country districts, are 
 confessedly feeble in their science teaching, even if they 
 attempt it at all. There is a crying need for good secondary 
 and technical schools in rural centres, but little progress has 
 as yet been made in this direction. That sound instruction 
 in scientific principles by scientific method should be made 
 
 5 
 
 3592o^ 
 
EDITOR'S PREFACE 
 
 a part of the early training of boys and girls, is an ideal which 
 we all hope to see realised; but so far as concerns the 
 agricultural community, this ideal, although at present remote, 
 must be seriously kept in view in any scheme of education 
 having for its object the intellectual advancement of the 
 British farmer. 
 
 In the meantime the County Councils, provided with the funds 
 for Technical Education, have in many agricultural counties 
 developed a laudable desire to improve the status of the 
 agriculturalist by placing the means of acquiring sound' 
 instruction within his reach. In most parts of the country 
 where such facilities have been offered, the younger generation 
 of farmers have been found willing to avail themselves of them. 
 Those counties which have failed hitherto to touch the 
 agricultural community would do well to reconsider the policy 
 which their Technical Instruction Committees have adopted. 
 
 With regard to a science of such fundamental importance 
 as Chemistry, it is most desirable to arrest the attention and 
 to arouse the interest of the student by enabling him to 
 acquire his knowledge of general principles through practical 
 work carried out in the laboratory with materials and by 
 means of illustrations drawn as far as possible from sources 
 with which his ordinary observation makes him daily familiar. 
 This method may possibly lend itself to the criticism that 
 it is wrong in principle to attempt too early a specialisation 
 before the rudiments have been acquired. Nevertheless I am 
 convinced that such a system can be successfully followed if 
 judiciously carried out and not driven to the unwarrantable 
 extreme of endeavouring to convert the agricultural student 
 into an expert chemist. 
 
 The author of the present book has on these lines prepared 
 a course of practical chemistry which has to my knowledge 
 been most successful with agricultural students in the Central 
 Laboratories of the Essex County Council at Chelmsford. At 
 my suggestion he now offers this course to a wider public, and 
 I can confidently recommend the work to all those who are 
 practically engaged in teaching this science to a class of pupils 
 whose welfare is so intimately associated with the progress of 
 chemical knowledge. 
 
 R. Meldola. 
 
AUTHOR'S PREFACE 
 
 A farmer does not need to be a chemist ; at the same time 
 he needs the training in accuracy, careful observation, and 
 experimental method which a study of chemistry, properly 
 carried out, imparts, and he needs a knowledge of the ele- 
 mentary principles of chemical change and of the properties 
 of certain chemical substances, both inorganic and organic. 
 The customary four years' course of inorganic and organic 
 chemistry goes far beyond the requirements of an agricultural 
 student, and is usually beyond the time at his disposal. 
 
 The following course is designed to enable an agricultural 
 student to acquire the knowledge and training he needs by 
 a short experimental study of the chemical substances with 
 which agriculture is concerned, his attention being directed 
 at the same time to the practical application of each subject 
 dealt with to rural industry. The course upon which the 
 work is founded has been in use during the past three years 
 in some of the grammar schools and evening continuation 
 schools in the rural districts of Essex, and has also been used 
 in the County Technical Laboratories at Chelmsford by the 
 students of the agricultural classes, and as a preparatory 
 course for elementary school teachers who wish to qualify 
 themselves to teach chemistry in the agricultural parts of 
 the county. 
 
 In rural districts the introduction of the study of experi- 
 mental science is often prevented by the costliness of 
 apparatus and laboratory accommodation. With a view, 
 therefore, to economy, the experiments have been designed 
 for simple and inexpensive apparatus and chemicals. The 
 
 7 
 
g AUTHOR'S PREFACE 
 
 set required for twelve students, given in the Appendix, can 
 be purchased for about ^40. Neither need the fitting of a 
 laboratory for experimental work be a costly undertaking. 
 A demonstration table, provided with drawers and a sink, 
 working benches for twelve students, provided with a rack 
 for reagents, fume cupboard, apparatus cupboard, shelves 
 for chemicals, blackboard, balance shelf, and distillation table, 
 also provided with a sink, together with gas and water supplies, 
 constitute the equipment necessary, and cost from ^50 up- 
 wards, according to the style of work. It is very desirable 
 that for experimental work of this character the working 
 benches should be so placed that the students face the 
 demonstration table. 
 
 The course is divided into thirty-six experimental studies, 
 through each of which the student, under the supervision of 
 the teacher, is expected to work. Each student should work 
 independently, and only in exceptional cases should two 
 students be allowed to work together for a particular experi- 
 ment. Each day's work should be accompanied by a revision 
 class. Revision is quite as essential as the experimental work ; 
 for it is by this means that the teaching of each experiment 
 is brought home to the student. It is desirable, and in the 
 absence of revision necessary, that the student should answer 
 in writing the questions and problems set. A written and 
 practical examination should follow the conclusion of each 
 part of the course. The sections on special subjects the 
 teachers are recommended to expand into lectures to the 
 class \ it is not intended that the students should themselves 
 make the experiments described in these sections. 
 
 The value of this course as a means of training will, to 
 a large extent, depend upon the care, thoroughness, and 
 accuracy with which the experimental work is carried out. 
 In such work it is especially necessary to remember that 
 whatever is worth doing at all is worth doing well. 
 
 My thanks are due to Mr. F. Hughes, who has kindly made 
 the drawings for the figures which illustrate this volume. 
 
 T. S. D. 
 
CONTENTS 
 
 of the Air 
 and Ice 
 
 Professor Meldola's Preface 
 Author's Preface. 
 
 PART I 
 I. Weights and Measures 
 II. The Atmosphere . 
 
 III. Composition of Air 
 
 IV. Oxygen Gas. 
 V. The Third Constituent 
 
 VI. Aqueous Vapour, Water 
 VII. Water as a Solvent 
 VIII. Density 
 IX. Composition of Water 
 X. Hydrogen Gas 
 XI. Conclusions 
 
 Questions and Problems for Revision and Exam in a 
 tion ...... 
 
 PART II 
 
 XII. Basic Oxides, Acid Oxides, and Salts. 
 
 XIII. The Metals— The Metallic Oxides 
 
 XIV. Combining Weights of the Elements . 
 XV. Composition of the Basic Oxides and Hydrates 
 
 XVI. The Non-metallic Elements— Sulphur 
 
 9 
 
 5 
 7 
 
 ii 
 
 13 
 16 
 
 19 
 
 22 
 26 
 28 
 31 
 
 36 
 38 
 
 4i 
 
 43 
 
 Si 
 53 
 61 
 
 63 
 66 
 
IO 
 
 CONTENTS 
 
 XVII. Sulphuric Acid 
 XVIII. The Sulphates. 
 XIX. Common Salt— Hydrochloric Acid 
 XX. Chlorine 
 
 XXI. Nitrogen— Ammonia . 
 XXII. Nitric Acid and the Nitrates 
 
 XXIII. Phosphorus and Phosphoric Acid 
 
 XXIV. Silica— Sand and Clay 
 XXV. Carbon— Marsh Gas . 
 
 XXVI. The Oxides of Carbon 
 
 XXVII. The Carbonates 
 
 XXVIII. Conclusions 
 
 Questions and Problems for 
 Examination . 
 
 PART III 
 XXIX. The Carbohydrates . 
 XXX. The Hydrocarbons 
 XXXI. The Alcohols— Fermentation 
 XXXII. The Organic Acids 
 XXXIII. Fats and Soaps 
 XXXIV. Ammonia Derivatives— Alkaloids 
 XXXV. The Albuminoids 
 XXXVI. Conclusions 
 
 Questions and Problems for 
 Examination . 
 
 Revision 
 
 List of Apparatus and Chemicals 
 Index .... 
 
 AND 
 
 and Amides 
 
 Revision and 
 
AN EXPERIMENTAL COURSE 
 OF CHEMISTRY 
 
 FOR AGRICULTURAL STUDENTS 
 
 PART I 
 
 1. WEIGHTS AND MEASURES 
 
 In this course a knowledge of chemistry is to be sought by an 
 experimental study of the composition and properties of those 
 substances with which agriculture is concerned. In doing this 
 it will be necessary to determine the quantity of substances both 
 by weight and volume. In science a decimal system of weights 
 and measures is employed. The standard of weight is the 
 gram j the parts of the gram are the decigram, centigram, and 
 milligram; the multiples are the dekagram, hectogram, and 
 kilogram. By means of a chemical balance determine how 
 many decigram and centigram weights make a gram and how 
 many grams there are in a dekagram and hectogram. 
 
 In using a chemical balance observe the following rules : — Place the 
 thing to be weighed in the left hand pan, the weights in the right. Never 
 touch the weights with the fingers, but with the nippers only. Never place 
 anything upon or remove anything from the pan while it is swinging. When 
 reckoning up the weights do so while they are on the pan, then enter the 
 amount in the notebook and check it by again counting the weights while 
 returning them to the box. 
 
 11 
 
12 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 As the names imply, it will be found that — 
 
 i decigram = .1 gram. i dekagram = 10 grams. 
 
 i centigram = .01 gram. 1 hectogram =100 grams. 
 
 1 milligram = .001 gram. 1 kilogram = 1000 grams. 
 The relations between this — the metric — and the avoirdupois 
 systems are the following : — 1 gram = 15.432 grains; 1 ounce 
 = 28.35 grams; 1 kilogram = 2.2 lbs. 
 
 The metric standard of length is the meter, the parts ancl 
 multiples of which are similar to those of a gram. Examine 
 a meter measure and note that — 
 
 1 decimeter = .1 meter. 1 dekameter =10 meters. 
 
 1 centimeter = .01 meter. 1 hectometer =100 meters. 
 
 1 millimeter = .001 meter. 1 kilometer = 1000 meters. 
 Of the relations between the metric and the British systems, 
 1 meter = 39.37 inches, 1 inch = 2.54 centimeters, 1 mile = 
 1.6 kilometers. 
 
 The standard of capacity is the liter. Examine a cube 
 having a volume of 1 liter, and note that it is the measure of 
 1 cubic decimeter or 1000 cubic centimeters. Hence — 
 .001 liter = 1 cubic centimeter. 
 1 liter = 1 cubic decimeter. 
 1000 liters = 1 cubic meter. 
 Quantities measuring less than a liter are usually spoken of as 
 so many cubic centimeters (" c.c."). Of the relations between 
 the metric and British systems, 1 liter = 1.76 pints and 1 
 pint = 567 c.c. 
 
 A cubic centimeter of pure water measured at 4 C. weighs 1 
 gram. This simple relation between volume and weight pro- 
 vides a means of correcting . the graduation of glass measures, 
 these being often unreliable. Calibrate a 20 c.c. measure as 
 follows -.—Having cleaned and dried the measure, first weigh 
 it empty. Then fill it with pure water from a wash bottle to 
 the 10 c.c. mark and weigh again. Now fill it to the 20 c.c. 
 mark and weigh a third time. Subtract the weight of the 
 measure from the weight of the measure and water, in order 
 
THE ATMOSPHERE 
 
 13 
 
 to find the weight of each 10 c.c. of water. Repeat the deter- 
 mination until uniform results have been obtained. Is the 
 measure correctly graduated, and are the two halves uniform ? 
 
 Glass measures are usually graduated in such a way that each (so-called) 
 cubic centimeter is the volume of 1 gram of water at 15 C. (the usual 
 temperature of the laboratory), so that the water taken for the foregoing 
 experiment should be at this temperature. 
 
 II. THE ATMOSPHERE 
 
 Having acquired a knowledge of the methods of determining 
 the quantity of substances, the study of the 
 air may now be commenced. Firstly, has air 
 the property of weight ? 
 
 Fit a liter flask with a cork, glass and india- 
 rubber tubes, and glass stoppers as figured, 
 and weigh it accurately upon the balance. 
 Now remove one stopper, suck out the air 
 as completely as possible, replace the stopper 
 without readmitting air, and weigh again. Has 
 the flask lost weight, and if so, what is the 
 weight of air removed ? Retain the apparatus 
 for future experiments. 
 
 Fig. i. 
 
 This experiment, in common with all scientific experiments, will only 
 succeed if the apparatus is perfect. Practise cork-boring on old corks 
 until true and clean bores can be made, and tube-bending on odd bits of 
 glass tubing until the bends are rounded and regular. Start boring a cork 
 from both ends so that the bores meet in the middle. To cut a glass tube 
 draw a file once only across it and snap the tube with the fingers. To bend 
 a tube use a fish-tail burner ; hold the tube near the top of the flame, 
 constantly turning it round, till the glass is soft ; then remove and bend. 
 Before pushing a glass tube through a cork, or fitting it with rubber tubing, 
 always round off the sharp edges by just melting the glass in the Bunsen 
 
i 4 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 flame. Seal up the ends of a tube by melting in the Bunsen flame till the 
 glass runs together ; on now blowing through the open end the sealed end 
 will expand into a little bulb. 
 
 By employing a stout glass flask which can be completely 
 exhausted of air by means of an air-pump, the weight of a 
 volume of air can be determined. Under normal conditions 
 (see p. 39) a liter of dry air is found to weigh 1. 226 grams. The 
 atmosphere is known to extend in appreciable quantities to the 
 height of one hundred miles above the earth, and its total 
 weight and consequent pressure upon the earth's surface must 
 be very great. What this amounts to can be ascertained by 
 the following experiment : — 
 
 Fill a stout glass tube, at least 4 millimeters in bore, 8 deci- 
 meters long and closed at one end, with pure dry mercury. 
 n Remove all bubbles of air by tapping the tube or 
 other means, then close the open end with the finger 
 and invert the tube into a capsule or trough con- 
 taining mercury. Now remove the finger, and note 
 that the mercury remains supported in the tube to a 
 certain height. By means of a three-foot rule or 
 meter measure, accurately determine the height of 
 the column from the surface of the mercury in the 
 trough. Compare the height with that in a tube of 
 
 7 different length used by another student, and note 
 that it is independent of the length of the tube 
 Convey the apparatus to the top of the building, and 
 note that, if 40 feet above the laboratory, the column 
 of mercury now supported is at least one millimeter shorter. 
 This must be due to the smaller atmospheric pressure at the 
 greater altitude ; and the experiment shows that the mercury 
 in the tube is balanced and supported by the atmosphere, 
 and that its height is an accurate measure of the atmospheric 
 pressure. 
 
 Whenever mercury is used, the experiment must be made on a tray or 
 special table designed to catch falling particles. Without this precaution 
 
 v 
 
THE ATMOSPHERE 15 
 
 great waste of mercury must occur even in experienced hands. The mercury 
 used in the foregoing experiment must be perfectly dry. 
 
 This instrument is known as the barometer (weight-measurer). 
 Owing to the relation that exists between the atmospheric 
 pressure and the weather, it becomes a useful weather glass. 
 Repeat the observation of the height of the mercury column 
 
 DATE 
 
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 30 ■ 
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 29 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ■ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Fig. 3. 
 
 at the same hour daily for one month, marking each observation 
 by means of a dot on the accompanying chart, and at the same 
 time record the character of the weather {e.g. wind, rainfall, 
 temperature, and sunshine) in the notebook. At the end of 
 the period, connect the dots on the chart by straight lines, and 
 compare the rise and fall with the variations in the weather. 
 
16 CHEMISTR Y FOR A GRICUL TURAL STUDENTS 
 
 At the level of the sea, the average height of the barometer is 30 inches 
 or 760 millimeters, and this is taken as the normal or standard pressure. 
 The old-fashioned weather glass consists of a j, -shaped barometer tube, in 
 which a fall of the mercury in the long limb is accompanied by a rise ol 
 mercury in the short and open limb. Upon the surface of the mercury in 
 the short limb is a metallic float connected by a cord with a wheel to 
 which a pointer working against a dial is connected. The aneroid barometer 
 consists of a partially exhausted box having a flexible side, and which 
 expands or contracts with changes of pressure, the variation being exhibited 
 by means of a dial and pointer. Such an instrument, being portable, is 
 especially useful in determining altitudes by means of difference of atmos- 
 pheric pressure. The action of the suction pump also depends upon the 
 atmospheric pressure. Mercury being 13^ times as heavy as water, it is 
 theoretically possible to draw water from a depth 13^ times as great as the 
 barometric column. Owing, however, to dissolved gases and imperfect 
 valves, 28 feet is the greatest depth from which it is practically possible to 
 draw water by this means. 
 
 III. COMPOSITION OF AIR 
 
 To learn what air is, a careful study must be made of some 
 of those changes which are observed constantly taking place in 
 air, e.g. rusting and burning. 
 
 When iron rusts, the change which occurs might be 
 due to absorption of air or of a constituent of it. If so, 
 the weight of the rust would be greater than that of the 
 ^^^ original iron, since air has weight. Place some iron 
 filings in a capsule and weigh. Now expose the 
 capsule to the air, and, when the filings have begun 
 to rust, weigh again. Do the filings weigh more after 
 rusting ? 
 
 A further experiment is needed to determine whether 
 air has actually disappeared. Shake some fine iron 
 filings in a wide graduated tube, previously wetted 
 with water so that the filings adhere to the side, 
 Fig. 4. and quickly invert the tube into a vessel of water. 
 
 ^ 
 
 7 
 
COMPOSITION OF AIR 
 
 17 
 
 Should the air in the tube diminish in volume in the course of a 
 few hours, it must be concluded that the rust is the result of the 
 absorption of air by iron. 
 
 Continue the experiment long enough to determine whether 
 the air is entirely absorbed, and, if not, what are the propor- 
 tions of the active and inactive constituents. Should only a 
 portion of the air be absorbed, ascertain whether the unab- 
 sorbed part differs from the original air in any respect other 
 than its inability to cause iron to rust. For instance, try 
 whether it still supports the combustion of a taper. To do 
 this, cover the orifice of the tube with a glass plate while under 
 water, then remove the tube, turn up, and, having removed the 
 plate, insert a lighted taper. 
 
 It is very important that (1) the object of each experiment, (2) the 
 drawing and description of the apparatus, (3) every detail of the observa- 
 tions made, and (4) the conclusions arrived at, should be recorded in the 
 student's notebook while the investigation is in progress. Weighings 
 should be entered thus : — 
 
 Capsule and iron filings taken . . = 10.543 grams. 
 
 Capsule and iron filings after rusting . = 10.568 grams. 
 
 Increase of weight = .025 grams. 
 
 The measurements of volume of air should be recorded thus : — 
 
 Air in tube at 10 o'clock = 200 c.c. (experiment begun). 
 
 5) II , 
 
 = 190 c.c. 
 
 >> 12 , 
 
 = 180 c.c. 
 
 >> I J 
 
 = 170 c.c 
 
 „ 2 , 
 
 = 160 c.c. 
 
 » 3 . 
 
 = 158 c.c. 
 
 » 4 , 
 
 = 158 c.c. 
 
 and the volumes of active and inactive constituents per cent, of air should 
 then be calculated. 
 
 Should the preceding experiment indicate that the air, 
 deprived of that portion which combines with the iron to 
 form rust, no longer supports the combustion of a taper, it 
 must be surmised that rusting and burning are phenomena of 
 
,8 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 a similar kind, and an experiment on combustion should now 
 
 be made. 
 
 Cut under water a piece of phosphorus the size of a large 
 pea, and after drying it by means of blotting paper (taking care 
 not' to touch it with the fingers on account of its inflamma- 
 bility), place it on a capsule floating in a trough of water, and 
 ignite it. Place over the capsule an open bell 
 jar, and quickly close it with a stopper. Note 
 whether, in this case also, only a portion of 
 the air is consumed, and whether in proportion 
 it is approximately equal to that absorbed by 
 the iron filings. Does the residual gas support 
 the combustion of a taper ? Observe the fumes 
 of a white solid substance, which may be 
 supposed to be to phosphorus what iron rust is 
 
 *&- 
 
 F to iron, i.e. the product of the absorption of the 
 
 active constituent of the air. Observe also that 
 these fumes slowly dissolve in the water and render it acid, 
 this being shown not only by its taste, but also by its power 
 of changing the colour of a solution of litmus from blue to red, 
 a characteristic property of acid liquids. 
 
 It will be noticed that the products of the rusting of iron 
 and the burning of phosphorus are entirely different in pro- 
 perties from the iron, the phosphorus, and the gas of which 
 they are composed. Iron rust is red in colour and devoid of 
 metallic lustre, and will be found to be, unlike iron, not 
 attracted by a magnet. The fumes from burning phosphorus 
 are not inflammable and are soluble in water, forming an acid 
 liquid. Nor has either substance any of the properties of the 
 gaseous constituent that has been absorbed. It is obvious that 
 tin- two constituents of each product have become united or 
 combined together so intimately that the characteristic pro- 
 perties of each constituent have been entirely changed, the 
 compounds having none of the properties that a mere mixture 
 would possess. 
 
OXYGEN GAS 19 
 
 From these experiments it must therefore be concluded that 
 the air is not homogeneous, but consists of at least two gases 
 mixed together — (1) an active gas — oxygen — constituting about 
 one-fifth of the air, and (2) an inactive gas — nitrogen — consti- 
 tuting about four-fifths; and that when substances undergo 
 changes due to atmospheric action, such as rusting and burn- 
 ing, chemical combination of the substance with the oxygen of 
 the air occurs, chemical compounds being formed having pro- 
 perties entirely different from the original substances. These 
 substances, if they be not themselves compounds, are termed 
 elements. The compounds of oxygen may be called oxides. 
 Thus, iron rust is oxide of iron, and the product of the com- 
 bustion of phosphorus is oxide of phosphorus. 
 
 IV. OXYGEN GAS 
 
 The nitrogen gas left behind when the oxygen has been 
 removed from air by burning phosphorus or rusting iron is 
 distinguished by its inability to support combustion or to 
 promote rusting. It is now necessary to try to procure the 
 oxygen gas of the air in the pure state, in order that its pro- 
 perties may also be studied. 
 
 The oxide of iron (iron rust) already produced contains 
 oxygen derived from the air. Can the oxygen be obtained 
 from it ? Since heat decomposes many chemical compounds, 
 such as the constituents of wood and coal with the production 
 of gas, try heating some iron rust in a test-tube. Should no 
 decomposition occur at the highest temperature obtainable, try 
 heating the oxides of other metals, e.g. the black oxide of 
 copper, the red oxide of mercury, and the red oxide of lead 
 (red lead), all of which can be obtained by gently heating the 
 
20 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 metals in air. Should one or more of these oxides yield up 
 their oxygen, or a portion of it, on heating to a high tempera- 
 ture, a method will have been found of preparing the oxygen 
 gas of the air in a pure state. A smouldering splint will 
 indicate whether the gas is being evolved. 
 
 Heat some red lead or red oxide of mercury in a hard glass 
 tube, fitted with a cork and bent tube, as shown in Fig. 6, 
 supported on the ring of a retort stand, and collect the gas 
 
 evolved by allowing it to bubble 
 up into an inverted test-tube or 
 cylinder filled with water. When 
 all the water has been displaced, 
 and the tube is full of gas, place 
 the thumb or a glass plate over 
 the orifice while still under 
 water; then turn up and ex- 
 amine the properties of the gas. 
 In taste, odour, and colour it 
 would be expected to be indis- 
 tinguishable from air, air being tasteless, odourless, and 
 colourless, but, being the pure active constituent, it should 
 support combustion more readily. Try with a taper and a 
 smouldering splint. 
 
 Fill a bottle with oxygen (supplied) by water displacement, 
 and having placed a bit of phosphorus in a deflagrating spoon, 
 and set fire to it, plunge it into the bottle. Repeat the experi- 
 ment, using sulphur instead of phosphorus. Then 
 try a lump of charcoal supported by a copper 
 wire passing through the brass plate of the spoon. 
 Finally, try a steel watch spring, to the end of 
 which a bit of taper is fixed to serve as a fuse, the 
 other end of the spring passing through the brass 
 plate. Observe in each case that the oxygen is 
 more active as a supporter of combustion than 
 Fig. 7. air, but that the product of combustion is the 
 
 Fig. 6. 
 
OXYGEN GAS 21 
 
 same. Carefully note the properties of these products, i.e, 
 the oxides produced, with respect to appearance, odour, 
 solubility, and, if soluble, acidity of the solution. Be careful 
 to enter each observation in the notebook during the progress 
 of the experiment. 
 
 It will be noticed that while heat caused the decomposition 
 of the oxides of mercury and lead, heat was produced when 
 phosphorus, sulphur, charcoal, and iron combined with oxygen. 
 In subsequent experiments, note whether heat is invariably 
 produced when chemical combination occurs. Again, heat 
 appears to promote chemical change, for the oxides were only 
 formed rapidly when the elements had been heated sufficiently 
 to ignite them. Is this observation also general ? 
 
 When iron rusts, increase of weight occurs because the 
 oxygen of the air with which it combines also possesses 
 weight. Is there any definite proportion between the weights 
 of substances which combine together. Determine, for 
 instance, whether red oxide of mercury contains definite pro- 
 portions of mercury and oxygen. 
 
 Construct a hard glass tube as figured, using a blow-pipe for 
 softening and working the glass, and weigh by suspending it to 
 the arm of the balance by a piece of copper or, 'better, platinum 
 wire. Place in the bottom of the tube X y\ 
 
 about five grams of red oxide of mer- ^—/^ f\rSs 
 
 cury, previously heated in the hot water S^S 
 oven to dry it, and weigh again. The ^^ F g 
 difference will be the exact weight of 
 
 the oxide taken. Heat till the whole of the oxide has been 
 decomposed, care being taken not to heat the upper portion of 
 the tube, allow to cool, and weigh. The difference in weight 
 between the mercury left and oxide of mercury taken will be 
 the oxygen evolved. Calculate the amount of oxygen combined 
 with ioo parts by weight of mercury. Repeat the experiment 
 till concordant results are obtained. 
 
 Compare the result with the results obtained by other 
 
22 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 students who, if possible, should use different specimens of 
 the red oxide. Should they have found the same combining 
 proportions, it must be concluded that mercury and oxygen 
 combine in definite proportions by weight. Subsequent ex- 
 periments will show whether this is true of the elements of other 
 chemical compounds. 
 
 V. THE THIRD CONSTITUENT OF THE AIR 
 
 Besides rusting and burning, another familiar change that 
 takes place in air is the conversion of lime into chalk. 
 Expose some solution of lime ("lime water") in a beaker to 
 the air. Note that in a few minutes it becomes covered with 
 a white scum of chalk, chalk being distinguished from lime by 
 being insoluble in pure water. Repeat the experiment, but 
 use a stoppered bottle filled with air instead of an open 
 beaker. Note that the amount of chalk now formed is 
 extremely small, and that no appreciable absorption of the air 
 in the bottle occurs. These experiments show that there is a 
 constituent in the air which converts lime into chalk, but that 
 it is present in very minute quantities, and that the oxygen and 
 nitrogen of the air are not concerned in the change. 
 
 Since the product of combustion of charcoal or carbon — the 
 oxide of carbon — is a gas, it is very probably a constituent 
 of the air, and it may be this which converts lime into chalk. 
 Burn some charcoal in a bottle of oxygen (supplied), and test 
 the gas produced with lime water. Should chalk now be 
 formed, this third constituent of the air will have been 
 identified as the oxide of carbon. 
 
 Re-examine the properties of this gas as prepared by the 
 combustion of charcoal in oxygen. Try whether it is able or 
 unable to support the combustion of a taper. Leave a bottle 
 of the gas open, and test it from time to time with a burning 
 
THE THIRD CONSTITUENT OF THE AIR 23 
 
 taper. Note that the escape of the gas from the bottle is very 
 slow, for it remains at the bottom like a liquid. Try to pour 
 it from one bottle to another like water. Pour some water 
 into a cylinder of the gas, and, having covered with a greased 
 plate, shake vigorously. Now attempt to remove the plate, 
 and note whether there is evidence of the gas being soluble. 
 Test the liquid in the bottle with litmus solution, and note 
 whether it is acid. These experiments show that the gas is 
 unable to support combustion, heavier than air, and soluble 
 in water forming an acid solution. 
 
 Air and Ventilation. — This oxide of carbon, usually known as 
 carbonic acid gas, is a product of combustion, not only of charcoal, but of 
 all ordinary fuels, solid, liquid, and gaseous, all of which contain combined 
 carbon. This may be shown by burning a candle, a jet of coal gas, etc. 
 in a bottle, closed at the top with a brass plate, until the flame expires, 
 and then testing the contents of the bottle with lime water. Carbonic acid 
 gas is also a product of animal respiration. If a jar of air expired from the 
 lungs be collected over water, it will be found to render lime water milky, 
 and to • be so rich in carbonic acid gas and deficient in oxygen as to 
 extinguish a lighted taper. The amount of carbonic acid gas normally 
 present in air is not more than .03 or .04 per cent., and this small amount 
 is not injurious to health. In the air of towns it may reach .06 per cent., 
 and quantities in excess of this are held to be prejudicial to health. In 
 London air . I per cent, is sometimes observed, while in a crowded room it 
 may reach .3 per cent. Air containing 3 per cent, extinguishes a lighted 
 taper, while air containing 4 per cent, is fatal to life. 
 
 An adult breathes out about .6 cubic feet of carbonic acid gas per hour, 
 while a jet of coal gas burning at the rate of 3 cubic feet per hour produces at 
 least 1.4 cubic feet of carbonic acid gas. The carbonic acid gas in the air 
 cf a room having a capacity of 10,000 cubic feet, would therefore in one 
 hour increase from .04 to .06 per cent, (the healthy limit) by the respira- 
 tion of one man and combustion of one gas jet, if there were no ventila- 
 tion. As vitality is reduced by breathing vitiated air, and the germs of 
 disease flourish in a close and heated atmosphere, the efficient ventilation 
 of dwelling-rooms and public buildings, as well as of sheds where farm 
 stock are housed, is a matter of very great importance ; and many instances 
 are recorded of the spread of disease among human beings and among 
 cattle owing to want of ventilation. 
 
 Ventilation is effected by utilising three principles :— (0 Gases diffuse 
 
24 C HEM IS TR Y FOR A GR1CUL TURA L STUDENTS 
 
 OO 
 
 & 
 
 OD 
 
 into each other independently of their weight. If an inverted jar of coal 
 gas, which is lighter than air, be placed over a jar of carbonic acid gas, 
 heavier than air, the gases will be found in a few minutes' time completely 
 mixed, as shown by the inflammability of the gas in each jar, and the 
 milkiness it produces in lime water. It is due to this diffusion of gases 
 that the carbonic acid gas does not settle on the floor of a room, and that, 
 if apertures are provided, complete admixture with the outer air gradually 
 takes place. 
 
 (2) Diffusion takes place through porous materials ; the rate of diffusion 
 of two gases is inversely as the square roots of their relative weights. This 
 is best illustrated by the apparatus figured. A porous earthenware cell is 
 fitted with an india-rubber cork and glass U tube half 
 filled with a coloured liquid. A bell jar filled with 
 coal gas is placed over the cell. The lighter coal gas 
 enters the cell more quickly than the heavier air escapes, 
 and, in consequence of increased pressure in the cell, the' 
 red liquid is depressed. On now removing the bell jar, 
 the coal gas escapes from the cell more quickly than the 
 air enters, and, in consequence of the diminished pressure 
 in the cell, the red liquid rises. Bricks, mortar, plaster, 
 etc. , are porous ; iron and wood are non-porous. Brick 
 walls provide better ventilation than walls of wood or 
 corrugated iron, and whitewashed walls better than 
 painted walls. The effect of diffusion is often well seen 
 on a kitchen ceiling, where blackened strips between 
 the beams show where air has diffused through, and 
 black particles of soot and dust filtered out. 
 
 (3) Gases expand by heat, consequently become 
 lighter and rise ; air currents are thus produced. The 
 best illustration of the expansion of gases by heat is 
 the air thermometer, the movement of the liquid in the stem indicating 
 c\pmsion or contraction of the air in the bulb, due to changes of tern - 
 
 perature. The air current thus 
 
 " produced may be illustrated by an 
 aspirating bottle in which a candle 
 is burning. The candle will shortly 
 be extinguished unless the cork 
 from the lower aperture is opened, 
 thus giving rise to an air current 
 The modern contrivances for the ventilation of rooms 
 
 &ISS&£ admission of air and ■— "- <* * — 
 
 ^3 
 
 Fig. 9. 
 
 Pia. 10. 
 
 and ventilation. 
 
THE THIRD CONSTITUENT OF THE AIR 25 
 
 In what proportion are carbon and oxygen combined in 
 carbonic acid gas? In order to determine this, charcoal is 
 burnt in a hard glass tube in a current of oxygen.* The 
 carbonic acid gas produced together with the excess of 
 oxygen is passed through a solution of caustic potash, and 
 finally through a tube containing lumps of caustic potash, 
 this being a substance which, like lime, absorbs carbonic 
 acid gas, but allows the excess of oxygen to escape. The tube 
 containing the charcoal, and the bulbs and tube containing the 
 caustic potash, are weighed before and after the experiment. 
 The former gives the carbon consumed, the latter the carbonic 
 acid gas produced ; the difference between the two will be the 
 oxygen combined with the carbon. 
 
 The following numbers were obtained from an experiment : — 
 
 Tube and charcoal before experiment = 78.65 
 „ „ after „ = 78.51 
 
 Carbon burnt = .14 
 
 Potash bulb and tube before experiment = 96.19 
 
 » n after „ = 96.70 
 
 Carbonic acid gas produced » .51 
 
 From these figures calculate the proportion of carbon and 
 oxygen per cent, of carbonic acid gas, and also calculate the 
 
 * This experiment is too difficult for elementary students, and therefore 
 only a bare outline of the method is given. It should, however, be per- 
 formed by the teacher with the aid of his students. To ensure a correct 
 result, the oxygen should be dried by passing through a U tube containing 
 pumice soaked with oil of vitriol, the charcoal must be previously heated 
 in a current of chlorine to eliminate every trace of hydrogen, and the 
 products of combustion of the charcoal must be passed through a heated 
 tube of oxide of copper, to ensure complete oxidation before passing into 
 the solution of caustic potash which should be contained in properly con- 
 structed potash bulbs. Two or three experiments can be made with the 
 same charcoal and potash, one after the other. 
 
26 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 amount of carbon combining with 8 parts of oxygen {i.e. 
 the amount which was found to combine with ioo of mercury). 
 Numerous experiments have shown that carbonic acid gas 
 invariably has a uniform composition ; like mercury, carbon 
 combines with oxygen in definite proportions by weight. 
 
 VI. AQUEOUS VAPOUR, WATER, AND ICE 
 
 Besides rusting and burning and the conversion of lime into 
 chalk, another change that is often noticed taking place in the 
 air is the deliquescence of certain substances, such as common 
 salt and chloride of calcium. Place some of the latter in a 
 covered dish and weigh, then expose to the air till partially 
 liquid and weigh again. Should the substance now weigh 
 more, it may be assumed that the liquefaction is due to the 
 absorption of atmospheric moisture in which the chloride of 
 calcium has dissolved. To confirm, heat the partially liquid 
 substance in a test-tube, and notice whether moisture is given off 
 and deposited on the sides of the tube. This change may be 
 \fl n observed even in the driest weather, showing 
 
 that water vapour is always a constituent of the 
 111 iL atmosphere. 
 
 Besides existing in the gaseous state, as water 
 vapour or steam, and in the liquid state, water 
 exists in the solid state as ice. The tempera- 
 tures at which these changes of state take place 
 are called the boiling and freezing points. 
 Determine the boiling point of water by finding 
 the temperature of the steam escaping from 
 rapidly boiling water contained in a flask fitted 
 with a cork, tube, and centigrade thermometer 
 
 Fig. ii. 
 
AQUEOUS VAPOUR, WATER, AND ICE 27 
 
 as figured. Continue the experiment till a constant reading is 
 obtained. 
 
 The temperature of boiling water depends upon the purity of the water, 
 the temperature of the steam is constant ; hence the latter is determined. 
 A small flame without wire gauze is best for heating the water, otherwise 
 the sides of the upper part of the flask are apt to become superheated. 
 Since the recording of the temperature by the thermometer depends upon 
 the expansion of the mercury by heat, the mercury in both bulb and stem 
 must be in the steam. Water only boils when it is so hot that the pressure 
 of the water vapour is able to overcome the pressure of the atmosphere. 
 The boiling point, therefore, varies with the atmospheric pressure ; and 
 hence, when a boiling point is determined, the reading of the barometer 
 must also be noted. 
 
 The boiling point of water is also the condensing point of 
 steam; likewise, the freezing point of water is the melting 
 point of ice. Determine the latter by immersing the end of a 
 thermometer in a beaker filled with melting snow, or with 
 finely powdered ice saturated with water. Constantly stirring 
 the mixture with the thermometer, repeatedly note the tem- 
 perature without removing the thermometer from the beaker 
 till a constant reading is obtained. 
 
 The graduation of a thermometer is seldom quite correct, 
 and future readings should always be corrected for any error 
 thus found. On the centigrade scale, the freezing point is the 
 zero (" o° C"), and the distance between that and the boiling 
 point is divided into 100 degrees. On the Fahrenheit scale, 
 the freezing point is 32 degrees above the zero, and the distance 
 between this and the boiling point is 180 degrees, the boiling 
 point being "212 F." Each degree Fahrenheit is therefore 
 \%% of a degree centigrade. Compare the reading of a centi- 
 grade and Fahrenheit thermometer. Do they record the same 
 temperature ? 
 
2 8 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 VII. WATER AS A SOLVENT 
 
 Shake some common salt, gypsum, and sand separately with 
 pure water, filter the liquids, from undissolved substance, 
 through a cone of porous paper fitted in a funnel as figured, 
 into porcelain basins, and evaporate each to dryness over 
 
 Fig. 12. 
 
 Fig. 13. 
 
 beakers of boiling water (Fig. 13). Judging from the residue, 
 which substance would be described as insoluble, which as 
 slightly soluble, and which as very soluble in water? 
 
 Determine the solubility of gypsum. Stir excess of pure 
 gypsum with pure water (at 15 C.) in a beaker until, after 
 prolonged stirring, a saturated solution is obtained. Then 
 filter and evaporate 25 grams of the filtrate in a weighed 
 porcelain basin to dryness on the water bath. Weigh the dish 
 and residue. Calculate the amount of gypsum dissolved by 
 1 gram of water (the " co-efficient of solubility " of gypsum). 
 Repeat the experiment until concordant results are obtained. 
 
 The solubility of a solid in water usually increases with rise in tempera- 
 ture, for heat tends to promote change from the solid to the liquid state. 
 It is therefore necessary to adopt a standard temperature in the determina- 
 tion of solubilities. The usual temperature of the laboratories is 15° C, 
 and this is therefore generally adopted. 
 
WATER AS A SOLVENT 
 
 29 
 
 Liquids and gases, like solids, vary in their solubility in water. 
 Compare the solubility of alcohol, chloroform, and paraffin oil 
 by shaking the liquids, added drop by drop, in large test-tubes 
 of water. Compare the solubility of carbonic acid gas (sup- 
 plied) and air by inverting test-tubes of the gases in recently 
 boiled and cooled water, and noting the height to which the 
 water rises in the tubes. Since heat tends to promote change 
 from the liquid to the gaseous state, it is to be expected that a 
 gas will be more soluble in cold than in hot water. Heat some 
 rain water in a test-tube, and note that, as the temperature 
 rises, bubbles of gas are given off. 
 
 The foregoing experiments indicate a method of obtaining 
 perfectly pure water by distillation) for on boiling water, 
 the dissolved gases are first evolved, the dissolved solids are 
 left behind, and the steam is pure water vapour which can be 
 condensed to pure water. Distil some water in a retort, and 
 
 lead the steam into a flask kept cold by a trough of cold water, 
 in order that the temperature may be reduced below the con- 
 densing point of steam. Reject the first part of the distillate, 
 and collect that which comes over afterwards. Note that the 
 dissolved solids are left as a residue in the retort. 
 
 Rain, Spring, and Sea Water.— Water exercises an appreciable 
 vapour pressure at all temperatures, and this increases as the temperature 
 rises, until at the boiling point it is equal to the atmospheric pressure. It is 
 
30 CHEM1STR Y FOR A GRIC UL TURAL STUDENTS 
 
 due to this that evaporation of water takes place much more rapidly in hot 
 weather than in cold, and that warm air can absorb much more water 
 vapour than cold air before it becomes saturated. The amount of water 
 vapour that can be retained by air, therefore, depends upon the tempera- 
 ture. Water vapour is always present, and however apparently dry the 
 air maybe, a temperature is reached on cooling — the "dew-point" — at 
 which water vapour begins to condense in the form of mist or dew. This 
 temperature is most easily determined by the dew-point hygrometer, but it 
 can also be ascertained by calculation from the difference between a wet and 
 a dry bulb thermometer. These thermometers will record the same tem- 
 perature when the air is saturated, but the drier the air is the more will the 
 reading of the wet bulb fall below that of the dry, because greater evapora- 
 tion from the wet bulb takes place, and more heat is absorbed in conse- 
 quence (see p. 34). The deposition of dew when air is cooled is con- 
 veniently illustrated by bringing a flask of ice-cold water into a warm 
 room. 
 
 The distillation of water that occurs in nature will now be understood. 
 Air into which water has evaporated from sea and land deposits its water 
 when cooled in the form of cloud, mist, or dew. From cloud, water is 
 precipitated as rain ; so that rain is distilled water, free from all dissolved 
 solids, and only containing the dissolved oxygen, nitrogen, and carbonic 
 acid gas of the atmosphere. These gases may be obtained for examination 
 by completely filling an apparatus, such as that figured, with rain water, 
 
 Fig. 15. 
 
 and heating the flask until the gases are expelled. When rain water sinks 
 through the soil and the underlying strata, it dissolves the soluble sub- 
 stances ; so that river and spring water contain dissolved solids varying in 
 
DENSITY 
 
 V 
 
 their character and quantity according to the soil and rock strata through 
 which the water has passed. Such water ultimately finds its way to the 
 sea, and there again undergoes evaporation, leaving the solids behind either 
 
 n 
 
 Fig. 16. 
 
 dissolved or deposited, so that the sea is the liquid residue of ages of evapo- 
 ration. The action of rain water as a solvent on soil may be illustrated by 
 percolating soil with rain water in the apparatus figured, and comparing the 
 residues of evaporation of the rain and drainage water. 
 
 VIII. DENSITY 
 
 It is well known that salt water is more buoyant than pure 
 water. This is owing to its greater density. Compare the 
 densities of water and a saturated solution of salt by com- 
 paring the weights of equal volumes of the liquids. Run 
 20 c.c. of the salt solution from a burette into a small 
 
32 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 weighed flask and weigh. Subtract the weight of the flask 
 to obtain the weight of the salt solution. Since 20 c.c. of 
 water (at 15 C, see page 13) as run from 
 the burette will weigh 20 grams, the relative 
 weights of equal volumes of the salt solution 
 and water can thus be ascertained. Taking 
 the density of water as 1, what is the relative 
 density of the salt solution ? 
 
 The density of a solid or liquid is always compared 
 
 with water as unity. The number thus obtained is the 
 
 Fig. 17. relative density (or specific gravity) of the substance. 
 
 A customary method for taking specific gravities is by 
 
 the specific gravity bottle, constructed to hold exactly 50 or 100 grams 
 
 of water at 15 C. (Fig. 17). An improvement on this method is 
 
 described in the next paragraph. 
 
 In repeating the determination to obtain concordant results 
 employ a U tube (Fig. 18), by the use of which the tempera- 
 ture of the liquid can be controlled. Construct 
 such a tube out of a piece of soft glass tubing 
 having a 5 or 6 m.m. bore, and weigh it. Now 
 fill with water by attaching an india-rubber tube 
 and sucking up the water through the drawn-out 
 end. Having removed the india-rubber tube, 
 the drawn-out end of the U tube should remain 
 filled with water, while the water in the other 
 end will sink to a certain point. Mark this 
 point with a file. Immerse the tube in a 
 beaker of water at 15 C. for a few minutes; 
 then, if necessary, run a little water in, or suck 
 a little out by pressing a bit of filter paper to 
 the drawn-out end, until the height of the water in the one 
 limb exactly coincides with the mark when the tube is quite 
 upright, and, having dried the outside of the tube, weigh. 
 Empty the tube, and having first rinsed it out with the salt 
 
 XJ 
 
 Fig. 18. 
 
DENSITY 
 
 33 
 
 solution, fill it with the solution ; when it stands at the mark 
 after suspending in the beaker of water at 15 C. for a few 
 minutes, dry and weigh. 
 
 Like liquids, solids differ in their density. Wood floats on 
 water, but iron sinks. Compare the densities of glass and 
 water. Weigh a piece of stout glass rod. Immerse it in the 
 water in a half-filled burette, and read off the increase in the 
 height of the water. The increase will be an amount of 
 water equal in volume to the glass rod. From this calculate 
 the relative density of the glass. 
 
 Solids weigh less when immersed in water than in air ; the 
 loss in weight is found to be equal 
 to the weight of water displaced. 
 Weigh the glass rod under water, by 
 suspending it to the arm of the 
 balance by a hair, as figured. The 
 loss in weight will be found to be 
 equal to the weight of water it dis- 
 placed, as found in the previous 
 experiment. This provides an exact 
 method for determining the relative 
 density of solids. Weigh the solid 
 first in air and then in water, and 
 compare its weight in air with the loss in weight, i.e. the weight 
 of an equal volume of water. 
 
 It is obvious that the loss in weight of a solid when immersed 
 in a liquid will depend upon the density of the liquid, for the 
 loss in weight is equal to the weight of an equal volume of the 
 liquid. Hence this method also provides a means of deter- 
 mining the density of liquids. For example, to determine the 
 relative density of the salt solution, compare the loss in weight 
 of the glass rod when immersed in the salt solution with its 
 loss in weight when immersed in water, i.e. the weight of equal 
 volumes of salt solution and water. 
 
 This principle is adopted in the rough determination of 
 
 3 
 
 Fig. 19. 
 
34 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 relative densities by means of the hydrometer. This is an 
 instrument constructed to float upright in a liquid, and which 
 records the relative density of the liquid by the depth to which it 
 sinks, the stem being graduated in " degrees of specific gravity," 
 water being taken as iooo. The liquid must be at 15 C. 
 Compare the relative density of the salt solution as determined 
 by the hydrometer with that determined by the previous 
 methods. 
 
 Other Properties of Water. — Water has a great heat capacity. If 
 beakers of water and mercury be placed side by side in a bath of hot 
 water, the mercury will become hot much sooner than the water, and, when 
 both are hot, the water will remain hot much longer. Water has also a 
 greater heat capacity than the constituents of rocks and soil. If into each 
 of two beakers, the one containing a pound of cold water and the other a 
 pound of sand, a pound of boiling water be poured, and each stirred with 
 a thermometer, the temperature of the mixture of sand and water will be 
 found to be the higher, the heat capacity of the sand being less than the 
 water, and requiring less heat to heat it than the cold water. The heat 
 that would raise I lb. of water i° C. would raise 5 lbs. of sand i°, and would 
 raise I lb. of sand 5 . The relative or specific heat capacity of sand is 
 therefore .2 (water=i). Water is taken as the standard, as it has the 
 greatest heat capacity of all ordinary solid or liquid substances. It is 
 partly for this reason that Great Britain, being surrounded by water, has so 
 temperate a climate, because the sea absorbs more heat in summer and 
 gives up more heat in winter than land. For the same reason a dry, sandy 
 soil is "warmer" than a clay soil, because the latter retains so large a 
 quantity of water. 
 
 When change of state occurs from a solid to a liquid, or a liquid to a gas, 
 heat is absorbed. Since heat is again produced when these changes of state 
 are reversed, it is spoken of as the latent heat of liquefaction, and the 
 latent heat of vaporisation. An example of the latter is seen in the 
 wet and dry bulb thermometers. The wet bulb thermometer will read the 
 lower, unless the air be saturated with water vapour, because the evapora- 
 tion from the surface is accompanied by absorption of heat. An example 
 of the former is the freezing mixture produced by mixing salt and 
 snow. The salt produces rapid melting of the snow, and heat is conse- 
 quently absorbed, the temperature falling to-2i° C. The loss of heat by 
 the great evaporation from the sea during the summer is another cause of 
 the temperate character of the climate of Great Britain. For this reason 
 
DENSITY 
 
 35 
 
 also, a sandy soil is "warmer" than a clay soil, and a room with damp 
 walls is chilly. 
 
 Water vapour is an athermanous gas, i.e. it does not readily allow the 
 radiation of heat through it, unlike the other gases of the atmosphere, which 
 are diathermanons. The atmosphere of Great Britain being humid, the 
 intensity of the sun's heat in summer, and the radiation of the earth's heat 
 into space in winter, is less than in drier countries in the same latitude, and 
 the climate is consequently more temperate. 
 
 Water contracts when it cools from ioo° to 4 C, but, unlike other liquids, 
 expands from 4 to O , and, on freezing, further expands to the extent of 
 9 per cent, of its volume. These changes may be studied by filling a large 
 thermometer tube and bulb with hot water (Fig. 10), and gradually cooling 
 to a temperature below the freezing point. They explain the necessity for 
 observing the temperature in calibrating burettes (p. 12), and in deter- 
 mining the density of solids and liquids (p. 31). They are of import- 
 ance ( 1 ) in the production of ocean currents, another factor having a great 
 influence on the climate of Great Britain ; (2) in the preservation of animal 
 life in lakes and ponds ; (3) in the rupture and decay of vegetable tissue ; 
 (4) in the heating of buildings by hot water ; (5) in the bursting of water 
 pipes during frost ; and (6) in the disintegration of rocks and soil by frost. 
 
 The physical properties of water are compared with those of mercury and 
 alcohol in the following table. 
 
 Physical Properties of Liquids. 
 
 
 Water. 
 
 Mercury. 
 
 Alcohol. 
 
 Specific gravity 
 
 i.oooat4° 
 
 I3-596T 
 
 o.794if 
 
 Specific heat (at 15 ) 
 
 1. 000 
 
 0-033 
 
 0.612 
 
 Latent heat of fusion, in 
 
 
 
 
 heat units 
 
 79-25 
 
 2.82 
 
 ? 
 
 Latentheat of vaporisation, 
 
 
 
 
 in heat units 
 
 535-77 
 
 62.OO 
 
 208.92 
 
 Boiling point (at 760 m.m. ) 
 
 IOO° 
 
 35 f 
 
 78.4 
 
 Freezing point . 
 
 o° 
 
 -38. 5° 
 
 -130. 5° 
 
 Vapour pressure at 15° in 
 
 
 
 
 mm. of mercury . 
 
 12.67 
 
 0.04 
 
 32-44 
 
 Co-efficient of expansion 
 
 
 
 
 from o° to ioo° 
 
 0.00043 
 
 0.00018 
 
 0.00127 
 
 Thermal conductivity 
 
 0.083 
 
 0.925 
 
 0.029 
 
CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 IX. COMPOSITION OF WATER 
 
 Is water an element or a compound, and if the latter, what are 
 its constituents? To answer this question an attempt must 
 be made to decompose it. The effect of heat, however, which 
 has been found to decompose certain chemical compounds, is 
 simply to change its state from water to steam. No chemical 
 change occurs similar to that which resulted from heating oxide 
 of mercury, for in this, and in all the other chemical changes 
 studied, substances have been formed having entirely different 
 properties from the original substances, and the changes are 
 permanent and not simply changes of state. Possibly, however, 
 steam, like air, can act chemically on iron, charcoal, etc., 
 especially if these be heated to promote the chemical change: 
 
 Fit up the apparatus figured, and place in the wide tube, 
 which must be constructed of hard glass, some iron filings 
 
 Fig. 20 
 
 (or, better, some iron turnings). Heat the filings to a low 
 red heat; pass steam from the flask of boiling water 
 very s'owly through the tube, and lead the escaping gas or 
 
COMPOSITION OF WATER 
 
 37 
 
 vapour into a trough of water. Note whether the iron filings 
 become changed in appearance. Note, also, whether the 
 escaping gas condenses in the water of the trough like steam, 
 or whether it is a permanent gas. If the latter, collect some 
 in an inverted tube of water, and study its properties. Is it 
 a supporter or non-supporter of combustion, and is it com- 
 bustible ? Is the change in the iron due to its having com- 
 bined with one element of the water, the other element, which 
 from its source might be termed "hydrogen" — i.e. water 
 producing — gas, being liberated ? If so, water is a compound 
 of this hydrogen with the element with which the iron has 
 corrfbined. If — 
 
 water + iron = (iron + x) + hydrogen, 
 water = hydrogen + x. 
 The iron compound exactly resembles that which is obtained 
 by heating iron in air, and it may therefore be an oxide of 
 iron. If so, water must be oxide of hydrogen. An easy 
 method of testing this supposition will be to burn hydrogen 
 in air, when — since combustion in air consists in combination 
 with the oxygen — water should be formed. For this purpose, 
 
 Fig. 21. 
 
 prepare some hydrogen gas in the apparatus figured, by pouring 
 cold dilute sulphuric acid ( i of acid to 6 of water) through the 
 thistle funnel on to some granulated zinc placed in the flask A. 
 
3« 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 To purify the gas thus obtained, pass it through the U tube, 
 B, filled with pieces of pumice soaked with solution of potash 
 (i gram of caustic potash dissolved in 3 c.c. of water) ; and to 
 dry it, through the U tube, C, filled with lumps of calcium 
 chloride. When all the air has been 
 expelled from the apparatus, and 
 pure hydrogen issues from D, ignite 
 the gas, and, by means of an as- 
 pirator, draw the products of com- 
 bustion through a small thistle 
 funnel into a U tube half immersed 
 in cold water (Fig. 22). Is the 
 liquid, which condenses in the U 
 tube, water? Has it the physical properties of water? To 
 answer this question, run it into a small flask, fitted with a ther- 
 mometer, and having an aperture to allow steam to escape, 
 and determine its boiling point. If this be ioo° C, it is water. 
 Water must therefore be the oxide of hydrogen. 
 
 Hydrogen and air form a dangerously explosive mixture. To ensure 
 absence of air from the gas before lighting it at the jet, collect a test-tube 
 by upward displacement of air, and ignite it. If air is still present, an 
 explosion will be produced ; if the gas is pure, it will burn quietly. 
 
 Fig. 22. 
 
 X. HYDROGEN GAS 
 
 It has been found that hydrogen differs from oxygen, nitrogen, 
 and carbonic acid gas, in being combustible. It is also 
 lighter in weight, for it has been possible to collect it by 
 upward displacement of air. Compare its density with that 
 of air. The density of gases may be compared, like liquids, 
 by weighing equal volumes. Attach the flask (Fig. 1) to the 
 
HYDROGEN GAS 
 
 39 
 
 hydrogen apparatus, in such a way that the purified gas is led 
 into the top of the flask while the air is driven out from the 
 bottom. When every trace of air has been expelled, and it is 
 completely filled with the hydrogen, detach the flask, stopper 
 and weigh it. Now, by means of an aspirator, draw air, dried 
 by slowly passing through the calcium chloride tube, into the 
 flask the reverse way, until all the hydrogen has been driven 
 out ; detach, stopper, and weigh again. Next find the capacity 
 of the flask by filling the flask and tubes with water and 
 measuring the water. At 15 C, the temperature at which both 
 the air and hydrogen should be, and when the barometer stands 
 at 30 inches, 1000 c.c. of dry air weighs 1.226 grams. From 
 this calculate the weight of air in the flask, and subtract it 
 from the weight of the flask filled with air, in order to deter- 
 mine the weight of the flask. The weight of hydrogen can 
 now be determined by subtracting the weight of the flask from 
 the weight of the flask and hydrogen. The weights of equal 
 volumes of air and hydrogen being now found, calculate the 
 relative density of air, taking hydrogen as 1, and that of hydro- 
 gen, taking air as 1. Repeat the determination until concor- 
 dant results are obtained. 
 
 In the foregoing experiment great care must be taken completely to fill 
 the flask with the gas. Until stoppered the flask must on no account be 
 touched with the hands, as this would warm and expand the gas. The 
 ollowing example will serve to illustrate the method of working : — 
 Capacity of the flask = 1000 c.c. 
 
 1000 c.c. of dry air at 15 C. and 760 m.m. pressure weighs 1.226 grams. 
 Weight of flask and air = 101.226 grams. 
 
 Weight of air = 1.226 ,, 
 
 Weight of flask = 100.000 „ 
 
 Weight of flask of hydrogen = 100.085 grams. 
 Weight of flask = 100.000 ,, 
 
 Weight of hydrogen = 0.085 ,, 
 Hence if air = 1, the relative density of hydrogen = .069, and if 
 
4 o CHE MIS TR Y FOR A GR1CUL TURAL STUDENTS 
 
 hydrogen = I, the relative density of air = 14.4. Hydrogen, being the 
 lightest gas known, is usually taken as unity. 
 
 When heated, gases expand much more than liquids or solids, and, unlike 
 liquids and solids, they all expand equally and also regularly for each 
 increment of temperature. On heating from o° to 1° C, a gas expands 
 ifa of its volume, from i° to 2° ^fj, and so on. Thus 273 c.c. of air at o° 
 become 288 c.c. at 15 ; 288 c.c. at 15 become 283 c.c. at io°. The 
 necessity for knowing the temperature in calculating the weight of air, and 
 for having the hydrogen and air at the same temperature in the foregoing 
 experiment, will now be understood ; and should the temperature not be at 
 1 5 , it will be possible to calculate the weight of air in the flask 
 at any other temperature. 
 
 Gases are far more elastic and compressible than liquids 
 and solids. The volume of any gas varies inversely with the 
 pressure put upon it. Thus 1 000 c.c. of air under a pressure 
 of 30 inches of mercury become 1500 c.c. under 20 inches. 
 This may be illustrated by means of the tube figured. If a 
 little mercury at the bottom of the tube stand at the same level 
 in both limbs, the air in the closed limb will be at the atmos- 
 pheric pressure (say 30 inches of mercury). If now mercury be 
 poured into the tube until it stands 30 inches higher in the 
 long limb than in the short, the pressure upon the air in the 
 short limb will be doubled, and the volume will be found to be 
 reduced to half. If another 30 inches of mercury be added the 
 pressure will be trebled, and the volume of gas reduced to one- 
 third. In the foregoing experiment it is obviously necessary to 
 take the barometric pressure into account, and should the 
 barometer not stand at 30 inches, it is possible to calculate the 
 
 Fig. 23. weight of 1000 c.c. of air under any other pressure. 
 
 In what proportion does hydrogen unite with oxygen to form 
 water? This may be determined by finding the quantity of 
 water formed by the action of hydrogen on a known weight of 
 heated oxide of copper, when the following change occurs : — 
 
 Hydrogen + oxide of copper = copper -f oxide of 
 hydrogen. 
 
 Fit up the apparatus figured. In the hard glass tube E 
 place some oxide of copper. Heat the tube to a low red heat, 
 and draw a current of air through the apparatus till every trace 
 of moisture has been driven off; allow to cool ; plug the holes 
 
CONCLUSIONS 41 
 
 in the corks with little stoppers made of glass tubing, and 
 weigh. Fill the tube F with lumps of chloride of calcium and 
 weigh. Connect the tubes and attach 
 E to the U tube C of the freshly CTZI^-^-^Zn&Qi 
 charged hydrogen apparatus (Fig. 21). ' ( F 
 
 When the whole apparatus is free 
 from air and completely filled with V-^y 
 
 pure hydrogen slowly passing through, Fig. 24. 
 
 heat the tube E till a portion of 
 
 the oxide of copper has been decomposed. Allow the tube 
 to cool, and when every trace of moisture has been carried 
 forward by the current of hydrogen into tube F, detach the 
 tubes E and F, plug and weigh them separately. The loss in 
 weight of E will be the weight of oxygen used. The gain in 
 weight of F will be the weight of water produced. The differ- 
 ence between the weight of water produced and oxygen used 
 will be the weight of hydrogen used. Calculate the percentage 
 composition of water, and from that the quantity of hydrogen, 
 combining with 8 parts by weight of oxygen, i.e. the combining 
 weight of oxygen up to the present taken. 
 
 In repeating the determination to obtain a concordant result, use the 
 same tube of copper oxide, care being taken that no damp air gains access 
 to it, copper oxide being a very hygroscopic substance. If necessary 
 reoxidise the copper by passing air through the heated tube. If more 
 dilute sulphuric acid is required during the progress of the experiment, pour 
 in a few drops at a time down the side of the funnel tube, so that no air, 
 which would, of course, be fatal to a correct result, be admitted. 
 
 XI. CONCLUSIONS 
 
 The foregoing studies in natural science are of two kinds : — 
 (1) Those which have reference to the properties of the 
 
42 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 substances dealt with are physical ', and (2) those which have 
 reference to their composition are chemical. The systematised 
 knowledge obtained by a study of the properties of matter 
 constitutes the science of Physics \ that obtained by a study of 
 its composition constitutes the science of Chemistry. The 
 changes observed which have involved alteration in composition, 
 such as the rusting of iron, are chemical changes ; those which 
 have not necessarily involved any alteration in composition, 
 such as the change of state of water to steam, are physical 
 changes. 
 
 The chemical changes are of two kinds : — Those which are 
 concerned with the decomposition of compounds into simpler 
 compounds or into elements, such as the change produced by 
 heating oxide of mercury, and those which are concerned with 
 combination and the formation of compounds, such as the 
 combustion of phosphorus. Very often a chemical change 
 involves both chemical decomposition and combination, as in 
 the action of steam on heated iron filings. It has been noticed 
 that chemical change is promoted by heat, but that whereas 
 chemical combination is accompanied by production of heat, 
 it has been necessary to put back heat into a substance to 
 decompose it. It is easily conceivable that if, owing to a force 
 of chemical attraction between two elements, heat is produced 
 when they unite, it would be necessary to employ a force, such 
 as heat, capable of overcoming this attraction, to decompose a 
 chemical compound. 
 
 Two methods are therefore available for investigating the 
 composition of matter: — (1) Analysis, i.e. splitting up the 
 compound in order to obtain its constituents j (2) Synthesis, 
 i.e. putting together the constituents in order to obtain the 
 compound. The composition of red oxide of mercury was 
 found by analysis, that of carbonic acid gas by synthesis. 
 
 These investigations have shown that chemical combination 
 takes place in definite proportions by weight. With 8 parts by 
 weight of oxygen, 1 of hydrogen, 3 of carbon, and 100 of 
 
CONCLUSIONS 
 
 43 
 
 mercury were found to combine to form water, carbonic acid 
 gas, and red oxide of mercury. In the second part of these 
 studies an inquiry will be made into the proportions in which 
 other elements combine. 
 
 It has been observed that when hydrogen and oxygen 
 combine they do so in definite proportions, a liquid — water — 
 is formed, the properties of which are entirely and permanently 
 different from the component gases, and heat is produced. 
 These three characteristics of chemical combination show that 
 water is a chemical compound. Air consists of oxygen, 
 nitrogen, carbonic acid gas, and water vapour in variable 
 proportions. If these gases be mixed together no heat is 
 produced, but the mixture has the same properties as air. Air 
 has therefore none of the characteristics of a chemical 
 compound, and is merely a mixture. 
 
 For identifying chemical substances, both physical and 
 chemical methods are available. Thus, the co-efficient of 
 solubility of gypsum, the boiling point and freezing point of 
 water, and the relative density of hydrogen gas are " physical 
 constants " which are available for identifying these three sub- 
 stances. By chemical methods red oxide of mercury could be 
 distinguished from red lead, as they behave differently on 
 heating, and nitrogen from carbonic acid gas, as they differ in 
 their action upon lime water and litmus. 
 
 QUESTIONS AND PROBLEMS FOR REVISION AND 
 EXAMINATION. 
 
 The problems marked with an asterisk (*) are intended for practical 
 examination. 
 
 Weights and Measures. 
 
 1. Express 2195.817 grams in kilograms, hectograms, etc. 
 
 2. Express I hectogram, 6 grams, 4 centigrams, and 9 milligrams in 
 
 grams. 
 
 3. Calculate the number of milligrams in a kilogram. 
 
44 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 4. Express 30 inches in millimeters. 
 
 5. What is the weight of 10 liters of pure water at 4 C. ? 
 *6. Calibrate the burette. 
 
 The Atmosphere. 
 
 7. Describe how the weight of a liter of air can be ascertained. 
 
 8. To what is the atmospheric pressure due, and how may it be proved 
 
 that the height of the mercury in a barometric tube depends upon 
 the atmospheric pressure ? 
 
 9. Mercury is 13 \ times as heavy as water. Calculate the pressure of 
 
 the atmosphere upon the surface of the earth at sea level in grams 
 per square centimeter, and in lbs. per square inch. 
 
 10. Mercury is 11,000 times as heavy as air at sea level ; what would be 
 
 the height of the atmosphere in miles, were the density the same 
 throughout ? 
 
 11. The action of a suction pump in drawing water depends upon the 
 
 atmospheric pressure. Calculate the height to which it would be 
 theoretically possible to draw water, were the water absolutely 
 pure and the valves of the pump air-tight. 
 *I2. The daily barometric readings for March 1898 were — 30.5, 30.6, 30.4, 
 30.3, 30.0, 30.4, 29.9, 29.6, 28.8, 29.7, 29.2, 29.7, 30.0, 30.0, 
 30.0, 29.8, 29.8, 29.1, 29.1, 29.3, 28.8, 29.5, 29.5, 29.3, 29.3, 
 29.6, 29.9, 30.1, 30.2, 30.2, 30.3. Express these variations 
 graphically on the square paper. 
 
 Composition of Air. 
 
 13. Name the active and the inactive constituents of the air, and state in 
 
 what proportion they are present. 
 
 14. When iron rusts under a bell jar standing over water, what changes 
 
 take place in (1) the weight and properties of the iron, and (2) the 
 volume and properties of the air ? 
 
 15. When phosphorus burns, what happens to the phosphorus and to the 
 
 air ? In wnat respects is the combustion of phosphorus similar to 
 the rusting of iron ? 
 
 16. What is an oxide? How may the oxides of iron and phosphorus be 
 
 formed ? 
 
 17. What is a chemical compound, and how would a chemical compound 
 
 of two elements be distinguished from a mixture? Illustrate your 
 answer by the compounds of oxygen with iron and phosphorus. 
 *l8. Prepare a bottle full of nitrogen gas. 
 
QUESTIONS AND PROBLEMS 45 
 
 Oxygen Gas. 
 
 19. Of the red oxides of iron, lead and mercury and the black oxide ol 
 
 copper, which yield oxygen on heating, and what are the residues 
 left when oxygen ceases to be evolved ? 
 
 20. Fully describe a method for preparing a bottle of pure oxygen gas. 
 
 Illustrate your description by a drawing of the apparatus used. 
 
 2 1 . Compare the properties of oxygen and nitrogen. 
 
 22. Describe the combustion of phosphorus, sulphur, charcoal, and iron 
 
 in oxygen gas. Of each product describe the appearance and 
 smell. Is it a solid or a gas ? Is it soluble in water and is the solu- 
 tion acid in reaction ? 
 
 23. Judging from the examples dealt with so far, what appears to be the 
 
 relation of heat towards (1) chemical change in general, (2) chemical 
 combination, and (3) chemical decomposition? 
 
 24. Describe minutely how the composition of red oxide of mercury by 
 
 weight may be determined, and state the amount of oxygen existing 
 in this compound combined with 100 grams of mercury. 
 
 "25. Identify the metallic oxide (red oxide of iron, red oxide of mercury or 
 red lead). 
 
 *26. Frepare a bottle full of oxygen gas. 
 
 Carbonic Acid Gas. 
 
 27. In what proportion does carbonic acid gas exist in the air? How may 
 
 its presence be demonstrated, and to what is it due ? 
 
 28. Describe a method for preparing carbonic acid gas. 
 
 29. Give the properties of the gas. Does it support combustion ? Is it 
 
 soluble in water, and if so, what is the action of the solution on 
 litmus? Is the gas heavier or lighter than air, and how does it 
 behave to lime water and solution of potash ? 
 
 30. Fully describe the method of determining the composition of carbonic 
 
 acid gas, and state in what proportions carbon and oxygen are 
 combined in this compound. 
 
 31. Why should the ventilation of rooms be necessary? In your reply 
 
 state to what the vitiation of air is due, to what extent may the 
 composition of air in rooms be altered, and what is the effect upon 
 the health of breathing vitiated air. 
 
 32. State what you know about the diffusion of gases. How may this 
 
 principle be utilised in ventilation ? 
 
 33. What is the effect of heat upon the volume of a gas, and how may this 
 
 effect be utilised in promoting ventilation ? 
 *34. Identify the gas (oxygen, nitrogen, carbonic acid gas, or air). 
 
46 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Aqueous Vapour, Water, and Ice. 
 
 35. What is meant by "deliquescence," and to what is it due? Name 
 
 two substances that commonly exhibit this phenomenon. 
 
 36. What are the " three states of matter," and what is meant by u change 
 
 of state"? 
 
 37. What do you understand by " temperature"? Name the instrument 
 
 used for measuring temperature, and describe its construction and 
 action. Why can water not be employed instead of mercury or 
 alcohol in its construction? (See Study VIII.) 
 
 38. What is meant by the "boiling point " and "freezing point " ? Why, 
 
 in the determination of the former, must the atmospheric pressure 
 be taken into account ? 
 
 39. Into what number of degrees are the Fahrenheit and centigrade scales 
 
 of temperature divided, and what is taken as the zero for each 
 
 scale ? What fraction of a degree centigrade is a degree Fahrenheit ? 
 
 Calculate 15 C. into degrees Fahrenheit, and 20 F. into degrees 
 
 centigrade. 
 *40. Determine the boiling point of the liquid. 
 *4i. Is the zero point of the centigrade thermometer correct? 
 
 Water as a Solvent. 
 
 42. What is meant by the terms solubility and insolubility? Illustrate 
 
 your answer by examples of solids, liquids, and gases. When is a 
 solution said to be saturated ? 
 
 43. What is the usual effect of rise in temperature upon the solubility of 
 
 (1) a solid, (2) a gas? Trace the relation between this and the 
 effect of temperature upon change of state of solids and gases. 
 
 44. Explain distillation with reference to change of state. How may dis- 
 
 tillation be employed to produce pure water from water containing 
 solid and gaseous impurities ? 
 
 45. Why does evaporation of water take place at temperatures below the 
 
 boiling point? Will evaporation from the soil take place more 
 rapidly in dry weather or damp, warm weather or cold ? 
 
 46. If the air be saturated with water vapour, what takes place if the 
 
 temperature falls? What is meant by the "dew point"? Why 
 does the wet bulb thermometer read lower than the dry except 
 when the air is saturated with water vapour ? 
 
 47. Give an account of the distillation of water that takes place in nature ; 
 
 trace the history of water from the point at which it is evaporated 
 from land or sea, through its existence as rain, spring, river, and 
 sea water, with especial reference to the gaseous and solid sub- 
 stances it dissolves. 
 
QUESTIONS AND PROBLEMS 47 
 
 *4& Determine the co-efficient of solubility of pure salt at 15 C. 
 
 *49. Determine the percentage volume of gas evolved by boiling the tap 
 water. 
 
 *50. Determine the percentage of total solids in the tap water. 
 
 *5i. Percolate 100 grams of the soil with distilled water, previously boiled 
 and cooled, until completely exhausted, and determine the per- 
 centage of soluble matter in the soil. 
 
 Density. 
 
 52. What is meant by "density," and how may it be expressed? What 
 
 is meant by saying that the • ' relative density " or specific gravity 
 of brine (saturated at 15° C.) is 1. 207? 
 
 53. A bottle holds 28.35 grams of water and 29.30 grams of milk at the 
 
 same temperature. What is the specific gravity of the milk ? 
 
 54. Twenty-five c.c. of a liquid weigh 30.5 grams. What is its relative 
 
 density ? 
 
 55. A piece of glass weighing 25 grams displaces 10 c.c. of water (at 4 C). 
 
 What is the relative density of the glass ? 
 
 56. To what extent does a solid lose weight when immersed in a liquid ? 
 
 If the density of the solid be less than the density of the liquid, will 
 it float or sink ? Try to explain why. 
 
 57. A piece of hard glass weighs 27 grams in air, 16 grams in water, and 
 
 1 1 grams in brine. What is the relative density of the glass and of 
 the brine? 
 
 58. Fully describe the construction of the hydrometer. How can it be 
 
 employed for the determination of the relative density of a liquid, 
 
 and why must the temperature of the liquid be ascertained ? 
 *59. Determine the relative density of the liquid by means of a U tube 
 
 (at \f). 
 *6o. Determine the relative density of the glass, and then, by means of 
 
 the glass, that of the spirit. 
 
 Other Properties of Water. 
 
 61. What is meant by "heat capacity" ? Name the substance which has 
 
 the highest heat capacity of all ordinary solids or liquids. If beakers 
 of water and oil were heated equally, which would become hot the 
 quicker? When both are hot, which would cool the quicker? 
 
 62. If 1 lb. of boiling water be poured into I lb. of water at 15 , the 
 
 temperature of the mixture is found to be 57-5°. If 1 lb. of boiling 
 water be poured into I lb. of sand at 15 , the temperature of the 
 mixture is found to be 86°. What is the heat capacity of the sand 
 compared with that of water as unity ? 
 
a8 CHEMISTR Y FOR A GR1CUL TURAL STUDENTS 
 
 63. Point out how the great heat capacity of water renders (1) the climate 
 
 of Great Britain temperate, (2) a wet soil cold, and (3) a damp 
 room chilly. 
 
 64. Point out the relation of heat to change of state, both from a liquid to 
 
 a solid and a gas, and from a solid and a gas to a liquid. Explain 
 the difference of temperature exhibited by a wet and dry bulb 
 thermometer. Why does a mixture of salt and snow act as a freez- 
 ing mixture ? 
 
 65. Point out how the high latent heat of vaporisation possessed by water 
 
 helps to render (1) the climate of Great Britain temperate, (2) a wet 
 soil cold, and (3) a damp room chilly. Explain why the high latent 
 heat of liquefaction of ice gives rise to a raw, cold feeling during a 
 thaw. 
 
 66. What is meant by the terms " athermanous" and " diathermanous " ? 
 
 How does the athermancy of water vapour affect the climate of 
 Great Britain ? 
 
 67. Describe the effect of heating and cooling water upon its volume. 
 
 Point out how these changes in volume can be utilised in the hear- 
 ing of buildings. It is stated that the water in a deep pond whose 
 surface is frozen rarely sinks below 4 C. Explain this. Account 
 for the useful effect of a hard frost upon the soil. 
 
 68. Compare the use of alcohol and mercury in the construction of ther- 
 
 mometers, taking into account their difference in specific heat, 
 boiling point, freezing point, co-efficient of expansion, and thermal 
 conductivity. 
 
 Composition of Water. 
 
 69. Describe fully the experiments which showed that water was a com- 
 
 pound of hydrogen. State what change took place in (1) the iron 
 filings, (2) the steam. 
 
 70. Describe the experiment which established the composition of water 
 
 by synthesis, and state how the liquid produced was identified as 
 water. 
 
 71. Before a jet of hydrogen is ignited, what precaution must be taken 
 
 to ensure its purity ? Why should hydrogen and air constitute an 
 explosive mixture? 
 
 72. What do you mean by a "permanent" gas? 
 
 73. Two methods have now been employed to decompose chemical 
 
 compounds. What are they ? Illustrate your answer by examples. 
 *74- Identify the two gase* (hydrogen, and either oxygen, nitrogen, or 
 carbonic acid gas). 
 
QUESTIONS AND PROBLEMS 49 
 
 Hydrogen Gas. 
 
 75. Describe two methods for preparing hydrogen gas. 
 
 76. Compare the properties of hydrogen, in respect to combustibility, 
 
 smell, colour, solubility and density, with oxygen, nitrogen, and 
 carbonic acid gas. 
 
 77. Give an account of the method for determining the relative density of 
 
 hydrogen. 
 yS. Calculate the relative density of a gas (hydrogen = 1) from the 
 following data : — 
 Capacity of flask = 980 c.c— 
 
 Weight of flask and air at 15 C. and 760 m.m. = 88.303. 
 Weight of flask and gas at the same temperature and 
 
 pressure = 88.407. 
 A liter of air at 15 C. and 760 m.m. weighs 1.226 grams. 
 The relative density of hydrogen (air = 1) is .069. 
 
 79. To what extent do gases expand when heated ? What would 10 c.c. 
 
 of a gas at o° C. measure at ioo° C, and what would 15 c.c of a 
 gas at 1 5 C. measure at - 5 C. ? 
 
 80. To what extent do gases expand or contract under variations of 
 
 pressure ? What would a liter of air under the normal atmospheric 
 pressure measure under a pressure of 90 inches of mercury (3 
 atmospheres) ? 
 
 81. What weight of air would a liter flask hold at a temperature of 20 C. 
 
 and a pressure of 29 inches of mercury ? 
 
 82. Give an account of the determination of the composition of water by 
 
 weight, and illustrate by a drawing the apparatus used. Refer 
 especially to all the precautions that must be taken to obtain a 
 correct result. 
 *$%. Prepare a bottle full of pure hydrogen gas. 
 
 Conclusions. 
 
 84. Distinguish between the sciences of physics and chemistry. Give 
 
 examples of physical and chemical change. 
 
 85. Distinguish between the two kinds of chemical change, and illustrate 
 
 each kind by examples. Point out how in the action of steam on 
 heated iron, and of hydrogen on heated copper oxide, both kinds of 
 chemical change take place simultaneously. 
 
 86. Discuss the relation of heat to chemical change. 
 
 87. What are the two available methods for investigating the composition 
 
 of matter ? 
 
50 CHEM1STR Y FOR A GRIC UL TURAL STUDENTS 
 
 88. What are the three characteristics of chemical combination? Why 
 
 do we regard water as a chemical compound, and air as a mere 
 mixture of the constituent gases ? 
 
 89. In what proportions do mercury, carbon, and hydrogen combine 
 
 with oxygen to form red oxide of mercury, carbonic acid gas, and 
 water respectively? 
 
 90. For identifying chemical substances we can employ both physical and 
 
 chemical methods. Give illustrations of each. 
 
PART II 
 
 XII. BASIC OXIDES, ACID OXIDES, AND SALTS 
 
 In studying air and water, it has been found that oxygen forms 
 an important constituent of each. This is also true of the crust 
 of the earth. The older rocks, such as granite ; the stratified 
 rocks formed by the disintegration of the older rocks, such as 
 limestone or chalk, clay and sand ; and soil formed by the dis- 
 integration and mixture of the foregoing, almost entirely consist 
 of oxygen compounds. It is therefore necessary in commencing 
 a study of the constituents of the earth's crust to examine the 
 oxides more closely. 
 
 It has already been observed that certain oxides are soluble 
 in water, and that their solutions have acid properties ; for 
 they are sour in taste and turn blue litmus red. Prepare the 
 oxides of phosphorus and sulphur by burning the elements in jars 
 filled with air or oxygen (Fig. 7), and containing a little water 
 to dissolve the fumes of the oxides produced. Prepare the 
 oxides of the metals magnesium and potassium by heating in 
 the air (the latter in an iron spoon) till ignited. Dissolve the 
 oxide of potassium in water and filter the solution. Mix the 
 oxide of magnesium with a few drops of water in a dish, it being 
 only very slightly soluble. Compare the action of the four 
 liquids on blue and red litmus paper. Do they turn blue litmus 
 red or red litmus blue ? Are they acid or alkaline in reaction ? 
 
 It will be found that of these four oxides, two dissolve in 
 water forming acid, two dissolve forming alkaline liquids. The 
 
 61 
 
52 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 two alkali-forming or basic oxides were oxides of metals, the two 
 acid-forming or acidic oxides were oxides of elements which, 
 not being metallic, may be termed non-metals. Similarly, other 
 oxides will be found to be basic or acidic according to the 
 metallic or non-metallic nature of their respective elements. 
 Thus the more important oxides may be classified as follows : — 
 
 Metallic or Basic Oxides. 
 
 Oxide of aluminium (alumina). Oxide of magnesium (magnesia). 
 
 Oxide of barium (baryta). Oxide of manganese. 
 
 Oxide of calcium (lime). Oxide of mercury. 
 
 Oxide of copper. Oxide of potassium (potash). 
 
 Oxide of iron. Oxide of sodium (soda). 
 
 Oxide of lead (litharge). Oxide of zinc. 
 
 Non-metallic or Acidic Oxides. 
 
 Oxide of carbon (carbonic acid gas). Oxide of phosphorus (phosphoric 
 
 anhydride). * 
 Oxide of chlorine (hypochlorous Oxide of silicon (silica). 
 
 anhydride).* 
 Oxide of nitrogen (nitric anhydride).* Oxide of sulphur (sulphurous an- 
 hydride). * 
 
 For the next inquiry use the same solutions of the oxides of 
 potassium, phosphorus, and sulphur, but replace the magnesia 
 by solution of lime, that oxide being more soluble in water. 
 Take the solutions of potash and oxide of sulphur. Note the 
 greasy feel of the one and the sulphurous smell of the other. 
 Pour the one into a portion of the other, frequently stirring and 
 testing the acidity or alkalinity by transferring a drop by means 
 of a glass rod on to a piece of red or blue litmus paper, until 
 the mixture is exactly neutral and has no action on either red 
 or blue litmus. Note that the liquid has lost all greasy feeling 
 and sulphurous smell. Evaporate it to dryness on a water 
 bath, and note the crystalline residue or salt, a substance 
 
 * So called because of their relation to the corresponding acids. Nitric 
 anhydride is nitric acid without water. 
 
THE METALS: THE METALLIC OXIDES 53 
 
 which appears to be a compound of the two oxides employed, 
 for it has lost the distinctive properties of each. 
 
 Repeat the operation with the solution of lime and oxide of 
 phosphorus, pouring the latter into the former till a neutral 
 mixture is obtained. The " salt " appears in this case to be a 
 white insoluble compound of the two oxides. Filter and 
 evaporate the filtrate to dryness. Should there be no residue, 
 this must be the case. 
 
 The conclusions arrived at from these two instances are true 
 for the oxides of other elements. They may be stated thus : — 
 
 Basic oxides are oxides of metallic elements; if dissolved 
 by water they form alkaline liquids, and they unite with acidic 
 oxides forming salts. 
 
 The oxides of non-metallic elements are usually acidic; 
 if dissolved by water they form acids, and they unite with 
 basic oxides to form salts. 
 
 Salts are compounds formed by the admixture of basic ana 
 acidic oxides ; if dissolved by water they usually form neutral 
 solutions. 
 
 It will be observed that water is a neutral oxide. Thus basic and acidic 
 oxides can be dissolved in water without their properties being affected. 
 The element hydrogen, in fact, in its chemical behaviour, stands inter- 
 mediate between metals and non-metals. 
 
 XIII. THE METALS: THE METALLIC OXIDES 
 
 In order to compare the chemical activity of the metals, a study 
 may be made of their oxidisability and the methods by which 
 their oxides may be produced. Two methods have already 
 been found available for preparing oxide of iron from metallic 
 iron, viz. (1) the action of the free oxygen of the air and (2) 
 
54 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 the action of the combined oxygen of water, hydrogen being 
 in this case liberated. These two methods may be tried in the 
 case of other metals. 
 
 Cut small pieces of potassium and sodium the size of small 
 peas. Note that on exposure to air, even when cold, the 
 freshly cut surfaces become immediately tarnished, a film of 
 oxide being formed. Throw the bits into a little pure cold 
 water in a dish. Note that both metals quickly disappear, a 
 gas being evolved. In the case of the potassium, but not in 
 the case of the sodium, this gas catches fire spontaneously, 
 showing that the heat produced by the chemical combination 
 of potassium and oxygen is greater than that of sodium and 
 oxygen, and that the chemical activity of the former, in respect 
 to oxygen, is greater than the latter. Note that the flame is 
 tinged violet, due to a little of the potassium being volatilised, 
 this being the colour of the incandescent vapour of potassium 
 and its compounds. Set fire to the gas being liberated by the 
 sodium, and note that this is coloured yellow by the sodium 
 vapour. To identify the gas, invert a test-tube of water in the 
 dish (Fig. 25), and quickly insert small bits of sodium on the 
 
 
 — •- 
 
 
 
 
 
 
 
 
 Fig. 25. 
 
 point of a penknife, until a test-tube nearly full of the gas is 
 obtained. Shake the gas with the water remaining in the test- 
 tube, transfer by upward displacement of air to a smaller dry 
 test-tube, and ignite it. In its lightness, in its combustibility, 
 
THE METALS: THE METALLIC OXIDES 55 
 
 and in its producing moisture on the sides of the tube, when 
 burnt, has the gas the properties of hydrogen? Now test the water 
 in the dish with red litmus paper. Has it become alkaline, thus 
 showing that the metallic oxides, potash and soda, have been 
 formed and are dissolved in the water ? Does 
 Potassium + oxide of hydrogen = oxide of potassium + hydrogen? 
 
 The vapours of many metals and of their volatile compounds impart 
 characteristic colours to non- luminous flames. Thus, among other 
 metals : — 
 
 Sodium imparts a yellow colour. 
 
 Potassium ,, violet ,, 
 
 Calcium ,, red ,, 
 
 Strontium ,, crimson ,, 
 
 Barium ,, green ,, 
 
 These colours are best observed by heating a little of the compound on the 
 end of a platinum wire in the Bunsen flame. As many compounds are not 
 volatile, it is best to moisten the substance on the wire with hydrochloric 
 acid, volatile salts being thus produced. As potassium compounds are very 
 often impure with sodium compounds, it is best to examine the flame for 
 potassium through a solution of indigo, the blue of which absorbs the 
 yellow of the sodium. These coloured flames are useful for detecting and 
 identifying the metals in minerals, mineral waters, etc. This is best done 
 by examining the spectra by means of the prism of a spectroscope, in which 
 advantage is taken of the different refrangibilities of different coloured rays 
 of light in order to decompose the light emitted by each incandescent 
 vapour into its component colours. By this means it is possible to identify 
 the metals with certainty even in complex minerals. 
 
 The metals calcium, strontium, and barium are so costly that 
 their oxidisability cannot be practically investigated in this 
 course. They assume a position, however, intermediate be- 
 tween the metals just studied and those next referred to. 
 
 Take pieces of magnesium ribbon and zinc foil. Note that 
 in the air at ordinary temperatures the surface has very slowly 
 become tarnished, but that the film of oxide gradually formed 
 has preserved the metal beneath from further oxidation. Place 
 each in a test-tube of water, and note that no gas is evolved, 
 and therefore no oxide formed, even when the water is heated 
 
56 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 to boiling (if the metals are pure). Ignite each metal in the 
 Bunsen flame; note the similarity of the magnesia and the 
 oxide of zinc formed. Test the alkalinity of the oxides by 
 placing a little of each on a slip of red litmus paper and then 
 moistening with water. Lastly, boil some water in a wide- 
 necked Florence flask, and plunge into the steam an ignited 
 piece of one of the metals (preferably magnesium ribbon) held 
 by the crucible tongs. Note that the metal burns brilliantly 
 in the steam, the oxide being formed, while the escaping hydro- 
 gen catches fire and burns at the mouth of the flask. 
 
 Procure a piece of metallic iron. Note that, like magnesium 
 and zinc, it is oxidised by damp air, but that, unlike those 
 metals, the rust exfoliates and exposes a fresh metallic surface 
 to further oxidation. (Iron vessels are, for this reason, often 
 coated with tin which does not oxidise in damp air, or " gal- 
 vanised " with zinc, the film of oxide forming on which does 
 not exfoliate.) Note that the iron has no action on hot water. 
 It has been already observed that iron heated to a low red heat 
 decomposes steam. Note that the iron will not burn in the 
 air, unless it be heated to a white heat by the oxyhydrogen 
 flame, or unless it be in very small particles in the form of iron 
 filings, these being more easily heated to the temperature of 
 ignition, and presenting more surface for oxidation in propor- 
 tion to their size. 
 
 Study the oxidisability of copper and mercury. Note that 
 these do not oxidise in air in the cold. Heat some copper 
 filings in an open crucible, and note that oxide of copper is 
 
 IC 
 
 Fig. 26. 
 
 rapidly formed. Heat a little mercury in a tube (Fig. 26) 
 through which a slow current of oxygen gas is passing, and 
 note that the red oxide is formed on the tube just at the point 
 at which condensation of mercury takes place, £*., just below 
 
THE METALS: THE METALLIC OXIDES 57 
 
 the boiling point. The chemical activity in respect to oxygen 
 would seem to be greater in the case of copper, and this is also 
 shown by the fact that while oxide of mercury is decomposed 
 by heat, oxide of copper is not. In determining the composition 
 of water, evidence has already been obtained that heated 
 copper has no action on steam. In fact, under no conditions 
 are these metals oxidised by water. 
 
 Study the oxidisability of gold, silver, and platinum. Note 
 that under no conditions does direct oxidation take place 
 (hence noble metals as distinguished from base metals). In 
 fact, the oxides of these metals when formed by indirect 
 methods are all decomposed on heating. 
 
 It is now possible to arrange the metals in the following 
 groups : — 
 
 1. The metals of the alkalies (potash, soda, etc.), e.g. 
 
 potassium, sodium. 
 
 2. The metals of the alkaline earths (lime, strontia, baryta), 
 
 viz. calcium, strontium, barium. 
 
 3. The metals of the earths (magnesia, etc.), e>g. magnesium, 
 
 zinc, iron. 
 
 4. The heavy metals, e.g. copper, mercury. 
 
 5. The noble metals, e.g. silver, gold, platinum. 
 
 This arrangement shows that the metals fall into natural 
 groups, the members of each of which have several properties 
 in common. Thus the metals that belong to the first group, 
 because most oxidisable, form oxides both of which are cha- 
 racterised by their great solubility, while the metals which are 
 classed in the second group, on account of their feebler 
 oxidisability, all form oxides which are slightly soluble in 
 water. In physical as well as in chemical properties this 
 grouping often holds good. Thus sodium and potassium are 
 found to be both characterised by low specific gravity and low 
 melting point, and gold and silver are both characterised by 
 
58 CHEMISTR Y FOR A GRICUL TURAL S TUDENTS 
 
 their great malleability and ductility and high conductivity for 
 heat and electricity. 
 
 It is worthy of note that metals belonging to the same class are often 
 associated with each other in nature. Thus gold and silver are invariably 
 found together. Metals of weak chemical activity are usually found in 
 the free state, e.g. gold, silver, and platinum, and occasionally copper and 
 mercury. Metals of the other groups exist naturally in the combined state. 
 Of such metals many occur as oxides. Loadstone and haematite, emery, 
 tinstone, and pyrolusite are oxides of iron, aluminium, tin, and manganese 
 respectively. 
 
 Physical Properties of the Metals. — Metals are distinguished from 
 non-metals in their power of forming alloys with each other. This renders 
 it possible to impart to a metal the colour, permanence, hardness, tenacity, 
 etc., which is required. Thus brass — an alloy of copper and zinc which 
 has the permanence of copper — is more useful because much harder. The 
 following are the constituents of some of the principal alloys : — 
 
 British gold coin — gold, 22 ; copper 2 (22 " carat rt gold, pure gold being 
 24 carat). 
 
 British silver coin — silver, 925 ; copper, 75. 
 
 British bronze coin — copper, 95 ; tin, 4 ; zinc, I. 
 
 Brass — copper, 2 ; zinc, 1. 
 
 Aluminium gold — copper, 9 ; aluminium, 1. 
 
 Pewter — tin, I ; lead, I. 
 
 Britannia metal — tin, 84 ; antimony, 10 ; copper, 4 ; bismuth, 2. 
 
 Type metal — lead, 75 ; antimony, 20 ; tin, 5. 
 
 Gun metal — copper, 9 ; tin, 1. 
 
 Common solder — tin, I ; lead, 2. 
 
 An amalgam is an alloy with mercury. 
 
 The force of attraction that causes the cohesion of particles is exhibited 
 to a different extent in different metals. When the cohesion is small, as in 
 antimony and bismuth, the metals are brittle ; when great, as in gold and 
 silver, the metals are tenacious, malleable, or ductile. One grain of gold, 
 the most malleable of all metals, can be beaten out into 56 square inches of 
 gold leaf. One grain of silver, one of the most ductile of metals, can be 
 drawn into 500 feet of wire. This cohesive force in metals is measured by 
 the breaking strain. 
 
 Metals as a rule are good conductors of heat, but they differ in their 
 conductivity. If upon one end of rods of several different metals a small 
 piece of wax or phosphorus be placed, and the other end be heated, the 
 heat will be conducted from one end to the other, as shown by the melting 
 
THE METALS: THE METALLIC OXIDES 59 
 
 of the wax or ignition of the phosphorus, in times varying with the metals 
 employed. Silver and copper are good conductors, bismuth and antimony 
 bad conductors of heat. Good conductors of heat are also good con- 
 ductors of electricity. 
 
 Metals expand when heated. In the construction of railways and iron 
 bridges this fact has to be taken into account. Timepieces lose time in 
 hot weather, owing to the expansion of balance wheels and pendulums. 
 In chronometers advantage is taken of the different expansibilities of 
 metals to provide for automatic regulation. 
 
 Metals differ in heat capacity. The heat capacity of mercury being very 
 low (and its conductivity for heat being high), mercurial thermometers are 
 sensitive to rapid changes of temperature. 
 
 Metals differ in their density. Sodium and potassium float upon water, 
 but all the other common metals sink. All the commoner metals, with the 
 exception of gold, float upon, mercury, which is therefore one of the 
 heaviest metals known. 
 
 Metals differ in their fusibility. Mercury is liquid at the ordinary 
 temperatures ; sodium and potassium both liquefy below the boiling point 
 of water ; tin and lead below a red heat ; zinc and aluminium at a low red 
 heat, and copper at a bright red heat ; while iron only liquefies at a white 
 heat. Alloying one metal with another often lowers its melting point ; 
 thus fine solder has a lower melting point than either the tin or lead of 
 which it is an alloy. 
 
 Metals differ in their hardness. By comparing the power that solids 
 have of scratching each other, their hardness can be roughly ascertained. 
 Thus lead can be scratched by copper and copper by zinc. The presence 
 of an impurity even in small quantities often alters the hardness. Thus 
 steel, i.e. iron containing \ to I per cent, of carbon, is much harder than 
 iron. The hardness of steel also depends upon the rate of cooling. Thus 
 steel which has been " tempered " by heating and slow cooling is much 
 less hard and elastic than steel which has been cooled quickly. 
 
 The following table gives some of the physical constants for the principal 
 metals •— 
 
 [Table. 
 
6o 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 M -8 13 
 
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 8 
 
 8 
 
 8 
 
 
 
 
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 tC 
 
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 CO 
 
 
 
 
 
 
 
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 xpans: 
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 D IOO° 
 
 
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 N 
 
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 8 
 
 8 
 
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 ctric 
 
 m 
 
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 vo 
 
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 JJ 
 
 
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 CO 
 
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 CO 
 
 q 
 
 CO 
 
 O 
 
 w5 ^ 
 
 
 
 
 
 
 
 
 
 
 m j3 
 
 
 
 
 
 
 
 
 
 
 Melting 
 
 Point 
 n Degree 
 entigrad 
 
 
 
 
 
 
 
 
 
 
 co 
 
 5 
 
 O 
 
 io 
 
 vo 
 
 8, 
 
 
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 ON 
 CO 
 
 vo 
 
 CO 
 
 ^ 
 
 3- 
 
 CO 
 
 cs 
 
 VO 
 
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 — u 
 
 
 
 
 
 
 
 
 
 
 m 2" 
 
 00 
 
 DO 
 
 on 
 
 N 
 
 + 
 
 CO 
 
 t>. 
 
 co 
 
 VO 
 
 
 tA 
 
 t^. 
 
 00 
 
 t^. 
 
 £J 
 
 lA 
 
 ri 
 
 on 
 
 CO 
 
 WO 
 
 
 
 
 
 
 
 
 
 
 
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 S 
 
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 • 
 
 
 
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 CL, 
 
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 6 
 
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 N 
 
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 Q 
 
 
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 2 
 'o 
 O 
 
 o 
 1-1 
 
COMBINING WEIGHTS OF THE ELEMENTS 61 
 
 XIV. COMBINING WEIGHTS OF THE ELEMENTS 
 
 In the foregoing studies evidence has been accumulated that 
 chemical combination takes place in definite proportions by 
 weight, and that each element has its own combining weight. 
 It was found that i part by weight of hydrogen, 3 parts by 
 weight of carbon, and 100 parts by weight of mercury combine 
 with 8 parts by weight of oxygen, forming respectively water, 
 carbonic acid gas, and red oxide of mercury. The question must 
 now be asked — Do these elements unite in these proportions 
 only? 
 
 When lead is roasted in the air, the oxide of lead — litharge 
 — is formed. On further roasting, at a gentle heat, the 
 reddish yellow colour of the litharge darkens, and ultimately 
 red lead is obtained. It has been already found that red lead 
 at a higher temperature breaks up into litharge and oxygen. 
 Red lead must therefore be an oxide of lead, containing a 
 larger proportion of oxygen than litharge contains. Introduce 
 about 5 grams of red lead, previously dried by heating on a 
 water bath, into a weighed porcelain crucible, and weigh. 
 Heat very gently, taking care not to melt the contents of the 
 crucible, till oxygen ceases to be evolved, and the red lead is 
 entirely reduced to yellow litharge. Allow to cool, and 
 weigh. Calculate the proportions of litharge and oxygen per 
 cent, of red lead. 
 
 Not only lead, but hydrogen, carbon, mercury, and, in fact, 
 most of the elements, combine with oxygen in more than one 
 proportion. The relation between the composition of the 
 oxides, however, if there be more than one, is always a very 
 simple relation. Thus in the two compounds of hydrogen and 
 oxygen, the combining proportion in the one is 1 to 8, in the 
 other 1 to 16. It is usual, therefore, to take as the combining 
 weight of the element a simple number that represents the 
 proportion in which it enters into its various combinations, 
 
62 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 and to regard each compound as containing one, two, or more 
 combining weights of the element. 
 
 If hydrogen, having the lowest combining weight, be taken 
 as unity, that of oxygen is taken as 16, that of carbon as 12, 
 and that of mercury as 200. Water would then contain two 
 combining weights of hydrogen to one of oxygen, and may be 
 represented as H 2 0, taking H and O to represent respec- 
 tively single combining weights of the elements. Carbonic 
 acid gas would contain one combining weight of carbon to 
 two of oxygen, and may be represented as C0 2 , where C 
 represents a combining weight of carbon. Red oxide of 
 mercury would contain one combining weight of each element, 
 and may be represented as HgO where Hg represents a com- 
 bining weight of mercury {hydrargyrum). 
 
 In the earth's crust about seventy elements are known to 
 exist, but of these it is only necessary to give the combining 
 weights of twenty-two. These are : — 
 
 Aluminium (Al) . 
 
 27 
 
 Mercury {Hydrargyrum, 
 
 
 Barium (Ba) 
 
 137 
 
 Hg). . . . 
 
 200 
 
 Calcium (Ca) 
 
 40 
 
 Nitrogen (N) 
 
 14 
 
 Carbon (C) . 
 
 12 
 
 Oxygen (0) . 
 
 16 
 
 Chlorine (CI) 
 
 35-5 
 
 Phosphorus (P) . 
 
 3i 
 
 Chromium (Cr) . 
 
 52 
 
 Potassium {Kalium, K) 
 
 39 
 
 Copper {Cuprum, Cu) 
 
 63 
 
 Silicon (Si) . 
 
 28 
 
 Hydrogen (H) 
 
 1 
 
 Sodium {Natrium^ Na) . 
 
 2 3 
 
 Iron {Ferrum, Fe) 
 
 56 
 
 Strontium (Sr) 
 
 87 
 
 Lead {Plumbum, Pb) 
 
 206 
 
 Sulphur (S) . 
 
 32 
 
 Magnesium (Mg) . 
 
 24 
 
 Zinc(Zn) . 
 
 65 
 
 Manganese (Mn) . 
 
 55 
 
 
 
COMPOSITION OF THE BASIC OXIDES AND HYDRA TES 63 
 
 XV. COMPOSITION OF THE BASIC OXIDES 
 AND HYDRATES 
 
 The composition of the compound which the element 
 mercury forms with oxygen has been already determined. Of 
 the other metallic elements in the foregoing list, it has been 
 found by experiment that their most important oxides have the 
 following percentage compositions : — 
 
 Metallic Oxide. Metal. Oxygen. 
 
 Alumina 
 
 Baryta 
 
 Lime 
 
 Oxide of chromium .... 
 
 Cuprous oxide (the red oxide of copper) . 
 Cupric oxide (the black oxide of copper) . 
 
 Ferrous oxide 
 
 Ferric oxide (the red oxide of iron) . 
 
 Litharge . 
 
 Magnesia 
 
 Oxide of manganese 
 
 Peroxide of manganese (the black oxide) . 
 
 Red oxide of mercury 
 
 Oxide of potassium . 
 
 Oxide of sodium 
 
 Strontia . 
 
 Oxide of zinc . 
 
 Calculate the number of combining weights of each element 
 in the compounds, and express the results by the simplest 
 possible formulae. For example, if the quantities of 
 magnesium and oxygen per cent, of magnesia be divided by 
 their respective combining weights, viz. 24 and 16, the 
 number of combining weights of the two elements will be 
 found to be equal, viz. 2.5 for each element. Hence the 
 simplest possible formula for magnesia is MgO. Having 
 
 52.9 
 
 47.1 
 
 89-5 
 
 10.5 
 
 71.4 
 
 28.6 
 
 68.4 
 
 31-6 
 
 88.7 
 
 "•3 
 
 79.7 
 
 20.3 
 
 77.8 
 
 22.2 
 
 70.0 
 
 30.0 
 
 92.8 
 
 7.2 
 
 60.0 
 
 40.0 
 
 77.5 
 
 22.5 
 
 63.2 
 
 36.8 
 
 92.6 
 
 7-4 
 
 83.0 
 
 17.0 
 
 74.2 
 
 25.8 
 
 84-5 
 
 15.5 
 
 80.2 
 
 19.8 
 
64 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 obtained the formulae, arrange the oxides in groups as 
 ??ionoxides i dioxides, and trioxides. Calculate the formula that 
 most nearly expresses the composition of red lead as deter- 
 mined by the foregoing experiment. 
 
 To distinguish the oxides of a metal, it is usual to specify the colour, or 
 to use the terminations -oiis and -ic to represent the lower and higher 
 oxides respectively. Unstable higher oxides are usually distinguished as 
 peroxides. The highest oxides of metals are sometimes acidic. There 
 are, for instance, a chromium trioxide Cr0 3 , and manganese heptoxide, 
 Mn 2 7 , which exist combined with potash in " bichromate of potash" and 
 " permanganate of potash." The oxides of some metals, though basic, act 
 as acidic oxides to more basic oxides. Thus alumina dissolves in caustic 
 soda solution, forming a salt. This reaction serves to distinguish alumina 
 from the other bases met with in agriculture. 
 
 It has already been observed that the basic oxides, if 
 dissolved by water, form alkaline liquids, but they differ in 
 their solubility. Of the oxides studied, potassium and sodium 
 oxide will be found to be soluble in water in almost all pro- 
 portions ; lime, strontia, and baryta soluble to a limited extent ; 
 magnesia, litharge, ferrous oxide and oxide of zinc very slightly 
 soluble; the remaining oxides practically insoluble. Verify 
 these statements experimentally. The act of solution appears 
 to be accompanied by chemical combination, for heat is 
 produced. Slake some quicklime with cold water. Note 
 the change in appearance that takes place (immediately if the 
 lime be pure, slowly if impure), the heating of the mixture, 
 and the final disappearance of the water, all evidence of 
 chemical combination having occurred. The compound 
 produced (slaked lime) may be termed hydrate of lime. 
 
 Determine the proportions in which lime combines with water. 
 Heat a weighed quantity — say i gram — of pure quicklime to 
 low redness in a weighed capsule. Cover the capsule, allow to 
 cool in a dessicator (Fig. 27) over more quicklime, itself a good 
 drying agent, and, when cold, weigh, Add excess of water, 
 cover with a beaker till slaking is complete, and place in the 
 
COMPOSITION OF THE BASIC OXIDES AND HYDRA TES 65 
 
 dessicator for some hours. When dry, cover and weigh as 
 quickly as possible. Replace in the dessicator for an hour, 
 and weigh again. Should the weight 
 have changed, continue the dessica- 
 tion till the weight is constant. Hav- 
 ing found the water combined with 
 the lime, heat the capsule again to a 
 low red heat to decompose the hy- 
 drate and drive off the water; cool 
 as before, and weigh. Does the loss 
 in weight tally with the previous gain Fig. 27. 
 
 in weight? If not, repeat the pro- 
 cesses until concordant results are obtained. Express the 
 result as percentage composition of slaked lime. 
 
 Most basic hydrates can be decomposed by heat, but not all. Caustic 
 potash and caustic soda of commerce are the hydrates of potash and soda, 
 and it is not possible to decompose these by heating to redness. Since the 
 hydrates of basic oxides are compounds of metals with hydrogen and 
 oxygen, they are frequently spoken of as metallic hydroxides ; thus potas- 
 sium hydroxide or hydroxide of potassium. 
 
 The approximate percentage composition of the more impor- 
 tant hydrates of the metallic oxides is as follows : — 
 
 Basic Hydrate. 
 Hydrate of alumina (aluminium hydroxide) . 
 Hydrated oxide of copper (cupric hydroxide) 
 Hydrated oxide of iron (ferric hydroxide) 
 Slaked lime (calcium hydroxide) 
 Caustic potash (potassium hydroxide) . . 
 Caustic soda (sodium hydroxide) . 
 
 It is possible that if compounds unite, the proportions in 
 which they combine will be the sum of the combining weights 
 of the elements contained, or simple multiples thereof. Assum- 
 ing that this be so, calculate the combining weights of water and 
 the metallic oxides, and find the number of combining weights 
 of each in each hydrate. Ascribe the simplest possible formulae 
 5 
 
 Metallic Oxide. 
 
 Water. 
 
 . 65.4 
 . 81.4 
 
 34-6 
 18.6 
 
 . 74-8 
 
 25.2 
 
 . 75-7 
 . 83.9 
 
 24.3 
 16. 1 
 
 . 77-5 
 
 22.5 
 
66 CHEMISTRY POR AGRICULTURAL STUDENTS 
 
 to the compounds, regarding them both as hydrates of metallic 
 oxides, e.g. MO.H 2 0, and as metallic hydroxides, e.g. M(OH) 2 , 
 where M stands for any metal uniting with oxygen in single 
 combining proportions. Arrange them in groups of mono-, di-, 
 and tri-hydroxides. 
 
 The result of these calculations will show that the assump- 
 tion on which they were founded was perfectly justified. In- 
 deed, it may now be surmised that, not only do elements in 
 general unite in the proportion of their combining weights, or 
 in simple multiples of them, but that the proportion in which 
 a compound unites with another compound is the sum of the 
 combining weights of its elements or a multiple thereof. 
 
 XVI. THE NON-METALLIC ELEMENTS: 
 SULPHUR 
 
 It has been found that non-metallic elements are characterised 
 by forming anhydrides, i.e. oxides which, when combined with 
 water, form acids; whereas metals form basic oxides which 
 combine with water, forming basic hydrates. The elements 
 which are non-metallic in this sense are further characterised 
 by absence of metallic lustre. In this respect oxygen must be 
 classed as a non-metallic element; indeed, in that it forms 
 compounds with hydrogen and the metals, it may be regarded 
 as a typical non-metal. Just as the properties of oxygen and 
 the oxides have been studied, so we have now to study the 
 properties of the remaining non-metallic elements and their 
 compounds with hydrogen and the metals, in addition to the 
 compounds they form with oxygen, the acids formed by the 
 union of the oxides with water, and the salts formed by union 
 of acidic with basic oxides. 
 
THE NON-METALLIC ELEMENTS: SULTHUR 67 
 
 The non-metallic elements which have to be studied are 
 sulphur, chlorine, nitrogen, phosphorus, silicon, and carbon. 
 Of these, sulphur will first be considered. 
 
 Place some sulphur in a dry test-tube, and heat, using a 
 test-tube holder. Note the melting of the sulphur and the 
 singular changes in the colour and viscosity of the liquid, ti'.l 
 the boiling point is reached. Note that the deep red vapour 
 ignites spontaneously as it issues from the tube, this tempera- 
 ture being high enough to promote rapid chemical combination 
 between the sulphur and the oxygen of the air, the sulphurous- 
 smelling oxide being formed. Pour the remaining liquid in a 
 thin stream into cold water, and note the plastic consistency 
 of the rapidly cooled sulphur. Dissolve some ordinary sulphur 
 in a little bisulphide of carbon, and allow the clear liquid to 
 evaporate spontaneously in a dish. Preserve the octahedral 
 crystals formed. Try to dissolve some of the plastic sulphur 
 in the bisulphide of carbon, and evaporate the liquid. Note 
 that no crystals are obtained, showing that plastic sulphur is 
 insoluble. This is an instance of allotropy, that is, the exist- 
 ence of an element in "another condition" having different 
 properties. 
 
 Does sulphur, being a non-metallic element like oxygen 
 combine with metals and with hydrogen ? Mix together single 
 combining proportions of sulphur and iron filings (about 
 10 grams in all), place the mixture in a narrow test-tube, and 
 heat just the bottom of the test-tube strongly. Note that pre- 
 sently the contents of the tube begin to glow, heat being 
 obviously produced, thus showing that chemical combination 
 is occurring, and sulphide of iron is being formed. 
 
 Sulphur is found in Sicily and other volcanic districts in the free state, 
 but it occurs more abundantly in nature combined with metals. Thus 
 galena, stibnite, cinnabar, iron pyrites, and zinc blende, are native sul- 
 phides of lead, antimony, mercury, iron, and zinc respectively. Copper 
 pyrites is a double sulphide of iron and copper. With the exception of iron 
 pyrites, all these ores are used as sources of the metals. 
 
68 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 It has been noticed that there are metals which, when placed 
 in dilute sulphuric acid, cause the evolution of hydrogen gas. 
 It is possible that if the sulphides of these metals were placed 
 in dilute acid, the sulphide of hydrogen would be produced. 
 Try the sulphide of iron just obtained. Note that the escaping 
 gas is distinguished from hydrogen by its foul smell. Ignite it. 
 What are the two products of combustion, and what evidence 
 do these yield that the gas is indeed the sulphide of hydrogen, 
 or sulphuretted hydrogen^ The percentage composition is 
 found by analysis to be : — Sulphur = 94. 1 1 %, hydrogen = 5.88%. 
 What is the simplest formula that would represent the com- 
 pound ? 
 
 When organic matter containing sulphur decays, the sulphur is set free 
 combined with hydrogen. This accounts for the smell of rotten eggs, the 
 white of egg consisting of sulphur compounds. Rotting cabbages afnd 
 turnips have a similar odour, these being also rich in sulphur compounds. 
 The water of many springs is impregnated with sulphuretted hydrogen, 
 notably the Harrogate waters. 
 
 The composition of sulphuretted hydrogen shows that, like 
 oxygen, a single combining weight of sulphur combines with 
 two of hydrogen. In other words, sulphur is able to replace 
 oxygen, and this is true, not only of the compound with hydro- 
 gen, but also of compounds with other elements. Thus, the 
 formula for ferrous oxide was found to be FeO ; that for the 
 ferrous sulphide just prepared is FeS. 
 
 Burn some sulphur in a jar of air or oxygen. Shake the 
 gaseous sulphurous anhydride produced with water in order to 
 form a solution of sulphurous acid. Preserve a portion of the 
 solution in a corked test-tube, and expose the remainder in a 
 shallow dish to the air, or allow air slowly to bubble through it. 
 Note that after some time the smell of sulphurous acid 
 disappears from the liquid in the open dish, yet it still remains 
 acid to litmus, while in the closed tube the sulphurous acid 
 is unchanged. The sulphurous acid has apparently become 
 oxidised by the air to an acid which is odourless. What is the 
 
THE NON-METALLIC ELEMENTS: SULPHUR 
 
 69 
 
 anhydride of this new acid, and is it possible to obtain it by 
 the oxidation of sulphurous anhydride ? 
 
 To investigate these questions, fit up the apparatus figured. 
 In the combustion tube D, near the drawn-out end, place some 
 platinised asbestos, i.e. asbestos on which platinum has been 
 deposited in a finely divided state. In C place a strong 
 solution of sulphurous acid (supplied). Allow water to syphon 
 from A to B in order to drive air through the solution of 
 sulphurous acid, so that a mixture of air and sulphurous 
 anhydride, evolved from the acid, will pass through D. 
 
 Fig. 28. 
 
 Now heat the platinised asbestos in D. Judging from 
 the altered smell and appearance of the issuing vapours, 
 is oxidation of the sulphurous anhydride now taking place? 
 Allow the asbestos to cool, and heat an empty portion of the 
 tube. Does oxidation now occur ? Now heat the platinised 
 asbestos again, and pass the vapours into water by means of a 
 glass tube attached to D. Note whether an odourless acid 
 solution is obtained similar to that formed by the slow action 
 of the air on solution of sulphurous acid. 
 
 This experiment indicates that sulphurous anhydride and 
 oxygen do not combine under ordinary conditions even when 
 heated, but combine when brought into contact with hot 
 
70 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 finely divided platinum, an instance of chemical action being 
 brought about by contact with a third substance ("contact 
 action"). On the other hand, sulphurous acid is directly 
 oxidised at ordinary temperatures. The two anhydrides and 
 acids may be distinguished as sulphurous and sulphuric. 
 Analysis shows that equal weights of sulphur and oxygen are 
 combined in sulphurous anhydride, and that sulphuric 
 anhyd.ide contains of oxygen half as much again. What 
 formulae should be ascribed to the two compounds ? 
 
 The use of the fumes of burning sulphur, in presence of water vapour, as 
 a bleaching agent, is partly due to the oxidation of sulphurous to sulphuric 
 acid at the expense of the combined oxygen of the colouring matter, 
 colourless substances being formed. In presence of water vapour the 
 fumes are also a useful disinfectant, probably for the same reason. 
 
 XVII. SULPHURIC ACID 
 
 It is found by experiment that a single combining weight of 
 water combines with a single combining weight of sulphuric 
 anhydride to form sulphuric acid. Its formula is therefore 
 S0 3 .H 2 or H 2 S0 4 . The "oil of vitriol" of commerce is 
 sulphuric acid, with 2 to 6 per cent, of additional water. Its 
 specific gravity is 1.84. 
 
 Pour some oil of vitriol into a small beaker containing water. 
 Is there any evidence of chemical combination and the 
 formation of a hydrate of sulphuric acid ? Expose some strong 
 sulphuric acid in a beaker to the air for a few days. Does the 
 liquid increase in volume, indicating absorption of water 
 vapour ? The chemical attraction between sulphuric acid and 
 water may be made use of for drying gases. 
 
 In what proportion does sulphuric acid unite with bases to 
 form salts. Pour some pure sulphuric acid of known strength into 
 a small flask, cover with a watch glass, and weigh. Transfer 
 
SULPHURIC ACID 
 
 7i 
 
 about 25 c.c. to a J -liter flask containing some distilled water, 
 and weigh the small flask again. Now add distilled water to 
 the \ -liter flask till the liquid measures \ -liter at 15 C. 
 Calculate the strength of the dilute acid, i.e. the weight of pure 
 sulphuric acid in 1 c.c. of the liquid. 
 
 Into a small wide-mouthed flask quickly place several small 
 dry lumps of caustic soda, cork the flask, and weigh. 
 Quickly transfer 1 or 2 grams of the caustic soda to a 
 350 c.c. flask containing about 50 c.c. of distilled 
 water, recork the weighing flask, and weigh again 
 to find the exact weight of caustic soda taken. 
 Weigh out a second quantity of caustic soda 
 into a second flask containing water, and marked 
 with a file to distinguish it from the first. Allow 
 the caustic soda to dissolve in the water in each 
 flask, and add a few drops of solution of litmus 
 till the liquid is just rendered blue. Fill a burette 
 with the diluted sulphuric acid till the top mark 
 exactly coincides with the bottom of the meniscus 
 of the liquid when viewed exactly on the level, 
 the burette being perfectly upright. Allow the 
 acid to run into the caustic soda, constantly 
 shaking the flask meanwhile, till the blue colour of the 
 litmus is changed to purple. Boil the liquid and add a 
 few more drops of acid till again perfectly neutral; repeat the 
 process till a permanent purple colour is obtained. Having 
 read off the amount of acid used, add one more drop of acid. 
 If previously neutral, this will turn the liquid red. Treat the 
 second solution of caustic soda in the same way. If the 
 results be not concordant, a third and fourth determination 
 must be carried out. Calculate the reacting proportion of 
 sulphuric acid and caustic soda. Does it agree with that 
 expressed by the formulae — 
 
 Na 2 O.H 2 + S0 3 .H 2 
 or, 2 NaOH + H 2 S0 4 ? 
 
 Fig. 29. 
 
72 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 In chemical formuke and equations a small figure placed after a symbol 
 is held to refer to that symbol only. A large figure placed in front of a 
 symbol is held to govern the whole group of symbols. A point (.) between 
 two groups of symbols indicates that they are combined together. A 
 semicolon (;) is used to indicate a looser combination of compounds with 
 each other. A plus sign ( + ) between two formulae indicates that the 
 substances are mixed together, while the sign = points to reaction having 
 occurred between them and an equal weight of new substances formed. 
 
 In volumetric determinations it is very important that the measurements 
 should be systematically entered in the notebook. The following will 
 serve as an illustration : — 
 
 I. II. 
 
 Weighing flask and caustic soda . 22.315 grams. 20. 169 grams. 
 Weighing flask .... 20.075 » 17.761 „ 
 
 Caustic soda taken . . 2.240 ,, 2.408 ,, 
 
 Sulphuric acid used (1 c.c. = .098 
 
 grams H 2 S0 4 ) . . .28.0 c.c. 30.1 c.c. 
 
 and from this the quantity of sulphuric acid combining with a single 
 combining weight of caustic soda should then be calculated. 
 
 Basic and acidic oxides combine to form salts. When 
 caustic soda and sulphuric acid react, each being the hydrate 
 of the respective oxides, in addition to sulphate of soda, water 
 would also be produced, as expressed by the equation — 
 Na 2 O.H 2 + S0 3 .H 2 = Na 2 O.S0 3 + 2H 2 
 or, 2NaOH + H 2 S0 4 = Na 2 S0 4 + 2H 2 0, 
 so that the resulting salt would weigh less than the sum of 
 the reacting substances by two combining weights of water. 
 To test the truth of this assumption, evaporate one of the 
 neutral solutions to dryness in a weighed dish on the water 
 bath, heat strongly for a few minutes over the bunsen flame, 
 cool in the desiccator, and weigh the anhydrous salt. 
 
THE SULPHATES 73 
 
 XVIII. THE SULPHATES 
 
 The sulphates of other bases can be prepared like sulphate 
 of soda by neutralising sulphuric acid with the basic oxide or 
 its hydrate. Many of these sulphates occur in nature, or are of 
 importance in commerce. Procure and examine the following :— 
 
 Sulphate of potash .... K 2 O.S0 3 . 
 
 Sulphate of soda (Glauber's salt) . Na 2 O.S0 3 ; ioH 2 0. 
 
 Sulphate of magnesia (Epsom salt) . MgO.S0 3 ; 7H 2 0. 
 
 Sulphate of lime (gypsum, selenite) . CaO.S0 3 ; 2H 2 0. 
 
 Sulphate of baryta (heavy spar) . BaO.S0 3 . 
 Sulphate of alumina and potash 
 
 (potash alum) . . A1 2 3 .3S0 3 ; K 2 O.S0 3 ; 24HP. 
 
 Note that these salts are crystalline. Expose a weighed 
 crystal of sulphate of soda to the air ; observe that it effloresces 
 and loses its crystalline form and decreases in weight. Heat a 
 crystal in a test-tube ; note that it liquefies, water vapour escapes, 
 and the salt finally dries up as a white amorphous {i.e. form- 
 less) mass. The crystalline salt is therefore a hydrate of sul- 
 phate of soda. Many other salts combine with water forming 
 crystalline compounds. This water of crystallisation is generally 
 loosely combined, sometimes escaping at the ordinary tempera- 
 ture in dry air, and usually at ioo° C, but occasionally needing 
 a much higher temperature for complete dehydration. 
 
 Determine the water of crystallisation of gypsum, or its crys- 
 talline form, selenite. Heat a weighed quantity (say .5 gram) of 
 the finely powdered material in a weighed porcelain capsule in the 
 water oven at a temperature of ioo° C. until no further appreci- 
 able loss of weight occurs. (Before each weighing the capsule 
 must be cooled in the dessicator.) Having obtained the exact 
 weight, raise the temperature to a low red heat until the weight 
 is again constant. The residue is anhydrous sulphate of lime. 
 Calculate the percentage composition of the original gypsum, 
 
74 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 and of the intermediate hydrate, and represent them by 
 formulae. 
 
 The intermediate hydrate, which should have a composition represented 
 by the formula 2CaS0 4 .H 2 0, is "Plaster of Paris." This, when mixed 
 with a little water, combines and sets to a hard mass of gypsum. Plaster of 
 Paris is prepared by heating gypsum. If the temperature be raised too 
 high, the anhydrous sulphate, which combines with water very slowly, is 
 formed, and it becomes useless as a plaster. 
 
 Observe that each of the six salts is distinguished by a 
 different crystalline form. Examine the crystals of Epsom salt 
 with a lens. Note that each crystal is a prism, having the form 
 A (Fig. 30) or the modification B. Recrystallise some of the 
 
 fl=a 
 
 Fig. 30. 
 
 alum by dissolving in hot water and allowing the solution to 
 cool. Note that each crystal is an octahedron having the form 
 A (Fig. 31), or, owing to undue development of opposite faces 
 
 Fig. 31. 
 
 of the crystal, the modification B. Select one of the most 
 perfect crystals, suspend it by means of a hair from a glass rod, 
 
THE SULPHATES 
 
 75 
 
 then having filtered the solution of alum into a beaker, rest the 
 rod across the top of the beaker as figured, so that the crystal 
 
 Fig. 32. 
 
 remains suspended in the solution. Watch the gradual growth 
 of the octahedron. Observe that in the case of selenite (Fig. 
 
 Fig. 33. 
 
 33) the crystals are connected together in the form of "twin 
 crystals." 
 
 It has been noticed already that whereas zinc only when 
 strongly heated attacks water with liberation of hydrogen and 
 formation of oxide of zinc, it readily attacks water acidified with 
 sulphuric acid, hydrogen being briskly evolved and a clear liquid 
 
76 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 left, in which, it is to be expected, the salt produced by the 
 action of sulphuric acid on oxide of zinc is dissolved. 
 
 Zn + H 2 - ZnO + H 2 ; but Zn + H 2 O.S0 3 - ZnO.S0 3 + H^ 
 
 Dissolve zinc in dilute sulphuric acid, and, when action 
 ceases, pour off the clear liquid from the excess of zinc and 
 evaporate on a water bath until, on cooling, crystals are ob- 
 tained. When quite cold, drain the crystals and purify them 
 by recrystallisation, i.e. by redissolving in pure water and eva- 
 porating till crystals are again obtained. Dry by pressing 
 between folds of filter paper and preserve. Note that the 
 crystals are isomorphous (of the " same form ") with those of 
 Epsom salt, showing that even in respect to the properties of 
 their compounds these metals belong to the same class. 
 
 Only metals which are able to attack water, such as sodium, calcium, 
 zinc, and iron, are able to attack dilute sulphuric acid. Copper and mer- 
 cury are without action on the dilute acid, but their sulphates can, of 
 course, be obtained by the action of sulphuric acid on their oxides. Nearly 
 all the common metals are oxidised when heated with strong sulphuric acid, 
 sulphurous anhydride and water being produced ; the oxides formed react 
 with more of the sulphuric acid forming the corresponding sulphates. It 
 should be noted that the compound that acts as an oxidising agent is itself 
 reduced ; the substance that acts as a redttcing agent is itself oxidised. 
 
 While the formula equation given above represents the chemical change 
 in a simple way, it must not be supposed that the arrangement of the 
 elements in the compounds is in any way represented. The change in fact 
 might be represented more correctly thus : — 
 
 Zn + H 2 S0 4 = ZnS0 4 + H 2 , 
 
 in which the group S0 4 is regarded as combined with hydrogen in the acid 
 and zinc in the salt, the acid being sulphate of hydrogen and the salt sul- 
 phate of zinc. There are many reasons for preferring this nomenclature 
 for metallic salts. To take the simplest reason, it is inconvenient to speak 
 of sulphate of oxide of zinc, sulphate of oxide of iron, and sulphate of 
 oxide of copper. It is usual to call these substances — 
 
 Sulphate of zinc (white vitriol) . . . ZnS0 4 .7H 2 
 
 Sulphate of iron (green vitriol) . . . . FeS0 4 .7lLO 
 
 Sulphate of copper (blue vitriol) . . . CuSO4.5II.jO 
 
 and, to be consistent, to speak of the sulphates of sodium, potassium, mag- 
 
THE SULPHATES 
 
 11 
 
 nesium, calcium, etc., instead of the sulphates of soda, potash, magnesia, 
 lime, etc. The latter terms are, however, always employed in agriculture, 
 and it is very important that the student should be familiar with them and 
 understand their meaning. 
 
 When the solution of a free base or acid is added to the 
 solution of a salt of a different base or acid, reaction occurs. 
 Thus, if solution of caustic potash be added to a solution of 
 sulphate of sodium, sulphate of potassium is formed and caustic 
 soda set free, to an extent depending upon the amount of 
 caustic potash added, till an equilibrium is established between 
 the substances. But when the combined base or acid is 
 volatile and therefore escapes from the liquid, or is insoluble 
 and therefore is precipitated, more of the free base or acid will 
 take its place, until, if sufficient of the free base or acid has 
 been used, complete change has occurred. To a solution of 
 sulph//<? of sodium, i.e. the salt produced by the action of sul- 
 phuroz/j- acid and caustic soda on each other, add strong 
 sulphuric acid. Note that sulphurous acid is set free as indi- 
 cated by its smell, and being unstable, decomposes, gaseous 
 sulphurous anhydride being given off. To solution of sulphate 
 of copper add solution of caustic soda till the mixture is alkaline 
 in reaction. Note that the blue hydroxide of copper is precipi- 
 tated, and that this, when the mixture is heated, loses water and 
 is converted into the familiar black oxide. Filter the mixture 
 and evaporate the now colourless filtrate ; crystals of sulphate 
 of sodium should be obtained. Write equations to represent 
 the changes. These facts are of great importance because 
 they provide methods for preparing acids and bases which 
 cannot be directly or conveniently prepared from the elements. 
 Insolubility or volatility conditions, not only the formation 
 of a base or an acid, but also the formation of a salt. The 
 sulphate of barium is insoluble in water. If, then, to a solution 
 of sulphuric acid or a sulphate, a solution of baryta or a soluble 
 barium salt be added, sulphate of barium will be precipitated. 
 A.s this is the only insoluble barium salt unattacked by, and 
 
78 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 therefore insoluble in, acids, the reaction provides a test for 
 sulphuric acid and the sulphates. To (i) distilled water, (2) tap 
 water, and (3) solution of sodium sulphate, add a few drops of 
 baryta water and then nitric acid. A permanent white precipi- 
 tate will be obtained where sulphate was present. Write an 
 equation representing the reaction between sodium sulphate 
 and baryta. 
 
 XIX. COMMON SALT : HYDROCHLORIC ACID 
 
 Of the salts examined, so far none correspond in taste and 
 appearance with common salt. Recrystallise some common 
 salt by evaporating an aqueous solution till crystallisation 
 begins ; then allow to stand. Note that each 
 crystal has the form of a cube (Fig. 34). When 
 carefully crystallised, the cubes build them- 
 selves together into hollow inverted pyramids. 
 Insert a grain of salt on a platinum wire into 
 
 Fig. 34. a non-luminous flame ; note the yellow colora- 
 
 tion of the flame. What metal does this show 
 is present? Place some salt in a test-tube and add strong 
 sulphuric acid. Is a volatile acid thus liberated? Test the 
 vapour with blue litmus paper. 
 
 Prepare some of the acid from common salt in the apparatus 
 figured. In the flask A place 50 grams of salt, and in B 
 just enough water to cover the bottom of the flask and the 
 orifice of the glass tube, and thus to wash the gas as it passes 
 through. Pour a little strong sulphuric acid through the 
 funnel into A, adding more as required from time to time to 
 produce a constant flow of gas. Heat gently when necessary. 
 When the water in B has become saturated, collect the gas by 
 
COMMON SALT: HYDROCHLORIC ACID 
 
 79 
 
 downward displacement in C. Does the gas burn or support 
 the combustion of a taper ? Remove the delivery tube, cover 
 
 Fig. 35. 
 
 the orifice with a glass plate, insert in a trough of water, and 
 at the same instant remove the plate. Is the gas soluble in 
 water? Now cause the gas to bubble into water till a 
 saturated solution is obtained. Is the solution acid to litmus 
 and sour in taste ? Neutralise a little with caustic soda, and 
 evaporate. Are cubic crystals obtained having the taste of 
 common salt ? 
 
 By the early chemists all acids were supposed to be oxygen 
 compounds, and the acid from salt was called muriatic acid, 
 salt being supposed to be muriate of soda. The acid might, 
 however, be the hydrogen compound of a non-metallic 
 element, just as sulphuretted hydrogen, the solution of which 
 is also acid to litmus, is the hydrogen compound of sulphur. 
 In this case, common salt would be the compound of this 
 non-metallic element with sodium. This is now known to be 
 the case; the non-metallic element is chlorine, the acid is 
 hydrogen chloride or hydrochloric acid, and " salt " is chloride 
 
8o 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 of sodium. Hydrochloric acid and sodium chloride have been 
 found by experiment to contain 97.25 and 60.6 per cent, of 
 chlorine respectively. What are the simplest formulae that 
 represent their composition? 
 
 What are the reacting proportions of caustic soda and 
 hydrochloric acid ? If chloride of sodium be obtained by 
 neutralising hydroxide of sodium with chloride of hydrogen, 
 hydroxide of hydrogen (water) must be set free, and the salt 
 will weigh less than the base and acid taken by the water 
 formed. Investigate these problems by the following 
 experiment. 
 
 First find the strength of the saturated solution of hydrochloric 
 acid prepared in the preceding experiment. This can be done 
 most easily by determining the density, as the density of a 
 liquid varies with the dissolved constituents. Make two 
 determinations at 15 C. by the U tube method (Fig. 18), and 
 calculate the strength from the following figures : — 
 
 Relative Densities of Solutions of Hydrochloric Acid at 15 C. 
 
 Relative 
 
 Percentage 
 
 Relative 
 
 Percentage 
 
 Relative 
 
 Percentage 
 
 Density. 
 
 by Weight. 
 
 Density. 
 
 by Weight. 
 
 Density. 
 
 by Weight. 
 
 I. IOO 
 
 20.06 
 
 1-135 
 
 27.O4 
 
 1. 170 
 
 34.02 
 
 1. 105 
 
 2I.06 
 
 1. 140 
 
 28.04 
 
 I- 175 
 
 35-OI 
 
 i. no 
 
 22.o6 
 
 i- 145 
 
 29.03 
 
 1. 180 
 
 36.OI 
 
 1.115 
 
 23-05 
 
 1. 150 
 
 30.03 
 
 1. 185 
 
 37-OI 
 
 1. 120 
 
 24.05 
 
 i.iSS 
 
 3I-03 
 
 I. IQO 
 
 38.01 
 
 1. 125 
 
 25-05 
 
 1. 160 
 
 32.02 
 
 I- 195 
 
 39.OO 
 
 1. 130 
 
 26.04 
 
 1.165 
 
 33-02 
 
 I.200 
 
 4O.OO 
 
 Weigh out 25 grams of the acid into a quarter-liter flask, 
 and make up to 250 c.c. with distilled water measured at 
 1 5 C. Fill a burette with the dilute acid. Weigh out two 
 portions of caustic soda (say 2 grams each) into two flasks, 
 dissolve in water, add enough litmus solution to render just 
 blue and titrate with the acid, using all the precautions 
 described in Study XVIII. When concordant results have been 
 obtained, calculate the reacting proportions of caustic soda and 
 hydrochloric acid. Do they correspond with the equation 
 
COMMON SALT: HYDROCHLORIC ACID 81 
 
 given below? Now transfer the neutral liquids to weighed 
 porcelain dishes, evaporate on the water bath to dryness, 
 and weigh. Is the weight of salt obtained less than the 
 weight of caustic soda and hydrochloric acid used by the 
 weight of water that would be set free according to the 
 equation — 
 
 NaOH + HC1 = NaCl + H 2 ? 
 
 The existence of acids, which are compounds of non- 
 metallic elements with hydrogen, as well as those which are 
 compounds of acidic oxides with water, and which may be 
 distinguished as oxy-acids, makes it necessary to extend the 
 meaning of the term "acid" to compounds containing 
 hydrogen that is replaceable by metals with the formation of 
 salts. The term salt, too, must not be restricted to com- 
 pounds of basic and acidic oxides, but includes compounds 
 which, formed by the action of bases on acids with liberation 
 of water, are compounds of metals and non-metals. 
 
 Metallic chlorides occur very abundantly in nature. Enormous deposits 
 of rock-salt, i.e. chloride of sodium, usually mixed with a little chloride of 
 magnesium, which renders it deliquescent, and sulphate of calcium, are 
 found in many parts of the world. In England the principal deposits are 
 in Cheshire, where the salt is obtained by mining or by evaporating the 
 brine pumped from shafts sunk into the salt. In the North Sea the water 
 contains about 2.7 per cent, of sodium chloride and 0.5 per cent, of other 
 chlorides and sulphates, while in the Atlantic Ocean the water contains 
 about 3.3 per cent, of sodium chloride, and 0.3 per cent, of the other salts. 
 At Stassfurt, in Germany, there exist large deposits of "carnallite," 
 KCl.MgCl 2 ; 6H 2 0, from which the so-called "muriate of potash" 
 (chloride of potassium), used as an artificial manure, can be obtained by 
 simply dissolving the salt in water and evaporating till crystallisation com- 
 mences, the magnesium chloride and part of the potassium chloride being 
 left in solution. In the same deposits the "kainite," K 2 S0 4 .MgS0 4 . 
 MgCl 2 ; 6H 2 0, is found, which is also so largely used as a manure. 
 Small quantities of bromides and iodides, the corresponding salts of 
 bromine and iodine, two elements of properties analogous to chlorine, are 
 frequently found associated with chlorides. 
 6 
 
8 2 CHEM1STR Y FOR A GRIC UL TURAL STUDENTS 
 
 The chloride of silver is an insoluble salt of characteristic 
 appearance. Unlike other insoluble silver salts, it is not 
 acted upon by acids, but combines with ammonia, forming 
 a soluble compound. The solution of a chloride may there- 
 fore be distinguished by its giving a white precipitate with a 
 solution of nitrate of silver, insoluble in nitric acid, but soluble 
 in solution of ammonia. Test (i) distilled water, (2) tap 
 water, and (3) brine, for chlorides. 
 
 XX. CHLORINE 
 
 How can the element chlorine be obtained? If it were 
 possible to oxidise the hydrogen of hydrochloric acid to water 
 by means of the oxygen of the air, or an oxide which easily 
 loses a portion of its oxygen, such as red lead, chlorine might 
 be set free. Compare the action of litharge and red lead on 
 hot concentrated hydrochloric acid. Note that in each case a 
 salt — the chloride of lead — crystallises out when the liquid 
 cools, but that with red lead a new gas of characteristic odour 
 is given off. The reactions, though they no doubt take place 
 simultaneously, may be expressed in three stages as follows :— 
 
 Red lead = litharge + oxygen. 
 
 Litharge + hydrochloric acid = chloride of lead + water. 
 
 Oxygen + hydrochloric acid = chlorine + water. 
 
 Express these equations by chemical formulae. The composi- 
 tion of chloride of lead has not yet been referred to, but if lead 
 combines with oxygen, oxygen with hydrogen, and hydrogen 
 with chlorine in the proportions represented by the formulae 
 PbO, OH 2 , and HC1 (Fig. 36), the probable formula can be 
 deduced. 
 
CHLORINE 83 
 
 For the preparation of chlorine gas, the peroxide of man- 
 ganese is more economical than red lead. Place about 50 
 grams in the flask A (Fig. 35), pour in some 
 commercial hydrochloric acid (the impuri- 
 ties, viz. ferric chloride and sulphuric acid, 
 cannot interfere with the reaction), mix 
 thoroughly, and warm very gently. Pass the 
 escaping gas through water in B, and collect 
 some bottles of chlorine gas by downward fig. 36. 
 
 displacement of air. Then pass the gas into 
 a flask of cold water and prepare a saturated solution of 
 chlorine. The experiment must be conducted in a fume 
 chamber, as chlorine gas is highly injurious to inhale. 
 
 Note the colour and smell of chlorine. Insert a jet of 
 burning hydrogen into one of the bottles. Note that the gas 
 is incapable of being set fire to in the air, but that it supports 
 the combustion of hydrogen with production of white fumes. 
 Is hydrochloric acid the product of combustion? Let the 
 fumes dissolve in a little water shaken in the bottle, blow air 
 through the solution till free from chlorine, and test for the acid 
 with blue litmus paper, and also with silver nitrate 
 solution. In another bottle of the gas place a glowing 
 splint. Is chlorine able to support the combustion of 
 ignited carbon? Now thrust a lighted taper into the 
 gas. Note the formation of the fumes of hydrochloric 
 acid and the liberation of carbon, the paraffin wax of 
 the taper being a compound of hydrogen and carbon. 
 Ignite some metallic sodium in an iron deflagrating 
 spoon, and place in another jar of the gas. What 
 is the product of combustion? As a result of these 
 experiments state whether chlorine is able to unite 
 directly with oxygen, hydrogen, carbon, or sodium. 
 
 Fill a long glass tube, closed at one end, with the 
 saturated chlorine water, and invert it into a small wide- 
 necked flask also filled with the chlorine water. Slip a 
 
84 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 cork down the tube so as to fit loosely into the flask and 
 prevent loss of chlorine. Invert the whole apparatus for a 
 moment to get rid of any air which has got into the tube. 
 Set the apparatus in bright sunlight for a few hours. Note 
 that two or three inches of gas collect in the tube and that 
 the liquid becomes colourless. When the gas ceases to be 
 evolved, test it with a glowing splint. Is it oxygen? Has 
 the hydrogen of the water been attacked by the chlorine 
 forming hydrochloric acid and liberating oxygen, thus : — 
 
 Cl 2 +H 2 = 2 HCl + 0? 
 
 Test the liquid for hydrochloric acid with silver nitrate solu- 
 tion, and with blue litmus paper. 
 
 Bleaching Agents and Disinfectants. — The strong attraction that the 
 foregoing experiment shows to exist between chlorine and hydrogen causes 
 chlorine to be a powerful oxidising agent, and upon this depends its use 
 for bleaching, and as a disinfectant and deodoriser. A piece of turkey-red 
 cloth, when placed in a jar of chlorine, is bleached if moisture be present, 
 the red dye being oxidised to colourless substance by the oxygen set free 
 from the water by the action of chlorine upon it. Chlorinated lime, which 
 may be produced on a small scale by passing chlorine gas through a glass 
 tube containing a layer of slaked lime, and which consists of a compound 
 of calcium chloride and calcium hypochlorite (the salt derived from the hypo- 
 chlorous anhydride mentioned on p. 52), is more conveniently used. On 
 the addition of dilute acid to the powder chlorine is rapidly evolved, and even 
 the carbonic acid gas of the air very slowly liberates chlorine, so that it is 
 sufficient to sprinkle the powder wherever it may be required as a disin- 
 fectant or deodoriser. Another powerful oxidising agent and disinfectant 
 is the permanganate of potash, K 2 O.Mn 2 7 , contained in Condy's Fluid, 
 for the heptoxide of manganese easily gives up oxygen, and is reduced to 
 a lower oxide. Ozone, a condensed form of oxygen occurring in sea and 
 country air, and the peroxide of hydrogen, are also powerful oxidising and, 
 therefore, bleaching and disinfecting agents. It must be remembered that 
 sulphurous acid owes its bleaching power partly to its reducing action, 
 and therefore acts in the opposite way to the substances now under con- 
 sideration. 
 
NITROGEN: AMMONIA 35 
 
 XXI. NITROGEN: AMMONIA 
 
 Previous experiments have shown that the gaseous element 
 nitrogen is neither combustible nor a supporter of combustion. 
 The German and French names for nitrogen — sticksioff and 
 azote — express its inability to support life when respired. It 
 was found that atmospheric air consists mainly of a mixture of 
 oxygen and nitrogen in the proportion of about 1 to 4, or 
 more exactly 20.9 and 79.1 per cent, by volume. This 
 atmospheric nitrogen contains, however, about 1 per cent, of 
 argon, a gaseous element of still greater inactivity. 
 
 In the combined state, nitrogen is an essential constituent 
 of all animal and vegetable organisms. When nitrogenous 
 organic matter decays, or when it is destructively distilled, the 
 hydrogen compound of nitrogen, ammonia, is produced, just 
 as sulphuretted hydrogen is produced from organic matter 
 containing sulphur. Heat some horn shavings in a test-tube. 
 Note the pungent smell of the escaping ammonia gas (" spirit 
 of hartshorn "). Test the gas with litmus paper. Has it an 
 acid reaction like the hydrogen compounds of sulphur and 
 chlorine, or has it an alkaline reaction ? If the latter, it is a 
 base, and able to unite with acids forming salts. Hold a glass 
 rod moistened with hydrochloric acid to the mouth of the 
 tube. Is there any evidence of a salt, the hydrochloride of 
 ammonia, being formed ? Analysis shows that ammonia 
 contains 82.35 per cent, of nitrogen and 17.65 per cent, of 
 hydrogen. What is the simplest formula that would represent 
 its composition ? 
 
 Procure some commercial sal-ammoniac, the hydrochloride 
 of ammonia. Note its fibrous crystalline structure, its solu- 
 bility in water, its neutrality to litmus. Ammonia being a 
 volatile base, it may be prepared from this salt by taking 
 advantage of the facts stated on p. 77. Mix a little sal- 
 ammoniac with any fixed base, e.g. lime, potash, soda, etc. 
 
86 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Is ammonia set free ? Fit up the apparatus figured. Fill the 
 U tube with small lumps of quicklime to serve as a drying 
 agent. In the Florence flask place a 
 mixture of 20 grams of powdered 
 sal - ammoniac with twice its weight 
 of powdered quicklime, then fill up 
 the flask with lumps of quicklime, 
 and, having connected the U tube, 
 warm gently. Collect the gas in an 
 inverted jar by upward displacement 
 Note the colour, smell, and lightness of the pure 
 ammonia. Of its two component gases, neither are supporters 
 of combustion, and hydrogen alone is combustible. Examine 
 the properties of ammonia in these respects. Pass a rapid 
 stream of the gas into a flask containing a little cold water. 
 Is it soluble? Prepare a saturated solution. Neutralise a 
 little of the solution with hydrochloric acid, and evaporate 
 to dryness. Is sal-ammoniac left? 
 
 Fig. 38. 
 
 of air. 
 
 With respect to the combustibility of ammonia, it must be remembered 
 that while heat will be produced by the combustion of the hydrogen, heat 
 must first be absorbed in order to decompose the ammonia into its elements. 
 Hence, while there is a tendency for the gas to burn while the lighted taper 
 is held at the mouth of the jar, the combustion immediately ceases when 
 the heat of the burning taper is removed. 
 
 Determine the relative density of ammonia gas by means of 
 the density flask (Fig. 1). To do so recharge the ammonia 
 apparatus and attach a second U tube filled with quicklime to 
 dry the gas thoroughly. Pass a slow stream of the ammonia 
 into the top of the density flask until the gas issuing from the 
 long tube is completely soluble in water. Compare the 
 density (1) with air as unity, and (2) with hydrogen as unity. 
 
 Ammonia differs from the bases so far considered in not 
 being an oxide. Its action on acids to form salts must there- 
 fore be different from that of caustic potash or caustic soda. 
 
NITROGEN: AMMONIA 87 
 
 It may be supposed that ammonia would unite directly with 
 acids thus : — 
 
 NH 3 + HC1 = NH 3 .HC1 
 2NH3 + H 2 S0 4 m (NH 3 ) 2 .H 2 S0 4 . 
 To test the truth of this conjecture, place 20 cubic centimeters 
 of the diluted sulphuric acid of known strength, prepared for 
 Study XVIII., in a weighed dish, add the solution of ammonia, 
 prepared above, in slight excess (the excess will volatilise), 
 evaporate the solution to dryness on the water bath, and 
 weigh. Does the weight of the compound obtained correspond 
 with that calculated from the second of the formulae given? 
 Having found the formulae for sal-ammoniac and the sulphate, 
 write equations representing the action of quicklime upon 
 them. Deduce the formula for calcium chloride from the 
 formulae of calcium oxide and hydrochloric acid. 
 
 Instead of the formulae NH 3 .HC1 and (NH 3 ) 2 .H 2 S04, the compounds 
 might be represented as NH 4 C1 and (NH 4 ) 2 S0 4 , in which NH 4 is regarded 
 as taking the place of hydrogen in the acids and a metal in the salts. The 
 name ammonium is applied to this hypothetical metallic radicle, and the 
 salts are called chloride of ammonium and sulphate of ammonium, like 
 chloride of sodium and sulphate of sodium. In the same way the hydrate 
 of ammonia, produced by dissolving ammonia in water, may be regarded as 
 hydroxide of ammonium. Thus NH 4 C1, like NaCl, instead of NII 3 .HC1 ; 
 (NH 4 ) 2 S0 4 , like Na 2 S0 4 , instead of (NH 3 ) 2 .H 2 S0 4 ; NH 4 OH, like NaOH, 
 instead of NH 3 .H 2 0. The use in commerce of the term muriate and 
 sulphate of ammonia for chloride and sulphate of ammonium is obviously 
 not justifiable. 
 
 Ammonium compounds are easily recognised, for they 
 decompose when warmed with potash or soda, ammonia gas 
 being set free. The gas can be distinguished by its smell, 
 by its action on red litmus paper, and by the white fumes of 
 sal-ammoniac produced when the mouth of the tube in which 
 the test is made is brought near the mouth (or stopper) of the 
 hydrochloric acid bottle. By this means, test a sample of 
 " nitrogenous guano " and a sample of " barley manure " for 
 ammonium salts. 
 
88 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 XXII. NITRIC ACID AND THE NITRATES 
 
 Nitrogen, as its name implies, is a constituent of nitre or 
 saltpetre. Insert a grain of this salt on a platinum wire into a 
 non-luminous flame. What base does the coloration of the 
 flame show that the salt is a compound of? Repeat the 
 experiment with "Chili saltpetre." In what respect do the 
 salts differ? Warm a little of each salt in test-tubes with 
 strong sulphuric acid. Do the fumes of the acid evolved 
 appear to be identical ? Are they acid to litmus ? Note that 
 the vapour causes the inflammation of a glowing splint, showing 
 that the acid is an oxygenated acid that readily loses oxygen ? 
 These experiments show that saltpetre and Chili saltpetre are, 
 respectively, the potassium and sodium salts of an oxy-acid 
 (so called to distinguish acids which are the hydrates of 
 acidic oxides from acids which are compounds of non-metallic 
 elements with hydrogen). Being obtained from nitre, the acid 
 is called nitric acid. It is the hydrate of nitric anhydride, 
 
 N 2 5 . 
 
 N 2 5 + H 2 0- 2 HN0 3 . 
 
 A solution containing one gram of potash (K 2 0) when exactly 
 neutralised with a solution of nitric acid, and evaporated to 
 dryness on a water bath, leaves a residue of nitrate of potassium 
 weighing 2.149 grams. What formula will represent the com- 
 position of the salt? Judging from analogy, sodium and 
 potassium having been found to resemble each other in all 
 their chemical properties, what will be the formula for nitrate of 
 sodium. 
 
 Prepare some nitric acid. Place about 25 grams of 
 saltpetre in a retort (Fig. 14), and, by means of a thistle 
 funnel thrust down the neck, add to it about 15 c.c. of 
 strong sulphuric acid. Heat the mixture gently, using a rose 
 burner, and collect the distillate in a flask kept cool by water. 
 
 Nitrogen is an element with apparently a weak attraction 
 
NITRIC ACID AND THE NITRATES 89 
 
 for oxygen, for it is incapable of combustion in air or 
 oxygen excepting at enormously high temperatures. It 
 is to be expected, therefore, that nitric acid and the nitrates 
 would lose oxygen easily and act as powerful oxidising agents. 
 Pour a little of the strong nitric acid on to some red-hot 
 charcoal contained in a crucible. Is there evidence of 
 oxidation of the carbon? Mix together some powdered 
 charcoal, sulphur, and nitre. Ignite the mixture. Do 
 the charcoal and sulphur now burn so readily as to 
 lead to the belief that the nitre provides the oxygen for 
 combustion ? 
 
 To act as an explosive, the combustible mixture must contain enough 
 oxygen for combustion in absence of air. Its power as an explosive 
 will chiefly depend upon the rapidity with which complete ignition 
 occurs, and the amount of the gaseous products. The average composition 
 of the gunpowders made at Waltham Abbey is : — Nitre, 74.5 per cent.; 
 sulphur, 10. 1 per cent.; charcoal, 14. 1 per cent. The gaseous products of 
 explosion, chiefly consisting of nitrogen and carbonic acid gas, occupy 
 about 280 times the volume of these powders. 
 
 The oxidising effect of nitric acid renders its action on metals 
 entirely different from that of dilute sulphuric acid. To a piece 
 of granulated zinc in a test-tube add a little of the nitric acid. 
 Note that the gas evolved is not hydrogen, it being incom- 
 bustible. Repeat the experiment with granulated tin, and note 
 that the tin is oxidised to the white oxide of tin. This can 
 only be at the expense of the nitric acid, and the gases evolved 
 must therefore be products of its reduction, either nitrogen 
 i^ self, or gaseous oxides containing less oxygen than nitric 
 i nhydride. 
 
 These gaseous reduction products are : — 
 
 Nitrogen peroxide, N0 2 ; a red gas. 
 
 Nitric oxide, NO ; a colourless gas, but combining with oxygen to form 
 the red peroxide. 
 
 Nitrous oxide, N 2 ; a colourless gas, and powerful supporter of com- 
 bustion like oxygen ; does not combine with free oxygen. It is 
 twenty times as soluble as oxygen. 
 
 Nitrogen, N ; a colourless gas and non-supporter of combustion. 
 
90 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Probably all these gases will be present, but when the nitric acid is strong 
 the higher oxides will predominate; when weak the lower oxides and 
 nitrogen will predominate. The action of nitric acid on most metals 
 results in the formation of a nitrate of the metal. Thus if copper be dis- 
 solved in nitric acid the nitric acid is reduced, and the oxide of copper 
 formed dissolves in more of the nitric acid, forming a blue solution of 
 copper nitrate. From this solution crystals of the salt may be obtained by 
 evaporation. The reason why no nitrate is formed in the case of tin is that 
 the higher oxide of tin is produced, and this, like some other higher 
 metallic oxides, is an acidic, not a basic, oxide (see p. 64). It will have been 
 noticed that in the preparation of nitric acid reddish coloured fumes of 
 nitrogen peroxide were formed. This is due to the dissociation of the 
 vapour of nitric acid by heat into nitrogen peroxide, water, and oxygen. 
 Light has also the same effect, and a bottle of nitric acid exposed to sun- 
 light soon becomes reddish in colour. 
 
 If during the action of the zinc on the nitric acid the liquid 
 be kept very cold, it will soon acquire a green colour. The 
 colour is due to the presence of nitrous acid, a very unstable 
 compound soon decomposing into oxides of nitrogen and 
 water. This acid combines with ammonia, forming nitrite of 
 ammonium, but the salt is very unstable, for it decomposes 
 even at the ordinary temperature into nitrogen and water as 
 follows : — 
 
 NH 4 N0 2 = N 2 + 2 H 2 0. 
 
 This reaction provides a simple method for preparing nitrogen 
 gas. Dissolve in water 25 grams of the nitrite of sodium, and 
 place the solution in a flask connected with two wash-bottles, 
 the first containing caustic soda solution, the second oil of 
 vitriol. To the contents of the flask add ammonium chloride 
 in the proportion represented by the formulas NaN0 2 + NH 4 Cl, 
 and warm gently. The mixture of salts will behave like nitrite 
 of ammonium, and nitrogen will be evolved. Note that, when 
 once the temperature is reached at which reaction commences, 
 no further heat is required. Try to explain this. Pass the 
 nitrogen into the density flask, and determine the relative 
 density by the method described on p. 39. 
 
 Many other substances act as reducing agents on nitric acid. 
 
NITRIC ACID AND THE NITRATES 91 
 
 Among these is ferrous sulphate, which is oxidised by this 
 means to ferric salt. In this case nitric oxide is the product of 
 reduction, and as this combines with the excess of ferrous 
 sulphate to form a black compound, the reaction serves as a 
 test for nitric acid and the nitrates.* To a very weak solution 
 of saltpetre in a test-tube add a crystal of ferrous sulphate and 
 allow to dissolve. Then very carefully, down the side of the 
 tube, pour a few drops of pure strong sulphuric acid, so that it 
 forms a layer at the bottom of the liquid. Note that a black 
 ring is formed. 
 
 Another substance that reduces, and is oxidised by, nitric 
 acid is indigo. To the very weak solution of saltpetre (a solu- 
 tion of 1 in 10,000 is quite strong enough) add an equal volume 
 of pure, strong sulphuric acid, and, while the liquid is still hot, 
 add a solution of indigo in sulphuric acid drop by drop. Note 
 that the indigo is decolorised. The amount of indigo that 
 can be decolorised serves as a rough comparative test for the 
 quantity of nitrate present in two solutions. Test some dis- 
 tilled water, tap water, and the drainage water from arable 
 land for nitrates by both methods. 
 
 All nitrates are soluble in water, so that there is no precipi- 
 tant that serves as a test for nitric acid and the nitrates. 
 
 Putrefaction and Nitrification. — Saltpetre or nitre, the nitrate of 
 potassium, is found as an efflorescence on the soil round villages in hot 
 countries, due to the putrefaction of nitrogenous organic matter, the nitri- 
 fication of the ammonia thus produced, and the combination of the nitric 
 acid formed with the potash of the soil. By washing the soil with water 
 the nitre is dissolved out, and may be obtained by evaporating the solution. 
 The same series of changes may occur in a stable, where a strong smell of 
 ammonia, due to the putrefaction of the manure, is sometimes observed, 
 and crystals of nitrate of calcium found adhering to the mortar of the walls. 
 In cultivated soil, too, these changes are constantly going on, especially in 
 
 \6FeS0 4 + 3H 2 S0 4 + 30 = 3Fe 2 3S0 4 + 3H0O 
 FeS0 4 + NO = FeS0 4 .NO 
 
92 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 warm weather, and thus crops are provided with combined nitrogen in the 
 form that plants most easily assimilate. The nitrate of soda (Chili salt- 
 petre) occurring as a deposit in the rainless districts of South America, 
 and which is now so largely employed (together with sulphate of ammonia) 
 as a nitrogenous manure, owes its origin, no doubt, to the same cause. 
 
 Another very important application of these processes is the natural puri- 
 fication of water. When water has become contaminated with sewage, the 
 nitrogenous organic matter serves as a food for disease germs which, under 
 favourable conditions, multiply with enormous rapidity. But putrefaction 
 of the organic matter and the nitrification of the ammonia produced 
 deprives such germs of the means of development. In the analysis of 
 drinking waters determinations are made of (i) the amount of total organic 
 matter (as indicated by the quantity of permanganate of potassium it reduces, 
 and therefore decolorises in presence of acid — see p. 84) expressed as 
 "oxygen absorbed"; (2) the amount of nitrogenous organic matter 
 expressed as "albuminoid ammonia"; (3) the amount of "free am- 
 monia"; (4) the amount of "nitrates"; and (5) the amount of 
 chlorides expressed as "chlorine." Should the albuminoid ammonia 
 be high, recent sewage contamination is indicated, and the water would 
 be condemned for drinking purposes. Should the free ammonia be 
 high, the water would also be regarded with suspicion ; but should the 
 albuminoid and free ammonia be low, and the nitrates high, it indicates 
 that sewage contamination has at some time occurred, but that sufficient 
 time has passed for putrefaction and nitrification to go on, so that the water 
 need not necessarily be condemned. The presence of much chlorine is 
 suspicious, because common salt is an essential element of animal food, and 
 therefore occurs in sewage, but the salt may be derived from other sources. 
 The oxygen absorbed will be high if the organic matter be high, hence 
 potassium permanganate provides a rough test for the purity of water from 
 organic contamination. (Organic matter, however, is not necessarily highly 
 nitrogenous.) Acidify a cylinder full of the water with a few drops of pure 
 sulphuric acid, and then add a weak solution of permanganate, a drop at a 
 time, until it is no longer decolorised after standing. Compare distilled 
 water with tap water and rain water. Chlorides may be tested for with 
 nitric acid and nitrate of silver, and nitrates with sulphuric acid and indigo 
 solution. 
 
 The putrefaction of organic matter and the nitrification of ammonia are 
 fermentative changes due to the action of micro-organisms. Among the 
 conditions favourable to both kinds of fermentation are sufficient moisture, 
 sufficient air, and sufficient warmth. That air must be necessary to nitri- 
 fication is obvious when it is remembered that the conversion of ammonia 
 into nitric acid is a process of oxidation, and since nitrate is the form of 
 
PHOSPHORUS AND PHOSPHORIC ACID 93 
 
 combined nitrogen most easily absorbed by the roots of plants, the import- 
 ance of cultivating the soil and admitting air is understood. One of the 
 chief advantages of a long summer's fallow, in fact, is that nitrification 
 can go on during a long period, and a large amount of nitrate formed for 
 the ensuing crop. Since warmth favours fermentation, these changes take 
 place principally in the summer months, so that crops growing in the 
 summer and autumn are, other things being equal, more independent of an 
 artificial supply of combined nitrogen than a crop growing in the spring. 
 A fourth condition favourable to nitrification is a sufficiency in the soil of 
 a base able to neutralise the nitric acid produced, for this acid, being a 
 powerful oxidising agent, would otherwise destroy the nitrifying germs and 
 therefore stop further nitrification. The base usually applied for this pur- 
 pose, if there is insufficient in the soil, is lime. 
 
 The nitrates being all soluble in water, their loss by drainage is very great. 
 At Rothamsted it was found that drainage water from uncultivated land 
 contained on the average (19 years) as much as 5 grains per gallon of 
 nitrates calculated as nitrate of sodium, a loss which amounted to 214 lb. 
 per acre per annum. For this reason a long summer fallow should never 
 be carried out on light soils through which water can easily pass, as the 
 nitrate produced would thus be lost. It is moreover desirable, as far as is 
 possible, that crops should always be growing on such land so as to utilise 
 the nitrate as soon as formed. Salts of ammonia are not found to an 
 appreciable extent in drainage waters, owing to their reaction with the 
 double silicates of alumina and lime, magnesia or soda of the soil, the 
 ammonia being fixed and a salt of lime, magnesia or soda, set free 
 (see p. 99). For this reason sulphate of ammonia is sometimes preferred 
 as a nitrogenous manure to nitrate of soda. It must, however, be remem- 
 bered that since the ammonia has first to be nitrified, it is slower in its 
 action on crops, and that owing to the formation of these insoluble com- 
 pounds with soil constituents, it chiefly acts, when applied as a top dressing, 
 on shallow-rooted plants. 
 
 XXIII. PHOSPHORUS AND PHOSPHORIC ACID 
 
 The element phosphorus, like nitrogen, is an essential con- 
 stituent of all animal and vegetable organisms. When organic 
 matter containing much phosphorus decays, the hydride of 
 
94 
 
 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 phosphorus or phosphoretted hydrogen is often liberated. It 
 is a gas of an odour even more offensive than sulphuretted 
 hydrogen, and to it the smell of rotting fish is partly due. Iron 
 is often impure with phosphide of iron. Such iron, when 
 treated with dilute sulphuric acid, yields hydrogen mixed with 
 phosphoretted hydrogen (compare with sulphur, p. 68), 
 and this may be detected in the smell of the escaping gas, 
 and the colour of its flame when ignited. The composi- 
 tion of phosphoretted hydrogen is expressed by the formula 
 PH 3 . 
 
 Touch a fragment of dry phosphorus with a glass rod which 
 has been heated till it feels warm to the hand. Note that even 
 at this moderate temperature the phosphorus ignites, clouds 
 of oxide of phosphorus being produced. Hold another freshly 
 cut fragment on the point of a penknife. Note that, without 
 ignition, oxidation is proceeding. Examine it in the dark. 
 Note that this slow oxidation is accompanied by phosphorescence. 
 
 On account of its ready combustibility, phosphorus is used on the heads 
 of lucifer matches to promote their ignition. A mixture of phosphorus and 
 nitre is employed which, being explosive, is ignited by mere friction. 
 " Safety matches " are tipped with the oxidising agent, while the combustible 
 substance, a mixture of amorphous phosphorus and the sulphide of anti- 
 mony, is smeared on the box. To ignite 
 such matches, the match must, therefore, be 
 rubbed on the box. Amorphous phosphorus 
 is an allotropic modification of phosphorus 
 not spontaneously inflammable. It is formed 
 when phosphorus is heated to 240 C. in 
 absence of air. 
 
 Fill a dry bell jar resting on a dry 
 plate with dry oxygen gas (supplied), 
 and insert a deflagrating spoon con- 
 taining some ignited dry phosphorus. 
 Note the formation of white phos- 
 phoric anhydride. Collect this on a 
 spatula and plunge into cold water. 
 
 Fig. 39. 
 
PHOSPHORUS AND PHOSPHORIC ACID 95 
 
 What evidence is there of chemical combination ? Note the 
 formation of transparent glacial phosphoric acid, P 2 O r) .H 2 
 or HPO3. Boil the mixture for some time. A solution 
 of ordinary phosphoric acid, P 2 5 .3H 2 or H 3 P0 4 , will 
 thus be obtained. Note that the solution is sour in taste 
 and acid to litmus. Neutralise a little with caustic soda, and 
 evaporate to obtain crystals of the soluble phosphate of sodium. 
 
 Place 10 c.c. of the phosphoric acid solution, previously 
 largely diluted, in a small flask and run in lime water from a 
 burette, constantly shaking the flask, until the precise point is 
 reached when the precipitate at first formed no longer redis- 
 solves. Note the quantity of lime water used {x c.c). Test 
 the phosphate solution with litmus, and note that it is nearly 
 neutral. 
 
 Place 10 c.c. of the diluted acid in another flask, and run 
 in lime water, constantly shaking, until, after filtering, no 
 further precipitate is produced by the addition of more lime 
 water. Note that the quantity of lime used is rather more than 
 double that required by the first experiment {2.x c.c). On 
 testing with litmus the liquid will be found to be still neutral. 
 
 Into a third flask run three times the quantity of lime water 
 used in the first experiment (3^ c.c), and, having filled the 
 burette with the diluted phosphoric acid, run it into the lime 
 water, with constant shaking, until, after filtering, the liquid 
 ceases to be alkaline, and becomes just neutral. Note that 
 approximately 10 c.c. of the acid have again been used. 
 
 There are obviously three stages in the reaction between 
 phosphoric acid and lime, corresponding to the formation of 
 three distinct compounds which may be expressed thus : — 
 
 P 2 5 .3H 2 + CaO - P 2 5 .2H 2 O.CaO + H 2 
 P 9 5 -3 H 2 ° + 2CaO = P 2 5 .H 2 0.2CaO + 2H 2 
 P 2 5 . 3 H 2 + 3 CaO - P 2 5 . 3 CaO + 3 H 2 
 
 and of these the first compound is clearly the only one soluble 
 in water. The three compounds are distinguished as mono- 
 
96 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 calcic, dicalcic, and tricalcic phosphate. The two first are acid 
 salts, i.e. compounds intermediate between a salt and an acid, 
 and either can be produced by mixing the other with the acid 
 or the neutral salt, as the case may be, in the right proportion. 
 If the solution of monocalcic phosphate be mixed with the 
 liquid containing the precipitate of tricalcic phosphate, and 
 allowed to stand, the dicalcic phosphate will in time be formed. 
 
 Many other acids are able to convert the insoluble phos- 
 phates into the soluble monocalcic phosphate. To one portion 
 of the milky liquid add a few drops of dilute sulphuric acid ; 
 note that the precipitate dissolves. Add potash or lime water ; 
 note that it is reprecipitated. Through the other pass a stream 
 of carbonic acid gas (supplied) ; again note that the precipitate 
 dissolves, and is reprecipitated by potash. Write an equation 
 to represent the action of sulphuric acid on phosphate qf 
 calcium. 
 
 Phosphoric acid is distinguished by two characteristic in- 
 soluble compounds : the phospho-molybdate of ammonium 
 and the double phosphate of ammonium and magnesium. 
 Take a few drops of one of the liquids containing phosphate of 
 calcium, dissolve the precipitate by a drop of nitric acid, and 
 add the liquid to a solution of molybdate of ammonium (the 
 ammonium salt of the acid derived from the higher oxide of 
 the metal molybdenum) contained in a test-tube. On warming, 
 a characteristic yellow precipitate will be formed. To a small 
 portion of the solution of phosphoric acid add a mixture of 
 sulphate of magnesium, chloride of ammonium, and ammonia 
 solutions. A characteristic white crystalline precipitate of the 
 double phosphate will be deposited. 
 
 In the latter test ammonia is added to neutralise the acid, as otherwise no 
 precipitate would be formed ; the ammonium chloride must then be also 
 added in order to prevent the precipitation of magnesia from the magnesium 
 sulphate, a double salt of ammonium and magnesium being produced, from 
 which magnesia is not precipitated by ammonia. This reaction is also used 
 for the detection of magnesium ; for this purpose, ammonia, ammonium 
 
PHOSPHORUS AND PHOSPHORIC ACID 97 
 
 chloride, and sodium phosphate solutions are added to the liquid to be 
 tested. A white crystalline precipitate shows the presence of magnesium in 
 the solution. 
 
 Phosphates and Phosphatic Manures. — Phosphates occur very abun- 
 dantly in nature. Bones contain phosphate and other salts of calcium (in 
 addition to gelatine and fat), and "bone earth," the white ash left when bones 
 are burnt, chiefly consists of phosphate and carbonate of calcium. Peruvian 
 guano, the product of the partial decay of sea-birds' excrements, chiefly 
 consists of phosphate of calcium mixed, when the guano occurs in rainless 
 districts where the moisture is insufficient for complete putrefaction and 
 nitrification, with phosphate and urate of ammonium. The coprolites found 
 in Suffolk and Cambridgeshire chiefly consist of phosphate of calcium. 
 Canadian appatile is a double phosphate and chloride of calcium. 
 
 The phosphorus required by plants is absorbed from the soil in the 
 form of soluble phosphates, these being slowly formed by the action of the 
 carbonic and other acids of the soil and of the acids in the root sap upon 
 the insoluble phosphates. The soil is, however, frequently deficient in 
 "available," i.e. easily soluble, phosphates, and phosphatic manures are 
 then required. Now tricalcic phosphate as it occurs in bones, coprolites, 
 appatite, and phosphatic guano {i.e. guano containing little or no com- 
 bined nitrogen) is only very slowly dissolved by the weak acids existing in 
 the soil, even when in a fine powder, and it is usual, therefore, previously to 
 convert, into soluble phosphate by sulphuric acid. The "superphosphate 
 of lime " thus produced is a mixture of monocalcic phosphate and gypsum 
 for 
 
 Ca 3 2P0 4 + 2H 2 S0 4 = CaH 4 2P0 4 + 2CaS0 4 . 
 
 The substances produced are known as "dissolved guano," "dissolved 
 bones " or " bone superphosphate," and/' mineral superphosphate," accord- 
 ing to their source. 
 
 When the monocalcic phosphate has been used as a manure and has 
 been washed into and diffused through the soil by rain, it "reverts" into 
 the insoluble dicalcic phosphate owing to the action of the bases of the 
 soil. This being deposited in a fine state of division is easily redissolved, 
 and it is therefore " available " for plant food. The fact that nitrogenous 
 guano contains phosphate of ammonium renders this manure especially 
 valuable, for this soluble phosphate is a neutral salt and therefore does not 
 so easily "revert" in the soil into an insoluble form. "Reversion" is 
 also noticed when superphosphate of lime is kept for some time, for the 
 monocalcic phosphate reacts with unchanged tricalcic phosphate in the 
 manure yielding the intermediate dicalcic phosphate. 
 
 Iron made from Cleveland iron ore contains a large amount of phosphide 
 
 7 
 
98 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 of iron. To convert this into steel, the phosphorus is oxidised by a current 
 of heated air blown through the molten metal in contact with excess of 
 lime. An unstable basic phosphate of lime,* Ca 3 2P0 4 . CaO, is thus pro- 
 duced which, when finely ground to an impalpable powder, constitutes 
 11 basic slag," a substance which can be easily dissolved by weak acid, and 
 is therefore "available" as plant food. As this is a basic substance, it 
 must not, when used as a manure, be mixed with nitrogenous guano or 
 sulphate of ammonia, as ammonia gas would be set free and lost. 
 Similarly "superphosphate of lime" must not be kept mixed with nitrate 
 of soda, as, being an acid phosphate, it sets free nitric acid which, owing 
 to the heating of the mass, is volatilised. 
 
 XXIV. SILICA: SAND AND CLAY 
 
 Potassium and sodium have been found to be the most oxidis- 
 able of all the metals examined. So great is their greediness 
 for oxygen that the oxides of almost all elements are attacked 
 by them, potash or soda being formed and the element set free. 
 This reaction may be employed for preparing the element 
 silicon from its oxide silica. Heat some silver sand (nearly 
 pure silica) in a test-tube with a little sodium. Note that a 
 brown non-metallic substance, the element silicon, is liberated. 
 It has been found by experiment that silica contains 46.6 per 
 cent, of silicon and 53.3 per cent, of oxygen. What is the 
 simplest formula that represents its composition ? 
 
 Mix together 20 grams of silver sand with twice its weight of 
 caustic soda, and heat the mixture strongly on a clean iron dish 
 over a hot fire. When steam ceases to be given off and action 
 appears to be complete, allow the liquid mass to cool, lixiviate 
 with water, boil, and then filter the solution of silicate of sodium 
 produced. Evaporate a part of the solution till a thick syrupy 
 residue of " soluble glass " is obtained. 
 
 * A basic salt is a compound intermediate between a base and a salt, 
 just as an acid salt is intermediate between an acid and a salt. 
 
SILICA : SAND AND CLA V 99 
 
 Take two other portions of the solution, and dilute one of 
 them with ten times its bulk of water. Now add diluted 
 sulphuric acid (1 to 4) to each portion. Note that no change 
 occurs in the weak solution, the silicic acid, so far as it is 
 replaced by sulphuric acid in the sodium salt, remaining 
 dissolved, but that from the strong solution white gelatinous 
 silica is deposited, the silicic acid set free being unstable. 
 (Compare this action with that of dilute sulphuric acid on 
 weak and strong solutions of sulphite of sodium.) Evaporate 
 the weak solution containing silicic acid to dryness on the 
 water bath ; note the white residue of silica left. Add water 
 and hydrochloric acid ; note that in both it is insoluble. These 
 experiments show that silicic acid is a very unstable compound, 
 easily decomposing into silica and water ; and that silica, unlike 
 most anhydrides, is insoluble in water and incapable of recom- 
 bining with water to form silicic acid. They also provide a 
 method for distinguishing silicic acid or the silicates, as no 
 other substance would yield a white gelatinous precipitate 
 when hydrochloric acid is added to its solution, or a white 
 residue, insoluble in water and acid, when the acid mixture 
 is evaporated to dryness. 
 
 Silica, the oxide of the element silicon, is the most abundant constituent 
 of the earth's crust. It occurs uncombined as quartz, sand, and flint, minerals 
 which, though geologically different, are chemically identical. Silica also 
 occurs combined with bases. Felspar and mica, two minerals which, mixed 
 with quartz, constitute granite, are double silicates of aluminium with 
 either calcium, magnesium, potassium, sodium, or iron, while clay, pro- 
 duced by the weathering and consequent disintegration of felspathic rocks, 
 is essentially silicate of aluminium, still retaining, however, variable 
 quantities of the other silicates. Both clay and sand are usually coloured 
 yellow, brown, or red, due to the presence of ferric oxide. Asbestos is a 
 basic silicate of calcium and magnesium ; meerschaum and steatite (talc, 
 soapstone, or french chalk) are acid silicates of magnesium. 
 
 Like phosphoric anhydride silica combines with water and bases in more 
 than one proportion. Silicate of sodium has the formula Na 4 Si0 4 (that is, 
 Si0 2 .2Na 2 0), and with this the soluble silicic acid probably corresponds, 
 H 4 Si0 4 'or SiO s .2H 2 0). But the silicates occurring in nature more often 
 
loo CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 correspond to the acid H 2 Si0 3 (that is, Si0 2 .H 2 0). Thus a silicate of 
 calcium that occurs naturally is CaSi0 3 (or Si0 2 .CaO). China clay or 
 kaolin, a nearly pure silicate of aluminium, is 2AlHSi0 4 .H 2 (or 
 2Si0 2 .H 2 O.Al 2 3 ; H 2 0). 
 
 Dilute a little of a weak solution of silicate of sodium with 
 water, and add a few drops of solution of alum. Note that the 
 liquid is rendered turbid with a gelatinous precipitate of 
 hydrated silicate of aluminium (clay). Make a mixture of clay 
 and distilled water, and divide into two parts. To one add 
 distilled water and to the other lime water. Note that in the 
 latter the clay becomes granular and separates from the liquid \ 
 in the other the clay remains suspended. 
 
 To a portion of the strong solution of silicate of sodium add 
 a saturated solution of alum. Note that a solid jelly of 
 hydrated silicate of aluminium is formed. Heat the jelly on a 
 dish on the water bath. Note that the anhydrous silicate of 
 aluminium produced is porous and no longer gelatinous. Wash 
 the mass well with water. Then heat a little on the loop of a 
 platinum wire in the Bunsen flame. Note that it is infusible. 
 
 Owing to these properties clay is used as the principal ingredient in 
 pottery and porcelain. Vessels made of pure clay are, when baked, porous 
 and friable. The clay is therefore mixed with a little fusible silicate, for 
 instance, silicate of lime, which, in the baking, penetrates into the pores of 
 the clay. The glaze on the surface is also produced by covering with a 
 fusible silicate. Bricks are made from "brick earth," a mixture of clay and 
 sand in such proportions that the bricks bake to a solid mass without 
 cracking and warping. Tiles are made from a purer clay, as they need to 
 be less porous than bricks ; being thinner, they can be more easily baked. 
 
 Mix a very little of the syrupy silicate of sodium with a trace 
 of lime and fuse by means of a blow-pipe on the loop of a 
 platinum wire. Note that a bead of glass is produced. Dip 
 such beads into solutions of salts of manganese, chromium, and 
 cobalt, and heat again. Note the different colours imparted 
 to the beads — amethyst, green, and blue. 
 
SILICA: SAND'AtiD CLAY 
 
 101 
 
 The Bohemian glass used for chemical apparatus consists of silicates of 
 potassium and calcium, window or crown glass of silicates of sodium 
 and calcium, flint or crystal glass of silicates of potassium and lead, and 
 bottle glass of silicates of sodium and calcium and some iron and aluminium. 
 Glass containing sodium or lead is "soft" and easily fusible, that contain- 
 ing potassium and calcium is " hard " and infusible. 
 
 The Soil and its " Mechanical " Properties.— Soil essentially consists 
 cf sand and clay in varying proportions, mixed with more or less gravel, 
 chalk, and decaying vetegable matter ("humus"). The "mechanical 
 analysis," i.e. the determination of the pro- 
 portion of gravel, sand, and clay, may be 
 roughly carried out as follows :— From a 
 known weight of air-dried soil, sift out the 
 gravel and weigh it. Mix the sifted soil 
 thoroughly with water, and pour the mixture 
 into a wide tall cylinder (Fig. 40). Now 
 allow a very slow, steady stream of water to 
 run into the bottom of the cylinder, gently 
 stirring the contents from time to time with 
 the tube through which the water is passing, 
 and so arrange the supply of water that the 
 clay and very fine sand are washed away. 
 When, thoroughly washed, dry the residue and 
 weigh it. The quantity of clay and fine sand 
 is determined by difference. Express the 
 result as percentage of (1) gravel, (2) coarse 
 sand, (3) clay and fine sand. Upon the 
 proportion of sand and clay mainly depend 
 the dryness or wetness of a soil. This is 
 due, firstly, to the greater porosity of sand, 
 and secondly, to the greater capillarity of clay. 
 
 If sandy and clayey soils be percolated with water (Fig. 16), the water 
 will pass through the sandy soil more quickly, because the particles are 
 coarser, and the spaces between therefore larger. The sandy soil is, in 
 fact, more porous. The gelatinous nature of the hydrated silicate of 
 alumina constituting clay, also renders clayey soils less porous. If such 
 a soil be "burnt," the anhydrous silicate is produced, and the soil is 
 rendered more porous. The same effect will be produced by the application 
 of lime, which renders the gelatinous clay more granular. (See above.) 
 
 If two long glass tubes, filled with the two soils, previously thoroughly 
 dried and disintegrated, be allowed to stand in vessels of water (Fig. 41), 
 
 Fig. 40. 
 
 Fig. 41. 
 
102 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 the water will ultimately rise higher in the tube of soil consisting of the 
 smaller particles. The attraction which solids have for liquids is mani- 
 fested in the rise of liquids in small tubes, and it is therefore called 
 "capillary attraction." It is, however, simply dependent upon the amount 
 of surface the solid exposes to the liquid ; and as small particles present 
 more surface than large particles in proportion to their bulk, and the inter- 
 spaces between are smaller, the capillarity of a clay soil is greater than 
 that of a sandy soil. It is for this reason that clayey soils have more 
 power than sandy soils of sucking up moisture from below, and therefore 
 remaining moist in dry weather. 
 
 The cooling effect of moisture on soils, and the action of frost on soils, 
 have been referred to on pp. 34, 35. 
 
 XXV. CARBON: MARSH GAS 
 
 Heat strongly in separate test-tubes (1) a piece of wood and 
 (2) a piece of bone. Note that in each case charring occurs 
 owing to the decomposition of the organic matter, and that 
 finally black masses of (1) vegetable charcoal and (2) animal 
 charcoal are left, which, while they have retained the form of 
 the pieces of wood and bone used, are much lighter in weight, 
 having become porous. If the combustible portion of the 
 wood charcoal and " bone-black " be burnt off by kindling and 
 then placing in bottles of oxygen, it will be found that the gas 
 produced in each case renders lime water milky, and is therefore 
 carbonic acid gas, and that in each case also, a white ash, 
 " wood ashes," and " bone ash," is left. Both kinds of char- 
 coal, in fact, consist of the element carbon, together with the 
 mineral substances of the wood or bone from which the char- 
 coal is made. 
 
 Like sulphur and phosphorus, carbon exists in both crystalline and 
 amorphous modifications. Diamond, distinguished by its lustre, and 
 hence valuable as a precious stone, and by its extreme hardness, is a 
 nearly pure and colourless crystalline modification of carbon. Graphite 
 
CARBON: MARSH GAS 103 
 
 (plumbago or black lead), distinguished by its softness, and hence used as 
 a writing material, is a black modification also capable of existing in a 
 crystalline form. The carbon of (1) animal and vegetable charcoal; (2) 
 lamp-black, the soot produced by the incomplete combustion of oils 
 burning with a smoky flame ; (3) coke, the residue of the destructive dis- 
 tillation of coal in the manufacture of coal gas ; and (4) gas carbon, the 
 deposit in the upper parts of the retorts used for the same purpose, is the 
 black amorphous modification. "Charcoal burning," the process by which 
 wood is converted into charcoal, once an important industry, is still 
 carried on in woodland districts. Stacks of wood are set fire to, but by 
 covering the stacks with earth or turf the supply of air is so limited that 
 the wood is carbonised, but not burnt. 
 
 The wood ashes, produced by the complete combustion of wood, have a 
 high value as a fertiliser, owing chiefly to the large quantity of carbonate of 
 potassium they contain. When lixiviated with water, and the solution 
 evaporated to dryness, a residue of impure carbonate of potassium is 
 obtained, constituting, when calcined, the pearl-ash of commerce. 
 
 The attraction that exists between liquids and the surface of 
 solids has been already referred to (p. 102). Charcoal 
 exhibits this attraction in an extraordinary degree. Render 
 some water blue with solution of litmus, and shake with some 
 powdered animal charcoal for a few minutes. Now throw upon 
 a filter. Note that the filtrate is colourless, the dissolved 
 colouring matter having adhered to the charcoal. 
 
 This force of adhesion is also exerted between solids and 
 gases, and its extent will largely depend upon the amount of sur- 
 face exposed by the solid. Owing to its porousness, wood charcoal 
 presents an enormous surface, and exhibits an enormous power 
 of absorbing gases. Heat a lump of wood charcoal in a tube 
 to bright redness, so as to expel absorbed gases, cork the tube, 
 and allow to cool. When cold, counterpoise on the pan 
 of the balance, then remove the cork, and watch the gradual 
 increase in weight. Place a small lump of charcoal in a flask 
 of water. Note that it swims on the surface. Now boil the 
 water till the air has been expelled from the pores of the char- 
 coal. Allow to cool, and notice that the density of charcoal, 
 when free from air, being greater than water, the lump sinks. 
 
104 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Fill an inverted tube with ammonia gas (supplied) 
 by mercury displacement, and insert a lump of 
 charcoal previously heated to redness (Fig. 42). 
 Note the almost complete absorption of the 
 ammonia. 
 
 Owing to its power of absorbing gases, wood charcoal 
 is used as a deodoriser of sewer gases, etc. Not only 
 does it absorb noxious emanations, but, by condensing them 
 in its pores in close contact with the atmospheric oxygen, 
 also absorbed, it oxidises and disinfects them. As a rule, 
 FlG. 42. t h e m ore condensible and soluble a gas, the more is it 
 absorbed. Owing to its power of adhesion to dissolved 
 solids, animal charcoal is used as a decoloriser ; for instance, in sugar 
 refining. Blocks of animal charcoal are also employed as the filtering 
 medium in water filters, and, when fresh, serve to remove, and perhaps 
 oxidise, the microscopic living organisms in the water. 
 
 When organic matter decays, or when submitted to destruc- 
 tive distillation, a compound is produced of carbon and hydro- 
 gen. The bubbles of gas that rise from decaying vegetable 
 matter at the bottom of stagnant pools chiefly consist of this 
 compound, which has therefore received the name of " marsh 
 gas." It also constitutes the " fire-damp " in coal seams, to 
 which explosions in coal mines are generally due. Heat some 
 wood in the flask of the apparatus figured on p. 86. 
 Immerse the U tube in a beaker of cold water in order to 
 condense the creosote and other liquid products of distillation, 
 and collect the gas evolved in inverted test-tubes or cylinders 
 over water. Preserve the U tube and its contents for future ex- 
 amination. Apply a light to the gas in one of the cylinders, 
 and observe that it is combustible, and burns with a flame some- 
 what bluer than hydrogen, and slightly luminous. By the usual 
 methods it can be shown that pure marsh gas produces carbonic 
 acid gas and water when burnt, and therefore is a compound 
 of carbon and hydrogen ; but, produced as above, the gas is 
 not pure, but is mixed with free hydrogen, and with other com- 
 
THE OXIDES OF CARBON 
 
 '"5 
 
 pounds of carbon. Pure marsh gas has been found by experi- 
 ment to contain 75 per cent, of carbon, and 25 per cent, of 
 hydrogen. Calculate the simplest formula that would represent 
 its composition. 
 
 XXVI. THE OXIDES OF CARBON 
 
 It has been found that when carbon burns in air or oxygen, 
 the dioxide of carbon or carbonic acid gas, C0 2 , is formed. 
 The gas was found to be an acidic oxide, dissolving in water 
 to form a liquid acid to litmus, and combining with lime to 
 form chalk, which is therefore carbonate of lime. As this 
 compound is a gas, it should be possible to prepare it by the 
 action of a less volatile acid upon a carbonate (see p. 77). 
 Fit up the apparatus figured. In 
 the large flask place some lumps of 
 chalk or, better, marble. Pour in 
 some water and then a little hydro- 
 chloric acid. Wash the gas by 
 passing it through a flask containing 
 water. Collect the gas by downward 
 displacement of air. Test it with a 
 taper, blue litmus solution, and lime 
 water. Is it identical with that 
 obtained by the combustion of carbon ? Determine its 
 relative density by means of the apparatus figured on p. 13. 
 For this purpose, the gas must be dried by passing it through 
 a U tube containing pumice soaked with oil of vitriol attached 
 to the flask B. 
 
 Although carbonic acid gas does not support the combustion 
 of a taper, it may be capable of losing oxygen to other 
 
 Fig. 43. 
 
io6 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 combustible substances, and therefore of supporting their 
 combustion. Ignite a piece of magnesium and plunge it into 
 a bottle of the gas. Note that the magnesium continues to 
 burn, although apparently with some difficulty ; that the white 
 oxide, magnesia, is produced, together with a black substance 
 Pour a little hydrochloric acid into the bottle to dissolve the 
 magnesia, filter off the black particles, wash with water, and 
 dry. Heat the black substance in a dry test-tube. Does it 
 burn and produce carbonic acid gas ? If so, it is carbon. 
 Represent the reaction by an equation. 
 
 Carbonic acid gas even supports the combustion of carbon 
 itself. Attach the carbonic acid apparatus to a piece of 
 
 c 
 
 
 7 
 
 
 
 
 
 
 1 
 
 Fig. 44. 
 
 combustion tubing, flask, and bent tube, as figured. Fill the 
 combustion tube with lumps of dry charcoal, and place a 
 solution of caustic potash (1 gram to 3 c.c. of water) in the 
 flask through which the products of combustion pass. Heat 
 the combustion tube strongly, and then pass a very slow current 
 of carbonic acid gas through the apparatus. Note that the 
 gas after passing over the heated charcoal is no longer 
 completely absorbed by the caustic potash, as would be the 
 case if the carbon dioxide were unchanged. Collect some 
 
THE OXIDES OF CARBON 107 
 
 over water made alkaline with caustic potash. Does it now 
 turn blue litmus red and render lime water milky ? Is it com- 
 bustible ? Is carbonic acid gas the product of combustion ? 
 Observe that the charcoal in the tube has slowly burnt away. 
 
 The only possible explanation of this change is that the 
 carbon burns in the carbon dioxide, producing a lower oxide 
 of carbon. This lower oxide has no action on litmus or on 
 bases, and is therefore not an anhydride ; but it burns in the 
 air, producing carbonic acid gas. Analysis shows that its 
 composition is represented by the formula CO ; it is therefore 
 the monoxide of carbon, and has been produced thus : — 
 
 C0 2 + C = 2 CO. 
 
 This experiment explains the occurrence of a blue flame over a coke fire. 
 The coke burns without flame at the bottom of the fire to carbonic acid 
 gas, but this, on passing over more heated coke, is reduced to carbon 
 monoxide, which burns at the top of the fire with a blue flame to carbon 
 dioxide. In a slow combustion stove, where insufficient air is supplied for 
 complete combustion, the carbon monoxide escapes unburnt. As this gas 
 is very poisonous, care must be taken that no leakage occurs from the flues 
 of such a stove into the room. "Producer gas" is the product of the 
 action of air on excess of coke, and consists of carbon-monoxide and 
 nitrogen. "Water gas" is the product of the action of incandescent coke 
 on steam, — H 2 + C = CO + H 2 , — and therefore consists of a mixture of 
 carbon monoxide and hydrogen. Both these mixtures are largely used as 
 fuels. 
 
 Besides reducing carbon dioxide, charcoal can also be 
 employed to reduce the metallic oxides. Mix a little litharge 
 with sodium carbonate, and place the mixture in a small hollow- 
 on a lump of charcoal. Now heat the mixture by means of a 
 mouth blow-pipe flame, so regulating the air that the flame 
 directed upon the mixture is luminous. Such a flame contains 
 free carbon, which assists the reduction. Note that in a few 
 minutes globules of metallic lead are produced. Mix together 
 a little oxide of arsenic and powdered charcoal. Place the 
 mixture at the bottom of a very small bulb tube made of a 
 
1 08 CI1EMISTR Y FOR A GRICUL TURA L S TUDENTS 
 
 piece of glass tubing, and heat. Note the deposit of arsenic 
 formed upon the sides of the tube. 
 
 Owing to this power of carbon as a reducing agent, it is used in 
 metallurgy. Generally speaking, the metallic ores are roasted to convert 
 the sulphide, hydroxide, or carbonate of the metal, as the case may be, into 
 oxide, and then heated with charcoal, coal, or coke, either with or without 
 a fusible compound to act as a flux, until the oxide is reduced to the metal. 
 Iron, copper, antimony, manganese, tin, zinc, sodium, and potassium, are all 
 separated from their oxides by reduction by carbon. In some other cases, 
 e.g. magnesium, which is obtained from its chloride, the metal sodium is 
 used as a reducing agent, while in the case of lead and mercury, which are 
 obtained from their sulphides, no reducing agent is necessary, careful 
 roasting serving to burn off the sulphur as sulphur dioxide. Aluminium is 
 obtained^ by the electrolysis (i.e. decomposition by electricity) of fused 
 cryolite, a native double fluoride of aluminium and sodium. 
 
 XXVII. THE CARBONATES 
 
 Determine the proportion of lime and carbonic acid gas in 
 chalk. Into a weighed capsule provided with a lid place 
 about 2 grams of pure chalk, dry by warming in the hot 
 water oven for a few minutes, cool in a dessicator, and weigh. 
 Now heat to a full red heat until no further loss in weight 
 occurs, then cover the capsule, cool in a dessicator, and weigh 
 again. From the resulting weight of lime find the percentage 
 composition of chalk, and express this by the simplest formula 
 possible. Calculate what weight of quicklime should be 
 obtained by burning 100 tons of chalk in a kiln. What weight 
 of slaked lime would this produce ? 
 
 Carbonates occur abundantly in nature : thus magnesian limestone is 
 carbonate of magnesium ; dolomite is a double carbonate of calcium and 
 magnesium ; malachite is a double carbonate and hydroxide of copper ; 
 calamine is the carbonate of zinc ; clay ironstone is the carbonate of iron. 
 
THE CARBONATES 109 
 
 But by far the most abundant is the carbonate of calcium. This occurs in 
 chalk, limestone, marble, calc-spar, etc., substances which, though geologi- 
 cally different, are chemically identical, and consist of the nearly pure car- 
 bonate. From these minerals lime is obtained by " burning" in kilns, i.e. 
 by heating the carbonate by means of burning fuel, either placed beneath it 
 or mixed with it to dissociate it into lime, which remains in the kiln, and 
 carbonic acid gas, which escapes into the air, {Dissociation is reversible 
 decomposition. Thus the decomposition of chalk is dissociation because 
 the lime and carbonic acid gas recombine at a lower temperature. The 
 decomposition of red oxide of mercury is another instance of dissociation, 
 the chemical change being reversible.) 
 
 Mortar and Cements. — Mortar is prepared by slaking quicklime, adding 
 enough water to make into a paste, and mixing with three or four times its 
 weight of sharp sand. It "sets" in a few days owing to evaporation 
 of water, and gradually increases in hardness owing to absorption of 
 atmospheric carbon dioxide and the formation of chalk. Portland and 
 Roman cement are prepared by grinding mixtures of chalk and clay (or 
 river mud) with water, drying the mixture, "burning" in kilns, and 
 powdering. Unlike mortar, these cements, after mixing with water, have 
 the power of setting under water, and are therefore called "hydraulic 
 mortars." The setting is due to the power of absorbing water possessed 
 by both quicklime and anhydrous silicate of aluminium and the production 
 of solid- hydrates. The dissolved carbonic acid in the water is also 
 gradually absorbed. 
 
 If the foregoing determination shows that carbonate of 
 calcium is a compound containing lime and carbonic acid gas 
 in single combining proportions, it may be supposed that the 
 carbonate of sodium or potassium has a similar composition. 
 With a view to determine this, try whether these carbonates 
 are decomposed by heat, by heating strongly in test-tubes. If, 
 unlike the carbonates of other metals, those of the alkali metals 
 prove to be incapable of dissociation by heat, the method of 
 titration with an acid, using litmus as an indicator, can be 
 employed ; for soluble carbonates are, unlike most salts, 
 strongly alkaline to litmus. 
 
 Weigh out two portions of pure carbonate of sodium, say 
 1 gram each, into two flasks, dissolve in distilled water, render 
 
1 1 o C HEM IS TR Y FOR A GRIC ULTVRAL S TU DENTS 
 
 blue with solution of litmus, and titrate with the dilute sul- 
 phuric acid of known strength. Use all the precautions 
 described on p. 71, being particularly careful to boil off 
 the carbonic acid gas set free, as this, while in solution, is acid 
 to litmus. Having obtained concordant results, calculate from 
 the sulphuric acid employed the amount of sodium in the 
 carbonate of sodium taken (remembering that sulphate of 
 sodium has the formula Na 2 S0 4 ). Does it correspond with 
 the formula Na 2 C0 3 , and if so, do the proportions of carbon- 
 ate of sodium and sulphuric acid used correspond with the 
 equation : — 
 
 Na 2 CO, + H 2 S0 4 - Na 2 S0 4 + C0 2 + H 2 ? 
 
 Although carbonic acid gas is only slightly soluble in water under 
 ordinary atmospheric pressure, there is evidence that it does combine to 
 form an unstable carbonic acid, H 2 O.C0 2 or H 2 C0 3 . Thus its solution is 
 acid to litmus, and a bottle of aerated water, i.e. water charged with 
 carbonic acid gas under pressure, does not immediately lose all its excess of 
 the gas when opened, but the bubbles keep rising to the surface, especially 
 when the liquid is agitated or warmed, for a considerable time, indicating 
 that the acid is only slowly decomposed into its anhydride and water. In 
 its instability, carbonic acid resembles silicic acid and sulphurous acid. 
 
 Special attention must be drawn to the fact that carbonates neutralise 
 acids like free bases. The statements with respect to the use of lime in 
 promoting nitrification in the soil (p. 93) will therefore hold good for 
 chalk. Again, with regard to the incompatibility of manures, to mix chalk 
 with "superphosphate of lime" would be as undesirable as to mix lime 
 with it. 
 
 Through some lime water pass a current of carbonic acid 
 gas. Note that the precipitate of chalk first formed gradually 
 disappears, and a clear solution is at length obtained. Heat a 
 portion of the clear liquid. Note that bubbles of carbonic 
 acid gas are set free, and simultaneously the chalk is precipi- 
 tated. To another portion add some lime water, and note that 
 this also precipitates chalk. The simplest explanation of these 
 reactions is that a soluble acid-carbonate of calcium is formed, 
 
THE CARBONATES til 
 
 which is decomposed by heat, and acted upon by lime, as 
 
 represented in the equations : — 
 
 CaC0 3 + H 2 C0 3 = CaH 2 2C0 3 
 CaH 2 2C0 3 = CaC0 3 + H 2 4 C0 2 
 CaH 2 2C0 3 + Ca20H = 2 CaC0 3 + 2 H 2 0. 
 
 Hardness of Water. — Although the acid carbonate of calcium has, 
 owing to its instability, never been isolated, the acid carbonates or 
 "bicarbonates" of sodium and potassium are well-known and stable salts. 
 (These are produced by passing carbonic acid gas into cold saturated 
 solutions of the carbonates ; they are decomposed into the carbonate and 
 carbonic acid when warmed.) There is therefore good reason to believe that 
 the calcium compound can also exist in solution. Its probable existence 
 affords an explanation of the hardness of spring water which prevents the 
 lathering of soap until all the lime has been deposited as a curd. Such 
 water deposits its chalk on the sides of the kettles or boilers in which it is 
 heated in the form of " fur" ; hence, when the hardness is due to dissolved 
 chalk, it is said to be "temporary." To soften such water on a large 
 scale, lime may be placed in the reservoirs used for storing it. The hard- 
 ness of spring water may also be due to dissolved sulphates or chlorides 
 of calcium and magnesium, especially the sulphate of calcium. These salts 
 are, of course, not precipitated by boiling, and the hardness they produce is 
 said to be " permanent." To soften such water on a small scale, carbonate 
 of sodium may be added, which, in absence of dissolved carbonic acid, 
 completely precipitates the lime or magnesia as carbonate, thus : — 
 
 Na 2 C0 3 + CaS0 4 = Na 2 S0 4 + CaC0 3 . 
 As already pointed out on p. 30, spring water obtains its dissolved 
 salts from the soil or rock strata through which it passes. Owing to the 
 carbonic acid in rain water, much of the chalk contained in spring or river 
 water is dissolved from the soil, a fact that explains the necessity of the 
 application of lime or chalk every few years on most land. 
 
 The only other carbonate that need be examined is the 
 carbonate of ammonium. Procure a specimen of " lump 
 ammonia." Notice that it smells strongly of ammonia, 
 showing that even at the ordinary temperature it dissociates 
 into ammonia and carbonic acid. Dissolve a little in water, 
 and to the solution add a solution of gypsum. Note that 
 chalk is precipitated : — • 
 
 (NH 4 ) 2 C0 3 + CaS0 4 =-- (NH 4 ) 2 S0 4 + CaC0 3 
 
1 1 2 CUE MIS TR Y FOR A GR1CUL TURAL STUDENTS 
 
 Now mix some dry sulphate of ammonium and chalk together, 
 and warm the mixture. Note that ammonia is evolved. On 
 testing the residue it will be found to contain gypsum. Hence 
 the reverse change has now occurred, and — 
 
 (NH 4 ) 2 S0 4 + CaC0 3 = (NH 4 ) 2 C0 3 + CaS0 4 . 
 
 Explain why, under different conditions, the reaction should 
 be reversed. 
 
 Both these reactions are of agricultural importance. When, from a 
 fermenting manure heap, ammonia is found to be escaping, it is customary 
 to sprinkle the heap with gypsum to "fix" the ammonia, in accordance 
 with the first reaction. The occurrence of the second reaction shows the 
 inadvisability of mixing together a salt of ammonia with any substance 
 containing chalk previous to its application as a manure. 
 
 XXVIII. CONCLUSIONS 
 
 In Part I. it was observed that, in the case of certain oxygen 
 compounds, the elements were united in unalterable propor- 
 tions. In Part II. this observation has been extended to so 
 large a number of other compounds of various elements that 
 it may be stated as a primary law of chemical combination 
 that elements unite in definite proportions by weight. These 
 proportional weights, compared with hydrogen as unity, are 
 termed the combining weights of the elements. 
 
 It has, however, been noticed that elements frequently unite 
 in more than one proportion by weight, and it is consequently 
 difficult to assign fixed combining weights. There is, however, 
 always a simple relationship between the proportions, so that, 
 taking one of the proportions in which each element enters into 
 combination as the combining weight, it may be stated as a 
 second law of chemical combination, that elements unite in the 
 
CONCLUSIONS 
 
 "3 
 
 proportion of their combining weights, or in simple multiples of 
 these weights. 
 
 It has been found possible to derive the probable composi- 
 tion of a compound of two elements, by the proportion in which 
 each unites with a third. In other words, tivo elements usually 
 unite with a third in the proportion in which they unite with 
 each other. In the case referred to, a fourth element was 
 introduced, thus : — 
 
 Lead unites with oxygen in the proportion of 
 
 Oxygen „ hydrogen „ „ 
 
 Hydrogen „ chlorine „ „ 
 
 Therefore, 
 
 Chlorine „ lead „ „ 71:206 
 
 206 : 16 
 16 : 2 
 2 : 71 
 
 Pb ► o 
 
 ! I 
 
 Cl 2 < H 2 
 
 Fig. 45. 
 
 To explain these facts of chemical combination, it is con- 
 ceived that when elements combine, it is their ultimate particles 
 or atoms that unite with each other, and that the relative weights 
 of these atoms are the combining weights of the elements. Thus, 
 if the weights of atoms of oxygen and nitrogen be 16 and 14 
 times respectively the weight of an atom of hydrogen, oxygen 
 and nitrogen will combine in the proportion of these weights, 
 or in simple multiples of them. 
 
 The laws of chemical combination have been found to hold 
 good for compounds as well as elements. Thus, hydrochloric 
 acid combines with ammonia in definite proportions. There 
 is physical evidence that of both elements and compounds 
 there are ultimate particles or molecules indivisible, without 
 altering their nature. A molecule of hydrochloric acid must 
 8 
 
1 14 CHEMISTR Y FOR A GRICUL TURAL S TU DENTS 
 
 be a compound of atoms of hydrogen and chlorine, a molecule 
 of ammonia must be a compound of atoms of hydrogen and 
 nitrogen, and the weight of each must be the sum of the 
 weights of its component atoms. If, then, the weight of a 
 molecule containing an atom of hydrogen and an atom of 
 chlorine be 36.5 times the weight of an atom of hydrogen, 
 and the weight of a molecule containing three atoms of 
 hydrogen and one atom of nitrogen be 17 times that of an 
 atom of hydrogen, the proportions in which hydrochloric acid 
 and ammonia will combine will also be 36.5 : 17. This was 
 found by experiment to be the case. 
 
 The relative densities of four gases have been determined. 
 It is noticeable that the ratio of the relative densities of the 
 two compound gases, ammonia and carbon dioxide, is also the 
 ratio of the calculated molecular weights : — 
 
 Relative Density. Molecular 
 Air=i Hydrogen = 1 Weight. 
 
 Ammonia .589 8.5 17 
 
 Carbonic acid gas 1.524 22 44 
 
 Hydrogen .069 1 (2) 
 
 Nitrogen .970 14 (28) 
 
 This is found to be true of other volatile compounds, and 
 can only be explained by supposing that equal volumes of gases 
 contain an equal number of molecules (Avogadro's hypothesis). 
 Now the molecular weights of ammonia and carbon dioxide 
 are exactly double the densities compared with hydrogen as 
 unity ; and the relative densities of all gases being as the mole- 
 cular weights, it follows that the molecular weights of all other 
 gases must be double their relative densities. There is 
 abundant reason for believing that Avogadro's hypothesis holds 
 good for gaseous elements as well as gaseous compounds. 
 This being so, the molecular weights of hydrogen and nitrogen 
 must be 2 and 28 respectively, and therefore double the atomic 
 
CONCLUSIONS 
 
 "5 
 
 weights, or, in other words, the molecules of hydrogen and 
 nitrogen must each contain two atoms (H 2 and N 2 ). 
 
 This observation that the relative density is always half the 
 molecular weight is of use in determining the molecular com- 
 position of volatile substances. For instance, nitric oxide 
 might have the composition represented by either of the 
 formulae NO and N 2 2 . But the relative density is found 
 by experiment to be 15. Hence the molecular weight is 30, 
 and this corresponds with the formula NO. It also makes it 
 possible to calculate the weight of any volume of gas, if the 
 molecular weight be known, from the weight of a liter of hydro- 
 gen ( = .0896 grams when measured at o° C. and 760 m.m.). 
 For instance, the calculated molecular weight of ammonia 
 (NH 3 ) is 17. The weight of a liter of ammonia gas at o° and 
 
 760 m.m., will therefore be '—^ — ^-11=. 7616 grams. 
 
 2 
 
 In the foregoing studies it has been observed that the non- 
 metallic elements form compounds with hydrogen. These 
 substances differ in their composition : — 
 
 Hydrobromic acid HBr 
 
 Sulphuretted hydrogen H 2 S 
 
 Phosphoretted hydrogen PH 3 
 
 Silicon hydride SiH 4 
 
 Those elements which combine with one, two, three, and 
 four atoms of hydrogen are termed, respectively, univalent, 
 bivalent, trivalent, and quadrivalent. The metallic elements 
 have less tendency to combine with hydrogen, but they com- 
 bine with chlorine, which is univalent ; and they combine 
 with oxygen and sulphur, which are bivalent; so that their 
 valency is easily determined. Thus, sodium and potassium 
 are univalent, for they form the compounds Na'O', K'O', 
 Na 2 '0" and K 2 '0". Calcium, barium, magnesium, zinc, lead, 
 copper, and mercury are bivalent, for they form the com- 
 pounds Ca"0", Ba"Cl 2 ', Mg"Cl 2 ', Zn"0", Pb"0", Cu"S", Hg"0". 
 
 Hydrochloric acid 
 
 HC1 
 
 Water 
 
 H 2 
 
 Ammonia 
 
 NH 3 
 
 Marsh gas 
 
 CH 4 
 
1 1 6 CHEMISTR Y FOR A GRIC UL TURAL STUDENTS 
 
 Aluminium appears to be trivalent, for it forms the compound 
 A1 2 '"0 3 ". Frequently the elements have more than one valency, 
 for iron forms ferrous and ferric chlorides, Fe"Cl 2 ' and Fe"' Cl 3 \ 
 Groups of elements act like elements. Thus NH 4 , OH and 
 N0 3 are univalent like K and CI, forming (NH 4 )'C1', Na'(OH)' 
 and H'(N0 3 )' j CO s and S0 4 are bivalent, forming Na 2 '(C0 3 )" 
 and Ca"(S0 4 )"; P0 4 is trivalent, forming H 3 '(P0 4 )"' and 
 Ca 3 "2(P0 4 )'"; Si0 4 is quadrivalent, forming Na 4 '(Si0 4 )"". 
 
 This study of a few of the more important elements has shown 
 that they fall into groups having certain properties in common. 
 Of these groups may be mentioned potassium and sodium ; 
 calcium, strontium, and barium ; zinc and magnesium ; chlorine, 
 bromine, and iodine ; oxygen and sulphur ; nitrogen and phos- 
 phorus. The properties common to the elements of each group 
 are both physical and chemical, e.g. softness, density, oxidisa- 
 bility, solubility of salts, and valency, and therefore the composi- 
 tion of compounds. When three or more elements exist in a 
 group, it is found that the properties vary as the atomic weights. 
 Thus strontium has an atomic weight intermediate between 
 those of calcium and barium ; its properties, and the properties of 
 its compounds, are also intermediate. Bromine has an atomic 
 weight intermediate between those of chlorine and iodine; 
 chlorine is a gas, iodine a solid, and bromine a liquid. When 
 all the known elements are arranged in the order of their 
 atomic weights, it is found there is a periodic recurrence of 
 similar properties, so that if each period be placed one under 
 the other, the elements fall into groups (the elements men- 
 tioned above are arranged as they arrange themselves in these 
 groups); and it is possible even to foretell the properties of 
 any element by its atomic weight, and the position it would 
 therefore assume in relation to other elements. These facts 
 are mentioned, because it should be realised that the reactions 
 and properties of the substances studied in the foregoing 
 pages are not haphazard, but the result of this periodicity of 
 properties depending on the atomic weights. 
 
QUESTIONS AND PROBLEMS 117 
 
 QUESTIONS AND PROBLEMS FOR REVISION AND 
 EXAMINATION. 
 
 Basic Oxides, Acid Oxides, and Salts. 
 
 1. How are the oxides of magnesium and potassium distinguished from 
 
 the oxides of phosphorus and sulphur ? 
 
 2. What happens when a solution of a basic oxide is exactly neutralised 
 
 by a solution of an acidic oxide ? Give examples. 
 
 3. Define a basic oxide, an acidic oxide, and a salt, and give examples 
 
 of each of these classes of chemical compounds. 
 
 4. Give a method of distinguishing a metallic from a non-metallic 
 
 element. 
 
 5. Is the element hydrogen a metal or a non-metal ? Upon what fact 
 
 do you base your answer ? 
 *6. Of the three powders, identify the acidic oxide, the basic oxide, and 
 the salt. (Silica, magnesia, and gypsum.) 
 
 Chemical Properties of the Metals : The Metallic Oxides. 
 
 7. State two methods which may be employed to study the oxidisability 
 
 of the metals. 
 
 8. Compare the action of air in the cold on sodium, potassium, 
 
 magnesium, zinc, iron, copper, and mercury. Why does iron 
 corrode so much more than zinc ? What are tinned and gal- 
 vanised iron? 
 
 9. Describe fully the action of sodium and potassium on water, giving 
 
 the products of the reaction. In what respect does the action of 
 sodium differ from that of potassium, and what does this teach as 
 to the relative attraction of these two elements for oxygen ? 
 
 10. State what are the colours imparted to a non-luminous flame by the 
 incandescent vapours of sodium, potassium, calcium, strontium, 
 and barium compounds. When the colour of potassium vapour is 
 masked by that of sodium, how should the flame be viewed to 
 render the former colour visible ? 
 
 n. Explain the use of the spectroscope for identifying the incandescent 
 vapours of metals. 
 
 12. If in their oxidisability, calcium, barium, and strontium are inter- 
 
 mediate between sodium and magnesium, what should be their 
 behaviour towards air and water ? 
 
 13. State whether magnesium, zinc, and iron are combustible, and under 
 
 what conditions (if any) they attack water. Describe the experi- 
 ments made upon the subject. 
 
1 18 CHEMISTR Y FOR A GRICUL TURAL STUDENTS 
 
 14. Under what conditions (if any) can copper, mercury, silver, gold, and 
 
 platinum be oxidised? What experiment can you cite to show 
 that heated copper has no action on steam? 
 
 15. Distribute the metals barium, calcium, copper, gold, iron, 
 
 magnesium, mercury, potassium, sodium, strontium, and zinc, into 
 five groups, and ascribe a name to each group. 
 
 16. What is meant by the terms "alkali" and "alkaline earth"? 
 
 Why are gold and silver described as noble metals ? 
 
 17. Give two or three instances of the grouping of metals holding good 
 
 not only for oxidisability, but also for the solubility of the oxides, 
 and for the specific gravity, fusibility, malleability and ductility, 
 or conductivity of the metals. 
 
 18. Give an instance of metals of the same group occurring together in 
 
 nature. What metals are found in the free state in nature ? 
 
 What are the minerals loadstone, haematite, emery, tinstone, and 
 
 pyrolusite ? 
 *I9. To what group should the metal be ascribed, as judged by its 
 
 oxidisability? (Tin.) 
 *20. Identify the metal in the salt by the colour of its incandescent vapour. 
 
 (Sodium, potassium, calcium, strontium, or barium.) 
 *2i. Is the metallic oxide an "alkali," an "alkaline earth," or an 
 
 "earth"? (Soda, potash, lime, baryta, magnesia, or oxide of 
 
 zinc.) 
 
 The Metals: their Physical Properties. 
 
 22. What is an alloy ? Is the property of forming alloys possessed by all 
 
 the elements ? Why are gold and silver alloyed with copper for 
 purposes of coinage ? Why are tin and lead alloyed for use as 
 solder ? 
 
 23. What do you understand by the malleability and ductility of metals ? 
 
 Name the most malleable and one of the most ductile of metals. 
 
 24. Are metals as a rule good or bad conductors of heat and electricity ? 
 
 Name two of the best conductors. 
 
 25. Give an instance of the expansion of metals by heat and its effect 
 
 upon any structure or instrument. 
 
 26. Why should a mercurial thermometer be so sensitive to rapid changes 
 
 of temperature ? 
 
 27. Name a metal whose density is less than that of water, and a metal 
 
 whose density is greater than mercury. 
 
 28. Name metals which are (1) liquid at the ordinary temperature, (2) 
 
 fusible below ioo°, (3) fusible below a red heat, (4) fusible at a red 
 heat, and (5) only fusible at a white heat. If one metal be alloyed 
 
QUESTIONS AND PROBLEMS 119 
 
 with another, what is usually the effect upon the melting point ? 
 Give an example. 
 29. Name some soft and some hard metals. How may the relative hard- 
 ness be roughly determined ? What is the effect of I per cent, of 
 carbon in iron upon its hardness, and how may steel be made 
 harder or less hard by " tempering " ? 
 
 Combining Weights of the Elements. 
 
 30. What evidence is there that the same compound always contains the 
 
 same elements in the same proportions by weight ? Give 
 examples. 
 
 31. What evidence is there that two elements can combine in two or 
 
 more proportions? In this case is there any simple relation 
 between the proportions? 
 
 32. What is meant by the " combining weights " of the elements, and 
 
 with what are they compared as unity ? What are the combining 
 weights usually taken for hydrogen, oxygen, carbon, and mercury ? 
 
 33. The proportion in which hydrogen and oxygen are combined in 
 
 water is as I : 8, but the combining weight of oxygen is taken as 
 16 (hydrogen = 1 ). What number of combining weights then of 
 hydrogen and oxygen are combined together in water, and what 
 formula may be employed to express this shortly ? 
 
 34. Carbon combines with oxygen to form carbonic acid gas in the pro- 
 
 portion of 3 : 8. The combining weights of the elements are 12 
 and 16 respectively. Represent the composition of carbonic acid 
 gas by the simplest possible formula. 
 
 35. What does the formula " HgO " mean both as to the elements of the 
 
 compound and their quantities ? 
 
 36. For what elements do the following symbols stand : C, Cu, Fe, H, 
 
 Hg, Mg, Mn, N, Na, P, Pb, K, S, and Si ? 
 *37« Determine the proportions in which silver and oxygen are combined 
 together in the oxide of silver, after first drying in the water oven. 
 
 Composition of the Basic Oxides and Hydrates. 
 
 38. The composition of lime is expressed by the formula CaO ; calculate 
 
 its percentage composition. 
 
 39. From red lead 97.65 per cent, of its weight of litharge is obtained 
 
 on heating. Litharge contains 7.2 per cent, of its weight of 
 oxygen. What are the simplest formulae that will represent the 
 composition of litharge and red lead ? 
 
120 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 40. Two oxides of copper are known having the formulae Cu 2 and 
 
 CuO. How would they be distinguished by name ? An oxide 
 of hydrogen is known having the formula H 2 2 ; it yields oxygen 
 on heating. How would it be distinguished by name from water ? 
 
 41. What happens when quicklime is slaked with water? What 
 
 evidence is there of a compound being formed ? What are com- 
 pounds with water termed ? 
 
 42. Describe the method of determining the composition of slaked lime. 
 
 Describe the construction of the dessicator, and its use. It was 
 found that slaked lime contains 24.3 per cent, of combined water. 
 Express its composition by a formula. 
 
 43. Are the hydrates of metallic oxides usually decomposed by heat? 
 
 What hydrates resist decomposition, even at a red heat ? 
 
 44. When compounds combine, do they, like elements, combine in 
 
 definite proportions ? What relation does the proportion in which 
 they unite bear to the combining weight of the elements of which 
 they are composed ? Give examples. 
 
 45. What is meant by the term " metallic hydroxide " ? Ferric 
 
 hydroxide contains 52.34 per cent, of iron, 44.86 per cent, of 
 oxygen, and 2.80 per cent, of hydrogen. Express its composition 
 by a formula. 
 
 46. Of the two substances one is an oxide and one a hydroxide. Identify 
 
 the hydroxide. (Slaked lime and dried magnesia. ) 
 *47. Determine (1) the free water, (2) the combined water, in the metallic 
 hydroxide. (Calcium hydroxide, undried.) 
 
 The Non-metallic Elements : Sulphur. 
 
 48. How are non-metallic elements distinguished from metallic elements ? 
 
 For what reasons is oxygen classed as a non-metal ? 
 
 49. Describe the several changes that occur when sulphur is heated from 
 
 the solid, through the liquid, to the gaseous state. What occurs 
 when very hot molten sulphur is suddenly cooled, and how is the 
 modification formed distinguished from ordinary sulphur ? What 
 do you understand by '* allotropy "? 
 5^. Describe what happens when sulphur and iron filings are heated 
 together. State your reasons for believing that chemical combina- 
 tion occurs. If the product were a mere mixture, what would 
 be its behaviour to a magnet and to a solvent such as bisulphide 
 of carbon ? What formula expresses the composition of the 
 product ? 
 
QUESTIONS AND PROBLEMS 121 
 
 51. State whether sulphur is found in the free state in nature and where. 
 
 Mention some native metallic sulphides. What is meant by a 
 "double" sulphide? 
 
 52. When iron is treated with dilute acid, hydrogen gas is evolved. 
 
 When sulphide of iron is treated in the same way, what gas is then 
 produced ? What is the composition of this gas by weight ? 
 Express by a formula. 
 
 53. When organic matter containing sulphur decays, what is the product 
 
 of decomposition ? To what is the smell of Harrogate water due ? 
 
 54. What is meant by saying that one element can "replace" another in 
 
 a chemical compound ? Give examples. 
 
 55. What is the product of the combustion of sulphur? Express its 
 
 composition by a formula. When dissolved in water, what com- 
 pound is produced ? 
 
 56. What evidence is there that sulphurous acid becomes changed into 
 
 sulphuric acid by atmospheric oxidation ? 
 
 57. Under what conditions does sulphurous anhydride combine with 
 
 oxygen to form sulphuric anhydride? Illustrate your answer by 
 a drawing of the apparatus that may be used, and express the 
 reaction by an equation. Explain the term "contact action." 
 
 58. Would you regard sulphurous acid as a "stable" or an "unstable" 
 
 compound, and why ? 
 '59. Distinguish the metal from the metallic sulphide. (Iron and sulphide 
 
 of iron.) 
 ^60. Identify the powders. (Sulphur and quicklime.) 
 
 Sulphuric Acid. 
 
 61. In what proportion does sulphuric anhydride combine with water 
 
 forming sulphuric acid ? Is the oil of vitriol of commerce pure 
 sulphuric acid ? 
 
 62. What evidence is there that sulphuric acid itself combines with water ? 
 
 What practical use is made of this ? 
 
 63. Describe fully the method of determining the proportions in which 
 
 caustic soda and sulphuric acid react to form a neutral salt. 
 What is the result obtained ? 
 
 64. Express the neutralisation of caustic soda and sulphuric acid by an 
 
 equation, and state how it was proved that water was set free in 
 quantity corresponding with the equation. 
 *6$. Determine the strength of the sulphuric acid solution by means of 
 caustic soda or caustic potash. 
 
122 CHEMISTR Y FOR A GRIC UL TURAL STUDENTS 
 
 The Sulphates. 
 
 66. What are Glauber's salt, Epsom salt, gypsum, selenite, potash alum, 
 
 white vitriol, green vitriol, and blue vitriol ? Give a general 
 method by which they can all be produced. 
 
 67. What is meant by the "efflorescence" of a salt, and to what is it 
 
 due ? At what temperature is the water of crystallisation of a salt 
 usually given off? What is meant by an "amorphous" substance? 
 
 68. In what respect does plaster of Paris differ from gypsum ? Explain its 
 
 use as a plaster. When is plaster of Paris said to be " dead burnt " ? 
 
 69. In order to obtain a salt in a well-crystallised state, how would you 
 
 proceed? In what form does alum crystallise? Draw a perfect 
 alum crystal. 
 
 70. Name the groups, the metals of which are attacked by dilute sulphuric 
 
 acid. Give one reason why zinc and iron are more easily attacked 
 by dilute sulphuric acid than they are by water. 
 
 71. With what metallic sulphate are the crystals of zinc sulphate iso- 
 
 morphous? In what other respects do the two metals resemble 
 each other ? 
 
 72. What is the action of metals upon strong sulphuric acid when heated ? 
 
 What is meant by an "oxidising" and a "reducing" agent? 
 Give examples. 
 J 3. Discuss the use of the terms "sulphuric acid" and "sulphate of 
 hydrogen," "sulphate of soda" and "sulphate of sodium." In 
 what respects is the term "sulphate of sodium" preferable? 
 
 74. What is meant by "equilibrium" in solution. State what changes 
 
 might take place when the solutions (1) of a base and a salt, (2) 
 of an acid and a salt, and (3) of two salts, are respectively mixed 
 together, and point out what are the circumstances under which there 
 will be no equilibrium, but complete reaction between the mixed sub- 
 stances. Give examples to illustrate each of the six possible cases. 
 
 75. Describe a method for preparing oxide of magnesium from Epsom 
 
 salt ; also for preparing sulphurous anhydride from sulphite of 
 sodium ; also for preparing sulphate of barium and caustic soda 
 from sulphate of sodium and baryta. Give equations. To prepare 
 I gram of copper oxide, how much blue vitrol must be used ? 
 
 *76. Which of the salts contains water of crystallisation? (Sulphate of 
 calcium and sulphate of barium.) 
 
 '77. Identify the salts. (Sodium sulphite and ferric sulphate.) 
 
 ^78. Prepare a specimen of magnesia from the Epsom salt. 
 
 '79. From the copper and sulphuric acid prepare a well - crystallised 
 specimen of copper sulphate. 
 
QUESTIONS AND PROBLEMS 123 
 
 *8o. Determine the water of crystallisation in the sodium sulphate, and 
 ascribe a formula to the crystallised salt. 
 
 Common Salt : Hydrochloric Acid. 
 
 81. What is the characteristic crystalline form of common salt? Is the 
 
 pure substance deliquescent, or to what impurity is the deliques- 
 cence due ? 
 
 82. Hydrochloric acid and common salt not being compounds of oxygen, 
 
 give a definition of acids and salts which will include these two 
 compounds as well as oxygenated compounds. 
 
 83. Hydrochloric acid being volatile, use may be made of the same 
 
 method for its preparation that was found to serve for the prepara- 
 tion of sulphurous acid gas from its compounds. Fully describe 
 such a method of preparation, and give a drawing of the apparatus 
 employed. 
 
 84. What are the properties of hydrochloric acid gas in respect to density, 
 
 combustibility, colour, taste and smell, and solubility in water? 
 Why is it to be expected that the gas would not support com- 
 bustion ? 
 
 85. By what physical method may the strength of a solution of hydro- 
 
 chloric acid be determined ? 
 
 86. How would you prove that caustic soda and hydrochloric acid react 
 
 in accordance with the equation — 
 
 HC1 + NaOH = NaCl + H 2 ? 
 
 87. In what proportion does chloride of sodium exist in sea water ? To 
 
 what are the deliquescent properties of sea salt due ? From what 
 elements are the bromides and iodides derived, which also exist in 
 sea water in very minute quantities ? 
 
 88. Why was chloride of potassium first called "muriate of potash"? 
 
 How may it be prepared from "carnallite," the double chloride of 
 potassium and magnesium? What is "kainite," and for what 
 purpose is it employed ? 
 
 89. How may chlorides be distinguished from the salts of other common 
 
 acids ? 
 '90. Prepare a bottle full of hydrochloric acid gas. 
 '91. Volumetrically determine the strength of the hydrochloric acid 
 
 solution. Confirm by its relative density. 
 '92. Identify the three acids. (Sulphurous, sulphuric, and hydrochloric 
 
 acids. ) 
 '93. Examine the tap water and the drainage water for chlorides and 
 
 sulphates. 
 
I2 4 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Chlorine. 
 
 94. By what general method can hydrochloric acid be made to give up 
 
 its chlorine ? Fully explain the action of, for example, red lead 
 upon it. 
 
 95. Give an account of the preparation of chlorine gas, and represent the 
 
 reaction by which it is formed by an equation. 
 
 96. What are the properties of chlorine in respect to colour, smell and 
 
 taste, density, solubility, and combustibility ? Is it a supporter of 
 combustion to all the elements which burn in air, or only to some 
 of them ? Explain the peculiar flame observed when a lighted 
 taper is thrust into chlorine gas. 
 
 97. Describe fully the action of sunlight upon chlorine water. Is light a 
 
 force which, like heat, can overcome chemical attraction ? 
 
 98. Explain why chlorine is only able to act as a bleaching agent when 
 
 water is present. 
 
 99. What is bleaching powder, how is it made, and of what does it 
 
 consist ? What substances can be used to liberate its chlorine 
 when required as a bleaching agent or disinfectant? 
 100. What is permanganate of potash, ozone, and peroxide of hydrogen ? 
 Why should these substances act as oxidising agents ? Compare 
 their action and that of chlorine with the action of sulphurous acid 
 as bleaching agents. 
 *loi. Of the two liquids one is an oxide, the other the solution of a per- 
 oxide. Identify the peroxide by its action as an oxidising agent. 
 (Water and peroxide of hydrogen solution. ) 
 
 Nitrogen : Ammonia. 
 
 102. Recapitulate the properties of nitrogen gas. What purpose does it 
 
 serve in the atmosphere in respect to combustion? How may 
 nitrogen be obtained from the air? What impurity will such 
 nitrogen contain ? 
 
 103. What compound of nitrogen is produced when nitrogenous organic 
 
 matter decays or is destructively distilled? In what important 
 respect does this compound differ from the corresponding com- 
 pounds of chlorine and sulphur ? 
 
 104. How is ammonia gas prepared ? Why must quicklime, and not oil 
 
 of vitriol, be employed to dry the gas? 
 
 105. Describe the properties of ammonia gas in respect to its colour, 
 
 smell, density, combustibility, and solubility in water. What 
 makes ammonia gas difficult to burn, and how could it be 
 rendered combustible ? 
 
QUESTIONS AND PROBLEMS 125 
 
 106. What is the relative density of ammonia, and how is it determined ? 
 
 107. What is the composition of sal-ammoniac, and how may it be 
 
 determined synthetically ? 
 
 108. What is meant by the term " ammonium," and why is it employed ? 
 
 109. How may ammonium salts be recognised ? 
 no. Prepare a bottle full of ammonia gas. 
 
 in. Determine the strength of the solution of ammonia. 
 
 112. Identify the salts. (Ammonium chloride and barium chloride.) 
 
 Nitric Acid and the Nitrates. 
 
 113. What are saltpetre and Chili saltpetre, and how are they dis- 
 
 tinguished ? 
 
 114. What evidence is there that nitric acid is an oxygenated acid? 
 
 Give the formulae for nitric acid and nitric anhydride. 
 
 115. A solution containing 1 gram of potash (K 2 0) when exactly 
 
 neutralised with a solution of nitric acid and evaporated, leaves a 
 residue weighing 2.149 grams. What formula will represent the 
 composition of the salt ? What reasons are there for supposing 
 that sodium nitrate would have an analogous composition ? 
 
 116. How may nitric acid be prepared? Explain the occurrence of red 
 
 fumes during the process. 
 
 117. For what reason is nitric acid spoken of as a powerful oxidising 
 
 agent ? Illustrate your answer by examples. 
 
 118. What is an explosive? Illustrate your answer by the composition 
 
 and action of gunpowder. 
 
 119. Fully describe the action of nitric acid upon metals. Explain the 
 
 difference in the gaseous products, depending upon the strength 
 of the acid employed ; also the difference in the solid product of 
 the action of tin from that of the action of copper on nitric acid. 
 
 120. Name the three gaseous oxides of nitrogen, express their composition 
 
 by formulae, and state how they may be distinguished from each 
 other and from nitrogen. 
 
 121. What is nitrous acid, and how may it be produced? What is the 
 
 anhydride of nitrous acid, and into what two oxides of nitrogen 
 should this unstable anhydride be decomposed when warmed ? 
 
 122. How may nitrogen gas be prepared from a mixture of solutions of 
 
 sodium nitrite and sal-ammoniac ? Explain the reaction, and 
 state why, when once the temperature is reached at which it 
 begins, no further heating is necessary. 
 
 123. What is the density of nitrogen gas compared with hydrogen as 
 
 unity, and how may it be determined ? 
 
126 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 124. What is the action of ferrous sulphate upon nitric acid? Describe 
 
 how it may be used as a test for nitrates. 
 
 125. What is the action of nitric acid on indigo solution ? Describe how 
 
 it may be used as a test for nitrates. 
 
 1 26. What do you know about the solubility of metallic nitrates ? 
 
 "127. Distinguish the nitrite from the nitrate. (Sodium nitrite and sodium 
 
 nitrate.) 
 *I28. Volumetrically determine the strength of the nitric acid. 
 *I29. Identify the gaseous oxide of nitrogen. (Nitrous oxide, nitric oxide, 
 
 and nitrogen peroxide.) 
 *I30. Prepare a bottle full of nitrogen gas 
 
 Putrefaction and Nitrification. 
 
 131. What is meant by the terms putrefaction and nitrification? 
 
 Account for the nitrate of potassium found as an efflorescence on 
 the soil round an Indian village, the nitrate of calcium crystals on 
 a stable wall, and the deposits of nitrate of sodium in Chili. 
 
 132. What is the danger in the use of water contaminated with sewage 
 
 for drinking purposes ? An analyst's report upon a water is given 
 in terms of "oxygen absorbed," "albuminoid ammonia," 
 "free ammonia," "nitrates," and "chlorine." Discuss the 
 importance of each. 
 
 133. State the conditions that are necessary to promote putrefaction and 
 
 nitrification. How would you apply these conditions (1) to the 
 purification of drinking water, and (2) to the increase in fertility 
 of the soil ? 
 
 134. Of the nitrates or ammonium salts of the soil, which are found 
 
 most abundantly in drainage waters from arable land ? Under 
 what conditions does loss of nitrate from the soil occur most 
 freely, and how may it be prevented? Discuss the use of 
 sulphate of ammonia instead of nitrate of soda as a manure. 
 
 135. Report upon the suitability of the water for drinking purposes. Is 
 
 it almost free from organic matter, nitrates, and chlorides ? 
 
 Phosphorus and Phosphoric Acid. 
 
 136. What compound does phosphorus form with hydrogen? Mention 
 
 two cases in which its production may be observed. 
 
 137. Is phosphorus easily oxidised? Does it oxidise at the ordinary 
 
 temperature ? What is meant by "phosphorescence " ? 
 
QUESTIONS AND PROBLEMS 127 
 
 138. With what explosive mixture are lucifer matches tipped? How are 
 
 safety matches prepared ? What is " amorphous phosphorus " ? 
 
 139. Describe the preparation of phosphoric anhydride. Why must the 
 
 materials and apparatus used be perfectly dry ? What happens 
 when it is mixed with water, and what further change takes place 
 on boiling the liquid ? 
 
 140. Give an account of the experiments made which showed that there 
 
 were three phosphates of calcium. Express their composition by 
 formulae, and state which of them is soluble in water. What is 
 meant by an "acid salt." How may the three salts be dis- 
 tinguished by name? 
 
 141. Of what do bone ash, appatite, and coprolite consist? What is the 
 
 action of sulphuric acid upon them, and of what does the 
 11 superphosphate of lime," thus obtained, consist ? Illustrate the 
 reaction by an equation. 
 
 142. What is meant by " reverted phosphate," and under what conditions 
 
 does reversion take place? For what reason is the ammonium 
 phosphate contained in Peruvian guano likely to be more easily 
 absorbed by crops, when applied as a manure, than super- 
 phosphate of lime ? 
 
 143. What is the source of "basic slag," and of what is it composed ? 
 
 144. Give two methods for identifying phosphoric acid. 
 
 ^145. Find whether the phosphatic material contains soluble or insoluble 
 phosphate, or both. (Superphosphate of lime, bone meal, or 
 guano. ) 
 
 Silica: Sand and Clay. 
 
 146. What is silica, and how may silicon be obtained from it ? Express 
 
 the reaction by an equation. 
 
 147. What is soluble glass, and how may it be prepared ? Illustrate by 
 
 an equation. 
 
 148. What is the action of sulphuric acid upon (1) a weak and (2) a 
 
 strong solution of silicate of sodium ? Compare with the action 
 of sulphuric acid upon a weak and a strong solution of sulphite of 
 sodium. 
 
 149. How may silica be obtained from a solution of silicic acid? What 
 
 are the properties of silica in respect to colour and its solubility 
 in water, acids, and alkalies ? 
 
 150. How does uncombined silica occur in nature? What is the com- 
 
 position of the minerals felspar, mica, china clay, asbestos, 
 meerschaum, and steatite ? 
 
128 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 151. In what proportions does silica exist in its compounds with bases? 
 
 Compare phosphoric anhydride with silica in this respect. 
 
 152. How may silicate of aluminium (clay) be artificially produced? 
 
 What is the distinctive character of the precipitate obtained, and 
 what is the effect (1) of lime upon it, and (2) of heating it ? 
 
 153. What silicates are fusible and what infusible? How may the 
 
 properties of the silicates in this respect be utilised in pottery 
 making? From what are bricks made, and how does the 
 material used differ from that required for tile-making ? 
 
 154. Of what is glass composed ? What silicates render glass " soft" or 
 
 fusible, and what silicates render it ' • hard " or infusible ? To 
 what is the green colour of bottle glass due ? 
 
 155. Of what does soil consist, and how may the proportions of gravel, 
 
 sand, and clay be determined ? 
 
 156. Upon what does the wetness of a soil depend? State what is 
 
 meant by the "capillarity" of a soil. By what means may the 
 porosity of a heavy soil be increased ? 
 "157. Examine the tap water for dissolved silicates. 
 
 Carbon : Marsh Gas. 
 
 158. How are animal and vegetable charcoal prepared, and of what do 
 
 they consist? Describe the process of " charcoal burning." 
 
 159. Name the three allotropic modifications of carbon. Name three 
 
 other elements already studied which exist in allotropic forms. 
 Which modification of carbon exists in lamp-black, coke, and 
 gas carbon, and how is each of these substances produced ? 
 
 160. Upon what does the use of " bone-black" as a decoloriser depend ? 
 
 What is the purpose of the block of animal charcoal used in a 
 charcoal filter? 
 
 161. Explain the power possessed by wood charcoal of absorbing gases. 
 
 Describe experiments which show its porosity and absorptive 
 power. How does this explain the use of charcoal as a deodoriser 
 and disinfectant? What relation exists between the condensibility 
 of gases, their solubility, and their absorption by charcoal ? 
 
 162. What is marsh gas, and how is it produced in nature? Explain the 
 
 danger of " fire - damp " in coal mines. What is meant by 
 
 " destructive distillation," and from what substances can impure 
 
 marsh gas be produced by this means ? 
 •163. Determine the percentage of ash in the charcoal. 
 "164. Determine the percentage increase of weight of wood charcoal 
 
 (previously heated to redness in a tube) on exposure to air. 
 
QUESTIONS AND PROBLEMS 129 
 
 "165. Identify the solids. (Powdered charcoal, black oxide of manganese, 
 and black oxide of copper. ) 
 
 The Oxides of Carbon. 
 
 166. Describe the method of preparation of carbonic acid gas. Explain 
 
 why carbonates are decomposed by hydrochloric acid. When 
 chalk or marble are used, why should hydrochloric, and not 
 sulphuric, acid be employed ? 
 
 167. To what substances does carbonic acid gas act as a supporter of 
 
 combustion? State whether potassium and sodium would burn 
 in the gas if magnesium is able to do so. Represent the reaction 
 that would occur by an equation. 
 
 168. Describe the reaction that occurs when carbonic acid gas is passed 
 
 over heated charcoal. Explain the occurrence of a blue flame 
 over a coke fire. What is the danger in the use of slow combus- 
 tion stoves ? What are " producer gas " and " water gas " ? 
 
 169. What are the properties of carbon monoxide? How is it distin- 
 
 guished in (1) properties and (2) percentage composition from 
 carbon dioxide ? 
 
 1 70. Describe the use of carbon as a reducing agent of metallic oxides. 
 
 State how the reduction may be carried out on a small scale, and 
 name some of the metals which are produced by this means on a 
 large scale. In the case of the metallurgy of magnesium from 
 magnesium chloride, what reducing agent is employed ; and in the 
 case of mercury, why is no reducing agent necessary ? 
 
 *i7i. Distinguish the three gaseous compounds of carbon from each other. 
 (Marsh gas, carbon monoxide, and carbon dioxide.) 
 
 *I72. Identify the three gases. (Oxygen, hydrogen, nitrogen, ammonia 
 [nitrous oxide, nitric oxide, nitrogen peroxide], sulphur dioxide, 
 sulphuretted hydrogen, chlorine, hydrochloric acid gas, marsh 
 gas, carbon monoxide, carbonic acid gas, or air.) 
 
 *i73. The oxide is believed to be either ferric oxide or an oxide of lead, 
 To distinguish, reduce with carbonate of sodium on charcoal by 
 means of a blow-pipe. Lead will give soft metallic globules, 
 iron a black magnetic powder. 
 
 The Carbonates. 
 
 174. In what proportion is lime combined with carbonic acid gas in 
 chalk? Calculate what weight of quicklime is obtained from 100 
 tons of chalk, and what weight of dry slaked lime will it yield ? 
 
 9 
 
1 30 CHE MIS TR Y FOR A GRIC UL TCRA L S TU DENTS 
 
 175. Mention some of the important metallic carbonates occurring in 
 
 nature. In what geological forms does carbonate of calcium 
 exist, and how is lime obtained from them on the large scale ? 
 
 176. What is meant by dissociation ? Illustrate your answer by examples, 
 
 and give examples of chemical decomposition which are not 
 cases of dissociation ? 
 
 177. What is mortar, and why does it "set"? What are "hydraulic" 
 
 cements, and what is the cause of the " setting " of these ? 
 
 1 78. Express the composition of carbonate aud bicarbonate of sodium by 
 
 formula?. State whether the carbonates of the alkali metals 
 (including ammonium) are soluble in water, and whether any 
 other metallic carbonates are soluble. State also whether the 
 alkaline carbonates can be dissociated by heat, and whether 
 carbonates of other classes of metals resist dissociation. 
 
 1 79. What evidence is there for the existence of carbonic acid ? Has it 
 
 ever been obtained in the pure state ? What other unstable acids 
 does carbonic acid resemble in composition and properties ? 
 
 1 80. What would be the effect of mixing together the soluble phosphate 
 
 of calcium and chalk ? Illustrate by an equation. 
 
 181. When carbonic acid gas is passed into water containing suspended 
 
 chalk, the chalk dissolves. To what is this due ? What happens 
 when the liquid is boiled or mixed with an alkali ? 
 
 182. To what is the hardness of spring water due ? Why is the hardness 
 
 sometimes called "temporary," sometimes "permanent"? How 
 may water, both temporarily and permanently hard, be softened ? 
 Illustrate by equations. 
 
 183. Describe the properties of carbonate of ammonium. What occurs 
 
 when solutions of carbonate of ammonium and gypsum are mixed 
 together, and when dry sulphate of ammonium and chalk are 
 warmed together ? Explain the reason of the occurrence of both 
 reactions. 
 
 *i84. By titrating with standardised sulphuric acid, determine whether the 
 salt is carbonate of potassium or carbonate of sodium. 
 
 *i85. Determine the percentage of carbonate in the bicarbonate by 
 strongly heating a weighed quantity till no further loss in weight 
 occurs. 
 
 *i86. Estimate the carbonates in the tap water by means of standardised 
 sulphuric acid. Express the result as milligrams of calcium 
 carbonate per liter. 
 
 "187. Identify the salts of calcium. (Calcium sulphate, bleaching powder, 
 calcium phosphate, calcium dihydrogen phosphate, calcium car- 
 bonate, calcium silicate, calcium choride.) 
 
QUESTIONS AND PROBLEMS 131 
 
 The Metals and their Salts. 
 I. Potassium and Sodium. 
 
 188. Mention the principal compounds of potassium and sodium occurring 
 
 in nature. 
 
 189. Describe the principal physical and chemical properties of the two 
 
 metals, pointing out how they are distinguished from other metals, 
 and how they differ from each other. 
 
 190. Suggest a method for preparing the hydroxides (1) from the metals, 
 
 (2) from the carbonates. Can the oxides be obtained from the 
 hydroxides by heating? 
 
 191. Represent the composition of the carbonates and bicarbonates by 
 
 formulae. How may the latter be prepared from the former? 
 Calculate the percentage loss in weight when the bicarbonates are 
 heated. Name one of the principal sources of carbonate of 
 potassium. 
 
 192. Mention some of the principal sources of common salt. Illustrate 
 
 its crystalline form by a drawing. How may chloride of potassium 
 be obtained from carnallite? Are the crystalline chlorides of 
 potassium and sodium hydrated or anhydrous salts ? 
 
 193. How may the sulphates of potassium and sodium be prepared from 
 
 (1) the metals, (2) the hydroxides, (3) the carbonates, (4) the 
 chlorides, (5) the sulphites, and (6) the nitrates? Represent each 
 reaction by an equation. Represent the composition of Glauber's 
 salt by a formula. 
 
 194. What are the principal natural sources of the nitrates of potassium 
 
 and sodium ? Give several methods for their artificial preparation. 
 State the principal uses to which these two nitrates are put. 
 
 195. Give formulae for the three phosphates of potassium and sodium, and 
 
 state how each could be prepared. 
 
 196. How is soluble glass prepared, and of what does it coicist? In 
 
 what respect does glass containing sodium silicate differ from 
 glass containing potassium silicate ? 
 
 197. By what test may the salts of potassium and sodium be distinguished 
 
 from each other, and from the salts of all other metals ? 
 
 198. In respect to the solubility of their salts, how are the metals of the 
 
 alkalies distinguished from the metals of all other groups? 
 
 2. Calcium. 
 
 199. Name the most abundant compounds of calcium occurring in nature. 
 
 200. How is the metal calcium distinguished in its chemical properties 
 
 from the metals potassium and sodium, and magnesium and zinc ? 
 
 201. How are the oxide and hydroxide of calcium prepared on the large 
 
132 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 scale? Compare the solubility of the hydroxide with that of 
 caustic soda and magnesia. What purpose does the lime serve 
 in mortar and hydraulic cement? 
 
 202. Name the principal natural forms of calcium carbonate. How may 
 
 the carbonate be produced by precipitation from (i) lime water 
 and (2) chloride of calcium solution ? What evidence is there of 
 the existence of a bicarbonate of calcium ? Give two methods for 
 softening water containing the dissolved bicarbonate. Illustrate 
 by equations. 
 
 203. Describe a method for producing chloride of calcium. Name its 
 
 characteristic property, and state for what purpose it may there- 
 fore be used. 
 
 204. How does sulphate of calcium occur in nature ? How is plaster of 
 
 Paris prepared, and what is the explanation of its use as a plaster ? 
 Compare the solubility of sulphate of calcium with that of the 
 sulphates of sodium and magnesium. When water is permanently 
 hard with calcium sulphate, how may it be softened ? Illustrate 
 by equations. 
 
 205. Name some of the natural sources of calcium phosphate. Explain 
 
 the action of acids, e.g. hydrochloric, sulphuric, and phosphoric 
 acid, upon calcium phosphate, expressing the reaction by 
 equations. What is " superphosphate of lime " ? What is the 
 action of chalk on superphosphate ? 
 
 206. Give some methods for the preparation of calcium silicate. Explain 
 
 the solubility of freshly precipitated calcium silicate in dilute 
 acids. Is calcium silicate a fusible salt ? 
 
 207. Name a test by which calcium salts may be distinguished. 
 
 3. Magnesium. 
 
 208. Name the principal natural sources of magnesium, and describe the 
 
 physical and chemical properties of the metal. 
 
 209. How may magnesia be prepared (1) from the metal, (2) from the 
 
 carbonate, (3) from any soluble salt ? Describe its properties. 
 
 210. How may magnesium carbonate be prepared ? 
 
 211. What is the distinctive property of magnesium chloride? 
 
 212. Give the formula for Epsom salt, and name the salt of another 
 
 metal with which it is isomorphous. 
 
 213. Name some naturally occurring silicates of magnesium. 
 
 214. By what test may soluble magnesium salts be identified? 
 
 4. Iron. 
 
 215. Name the principal ores of the metal iron. 
 
 216. How may the metal be isolated from its oxide? Give the physical 
 
QUESTIONS AND PROBLEMS 133 
 
 and chemical properties of iron. What is steel, and how is it 
 tempered ? In the conversion of impure iron into steel by the 
 Bessemer process how is phosphorus eliminated ? 
 
 217. How may ferrous sulphate be prepared from metallic iron? Give 
 
 the formula of the crystallised salt. How may ferric sulphate be 
 obtained from ferrous sulphate ? Illustrate by equations. 
 
 218. Similarly describe how ferrous and ferric chloride may be prepared. 
 
 What is the difference in colour between soluble ferrous and ferric 
 salts ? 
 
 219. How may ferrous and ferric oxide be respectively obtained from 
 
 soluble ferrous and ferric salts ? State also how ferric oxide may 
 be prepared from (1) metallic iron, (2) ferrous oxide, and (3) ferric 
 carbonate. 
 
 220. How may ferrous sulphide be prepared (1) from metallic iron and 
 
 (2) from a soluble ferrous salt? Explain the action of dilute 
 acids upon ferrous sulphide. 
 
 5. Manganese. 
 
 221. Name one of the principal ores of manganese. 
 
 222. Mention three oxides of manganese, and state whether all are basic. 
 
 If not, state which is the basic and which the acidic oxide of the 
 three. 
 
 223. Which of the oxides yield oxygen on heating, and act as oxidising 
 
 agents? What is the action of each on hydrochloric acid? 
 ' Illustrate by equations. 
 
 224. Express the composition of potassium permanganate by a formula, 
 
 and state how much "available " oxygen it possesses when acting 
 as an oxidising agent. 
 
 6. Aluminium. 
 
 225. How does aluminium occur in nature ? 
 
 226. Describe the chemical and physical properties of the metal. 
 
 227. How does alumina occur in nature, and how can it be prepared 
 
 from alum ? How is alumina distinguished from the other basic 
 oxides met with in agriculture ? 
 
 228. Judging from the analogous production of a sulphate from a carbonate, 
 
 how should it be possible to prepare aluminium sulphate from 
 the silicate ? What is alum, and how may it be prepared from 
 aluminium sulphate ? Illustrate by equations. 
 
 229. Name some of the principal silicates of aluminium occurring in 
 
 nature. What property does this salt possess that renders it of 
 value in pottery making? What is essentially the chemical 
 change in the burning of bricks ? 
 
134 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Conclusions. 
 
 230. State the three laws of chemical combination. Illustrate them by 
 
 examples. 
 
 231. What is meant by an "atom," and how does the assumption of the 
 
 existence of atoms help us to understand each of the three laws of 
 chemical combination ? Illustrate your answer by examples. 
 
 232. What is meant by a " molecule " ? Calculate the molecular weights of 
 
 water, sulphuric acid, and alum, assuming that the formulae given 
 for these compounds represents the number of atoms in each 
 molecule. 
 
 233. The laws of chemical combination have been found to hold good for 
 
 compounds as well as elements. How does the assumption of 
 the existence of molecules help us to understand this ? Illustrate 
 your answer by examples. 
 
 234. What is the constant relation between the relative densities of gaseous 
 
 compounds and their molecular weights ? State the hypothesis 
 which renders this relation intelligible. Upon what grounds do 
 we assign the molecular formulae H 2 and N 2 to hydrogen and 
 nitrogen ? 
 
 235. The molecular formula of a certain gas is C 2 H 6 . What should be 
 
 its relative density (H = 1) ? 
 
 236. The relative density of nitric oxide gas is 15. Is its molecular 
 
 formula NO or N 2 2 ? 
 
 237. Ozone is described as an allotropic modification of oxygen. Its 
 
 relative density is 24. What is its molecular relation to oxygen 
 gas? 
 
 238. What volume of hydrogen gas at o° and 760 m.m. will be produced 
 
 by dissolving 6.5 grams of zinc in dilute sulphuric acid ? 
 
 239. What volume of oxygen gas at 15 and 740 m.m. can be obtained 
 
 by heating 1 gram of red oxide of mercury ? 
 
 240. What volume of hydrogen gas at ioo° will unite with 10 c.c. of 
 
 oxygen gas at the same temperature, and what volume of water 
 vapour at ioo° will be produced ? 
 
 241. When 1 c.c. of water at 4 C. is converted into steam at ioo° C, 
 
 what volume will the steam occupy under normal atmospheric 
 pressure? 
 
 242. To obtain 1 liter of chlorine gas, at 15 and 750 m.m., from hydro- 
 
 chloric acid, what weight of black oxide of manganese must be 
 employed ? 
 
 243. What is meant by "valency"? State the valency of chlorine, 
 
 nitrogen, carbon, and oxygen, illustrating your answer by the 
 formulae of compounds these elements form with hydrogen. 
 
QUESTIONS AND PROBLEMS 135 
 
 244. How would you deduce the valency of elements which do not unite 
 
 with hydrogen? Give examples of univalent, bivalent, and 
 trivalent metals. Name some metals which have more than one 
 valency, as shown by the existence of two series of salts. 
 
 245. Give examples of univalent, bivalent, trivalent, and quadrivalent 
 
 groups of elements or "radicles," and illustrate each by examples. 
 
 246. Write the formulae for calcium nitrate, aluminium phosphate, 
 
 ferrous carbonate, cupric silicate, and ammonium sulphite. 
 
 247. The properties of the elements are said to be dependent upon their 
 
 atomic weights. Illustrate this by the variation in properties 
 between the elements of (1) a group of metals and (2) a group of 
 non-metals. 
 
 248. Tabulate the chlorides, hydroxides, oxides, sulphides, nitrates, 
 
 sulphites, sulphates, carbonates, phosphates, and silicates of 
 hydrogen, ammonium, potassium, sodium, calcium, magnesium, 
 iron (ferrous and ferric), and aluminium, referred to in the fore- 
 going studies. Use the formulae, not the names of the 
 compounds. 
 "249. Determine the relative density of carbon monoxide (H = i), and 
 from this calculate the molecular weight. Does it correspond 
 with the formula CO ? 
 
PART III 
 
 XXIX. THE CARBOHYDRATES 
 
 In studying the chemistry of the principal constituents of the 
 earth's crust, oxygen is the element to which direction is 
 constantly directed : it is the oxides of the elements, and the 
 compounds of these oxides with each other, which form ks 
 principal constituents ; it is the properties and composition of 
 the oxides which especially serve to differentiate the elements. 
 In studying the chemistry of the animal and vegetable king- 
 doms, carbon is the element round which interest centres, and 
 it is the compounds of carbon with hydrogen, oxygen, and 
 nitrogen, obtained directly or indirectly from animal or veget- 
 able products, with which Part III. of these studies will 
 especially deal. If any dry animal or vegetable substance be 
 heated in a test-tube the substance chars, indicating that 
 carbon is a constituent. 
 
 With respect to the constituents of plants, there are three 
 substances especially characteristic, viz. — (i) cellulose, the 
 substance of which the fibre of plants mainly consists, and 
 which constitutes the membrane of the cells ; (2) starch, a 
 granular substance produced by all green plants, and deposited 
 in large quantities in the root, stem, or seed of certain plants ; 
 and (3) sugar, a soluble substance existing in the sap. Dry 
 specimens of these in the water oven and then heat in test- 
 tubes. Note that they decompose, charcoal and water being 
 produced, showing that carbon, hydrogen, and oxygen are 
 
 136 
 
THE CARBOHYDRATES 137 
 
 constituents. Prepare a strong warm solution of cane sugar. 
 Place it in a large beaker standing upon a plate, and pour in 
 concentrated sulphuric acid. Note that charcoal is set free, 
 the combined water being withdrawn by the acid. Analysis 
 shows that each substance consists of hydrogen and oxygen, 
 in the proportion in which they form water, combined with 
 carbon. They are therefore termed carbohydrates. 
 
 Examine some starch grains under a microscope. Note the 
 shape, the nucleus, and concentric markings. To a little 
 starch add a drop of solution of iodine in solution of iodide 
 of potassium. Note the deep blue coloration, due to the 
 formation of an iodide of starch. Test for starch by this 
 method in a sliced potato, wheat grains, a turnip, and any 
 other vegetable substance, and note in what variable quantities 
 the starch is present. Shake a few grains of starch with cold 
 water in a test-tube, then boil till the starch granules, which 
 swell and burst, have become completely mingled with the 
 water, and a thin starch paste or mucilage has been produced. 
 Dilute a portion of this with water, and add iodine. Note that 
 a blue solution is formed. Heat nearly to boiling : the solution 
 becomes colourless. Allow to cool : the colour reappears. 
 It is clear that the blue compound of iodine and starch is an 
 unstable compound easily dissociated by heat. 
 
 To another portion of the starch mucilage add some dilute 
 sulphuric acid and warm gently. Observe that the starch dis- 
 solves and the liquid becomes clear. Test a few drops of the 
 solution with iodine in another test-tube, and note that the 
 " soluble starch " formed still gives the blue compound. Now 
 boil the main solution for a few minutes and test a few drops 
 again with iodine. Note that a red coloration is now produced, 
 showing that the starch has been converted into a new sub- 
 stance. This new product is dextrin, or "British gum," of 
 which in the impure state this reaction with iodine is charac- 
 teristic. Continue boiling the main solution, until on again 
 testing a few drops with iodine no coloration whatever is 
 
138 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 produced, showing that the dextrin has in turn been converted 
 into a new body. Now add to the boiling liquid a drop of 
 solution of sulphate of copper, and then caustic soda or potash 
 till alkaline. Note that instead of getting black cupric oxide 
 as would be expected, red cuprous oxide is precipitated, 
 showing that a reducing agent is now present. This sub- 
 stance, into which the dextrin has been converted, is a sugar. 
 
 The foregoing changes can be carried out by alkalies as well as by acids ; 
 by "diastase," a substance existing in the leaves and germinating seeds of 
 plants; and by " ptyalin," a substance existing in the saliva of animals. 
 Dry heat has a similar action, and dextrin is produced on the large scale 
 by merely heating starch. 
 
 The starch of commerce is prepared from cereal grains such as wheat, 
 maize, and rice ; from the stem of the sago palm ; from arrowroot and 
 from potatoes ; by grinding or grating, mixing with water rendered alkaline 
 with caustic soda, straining the mixture from fibre and other impurities, 
 and allowing it to stand for the starch to deposit. The various starches 
 are distinguished by the size, shape, and markings of the granules. Arti- 
 chokes contain a variety of starch known as inulin. This is distinguished 
 by giving no blue colour with iodine. It is converted into fruit sugar by 
 boiling with dilute acid. 
 
 Procure some cotton wool (nearly pure cellulose). Note 
 that it is unchanged by boiling with water, and that iodine has 
 no action upon it, but that it is soluble in strong sulphuric 
 acid forming a sulphate. To some concentrated acid in a 
 beaker kept cool by water, add cotton wool in small quantities 
 at a time, and stir till dissolved. Dilute this solution of sul- 
 phate of cellulose very largely with water, and boil. Test a 
 few drops of the resulting liquid with iodine, and, after longer 
 boiling, with sulphate of copper and then potash till alkaline. 
 Note that at first iodine gives the brown coloration charac- 
 teristic of dextrin, and that afterwards the red precipitate of 
 cuprous oxide, characteristic of a sugar, is obtained. 
 
 The percentage composition of cellulose, starch, and dextrin, as obtained 
 by analysis, is represented by the formula C II 10 O 5 . The molecular 
 formula is undoubtedly a multiple of this, for the sulphate has the formula 
 
THE CARBOHYDRATES 139 
 
 C 12 H 14 4 .3S0 4 , and a nitrate is obtainable having the formula C 12 H 14 4 . 
 6NO3. The reaction by which this is produced shows that the cellulose 
 contains hydroxyl groups like metallic hydroxides. Just as 
 
 KOH + HNO3 = KN0 3 + H 2 0, 
 so C 12 H 14 4 . 60H + 6HNO3 - C 12 H 14 4 . 6N0 3 + 6H 2 0. 
 It is obvious, therefore, that if cellulose has the formula C 6 H 10 O 3 it could 
 not form a hexanitrate, for there could not be six replaceable hydroxyl 
 groups. 
 
 The nitrate is produced by the action of a mixture of nitric and sulphuric 
 acids on cotton wool, the object of the sulphuric acid being to combine 
 with the water as it is liberated. If allowed to act for a short time only, 
 the tri-, tetra-, or penta-nitrates are produced, which, when dissolved in 
 alcohol and ether, constitute collodion. If the action is prolonged the 
 hexanitrate — gun-cotton — is formed. Both cotton and flax consist of 
 nearly pure cellulose. Cotton and linen rags, together with the impure 
 cellulose constituting the fibre of straw and wood, are utilised in the 
 manufacture of paper. For this purpose these materials are completely 
 disintegrated and made into a pulp with water, which is then passed 
 between rollers. 
 
 Procure some cane sugar and grape sugar. To a solution of 
 each add copper sulphate solution and then potash till alkaline. 
 Note that in neither case is a precipitate obtained, owing to 
 the property that sugars possess of forming soluble compounds 
 with many basic oxides. Now warm the solutions. Note 
 that the cane sugar solution is unchanged, but that the grape 
 sugar reduces the cupric to red cuprous oxide, which is precipi- 
 tated. Warm another portion of the cane sugar solution with 
 dilute sulphuric acid for a few minutes, and repeat the test. 
 Note that the cupric oxide is now reduced to cuprous, show- 
 ing that grape sugar has been formed by warming the cane 
 sugar with acid. 
 
 " Cane sugar " occurs in unripe fruits and in the sap of plants, especially 
 the sugar cane, sugar maple, sorghum, and sugar beet. Sugar is pre- 
 pared from these. An aqueous solution is obtained, which is decolorised 
 by animal charcoal and evaporated till crystallisation commences. Among 
 agricultural crops, mangolds and beet are the richest in sugar. " Grape 
 sugar" occurs, together with an equal quantity of "fruit sugar," in ripe 
 fruits, obviously produced from the cane sugar in the unripe fruit. It is 
 
140 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 prepared commercially by the action of dilute acid on starch. " Milk 
 sugar " is a constituent of milk, and can be obtained by evaporating the 
 whey of milk. On warming with acids it is converted into equal quantities 
 of grape sugar and a sugar called "galactose." " Maltose " is the sugar 
 first produced by the action of acid or diastase on starch ; the acid, however, 
 further converts it into grape sugar. In addition to the foregoing carbo- 
 hydrates, gums belong to the same group. The "arabin" of gum-arabic 
 has the formula C^H^On. 
 
 The relation of the carbohydrates to each other will be best 
 understood by reference to the table on the opposite page. 
 The formulae show that the action of dilute sulphuric acid 
 in converting starch, cellulose, and dextrin into malt sugar, and 
 maltose, cane sugar, and milk sugar into fruit sugar, grape 
 sugar, and galactose, is a process of hydrolysis, i.e. the decom- 
 position of a substance by water, thus : — 
 
 ^12^22^11 + H 2 = C 6 H 12 G + C 6 H 12 6 . 
 
 XXX. THE HYDROCARBONS 
 
 The conversion of wood into charcoal is essentially decomposi- 
 tion of cellulose into carbon and water. This carbonisation 
 takes place in nature. Peat and lignite are partially carbonised 
 vegetable matter, bituminous coal more completely, while 
 anthracite consists almost entirely of carbon. The following 
 results of analyses show the progressive carbonisation that has 
 taken place : — 
 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Wood 
 
 ioo 
 
 I2.I8 
 
 83.07 
 
 Peat 
 
 IOO 
 
 9.85 
 
 55-67 
 
 Lignite 
 
 IOO 
 
 8.37 
 
 42.42 
 
 Bituminous coal 
 
 IOO 
 
 6.12 
 
 21.23 
 
 Anthracite 
 
 IOO 
 
 2.84 
 
 1-74 
 
THE HYDROCARBONS 
 
 141 
 
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142 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 It was found (p. 104) that when wood is distilled 
 inflammable gases are obtained, one of which is the hydro- 
 carbon marsh gas. Similarly, when coal is distilled, the product 
 is the mixture of hydrocarbons and other gases known as coal 
 gas. When the carboniferous shale of the coal measures is 
 distilled the chief product is a mixture of hydrocarbons called 
 paraffin. American petroleum has a composition similar to 
 paraffin, and is perhaps a product of the natural distillation of 
 carbonaceous substances. It is obtained in Pennsylvania and 
 other districts from borings through the strata overlying the 
 sand or gravel in which the petroleum exists. Analyses and 
 determinations of the vapour density show that both petroleum 
 and paraffin are mixtures of hydrocarbons differing in their 
 proportion of carbon to hydrogen and in molecular weight. 
 Marsh gas or methane is the simplest of these hydrocarbons, 
 and that which contains the largest proportion of hydrogen. 
 Of the other hydrocarbons in the mixture a few are gases, but 
 the more complex are liquids and the most complex are 
 solids. The relation between the physical properties and 
 chemical composition is shown in the following table : — 
 
 Gaseous Hydrocarbons. 
 
 Liquid Hydrocarbons. 
 
 
 Liquefying 
 Point. 
 
 
 Boiling 
 Point. 
 
 Methane, CH 4 
 
 . - 164° 
 
 Pentane, C 5 H 12 
 
 • 38° 
 
 Ethane, C 2 H 6 
 
 ? 
 
 Hexane, C 6 H 14 
 
 . 7i° 
 
 Propane, C 3 H 8 
 Butane, C 4 H 10 
 
 -17° 
 + 1° 
 
 etc. etc. 
 Pentadecane, C 15 H 32 
 
 etc. 
 • 271° 
 
 
 Solid Hydrocarbons. 
 
 
 
 Melting 
 Point. 
 
 
 
 Hexadecane, C 16 H 34 . 18 
 
 
 
 Heptadecane, C^Hgg . 23 
 Octadecane, C 18 H 38 . 28 
 
 
 
 etc. et 
 
 c. etc. 
 
 
 By fradio?ial distillatio?i petroleum can be separated into : — 
 (1) A gas used for heating and lighting. 
 
THE HYDROCARBONS 
 
 143 
 
 (2) Light petroleum, — naphtha, gasoline, benzoline, benzine, 
 kerosene, — volatile liquids used as solvents, fuels, and 
 illuminants. 
 
 (3) Heavy petroleum,' — mineral sperm oil, etc., — oily liquids 
 used chiefly as lubricants. 
 
 (4) Petroleum jelly — vaseline, etc. — used chiefly as lubricants 
 and unguents. 
 
 Similar products are obtained from Russian petroleum and 
 from paraffin. From the latter the product corresponding to 
 liquid petroleum is termed paraffin oil. The solid product is 
 paraffin wax. 
 
 Fig. 46. 
 
 Fractionate some crude petroleum by means of an 
 apparatus such as that figured. The purpose of the tube 
 bearing the thermometer is to allow the condensation 
 
1 44 CHE MIS TR Y FOR A GRIC UL TURAL STUDENTS 
 
 of the heavier hydrocarbons carried up with the 
 vapour of the lighter hydrocarbons. Heat the flask very 
 cautiously at first by means of a water bath, and avoid having 
 any light near. Then, when nothing further distils, the flask 
 may be safely heated by means of a Bunsen burner. Should, 
 at first, some incondensible gas be obtained, collect a tube full 
 by downward displacement ; ignite it, and note that it burns 
 with a flame much more luminous than pure marsh gas, for it 
 contains hydrocarbons richer in carbon. As the temperature 
 shown by the thermometer gradually rises, collect liquid 
 fractions below 200 (light petroleum) and between 200 and 
 400 (heavy petroleum). Pour a few drops of each upon the 
 hand, and note the difference in the volatility. Allow the 
 residue to cool in the flask to obtain the semi-solid hydro- 
 carbon residue. 
 
 Fig. 47. 
 
 To illustrate the manufacture of coal gas by the destructive 
 distillation of coal, employ the apparatus figured. Roughly 
 powder some coal, introduce into a Florence flask, and heat 
 strongly. Pass the volatile products of distillation through a 
 flask containing water in order to separate condensible 
 products, and collect the purified coal gas in a cylinder over 
 water. Ignite a cylinder of the gas. Note that it burns with a 
 flame more luminous than the wood gas, indicating the 
 
THE HYDROCARBONS 145 
 
 presence of hydrocarbons richer in carbon. When the distilla- 
 tion is completed note (1) that coke is left behind in the 
 Florence flask, (2) that coal tar has collected in the wash flask, 
 (3) that the aqueous liquid in the wash flask is alkaline to 
 litmus, and has the pungent smell of ammonia. Pour off this 
 " ammoniacal liquor " into a distillation flask, add lime, and distil 
 off the ammonia into a little dilute sulphuric acid. Evaporate 
 the solution in a dish to obtain crystals of sulphate of 
 ammonium. To a portion add caustic potash solution. Note 
 the smell of ammonia gas set free. 
 
 Coal Gas. — For the manufacture of coal gas, coal is heated in fire-clay 
 retorts. The volatile products are passed into the "hydraulic main" — 
 a reservoir where tar and an aqueous liquid condense. The gas now 
 traverses " condensers," — upright iron tubes exposed to the air, in which a 
 further quantity of tar and water condense, and "scrubbers," — towers in 
 which the gas is met by a stream of water to dissolve out ammonia. The 
 gas next passes through "purifiers," in which it is first led over 
 hydrated ferric oxide to remove the last traces of sulphuretted hydrogen 
 (a part having previously been removed with the ammonia), the product 
 of combustion of which — sulphur dioxide — is injurious, and then over 
 slaked lime to remove carbonic acid gas, which diminishes the luminosity 
 of burning coal gas. The coal gas is finally stored in gas-holders. 
 
 With respect to its composition, coal gas may contain — 
 
 Heat Givers. 
 
 Hydrogen, H . . .5°% 
 Marsh gas, CH 4 . . -35% 
 Carbon monoxide, CO . . 8% 
 
 Light Givers. 
 
 Ethylene, C 2 H 4 . . . • 2% 
 
 Propylene, C 3 H 6 . . .1% 
 
 Benzene, C 6 H 6 . . .1% 
 
 Impurities. 
 
 Nitrogen 1% 
 
 Carbon dioxide 1% 
 
 Sulphuretted hydrogen and oxygen . Traces 
 
 The proportion of illuminants will depend upon (1) the kind of coal used, 
 cannel coal yielding a much larger proportion than other bituminous coal ; 
 and (2) the temperature of distillation, a larger proportion being formed at 
 low than at high temperatures. Gas of low illuminating power may be 
 enriched by vapours of oils of high illuminating power. 
 
146 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Among the by-products of coal gas manufacture, the most important 
 are: (i) Coke. (2) Gas carbon, formed as a deposit within the retorts, 
 and used for the "carbons" of galvanic batteries, and the poles of the 
 electric arc light. (3) Coal tar. From this, coal tar oil is separated by 
 distillation, pitch being left as a residue. From the coal tar oil are 
 obtained the hydrocarbons benzene or benzole, C 6 H 6 ; naphthalene, C 10 H 8 ; 
 and anthracene, C 14 H 10 ; from which the aniline, naphthalene, and 
 alizarine dyes are respectively derived. (4) Ammonia in the form of 
 sulphate. (5) Gas lime, a mixture containing chalk and unchanged slaked 
 lime, together with the sulphide and oxysulphide of calcium in cases 
 where the sulphur has not been removed by hydrated ferric oxide. 
 
 Hydrocarbons burn with flames which are (1) non-luminous, 
 (2) luminous, and (3) smoky, depending upon the proportion 
 of carbon they contain. The luminosity of flame, in fact, 
 appears to be chiefly due to the incandescence of particles of 
 carbon set free owing to the decomposition of the hydro- 
 carbons. Place a clean white dish in any luminous hydro- 
 carbon flame. Note that it becomes covered with soot. 
 Observe that the flame essentially consists of three parts — (1) 
 a dark interior, consisting of unburnt but decomposing gases ; 
 (2) a luminous zone, consisting of burning but incompletely 
 burnt gases ; and (3) a non-luminous envelope, in which com- 
 plete combustion to carbonic acid gas and water is taking 
 place. (This envelope may be rendered visible by volatilising 
 a little common salt on a piece of platinum wire 
 in the flame.) Depress a sheet of paper into the 
 flame of a paraffin candle. Note that a ring of 
 charred paper is produced round an uncharred 
 interior, showing that the flame is hollow. When 
 air is admitted into the interior of a hydrocarbon 
 jm| flame, carbon is no longer set free, and the flame 
 
 a-JL-'^-- ' i s thus rendered non-luminous. In the Bunsen 
 
 *- -3 burner (Fig. 48) air is admitted by holes at the 
 
 Fig. 48. bottom of the tube. . If these be closed, the 
 flame becomes luminous. 
 
 Fuels. — The combustibles used for heating must yield gaseous and non- 
 injurious products of combustion. These conditions are alone fulfilled by 
 
THE HYDROCARBONS 147 
 
 carbon and hydrogen and their compounds. The "heat of combustion" 
 of hydrogen is much greater than that of carbon, and the amount of heat 
 produced by combustion of hydrocarbons will therefore vary with the 
 proportion of hydrogen. The "pyrometric effect," that is, the highest 
 temperature attainable by burning the fuel, will, however, largely depend 
 upon the heat absorbed by the gaseous products, and is found to be greater 
 for carbon than for hydrogen. The oxyhydrogen flame is intensely hot, 
 partly because, being fed within with oxygen, combustion of the 
 hydrogen takes place in a very small space. The Bunsen and blow-pipe 
 flames are hot for the same reason. For furnaces where a very high 
 temperature is required, coke or anthracite, which burn with very little 
 flame, are employed. These relations are shown in the following table, 
 in which the heat of combustion of a gram of substance is compared with 
 the temperature attainable when the substance is used as fuel. A "heat 
 unit " is the heat that would raise a gram of water 1° C. 
 
 Fuel. Heat of Combustion. Tn Pyometric Effect, 
 
 In Oxygen. In Air. 
 
 Wood with 20 % water 
 
 2,800 heat units 
 
 — 
 
 — 
 
 Dry wood 
 
 3,600 
 
 11 
 
 — 
 
 — 
 
 Charcoal 
 
 7>°5o 
 
 >» 
 
 — 
 
 — 
 
 Pure carbon, C 
 
 8,080 
 
 11 
 
 9873 
 
 2458' 
 
 Olefiant gas, C 2 H 4 
 
 11,858 
 
 »> 
 
 5793° 
 
 2090' 
 
 Marsh gas, CH 4 
 
 I3.063 
 
 11 
 
 4800 
 
 i945 c 
 
 Hydrogen, H 
 
 34,462 
 
 >» 
 
 3172 
 
 i6ii c 
 
 It is noticeable that water, both free and combined, diminishes heat 
 production, because to eliminate, vaporise, and raise it in temperature, heat 
 must be absorbed. Partly for the same reason, the heating effect produced 
 by combustion in air is less than by combustion in oxygen, because the 
 nitrogen of the air absorbs heat. 
 
 In the foregoing study, attention has been drawn to compounds 
 that apparently form the starting-points of several series of hydrocarbons, 
 the members of each of which differ from each other by CH 2 . The series 
 of which methane (marsh gas) CH 4 , ethane C 2 H 6 , and propane C 3 H 8 , 
 form the first members, is called the "paraffin series" of hydrocarbons ; 
 the members may be represented by the general formula C n H 2n + 2 . 
 Ethylene (olefiant gas) C 2 H 4 , and propylene C 3 II 6 , form the first 
 members of a second series, the " defines," having the general formula 
 C n H 2n . Acetylene C 2 H 2 , a gas of very high illuminating power, is the 
 first member of a series C n H 2n - 2 . The "terpenes" occurring in the oil 
 of turpentine, obtained by distilling the resinous exudation of certain 
 
148 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 conifers, and in most of the volatile oils of plants, are hydrocarbons having 
 the formula C 10 H 16 . Benzene, C 6 H 6 , is the first member of an important 
 series, having the general formula C n H 2n _ 6 ; while naphthalene and 
 anthracene are the starting-points of a series of hydrocarbons containing a 
 still larger proportion of carbon. 
 
 XXXI. THE ALCOHOLS: FERMENTATION 
 
 Dissolve 150 grams of sugar in a liter of water, place the solu- 
 tion in a flask fitted with a cork and delivery tube as figured, 
 
 Fig. 49. 
 
 and add a few grams of yeast. Note that fermentation soon 
 commences, and a gas is given off which, if collected in a test- 
 tube or cylinder, will be found to extinguish a taper, and to 
 render lime water milky. Keep the apparatus in a warm place 
 for a few days, — a temperature of 25 to 30 C. will be found 
 most favourable, — then, if evolution of gas has ceased, replace 
 the delivery tube by a Liebig's condenser, and distil the mix- 
 ture from a water bath, keeping the whole flask covered with a 
 cloth to aid the process. Note that the alcohol thus obtained 
 
THE ALCOHOLS: FERMENTATLON 149 
 
 has the properties of spirits of wine ; for, if a glass rod be dipped 
 in the liquid, the adhering alcohol is inflammable and burns 
 with a pale blue flame. 
 
 In order to separate from water, distil the weak alcohol 
 from a smaller flask. Shake the first portion of the distillate 
 with anhydrous carbonate of potassium, a useful drying agent, 
 then mix the alcohol with quicklime, and allow to stand for a 
 few hours ; finally distil from a flask fitted with a ther- 
 mometer. Note that the nearly anhydrous alcohol begins to 
 distil at 7 8° or a little over, but that the boiling point gradually 
 rises as the distillation proceeds, this being due to other pro- 
 ducts of fermentation of higher boiling point. The alcohol 
 may be "rectified" by fractional distillation from these im- 
 purities, which constitute, when thus separated, "fusel oil." 
 
 Yeast consists of a mass of minute organisms termed the "yeast plant," 
 together with a chemical compound called invertase. The invertase first 
 converts the cane sugar into grape and fruit sugar, 
 
 Q2H22O11 + ^ 2< ^ = ^6^1206 + Q»Hu|Q(| 
 
 which are then converted by the yeast plant into alcohol and carbonic acid 
 gas, 
 
 C 6 H 12 6 = 2C 2 H 6 + 2C0 2 . 
 
 Both changes are said to be "fermentative," being brought about by organic 
 substances of animal and vegetable origin, which remain the same before 
 and after the reaction. The yeast plant is an "organised ferment," the 
 invertase a "soluble ferment." 
 
 Bread. — This consists of dough which has been "raised" by aeration 
 with carbonic acid gas and then baked. The aeration is usually effected 
 by mixing the dough with yeast. A portion of the starch in the dough is con- 
 verted into maltose, and the maltose into alcohol and carbonic acid gas, which 
 renders the dough spongy. On baking, the air-spaces are further distended 
 by the rise in temperature, while on the outside a crust is formed in which 
 a part of the starch has been converted into dextrin by heat. Instead of 
 yeast a baking powder is sometimes employed ; for instance, a mixture of 
 bicarbonate of sodium and tartaric acid, which react with each other when 
 moistened with water, carbonic acid gas being given off and tartrate of 
 
1 50 CHEM1STR Y FOR A GRIC UL TURAL STUDENTS 
 
 sodium formed. "Aerated bread" is made by mixing the flour with 
 aerated water under pressure. 
 
 Alcohol mixes with water in all proportions. The spirit of 
 wine of commerce is a mixture of alcohol and water. The 
 specific gravity of pure alcohol is .795 at 15.6° C, but that 
 of aqueous alcohol is higher, and varies with the proportion of 
 water ; so that the strength of a spirit can be found by deter- 
 mining the specific gravity. The strength is stated in per- 
 centage of alcohol under or over "proof spirit," i.e. a spirit 
 containing 57 per cent, of alcohol by volume and having a 
 specific gravity of .920. Rectified spirit has a specific gravity 
 of .837, and is 56 per cent, over proof, and therefore contains 
 88.9 per cent, of alcohol. It can obviously be reduced to proof 
 spirit by diluting 100 c.c. to 156 c.c. with water. Perform the 
 experiment, using 50 c.c. of rectified spirit for the purpose. 
 Has the product the specific gravity of proof spirit as deter- 
 mined by the hydrometer ? 
 
 In chemical properties alcohol resembles an inorganic 
 hydroxide, and its formula should therefore be written C 2 H 5 OH, 
 hydroxide of ethyl, ethyl, C 2 H 5 , being an " organic radicle," 
 i.e. a group of elements of which carbon is one that plays the 
 part of a single element. Thus alcohol combines with acids 
 forming "ethereal salts," 
 
 C 2 H 5 OH + H 2 S0 4 = C 2 H 5 HS0 4 + H 9 
 like KOH + H 2 S0 4 - KHS0 4 + H 2 0, 
 
 and when heated with a dehydrating agent loses water and is 
 converted into the ethereal oxide " ether," 
 
 2 C 2 H 5 OH— H 2 - (C H 5 ) 2 
 like 2 KOH— H 2 = K 2 b. 
 
 To illustrate the formation of an ethereal salt, nitrite of ethyl 
 or nitrous ether, the principal active constituent of sweet spirit 
 of nitre, may be prepared. Dissolve 34.5 grams of sodium 
 nitrite in water, dilute to 120 c.c, pour into a glass cylinder, 
 
THE ALCOHOLS: FERMENTATION 151 
 
 and cool below o° C. by surrounding the cylinder with ice 
 sprinkled over with salt. Add 13.5 c.c. of concentrated 
 sulphuric acid to a well-cooled mixture of 32 c.c. of rectified 
 spirit, with an equal volume of water ; dilute the mixture to 
 120 c.c. with water, and cool below o° C. Run the acid liquid, 
 by means of a thistle funnel passing to the bottom of the 
 cylinder (Fig. 40), into the nitrite solution, little by little, and 
 constantly stirring with the thistle funnel. Note that a layer 
 of nitrite of ethyl is formed, due to the action on the alcohol 
 of the nitrous acid, produced from the sodium nitrite and 
 sulphuric acid. 
 
 C 2 H 5 OH + HN0 2 = C 2 H fi N0 2 + H 2 0. 
 Pour off the nitrous ether into a separating funnel, shake with a 
 little ice-cold water, run off the water, dry the ether by shaking 
 with fused potassium carbonate, and preserve in a stoppered 
 bottle. 
 
 Ethereal salts are more or less easily decomposed by water. 
 Shake a little of the nitrous ether with water, and note that 
 hydrolysis occurs, red nitrous fumes being formed. 
 C 2 H 5 N0 2 + H 2 = C 2 H 5 OH 4- HN0 2 . 
 Decomposition generally takes place more readily in presence 
 of an alkali. If some of the ethyl nitrite be mixed with strong 
 alcoholic potash, and the mixture warmed in a flask fitted with 
 an upright condenser, the ether is decomposed, nitrite of 
 potassium being in this case produced. 
 
 C 2 H 5 N0 2 + KOH = C 2 H 5 OH + KN0 2 . 
 Such a decomposition is termed saponification (see p. 157). 
 
 Alcohol, C 2 H 5 OH, may obviously be regarded as ethane, C 2 H 6 , in which 
 hydrogen has been replaced by hydroxyl. Other hydrocarbons have 
 alcohols corresponding to them, those derived from propane, butane, and 
 pentane being constituents of fusel oil, and therefore products of alcoholic 
 fermentation. The alcohol corresponding with methane is a constituent 
 of the " wood spirit " contained in the aqueous distillate from wood (p. 104), 
 and from which it may be obtained by distillation. The alcohol corres- 
 ponding with benzene, termed phenol, or " carbolic acid," and that corres- 
 ponding with toluene, termed cresol, are constituents of coal tar. 
 
Alcohol. 
 
 Boiling Point. 
 
 Methyl alcohol, CH 3 OH 
 
 66° C. 
 
 Ethyl alcohol, C 2 H 5 OH 
 
 78 
 
 Propyl alcohol, C 3 H 7 OH 
 
 97° 
 
 Butyl alcohol, C 4 H 9 OH 
 
 io8° 
 
 Amyl alcohol, C 5 H n OH 
 
 i3i° 
 
 152 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Hydrocarbon. 
 Methane, CII 4 
 Ethane, C 2 H 6 
 Propane, C 3 H 8 
 Butane, C 4 H 10 
 Pentane, C 5 H 12 
 
 Benzene, C 6 H 6 Phenol, C 6 H 5 OII i8i° 
 
 Toluene, C 7 H 8 Cresol, C 7 H 8 OH i88° 
 
 These alcohols are all monohydric, but, as is the case with inorganic 
 hydroxides, polyhydric alcohols can exist. For instance, it was found 
 that cellulose contained six replaceable hydroxyl groups. Glycerine is a 
 trihydric alcohol derived from propane, having the formula C 3 H 5 (OH) 3 , 
 glyceryl trihydroxide, and it forms, when treated with nitric and 
 sulphuric acids, a glyceryl trinitrate, or "nitroglycerine," which, when 
 mixed with infusorial earth, constitutes the explosive dynamite. 
 
 Brewing. — Malt is prepared by steeping barley in water, then exposing 
 the softened grain to the air till germination has taken place, in order that 
 the soluble ferment diastase may be produced, and finally drying in kilns. 
 The radicles or " combes" having been separated from the corn by treading 
 and sifting, the malt is crushed and mashed with water at about 70° t C. 
 During this process the starch is gelatinised and converted into dextrin and 
 maltose by the diastase previously formed, and the soluble carbohydrates 
 thus produced are extracted. The liquor or wort, when separated from 
 the spent " brewer's grains," is next boiled with hops ; then, after cooling, 
 fermented with yeast, alcohol and carbonic acid gas being formed. After 
 sufficient fermentation has taken place, and two or three per cent, of alcohol 
 has been produced, the yeast is skimmed off the surface, and the beer stored 
 in casks. Wines are prepared by directly fermenting grape juice. Spirits 
 are the products of distillation of wine and other fermented liquors. 
 
THE ORGANIC ACIDS 153 
 
 XXXII. THE ORGANIC ACIDS 
 
 Place a pint of beer in a large flat-bottomed dish and leave 
 exposed to the air for a week. Observe that the beer becomes 
 sour in taste and acid to litmus. Vinegar has, in fact, been 
 produced, the alcohol having been oxidised to acetic acid by 
 atmospheric oxygen : — 
 
 C 2 H 6 + 2 = C 2 H 4 2 + H 2 0. 
 This oxidation is effected by a microscopic fungus, — the vinegar 
 plant, — the germs of which exist in the air ; and it is desirable 
 to partly immerse in the beer a few beechwood shavings, upon 
 which the fungus will develop, and which will therefore pro- 
 mote the chemical change. 
 
 Neutralise some vinegar with caustic soda, evaporate to a low 
 bulk, slightly acidify with sulphuric acid and distil over the 
 acetic acid, being careful to stop the process when charring 
 commences. Note that this volatile organic acid has all the 
 properties of an inorganic acid ; it is sour in taste, it turns blue 
 litmus red, and it neutralises alkalies and decomposes carbon- 
 ates with the formation of salts. 
 
 Acetic acid is also obtained by the distillation of wood. If 
 the aqueous liquid thus obtained (p. 104) be neutralised with 
 soda, the wood spirit evaporated off and the residue distilled 
 with sulphuric acid, impure acetic acid — " pyroligneous acid " 
 — is obtained. 
 
 Just as acetic acid is obtained from ethyl alcohol by oxida- 
 tion, so other organic acids may be produced from the alcohols 
 with which they correspond in number of carbon atoms. Thus 
 methyl alcohol, CH 4 0, yields formic acid, CH 2 2 , and butyl 
 alcohol, C 4 H 10 O, yields butyric acid, C 4 H s 2 . To a mixture of 
 sulphuric acid and bichromate of potassium (a strong oxidising 
 agent) add a few drops of butyl alcohol. Warm gently in a 
 test-tube till action is complete, then boil and notice the 
 cheese-like odour of the product of oxidation — butyric acid. 
 
154 CHEMISTR Y FOR A GRICUL TURAL STUDENTS 
 
 Oxidation of alcohols proceeds in two stages. Two atoms of hydrogen 
 are first withdrawn, and an aldehyde {i.e. alcohol flfe/zyafrogenatum) left, and 
 then an atom of oxygen is introduced and an acid formed. Formic alde- 
 hyde, CH a O, intermediate between methyl alcohol and formic acid, is the 
 useful antiseptic and preservative, the solution of which is known in com- 
 merce as "formalin." Benzoic aldehyde, C 7 H 6 0, constitutes the volatile 
 oil of bitter almonds. It should be noted that oxidation does not always 
 imply addition of oxygen to the substance. The withdrawal of hydrogen, 
 with formation of water, is also held to be a process of oxidation. Con- 
 versely, reduction may imply either elimination of oxygen or addition of 
 hydrogen. 
 
 By oxidising monohydric alcohols, monobasic acids, i.e. 
 acids containing only one atom of hydrogen replaceable by 
 metals, are obtained, but polyhydric alcohols can yield poly- 
 basic acids, i.e. acids containing two or more replaceable hydro- 
 gens. To show the basicity of the acids, it is convenient to 
 represent them by formulae in which the replaceable hydrogen 
 precedes the remainder of the formula. 
 
 Formic acid, HCH0 2 , occurs in ants and nettles. 
 
 Acetic acid, HC 2 H 3 2 , ,, vinegar and pyroligneous acid. 
 
 Lactic acid, HC 3 H 5 3 , ,, sour milk. 
 
 Butyric acid, HC 4 H 7 2 , ,, cream and butter as butyrate of glyceryl. 
 
 Myristic acid, HC^H^C^, ,, cream and butter as myristate of glyceryl. 
 
 Palmitic acid, HC 16 H 31 2 , ,, palm oil and soft fats as palmitate of 
 
 glyceryl. 
 Stearic acid, HC 18 H 35 2 , ,, hard fats as stearate of glyceryl. 
 Oleic acid, HC 18 H 33 2 , ,, olive oil and soft fats as oleate of 
 
 glyceryl. 
 Benzoic acid, HC 7 H 5 2 , ,, gum benzoin. 
 Salicylic acid, HC 7 H 5 3 , ,, oil of wintergreen as salicylate of 
 
 methyl. 
 Oxalic acid, H 2 C 2 4 , ,, sorrel as acid oxalate of potassium (salts 
 
 of sorrel). 
 Tartaric acid, H 2 C 4 H 4 O , ,, grape juice as acid tartrate of potassium 
 
 (cream of tartar). 
 Citric acid, H 3 C 6 H 5 7 , ,, lime and lemon juice. 
 
 According to the formula given, oxalic acid is a di-basic 
 acid. To confirm this, prepare a deci-normal solution, i.e. a 
 
FA TS A ND SOAPS 1 55 
 
 solution containing in one liter one-tenth of a molecular weight 
 of crystallised oxalic acid, H 2 C 2 4 .2H 2 0, in grams. Weigh 
 out two half-gram portions of pure and previously heated sodium 
 carbonate, dissolve each in water, and titrate with the acid, 
 using all the precautions described on p. 71. Does the 
 quantity of acid required correspond with that necessary to 
 form the compound Na 2 C 2 4 ? 
 
 XXXIII. FATS AND SOAPS 
 
 Organic, like inorganic, acids are able to form ethereal salts 
 with organic hydroxides, i.e. alcohols. There is, for instance, 
 the acetate of ethyl or acetic ether, C 2 H 5 .C 2 H 3 2 , produced by 
 distilling a mixture of alcohol, acetate of sodium, and strong 
 sulphuric acid. The most important of these compounds are the 
 oils or fats occurring in animal or vegetable organisms, which 
 generally consist of oleifi, palmitin, and stearin, the oleate, 
 palmitate, and stearate of glyceryl. Olein is an oil, while pal- 
 mitin and stearin are solid fats, the latter having the higher 
 melting point ; hence hard fats largely consist of stearin, soft 
 fats of palmitin and olein. Olive oil, sperm oil, and cod-liver 
 oil are rich in olein, human fat and palm oil in palmitin, suet, 
 tallow, and lard in stearin. 
 
 Just as the alcohols and hydrocarbons are distinguished from 
 each other by their boiling points, the fats may be distinguished 
 by their melting points. Procure some pure palmitate and pure 
 stearate of glyceryl. Prepare a few capillary glass tubes from 
 some odd bits of glass tubing, and seal the points. Into the 
 fine end of one of these thrust a minute fragment of one of 
 the pure fats, and attach the tube to a thermometer, as figured 
 (Fig. 50) by means of india-rubber bands. Make a stirring rod 
 
CO 
 
 s* 
 
 1 56 CHE MIS TR Y FOR A GRICUL TURAL STUDENTS 
 
 of copper wire, with the end bent into a ring 
 of such a size that it will easily move up and 
 down in the vessel of water without touching 
 the thermometer and tube. Having arranged 
 the apparatus, as figured, slowly heat the 
 water, with constant stirring, until the frag- 
 ment of fat is just melted. Note the 
 melting point. Now allow to cool, still 
 constantly stirring, and note the solidifying 
 point. Repeat the alternate heating and 
 cooling until the exact melting point and 
 solidifying point are ascertained with cer- 
 tainty. Then determine the melting point 
 of the other fat. 
 
 The melting points of the fats of special 
 importance and their specific gravities (deter- 
 mined at 66° C. and compared with water at 
 
 Of) 5^ 
 
 JW 
 
 Fig. 50. 
 
 the same temperature) are as follows :- 
 
 Fat. Melting Point. 
 
 Specific Gravity. 
 
 Butynn, C 3 H 5 . 3 C 4 H 7 2 ? 
 
 
 1. 021 
 
 Myristin, C 3 H 5 . 3 C 14 H 27 2 55° C. 
 
 
 ? 
 
 Palmitin, C 3 H 5 .3C 16 H 31 2 62 C. 
 
 
 0.900 
 
 Olein, C 3 H 5 .3C 18 H 33 2 -6° C. 
 
 
 0.900 
 
 Stearin, C 3 H 5 .3C 18 H 35 2 72 C. 
 
 
 0.892 
 
 It will have been noticed that the boiling point or melting point of the 
 hydrocarbons and alcohols of any homologous series rise as the molecular 
 weight of the compound increases. This is obviously the case also with 
 the fats, but with one apparent exception, viz. olein. If, however, the 
 formulae are examined, it will be found that whereas all the other fats are 
 referable to the general formula, C 3 H 5 .3C n H 2n _ 1 2 , and therefore belong 
 to the same series, olein is not referable to this formula ; so that the apparent 
 discrepancy is understood. As a matter of fact, while butyric, myristic, 
 palmitic, and stearic acids are derived from the paraffin series of hydro- 
 carbons, oleic acid is derived from the olefine series. The same variation 
 in the physical properties, with the increase in the molecular weights, is 
 observed in the acids themselves. While formic, acetic, and butyric acids 
 
FATS AND SOAPS 
 
 »57 
 
 are volatile and soluble in water, myristic, palmitic, and stearic acids are 
 insoluble_in water, and not easily volatilised ; while the acids of intermediate 
 molecular weight have intermediate properties. In fact, the boiling points 
 are found to rise, and the solubility to diminish, as the molecular weights 
 in a series increase. 
 
 Among the properties of fats that need to be especially 
 noticed are (1) solubility in ether, (2) emulsification, and (3) 
 saponification with an alkali. Bruise any dry vegetable sub- 
 stance, e.g. straw, maize, rice meal, linseed, or bran, in a mortar, 
 and, having transferred to a test-tube, shake with ether. Pour 
 off the ethereal liquid and evaporate in a dish over the water 
 bath. The residue will consist of the fat (together with wax) 
 of the vegetable substance. 
 
 Shake some olive oil with water ; notice that the oil quickly 
 separates from the water, and, being lighter, rises and floats 
 upon the surface. Now add a drop of solution of caustic 
 potash, and shake again. Observe that an emulsion is now 
 produced, the fat being separated into minute particles which 
 do not readily aggregate. 
 
 When fats are decomposed by saponification with an alkali, 
 glycerine and a soap are formed. Thus : — 
 
 C 3 H 5 . 3 C 18 H 35 2 + 3 NaOH - C 3 H 53 OH + 3 NaC 18 H 35 2 . 
 
 Glyceryl stearate Caustic Glycerine. Sodium stearate 
 
 or stearin. soda. or soap. 
 
 Boil together in an iron dish 50 grams of tallow with caustic 
 soda, in slight excess as calculated from the equation, dissolved 
 in 250 c.c. of water, until complete saponification has occurred. 
 Add strong brine to the mixture to " salt out " the soap, it being 
 insoluble in solution of common salt. Separate from the soap 
 the aqueous liquid containing the glycerine, evaporate it to 
 dryness, dissolve out the glycerine from the residue with strong 
 alcohol, and evaporate the alcoholic solution until a syrupy 
 residue of the glycerine is obtained. Note its sweet taste. 
 Dissolve a portion of the soap in water, place the solution in 
 
1 58 CHEMISTR Y FOR A GRICUL TURAL STUDENTS 
 
 a cylinder, and add to it dilute sulphuric acid till slightly acid 
 Note the separation of solid stearic acid. 
 
 NaC 18 H 35 2 + H 2 S0 4 = NaHS0 4 + HC ls H 35 2 . 
 
 For preparing glycerine and the fatty acids on a large scale, fats are hydro- 
 lysed by distilling with superheated steam. The distillate consists of a 
 solution of glycerine and a separate layer of the fatty acid. The latter is 
 employed in the manufacture of "stearine" candles; the pure glycerine is 
 obtained by evaporating the aqueous liquid. Fats are sometimes described 
 as glycerides of the fatty acids. Thus stearin is the glyceride of stearic 
 acid, olein the glyceride of oleic acid, etc. 
 
 It is evident that soaps are oleates, palmitates, or stearates of 
 potassium or sodium. Potassium soaps are soft ; sodium soaps 
 are hard. When dissolved in water for washing purposes, a 
 little hydrolysis occurs, and soda or potash is set free, which 
 dissolves the grease from, and therefore cleanses, the hands. 
 When used with hard water, a curd is formed owing to the for- 
 mation of insoluble oleates, palmitates, and stearates of calcium 
 and magnesium, the soaps of the alkali metals being the only 
 soaps soluble in water. To the solution of the soap add dilute 
 solutions of calcium and magnesium salts. Note the curdy pre- 
 cipitates of the calcium and magnesium salts of the fatty 
 acids. 
 
 2NaC ls H 35 2 + CaH 2 2C0 3 = 2NaHC0 3 + Ca2C 18 H 35 2 
 
 2 NaC ls H 35 2 + MgS0 4 = Na 2 S0 4 + Mg 2 C 18 H 35 2 . 
 
 By making use of these reactions, the total, permanent and 
 temporary hardness of tap water may be compared and approxi- 
 mately determined. To determine the total hardness place 70 
 c.c. of the water in a stoppered bottle, and run in — in very small 
 quantities at a time, until a permanent lather is produced after 
 shaking — a standardised solution of soap in weak alcohol (sup- 
 plied), of such a strength that 1 c.c. of the solution will exactly 
 precipitate .001 gram of calcium carbonate in a state of solu- 
 tion in 70 c.c. of water. Each c.c. of the soap solution used 
 will then represent one " degree of hardness," i.e. one grain of 
 
FATS AND SOAPS 159 
 
 calcium carbonate in one gallon of the water (70,000 grains). 
 To determine the permanent hardness repeat the determination 
 with a second 70 c.c. of the water; but first boil it gently for 
 half an hour to precipitate the carbonates of calcium and mag- 
 nesium, and make up again to 70 c.c. with boiled distilled 
 water. The number of c.cs. of soap solution now required 
 will indicate the degrees of permanent hardness. The difference 
 between the two results gives the temporary hardness. 
 
 Butter. — The cream that rises to the surface of milk consists of minute 
 globules of fat. These aggregate when agitated by churning and form 
 butter. Butter, therefore, consists chiefly of fat, but also contains 8 to 16 
 per cent, of water, and I to 2 per cent, of curd, with a variable quantity of 
 added salt. The fat consists of the glycerides of oleic, palmitic, stearic, 
 and myristic acids (the last in small quantity), together with the glycerides 
 of certain volatile acids soluble in water, the chief of which is butyric acid. 
 Of these combined acids the volatile acids form about 8 per cent. , the oleic 
 acid 36 per cent. , and the palmitic, stearic, and myristic acids about 49. 5 
 per cent, of the butter fat. The specific gravity of butter fat varies be- 
 tween .910 and .914 at 37. 7° C. Animal fats used to adulterate butter, and 
 in the manufacture of oleo-margarine, are devoid of the glycerides of the 
 soluble acids ; and the specific gravity of these being higher than that of 
 olein, p'almitin, and stearin, such fats have a lower specific gravity — .903 to 
 .905 at 37. 7° C. The purity of butter can therefore be determined by 
 taking the specific gravity. For this purpose the butter is melted, and the 
 liquid fat poured off from the water and curd, and filtered into the specific 
 gravity bottle. The specific gravity is determined at 37. 7° C. (ioo° F.). 
 It is not always possible to detect a small amount of foreign fat in butter by 
 this method, and in this case the purity of the butter is determined by 
 saponifying, acidifying the soap produced, weighing the insoluble acids 
 thrown out of solution, and titrating the aqueous liquid containing the 
 soluble acids with a standard solution of alkali. In this way the proportion 
 of the soluble and volatile acids to the insoluble and non-volatile acids is 
 determined. 
 
[6o CHEMISTR Y FOR A GRIC UL TURAL STUDENTS 
 
 XXXIV. AMMONIA DERIVATIVES— ALKALOIDS 
 AND AMIDES 
 
 In the foregoing studies it has been observed that organic 
 compounds may be regarded as simple inorganic compounds 
 in which an element is replaced by an organic radicle, i.e. a 
 group of elements, of which carbon is one, which plays the part 
 of an element. Thus alcohol, C 2 H 5 .OH, is water, H.OH, in 
 which hydrogen has been replaced by ethyl. Acetic acid, 
 H.C 2 H 3 2 , is hydrochloric acid, H.C1, in which the acetic 
 radicle has been substituted for chlorine. Similarly there is a 
 group of organic compounds which are regarded as substituted 
 ammonias, i.e. ammonia, NH 3 , in which one or more atoms of 
 hydrogen are replaced by organic radicles. These compounds 
 are termed amines and alkaloids. They are alkaline in re- 
 action, like ammonia, and combine with acids forming salts. 
 
 An important amine is trimethylamine, N(CH 3 ) 3 , the sub- 
 stance to which the fishy smell of herring brine is due. 
 Pyridine — NC 5 H 5 — is a volatile base of powerful odour pro- 
 duced in the distillation of coal, and usually found as the 
 sulphate in small quantities in commercial sulphate of ammonia. 
 Alkaloids frequently exist in plants, and to them the medicinal 
 or toxic properties of plants are often due. Thus quinine, 
 an alkaloid found in cinchona bark, atropine or atropia in 
 belladonna, aconitine in aconite, morphine or morphia in 
 opium, and nicotine in tobacco, are the active constituents 
 of these plants. 
 
 Mix some sulphate of quinine with water in a stoppered 
 separatory funnel. Note that this salt is almost insoluble. 
 Now add a little dilute sulphuric acid to convert the sulphate 
 into the soluble acid sulphate, and to the clear solution thus 
 obtained add solution of caustic soda in order to precipitate the 
 alkaloid itself. Shake the white mixture with ether until the 
 alkaloid is completely dissolved in the ether, run off the water, 
 
AMMONIA DERIVATIVES— ALKALOIDS AND AMIDES 161 
 
 wash the ethereal solution by shaking with a little water, and 
 finally pour into a dish and evaporate off the ether over warm 
 water. Moisten the white residue with water, and test its 
 alkalinity with red litmus paper. 
 
 These reactions show that in all chemical respects an 
 alkaloid behaves like ammonia. The reactions may be 
 expressed as follows. Since quinine has the complex molecular 
 formula C 20 H 24 N 2 O 2 , it is symbolised in the equations by the 
 letter A. 
 
 A 2 .H 2 S0 4 + H 2 S0 4 = 2(A.H 2 S0 4 ) 
 
 like (NH 3 ) 2 .H 2 S0 4 + H 2 S0 4 - 2 (NH 3 .H 2 S0 4 ) j 
 A.H 2 S0 4 + 2NaOH = A + Na 2 S0 4 + 2H 2 
 
 like NH 3 .H 2 S0 4 + 2 NaOH = NH 8 + Na 2 S0 4 + 2 H 2 0. 
 
 The ammonia derivatives in which hydrogen has been re- 
 placed by an acid radicle are termed amides. To this group 
 belong caffeine or theine, the stimulating constituent of tea and 
 coffee; the theobromine of cocoa; asparagine, an abundant 
 constituent of asparagus and many root crops ; and the uric acid 
 of urine. 
 
 Another amide is the urea or carbamide, CO(NH 2 ) 2 , of urine. 
 Evaporate half a liter of urine to about one quarter its bulk, 
 and after cooling add nitric acid until crystals of the nitrate 
 of urea begin to separate. Allow to stand, till the precipita- 
 tion of crystals is complete. Filter, dissolve the crystals in a 
 very little water, and then add strong nitric acid in which the 
 salt is only slightly soluble. Collect the crystals which are 
 deposited, press between filter paper to dry them, and preserve. 
 A stable or urinal frequently smells strongly of ammonia. 
 This is due to the hydrolysis of the urea of the urine by the 
 action of a micro-organism, ammonia and carbonic acid gas 
 being formed. 
 
 CO(NH 2 ) 2 + H 2 = C0 2 + 2NH3. 
 
 The hydrolysis may also be effected by heating with strong 
 caustic potash, ammonia and carbonate of potassium being 
 11 
 
1 62 CHE MIS TR Y FOR A GRIC UL TURA L ST U DENTS 
 
 produced. Try the experiment, and observe whether ammonia 
 is evolved. 
 
 Among other nitrogenous organic compounds should be mentioned 
 cyanogen, CN, an organic radicle resembling in many respects chlorine. 
 Thus it forms hydrocyanic acid (prussic acid), HCN, like hydrochloric 
 acid, and cyanide of potassium, KCN, like chloride of potassium, etc. 
 These cyanides have a great tendency to form double salts. Among the 
 most important of these is ferrocyanide of potassium ("yellow prussiate of 
 potash "), K 4 Fe(CN) G . When treated with a solution of ferric chloride, this 
 yields ferric ferrocyanide, the well-known pigment " prussian blue." It 
 forms, therefore, a very delicate test for iron. If the ferrocyanide of 
 potassium be warmed with dilute sulphuric acid, hydrocyanic acid will 
 be set free, and if smelt cautiously (it is intensely poisonous) will serve to 
 illustrate the characteristic odour of oil of bitter almonds possessed by this 
 acid. 
 
 XXXV. THE ALBUMINOIDS 
 
 The albuminoids, as their name implies, resemble albumin or 
 white of egg in general properties. Their constitution is not 
 fully known, and they possess a somewhat indefinite com- 
 position, but all contain 50 to 55% carbon, 6.9 to 7.5% 
 hydrogen, 20 to 24% oxygen, 15 to 18% nitrogen, and (pos- 
 sibly with some exceptions) .3 to 2% sulphur. Dry some white 
 of egg over a water bath, mix it with soda lime, and heat 
 strongly in a test-tube. Note that ammonia is given off, show- 
 ing that the albuminoid is a nitrogen compound. Empty the 
 solid residue into a beaker, and add excess of dilute sulphuric 
 acid. Note that sulphuretted hydrogen, recognised by its 
 smell and by the black stain of sulphide of lead it produces on 
 paper soaked in a solution of lead acetate, is evolved, showing 
 that sulphur also is a constituent of the albuminoid. 
 The albuminoids have not yet been synthetically prepared in 
 
THE ALBUMINOIDS 163 
 
 the laboratory : they are products of vegetable life, and form an 
 essential part of the food and of the substance of animals. 
 Bruise some fresh clover plants in a mortar, press out the sap, 
 filter into a test-tube, and warm. Note that a substance pre- 
 viously dissolved coagulates on warming. An albumin-like sub- 
 stance is thus shown to be present. Repeat the experiment 
 with fresh meat juice. Notice here again the presence of an 
 albuminoid. 
 
 While found in animal or vegetable substance in a soluble 
 state, albuminoids also exist in the insoluble or coagulated 
 state. Make some wheat flour into a dough with water, enclose 
 in a muslin bag, and knead in a basin of water until the starch 
 has been entirely washed out. On opening the bag, a tough 
 elastic substance, the " gluten " of wheat, will be found, this 
 being a mixture of albuminoids mostly insoluble in water. 
 
 The albuminoids arrange themselves in several classes dis- 
 tinguished by different properties. Among these distinguishing 
 features are the different conditions under which coagulation 
 occurs. To illustrate these, the coagulation of the albumin of 
 egg, the casein of milk, and the fibrin of blood or myosin of 
 flesh, may be studied. 
 
 Separate the white of a fresh egg. Shake it vigorously with 
 about ten times its bulk of water, and strain the liquid several 
 times through muslin until a clear solution of albumin is 
 obtained. Heat a portion in a test-tube. Observe that it 
 coagulates at a temperature below 75 C. To another portion 
 add nitric acid, and notice that this also causes coagulation. 
 
 Allow some milk to stand for a day in a cylinder in order 
 to allow the cream to separate. Remove some of the skim 
 milk by means of a pipette, and heat it in a test-tube. Note that 
 no change occurs. Now add some nitric acid, and observe the 
 curdling of the milk due to coagulation of the casein. To 
 another portion add rennet {i.e. the solution of a soluble 
 ferment obtained from the fourth stomach of calves). Coagula- 
 tion will again take place. 
 
i6 4 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Procure some fresh blood. Notice that after a very few 
 minutes' exposure to the air the blood spontaneously coagu- 
 lates, a " clot " containing the fibrin being formed, while the 
 " serum," containing blood albumin, separates. Enclose the 
 clot in a muslin bag tied over the nozzle of a water tap, and 
 allow water to run through, constantly kneading it with the 
 hand meanwhile until the red colouring substance is washed 
 away, and the fibrin is left white. 
 
 Procure some raw meat. Note that the solid matter is 
 already insoluble and coagulated. Knead it in a muslin bag 
 under water until colourless myosin is obtained. 
 
 The albuminoids are then all characterised by this property 
 of coagulation, but while fibrin and myosin spontaneously 
 coagulate, albumin only coagulates on heating or upon the 
 addition of acid, and casein, which does not coagulate on 
 heating, does so on the addition of either acid or rennet. 
 The albuminoids are further distinguished as a class by the 
 property of peptonisation, i.e. the conversion of the coagulated 
 albuminoids into soluble compounds termed peptones. This 
 chemical change may be brought about by dilute acids, but it is 
 most easily effected by certain soluble ferments acting in some 
 cases in acid, and in some cases in alkaline liquids. 
 
 Cut a little of the white of a boiled egg into thin strips, and 
 mix with a solution of pepsin (a soluble ferment found in the 
 gastric juice of the stomachs of animals) in dilute hydrochloric 
 acid, and digest for a few hours at a temperature of 3 6° C. 
 (blood heat). Note that the albumin dissolves. Boil the liquid : 
 coagulation no longer occurs ; the albuminoid has been con- 
 verted into a soluble peptone. 
 
 The solutions of albuminoids and peptones are further dis- 
 tinguished by their behaviour on diffusion. To illustrate liquid 
 diffusion or osmose, securely tie pieces of parchment paper over 
 the mouths of two thistle funnels. Run into the one funnel a 
 solution of magenta and into the other a solution of cochineal, 
 and then place the inverted funnels in beakers of distilled water. 
 
THE ALBUMINOIDS 165 
 
 Note that the magenta soon begins to pass through the parch- 
 ment into the water, but the cochineal diffuses much less 
 readily. Now repeat the experiment with starch mucilage and 
 solution of sugar, and after a short time test the water in each 
 beaker by appropriate tests for starch and sugar. It will be 
 found that, as in the previous case, it is the crystallisable sub- 
 stance, or crystalloid, that is readily capable of diffusion, while 
 the non-crystallisable substance, or colloid, does not easily 
 diffuse. Now try the experiment with a solution of albumin 
 before and after peptonisation, testing the water for diffused 
 substance by evaporating a portion to dryness. Note that the 
 unchanged albumin is colloid j the peptone is crystalloid. 
 
 This process obviously provides a method of separating crystalloids from 
 colloids in solution. The method is known as dialysis. In the foregoing 
 experiments it will be found that liquid passes through the diaphragm 
 in each direction ; and, in the cases of difficultly diffusible substances, 
 more liquid passes into the funnel than passes out. This gives rise to 
 increase of volume in the funnel, and consequent increase of pressure. It 
 is this osmotic pressure to which, in the cells of plants, is largely due the 
 flow of sap. 
 
 Milk. — I. Composition. — A drop of milk examined under a microscope 
 is seen to be an " emulsion," and to consist chiefly of minute globules of fat 
 floating in an aqueous liquid. The fat has a lower specific gravity than the 
 aqueous portion, and therefore separates as "cream" on standing, or on 
 submitting the milk to a rotatory movement in a "separator," when the 
 greater centrifugal force of the heavier liquid causes its separation from the 
 fat globules. This watery liquid, or "skim milk," contains the dissolved 
 albuminoids, and of these the casein coagulates on the addition of rennet to 
 the milk, a curd being produced, which, when compressed into a solid 
 mass, and then ripened by keeping, constitutes "cheese." (Cheeses contain 
 24 to 41 per cent, of water, 23 to 39 per cent, of fat, depending on the 
 proportion of cream in the milk used, 27 to 32 per cent, of casein, and 
 0.7 to 4.4 per cent, of salt.) 
 
 The "whey" from the curd still contains the albumin of milk, and this 
 may now be coagulated by heating. If the precipitate be filtered off, and 
 the filtrate evaporated to a low bulk, crystals of the sugar of milk are 
 obtained. If the mother-liquor from these crystals be evaporated to dry- 
 
166 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 ness, and the residue ignited, an ash is left, consisting of the phosphates 
 and chlorides of potassium, sodium, calcium, and magnesium. 
 
 2. Souring of Milk. — This is due to the action of the lactic ferment, a 
 micro-organism which converts milk sugar into lactic acid by hydrolysis : — 
 
 C 12 H 22 O u + H 2 = 4C 3 H 6 3 . 
 
 Lactic acid is able to coagulate the albuminoid of milk. Warmth aids 
 coagulation, and in hot weather it is sometimes noticed that spontaneous 
 coagulation occurs when only very small quantities of lactic acid have been 
 produced. This souring of milk is prevented by cooling the milk to near 
 the freezing point, which inhibits the action of the organisms, or by heating 
 under pressure to 120 C, a temperature which destroys the organisms, and 
 afterwards excluding air. The souring is also retarded ( I ) by heating to 
 56° C, a temperature which destroys some germs but does not affect the 
 taste of the milk, (2) by cooling even a few degrees, and (3) by the use of anti- 
 septics, such as boracic acid (H 3 B0 3 or B 2 3 .3H 2 from the non-metallic 
 element boron), borax (Na 2 B 4 7 or 2B 2 3 .Na 2 0), salicylic acid and formic 
 aldehyde, the addition of which are, however, considered inadmissible. ' 
 
 3. Adulteration. — Owing to the great variability in the composition of 
 milk due to the animal, the time of milking, the pasturage, etc., the detec- 
 tion of adulteration by water is a matter of some difficulty. The usual 
 method is to determine the specific gravity at 15. 5 C. by means of the 
 hydrometer (sp. gr. = 1.028 to 1.035 for pure milk ; mean, 1.032), to weigh 
 the total solids obtained by evaporating 5 grams of milk in a weighed dish 
 on the water bath, until the weight is constant (12 to 14.5 grams per 100 
 grams of pure milk ; mean, 12.9) ; and lastly, to estimate the fat by 
 extracting it with ether or by means of a butyrometer (2.7 to 4.3 per cent.; 
 mean, 3.77). It has been found that there is a constant relation between 
 the fat and the specific gravity and total solids : — ■ 
 
 „ „ /iooS-ioo\ 
 F = .8 33 T-2.22 (^ g J 
 
 in which F = the fat, T = total solids, and S = specific gravity ; hence it is 
 possible to find the amount of fat by calculation, if the specific gravity and 
 total solids are known, or the total solids by calculation if the specific 
 gravity and fat are known. 
 
 The Chemistry of Animal and Vegetable Life. — 1. Plants. — To pro- 
 mote the germination of seeds, warmth, moisture, and atmospheric oxygen 
 are necessary. The starch of the seed is converted into sugar by the diastase 
 formed during germination, and the albuminoids are converted into peptones 
 or amides ; these substances, being soluble and dialysable, can supply the 
 growing part of the plant with nutriment. The root penetrates the soil, 
 and thus procures the phosphates, sulphates, and nitrates of potassium, 
 calcium, magnesium, and iron, which the acid root sap assists in dissolving. 
 
THE ALBUMINOIDS 167 
 
 The stem and leaves expand into the air, where, through the agency of light, 
 " chlorophyll " is produced, and they become green. Atmospheric carbonic 
 acid is absorbed by the leaves, and, through the agency of the chlorophyll, 
 in presence of sunlight and warmth, reacts with water absorbed by the 
 roots, carbohydrate being produced and oxygen set free into the air : — 
 
 6C0 2 + 5H 2 = C 6 H 10 O 5 + 60 2 . 
 
 From the same materials, together with the inorganic nitrates and sulphates 
 absorbed from the soil, albuminoid is also produced. The carbohydrate 
 and albuminoid, being convertible into soluble substances by the soluble 
 ferments, acids, or salts also contained in the leaves, can be conveyed by 
 the sap to the growing part of the plant, or to the seed, stem, and root, 
 where storage of reserve material is required, and then may be deposited in 
 an insoluble form. Thus the cotnplex organic constituents of plants are 
 products of redtiction fi-om simple inorganic substances, sunlight and heat 
 being absorbed. 
 
 2. Animals. — Animals have no power of elaborating complex organic 
 compounds from simple inorganic substances, and their food consists there- 
 fore, directly or indirectly, of vegetable products. These foods are usually 
 insoluble and require digestion, i.e. conversion into a form in which they 
 can pass through the membranes of the stomach and intestines into the blood. 
 The digestive fluids are — (1) the saliva, an alkaline fluid containing a 
 soluble ferment, ptyalin, which converts starch into malt sugar and grape 
 sugar ; (2) the gastric juice, a fluid, acid with hydrochloric acid, containing 
 a soluble ferment, pepsin, which converts coagulated albuminoids into 
 peptones ; (3) the bile, pancreatic juice, and intestinal juice, alkaline fluids, 
 also containing soluble ferments, which complete the conversion of starch 
 into sugar and albuminoids into peptones, and which also emulsify and 
 partially saponify the fats. 
 
 The blood, into which all the digested food passes, contains a purplish red 
 compound, haemoglobin, which becomes oxidised in the lungs to bright red 
 oxyhemoglobin. This compound is capable of oxidising the carbon and 
 hydrogen of assimilated food constituents to carbonic acid gas and water, 
 the oxyhemoglobin being reduced to haemoglobin. This carbonic acid gas 
 remains dissolved in the blood till it reaches the lungs, when it is set free 
 and oxygen again absorbed. Thus respired air becomes rich in carbonic 
 acid gas and deficient in oxygen (see p. 23). The water produced is excreted 
 by the lungs, pores of the skin, or kidneys. 
 
 The heat produced by the oxidation of the carbon and hydrogen provides 
 the power of doing work. When more carbohydrate and fat is digested 
 than is required for oxidation, they may be deposited as fat, and this will 
 serve as a store of fuel, and undergo oxidation when required. Work is 
 
1 68 CHE MIS TR Y FOR A GRIC UL TURA L S TU DENTS 
 
 done through the agency of muscle, which, since it is constantly under- 
 going oxidation, must be constantly renewed by a fresh supply of albuminoid 
 derived from the peptones of the digested food. When albuminoids are 
 oxidised, in addition to carbonic acid gas and water, urea is one of the 
 products ; and this, being excreted from the blood by the kidneys, is found 
 in urine. Thus the simple substances excreted by animals are oxidation 
 products of complex organic compounds, heat being produced during the 
 process. 
 
 3. Food. — The constituents of food are classified into (1) heat-producers, 
 viz. carbohydrates, fats, and amides ; (2) flesh - formers and heat- 
 producers, viz. albuminoids ; (3) inorganic salts, including especially 
 phosphate of calcium and chloride of sodium. In addition to these, water 
 is a necessary constituent as the food-carrier, and certain alcohols and 
 ethereal salts in the spices, alkaloids in tea, coffee, and cocoa, and the 
 ethyl alcohol of fermented liquors, may serve a useful purpose as stimulants. 
 
 The value of a food will depend upon (1) composition and (2) digestibility. 
 The value of food constituents as heat-producers depends upon their heat of 
 combustion. Thus the heat of combustion of cane sugar is 97, albumin 
 107, fat 229, and asparagine 49, if that of starch be taken as 100. The 
 albuminoid ratio {i.e. the proportion of albuminoids to the equivalent in 
 starch of the other organic constituents), required in a diet, will depend upon 
 the kind and age of the animal and the functions it is expected to perform, 
 and will vary from 1:2 to 1:14. Digestibility varies with the kind and 
 condition of the food and the kind of animal, ruminating animals having a 
 considerable power of digesting cellulose, while man has none. Cooking 
 materially affects digestibility : for instance, baking of bread and toasting 
 it converts a portion of the starch into dextrin, and therefore increases 
 digestibility ; but the prolonged heating of albuminoids renders them much 
 less digestible. 
 
 XXXVI. CONCLUSIONS 
 
 The carbon compounds dealt with in the foregoing studies, of 
 which the constitution is understood, have been regarded as 
 inorganic hydrogen compounds, in which the hydrogen, or 
 other element, has been replaced by an organic radicle j and 
 
CONCLUSIONS 
 
 169 
 
 each class of organic compounds therefore resembles some 
 inorganic compound, which serves as a type. Thus : — 
 
 Hydrogen, HH, 
 Water, HOH . 
 Water, H 2 . 
 Potassium chloride, KC1 
 Ferric hydroxide, Fe(OH) 3 
 Hydrochloric acid, HC1 
 Hydro-sulphuric acid, H 2 S 
 Sodium chloride, NaCl 
 Ferric chloride, FeCl 3 
 Ammonia, NH 3 
 
 is a type of a hydrocarbon, e.g. ethane, 
 CH 3 CH 3 . 
 „ alcohol, e.g. ethyl alcohol, 
 
 C 2 H 6 OH. 
 „ ether, e.g. ethyl ether, 
 
 (C 2 H 5 ) 2 0. 
 ,, ethereal salt, e.g. ethyl 
 
 nitrite, C 2 H 5 N0 2 . 
 ,, polyhydric alcohol, e.g. 
 
 glycerine, C 3 H 5 (OH) 3 . 
 ,, monobasic acid, e.g. acetic 
 
 acid, HC 2 H 3 2 . 
 ,, polybasic acid, e.g. oxalic 
 
 acid, II 2 C 2 4 . 
 ,, soap, e.g. sodium stearate, 
 
 NaC»H»Oj. 
 „ fat, e.g. stearin, 
 
 CsH 5 ( C 18 H 35 2 ) 3 . 
 „ amine, e.g. trimethylamine, 
 
 N(CH 3 ) 3 . 
 
 "In mineral chemistry the radicles are simple, in organic 
 chemistry they are compound; therein consists the whole 
 difference. The laws whereby the compounds are formed, and 
 their reactions regulated, are the same in both." (Dumas.) 
 
 To understand the relation between the members of each 
 group of organic compounds, it must be pointed out that, just 
 as in an inorganic compound an atom of hydrogen can be re- 
 placed by, or substituted for, an atom of another monad 
 element (e.g. H in HC1 by Na in NaCl), so, in an organic 
 compound, an atom of hydrogen can be replaced by a monad 
 organic radicle. Thus, an atom of hydrogen in methane, CH 4 , 
 can be replaced by methyl, CH 3 , forming ethane, CH 3 - CH 3 
 or C 2 H 6 . One atom of hydrogen in ethane, CH 3 — CH 3 , can 
 be replaced by methyl to form propane, CH 3 - CH 2 - CH 3 
 or C 3 H 8 . So, also, an atom of hydrogen in ethyl alcohol 
 
170 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 CH 3 -CH 2 OH, can be replaced by methyl to form propyl 
 alcohol, CH 3 - CH 2 - CH 2 OH. Thus, each member of each 
 group will differ from the preceding member by CH 2 , and the 
 difference being constant, each group can be represented by a 
 genera] formula. Thus, all the paraffin hydrocarbons are 
 found to have the composition C n H 2n+2 , and all the corres- 
 ponding alcohols the composition C n H 2n+1 OH. It has been 
 observed that the physical properties of each group vary with 
 the molecular complexity; the melting points of the hydro- 
 carbons, and the boiling points of the alcohols, rose, and the 
 relative densities of the fats fell, with each addition of CH 2 to 
 the molecular formula. 
 
 Each class of compounds is characterised by a distinguish- 
 ing group. The — CH 3 group of the hydrocarbons becomes 
 
 - CH 2 (OH) in the alcohols, — CHO in the aldehydes, 2nd 
 
 - CO(OH) in the acids. The relation of methane, ethane, 
 propane, and butane, to their corresponding alcohols, alde- 
 hydes, and acids, will be made clear by the following table : — 
 
 Hydrocarbon 
 R.CH 3 
 
 Methane 
 H.CH3 
 
 Ethane 
 CH 3 .CH 3 
 
 Propane 
 C 2 H 5 .CH 3 
 
 Butane 
 C 3 H 7 .CH 3 
 
 Alcohol 
 R.CH 2 OH 
 
 Methyl alcohol 
 H.CH 2 OH 
 
 Ethyl alcohol 
 CH 3 .CH 2 OH 
 
 Propyl alcohol 
 C 2 H 5 .CH 2 OH 
 
 Butyl alcoho 
 C 3 H 7 .CH 2 OI 
 
 Aldehyde 
 R.CHO 
 
 Formic alde- 
 hyde 
 H.CHO 
 
 Acetic alde- 
 hyde 
 CH 3 '.CHO 
 
 Propionic alde- 
 hyde 
 C 2 H 5 .CHO 
 
 Butyric aide 
 
 hyde 
 C 3 H 7 .CHO 
 
 Acid 
 R.COOH 
 
 Formic acid 
 H.COOH 
 
 Acetic acid 
 CH 3 .COOH 
 
 Propionic acid 
 C 2 H 5 .COOH 
 
 Butyric acid 
 C 3 H 7 .COOI 
 
 It is these characteristic groups that give to each class of 
 organic compounds their distinctive properties. Thus, the 
 group CO(OH) renders a compound an acid, because it is 
 
CONCLUSIONS 171 
 
 the hydrogen of this group that is capable of being replaced 
 by a metal or an organic radicle, forming a salt or ethereal salt 
 respectively. For example, acetate of sodium is CH 3 .CO(ONa), 
 and acetic ether is CH 3 .CO(OC 2 H 5 ). It follows that a dibasic 
 acid must contain two CO(OH) groups, and a tribasic acid 
 three. A glance at the formulae of the organic acids given on 
 p. 154, shows that this can be the case; indeed, oxalic acid 
 is obviously composed of 2CO(OH). A study of all organic 
 compounds shows how exactly are their chemical, as well as 
 their physical properties, in accordance with their molecular 
 constitution. 
 
 Very early in these Studies the relation was observed between 
 heat and the force of chemical attraction. A large number 
 of additional facts have now been deduced, which show that, 
 when chemical combination occurs, heat, or sometimes light 
 or electricity, are produced, and, conversely, to decompose 
 a chemical compound, heat, or sometimes light or electricity, 
 are required. Energy is never lost; there is a definite rela- 
 tion between the energy employed and the work done : the 
 heat. of combustion of two elements is a means of measuring 
 their chemical attraction; the amount of a chemical com- 
 pound decomposed by an electric current is a means of 
 measuring the quantity of electricity used. 
 
 This conservation of energy is well illustrated in the chemical 
 processes of the animal and vegetable worlds. The chemical 
 changes in the leaves of plants are essentially processes of re- 
 duction, carbonic acid gas and water being used, and carbo- 
 hydrates and oxygen being produced. The chemical changes 
 in the animal are essentially processes of oxidation, carbo- 
 hydrate and oxygen being used, and carbonic acid gas and water 
 produced. The former is a heat-absorbing, the latter a heat- 
 producing, change. The energy derived from the sun's heat 
 and light is stored as chemical energy in the combustible con- 
 stituents of food, and the oxygen set free, until, when con- 
 sumed as animal food, recombination takes place, and heat 
 
1 72 CHEMISTR V FOR A GRIC UL TURA L STUDENTS 
 
 is again produced. It is the manifestations of this force of 
 chemical attraction between elements and groups of elements 
 with which the science of chemistry is concerned. 
 
 In the course now completed, the student has dealt with 
 the composition of air and water, the minerals of the earth's 
 crust, and the products of animal and vegetable life, as far as 
 w r as necessary to enable him to understand the principal laws 
 that govern the composition of matter, and the properties of 
 the substances with which he would be most intimately con- 
 nected on the farm. He has become accustomed to regard 
 change, whether in the animal, vegetable, or mineral kingdoms, 
 as involving chemical changes, similar in kind to the examples 
 which have been dealt with in the laboratory ; and which can 
 be controlled and modified, provided they are understood. 
 Not only, therefore, should the knowledge acquired enable 
 him to understand the processes of the farm, but he should 
 now view them from an intelligent standpoint, and hence be 
 better prepared to attack the problems presented for solution 
 in all agricultural pursuits. 
 
 QUESTIONS AND PROBLEMS FOR REVISION AND 
 EXAMINATION. 
 
 The Carbohydrates. 
 
 What is a "carbohydrate"? Name some. How do carbohydrates 
 behave when they are heated ? Explain the action of concentrated 
 sulphuric acid on sugar. 
 
 Name the principal sources of starch, and state how it is prepared. 
 How may starches be distinguished from each other, and by what 
 chemical test can starch be identified ? 
 
 Describe the action of dilute sulphuric acid on starch mucilage, and 
 state what is the behaviour of the liquid at each stage to solution 
 of iodine and to alkaline copper sulphate solution. What sub- 
 stances, other than sulphuric acid, are able to bring about the 
 same series of changes ? 
 
QUESTIONS AND PROBLEMS 173 
 
 4. Describe the method by which cellulose can be converted into sugar. 
 
 Express the formation of sulphate of cellulose by an equation. 
 
 5. What are collodion and gun-cotton, and how are they produced ? 
 
 What purpose does the sulphuric acid serve ? Explain how the 
 existence of a hexanitrate of cellulose is evidence of the molecular 
 formula of cellulose being a multiple of C 6 H 10 O 5 . 
 
 6. State what happens when to solutions of cane sugar and grape sugar, 
 
 solutions of sulphate of copper and then caustic alkali are added. 
 Express the changes in the copper compounds by equations. 
 
 7. How may cane sugar be converted into grape and fruit sugar ? 
 
 Suggest an explanation of the occurrence of the former in unripe, 
 and the latter in ripe fruits. Explain why this conversion is 
 spoken of as a "hydrolytic" change. 
 
 8. Name the chief sources of cane sugar. What is milk sugar, and how 
 
 is it obtained ? Into what sugar is starch first converted by 
 hydrolysis ? 
 
 9. Draw up a scheme illustrating the conversion of carbohydrates of the 
 
 C 6 H 10 O 5 and C^H^On groups into carbohydrates of the C 6 H 12 6 
 group. 
 
 10. Identify the carbohydrate. (Starch, inulin, dextrin, cane sugar, or 
 
 grape sugar.) 
 
 11. Find out whether the vegetable substances contain either starch, 
 
 inulin, cane sugar, or grape sugar. (Potato, turnip, mangold, 
 . artichoke, carrot, apple, barley, and malted grain. ) 
 
 The Hydrocarbons. 
 
 12. What is meant by carbonisation? Give an account of the gradual 
 
 carbonisation that goes on in nature, and give examples of 
 artificially carbonised substances. 
 
 13. Distinguish between a hydrocarbon and a carbohydrate. 
 
 14. Give an account of the sources of petroleum and paraffin, the 
 
 products of their fractional distillation, and the several uses of 
 these. 
 
 15. In what respects do the physical properties of the hydrocarbons of 
 
 the paraffin series depend upon their composition ? 
 
 16. Give a full account of the manufacture of coal gas and its purification. 
 
 Of what does coal gas consist, and to what constituents are the 
 illuminating properties chiefly due ? State how the temperature of 
 the retorts affects the quality and quantity of the gas. What are 
 the by-products of coal gas manufacture ? 
 
 17. Describe the structure of a hydrocarbon flame, and state to what the 
 
 luminosity is due. Describe the principle of the Bunsen burner. 
 
1 74 CUEMISTR Y FOR A GRICUL TVR A L STUDENTS 
 
 18. Distinguish between the quantity of heat produced by the combustion 
 
 of fuels, and the temperature attained. Upon what will the latter 
 depend ? Explain why a Bunsen flame is hotter than a luminous 
 gas flame, and why combustion in oxygen gives rise to a higher 
 temperature than combustion in air. 
 
 19. How many grams of water could be raised i° in temperature by the 
 
 combustion of 1 gram of carbon and of I gram of hydrogen 
 respectively. Explain why the heat of combustion of marsh gas 
 should be greater than that of defiant gas. Why should dry wood 
 produce more heat when burned than wet wood, and charcoal 
 more heat than either ? 
 
 20. Tabulate the hydrocarbons referred to, assigning each to its proper 
 
 series, and showing the simple relation that exists between the 
 
 members of each series. 
 *2i. Prepare a pure specimen of hexane from the gasoline. 
 *22. Determine the relative density of the coal gas (air=l). 
 
 The Alcohols : Fermentation. 
 
 23. Fully describe the preparation of alcohol from cane sugar by 
 
 fermentation. How can the alcohol be dried and rectified ? 
 
 24. Of what does yeast consist? Distinguish between the "organised" 
 
 and the " soluble " ferment, and illustrate by equations the 
 principal change in sugar which each brings about. 
 
 25. Describe the use of yeast in bread-making, and the changes that 
 
 go on during the raising and baking of bread. Name two means 
 of raising bread other than by yeast. 
 
 26. What is "proof spirit"? How could a spirit 56 per cent, over proot 
 
 and a spirit 56 per cent, under proof be converted into proof spirit ? 
 
 27. What is meant by an "organic radicle," and of what organic radicle 
 
 is alcohol the hydroxide ? In what respects does alcohol resemble 
 in its properties an inorganic hydroxide ? 
 
 28. Give an account of the preparation of nitrous ether. 
 
 29. What is the action of potash upon nitrous ether ? Give examples of 
 
 inorganic salts which are decomposed by the same means. 
 
 30. Point out the similarity in the relation of water to hydrogen with that 
 
 of ethyl alcohol to ethane. What alcohols are present in fusel oil, 
 wood spirit, and coal tar oil, and to what hydrocarbons does each 
 " correspond " ? 
 
 31. The physical properties of the hydrocarbons were found to vary with 
 
 the molecular weights ; does this also hold good for the alcohols ? 
 Give examples. 
 
QUESTION'S AND PROBLEMS 175 
 
 32. What is meant by " monohydric " and "polyhydric" alcohols. 
 
 Give examples. Mention some inorganic hydroxides that 
 resemble monohydric, dibydric, and trihydric alcohols in their 
 composition. 
 
 33. In what respect is cellulose an alcohol ? 
 
 34. What is the composition of glycerine ? Show by an equation how it 
 
 is converted into "nitroglycerine." 
 
 35. Fully describe the process of malting barley and the subsequent 
 
 production of beer. 
 *36. Identify the alcohol by its boiling point. (Methyl, ethyl, propyl, or 
 
 amyl alcohol.) 
 *37. Ascertain whether the alcohol is " rectified spirit " or absolute alcohol 
 
 by the hydrometer. Reduce to proof spirit by adding the required 
 
 volume of water. 
 *38. Prepare a pure specimen of ethyl nitrite. 
 
 The Organic Acids. 
 
 39. To what is the souring of beer due ? Describe the method for the 
 
 production of acetic acid. 
 
 40. What is pyroligneous acid, and how is it obtained ? 
 
 41. What is an "aldehyde," and what relation do aldehydes bear to 
 
 alcohols and organic acids ? 
 
 42. By what means can alcohols other than ethyl alcohol be converted 
 
 into the corresponding acids ? Give equations illustrating the 
 oxidation of methyl, ethyl, propyl, and butyl alcohols into the 
 corresponding formic, acetic, propionic, and butyric acids. 
 
 43. Give examples of monobasic, dibasic, and tribasic acids, both organic 
 
 and inorganic. Point out the relation between the basicity of the 
 acids and the number of hydroxyl groups in the corresponding 
 alcohols. 
 
 44. Assign formulae to cream of tartar (acid potassium tartrate), salts of 
 
 sorrel (acid potassium oxalate), sugar of lead (acetate of lead), and 
 verdigris (hydroxy-acetate of copper, i.e. a compound intermediate 
 between the hydroxide and the acetate). 
 
 45. Give some of the natural sources of formic, acetic, lactic, butyric, 
 
 myristic, palmitic, stearic, oleic, benzoic, salicylic, oxalic, tartaric, 
 and citric acids. 
 "46. Identify the crystalline acid by a volumetric determination of the 
 quantity of a standard solution of alkali necessary to neutralise it. 
 (Oxalic, tartaric, or citric acid.) 
 
176 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 Fats and Soaps. 
 
 47. What is meant by a "fat" ? Name the three principal fats, give their 
 
 composition, and mention some of their sources, What are the 
 general properties of fat ? 
 
 48. What is the relation between the molecular weights of the fats and 
 
 their physical properties, including the melting points and specific 
 gravities ? Do the boiling points and solubility of the free acids also 
 vary with the molecular weights ? 
 
 49. What is meant by "saponification"? Show by an equation how 
 
 stearin is saponified by caustic soda. Describe a method for the 
 preparation of soap, and state how the free fatty acid may be pre- 
 pared from it. 
 
 50. Give two methods for the preparation of glycerine from fat. 
 
 51. State the difference between hard and soft soaps, and explain the use 
 
 of soap for washing purposes. 
 
 52. To what is the curd produced by soap in hard water due ? By means 
 
 of equations express the formation of these curds both with the con- 
 stituents which render water temporarily, and also those which 
 render it permanently, hard. 
 
 53. Describe how the temporary and permanent hardness of water can be 
 
 determined. 
 
 54. What is the composition of butter, and how does it differ from all 
 
 other kinds of animal fat ? By what two methods may the purity 
 
 of butter be ascertained ? 
 *55. Accurately determine the melting point of the fat. 
 *56. From the pure Castile soap prepare a specimen of the fatty acid of 
 
 which it is a glyceride. 
 *57. Determine the approximate temporary and permanent hardness of the 
 
 tap water. 
 *58. Is the substance butter or oleo-margarine ? 
 
 Ammonia Derivatives : Alkaloids and Amides. 
 
 59. What is meant by a "substituted ammonia," and in what respects 
 
 will such a compound resemble ammonia ? Give examples. 
 
 60. Give examples of the alkaloids found in plants. How may the alkaloid 
 
 quinine be prepared from its sulphate ? Illustrate the reactions by 
 equations. 
 
 61. Name some amides, and state how the amides differ in their com- 
 
 position from amines. 
 
 62. How may urea in the form of nitrate be obtained from urine ? When 
 
QUESTIONS AND PROBLEMS 177 
 
 urine undergoes fermentation, a smell of ammonia is noticed. Illus- 
 trate by an equation the change in the urea that then takes place. 
 63. What is cyanogen, and what element does it particularly resemble ? 
 Illustrate this resemblance by formulae representing the composition 
 of hydrocyanic acid and potassium cyanide. Ferrocyanide of 
 potassium reacts with ferric chloride forming prussian blue. Repre- 
 sent the change by an equation. 
 
 *64- From the quinine supplied prepare a well-crystallised specimen of the 
 sulphate. 
 
 *6$. The commercial hydrochloric acid sometimes contains ferric chloride. 
 Dilute and test for iron by the prussian blue test. 
 
 The Albuminoids. 
 
 66. What is an "albuminoid"? Of what elements does it consist, and 
 
 how may each of these be shown to be present ? 
 
 67. What is meant by the "coagulation" of albuminoids? Name three 
 
 methods by which albuminoids may be coagulated, and give ex- 
 amples of each method. 
 
 68. Give instances of albuminoids which exist naturally in the soluble and 
 
 in the coagulated state. Describe the preparation of gluten of 
 wheat, myosin of flesh, and fibrin of blood. 
 
 69. What is understood by the " peptonisation " of albuminoids, and what 
 
 are the substances capable of producing it ? 
 
 70. Of what is milk composed, and how may its constituents be sepa- 
 
 rated ? 
 
 71. To what is the souring and spontaneous curdling of milk due, and by 
 
 what means may souring be retarded or prevented ? 
 
 72. What are the three data by which the purity of milk is judged, and 
 
 how are they determined ? 
 
 73. Describe the principal chemical changes that take place in seeds 
 
 during germination, and their purpose. State what compounds 
 are absorbed by the leaves and roots of the young plant from the 
 air and soil, what are the substances elaborated in the leaves, and 
 what are the means employed by the plant for their production. 
 Give an equation representing the formation of starch, and state 
 how this substance, produced in the leaves, yet finds its way into the 
 root or seed. 
 
 74. What do you understand by " osmose " and " dialysis " ? Define the 
 
 terms " crystalloid" and " colloid," and give examples of chemical 
 compounds belonging to both classes. How are albuminoids 
 altered in this respect when converted into peptones? Under 
 what circumstances is "osmotic pressure" exhibited? 
 12 
 
78 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 75. Describe the chemical processes by which animals digest their food. 
 
 State how each constituent of the digested food is utilised, and 
 mention the several products of excretion. 
 
 76. Classify the constituents of food according to the purposes that each 
 
 serves. Give the different heat values of the various constituents, 
 and explain what is meant by the albuminoid ratio of a food. Upon 
 what does the digestibility of food depend, and how does cooking 
 affect digestibility ? 
 
 h 77. Is the milk free from adulteration with water? 
 
 '78. Identify the substances. (Starch, sugar, asparagine, albumin.) 
 
 Conclusions. 
 
 79. What is an " organic radicle " ? Illustrate by examples the statement 
 
 that "in inorganic chemistry the radicles are simple, in organic 
 chemistry they are compound." 
 
 80. What is meant by a " type " of any class of carbon compounds ? Give 
 
 inorganic compounds that serve as types of hydrocarbons, alcohols, 
 ethers, monohydric and polyhydric alcohols, monobasic and poly- 
 basic acids, ethereal salts, fats and amines. 
 
 81. Point out the relation between the hydrocarbons — methane, ethane, 
 
 propane, and butane; the alcohols— methyl, ethyl, propyl, and 
 butyl alcohol ; the acids — formic, acetic, propionic, and butyric. 
 Express each group by a general formula which holds good for 
 each member. Point out how the physical properties of the mem- 
 bers of a group vary with their molecular weights. 
 
 82. Give the radicles characteristic of each group of carbon compounds, 
 
 including (1) the hydrocarbons, (2) the alcohols, (3) the aldehydes, 
 and (4) the acids. 
 
 83. Point out the connection between the basicity of the acids and the 
 
 number of carboxyl groups contained. 
 
 84. Tabulate the carbon compounds referred to in the course, showing on 
 
 the one hand the hydrocarbons from which they are derived, and 
 on the other the type to which they correspond in composition. 
 
 85. What is meant by the "conservation of energy"? Illustrate your 
 
 answer by observations made during the course of inorganic chem- 
 istry, and by the chemical changes that take place in animal and 
 vegetable life. 
 
 86. Define the "science of chemistry." 
 
LIST OF APPARATUS AND CHEMICALS REQUIRED 
 BY A CLASS OF ONE DOZEN STUDENTS 
 
 A. Apparatus. 
 
 Weights, Measures, etc. 
 
 I balance, to weigh from .001 to 100 grams. 
 
 I „ „ .1 to 1000 „ 
 
 1 box of weights, .001 to 50 grams. 
 
 I „ „ 1 to 500 „ 
 
 1 meter measure, graduated in tenths of an inch and millimeters. 
 
 1 decimeter cube, divided into square centimeters. 
 
 1 set glass measures, 10 c.c, 50 c.c, and 250 c.c 
 
 1 graduated liter measure, stoppered. 
 
 1 graduated pipette, 5 c.c. 
 
 1 set pipettes, 10 c.c, 25 c.c, and 50 c.c 
 
 1 dozen burettes, 60 c.c. 
 
 \ „ graduated flasks, \ liter. 
 
 Physical Apparatus. 
 
 \ dozen barometer tubes. 
 I ,, barometric charts. 
 1 Boyle tube. 
 1 porous cell, cylindrical. 
 1 each hydrometers, 700-1000, and 1000-2000. 
 1 sheet parchment paper. 
 1 dozen thermometers, -5 to 100 C. 
 i m » -20°to36o°C. 
 
 1 Fahrenheit alcohol thermometer. 
 
 1 dozen glass rods for density determinations, 75x10 m.m., with 
 hooks. 
 
 Hardware and Wooden Apparatus. 
 
 1 blow-pipe and bellows, 
 i dozen mouth blow-pipes. 
 
 179 
 
l8o CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 I dozen wooden blocks, assorted sizes. 
 I ,, Bunsen burners, with valve. 
 I only ,, large size. 
 
 \ dozen roses for burners. 
 I ,, sand baths, 6 inches diameter. 
 
 1 ,, tinned iron dishes, 8 inches diameter. 
 
 \ gross each corks, f , J, f , f , |, and I inch diameter (small end). 
 
 2 sets cork borers, I to 3. 
 1 dozen spring clips. 
 
 \ ,, screw clips. 
 
 \ ,, triangular files. 
 
 \ ,, rat-tailed files. 
 
 1 copper hot-water oven and bath, 12 x 10 x 10 inches, on stand. 
 
 1 dozen retort stands with three rings, 18 inches high. 
 
 1 large retort stand with rings and three clamps. 
 
 \ dozen deflagrating spoons. 
 
 1 iron spoon. 
 
 I dozen crucible tongs. 
 
 I „ wire tripods. 
 
 \ ,, pipe-clay triangles. 
 
 I ,, steel watch springs. 
 
 I square foot wire gauze. 
 
 1 dozen burette stands. 
 
 1 ,, test-tube stands, 6 holes. 
 
 Porcelain and Earthenware Apparatus. 
 
 1 dozen capsules, 2.\ inches diameter. 
 1 ,, crucibles with lids, if inches diameter. 
 1 ,, each basins, 3 inches and 4 inches diameter. 
 £ ,, mortars and pestles, 4^ inches diameter. 
 £ ,, soup plates. 
 
 I ,, pneumatic troughs, 12 inches, with small beehives, I \ inches 
 high. 
 
 Glass Apparatus {Light). 
 
 1 dozen each beakers, 4 oz. and 12 oz. 
 
 I ,, ,, flasks, 4 oz., 16 oz., and 40 oz, 
 
 1 ,, wide-mouthed flasks, 2 oz. 
 
 2 ,, Florence flasks, 6 oz. 
 
 1 ,, filter funnels, 3 inches. 
 
 I filter funnel, 6 inches. 
 
 X dozen thistle funnels, plain, 12 inches. 
 
LIST OF APPARATUS AND CHEMICALS 181 
 
 I dozen thistle funnels, safety, 12 inches. 
 I ,, retorts, stoppered, 10 oz. 
 I ,, calcium chloride tubes, 7 inches. 
 £ ,, fractionation tubes, 1 bulb. 
 I gross test-tubes, 5 by £ inches. 
 
 1 dozen each test-tubes, 7 by £ and 7 by i| inches. 
 
 3 ,, U tubes, with connecting tubes attached, 4 inches. 
 
 2 ,, watch glasses, 2 inches. 
 
 Glass Apparatus {Heavy). 
 
 £ dozen stoppered bell jars, 9 by 5 inches. 
 
 1 „ „ narrow-mouth bottles, 150 c.c 
 
 £ ,, ,, wide-mouth „ „ 
 
 1 aspirating bottle, I gallon. 
 
 £ dozen lamp glasses. 
 
 £ ,, Liebig's condensers, 14 inches. 
 
 1 dessicator, including bell jar, 11 inches diameter, ground glass 
 
 plate, porcelain dish, and perforated zinc plate. 
 1 stoppered separating funnel, 150 c.c. 
 1 dozen wide-mouth bottles, with ground tops, 40 oz. 
 1 ,, narrow-mouth bottles, 32 oz., fitted with cork and tubes, as 
 
 wash bottles. 
 1 ,, ground glass plates, 3 inches. 
 I ,, cylinders, with ground tops, 10 by i| inches. 
 I only „ „ 15 by 2 „ 
 
 Tubing. 
 
 10 lbs. glass tubing, 3 to 5 m.m. bore. 
 1 lb. soft glass tubing, 15 m.m. ,, 
 7 lbs. combustion tubing, 12 m.m. bore. 
 6 feet india-rubber tubing, \ in. „ 
 
 3° » » » I in « » 
 
 1 foot thermometer tubing, cylindrical bore. 
 
 B. Chemicals. 
 
 All the folloiving Chemicals to be of commercial quality unless 
 otherwise stated. 
 
 \ lb. acetic acid, glacial. 
 
 2 lbs. alcohol (rectified spirit). 
 
 J lb. fusel oil. 
 
 1 oz. aluminium foil. 
 I ,, alumina. 
 
 emery (specimen). 
 
182 CHEMISTRY FOR AGRICULTURAL STUDENTS 
 
 1 lb. potash alum. 
 
 kaolin (specimen), 
 mica (specimen), 
 felspar (specimen). 
 
 2 lbs. solution of ammonia, cone. 
 I lb. ammonium carbonate. 
 
 4 lbs. sal-ammoniac. 
 ^ lb. ammonium molybdate solu- 
 tion. 
 £ ,, ammonium oxalate. 
 I ,, ,, sulphate. 
 
 I oz. arsenious oxide. 
 
 asparagine (specimen). 
 i ,, asbestos, coarse fibre. 
 £ „ platinised asbestos. 
 i ,, butyric acid. 
 4 lb. barium chloride. 
 J „ baryta. 
 
 heavy spar (specimen). 
 
 caffeine (specimen). 
 I grain calcium. 
 4 lbs. quicklime. 
 I lb. calcium chloride, gran. 
 I ,, calcium carbonate. 
 7 lbs. marble. 
 
 calc spar (specimen). 
 
 chalk (specimen). 
 I lb. calcium sulphate, pure. 
 
 selenite (specimen). 
 £ „ calcium phosphate. 
 
 apatite (specimen). 
 
 basic slag (specimen). 
 
 superphosphate of lime (speci- 
 men). 
 
 Peruvian guano (specimen). 
 
 coprolite (specimen). 
 
 bone meal (specimen). 
 I „ wood charcoal. 
 
 gas carbon (specimen). 
 
 lamp-black (specimen). 
 
 graphite (specimen). 
 £ „ chloroform, methylated. 
 
 I oz. cobalt chloride solution. 
 I ,, cochineal solution. 
 £ lb. cotton wool. 
 I ,, copper turnings. 
 £ ,, fine copper wire. 
 brass (specimen). 
 I ,, cupric oxide, gran. 
 \ ,, copper sulphate. 
 5 ,, citric acid. 
 J „ dextrin. 
 \ ,, ether, methylated. 
 I ,, glycerine. 
 \ doz. gold leaves. 
 \ lb. hydrogen peroxide, 5 vol. 
 
 1 w. qt. hydrochloric acid, coml. 
 
 2 lbs. hydrochloric acid, pure. 
 
 \ lb. iodine in potassium iodide 
 solution, 
 iron plate (specimen), 
 steel plate (specimen). 
 
 1 ,, iron filings. 
 \ ,, ferric oxide. 
 
 £ ,, ferrous sulphate. 
 | „ „ sulphide. 
 
 haematite (specimen). 
 
 iron pyrites (specimen). 
 \ lb. indigo solution. 
 
 lead plate (specimen). 
 \ ,, litharge. 
 
 2 lbs. red lead. 
 
 I oz. lead acetate. 
 
 I lb. litmus solution. 
 
 i dozen books litmus paper, red 
 
 and blue. 
 I oz. lactic acid. 
 I ,, magenta. 
 I „ magnesium ribbon. 
 \ lb. „ sulphate. 
 
 I Oz. magnesia. 
 
 dolomite (specimen). 
 
 magnesian limestone (speci- 
 men). 
 
LIST OF ATFARATUS AND CHEMICALS 
 
 iS 
 
 steatite (specimen). 
 
 1 lb. sodium. 
 
 4 lbs. manganese dioxide. 
 
 1 ,, „ chloride, pure. 
 
 14 ,, mercury. 
 
 10 lbs. common salt. 
 
 £ lb. mercuric oxide. 
 
 £ lb. sodium carbonate, pure. 
 
 1 w. qt. nitric acid, coml. 
 
 ^ ,, ,, bicarbonate. 
 
 1 bottle compressed oxygen. 
 
 1 ,, caustic soda, sticks. 
 
 \ lb. oxalic acid. 
 
 2 lbs. caustic soda, powder. 
 
 1 oz. oleic acid. 
 
 £ lb. sodium sulphate. 
 
 1 ,, triolein. 
 
 £ „ ,, sulphite. 
 
 2 feet platinum wire. 
 
 1 „ ,, nitrate. 
 
 1 oz. palmitic acid. 
 
 1 „ ,, nitrite. 
 
 1 ,, tripalmitin. 
 
 1 ,, „ silicate. 
 
 1 qt. crude petroleum. 
 
 I ,, soda lime. 
 
 1 lb. petroleum spirit. 
 
 1 ,, standard soap solution. 
 
 \ ,, paraffin wax. 
 
 1 ,, starch. 
 
 I oz. phosphorus. 
 
 \ ,, grape sugar. 
 
 \ ,, amorphous phosphorus. 
 
 i ,, milk sugar. 
 
 1 ,, phosphoric acid. 
 
 £ ,, inulin. 
 
 1 „ pepsin. 
 
 4 lbs. cane sugar, lump. 
 
 1 ,, potassium. 
 
 I lb. sulphur, roll. 
 
 I lb. caustic potash, sticks. 
 
 I w. qt. sulphuric acid, coml. 
 
 1 ,, potassium carbonate, fused. 
 
 4 lbs. sulphuric acid, pure. 
 
 1 „ „ nitrate. 
 
 1 lb. liquefied sulphur dioxidf 
 
 \ ,, ,, bichromate. 
 
 j. oz. stearic acid. 
 
 1 „ „ permanganate. 
 
 I ,, tristearin. 
 
 £ „ ,, ferrocyanide. 
 
 \ lb. tin, gran. 
 
 1 oz. „ cyanide. 
 
 solder (specimen). 
 
 kainite (specimen). 
 
 I lb. tartaric acid. 
 
 | „ quinine. 
 
 1 oz. urea. 
 
 1 ,, silica. 
 
 1 carboy distilled water. 
 
 4 lbs. silver sand. 
 
 1 lb. zinc, gran. 
 
 flint (specimen). 
 
 1 oz. zinc foil. 
 
 quartz, crystal (specimen). 
 
 £ lb. zinc sulphate. 
 
 I oz. salicylic acid. 
 
 1 oz. zinc oxide. 
 
 £ ,, silver nitrate. 
 
 
 The cost of the foregoing set of apparatus and chemicals as estimate* 
 by Messrs. Baird & Tatlock, is ^45 12s., net. 
 
INDEX 
 
 When the reference to a metallic salt is required, turn to the particular salt 
 and particular metal ; the pages common to each will contain the reference. 
 
 Acetates, 155, 162. 
 Acetic acid, 153. 
 
 ether, 155. 
 
 Acetylene, 147. 
 Acid reaction, 18, 51. 
 
 salts, 96, 98, 99, no, in, 150, 
 
 154, 160. 
 Acidic oxides, 51, 53, 66. 
 Acids, 66, 79, 81. 
 
 action on metals, 76, 89. 
 
 basicity, 154, 171. 
 
 organic, 154, 170. 
 
 Aconjtine, 160. 
 Adhesion, 102, 103. 
 Air, a mixture, 43. 
 
 composition, 16, 85. 
 
 density, 40. 
 
 weight, 14, 39. 
 
 Albumin, 163, 165. 
 Albuminoid, 162, 165-168. 
 
 ratio, 168. 
 
 Alcohol, 148-155. 
 
 physical properties, 35. 
 
 Alcohols, 151-153, 170. 
 
 mono- and polyhydric, 152, 154. 
 
 Aldehydes, 154, 170. 
 Alizarine, 146. 
 Alkalies, 57. 
 Alkaline earths, 57. 
 
 reaction, 51. 
 
 Alkaloids, 160, 168. 
 Allotropy, 67, 84, 94, 102. 
 Alloys, 58, 59. 
 Alum, 73. 
 Alumina, 52. 
 test for, 64. 
 
 Aluminium, 60, 108. 
 
 gold, 58. 
 
 occurrence, 58, 100. 
 
 oxide ; see alumina. 
 
 salts, 73, 99, 100. 
 
 Amalgam, 58. 
 
 Amides and amines, 160, 166, 168. 
 Ammonia, 85, 104, in, 112, 114, 145, 
 146. 
 
 derivatives, 160. 
 
 sulphate of, 87, 92, 93, 112, 146. 
 
 test for, 87. 
 
 Ammoniacal liquor, 145. 
 Ammonium, 87, 116. 
 
 salts, 86, 87, 90, 97, 112, 161. 
 
 Amorphism, 73, 94, 102. 
 Analysis, 42. 
 Anhydrides, 52. 
 Aniline, 146. 
 Animal life, 166, 171. 
 Anthracene, 146, 148. 
 Anthracite, 140. 
 Antimony, 108. 
 
 occurrence, 67. 
 
 sulphide, 67. 
 
 Antiseptics, 154, 166. 
 Apatite, 97. 
 Arabin, 140. 
 Argon, 85. 
 Arsenic, 107. 
 Asbestos, 99. 
 Asparagine, 161. 
 Atmosphere, the, 13. 
 
 pressure of, 14-16. 
 
 Atomic weights, 62, 113. 
 
 physical properties and, 116. 
 
 185 
 
i86 
 
 INDEX 
 
 Atoms, 113. 
 
 Atropia, 160. 
 
 Availability of soil constituents, 97, 9 
 
 Avogadro's hypothesis, 114. 
 
 Baking powder, 149. 
 Barium, 55, 57, 62. 
 
 occurrence, 73. 
 
 oxide ; see baryta. 
 
 salts, 73, tj. 
 
 test for, 55. 
 
 Barometer 15, 16. 
 Baryta, 52, 77. 
 Bases, 51, 85, 160. 
 Basic oxides, 51, 63, 64. 
 
 hydrates, 65. 
 
 salts, 98, 99. 
 
 slag, 98. 
 
 Basicity of acids, 154, 171. 
 Beer, 152, 153. 
 
 Benzene or benzol, 145, 146, 148. 
 Benzine and benzoline, 143. 
 Benzoic acid, 154. 
 
 aldehyde, 154. 
 
 Bicarbonates, in, 158. 
 Bichromate of potash, 64, 153. 
 Bile, 167. 
 Black lead, 103. 
 Bleaching agents, 70, 84. 
 Blood, 164, 167. 
 Blue stone ; see vitriol, blue. 
 Boiling points, 26, 35, 142, 152. 
 Bone, 97, 102. 
 
 ash or earth, 97, 102. 
 
 black, 102. 
 
 Boron, boracic acid, and borax, 166. 
 
 Brass, 58. 
 
 Bread, 149. 
 
 Breaking strain of metals, 58, 60. 
 
 Brewing, 152. 
 
 Bricks and brick earth, 100. 
 
 Britannia metal, 58. 
 
 British gum, 137. 
 
 Bromine and bromides, 81. 
 
 Bronze coin, 58. 
 
 Bunsen burner, 146. 
 
 Butane, 142. 
 
 Butter, 154, 159. 
 
 Butyrate of glyceryl, 154, 156, 159. 
 
 Butyric acid, 153, 154, 159. 
 
 Butyrin, 156, 159. 
 
 Caffeine, 161. 
 Calamine, 108. 
 Calc spar, 109. 
 
 Calcium, 55, 57, 62. 
 
 occurrence, 73, 97, 99, 109. 
 
 oxide and hydroxide ; see lime. 
 
 salts, 26, 53, 73, 75, 81, 91, 95, 97, 
 
 98, 100, 108, 109, in, 158. 
 
 test for, 55. 
 
 Calibration, 12. 
 
 Candles, 158. 
 
 Cane sugar, 139, 141, 148, 149, 168. 
 
 Capillarity, 101, 102. 
 
 Carbamide, 161. 
 
 Carbohydrates, 136, 141, 167, 168, 171. 
 
 Carbolic acid, 151, 152. 
 
 Carbon, 23, 25, 62, 83, 102, 106-108, 
 
 136, 140, 146, 147. 
 
 dioxide ; see carbonic acid gas. 
 
 monoxide, 107, 145. 
 
 Carbonates, 103, 108-112, 158. 
 
 Carbonic acid, no. 
 
 gas, 22-26, 43, 52, 105-107, no, 
 
 in, 114, 145, 149, 152, 167. 
 Carbonisation, 102, 141. 
 Carnallite, 81. 
 Casein, 163, 165. 
 Cellulose, 136, 138, 140, 141, 152. 
 
 salts, 139. 
 
 Cements, 74, 109. 
 Chalk, 22, 108. 
 
 French, 99. 
 
 Charcoal, 25, 89, 102-104, 107, 147. 
 
 Chemical change, 42, 171. 
 
 combination, 19, 42, 43, 66, 70, 
 
 112-114, 171. 
 
 compounds, 19, 43. 
 
 elements, 19, 62. 
 
 equations, 72. 
 
 equilibrium, jj. 
 
 formulae, 62, 72, 82, 115, 116. 
 
 Chemistry, science of, 42, 172. 
 
 Chili saltpetre, 88. 
 
 Chlorides, 26, 78-82, 87, 92, 113. 
 
 occurrence, 81. 
 
 test for, 82. 
 
 Chlorinated lime, 84. 
 Chlorine, 62, 79, 82-84. 
 
 oxide, 52, 84. 
 
 Chlorophyll, 167. 
 Chromium, 62. 
 
 trioxide, 64. 
 
 Cinnabar, 67. 
 
 Classification of elements, 52, 116. 
 
 metals, 57. 
 
 organic compounds, 170. 
 
 Clay, 99-102. 
 ironstone, 108. 
 
INDEX 
 
 [87 
 
 Climate, 34, 35. 
 Coagulation, 163-166. 
 Coal, 140, 142. 
 
 gas, 142, 144-146. 
 
 tar, 145, 146, 151. 
 
 Cohesion, 58. 
 
 Coinage, 58. 
 
 Coke, 103, 145, 146. 
 
 Collodion, 139. 
 
 Colloids, 165. 
 
 Combination and compounds ; see 
 
 chemical. 
 Combining proportions, determination 
 
 of, 81, 25, 40, 61, 64, 71, 73, 80, 87, 
 
 108, 155. 
 
 weights, 42, 61, 62, 66, 112, 113. 
 
 Combustion, 17, 20, 23, 37, 56, 83, 86, 
 
 89, 94, 104, 106, 107, 146, 147. 
 Conductivity, 35, 59, 60. 
 Conservation of energy, 171. 
 Contact action, 70. 
 Cooking, i6«. 
 Copper, 56-60, 62, 76, 90, 108. 
 
 occurrence, 67, 108. 
 
 oxides, 40, 52, 63, 77, 138. 
 
 salts, 76, 77, 90, 138. 
 
 Coprolite, 97. 
 
 Correspondence of organic compound, 
 
 151, 170. 
 Cotton wool, 139. 
 Cream, 154, 159, 165. 
 
 of tartar, 154. 
 
 Creosote, 104. 
 
 Cresol, 151, 152. 
 
 Crops, carbohydrates in, 138, 139. 
 
 Crystalline form, 73-76, 78. 
 
 Crystallisation, 75, 76. 
 
 water of, 73. 
 
 Crystalloids, 165. 
 
 Cuprous and cupric oxides ; see copper, 
 
 oxides of. 
 Cyanogen and cyanides, 162. 
 
 Decolorisers, 104 ; see also bleach- 
 ing agents. 
 
 Dehydration, 65, 73, 137, 170. 
 
 Deliquescence, 26. 
 
 Density, 31-35, 38-40, 59, 60, 80, 86, 
 114, 150, 156, 159, 166. 
 
 Deodorisers, 84, 104. 
 
 Derivatives of ammonia, 160. 
 
 hydrocarbons, 170. 
 
 Dessication, 65. 
 
 Dew-point, 30. 
 
 Dextrine, 137, 138, 141, 152. 
 
 Dextrose ; see grape sugar. 
 Dialysis, 165. 
 Diamond, 102. 
 Diastase, 138, 152, 166. 
 Diffusion, 24, 164, 165. 
 Digestibility of foods, 168. 
 Digestive fluids, 167. 
 Disinfectants, 70, 84, 104. 
 Dissociation, 19, 21, 61, 65, 73, 90, 
 
 109, in. 
 Distillation, 29. 
 
 destructive, 85, 104, 142, 144. 
 
 fractional, 142, 149. 
 
 Dolomite, 108. 
 
 Double salts, 67, 73, 81, 97, 99, 108. 
 
 Drainage, 31, 93, 101. 
 
 Dyes, 146. 
 
 Earth's crust, 51. 
 
 Earths, 57. 
 
 Efflorescence, 73. 
 
 Electrolysis, 108, 171. 
 
 Elements ; see chemical. 
 
 Emery, 58. 
 
 Emulsion, 157, 165. 
 
 Epsom salt, 73. 
 
 Equations, 72. 
 
 Ethane, 142, 147, 151, 169, 170. 
 
 Ether, 150, 157. 
 
 acetic, 155. 
 
 nitrous, 151. 
 
 Ethereal salts, 150-152, 154, 155, 171. 
 Ethyl, 150. 
 
 salts, 150, 151, 155. 
 
 Ethylene, 145, 147. 
 Excreta, 161, 167, 168. 
 Expansion, 24, 35, 40, 59, 60. 
 Explosives, 89, 94, 139, 152. 
 
 Fats, 155-159, 165, 167, 168. 
 
 Felspar, 99. 
 
 Fermentation, 92, 141, 148, 149, 152, 
 
 161, 166, 167 ; see also putrefaction. 
 Ferments, 149, 166, 167. 
 Ferrocyanides, 162. 
 Ferrous and ferric compounds, 63, 91, 
 
 116 ; see also iron. 
 Fibrin, 163, 164. 
 Filters, 28, 104. 
 Fire damp, 104. 
 Flint, 99. 
 Food, 168. 
 Formalin, 154, 166. 
 Formic acid, 153, 154. 
 aldehyde, 154, 166. 
 
i88 
 
 INDEX 
 
 Formulae, 62, 72, 82, 115, 116. 
 Fractionation, 143, 149. 
 Freezing mixture, 34. 
 
 points, 27, 35. 
 
 Fruit sugar, 139, 141, 149. 
 Fuels, 107, 140, 143, 146, 147. 
 Fusel oil, 149, 151. 
 
 Galactose, 140, 141. 
 
 Galena, 67. 
 
 Gas carbon, 103, 146. 
 
 lime, 146. 
 
 Gases, athermancy, 35. 
 
 density, 38-40, 86, 114. 
 
 diffusion, 23, 24. 
 
 effect of pressure, 40. 
 
 — — expansion, 24, 40. 
 
 solubility, 29. 
 
 Gasoline, 143. 
 Gastric juice, 167. 
 Germination, 152, 166. 
 Glass, 100, 101. 
 
 density, 33. 
 
 Glauber's salt, 73. 
 Glucose ; see grape sugar. 
 Gluten, 163. 
 Glycerides, 158, 159. 
 Glycerine, 152, 157. 
 Glyceryl, 152. 
 
 salts, 152, 155-159. 
 
 Gold, 57. 
 
 coin, 58. 
 
 — — occurrence, 58. 
 
 physical properties, 58-60. 
 
 Granite, 51, 99. 
 
 Grape sugar, 139-141, 149, 167. 
 
 Graphite, 102. 
 
 Groups, 170. 
 
 Guano, 97. 
 
 Gums, 140. 
 
 Gun cotton, 139. 
 
 metal, 58. 
 
 powder, 89. 
 
 Gypsum, 73, 74, 97, in, 112. 
 
 Hematite, 58. 
 Haemoglobin, 167. 
 Hardness of metals, 59. 
 Hard water, in, 158. 
 Heat and chemical change, 21, 43, 54, 
 65, 86, 89, 137, 147, 166-168, 171. 
 
 capacity, 34, 35, 59, 60. 
 
 latent, 34, 35. 
 
 of combustion, 86, 147, 168. 
 
 unit, 35, 147. 
 
 Heavy metals, 57. 
 
 spar, 73. 
 
 Heptadecane, 142. 
 
 Hexane and hexadecane, 142. 
 
 Homologous series, 156. 
 
 Humus, 101. 
 
 Hydrates, 64-66, 70, 73, 74, 87, 109. 
 
 Hydrocarbons, 104, 140, 142-148, 170. 
 
 Hydrochloric acid, 78-83. 
 
 Hydrocyanic acid, 162. 
 
 Hydrogen, 37-41, 53, 62, 83, 145, 147. 
 
 oxide ; see water. 
 
 peroxide, 84. 
 
 Hydrolysis, 140, 151, 161, 166. 
 
 Hydrometer, 34. 
 
 Hydro-sulphuric acid ; see sulphuretted 
 
 hydrogen. 
 Hydroxides, 65, 87, 108, 139, 150, 152. 
 Hydroxyl, 139. 
 Hygrometer, 30. 
 Hypochlorite of calcium, 84. 
 Hypochlorous anhydride, 52, 84. 
 
 Ice, 26, 27. 
 
 Identification of chemical substances, 
 
 43- 
 
 Illuminants, 142, 146. 
 Indigo, 91. 
 Intestinal juice, 167. 
 Inulin, 138. 
 Invertase, 149. 
 
 Iodine and iodides, 81, 137, 141. 
 Iron, 16-20, 36, 56, 57, 62, 94, 97, 
 108. 
 
 galvanised, 56. 
 
 occurrence, 58, 67, 99, 108. 
 
 oxides, 19, 37, 52, 58, 63, 65, 99. 
 
 physical properties, 59, 60. 
 
 pyrites, 67. 
 
 salts, 76, 91, 162, 166. 
 
 sulphide, 67. 
 
 test, 162. 
 
 tinned, 56. 
 
 Isomorphism, 76. 
 
 Kainite, 81. 
 Kaolin, 100. 
 Kerosine, 143. 
 
 Lactic acid, 154, 166. 
 Lactose ; see milk sugar. 
 Lamp black, 103. 
 Latent heat, 34, 35. 
 Laws of chemical combination, 112, 
 113. 
 
INDEX 
 
 189 
 
 Lead, 62, 107, 108. 
 
 alloys, 58. 
 
 occurrence, 67. 
 
 oxides, 52, 61, 63, 82. 
 
 physical properties, 59, 60. 
 
 salts, 82, 113, 162. 
 
 sulphide, 67, 162. 
 
 Light and chemical change, 84, 90, 
 
 166, 167, 171. 
 Lignite, 140. 
 Lime, 52, 57, 63-65, 86, 93, 98, 100, 
 
 108-111. 
 
 stone, 109. 
 
 water, 22. 
 
 Liquefying points, 142. 
 
 Liquids, determination of density, 31- 
 
 34- 
 
 physical properties, 35, 142, 152. 
 
 solubility, 29. 
 
 Litharge, 52, 61, 63, 82. 
 Litmus, 18, 51, 103. 
 Loadstone, 58. 
 Lubricants, 143. 
 Luminosity, 144, 146. 
 Lump ammonia, 111. 
 
 Magnesia, 51, 52, 55, 56, 63, 96. 
 Magnesian limestone, 108. 
 Magnesium, 55-57, 62, 106, 108. 
 
 occurrence, 81, 99, 108, ill. 
 
 oxide ; see magnesia. 
 
 salts, 73, 74, 76, 81, 96, 99, 108, 
 
 in, 158, 166. 
 
 test for, 96. 
 
 Malachite, 108. 
 
 Malt, 152. 
 
 Maltose, 140, 141, 149, 152. 
 
 Manganese, 62, 108. 
 
 occurrence, 58. 
 
 oxides, 52, 58, 63, 64, 83, 84. 
 
 Manures, 81, 87, 91, 93, 97, 98, 112, 
 
 161. 
 
 mixture of, 98, no, 112. 
 
 Marble, 105, 109. 
 
 Marsh gas ; see methane. 
 
 Matches, 94. 
 
 Meerschaum, 99. 
 
 Melting point, 27, 35, 60, 142, 155, 
 
 156. 
 Mercury, 35, 56-60, 62, 108. 
 
 occurrence, 58, 67. 
 
 oxide, 19-21, 52, 56, 63. 
 
 - physical properties, 35, 60. 
 
 sulphide, 67. 
 
 Metallurgy, 107, 108. 
 
 Metals, 52-60. 
 
 action on acids, 76, 89, 90. 
 
 action on water, 36, 54-57. 
 
 alloys, 58, 59. 
 
 classification, 57. 
 
 hydroxides, 65. 
 
 noble and base, 57. 
 
 occurrence, 58, 67, 73, 81, 92, 97, 
 
 99, 108, 109. 
 
 oxides, 51-57, 63-65. 
 
 oxidisability, 53-58. 
 
 physical properties, 58-60. 
 
 sulphides, 67. 
 
 Methane, 104, 142, 145, 147. 
 Metric system, n, 12. 
 Mica, 99. 
 Milk, 165, 166. 
 — — analysis, 166. 
 
 sugar, 140, 141, 165, 166. 
 
 Molecular constitution, 171. 
 
 weights and physical properties, 
 
 142, 152, 156, 170. 
 Molecules and molecular weights, 
 
 Molybdenum and molybdate of am- 
 monium, 96. 
 
 Morphia, 160. 
 
 Mortar, 109. 
 
 Muriate of potash, 81. 
 
 ammonia, 87. 
 
 Muriatic acid and muriates, 79 ; see also 
 hydrochloric acid and chlorides. 
 
 Myosin, 164. 
 
 Myristates, 154, 156, 159. 
 
 Myristic acid, 154. 
 
 Myristin, 156. 
 
 Naphtha, 143. 
 Naphthalene, 146, 148. 
 Neutrality, 52, 71. 
 Nicotine, 160. 
 Nitrate of soda, 88, 92, 93. 
 Nitrates, 88-93, I 39> I 5 2 > *66. 
 
 tests for, 91. 
 
 Nitre, 88, 89, 91. 
 Nitric acid, 88-93, I 39' 
 
 anhydride, 52. 
 
 oxide, 89, 91. 
 
 Nitrification, 91-93, no. 
 
 Nitrites, 90, 150, 151. 
 
 Nitrogen, 19, 62, 85, 89, 90, 145, 147, 
 
 oxides, 52, 89, 90. 
 
 Nitro-glycerine, 152. 
 Nitrous acid, 90, 151. 
 oxide, 89. 
 
I9D 
 
 INDEX 
 
 Noble metals, 57. 
 Nomenclature of oxides, 64. 
 
 salts, 76, 77. 
 
 Non-metallic oxides, 52. 
 Non-metals, 52, 66. 
 
 OCTADECANE, 142. 
 
 Oils, IS4-I59. 
 
 volatile, 148, 154. 
 
 defiant gas ; see ethylene. 
 
 defines, 147. 
 
 Oleic acid and oleates, 154-159. 
 
 Olein, 155, 156. 
 
 Oleo-margarine, 159. 
 
 Organic acids, 153-155, 170, 171. 
 
 radicles, 150, 160, 162, 168, 169. 
 
 Osmose and osmotic pressure, 164, 
 
 165. 
 Oxalic acid and oxalates, 154, 171. 
 Oxidation, 16-20, 37, 53-57, 69, 70, 
 
 76, 82, 84, 89-94, 10 4> I 53> x 54> 
 
 167, 171. 
 Oxides, 19, 52, 63, 64. 
 
 mon-, di-, and tri-, 64. 
 
 Oxidising agents, 53, 76, 82-84, 89, 
 
 153. 167. 
 Oxy-acids, 81, 88. 
 
 Oxygen, 19-22, 54, 62, 66, 84, 90, 167. 
 Oxyhydrogen flame, 147. 
 Ozone, 84. 
 
 Palmitic acid and palmitates, 
 
 154-159. 
 Palmitin, 155. 
 Pancreatic juice, 167. 
 Paraffin, 142, 143. 
 
 series, 147. 
 
 — — wax, 143. 
 
 Paper, 139. 
 
 Pearl ash, 103. 
 
 Peat, 140. 
 
 Pentane and pentadecane, 142. 
 
 Pepsin, 164, 167. 
 
 Peptones and peptonisation, 164, 165, 
 
 167, 168. 
 Periodicity, 116. 
 Permanent gases, 37. 
 Permanganate of potash, 64, 84, 92. 
 Peroxides, 64. 
 Petroleum, 142, 143. 
 Pewter, 58. 
 Phenol, 151, 152. 
 Phosphates, 95-98, 166, 168. 
 ■ occurrence, 97. 
 tests for, 96. 
 
 Phosphides, 94, 97. 
 Phosphorescence, 94. 
 Phosphoretted hydrogen, 94. 
 Phosphoric acid, 95. 
 
 anhydride, 52, 94. 
 
 tests for, 96. 
 
 Phosphorus, 18, 62, 93, 94. 
 
 amorphous, 94. 
 
 hydride, 93. 
 
 oxide, 51, 52, 94. 
 
 Physical constants, 43. 
 Physics and physical change, 42. 
 Plants and plant food, 166. 
 Plaster of Paris, 74. 
 Platinum, 57, 58, 69. 
 Plumbago, 103. 
 Porcelain and pottery, 100. 
 Porosity of soil, 101. 
 
 charcoal, 103, 104. 
 
 Potash (caustic), 25, 51, 52, 54, 55, 57, 
 
 63, 65, 77, 88, 158. 
 Potassium, 51, 54, 55, 57, 59, 62, 108. 
 
 occurrence, 81. 
 
 oxide ; see potash. 
 
 physical properties, 59. 
 
 salts, 64, 73, 77, 81, 84, 88, 89, 
 
 91, 101, 103, 109, xix, 150, 151, 
 
 154, 158, 162, 166. 
 
 test for, 55. 
 
 Precipitation, 77. 
 
 Producer gas, 107. 
 
 Proof spirit, 150. 
 
 Propane, 142, 147, 170. 
 
 Propylene, 145, 147. 
 
 Prussian blue, 162. 
 
 Prussiate of potash, 162. 
 
 Prussic acid, 162. 
 
 Ptyalin, 138, 167. 
 
 Putrefaction, 68, 85, 91-93, 104. 
 
 Pyridine, 160. 
 
 Pyroligneous acid, 153. 
 
 Pyrolusite, 58. 
 
 Pyrometric effect, 147. 
 
 Quartz, 99. 
 Quinine, 160. 
 
 Rectified spirit, 150. 
 
 Red lead, 19, 61, 82. 
 
 Reducing agents, 76, 84, 90, 91, 107, 
 
 108, 138, 141. 
 Reduction, 76, 89, 107, 108, 138, 154, 
 
 167, 171. 
 Rennet, 163. 
 Replacement, 68, 160, 169. 
 
INDEX 
 
 191 
 
 Respiration, 23, 167. 
 Reversion of phosphates, 97. 
 
 Sal-ammoniac, 85, 86. 
 
 Salicylic acid, 154, 166. 
 
 Saliva, 138, 167. 
 
 Salt, 34, 78-81. 
 
 Saltpetre, 88, 89, 91. 
 
 Salts, 52, 53, 73, 76, 77, 150, 171. 
 
 of sorrel, 154. 
 
 Sand, 34, 98, 99, 101, 102. 
 Saponification, 151, 157, 167. 
 Selenite, 73, 75. 
 Silica, 52, 98, 99. 
 Silicates, 98-101. 
 
 occurrence, 99. 
 
 test for, 99. 
 
 Silicic acid, 99. 
 Silicon, 62, 98. 
 
 oxide ; see silica. 
 
 Silver, 57. 
 
 ■ coin, 58. 
 
 physical properties, 58, 59. 
 
 salts, 82. 
 
 Soap, 157-159* 
 
 stone, 99. 
 
 Soda (caustic) 52, 54, 55, 57, 63, 65, 71, 
 
 77, 80, 81, 98, 157, 158. 
 Sodium, 54, 55, 57, 59, 62, 83, 108. 
 
 occurrence, 81. 
 
 oxide ; see soda. 
 
 physical properties, 59. 
 
 salts, 71, 72, 73, 77, 78-81, 88, 
 
 90. 9 2 > 93- 95, 9 8 ~ l oi, 109-111, 155, 
 
 157, 158, 171. 
 
 test for, 55. 
 
 Soil, 31, 34, 35, 51, 91-93, 97, 101, 102, 
 
 in, 166. 
 
 mechanical analysis, ior. 
 
 Solder, 58, 59. 
 
 Solids, determination of density of, 33. 
 
 Solubility, 28-31, 64, 77, 93. 
 
 Soluble glass, 98. 
 
 Solutions, saturated, 28. 
 
 Solvents, 143. 
 
 Specific gravities, 35, 6o, 80, 114, 150, 
 
 156, 159, 166 ; see also density. 
 
 heat, 34, 35, 59, 60. 
 
 Spectra, 55. 
 
 Sperm oil, 143. 
 
 Spirit of hartshorn, 85. 
 
 ■ nitre, sweet, 150. 
 
 — — salts ; see hydrochloric acid. 
 
 ■ wine, 150. 
 Spirits, 152. 
 
 Starch, 136, 137, 141, 149, 152, 167, 
 
 168. 
 
 soluble, 137. 
 
 States of matter, 26. 
 
 Stearic acid and stearates, 154-159. 
 
 Stearin, 155-157. 
 
 Steel, 59, 60, 98. 
 
 Stibnite, 67. 
 
 Strontia, 57. 
 
 Strontium, 55, 57. 
 
 test for, 55. 
 
 Substitution, 68, 160, 169. 
 
 Suction pump, 16. 
 
 Sugar of milk, 140, 141, 165, 166. 
 
 Sugars, 136-141, 148, 149, 165-168. 
 
 Sulphate of ammonia as manure, 93. 
 
 Sulphates, 71, 73-78, 81, 87, 91, 97, 
 
 in, 112, 139, 145, 150, 158, 161, 166. 
 
 occurrence, 73. 
 
 test for, 78. 
 
 Sulphides, 67, 68, 108, 146. 
 
 occurrence, 67. 
 
 Sulphites, 77. 
 
 Sulphur, 62, 67, 68, 70, 89, 162. 
 
 oxides, 51, 52, 68-70, 77, 145. 
 
 test for, 162. 
 
 Sulphuretted hydrogen, 68, 145, 162. 
 Sulphuric acid, 70-72, 75-78, 87, 97, 
 
 99, no, 137, 138, 140, 160. 
 
 anhydride, 70. 
 
 Sulphurous acid, 68, 70, 77, 84. 
 
 anhydride, 52, 68-70, 77, 145. 
 
 Superphosphate of lime, 97, 98. 
 Synthesis, 42. 
 
 Talc, 99. 
 
 Tartaric acid and tartrates, 154. 
 
 Temperature, 27. 
 
 Terpenes, 147. 
 
 Theine, 161. 
 
 Theobromine, 161. 
 
 Thermometers, 27, 30, 34, 59. 
 
 Tiles, 100. 
 
 Tin, 58-60, 89, 108. 
 
 occurrence, 58. 
 
 oxide, 58, 89, 90. 
 
 stone, 58. 
 
 Toluene, 152. 
 Trimethylamine, 160. 
 Turpentine, oil of, 147. 
 Type metal, 58. 
 Types, 169. 
 
 Urate of ammonium, 97. 
 Urea, 161, 168. 
 
192 
 
 INDEX 
 
 Uric acid, 161. 
 Urine, 161, 168. 
 
 Valency, 115, 116. 
 Vapour pressure, 27, 29, 35. 
 Vaseline, 143. 
 
 Vegetable life, 166, 167, 171. 
 Ventilation, 23, 24. 
 Vinegar, 153, 154. 
 Vitriol, oil of, 70. 
 
 blue, green, and white, 76. 
 
 Volatile oils, 148, 154. 
 Volumetric determinations, 71, 8o, 87 
 95. 109, 154. 
 
 Water, 26-38, 43, 53, 62, 92, 102, 111 
 
 150.. 
 
 analysis, 92. 
 
 chemical properties, 53-57, 64-66 
 
 70, 75, 76, 84, 107, 109, 140, 149 
 
 161, 167. 
 
 composition, 36-38, 40, 41, 62. 
 
 hardness, in, 158. 
 
 Water in fuels, 147. 
 
 of crystallisation, 73, 74, 109. 
 
 physical properties, 26-35. 
 
 rain, spring, and sea, 29-31, 81, 
 
 92, in. 
 Water gas, 107. 
 Weights and measures, 11-13. 
 Whey, 165. 
 Wine, 152. 
 Wood, 102, 140, 147. 
 
 gas, 104. 
 
 spirit, 151. 
 
 Work, 167. 
 
 Yeast, 149, 152. 
 
 Zinc, 55-60, 62, 67, 75, 76, 89, 108. 
 
 alloys, 58. 
 
 blende, 67. 
 
 occurrence, 67, 108. 
 
 oxide, 52, 55, 56, 63, 64, 76. 
 
 physical properties, 60. 
 
 salts, 76, 108. 
 
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