266 



NA TURE 



\yan. 19, 1 



with some other kind of matter, the most Hkely source of 

 which is the air. We then read :— 



" We must now make two assumptions which can be, 

 and have been, proved by accurate experiments. We 

 shall assume (i) that the air is a mixture of at least two 

 gases called oxygen and nitrogen ; (2) that water is a 

 compound of two gases, hydrogen and oxygen. If then 

 hydrogen is brought into contact with a heated soHd sub- 

 stance and water is produced, it follows that oxygen 

 must have been taken away from the heated solid by the 

 hydrogen." 



The student is therefore directed to heat the copper 

 oxide previously obtained in a current of hydrogen, and 

 finally to weigh the tube. The weight is the same 

 as at the beginning of the series of experiments. 



" You have therefore proved, oil the basis of certain as- 

 sumptions, that when copper is heated in air it combines 

 with oxygen in the air to produce a new kind of matter 

 called copper oxide ; and that the weight of the copper 

 oxide thus produced is greater than that of the copper 

 from which it has been produced. By experiments too 

 difficult to be performed at p>rese?tt it can be proved that 

 the difference between these weights is the weight of the 

 oxygen which has combined with the copper." 



The effect of such teaching must be that the mind of a 

 student with inborn intelligence, instead of having logic 

 infused into it, will have become filled with profound con- 

 tempt of chemical experiments ; it is impossible that it 

 should lead to the acquisition of precision of thought or 

 judgment. In a properly chosen series of experiments 

 everything should be proved ; no assumption should be 

 necessary. 



" The arrangement of the course and the selection of 

 the experiments are the outcome of the experience gained 

 in teaching chemistry for many years " (preface). Having 

 in mind the manifestos issued at various times by one of 

 the authors, we naturally are led by this paragraph to 

 expect an entirely original treatment of the subject. But, 

 alas ! we fear we may safely say that " what is true is not 

 new, and what is new is not true " ! Thus, in Chapter IV., 

 which bears the imposing heading, " Conservation of 

 Mass of Matter/' we no longer meet with the classical 

 candle experiment, and we confess that we little regret 

 its banishment ; but what have we in its place ? , An ex- 

 periment in which zinc is dissolved in diluted sulphuric 

 acid, the hydrogen being retained in a tube ; and a 

 second, in which marble is dissolved in acid, the carbon 

 ■dioxide being prevented from escaping by potash solu- 

 tion. We venture to think that neither experiment is 

 calculated to impress the beginner, and that the only 

 proper demonstration in this case is by some form of 

 combustion experiment in which there is an apparent 

 destruction of matter ; but we hold that it is far better 

 simply to lead the student to observe that in every case 

 of apparent disappearance a new form or forms of mat- 

 ter are produced, and to postpone any attempt to teach 

 the law of the "conservation of matter" until a time 

 when the results of the gigantic labours of men like Stas 

 can be appreciated. Again, is a blue crystalline solid 

 obtained (Experiment 3, Chapter III.), on dissolving 

 copper in sulphuric acid and evaporating the liquid 

 nearly, but not quite, to dryness — we presume in a water- 

 bath, as directions have previously been given (p. 3) 

 always to use a water-bath, unless otherwise directed. 



In Experiment 8, Chapter V., the student is directed to 

 electrolyze water containing a little sulphuric acid, and 

 the accompanying cut represents a basin in which tubes 

 are inserted over electrodes connected with two bunsen 

 cells; in the figure the bunsens are 7/16 of an inch in 

 diameter, the basin is i inch across at the base, and the 

 liquid column 3/16 of an inch deep. Assuming the 

 bunsens used to be 4 inches in diameter, the basin 

 would be 7 inches across at the base, and the liquid 

 iy\ inches deep; there would consequently be a fairly 

 respectable quantity of water to electrolyze. Yet, at p. 7 

 of the " Elementary Chemistry" we read: " If the pro- 

 cess is continued, the water will at last entirely disappear, 

 and in place of it we shall have two colourless gases. 

 This result of " experience gained in teaching chemistry 

 for many years " is indeed remarkable ; the store of 

 energy in two bunsen cells is truly marvellous, and we 

 had not previously realized how great is the capacity of 

 tubes such as are figured. At p. 3 the direction is given to 

 add sodium to water in a basin, and, when the sodium is 

 all gone, to place the basin on a water-bath and evapor- 

 ate until the water is wholly removed. A white hard 

 lustreless solid called caustic soda is said to be obtained. 

 Here, again, the authors' experience is probably extra- 

 ordinary. We are also under the impression that the 

 student would be disappointed with the result of the 

 experiment figured on p. 30 of the " Elementary 

 Chemistry." 



Next, as to the arrangement of the course. What 

 strikes us most, and what we are least prepared to excuse, 

 in the " Practical Chemistry," is the entire absence of any- 

 thing approaching to a .$/.y/^w<;?//f arrangement. Part I. 

 consists of 102 pages, and the chapters bear the following 

 headings: I. Chemical and physical change; II. Ele- 

 ments and not-elements ; III. Not-elements divided into 

 mixtures and compounds ; IV. Conservation of mass of 

 matter ; V. Methods of bringing about chemical changes ; 



VI. Chemical properties of water; VII. Classification of 

 oxides; VIII. Acids and salts; IX. Classification of 

 salts ; X. Alkalis, and alkaline hydroxides; XI. Reactions 

 between acids and salts; XII.-XV. Classification of ele- 

 ments ; XVI. Conditions which modify chemical change ; 

 XVII. Oxidations and reductions; XVIII. Strong and 

 weak acids. In Part II. (78 pages) the chapters are headed : 

 I. Laws of chemical combination ; II. Equivalent and 

 combining weights ; III. Molecular and atomic weights ; 

 IV. Dissociation ; V. Reacting weights of compounds 

 determined by chemical methods ; VI. Chemical change; 



VII. Chemical classification. At the outset the authors 

 are strictly conservative, and in the most orthodox manner 

 possible in the first three chapters instruct the student to 

 dabble with a variety of substances never heard of for 

 the most part in ordinary life, and to this we most stren- 

 uously object. We are convinced that the only way of 

 beginning to teach chemistry, if the object be to cultivate 

 the faculties of experimenting, observing and reasoning, 

 is to deal with familiar objects and phenomena ; and that 

 at the very outset, after as fat as possible determining 

 the properties of familiar objects by means of ordinary 

 appliances, we ought to set our students to analyze. We 

 hold that air and the phenomena of combustion should be 

 first studied : the composition of air should be determined, 

 and oxygen should be discoveredhy\hQ student. This we 



