NA TURE 



193. 



THURSDAY, DECEMBER 27, 1S94. 



A STANDARD TREATISE ON CHEMISTRY. 

 A Treatise on Cheiitistry. By Sir H. E. Roscoe, F.R.S., 

 and C. Schorlemmer, F.R.S. Vol. I. "The Non- 

 Metallic Elements." New edition, completely revised 

 by Sir H. E. Roscoe, assisted Isy Drs. H. G. Colman 

 and A. Harden. Pp. xi. 888. (London : Macmillan 

 and Co., 1S94). 



TO write a satisfactory review of this book is no easy 

 task. The word which shall e.xpress an appreci- 

 ation and a criticism does not come readily to one's pen. 

 Turning over the pages and reading the lucid descrip- 

 tions of preparations and properties of element after 

 element, and compound following compound, one is 

 depressed, and borne down by the burden of many facts 

 and much learning. But to this depression succeed the 

 pleasure and the sense of power that belong to the 

 gaining of knowledge, and the feeling of security that 

 remains with the man who has got down to fund imental 

 facts. 



In the preface to the first edition of this " Treatise," the 

 authors said : 



" It has been the aim of the authors ... to place 

 before the reader a fairly complete, and yet a clear and 

 succinct, statement of the facts of modern chemistry, 

 whilst at the same time entering so far into a discussion 

 of chemical theory as the size of the work and the pre- 

 sent transition state of the science permit." 



In his preface to the present edition. Sir Henry Roscoe 

 says: 



"In this new, completely revised and reprinted, edition 

 I have endeavoured to carry out the aims which were put 

 forward in the preceding preface seventeen years ago.' 



The aim and scope of the work are made evident by 

 these extracts from the prefaces. There can be no doubt 

 that the authors succeed in giving " a fairly complete, 

 and yet a clear and succinct, statement of the facts of 

 modern chemistry." The descriptions of the properties 

 of elements and compounds are lucid, full, and accurate ; 

 where all the properties of a substance cannot be 

 described, the selection made is satisfactory, sometimes, 

 one may suppose a student to say, too satisfying. But 

 this even llow of excellent description does not inspire 

 with enthusiasm him who reads; it does not open up 

 glimpses of the unexplored regions ; it fails to stir the 

 emotions. The book is wanting in the charm that 

 accompanies the "twilight of dubiety." 



It is difficult always to agree with the authors in their 

 estimate of the relative importance of chemical facts. The 

 most important fact of modern chemistry I take to be the 

 statement that "the properties of the elements and com- 

 pounds,and the compositions of compounds, vary periodi- 

 cally with the atomic weights of the elements." This 

 f.ict ought, I think, to be made the basis of every treatise 

 on descriptive chemistry ; because only by doing this 

 can the facts regarding individual substances appear in 

 right perspective. The great fact which we owe to the 

 genius of MendeU'cfi' will find expression in a later 

 volume of this "Treatise" (sec p. 53); but the student who 

 uses the book will then probably have arranged the intel- 

 NO. 131 3, VOL. 51] 



lectual contents of his mind, so far as chemistry is con- 

 cerned, in many little parcels, each tied up separately, 

 and he will find much difficulty in untying the parcels, 

 arranging their contents afresh, and getting them all 

 within the compass of the one binding generalisation. 



.-\s regards the statements of the properties of the 

 different non-metallic elements and their chief com- 

 pounds, no detailed appreciation is called for. Where 

 all is excellent, a general expression of praise is sufficient. 

 The chapters wherein are described hydrogen, fluorine, 

 oxygen, sulphur, nitrogen, and the other non-metals, and 

 the principal compounds which these element form by 

 combining with one another, contain all that student 

 of chemistry requires to know about these elements and 

 compounds, except the comparison and contrast — that is 

 to say, the classification — of the substances described 

 The student has presented to him, in this volume of 

 the " Treatise, " the material that is needed for acquiring a 

 real knowledge of the chemistry of the non-metallic 

 elements. 



Some of the expressions, and the ways of putting 

 descriptive facts, might be improved, in my opinion. 



" Hydrogen occurs almost solely in a state of com- 

 bination in nature" (p. 129). 



" In a state of combination hydrogen occurs in water " 

 (p. 129). 



'' Bromine does not occur in the free state in nature ' 

 (p. 188). 



Expressions like these seem to me to be survivals 

 from the alchemical times, when, to take an example, 

 nitric acid was looked on as water endowed with acidic 

 qualities, which could be removed or restored at pleasure, 

 and hence was called aqua for/is. Surely it is not 

 hydrogen that occurs "in a state of combination," but 

 compounds of hydrogen that occur in nature. Similarly 

 if bromine occurs at all it must be "in the free state," 

 else it would not be bromine but something else. Each 

 compound of hydrogen, and each compound of bromine 

 is just as definitely a chemical individual as hydrogen, or 

 bromine, itself. 



I do not think that the object of chemistry, namely 

 the study of the connexions between changes of 

 composition and changes of properties, is set forth with 

 sufficient clearness. The statement on pp. 51, 52, for 

 instance, that 



" the science of chemistry has for its aim the experi- 

 mental examination of the elements and their com- 

 pounds, and the investigation of the laws of their com- 

 bination one with another," 



cannot be regarded as satisfactory. On the other hand, 

 the examples given of chemical action, in the pages 

 preceding that where the sentence just quoted occurs, 

 undoubtedly serve to keep before the student the 

 fundamental fact that change is the essential note of all 

 chemical occurrences. 



The term density is sometimes applied to gases in a 

 wav that is confusing. For instance, on p. 160 the term 

 is applied to the relative density of chlorine, referred to 

 hydrogen as unity, and also referred to air as unity, 

 without an indication that the unit has been changed. 



A feature of the book which is much to be commended 

 is the giving of the defi'nite experimental data from 

 which important conclusions are deduced. A good 



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