Jan. 19, 1888] 



NATURE, 



267 



believe to be both historically and scientifically the correct 

 method. The composition of water should next be quali- 

 tatively ascertained. It is a sine quel tton that the experi- 

 ments made with the object of solving such problems be 

 throughout logically interrelated ; each experiment should 

 be suggested by the experiment or experiments previously 

 made, and should be made with the object either of 

 verifying or extending the information previously gained. 

 When a student is told to perform experiments selected 

 by the teacher for no apparent reason and merely with 

 the object of demonstrating some particular point, their 

 value as a logical exercise is practically ;«7. In solving 

 such problems as the composition of air and water, &c., 

 the student insensibly realizes the distinctions which are 

 to be drawn between mixtures, compounds and elements, 

 and soon learns to appreciate the characteristic difference 

 between chemical and so-called physical change ; but we 

 hold it to be a positive advantage not to insist too strongly 

 on the presumed difference now that it is becoming prob- 

 able that many phenomena hitherto regarded as physical 

 essentially depend on a change in molecular composi- 

 tion. 



These remarks apply also toChapter IV., already referred 

 to, and to Chapter V. ; in this latter, the slain of previous 

 chapters are rekilled. Chapter VI. is headed " Chemical 

 Properties of Water." Experiment i was quoted above 

 and appears to be intended to serve as proof of the com- 

 position of water. Experiments 2-7 have nothing what- 

 ever to do with water, but relate to the preparation 

 and properties of hydrogen and oxygen. Experiment 8 

 involves the examination of the residues from the pre- 

 paration of hydrogen and oxygen. Then follows the 

 oracular sentence : " Water is a compound of hydrogen 

 and oxygen ; let us examine a few of its properties." Ex- 

 periment 9 therefore directs the student to add powdered 

 copper sulphate crystals, potassium nitrate and tartar 

 emetic to separate portions of water, and to take note 

 that water acts on these as a solvent, inasmuch as their 

 composition is not changed by it. Experiment 10 con- 

 sists in adding anhydrous copper sulphate, and also solid 

 sulphur trioxide to water ; in both cases, it is found 

 that the water not only dissolves but acts upon the 

 substances. Here the chapter ends : we question whether 

 the most conscientious performance of the experiments 

 will lead the student to acquire any clear conception of 

 the " chemical properties of water." 



Thus far we have confined our remarks to the opening 

 chapters, it being our opinion that these are all-important 

 in a work which purports to teach the elements of 

 chemistry. But there is much in the arrangement of the 

 remainder of the book to which we venture altogether to 

 take exception. Thus a fatal error of judgment has led 

 the authors to postpone the experimental discussion of 

 the laws of chemical combination and of equivalent and 

 combining weights, as well as of molecular and atomic 

 weights, to Part II., placing in advance of these all-im- 

 portant subjects a variety of matters — among others a 

 discussion of the properties of the various elements 

 classified in groups in accordance with the periodic law — 

 which cannot properly be considered without a fairly 

 complete knawledge of the laws of chemical combination. 

 It is obvious that the authors to some extent recognize 

 their mistake, as the order is different in the companion 



volume, the laws of chemical combination, and symbols 

 and formulae being discussed in Chapters V. and VI. 



The ''Elementary (Jhemistry" contains a third part 

 dealing with subjects which are only touched on in the 

 companion volume ; this part is to be used in conjunction 

 with portions of the " Principles of Chemistry," by one 

 of the authors. Chapter I. of this part should have been 

 included in Part I. ; the remaining chapters ought never 

 to have been introduced into an "Elementary Chemistry," 

 and are obviously only included because of the senior 

 author's well-known tendency to worship physical con- 

 stants. Thus Chapter II. is headed Dissociation, and 

 directions are given for the performance of Lemoine's 

 experiments on the dissociation of hydrogen iodide, and 

 of Horstniann's on ammonium carbamate : the authors 

 evidently to some extent foresee the probable result of 

 making such experiments, as, in summing up those on 

 hydrogen iodide, they say : " The results of your experi- 

 ments ought to show " that such and such is the case. 

 How often would they? Chapter III. bears the title, 

 " Relative Affinities of Acids," and in it experiments are 

 described illustrating Thomsen's and Ostwald's methods ; 

 the same subject is briefly referred to in Chapter XVIII., 

 Part I. The main objection to this chapter is that 

 students of elementary chemistry are incapable of per- 

 forming such experiments with sufficient accuracy. 

 Moreover, it cannot yet be admitted that the conception 

 introduced by Thomsen is warranted : until the part 

 which the water plays is determined, neither Thomsen's 

 nor Ostwald's results can be accepted as furnishing 

 estimates of the relative affinities of acids for a given 

 base. A similar remark applies to Menschutkin's 

 etherification experiments, the repetition of, which is 

 directed in Chapter IV. : the complete interpretation of 

 these is yet to be given. 



Nothing is farther from our intention than the desire to 

 disparage the study of so-called physical properties — on 

 the contrary, we hold it to be of primary importance that 

 a proportionate amount of attention should be devoted by 

 students of chemistry to the physical side of their science ; 

 but let them learn before all things to regard the pheno- 

 mena from the true chemist's point of view. Chemistry 

 is to a large extent an art : a large number of relationships 

 and peculiarities which are obvious to the skilled chemist 

 will probably always elude mathematical treatment ; it 

 appears, indeed, to be as impossible to give formal expres- 

 sion to them by means of physical constants as it would 

 be to define the work of a great painter after spectroscopic 

 analysis in terms of wave-lengths. Especially have we 

 felt this to be the case on reading through Ostwald's 

 invaluable work : it has frequently struck us that he has 

 perhaps unduly forgotten his art as chemist in the exercise 

 of his great technical skill in determining and setting 

 forth physical constants, the result being a picture which 

 fails to satisfy. But it is not to be denied that chemists 

 as a class have not yet acquired that belief in the power 

 of physicists to help them forward which, with or without 

 reason, is demanded of them ; and this is not difficult 

 to understand. The establishment of the doctrine of 

 structure — the great achievement of modern chemistry — is 

 the outcome solely of chemists' labours ; in this particular 

 case, the study of physical properties has served to con- 

 firm the conclusions of chemists, but there is nothing to 



