50 



Mature 



[May ]8, 1893 



CH3.C(OH):CH.CO.CH, and CH3.C(OH):C.C(OH) 

 CH3, took place. 



But physical methods can be applied to the study of 

 the phenomena of chemical change as well as to those of 

 ■chemical structure. Change of any kind taking place in 

 material substances is to be sought in the nature of the 

 energy associated with those substances, and chemical 

 change has therefore to be sought in the nature of 

 chemical energy. Of the nature of chemical energy, how- 

 ever, we know but little. Although it is the source of 

 most of the energy turned to practical account in the 

 arts and manufactures, and indeed, directly or indirectly, 

 ■of all vital energy, it cannot be directly measured, and 

 its nature is, as yet, but a matter for speculation. 



Part I of vol. ii. of the " Lehrbuch " is concerned with 

 making clear the present position of knowledge on this 

 subject of chemical energy. To begin with, energy in 

 general is discussed, the various forms under which it is 

 known to us, and the units in which they are measured. 

 Particular attention is directed to the factors which enter 

 into the expressions denoting several of the types of 

 •energy, and more especially to the intensity factor. In 

 the case of heat, for example, the intensity factor is tem- 

 perature, and temperature, of course, determines whether 

 heat energy shall be transferred from one body to another. 

 A heat change between two bodies is conditioned by their 

 temperature, and if the factors entering into the expres- 

 sion for chemical energy could be ascertained, the cause 

 of chemical change might be traced in a similar way. 



But although chemical energy cannot be directly 

 measured, it can be transformed into other kinds of 

 «nergy, and in turn other kinds of energy may pass into 

 chemical energy. The amounts of these other kinds of 

 energy which are thus involved in chemical processes are 

 often capable of accurate measurement, and from such 

 measurements alone can an insight into the nature of 

 chemical energy be at present obtained. With such 

 measurements the rest of the part is concerned. 



During chemical change, chemical energy passes most 

 readily and most completely into heat, and hence thermo- 

 chemistry is first dealt with. A general historical dis- 

 cussion of the subject is succeeded by chapters on the 

 non-metals, salt formation in aqueous solutions,the metals, 

 and organic compounds. The concluding chapters 

 deal with the " energetics " of heat, wherein is to be 

 found the material which can be grouped around the 

 second law of thermodynamics and the nature of heat 

 energy in general, and with " chemical energetics " which 

 treats of such attempts as have been made to arrive at 

 the nature of chemical energy and its relations to heat 

 energy. Where possible, connections between the 

 chemical nature of substances and the heat energy 

 to which they give rise during chemical change are 

 pointed out, and the general application of thermal re- 

 sults to problems in chemical structure is kept well to the 

 front. 



The subject of electro-chemistry, which his been entirely 

 recast, now occupies some 500 pages, as compared with 

 little more than 100 in the first edition. It consists 

 •of a historical introduction, and of chapters on electrical 

 energetics, Faraday's law, the migration of the ions, the 

 conductivity of electrolytes, the constitution of electro- 

 ytes and the properties of ions, electromotive force, the 

 NO. 1229, VOL. 48] 



differences of potential in cells, and on electrolysis and 

 polarisation. In this section the author has collected 

 and generalised the mass of communications which have 

 recently been brought into existence by the fruitful 

 hypothesis of electrolytic dissociation, and has connected 

 them up with previous knowledge on the electrical 

 properties of solutions. In conjunction with other por- 

 tions of the " Lehrbuch " on the stoichiometry of solutions, 

 this section gives the only full and systematic account of 

 the new theory of solutions which is available to the 

 general reader. 



The third and last book of this part takes up the sub- 

 ject of photo-chemistry. The nature of radiant energy, 

 which plays so important a part in the economy of nature 

 and its relations to chemical energy, are first discussed. 

 Then follow chapters on actinometry, the law of photo- 

 chemical action, and on special photo-chemistry, which 

 deals with the assimilation of carbon by plants, and the 

 action of light on various chemical substances. 



Enough has been stated to show that the work is unique. 

 There is no other book which even attempts to cover the 

 same ground. No chemical library can be regarded as 

 complete without a copy of Ostwald's "Lehrbuch." It con- 

 tains an enormous amount of information, both theoretical 

 and practical, which is simply indispensable to the chemist 

 and to the physicist. It is, indeed, difficult to overestimate 

 the value of such a work. 



Butatthesametime,mainly for the reason that it touches 

 upon so many subjects, its usefulness in certain directions 

 may to some extent be interfered with. One cannot fail 

 to notice that the character of the work frequently savours 

 more of a dictionary than a handbook. In the chapters 

 on solutions and electro-chemistry there is, perhaps, not 

 much room for this objection, for there the author 

 has a definite purpose in view— the elucidation oi 

 the "new theory" — and writes around it, moulding 

 his information and shaping the issues in a way thai 

 leaves little to be desired, if his standpoint be granted 

 Contrasted with the treatment of these sections we have 

 on the other hand, that of the book generally. Here are set 

 out short abstracts, in many cases but fragmentary, of the 

 more important researches on the subject under discussion, 

 but little attention being paid however to generalising the 

 results or smoothing down the discrepancies, or indeed the 

 contradictions which occasionally arise. For example, 

 under the subject of the molecular volumes of liquids Kopp's 

 work comes first, and his method of obtaining atomic 

 volumes is given, the values of carbon and hydrogen being 

 derived by the comparison of aromatic and fatty com- 

 pounds. In due course Horstmann's conclusion that the 

 ring-grouping of atoms exerts a marked effect on moleculai 

 volume finds a place, and the author passes on to other 

 researches. But if Horstmann's conclusion is justified 

 the whole superstructure of Kopp's calculated atotni| 

 volumes is subject to modification, as the effect of rin^ 

 grouping is ignored in the derivation of his atomic cow 

 stants. Again, here as elsewhere, the author gives 

 Schroder's work the prominence which has been more qi 

 less denied it in the past. Schroder's method, however, 

 involves different atomic constants to those of Kopp, 

 and it is left almost entirely to the reader to assess 

 the relative worth of the two systems. On oM 

 page of this chapter, too, Schiff's rule relating to 



