564 



NA rURE 



[M 



\v 27, 1909 



of a large number of students of physical chemistry. 

 Within the limitrs which the author has allowed 

 himself, a very large amount of experimental work 

 has been collected and discussed, and in this connec- 

 tion even the most recent work has received attention. 

 In the initial chapters, however, dealing with the 

 physical properties of substances, the author has been 

 somewhat niggardly, and one is struck by a want 

 of balance. Thus, whereas twenty pages have been 

 allotted to the discussion of surface tension and the 

 molecular weight in the liquid state, together with an 

 excellent account of the author's drop method, barely 

 a page has been devoted to refraction of light, and 

 no mention at all is made of the rotation of the 

 plane of polarised light. It must be confessed, also, 

 that at times the condensation of language makes 

 the reading of the book somewhat of a strain, and 

 is productive of want of lucidity; so that the book, 

 in parts, assumes the character of lecture notes rather 

 than that of a self-explanatory text-book. In many 

 cases, however, the author has been successful in 

 minimising this evil by the insertion of tables of 

 experimental results, and by the working out of 

 numerical examples. This last feature of the book 

 is indeed one to be greatly commended. No one 

 can obtain a useful grip of physical chemistry without 

 the study and actual working out of numerical 

 problems. The collection of such problems inserted 

 at the end of the book will therefore .be of great 

 value, both to the teacher and to the student. 



The author has not been afraid to employ the 

 methods of the calculus or to introduce the student 

 at an early point to the study of thermodynamics. 

 We can only wish that such a method might be 

 adopted with some prospect of success in this 

 country. 



During the period which has elapsed since the 

 appearance of the first edition, change has taken place 

 in the attitude of mind of the author. Before the 

 appearance of the third edition, the author states that 

 he had come under the influence of Ostwald's " Natur- 

 philosophie," and as a result he sets before himself 

 the aim " to distinguish sharply between hypothesis 

 and fact, avoiding the former as far as is possible." 



Now, it cannot be denied that among students of 

 science too little attention is usually paid to the 

 philosophical side of the subject, so that the true 

 meaning of a law, an hypothesis, and a theory is 

 insufficiently appreciated, leading as a result to the 

 confusion of hypotheses and theory with fact. Still, 

 it cannot be said that the cure for this is to discard 

 hypotheses altogether. Hypotheses are most valuable 

 for the development of a science, so long as they are 

 recognised as such, and are kept in their place. But 

 the author himself is apparently none too sure of his 

 ground here. It is, of course, perfectly competent for 

 him, if he thinks it good, to eliminate hypotheses and 

 theories, and to confine himself to what is experi- 

 mentally determinable, and to generalisations of such 

 observed facts, but when he states (p. 187) : " By the 

 word theory, then, we do not mean a hypothesis in 

 which something not observed is added to the facts 

 to ' explain ' them, but only a generalisation of ob- 



NO. 2065, VOL. 80] 



served facts," surely he is taking undue liberties with 

 language which can be productive only of confusion. 

 Such a standpoint is to be regretted, for it greatly 

 reduces the value of a book which has otherwise very 

 much to recommend it. 



(2) The second of the two books mentioned above 

 can be heartily welcomed. It is put forward by the 

 author as " an elementary introduction to physical 

 chemistry," and as such the reviewer believes that 

 it will, on the whole, be found very satisfactory. It 

 cannot, and does not pretend to, treat in detail the 

 whole subject of physical chemistry, but it does 

 attempt, and this successfully, to introduce the student 

 to the more important parts of the subject, special 

 stress being laid on the modern theory of solutions, 

 the principles of chemical equilibrium, electrical con- 

 ductivity, and electromotive force. 



The order in which the author treats his subject is 

 as follows : — Fundamental principles of chemistry ; 

 the atomic theory; gases; liquid solutions; dilute 

 solutions; thermochemistry; equilibrium in homogen- 

 eous systems ; law of mass action ; heterogeneous equi- 

 librium ; the phase rule ; velocity of reaction ; cata- 

 lysis; electrical conductivity; equilibrium in electro- 

 lytes ; strength of acids and bases ; hydrolysis ; 

 theories of solution ; electromotive force. 



In the above treatment the author intentionally 

 devotes comparatively little space to the discussion of 

 physical properties and their relation to chemical con- 

 stitution. In this, doubtless, he was wise; and yet 

 one cannot help feeling that the addition of twenty, 

 or even of ten, pages devoted to experimental results 

 would not have greatly added to the bulk of the 

 volume, and would certainly have been of great value 

 in giving the student some idea of the utility of 

 physical methods for the elucidation of chemical con- 

 stitution. 



In connection with the subject of dilute solutions, 

 the treatment is not altogether satisfactory, insuffi- 

 cient emphasis being laid on the probability that 

 solutions are essentially different from gases. Some 

 indication might have been given that there is not 

 only an experimental, but also a theoretical reason 

 for substituting the mass of the solvent for the 

 volume of the solution in the general osmotic equa- 

 tion ; also the unsatisfactory character of the kinetic 

 explanation of the mechanism of osmotic pressure 

 should have been pointed out. Further, rather more 

 definite guidance might have been given to the 

 student than merely to say, " other views are that it 

 {i.e. osmotic pressure) is connected with attraction 

 between solvent and solute, or perhaps with surface 

 tension effects," especialh' as the reviewer has pointed 

 out that the surface-tension theory is untenable. It 

 is true that the author inserts, as a saving clause, the 

 sentence " It may be pointed out that the equivalence 

 of osmotic pressure and gas pressure in great dilution 

 is no evidence that they arise from the same cause," 

 but the student will still probably continue to believe 

 that the kinetic explanation is the best one. 



The discussion of electrical conductivity and of 

 electromotive force, two very important subjects, is 

 very well done. 



