NATURE 



i6i 



THURSDAY, MAY i, 1919. 



TH^ COMPLETE PHYSICAL CHEMIST. 



A System of Physical Chemistry. By Prof. 



\V. C. McC. Lewis. (Text-books of Physical 



Chiemistry.) Second 'edition. In three 



volumes. Vol. i., "Kinetic Theory. " Pp. xii + 



net. Vol. ii., "Thermo- 



vi + 403. Price 155. net. 



viii + 209. 



494. Price 155. 



dynamics." Pp. 



Vol. iii., "Quantum Theory." Pp. 



Price 75. 6d. net. (London : Longmans, Green, 



and Co., 1918-19.) 



A REVIEW of the first edition of Prof. Lewis's 

 '^*- book appeared in these columns in Sep- 

 tember, 1916, and the fact that a second edition 

 has been called for so soon must be very gratify- 

 ing- to the author. Prof. Lewis has taken advan- 

 tage of the opportunity thus presented him of 

 introducing a few corrections and amendments, 

 and has considerably increased the subject-matter. 

 The principal changes include the insertion of a 

 section on X-rays and crystal structure, large 

 additions to the sections on colloids, catalysis, 

 t'tc. , a new chapter on osmotic pressure, and the 

 expansion of the last chapter of the original 

 vol. ii. into a separate vol. iii., dealing exclusively 

 with the quantum theory. The excisions are 

 remarkably few, and we have only noted one of 

 any imp>ortance. 



The author's method of treatment of his subject- 

 matter naturally remains unaltered. The more 

 classical portions are presented to the student in 

 much the same manner as in several of the older 

 text-books (and, it might be added, lecture 

 courses). As regards more recent work the author 

 is apparently well aware of his rather obvious 

 lack of the critical faculty, and in the presentation 

 does not emphasise any particular point of view 

 as being his own. This he achieves by giving 

 the results of each piece of work in, so far as 

 possible, "the investigator's actual words." But, 

 whatever we may think of the lack of criticism in 

 the presentation of any particular summary, we 

 must confess that, as a whole, the work included 

 in the survey of each section is usually admirable 

 in its selection. So broad is the field covered by 

 the author that we can scarcely expect a critical 

 and authoritative pronouncement on every separate 

 item. 



Considering more closely a few points in vol. i., 

 we should have thought, since the work of Bohr 

 and Moseley has now been embraced in the author's 

 survey (in vol. iii.), that there would be some 

 alterations in the first chapter. The author's 

 sense of values appears at fault when he once 

 again app>ortions more space to Nicholson's theory 

 of the atom than to the whole subject of radio- 

 activity. There are some parts of the subject, 

 such as those dealing with the nuclear charge and 

 isotopism, the omission of which seems particu- 

 larly regrettable. As it stands, this small section 

 has scarcely been brought up to the knowledge 

 of the year 1916, far less of 1918, and this is true 

 NO. 2583, VOL. 103] 



of other references to the subject, such as that 

 on p. 449, which also seems in urgent need of 

 revision. In the summary of the Braggs' work 

 presented in the second chapter we were struck 

 by the consistent use of the sequence (y, x, e) 

 instead of the customary {», y, z) in the naming 

 of intercepts, and by the referring to the sodium 

 chloride space lattice as face-centred, while 

 what is meant is face-centred relative to one 

 kind of atom. In chap iii. we once again 

 encounter " the more convenient logarithmic form 

 SvlogC = K" instead of the usual logK. On 

 p. 197 the last column in the first table is still 

 uncorrected. Prof. Lewis apparently now regards 

 methyl-orange as "essentially a basic indicator," 

 and in consequence inserts as a correction the 

 word basic on p. 256, with the result that we 

 are informed that, since methyl-orange is neutral- 

 coloured in a io~^ H' solution, "its (basic) dis- 

 sociation constant lies in the neighbourhood of 

 10-*." This should evidently be lo"^". On p. 440 

 the author introduces as a new term " the displace- 

 ment effect." In view of the use that has already 

 been made of the defining word in Wien's dis- 

 placement law, the term is not too happily chosen, 

 and "replacement effect" is perhaps as suitable 

 a descriptive term. 



Turning to vol. ii., we find that a great portion 

 consists in the presentation, with the aid of thermo- 

 dynamics, of matter which has already been 

 partly discussed in vol. i. Whether this separa- 

 tion is altogether desirable is an arguable point. 

 To select an example at random, we confess we 

 are unable to see the virtue in giving in vol. i. a 

 table of the temperature variation of a mass 

 action constant, while the theory of the variation 

 is given in vol. ii. Again, in the new chap, viii., 

 "the mechanism of osmotic pressure " might have 

 seemed more in place in the first volume, which 

 deals with the kinetic point of view. As it is, of 

 course, it fits in quite well. In the addition at the 

 end of chap, i., in speaking of the vapour pressure 

 in a column, the author remarks: "the pressure 

 at the top being entirely due to the kinetic bom- 

 bardment by the molecules." But surely it could 

 be argued that the pressure at the foot is also 

 entirely due to the kinetic bombardment by the 

 molecules, even if it is greater than the pressure 

 at the top by the weight of the column per unit 

 area. We note that the author has now adopted 

 " S " in place of " <^ " as the symbol for entropy. 

 In his brief reference to the entropy equation of 

 a perfect gas there is no adequate discussion of 

 C», and the evasion of the lower limits of the 

 integral is not too adroit. A symbol, by the way, 

 is omitted in the first equation on p. 46. The 

 footnote on p. 100 to the effect that "thermo- 

 dynamic reversibility has, of course, nothing to 

 do with reversibility in the chemical or mass action 

 sense " seems oF>en to question. On p. 140 the 

 author is evidently unable or unwilling to decide 

 against Planck, though Planck has undoubtedly 

 slipped. As regards the footnote on p. 142, there 

 is a laboratory method of measuring e.m.f. which 

 does not involve the use of a potentiometer. 



K 



