August 25, 1923] 



NATURE 



^7Z 



"fugacity/' "escaping tendency/' and "activity" 

 play a great part in the authors' development of the 

 thermodynaihics of simple substances and solutions, 

 both non-conducting and electrolytic. The galvanic 

 cell and single potentials receive adequate treatment, 

 and a long chapter is devoted to the Third Thermo- 

 dynamic Principle and the Chemical Constants of 

 Nernst. The chapters of the last section of the book 

 deal systematically with the entropies or free energies 

 of chemical elements and their chief compounds. It 

 is in this section that the book differs essentially from 

 all its predecessors. So far as data are available they 

 are utilised to calculate the changes in free energy 

 attending important chemical reactions. Thus, under 

 the heading " water " there is discussed the free energy 

 of formation of water (a) from measurements of its dis- 

 sociation at high temperatures, {b) from the dissociation 

 of silver oxide, (c) from the dissociation of mercuric 

 oxide, and {d^ from the equilibrium of the Deacon pro- 

 cess. Based on the mean of the independent and con- 

 cordant values obtained by these four methods, a final 

 value for the free energy of formation of liquid water is 

 given. The free energy changes in the vaporisation 

 and solidification of water are discussed, and finally 

 the free energy of formation of the hydroxide ion. A 

 table is given of standard free energies of formation at 

 25°, together with instructions for its use and numerous 

 examples. 



While admiring the skill and clearness with which 

 many abstruse conceptions are brought before the 

 reader, we must direct attention to a statement which, 

 if not exactly erroneous, is certainly misleading. The 

 authors (p. 115), after defining change of entropy, say : 

 " Thus entropy has the same dimensions as heat 

 capacity, and may be expressed in calories per degree." 

 Again (p. 144), calculating the difference of entropy 

 between solid and liquid mercury at the constant 

 temperature of its freezing-point, they say : " We have 

 from Equation (i) ^S = AH/T. If /\H is the heat of 

 fusion of one mol, namely 560 cal., and T is 234' i, we 

 may write A5'234.i = 56o/234'i = 2*39 cal. per deg." 

 Surely there is an essential difference between AH/AT 

 (heat capacity) and AH/T (entropy) ; and surely the 

 words " per degree " imply that the temperature is 

 variable, which is here not the case. Such minor 

 lapses as the above are most infrequent, and we have 

 nothing but praise for, the book in general. The 

 formulae are clear, and the notation employed is con- 

 sistent, although not always in accordance with the 

 table of International Physico-chemical Symbols. A 

 good index is a valuable adjunct to the volume. 



(2) A cordial welcome will he given to the new edition 

 of Nernst's '' Theoretical Chemistry." Written by one 

 who is a master of research and of exposition, the 

 NO. 2808, VOL. 112] 



book has been the guide of many generations of serious 

 physico-chemical students, and nothing better of its 

 type is ever likely to appear. It is not everywhere easy 

 reading, but close study of the text will always provide 

 an ample reward. In the present edition the chapters 

 on radioactivity and the theory of the solid state have 

 been largely rewritten, and sections have been added 

 dealing with the structure of atoms and the application 

 of X-rays to the determination of molecular dimensions. 

 The translator, by not following the German text 

 too slavishly, has provided a version which is both 

 readable and accurate, though finer shades of meaning 

 are not always faithfully reproduced : thus (p. 767) 

 Zusammenbacken is translated by solidification, (p. 885) 

 Wechselwirkung by conversion, (p. 874) hochstwahr- 

 scheinlich by certainly. It might be worth the atten- 

 tion of the publishers to consider the use in future 

 editions of italic letters for algebraic quantities, as in 

 the German original, instead of Roman letters, as in 

 this translation. The former catch the eye better and 

 facilitate reading. 



A Scientific Introduction to Biology. 



Elements of Plant Biology. By A. G. Tansley. Pp. 

 410. (London : G. Allen and Unwin, Ltd., 1922,) 

 105. 6d. net. 



TO write a text-book of botany is nowadays no 

 easy task. The subject itself has grown in 

 many directions, and it demands some knowledge of 

 all the main branches of science as a preliminary 

 to tackling even the simpler problems with which it 

 confronts the student. A book intended for use in 

 junior classes in a university must obviously then be 

 the outcome of careful sifting and artistic synthesis of 

 raw material if it is to be of any real value, and especi- 

 ally is this true when the demands of the student of 

 medicine have to be satisfied. Botany, properly pre- 

 sented, forms perhaps the best introduction to biology 

 for the purpose of the medical student, but how often 

 when he has asked for bread has he been put off with 

 unprofitable and altogether unattractive stones ! 



A modern introduction to botany ought to aim at 

 affording some real insight into the working mechanism 

 of life, and to make it possible to understand, at any 

 rate, the more outstanding features of that mechanism 

 as it behaves when in action. The machinery is 

 vastly complex, and we have only been able as yet 

 to certainly know fragments of the factory-processes 

 that go on so swiftly and so smoothly within the plant 

 cell. But it is possible, even now, to pick out and 

 illustrate those processes by judicious selection of 

 material, and so vividly to portray them in their larger 

 outlines. 



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