262 



NATURE 



[May 31, 1917 



of mankind." His book may be described as an 

 attempt to present and interpret the humanly 

 important aspects of plant nature in the light of 

 oiir modern scientific knowledge, and the test of 

 its value will be found, "not in whether my 

 colleagues consider it a well-proportioned com- 

 pendium of botanical fact, but in whether it leads 

 students to pursue the subject in an interested 

 and spontaneous spirit." Structure is treated 

 before function, because that is the more 

 practicable way, even though the reverse is more 

 logical. 



The present volume is Part i. of the whole 

 work, and is entitled "The Structures and 

 Functions of Plants." Part ii., "The Kinds and 

 Relationships of Plants," containing the descrip- 

 tion of the groups of plants and comprising about 

 125 pages, is delayed, but is expected to be ready 

 shortly. The subject-matter is divided into 

 chapters which deal successively with the various 

 organs, namely, leaves, stems, roots, flowers, 

 fruits, and seeds. A summary of the treatment 

 of the leaf will indicate the author's plan. The 

 distinctive characteristics are first noted, the 

 "green colour, flat form, and growth towards the 

 light"; their function consists in the exposure 

 of green tissue to light, under the action of which 

 the plant forms its food out of water and mineral 

 matters drawn from the soil and a gas receiyed 

 from the air. After a short account of general 

 structure an experimental account of photosyn- 

 thesis is given, which leads on to the study pf the 

 cellular anatomy and the characteristics of 

 protoplasm and other cell-contents. Transpira- 

 tion is then considered, and next the adjustments 

 of green tissues to light. Various forms of 

 foliage-leaves are described in association with 

 various habitats, and in the following section 

 the forms and functions of leaves othet- than 

 foliage, such as leaves for storage, the 

 insectivorous habit, climbing, bud-scales, and 

 stipules. A section on the nutrition of plants 

 which lack chlorophyll includes, besides phanero- 

 gamic parasites and saprophytes, a reference to 

 the fungi. Sections on the autumnal and other 

 coloration of leaves, and their economics and 

 treatment in cultivation, are followed by a final 

 section on the uses of photosynthetic food, which 

 deals briefly with the various classes of sub- 

 stances found in the plant and their use to man. 

 It is evident from this sketch that Prof. Ganong's 

 treatment is somewhat unconventional. The text 

 makes easy reading, and is facilitated by a large 

 number of good figures ; but there is sometimes 

 a suggestion of scrappiness. 



PHYSICAL CHEMISTRY. 



A Text-book of Thermochemistry and Thermo- 

 dynamics. By Prof. Otto Sackur. Trans- 

 lated and revised by Dr. G. E. Gibson. Pp. 

 xvi + 439. (London : Macmillan and Co. , Ltd. , 

 1917.) Price 125. net. 



AT the present time, when considerable atten- 

 tion is being given to the industrial import- 

 ance and value of chemistry, it is very necessary to 

 NO. 2483, VOL. 99] 



emphasise the factors which not alone place 

 chemical technology on a scientific basis, but are 

 absolutely essential for real industrial progress. 

 That much has been accomplished by more or 

 less empirical methods is undoubted, and in cer- 

 tain cases, as a matter of fact, " theory " lags 

 considerably behind "practice." This, however^ 

 is not an argument for relegating theoretical prin- 

 ciples to the background. Empiricism, which is 

 unavoidable when an industry is in an un- 

 developed state, is ultimately the greatest bar to 

 further progress. Modern synthetic chemistry, 

 in its widest sense, includes much more than the 

 purely descriptive. The success of a chemical 

 operation rests not only on whether the process 

 can be carried out at all, but also on the careful 

 elucidation of the best conditions under which to 

 carry it out. The discovery of these conditions does 

 not, or, rather, should not, be merely a matter of 

 trial and error. The rational control of a process 

 is determined by considerations of a wide and 

 general nature applicable to processes of the most 

 varied kind. To take an illustration. The prob- 

 lems of rapidity of w^orking, of yield and effi- 

 ciency, are intimately bound up with such general 

 considerations as reaction-speed and its depend- 

 ence upon concentration, temperature, pressure, 

 and the catalytic effects of the surroundings, with 

 the question of the equilibrium state as defined 

 by the equilibrium constant, and the variation of 

 this quantity with temperature and pressure. 

 Problems such as these represent some of 

 the technical applications of the principles of 

 physical chemistry. To go no further, it is evi- 

 dent that the technical chemist must be acquainted 

 with the principles of chemical kinetics and 

 chemical thermodynamics, especially the latter. 



In these circumstances a good text-book of 

 chemical thermodynamics, such as the late Prof. 

 Sackur's "Thermochemistry and Thermo- 

 dynamics," is an asset not alone for chemical 

 science, but equally so for chemical technology. 

 The book itself is an exceedingly lucid exposition 

 of the principles of thermodynamics, specially 

 adapted for the needs of the chemist. In addi- 

 tion to covering the ground which we now regard 

 as classical, it introduces us to those newer ideas 

 which mark some of the more recent advances in 

 physical chemistry. 'The problem of chemical 

 affinity, which is all-important for chemical opera- 

 tions, is particularly well done. One is impressed 

 by the essential unity of purpose underlying the 

 rnost diverse considerations and fields of investiga- 

 tion. In the old days it would scarcely have been 

 conceived that properties so very " physical " as 

 specific heats and vapour pressures, for example, 

 were ever likely to play any important part in 

 determining the direction and extent of chemical 

 change, but in the light of Nernst's heat theorem 

 and the recent work on the quantum theory we 

 are able to appreciate the truly chemical import- 

 ance of these and other physical properties. 



The experimental material with which Prof. 

 Sackur illustrates the conclusions arrived at is 

 ample and well chosen. Certain subjects, such as 

 liquid mixtures and fractional distillation, the 



