I30 



NATURE 



[April i, 1920 



sort of handbook of the subject, and is arranged 

 in three divisions. The first comprises sixty 

 pages, devoted to a theoretical introduction enun- 

 ciating general laws applying to binary and ter- 

 nary mixtures. The author gives empirical rules 

 for predicting whether azeotropism will occur in 

 a given binary mixture and for roughly calculating 

 the azeotropic composition and temperature. This 

 portion is concisely written, but rather, spoilt 

 by the frequency and length of the footnotes. 

 The second division, which is the largest portion 

 of the book, consists of tables giving experiment- 

 ally observed data for about 2500 liquid mixtures, 

 mainly binary. As a result of his own experi- 

 ments, the author points out that azeotropism 

 occurs fairly frequently, some 1000 new binary 

 systems possessing this property having been dis- 

 covered. In the third division is given a very 

 complete bibliography, and the book concludes 

 with an appendix containing notes on the prepara- 

 tion, in a state of purity, of some of the organic 

 substances employed in the course of the author's 

 researches. 



Soils and Manures. 



(i) Soils and Manures in New Zealand. By L. J. 

 Wild. (New Zealand Practical Handbooks.) 

 Pp. 134. (Auckland, Melbourne, and London: 

 Whitcombe and Tombs, Ltd., 1919.) Price 

 25. 6d. 



(2) A Student's Book on Soils and Manures. By 

 Dr. E. J. Russell. Second edition, revised 

 and enlarged. (The Cambridge Farm Institute 

 Series.) Pp. xii + 240. (Cambridge: At the 

 University Press, 1919.) Price 6s. 6d. net. 



IT is one of the special charms, as it is also 

 one of the special difficulties, of agriculture 

 to the student that it offers such infinite possibili- 

 ties of variation in its manifestations of the work- 

 ing of the fundamental laws of Nature, not only 

 from country to country, but also from farm to 

 farm, and even often within the confines of the 

 same field. 



How desirable it is, therefore, that the cultivator 

 of the soil shall be doubly armed, on one hand 

 with a sound grasp of the basal principles under- 

 lying the relationship of crops to soils, and on the 

 other with a knowledge of the characteristic local 

 environmental factors the resultant effect of which 

 determines the level of crop production attainable 

 on the particular area on which his efforts are con- 

 centrated ! Yet how can the wonderful complex 

 of chemical, physical, and biological relationships 

 involved in the growth of plants in the soil be so 

 simply resolved that he who ploughs may read ! 

 The exposition of scientific principles to the 

 NO. 2631, VOL. 105] 



farmer unversed in science, yet engaged in an 

 occupation which represents in its fundamentals 

 perhaps the very acme of complexity in applied 

 science, is a task of the utmost difficulty, and has 

 rarely been accomplished with even moderate 

 success. The common weakness of books of this 

 class, written professedly for the practical farmer, 

 as distinct from the college student, is a failure of 

 the author to keep consistently down to the educa- 

 tional level of his intended reader, to adhere closely 

 to essentials, and to repress the natural inclination 

 to demonstrate his own familiarity with the latest 

 developments of agricultural research, all-import- 

 ant and of absorbing interest to himself, but apt 

 to divert the attention of the reader from the 

 simple essentials which afford him ample material 

 for digestion. 



(i) Mr. Wild is fortunate in having in the New 

 Zealand farmer a reader probably on the average 

 better equipped by general education for serious 

 study than the main body of farmers in the home 

 country, and for the particular body of readers to 

 whom he appeals his book is but little open to the 

 foregoing criticisms, so far, at any rate, as the 

 simplicity and clearness of his exposition are con- 

 cerned. Within the compass of this small book 

 he has condensed a large body of information, 

 much of which will be readily assimilated and 

 found of practical utility by his readers. This 

 applies particularly to his outline of the character- 

 istics and manurial requirements of the various 

 soils of New Zealand. In the exposition of under- 

 lying principles to which the first half of the book 

 is devoted, however, we should have ruthlessly 

 eliminated all but the absolute essentials and 

 devoted the space thereby gained to a more 

 leisurely and more fully illustrated discussion of 

 the nature and the mode of action of the latter. 

 Unless we can assume an elementary knowledge 

 of chemistry, physics, and biology in the reader, 

 ic is surely better frankly to avoid the attempt at 

 scientific exposition and to concentrate upon im- 

 planting firmly in the reader's mind a knowledge 

 of those simple but important conclusions from 

 scientific reasoning and investigation without 

 which he must surely often go astray in his 

 practice. 



(2) It is a pleasing indication of the " revival 

 of learning " in British agriculture that a second 

 edition of Dr. Russell's book should have been 

 called for so closely upon its first issue. This work 

 is specifically intended for the young farmer taking 

 a course of instruction of intermediate grade in the 

 type of institution which is now being developed 

 in most counties under the designation of farm 

 mstitutes. With the teacher's hand to guide him 

 through the more difficult portions, the young 



