io6 



NATURE 



[April 3, 191, 



of total Ileal s, for example, rather than their ab- 

 solute amounts. 



Prof. Mollier, of Dresden, in 1906 published 

 tables and sheets of curves calculated on Calen- 

 dar's methods, and these were published by Sir 

 J. A. Ewing in the third edition of his book on 

 the steam engine in 1910. Prof. Smith and Mr. 

 Warren have recalculated all the numbers (with 

 slight divergences from Mollier's results), using 

 values of the constants which seem to them best, 

 and they reproduce Prof. Mollier's curves showing 

 total heat on an entropy base. They give both 

 Centigrade and Fahrenheit tables. If Prof. Calen- 

 dar's methods are right there can be no doubt 

 that Prof. Smith and Mr. Warren have done a 

 great service to steam engineers. They nowhere 

 state what is their unit of heat, but it is probably 

 that which agrees with /= 1399 or 1400. This will 

 not agree with their figures for the total heat of 

 water. It is also a pity that they do not give the 

 actual experimental results on which their calcula- 

 tions are based ; no doubt great w-eight is given 

 to the Joly-Callendar value of L at ioo° C, and to 

 Callendar's specific heat as well as the Munich 

 results. 



Fair agreement of the steam tables with 

 measured values of L, &c, is no proof that Prof. 

 Callendar's method is legitimate, because good 

 agreement may be effected even if we take c to be 

 a constant, b being the volume of water, or, 

 indeed, if we lake steam to be a perfect gas. The 

 only real test would be that the calculated specific 

 heat for various temperatures and pressures 

 should agree with measured values. This test 

 cannot be applied until we have better experi- 

 mental results. J. P. 



PRACTICAL AGRICULTURAL CHEMISTRY. 

 Practical Agricultural Chemistry. By Prof. 



S. J. M. Auld and D. R. Edwardes-Ker. Pp. 



xxiv + 243. (London: John Murray, 1913.J 



Price 55. net. 



UNTIL recently the teacher of agricultural 

 subjects in this country suffered from 

 the disadvantage (or advantage if one looks 

 upon it in that light) that very few text- 

 books were available to help him in his 

 teaching. The result was that each man had 

 to devise his own course and modify it as time 

 went on and experience accumulated. There is a 

 tendency at the present time for teachers to put 

 their courses on record, and the plan has much 

 to commend it. 



The latest scheme thus printed is the laboratory 



course for students of agricultural chemistrv used 



by Dr. Auld and Mr. Edwardes-Ker. It opens 



with a good section on plant-life which is dis- 



NO. 2266, VOL. 91] 



tinctly fuller than usual, including experiments 

 with certain plant constituents not commonly 

 studied in other laboratories. The teacher will 

 find material here that may be new to him and 

 that he may advantageously embody in his own 

 course. The section on soils presents few novel 

 features ; indeed, there are some directions in 

 which marked improvements might be made. 

 Above all things, it is necessary to be clear in 

 dealing with the agricultural student. But we 

 find that on p. 86 the "clay" in soil is estimated 

 by 'a method which will bring out particles less 

 than 0002 mm. in diameter; on p. 90 by a method 

 which brings out particles less than o'oi mm. in 

 diameter; while on p. 62 a scheme of classification 

 of soils is given which supposes that "clay" is 

 something altogether different from either. Yet 

 there is no hint that the word is being used in 

 three different senses. The precise definition of 

 clay must be a matter of convention ; it is much 

 better for the young student to begin on the British 

 convention and defer the detailed study of other 

 conventions until he is more advanced in the 

 subject. 



We should like also to have seen some of the 

 newer and improved methods of analysis brought 

 in. The Xeubauer method of examining soil 

 extracts, and the titration method for determining 

 phosphates, are much simpler and quicker than 

 those given, while the perchlorate method of 

 estimating potassium is at least as accurate as, 

 and much cheaper and more convenient than, the 

 costly and cumbersome platinum method. These, 

 however, are essentially matters of detail, and as 

 the authors have shown courage in introducing 

 some new matter in their course, it may be hoped 

 that they will have the further courage to test the 

 newer methods that are now available and adopt 

 them in their teaching. E. J. R. 



SCIEXT1FIC EGYPTOLOGY. 



(1) Service des Antiquitcs de VEgypte. Catalogue 

 General des Intiquite's Egypticnnes du Musee 

 du Caire. Nos. 61,051-61,100: The Royal 

 Mummies. By G. Elliot Smith, F.R.S. Pp. 

 vii+118+103 plates. (Le Caire: Imprimeiie 

 de 1'Institut Francais d'ArcheoIogie Orientale, 

 191 2. 1 



(2) British School of Archaeology in Egypt. 

 Studies Series. Vol. iii. The Formation of 

 the Alphabet. By Dr. W. M. Flinders Petrie, 

 F.R.S. Pp. iv-20 + 9 plates. (London: Mac- 

 millan and Co., Ltd., and Bernard Ouaritch, 

 1912.) Price 5s. net. 



(1) pROF. ELLIOT SMITH'S studies of 



L mummification, the result of work 



carried out during the years he spent in Egypt, 



