March 2, 1916] 



NATURE 



pressures up to the critical point. But since there 

 are no experimental data 'for the volume, or the 



■tal heat, or the specific heat, or the cooling-- 

 .-ifect, at pressures above 8 or 10 atmospheres, 

 it is impossible to decide between different equa- 

 tions satisfactorily at high pressures without 

 further experimental work. It is comparatively 

 easy to calculate values on suitable mathematical 

 assumptions with a fair degree of probability, but 

 it may reasonably be questioned whether it is 

 worth while to risk spoiling the approximation for 

 ordinary purposes for the sake of a doubtful ad- 

 vantage beyond the experimental range. 



The expression employed for the variation of 

 the specific heat with temperature gives a mini- 

 mum in the neighboui hood of 140° C, and the 

 values are nearly constant from 80° to 200° C. 

 The value at 100° C. and atmospheric pressure is 

 nearly the same as that recently found by Brink- 

 worth {Phil. Trans, y 1915)- The variation with 

 pressure agrees closely with that given by Callen- 

 dar over the experimental range. The agreement 

 is exact at 70 lb. and 300° F., and also at 200 lb. 

 and 500° F. The increase of Sq at low tempera- 

 tures cannot be verified experimentally, and is 

 theoretically improbable. The gradual increase 

 above 200° C. is not improbable in order of mag- 

 nitude, but the experimental evidence is so con- 

 flicting, and the importance of the variation so 

 small for steam engine work, that it may be 

 questioned whether it is worth while to attempt 

 to take account of it. These minor variations, 

 besides being somewhat uncertain, render all the 

 expressions so complicated as to be of little use 

 for practical calculations without reference to 

 tables. The adiabatic equation, in place of being 

 the same as that of a perfect gas, becomes quite 

 unmanageable, and there is no simple relation 

 between the volume and the total heat. 



The properties of saturated steam are deduced 

 from an empirical formula for the saturation 

 pressure of the general type, 



log/> = A + B/T + C log T+DT-rET-'-f-FT3 + GT<, 

 \vhich represents very closely the observations on 

 which it is founded. Clapeyron's equation is em- 

 ployed for deducing the latent heat and the heat 

 of the liquid, which serve as a rough verification 

 of the method. The general arrangement of the 

 tables follows familiar lines, but it is to be re- 

 gretted that they are restricted to British thermal 

 units on the Fahrenheit scale, according to the 

 common practice among American engineers, and 

 that no values are tabulated on the Centigrade 

 scale or expressed in metric units. The only 

 diagram given is that of Mollier, with total heat 

 and entropy as co-ordinates, which is useful for 

 NO. 2418, VOL. 97] 



adiabatic expansion, but has the disadvantage of 

 not showing the volume and of having a variable 

 scale of pressure. 



The properties of ammonia are developed and 

 tabulated in a similar manner to those of steam, 

 but with less elaboration, owing to the scanty 

 experimental data. The results are noteworthy 

 as the first serious attempt at consistent repre- 

 sentatian in the case of this vapour. The whole 

 work is admirably lucid, and should do much to 

 advance thermodynamic method in the construc- 

 tion of tables 



OUR BOOKSHELF. 



Limes and Cements : Their Nature, Manufacture, 

 and Use. An Elementary Treatise. By E. A. 

 Dancaster. Pp. xii + 212. (London: Crosby 

 Lockwood and Son, 1916.) Price 55. net. 

 This is especially suited for students who require 

 an elementary text-book on the subject, contain- 

 ing, as the author justly observes in his preface, 

 very little that will have to be unlearned at a later 

 period. It is sufficiently comprehensive to have 

 some value for many who are not beginners, for 

 though the matter is necessarily compressed in 

 view of the limited space, the ample bibliography 

 of modern publications dealing wholly or partly 

 with the materials under consideration will enable 

 fuller details to be found by such as may need 

 them. 



The work is admittedly based on Burnell's 

 "Limes, Cements, Mortars, etc.," but the altera- 

 tions and additions involved in bringing that 

 treatise up to date render the present volume 

 practically a new production. All the important 

 varieties of lime, artificial and natural cement, 

 mortar, concrete, etc., are noticed, however 

 briefly, including the mode of preparation or 

 occurrence, and the approved manner of using. 



A chapter on the chemical analysis of limes and 

 cements gives brief directions for the determina- 

 tion of the principal constituents, and another 

 chapter furnishes descriptions of the physical and 

 mechanical tests applied to some of the substances 

 in question, but chiefly to Portland cement. 



It is noteworthy that misprints, though not 

 entirely absent, are commendably rare. Illus- 

 trations are not very numerous, but will probably 

 be found sufficient except for special details. The 

 style of the descriptions is clear throughout the 

 book. J. A. A. 



Hancock's Applied Mechanics for Engineers. Re- 

 vised and rewritten by Prof. X. C. Riggs. Pp. 

 xiii + 441. (New York: The Macmillan Co.; 

 London : Macmillan and Co., Ltd., 1915.) Price 

 los. 6d. net. 

 The first edition of this book appeared in 1909, 

 and was reviewed in Nature for September 16 of 

 that year. Considerable alterations have been 

 made in the present edition, and graphical 

 methods have been used more freely. About two 

 hundred new problems have been added to the 



