REVIEWS 477 



Carnot and Lord Kelvin what Lagrange did for Newton's dynamics, and 

 the analogy is more than formal. Nernst has expressed the opinion that the 

 use of thermodynamic functions merely proves that an author has studied 

 the writings of his predecessors with intelligence. There are, however, 

 several results which have been deduced by analytical methods only, and 

 Nernst's description might be applied to the reverse process of translating these 

 into elementary modes of treatment. Both methods of treatment seem 

 desirable in a course of study. The reviewer is of the opinion that a purely 

 descriptive account of the fundamental laws of energy is possible, and would 

 not be without value to chemists who are not equipped with the modest 

 mathematical knowledge required for real study, but no practical applications 

 of these laws can, of course, be made without the calculus. 



The subjects treated in the book under notice are those usually dealt 

 with. Two chapters on the applications of the phase rule are a little foreign 

 to the subject, and the space might have been used in the last chapter (on 

 recent developments), which is a little too condensed. The definition of an 

 ideal gas is by no means clear : it would appear that a number of properties 

 are required, whereas many of these are implied in others. 



It is to be regretted that the price of the book is so high as to put it beyond 

 the means of numbers of students. 



J. R. Partington. 



Ammonia and the Nitrides. By E. B. Maxted. [Pp. viii + 114.] (London : 

 S. & A. Churchill, 192 1. Price 7s. 6d. net.) 



In this monograph the author devotes the first forty-eight pages to the 

 synthesis of ammonia from its elements. He gives a good account of the 

 work of Haber and his co-workers. But in the first line of the book he 

 plunges into thermodynamic formulae in a way which must be bewildering 

 to a reader not already well acquainted with the subject before opening the 

 book. 



On p. 9, in a discussion of the formulae which have been used to 

 express the heat of combination of nitrogen and hydrogen to form ammonia, 

 the author states : 



" The equations expressing the variation of Q with temperature are 

 of such a nature that they pass through a maximum, then decrease, 

 and at a still higher temperature pass through zero and become negative. 

 The point is of considerable interest in connection with the formation of 

 ammonia at very high temperatures . . . the equilibrium percentage of 

 ammonia should decrease with increasing temperature so long as the 

 reaction is exothermic, but should pass through a maximum value and 

 rise once more with any reversal, at high temperatures, of the sign of Q." 



The above word maximum should obviously read minimum. 



In this deduction the author has fallen into an amazing error. The 

 " equations expressing the variation of Q with temperature " are obtained 

 from the measurements of Q by Haber or calculated from measurements of 

 specific heats, and are of the type : 



Q = a + fci - cf^. 



An equation of this type is sufficiently accurate to represent the experi- 

 mental results up to perhaps 1,000° C, but as there are no measurements 

 of Q at high temperatures, an extrapolation of the above formulae is quite 

 unjustified. If the experimental results below 1,000° C. were more accurate, 

 we should probably express them by means of an equation of the type : 



Q = a +bt - ct^ + df. 



