266 I' 'i. IT. L. Callendai. col 



alcohol and carbon dioxide formed approximate to that found 

 in ordinary alcoholic fermentation. 



(6.) When the cell-juice is allowed to act on sugar either cane- 

 sugar or dextrose the quantity of sugar which disappears 

 is considerably in excess of that which can be accounted for 

 by the production of carbon dioxide and alcohol. 



" On the Therm ody n amical Properties of Gases and Vapours as 

 deduced from a Modified Form of the Joule-Thomson Equa- 

 tion, with Special Reference to the Properties of Steam." I'.y 

 H. L CALLENDAK, M.A., LL.D., F.R.S., Quain Professor of 

 Experimental Physics, University College, London. Received 

 and Read June 21, 1900. 



At the present time, the relations between the specific heats and 

 other thermodynamical properties of gases and vapours, and the devia- 

 tions from the behaviour of the ideal gaseous substance in isothermal 

 and adiabatic expansion, remain extremely obscure. The variation 

 of the latent heat of a vapour, and of its saturation pressure, are 

 generally expressed by purely empirical formulae, without theoretical 

 foundation. Various equations, such as those of Van der Waals, and 

 Clausius, have been proposed and have been very generally adopted to 

 represent some of the simplest of these relations, but owing to their 

 complexity, and to the number of empirical constants involved, their 

 utility is seriously limited, and the results to which they lead are in 

 some cases undoubtedly erroneous. 



The object of the present paper, which is founded mainly on experi- 

 ments on steam, is to develop the application of a modified form of the 

 Joule-Thomson equation, which is sufficiently simple to be of great 

 value in the discussion of the thermodynamical relations of gases and 

 vapours, and which leads directly to accurate formulae for many pro- 

 perties which have hitherto been represented empirically. 



To take the case of steam as an example, all tables of the properties 

 of steam are at present founded on Regriault's formula for the total 

 heat H of saturated steam at / C. reckoned from C., namely : 



H = 606-5 + 0-305/ ........................ (1), 



and on his empirical formula for the pressure of saturated steam, 

 namely : 



= a + bB' + cC* ........................ (2). 



The latter formula contains five empirical constants, but it is usual 



