f 288 ] 



XXXI. Thermodynamic Notes (No. 1). — On the Alleged Sign 

 of " Specific Heat of Saturated Ether Vapour" By K. 

 Tsuruta, Tokyo, Japan *. 



AS is well known, this is positive at ordinary temperatures 

 according to Clausius's calculation based on Regnault's 

 measurements, the other substances examined, like carbon 

 disulphide, chloroform, carbon tetrachloride, and aceton, 

 showing the opposite sign f. When, a few years ago, I was 

 occupied with some investigations on specific heats of gases 

 and vapours, I came across a difficulty with ethyl oxide 

 which, on further inquiry, seemed to point to the conclusion 

 that, contrary to what is universally accepted, the sign under 

 consideration must be negative. As I have been, and shall 

 perhaps continue to be, under circumstances which will 

 not allow me to fulfil my intention to verify or disprove my 

 result of calculation by experiments, I venture to publish my 

 note, imperfect as it is, substantially in the form I was able 

 to give to it. and hope to call attention of abler hands and 

 minds to the point in question. 



One of the assumptions which Clausius made in applying 

 the following formula to Regnault's measurements 



/4= <7T-T +H ' 



is that on the liquid line 



H= V 



h, which was called by Clausius the specific heat of saturated 

 vapour, may be conveniently called the specific heat along 

 the gas line; and H, which might be called the specific heat 

 of saturated liquid, the specific heat along the liquid line. 

 c p denotes the specific heat at constant pressure of the sub- 

 stance in the liquid form, the pressure being that of it3 

 saturated vapour. This assumption as applied to ether seems 

 ^o be quite allowable at ordinary tempeiatures, but not at 

 higher temperatures like + 120°. 



To show this, let us first consider any two infinitely near 

 isothermals, T and T + rfT. Let any point on one be joined 

 to any point on the other by an element of a reversible path. 

 Taking p and T as independent variables, we obtain for the 

 heat of the element 



* Communicated by the Author. 



t Clausius, Die mechanische Wcirmetheorie, pp. 139-143. 



