490 KEPORT— 1888. 



with rise of temperature. Regnault (p. 129) remarks that this increase 

 of specific heat with rise of temperature is probably true of all gases the 

 elasticity of which deviates much from Boyle's law. 



Volatile Liquids — Begnault. 



The specific heats of vapours of volatile liquids were determined by 

 Regnault, by experiments described in this memoir, in which the total 

 heat was dii'ectly given which was yielded by the body in the state of 

 vapour in passing from the temperature of the vapour to the temperature 

 of the calorimeter, in which the liquid was condensed : this heat consists 

 of the heat-capacity of the vapour from the highest temperature taken to 

 the temperature of condensation jjZhs the heat given off at this tempera- 

 ture by the mass of vapour in becoming liquid jj??6S the heat given out 

 by the liquefied vapour in passing from this temperature to the tem- 

 perature of the calorimeter. Thus the heat-capacity of the vapour as 

 such between two temperatures is not given by any one experiment. 

 Eegnault endeavours to get rid of the two unknown quantities of heat 

 simultaneously by eliminating them between two different experiments, 

 in the one the temperature of the vapour being lower than in the other ; 

 in each experiment the weight of the liquid condensed is found, as also the 

 difference between the highest temperature of the vapour and the tem- 

 perature of the calorimeter, whence can be calculated the total heat given 

 out by ^mit lueigld of the substance in passing from the temperature of the 

 vapour at starting to the temperature of the calorimeter. Now the results 

 of the two experiments differ in respect of the initial temperature of the 

 vapour and the final temperature of the liquid in the calorimeter ; the 

 initial temperature in one of the experiments is taken as high as con- 

 veniently can be, and the final temperatures are reduced to 0° by 

 adding to the total heat in the case of each experiment the total heat- 

 capacity of the liquid between the temperature of the calorimeter (say 

 about H° to 20°) and 0°. This last is a comparatively small correction for 

 each experiment, and the difference only of these corrections enters into 

 the result. For the result is obtained by subtracting the corrected result 

 of one experiment from that of the other, the difference being the total 

 heat-capacity of the vapour between the initial higher temperatures of 

 the pair of experiments. Dividing the number thus got by the interval 

 of temperature, the quotient is the mean specific heat of the vapour 

 between these temperatures. 



In addition to the bodies in the list given above, Regnault obtained 

 results for heat-capacities of equal volumes of the following gases and 

 vapours : marsh gas, defiant gas, sulphur dioxide, ethyl chloride, hydric 

 sulphide, ammonia ; and the vapours of water, ether, alcohol, carbon 

 disulphide, benzene, oil of turpentine, methyl alcohol, ethyl cyanide 

 (propionitril), ethyl bromide, ethyl sulphydride, ethyl acetate, acetone, 

 ethene dibromide, chloroform, bromine, silicon chloride, phosphorous 

 chloride, arsenious chloride, titanic chloride, stannic chloride. As the 

 result of the whole series of experiments on the bodies chosen, Regnault 

 comes to the conclusion that there is no general relation of the specific 

 heat and molecular weights of bodies in the state of gas or vapour cor- 

 responding to Dulong and Petit's law as to elements in the solid state. 



