488 KEPOET— 1888. 



case of liquids being rapid, so that the infernal work becomes a very 

 important part of the whole heat consumed in raising the temperature. 



Recently ScliifF has studied the specific heats of liquid organic com- 

 pounds,^ and has determined the specific heats of liquid hydrocarbons, 

 alcohols, acids, and ethereal salts at different tcmpei'atures, and arrives 

 at the following results among others : All ethereal salts of fatty acids, of 

 the formula C„H2„02, have the same specific heat at the same temperature, 

 being represented by the formula K ='44!l6 + •00088^. Again, following 

 "Van der Waals' method for finding points of comparison for bodies in the 

 liquid or gaseous state, he finds the critical temperature by the rule laid 

 down by Pawlewski -^ for the same ethereal salts — that their critical tem- 

 peratures are to be found by adding 1823 to their boiling-points at 760mm. 

 Schiff divides the distance of the critical temperature from the absolute 

 zero into 100 equal parts, which he calls critical degrees, and finds that 

 equal volumes of these liquids have the same heat-capacity at the same 

 critical degree. 



Specific Seat. Gases and Vapours. 



We will now consider the case of specific heats of bodies in the state 

 of gas or vapour. 



Gay-Lussac ^ gave an account of some experiments for determining 

 specific heats of gases at constant pressure, and concluded that the specific 

 heats (or heat-capacitiesj of equal volumes of bodies in the gaseous state 

 were equal ; but further investigations by himself and a number of other 

 physicists made it soon appear that the problem was more complex than 

 was supposed, and that variations of temperature are of vital consequence. 



It was not until Eegnault undertook his investigations that any 

 satisfactory collection of experimental results was obtained. From 1840 

 onwards Regnault occupied himself, among other physical and chemical 

 investigations, with the subject of specific heats of bodies in the solid, 

 liquid, and gaseous states. The work on this subject in respect of the 

 gaseous state is part of the vol. xxvi. of the 'Mem. de I'Acad. des Sc' 



BegnaiiU's Results for Gases and Va2')02irs. 



The following results were obtained by Regnault for atmospheric air 

 at atmospheric pressure approximately constant : — 



Between 30° and + 10° . . . . . + 100° . . . + 200° 



Specific heat 0-23771 . . . 0-23741 023751 



Lence the specific heat of air between 0° and 200° (for a certain nearly 

 constant pressure, viz., atmospheric pressure) is independent of the 

 temperature and = 0-2375. The temperatures were those of an air- 

 thermometer. 



For oxygen two experiments gave 0'21627, 0-21876, or a mean value 

 0-21751 for the specific heat between 7° and 200°. To compare the heat- 

 capacities of equal volumes of oxygen and air, 1-10563 being the specific 

 gravity of oxygen (air = 1), we have 1-10563 X 0-2175 to 0-2375, or 

 0*2405 to 0-2375 as the ratio of the heat-capacities. Thus the heat- 

 capacity of a volume of oxygen at 760 mm. and a temperature between 



' i. Ann. 234, p. 300 ; C. S. J. Ahs. 1887, p. 6. 

 2 Jier. 15, p. 2460; C. .S. J. Abs. 1883, p. 276. 

 =■ Jlcm. d'Arcueil, t. i. 1807, p. 180. 



