SUGGESTION CONCERNING THE NOMENCLATURE OF 



HEAT CAPACITY. 



By Theodore William Richards. 



Received December 19, 1900. Presented January 9, 1901. 



The word " calorie " has come to have so many significations as to have 

 lost definite meaning, unless qualified by an explanatory phrase. For 

 this unfortunate condition of affairs, which is due primarily to the varia- 

 bility of the specific heat of water, the best remedy seems to me to be 

 the general use of a new standard for the measurement of heat capacity. 



The growing tendency to refer all energy measurements to the centi- 

 meter-gram-second basis makes it fitting that heat also should be meas- 

 ured directly in these terms. It is not unusual to do this, as far as 

 heat-energy is concerned ; but the practice is hampered by the fact that 

 the standards of temperature and heat-capacity have no rational relation 

 to the so-called absolute units. One calorie equals about 42,000,000 

 ergs, or 4.2 joules. Would it not be a convenience to arrange the 

 standards of heat measurement so that the direct product of heat ca- 

 pacity and change of temperature would be expressed in joules ? Nearly 

 ten years ago Ostwald pointed out some of the advantages of such a 

 practice,* but the suggestion does not seem to have received the attention 

 which it deserves. 



One way to accomplish the desired result would be to construct a new 

 scale of temperature with degrees about f^ the size of the present cen- 

 tigrade degrees, and to retain the specific heat of water at a definite 

 temperature as the unit of capacity. This course retains one of the disad- 

 vantages of our present system, and is open to several other objections, 

 the chief of which would be the variability of the degree with each new 

 measurement of the value of the mechanical equivalent. 



Another obvious course is to retain the centigrade degree, measured 

 by the hydrogen or helium thermometer, as final, and to choose for the 

 unit of capacity that capacity which is warmed 1 degree centigrade by 



* Zeitschr. phys. Chein., 9, 577 (1892). 



