UNITS OF HEAT WHAT. 503 



and differs but immaterially from the results obtained by Favre 

 and Silbermann. Thus, according to Andrews, the combustion 

 of pure carbon with oxygen produces 7881 units of heat a 

 unit of heat being, as Liebig says, " not an ordinary degree, 

 but the amount of heat which a weight of water equal to that 

 of the burnt body receives when its temperature is raised one 

 degree of the centigrade scale. "* Wherefore, an ounce of pure 

 carbon, by combustion in oxygen, yields as much heat as raises 

 an ounce of water one degree centigrade 7881 times or, what 

 is the same thing, raises 7881 ounces of water one degree cen- 

 tigrade. But the degree centigrade is to the degree Fahren- 

 heit in extent as 1.8 to 1 ; whence, by inversion, 1 : 1.8 : : 

 7881 : 14,185 that is, the amount of heat represented by 

 one degree of the centigrade is to the amount of heat repre- 

 sented by one of Fahrenheit's thermometer in units as 7881 to 

 14,185 ; or, if a certain quantity of heat be expressed by 7881 

 oz. raised to one degree centigrade, the same quantity will 

 be expressed by 14,185 oz. raised one degree Fahrenheit. 

 Thus the estimate of Andrews differs but by 15 from that be- 

 fore cited, as the one yields 14,185 oz., while the other 

 makes the round number 14,200. Moreover, according to 

 Favre and Silbermann, the grams of water raised one de- 

 gree centigrade by the combustion in oxygen of one gram of 

 carbon are 8080 in number. Whence it may be seen that the 

 estimate here made differs from that of Andrews only by the 

 difference between 7881 and 8080. 



Thus there is not even ground to suppose that the idea so 

 prevalent of the quantity of carbonic acid produced in the re- 

 spiration of animals being inadequate to account for the usual 

 amount of animal heat rested at any recent period on a too 

 limited estimate of the number of degrees of heat evolved dur- 

 ing the combustion of carbon and oxygen. 



* 'Familiar Letters on Chemistry,' p 343. 



