516 M. Regnault on the Specific Heat of Simple Bodies, 



the calorimeter. In this manner the total quantity of heat 

 could be determined which the system possessed at the moment 

 at which the thermometer of the oven indicated its maximum. 

 The following are the data of the calorimetrie experiment : — 



Weight of selenium 200^*45 



Weight of brass vessel Sl^^'lS Value in 



Maximum reached by the therrao- water 7^'"*62. 



meter of the oven 200°-5 



Final temperature of the calorimeter 24°*65 

 Elevation of temperature after cor- 

 rection 9°115 



A 422P--54 



The quantity of heat acquired by the calorimeter, and which is 

 equal to that which the system gave up in setting itself in equi- 

 librium with it, that is, in decreasing to 24°* 65, is 

 422-54 . 9°-115 = 3851-5 units of heat. 

 This quantity of heat is composed of two parts : — 



1. Of that which would have been imparted to it by the oven, 

 if the selenium had not spontaneously disengaged heat. 



2. Of the quantity of heat which the molecular transform- 

 ation of the selenium liberated. 



It is the latter quantity of heat which it is important to know ; 

 we shall obtain it by subtracting from the total quantity of heat 

 given by the experiment, that which vitreous selenium gives up 

 when it cools from 98 degrees (the maximum to which bodies 

 usually reach in our oven) to 24'65. But we have found that 

 the specific heat of vitreous selenium is 0'1036 between 19°'5 

 and 87°'3 ; if we assume that it is the same between 24°*65 

 and 98°*0, the augmentation which tlie specific heat may undergo 

 from 87 to 98 degrees being attributable to the molecular trans- 

 formation, selenium in falling from 98 to 24-65 would abandon 

 a quantity of heat represented by 



200-45 X 0-1036 X 73-35 = 1523-2 

 The envelope of brass in cooling the same \ __ 558*9 

 number of degrees 7*62 x 73*35 . ./ ~2082-l 

 We obtain therefore for the number of units of heat disengaged 

 by the molecular transformation, 3851-5 — 2082-1 = 1769-4, 

 which have been produced by 200^^-45 of selenium. This 

 number would heat 200^-45 of selenium, supposing it to be 



the metallic modification by ^^ .p^,^,^^^ , or by 116-00, which 



differs little from the 114-2 which we have observed directly on 

 the thermometer of the oven at the moment at which it indi- 

 cated the maximum. But like the last, it must undergo im- 



