158 CALORIMETRIC APPARATUS. 



weight being equal to the weight of carbonic acid formed. It 

 has been found to be 0*2090 grm. in the above experiment. 

 This being established, let us calculate the heat produced. It 

 is equal to the product of the masses reduced to water and 

 multiplied by the variation of temperature ; Sft + At 



Sj u = 550 + 77'4 = 6274, 



A* = 14745 - 13-295, or 1-45 + p, 



p being the heat lost by cooling. 



Now, in the initial period of five minutes which preceded 

 explosion there was neither gain nor loss. The maximum was 

 established one minute and a half after explosion. In the five 

 following minutes (final period) the loss was regular and equal 

 to 0*01 per minute. This being determined between the fifth 

 and the sixth minute the loss may be estimated at the half, or 

 0-005; between the seventh and eighth it is 0-01. The total 

 correction will therefore be 0'015, which makes t = 1465. 



The heat liberated is 6274 X 1465 = 919-14 cal. But 

 this figure does not correspond to a total transformation of 

 ethane into gaseous carbonic acid and liquid water. In fact, 

 a certain quantity of water retains the gaseous state in the 

 interior of the bomb. This quantity is easy to calculate, for it 

 corresponds to the maximum tension of water vapour at 1474, 

 viz. 12*5 mms. according to Eegnault's tables. The capacity 

 of the bomb being 247 cub. cms., and the density of water 

 vapour at 14*7 being supposed theoretical (which is very near 

 the reality, according to Eegnault's experiments), the real 

 weight of the gaseous water remaining in the bomb may be 

 estimated at 



- 1 2 <F > 1 



0-806 grm. x -^- X X - - - = 0*0031 grm. 

 1000 760 1 + 0*00367 x 1474 



Now, the vaporisation of this weight of water at 15, still follow- 

 ing Eegnault, absorbs 1*85 cal., a quantity which must be 

 added with the contrary sign to 919*14 cal., which makes in 

 all + 920-99 cal. This is the heat liberated by the combustion 

 of the weight of ethane which gave 0-2090 grm. of carbonic 

 acid. 



But 1 equiv. of ethane C 2 H 6 = 30 grms., would have yielded 

 88 grms. of carbonic acid. It is therefore sufficient to calculate 

 the heat liberated by the formation of 88 grms. of carbonic 

 acid to obtain the heat of combustion of ethane at constant 

 volume, viz. 387*78 Cal. 



At constant pressure this figure must be increased by 1425, 

 according to the formula on page 154, which makes 389*21 Cal. 

 This is the heat of combustion of ethane deduced from the above 

 experiment. 



15. The method just described has been applied to the study 



