154 CALORIMETRIC APPARATUS. 



and sulphuretted gases can likewise be effected in the platinum 

 detonator which has just been described. 



9. Not only are permanent gases burnt in the apparatus 

 above described, but it is easy to burn in them every vapour 

 the tension of which is sufficient for it to be completely trans- 

 formed into gas in the volume of oxygen capable of completely 

 burning it. In this case the liquid is weighed in a small sealed 

 glass bulb, and the bulb is placed in the bomb ; the latter is 

 closed and filled with oxygen, then by a few shocks the bulb is 

 broken. In a few moments after vaporisation has taken place 

 the bomb is placed in the calorimeter. After five or six minutes, 

 during which the thermometer is observed, the gas is exploded, 

 and the carbonic acid is collected and weighed as above. 



By proceeding in this manner we have the advantage of 

 being able to control the weight of carbonic acid obtained, by 

 the weight of the original liquid. 



In the case of aldehyde, glycolic ether, hydrocyanic acid, 

 hydrochloric and hydrobromic ethers, methylic and ethylic 

 alcohols, etc., the operations have been carried out in the above 

 way. 



The combustions are total for every vapour having a consider- 

 able tension, such as that of bodies boiling below 50. 



But for the less volatile bodies, as benzene, there is no longer 

 the same certainty of total combustion, probably owing to the 

 condensation of some trace of matter on the walls and in the 

 grooves of the apparatus. In this exceptional case, the detona- 

 tion method loses some of its advantages and requires corrections 

 similar to the ordinary method by combustion. 



10. The figures obtained by detonation have not exactly the 

 same significance as those obtained in the ordinary heats of 

 combustion ; the latter are carried out at constant pressure, the 

 former at constant volume. By this method numbers are 

 obtained which are better adapted to the majority of theoretical 

 discussions. 



It is, moreover, easy to pass from the numbers obtained at 

 constant volume to those which would be obtained at constant 

 pressure. According to the formula given above 



Qtp = Qtv + 0-5424 (N - N') + 0-002 (1ST - W)t. 



Take, for example, the combustion of carbonic oxide at 15. 

 CO 4- = C0 2 liberates at constant volume + 68*0 Cal. In 

 order to pass from this to the heat liberated at constant pressure 

 we should note that on one hand CO occupies a unit of volume, 

 a half-unit. Therefore 



N = l. 



On the other hand C0 2 occupies a unit of volume. 



N' = l 

 N - N' = . 



