1513.] Specific Heat of the different Gases. 373 



According to the principles from which we set out, the spe- 

 eific heats of the different gases are inversely as the numbers in 

 the last column of the table. Hence, reckoning the specific 

 heat of air unity, we obtain the following numbers for the same 

 volumes of the other gases : — 



Specific heats of Ditto by the 



equal volumes. first method. 



Air 1 -000 1 -000 



Hydrogen 0-893 0'9033 



Carbonic acid 1311 ..1-2583 



Oxygen 0-974 0-9765 



Azote 1-000 1-0000 



Oxide of azote 1315 1-3503 



Olefiant gas I -680 J -5530 



Carbonic oxide . . . .0983 1 -0340 



The agreement between the results obtained by these two 

 processes is as great as could be expected from experiments 

 founded upon principles so different. As we consider our first 

 method as most exact, we shall not take the mean between the 

 two ; but satisfy ourselves with exhibiting the result of the second 

 set of experiments, as a proof of the accuracy of the first set. 



Section IV. 



Specific Heat of the Vapour of Water, that of Air being consi- 

 dered as Unity. 

 Aqueous vapour being an elastic fluid which produces a very 

 striking effect in many pbenomena, it was of importance to 

 obtain correct notions of its specific heat. It was scarce possible 

 to make experiments on this fluid in a state of purity; because 

 such experiments require the whole of the apparatus to be pre- 

 served at a temperature higher than that of boiling water. It 

 was necessary to have recourse to a mixture of vapour and air; 

 and even in this way of experimenting several difficulties pre- 

 sented themselves. It was necessary to employ temperatures 

 somewhat high, if we wished the vapour to constitute a eonsi- 

 derable portion of the mixture : both our apparatus and our 

 process were accommodated to this kind of experiment. It was 

 sufficient to observe at what temperature our calorimeter became 

 stationary when acted upon by a current of air saturated with 

 humidity, anil by the same current of air in a state of dryness. 

 We were able only to employ air saturated with vapour at the 

 temperature of 104°. To have employed a higher temperature 

 would have been very difficult : but at 'the temperature of 104°, 

 Midi i^ the tension of vapour, that it forms ,' ,th of the volume 

 of the air with which it is mixed. It is obvious that, operating 



