1813.] Specific Heat of the different Gases. 135 



Specific heat of Water 1 -000 



Atmospheric air 1*790 



Oxygen 4*7-49 



Azote 0793 



Carbonic acid 1'045 



Hydrogen 21-400 



Before the work of Crawford appeared, Lavoisier and Laplace 

 had made some experiments, which were not published till long 

 after. They bad employed their calorimeter of ice, through 

 which they passed a current of gas contained in a serpentine, 

 which enveloped on all sides the ice of the interior chamber. A 

 thermometer placed at each extremity of the serpentine enabled 

 them to observe the temperature of the gas when it entered and 

 came out of the calorimeter. The gas was heated by passing 

 through a serpentine surrounded with boiling water, before it 

 entered into the calorimeter. These experiments, though sus- 

 ceptible of much greater precision than those of Crawford, were 

 not free from very material imperfections. The method employed 

 by these philosophers to take the temperature of the gases at its 

 entrance into the calorimeter was insufficient, since the gas, in 

 passing through the exterior coating of ice, would lose a portion 

 of the heat which the thermometer had indicated, without con- 

 tributing by that to melt the ice in the interior chamber. On 

 the other hand, they do not say that they took any precautions to 

 dry the gases upon which they made their experiments. These 

 gases, charged with the humidity which the contact of water in 

 the gazometers would necessarily communicate, no doubt depo- 

 sited the whole of it when they passed through the calorimeter ; 

 but we know that vapour, when it condenses, gives out a great 

 deal of heat. It is proper, however, to remark, that the tem- 

 perature at which these experiments were made, being probably 

 but little elevated above the freezing point, the quantity of 

 vapour mixed with the gas would not be considerable. Lavoisier 

 and de Laplace only subjected to these experiments oxygen and 

 atmospherical air. They found for the specific heat of the first 

 (that of water being l'OO), 0'65, and for the second 0-33 ; but 

 Lavoisier acknowledges that the accuracy of these results cannot 

 be entirely depended on. 



Since that time, various attempts have been made to appre- 

 ciate, by indirect means, the specific heat of some gases. Mr. 

 Leslie has employed, in order to compare the specific heat of 

 hydrogen and atmospheric air, a process founded on the follow- 

 ing considerations. When a large receiver is partly exhausted of 

 air, if air be allowed to enter into it, the dilated air which it 

 contained will condense, and its temperature will be increased 

 by a constant quantity, whatever gas enter into it ; but the 



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