1813.] Specific Heat of the different Gttses. 2 1 1 



Article VIII. 



Memoir on the Determination of the Specific Heat of the 

 different Gases. By MM. F. Delaroche, M. D. and J. E. 

 Berard. 



(With a Plate.) 



(Continued from p. JS8.) 

 SECTION FIRST. 



Explanation of the Method folloived in our ResearcheSi 

 § I. — Description of the Calorimeter. 



The object which we had in view in the experiments that we 

 are about to describe was the determination of the specific heat 

 of several gases, according to the meaning usually attached to 

 that word; that is to say, to determine how much caloric is 

 necessary to raise them from a given temperature to a higher 

 temperature, likewise given; or, which comes to the same thing, 

 how much heat they give out in passing from the higher tempe- 

 rature to the lower. We have not attempted to determine the 

 effect produced by the change of their specific heat, in conse- 

 quence of a change of their temperature; a change which ought 

 to be more sensible in the gases, in consequence of their great 

 dilatability, than in other bodies, and which Gay-Lussac has 

 proved to exist, though it would have been very difficult for us 

 to determine it by means of our apparatus. 



The solution of the question, such as we consider it, is not 

 quite so simple as may at first sight appear; but presents consi- 

 derable difficulties, whatprocess soever we pursue. We hesitated 

 for some time about the plan that we ought'to follow in order to 

 gain our object. We rejected at once the process of Crawford, 

 and likewise the calorimeter of ice: 1st. Because it did not 

 seem susceptible of precision when such small quantities of heat 

 are employed as those that the gases give out in cooling some 

 degrees, fd. Because, when we employ it, there is almost an 

 impossibility of determining the temperature of the gases when 

 they enter the interior chamber. 3d. Because it is necessary to 

 use dry gases, which would make the apparatus too complicated. 

 We conceived the idea of employing a calorimeter, in which, 

 instead of determining the heat disengaged during the cooling of 

 the gases by the ice melted, we should determine it by the 

 quantity of water or ether evaporated ; but we found this process 

 attended with such difficulties as induced us to renounce it. At 

 last we determined to employ another, founded on die following 

 considerations: 



■e we have a constant and uniform source of heat, the 

 whole of which acts upon a body, A, suspended in the air; this 



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