DILATATION OF THE GASES. 25£J 



the heat coming brilkly out of the receiver, quickly drove off 

 the atmofpheric air that filled the tube, and after the 40° the 

 cock may be fafely left open during the remainder of the ope- 

 ration : I prefer however alternately opening and fhutting it, 

 becaufe I find that the gas of the receiver acquires the tem- 

 perature of the bath better. After 15 or 20 minutes of ebul- 

 lition, a time fufficicnt for the whole to acquire the fame 

 temperature, I difengage the extremity of the tube I, D, 

 from the mercury in order to re-eftablifh the equilibrium of 

 preflure between the exterior air and the gas of the receiver, 

 and I then clofe the cock. After having cooled the bath with 

 ice or water I take away the apparatus, I difengage the re- 

 ceiver from which I take the tube I, D, and the lever L, L, 

 and I plunge it altogether in a bath of a known temperature, 

 where I leave it a fufficient time to acquire its temperature. 



When the cock is opened a volume of water enters the re- The relative 

 ceiver, which when reduced to a level is precifely equal to b t u J£i. of the gas 

 fhat of the gas expelled by the heat. When the cock is thut peraturcs. deter- 

 I withdraw the receiver; I dry its exterior furface with care, mined by 

 and I weigh it in this flate. I then weigh it firfl full of water, 

 and then empty, and note the refults of each weight. By this 

 knowledge I obtain the capacity of the receiver by fubtracling 

 its weight when empty, from its weight when filled with wa- 

 ter ; and alfo the volume of the water which reprefents the 

 volume of air expelled by the heat from the receiver, by fub~ 

 trading again the weight of the receiver when empty, from 

 its weight when containing this water. Hence it is very eafy 

 to determine the proportion of the firft volume of the air to , 

 that of the dilated. 



This method has the advantage of being very exact ; for as This method h 

 the volumes are determined from the weights, any error that vcr J cxa «* 

 is committed in this determination muft.be very trifling, even 

 if the fcales employed ihould be but moderately fenlible. 



The apparatus I have juft defcribed is (imple enough in it- Another appa- 

 felf; but as it contains cement, and a cock which oflght to be rat "? ncar, y aS 

 made of iron on account of the mercury, it is rather difficult e afily con- 

 to execute. It will not therefore be amifs to defcribe another ftrucled. 

 apparatus which I employ, and which on account of its great 

 fimplicity and eafy execution, very nearly combines all the 

 advantages of the former. 



$2 It 



