plunged in mer- 

 cury } 



260 DILATATION OF THE GASIS. 



A body with a It is a fimple globe or body, and the neck of which muft be 

 duatedV ' 8ra " at * ea ** one decimetre (about lour inches) long. After having 

 filled it with the gas by the method already defcribed, I 

 plunge its neck about two centimetres (three quarters of an 

 inch) in mercury contained in a common glafs veflel, and I 

 fecure it by an iron frame like the preceding apparatus. If I 

 were to plunge it in this ftate into a bath of heated water, the 

 dilated gas in order to efcape would have to overcome not 

 only the preffure of the mercury in the glafs, but likewife that 

 A fmall tube to of the water of the bath. To remedy this inconvenience, 1 

 wiiSTthe 'outer "introduce into the neck of the receiver the extremity of a very 

 air when requi- -fine bended tube, taking the precaution to- keep the upper 

 aperture clofed till the tube is plunged beneath the mercury. 

 To fupport the tube I tie a firing about its middle, to the end 

 of which I fufpend a weight, and I pafs it over a fupport in 

 Yuch a manner, that the cord by its action (hall have a ten- 

 dency to draw the tube upwards. The apparatus being thus 

 difpofed I plunge it in a glafs veflel, the water in which mud 

 be on a level with that in the bath : I open the extremity of 

 the tube for an inftant, that the equilibrium of preflure with 

 ©bfervation of the external air may be reftored, and I then (hut it. As there 

 * c mcr £ ur y »n i s a f ca i e marked on the neck of the receiver whofe divifions 

 are extremely minute, I find exactly the level or ftation of 

 the mercury in the neck, and I note it, becaufe it is at this 

 ftation that the capacity of the receiver terminates. The lower 

 extremity of the tube mult rife clearly above the furface of the 

 mercury, which othervvife would flow into the tube and refill 

 the pafiage of the dilated gas. After all thefe operations, 

 which are longer in the defcription than the execution, I carry 

 When- the appa- the apparatus to a bath of hot water, and I open the upper 

 in tonh\gwat 8 er! extremity of the tube, after having plunged it into a fmall bath 

 the expanded gas of mercury, as in the preceding arrangement. When the re- 

 efcapes^by^the ce j ver y at t j ie temperature of boiling water I withdraw the 

 t h^n withdrawn, tube, the extremity of which muit be previoufly difengaged 

 Water is fuffered from the mercury, and I cool the bath. The mercury then 

 «» enter as it r jf es j nto ^ Q rece i vcr . Du t. it is eafy to fubftitute water as the 

 temperature diminifhes. The capacity of the receiver, and 

 the volume of water which replaces the gas expelled by heat, 

 and the expan- j s determined in the manner already defcribed ; excepting 

 ^Sht! ained that in thls determination to the weight of the empty receiver, 



iriufl 



