CHEMICAL APPARATUS. 

 Fig. 534. 



83 



the neck of a retort, or a tube for filling with gas ; and over 

 the top, supported by four rods, a reservoir with open top, 

 to suppl/ the gas holder with water as it is consumed, and 

 also to form a pressure on the gas. The reservoir and gas 

 holder are connected by two tubes with stop-cocks ; one of 

 the tubes yist entering the gas holder, the other passing 

 down nearly to the bottom. The first is to be opened in 

 filling the ga^, holder with water, and the other to form the 

 pressure on the gas in its discharge ; care being taken to 

 supply the reservoir with water as it may be required. At 

 the side near the top of each gas holder, is screwed a brass 

 stop-cock, conn.ected together by tubes branching out and 

 terminating in one jet, in which the gases meet. 



At the sides of each gas holder, there are cavities con- 

 taining stout glass tubes, connected at both ends with the 

 mterior, for showing the exact quantity of gas contained in 



