OXYGEN. 



245 



placing this by an iron pipe of three feet in length, one end 

 of which has been cut to the screw of the bottle. This pipe 

 may be bent like a in the figure, if the bottle is to be heated 



FIG. 30. 



in an open fire or in a furnace open at the top. From 8 to 9 

 pounds of the oxide may be introduced as a charge, according 

 to the quantity of gas to be prepared, each pound of the best 

 Exeter manganese yielding about 1400 cubic inches, or 5.05 

 gallons of gas. Upon the first application of heat, water comes 

 off, as steam, mixed with a gas which extinguishes flame; 

 this is owing to the impurity of the oxide. The products may 

 be allowed to escape, till the point of a wood-match red without 

 flame, applied to the orifice, is not completely extinguished, 

 but rekindled and made to burn with brilliancy; the gas is 

 then sufficiently pure, and means must be taken for collecting 

 it. A small flexible lead tube b, of any convenient length is 

 adapted to the iron pipe, by means of a perforated cork, by 

 which the gas is conveyed to a pneumatic trough, and collected 

 in glass jars filled water, as in the former experiment ; or, as 

 this process affords considerable quantities of oxygen, the gas 

 is more generally conducted into the inferior cylinder or drum 

 of a copper gas holder c, full of water. The water does 

 not flow out by the recurved tube which forms the lower 

 opening, but is retained in the vessel by the pressure of the 

 atmosphere on the surface of the water in that tube, as 



