AIR, PUMPS AND APPARATUS. 



219 



cock ; the whole is covered with the receiver having a sliding 

 rod, and let off by depressing the rod on the cup. If the 

 receiver be exhausted, and the flint be made to strike the 

 steel, no sparks will appear ; and if there were powder in 

 the pan it would be burned. The sparks produced by the 

 flint and steel, are owing to small portions of steel struck 

 off by the percussion, and burning in the air ; without the 

 air the combustion of the steel cannot take place. 



Price, with brass frame, $5.00. 

 " common construction, $3.00. 



229 - Apparatus to fire Gunpowder in 



Vacuo. (Fig. 229.) This apparatus 

 consists of a bell glass, with brass 

 cap, having a large stop-cock and 

 funnel ; in the key of the stop-cock 

 there is a cavity, into which a small 

 quantity of powder falls ; on turning 

 the key a little, the aperture is en- 

 tirely closed, and when half round 

 the powder falls on a round piece of 

 iron, previously made red hot, and 

 supported on a stand within the bell 

 glass receiver. The powder will 

 burn, but no explosion takes place ; 

 the smoke remaining at the bottom. 



Caution is required in performing the experiment, and the 

 bell glass should be exhausted after each charge is burnt. 



Price, $4.50. 



Apparatus for showing the effects 

 of burnt air. (Fig. 230.) This ap- 

 paratus consists of a glass receiver, 

 with aperture in the top about 

 three inches in diameter, truly 

 ground, covered by a brass plate 

 with stop-cock, to which a bent 

 metallic tube is screwed. To use, 

 place a pan of lighted charcoal so 

 that the end of the tube may be in 

 the flame ; first having exhausted the receiver, then open 

 the stop-cock, and the burnt air will pass through the tube 

 into the receiver, with which it may soon be filled. Take 



