AIR BURNING IN COAL GAS. 



193 



jet of oxygen in a vertical position; fill a cylinder or narrow- 

 mouthed bottle holding a quart or more with hydrogen at the 

 pneumatic trough, lift it up mouth downwards, and apply a light, 

 and then depress the bottle over the oxygen jet so that the latter 

 is inside and near the middle, like the candle in Expt. 107 (fig. 85). 

 The oxygen will be lit as the jet passes inwards 

 (unless the pressure be too great, so that the oxygen 

 issues too violently to bum steadily), and two flames 

 will be seen, one that of oxygen burning in hydrogen 

 inside the bottle, and the other hydrogen burning in 

 contact with the air at the mouth of the bottle. Do 

 not allow the flame to burn longer than a minute or so ; 

 otherwise it is possible that the flame at the month 

 may go out and air be sucked into the bottle, which 

 mixing with the remaining hydrogen may produce an 

 explosive mixture of gases ; withdraw the oxygen jet, 

 and extinguish the hydrogen flame at the mouth by 

 pressing a towel against it. 



Coal gas may be used instead of pure hydrogen in 

 this experiment, the bottle being filled by holding it 

 over an india-rubber tube attached to the gas main, 

 and filling by displacement mouth downwards. 



Expt. 213. Air burning in Coal Gas. Fig. 86 

 shows a somewhat different way of illustrating the Fig. 85. 

 same kind of action, a jet of air here burning in an Oxygen burn - 

 atmosphere of coal gas, whilst the surplus coal gas Jro<en y 

 burns in the air. A lamp chimney is fitted with a 

 doubly perforated cork, through which pass two glass tubes one, a, 

 connected with the coal gas main, the other, &, opening into the air. 

 The chimney is removed and the coal gas turned on slightly, so 

 that a small flame burns at the end of a ; the chimney is now 

 placed in position, when the flame burns steadily on a if the tube 

 b is wide enough to admit sufficient air. The coal gas supply is 

 now increased gradually by slowly turning on the tap ; with a 

 certain rate of supply more coal gas comes in than the air can burn 

 properly. At this stage the flame disappears from a, but reappears 

 at the top of b, so that a flame of air burning in coal gas is now 

 produced ; the surplus coal gas escapes at the top of the chimney, 

 where it may be lit, producing a flame of the ordinary kind, i.e., 

 coal gas burning in air. By properly regulating the gas supply, 

 the flame can be made at will to burn on a or b as desired. 



Expt. 214. Production of a Solid by the Chemical Action of 

 two Gases on one another. The gas ammonia (collected as in 

 Expt. 75) possesses the remarkable property of directly combining 



N 



