CARBON AND HYDROGEN. 421 



hydrogen ; but the combining measure and equivalent of this 

 compound are unknown. It is inodorous, neutral, respirable 

 when mixed with air, not more soluble in water than pure 

 hydrogen, and has never been liquefied. Carburetted hydrogen 

 requires twice its bulk of oxygen to burn it completely, and 

 affords water and an equal bulk of carbonic acid. In air it 

 burns, when lighted, with a strong yellow flame. It is a com- 

 pound of considerable stability, but is decomposed in part 

 when sent through a tube heated to whiteness, and resolved 

 into carbon and hydrogen. This gas is not affected in the dark 

 by chlorine, but when the mixture of these gases, in a moist 

 state, is exposed to light, carbonic and hydrochloric acid gases 

 are produced. 



Although instantly kindled by flame, carburetted hydrogen 

 requires a high temperature to ignite it. Hydrogen, sulphu- 

 retted hydrogen, and olefiant gas are all ignited by a glass rod 

 heated to low redness, but glass must be heated to bright red- 

 ness or to whiteness, to inflame carburetted hydrogen. Sir H. 

 Davy discovered that flame could not be communicated to an 

 explosive mixture of carburetted hydrogen and air, through a 

 narrow tube, because the cooling influence of the sides cf the tube 

 prevented the gaseous mixture contained in it from ever rising 

 to the high temperature of ignition. A metallic tube has a 

 greater cooling property, from its high conducting power, and 

 consequently obstructs to a greater degree the passage of flame, 

 than a similar tube of glass ; and even the meshes of metallic 

 wire-gauze, when they did not exceed a certain magnitude, were 

 found to be impermeable by flame. Experiments of this kind 

 may be made upon coal-gas, the flame of which will be found 

 incapable of passing through a sheet of iron-wire trellis, con- 

 taining not less than 400 holes in the square inch. If the gas 

 be allowed to pass through the trellis, and kindled above it, the 

 flame, it will be found, does not return through the apertures to 

 the jet whence the gas issues. Upon these observations, Sir 

 H. Davy founded his invaluable invention of the safety lamp, 

 an instrument indispensable to the safe working of the most 

 extensive and valuable of our coal fields. 



The safety lamp, as left by Davy, is simply an oil lamp, in- 

 closed in a cage of wire-gauze, the upper part of which is dou- 

 ble, (Fig. 43.) Mr. Buddie uses iron- wire gauze for the lamp, 



