CARBURETTED HYDROGEN. 223 



It is nearly twice as heavy as the light carburetted hy- 

 drogen just described, and contains twice the quantity 

 of carbon. It forms a small proportion of the Jire 

 damp, of mines, and salt borings, before described. 

 How is it pre- 553. PREPARATION. Heavy carburetted 

 pared? hydrogen is made from alcohol, by the de- 



composing action of sulphuric acid. Bring into a test- 

 tube a tea-spoonful of alcohol, with a little sand, and 

 add four times as much oil of vitriol. On heating over 

 a spirit lamp, the gas is evolved, and may be burned 

 like the gas just described, at the mouth of the tube. 

 The acid employed, has the effect of retaining part of 

 the elements of the alcohol, and allows the rest, to 

 escape as olefiant gas. The reaction* is more fully ex- 

 plained under the head of organic chemistry. 



554. ILLUMINATING GAS. Gas for illu- 



How is illu- 

 minating gas mination, is commonly prepared from bitu- 

 minous coal. Such coal is principally 

 composed of carbon and hydrogen. A portion of 

 these elements, pass off under the influence of a high 

 temperature, in the form of gas. The product, is 

 rather, a mixture of gases, among which light and 

 heavy carburetted hydrogen are the principal. The 

 process may be illustrated, by heating a little pulver- 

 ized bituminous coal in a test-tube. If the heat is in- 

 tense, coal tar will be produced at the same time. The 

 illuminating power of gas is principally derived from 

 heavy carburetted hydrogen. Its quality, within cer- 

 tain limits, depends on the relative proportion of this 

 constituent. 



* The term reaction, signifies, in chemistry, the mutual action ot 

 chemical 



