ACETYLENE GAS 279 



and as a result gas is formed. The gas produced in this way 

 is called natural gas. It is a cheap source of illumination, but 

 is found in relatively few localities and only in limited quantity. 

 Acetylene gas. The distillation of soft coal into illuminat- 

 ing gas is not practicable on a small scale and so illuminating 

 gas is seldom seen in small towns, villages, and farming regions. 

 An illumination which is widely used in thinly settled regions 

 is acetylene, a gas made from calcium carbide. Originally cal- 

 cium carbide was expensive, but in 1892 it was discovered that 

 it could be cheaply made by fusing lime and coal together in 

 the intense heat of an electric furnace. As a result of that dis- 

 covery, calcium carbide was soon made on a large scale and 

 sold at a moderate price. The cheapness of cal- 

 cium carbide has made it possible for the isolated 

 farmhouse to discard oil lamps and to have a pri- 

 vate gas system. When the hard, dry crystals of 

 calcium carbide are put in water, they give off 

 acetylene, a colorless gas which burns with a brilliant 

 white flame. Put bits of calcium carbide in a bottle 

 and close it with a cork in which is fitted a glass FlG 144 __ 

 tube, as shown in Figure 144. Pour a little water A simple 

 into the glass tube. As soon as the water reaches method o^ 

 the calcium carbide, bubbles of gas form and escape making acet- 



i <-r, . i i i ylene gas. 



into the air. 1 he escaping gas may be ignited by 

 a burning match held near the mouth of the tube. When 

 chemical action between the water and carbide has ceased, and 

 gas bubbles have stopped forming, slaked lime is left. 



When calcium carbide is used as a source of illumination, the 

 crystals are mechanically dropped into a tank containing water, 

 and the gas generated is automatically collected in a small slid- 

 ing tank, whence it passes through pipes to the various rooms. 

 The slaked lime, formed while the gas was generated, collects 

 at the bottom of the tanks and is removed from time to time. 



