146 



GENERAL SCIENCE 



Coal Gas. Coal gas is generated from bituminous coal. The 

 gas is used chiefly for cooking, heating and lighting. 



The products obtained from a ton of good coal are about 



10,000 cubic feet of gas; 

 1,400 pounds of coke; 

 120 pounds of tar; 

 20 gallons of ammonia. 



The coke is used to heat the bituminous coal or is sold as a fuel. 

 Tar is used for tarred paper, paint, preserving lumber and wood 

 pavings. Benzine and gasoline are extracted from it. Oils, dyes, 

 flavors, perfumes, material for moth balls and many other useful 

 products are obtained from tar. 



Experiment for the Preparation of Illuminating Gas. Arrange an appa- 

 ratus as shown in the illustration. In bottle C place some lime water, in bottle 



D some red litmus paper, which turns blue in the presence of ammonia, and some 

 water for the gas to bubble through. Fill test tube A two-thirds full of powdered 

 soft coal. Heat the coal in the test tube gently at first. Do not heat any one 

 part of the tube any great length of time, as the glass will melt and the gas 

 escape. Collect several bottles of the gas over the water and test with a match. 

 Smell bottle B for tar products. Notice bottle C for the evidence of carbon 

 dioxide, and the litmus paper in D for the presence of ammonia. 



Pressure Producer Gas (Fig. 114). Pressure producer gas is 

 made from a variety of fuels, such as bituminous coal, lignite, coke, 

 anthracite, charcoal, sawdust, wood refuse, etc. The gas is pro- 

 duced under slight pressure, hence the name pressure producer gas. 



Where the pressure producer gas plant supplies gas for an installation of 

 2000 H.P. or more, a by-product plant for the treatment of the tar is frequently 



