All About Engines

The Gas Engine 193 out in the cheapest way. When the gas engine was first introduced—and, indeed, for many years after- wards—the value of coal gas lay in its illuminating value, so that it was a dear fuel. But in 1878 Mr. J Emerson Dowson showed not only how to produce a cheaper gas, but also how this gas could be pro- duced wherever it was required, so that a town supply was no longer necessary. The principle was this . that if coal burns in an ample supply of air it forms carbon dioxide which is no longer inflammable, while if the air supply is limited, carbon monoxide is formed, and this gas will burn with a further supply of air, producing carbon dioxide. Thus, in a fairly deep fire, red hot throughout, a lambent blue ame will frequently be seen playing over the top. The oxygen in the air entering the lower part of the grate produces carbon dioxide, and this, passing through the red-hot carbon in the upper part, takes up carbon and forms carbon monoxide. Those who have learnt a little chemistry will recognise the equations corresponding to the two processes : c + o2 = c 02 c oa + C = 2 co The nitrogen, which forms four-fifths by weight of "the atmosphere, passes out unchanged with the carbon monoxide, and the mixture is known as producer gas. The apparatus consisted of a deep cylindrical furnace charged with coke fed by a hopper from the top. It was of sheet iron, lined with firebrick, and there were dampers at the bottom to regulate the