For those not understanding the above it will be as well to explain, that on the left-hand side of the equation are placed the compounds brought into contact, water (H_{2}O) and carbon (C), and on the right the products of the chemical action, carbon monoxide (CO), carbonic acid gas (CO_{2}), and hydrogen (H_{2}). The resulting water gas contains 60% of hydrogen and 20% of carbon monoxide, both of which are combustible gases. The proportions of the gases evolved can be varied at will by admitting more steam or using an excess of carbon; by this process a richer gas can be obtained— C + H_{2}O = CO + H_{2}, and 5 H_{2}O + 3 C = 2 CO_{2} + CO + 5 H_{2}. With 18 parts of steam and 12 parts of carbon we can obtain by the former equation 28 parts of carbon monoxide and 2 parts of hydrogen. This forms an extremely calorific mixture. There are several processes for preparing water gas which give good practical results, and the gas produced has been used in America and Germany for lighting towns on the incandescent gas-burner system. The Strong and Lowe processes consist of a furnace lined with fire-bricks, and in which is placed coal or coke. When this mass of carbon has reached a state of bright incandescence by playing upon it a stream of air, steam is admitted at high temperature, and is decomposed by the carbon forming oxides and liberating hydrogen. The gaseous products pass from the furnace to a reservoir. When the chemical action ceases, due to cooling of the carbon, the steam is shut off and the stream of air turned on till it becomes incandescent once more. The process of admitting steam is then repeated. About 2½ lbs. of coke are necessary to produce 20 cubic feet of water gas. Analysis of the gas reveals the following parts by volume of the constituents. (1) Water gas produced by the Strong process:— Hydrogen 53 volumes Carbon monoxide 35 ” Hydrocarbons 4 ” Other gases 8 ” ——— 100 volumes (2) Lowe process:— Hydrogen 30 volumes Carbon monoxide 28 ” Hydrocarbons 34 ” Other gases 8 ” ——— 100 volumes It is possible to entirely get rid of the cooling effect of the steam, by using instead a jet of air which passes up through the carbon. First of all carbon dioxide (CO_{2}) is formed near the bottom of the mass, but this gas passing upwards through it is reduced to carbon monoxide (CO) by the excess of carbon, and a mixture is obtained consisting of 34 parts by volume of carbon monoxide and 65 of nitrogen. This gas has been named after its inventor, Siemens gas.