yield varied from 13,440 to 16,016 cubic feet of 36.08 to 54.45 candlepower gas per ton (6 to 7.15 feet per pound). Experiments on cannel of different kinds have given various yields, from 3.8 feet of 20.52 candle-power gas per pound to 4.74 feet of 30.40 candle-power.
The principal impurities in coal-gas are, as already indicated, sulphuretted hydrogen and other gases containing sulphur and ammonia. The presence of a small amount of these cannot be avoided, and is not injurious, since the sum of the products of the combustion of these substances, formed by the burning of the gas from a single burner during an entire evening, is very small. In fact, the presence of a slight amount of ammonia is beneficial, in tending to neutralize the sulphurous and sulphuric acids formed by that portion of the sulphur which cannot be renewed. The limit prescribed by law for the London companies is 20 grains of sulphur and 22 grains of ammonia per 100 cubic feet. The specific gravity of illuminating gas is an important quality, since it increases in a nearly constant ratio with the candle-power, so that, knowing the one, the other can be told pretty nearly, and vice versa. It varies usually from 0.400 to 0.500; the specific gravity of air, 1.000, being taken for the unit. The denser the gas the more slowly it will pass through a given orifice, and so on this quality depends in great measure the quantity which passes through the consumer's meter and burner.
In regard to petroleum as a gas-making material experiments made by Prof. A. Wagner show that naphtha is better and more economical than it or any of the heavy oils. Fifty kilogrammes of petroleum produced 1,547 cubic feet of gas, while the same amount of naphtha produced 1,619 cubic feet. Both petroleum and naphtha produce a large amount of acetylene, a gas which contains a large proportion of carbon. In the experiments referred to, five per cent, of acetylene was evolved, 35.96 per cent, of other heavy (rich) hydrocarbons, and 59 per cent, of light (poor) hydrocarbon gas; the petroleum being split up, with deposition of carbon, into a mixture of acetylene, heavy and light hydrocarbon gas, and hydrogen. In this country, where petroleum and its products are much cheaper than they are in Europe, it has been found that on a large scale 60 to 80 cubic feet of 50 to 70 candle-power gas can be made from one gallon. In a series of thirteen experiments on crude petroleum made by Mr. C. D. Lamson, of the Boston Gaslight Company, the average yield per gallon was 72.71 cubic feet, and the average of six tests of candle-power was 45.73. In seven experiments on naphtha the average yield was 79 cubic feet, candle-power 53.48. This is equivalent to a yield per barrel respectively of 3,053.82 and 3,338.58 cubic feet. According to Mr. J. D. Patton, about 70 cubic feet of 80 candle gas, or 80 feet of 70 candle gas to the gallon, is the maximum yield of petroleum or naphtha. A much smaller burner than the ordinary must be used for gas obtained from pure Albertite, petroleum, or naphtha; otherwise the flame will smoke,