been considering, did not deem it practicable to change at once to the use of pure petroleum or naphtha gas in Boston, as the burners in use are, for reasons already given, not suitable; the works employed to produce coal-gas are not adapted to this, and as the flame of petroleum-gas "burning in an appropriate burner is a very small flame," it would not in their opinion prove satisfactory to consumers, although the amount of light would be the same if not greater. The objection that petroleum-gas in any form injures the metres was found to be without warrant.
The practice which obtains with the Detroit Mutual Company and others, of adding air to naphtha-gas to reduce its illuminating power so that it can be burned in an ordinary burner, was judged by the commissioners to be the reverse of economical, to both the company and consumer, because the deterioration of the gas by this means is in greater ratio than the increase of its volume. It is said that one per cent, of air will reduce the illuminating power six per cent., or more than carbonic acid, the removal of which is considered necessary by all gas-engineers for the sake of economy. It was for this reason that the first attempt to make illuminating gas from petroleum (that at Saratoga by the Gale and Rand process) failed.
What is true of the value of naphtha as a gas-making material used alone, is also true of its value as an enricher. Experiments already here referred to, although not expressed in terms of equality, imply the superiority of naphtha to Albertite, which is about the best of the enriching coals. The yield from a ton of the latter, which costs about $25, was, on the average of a number of experiments made by the Boston Gaslight Company, only 14,694.4 cubic feet of 55 candle gas; while the yield of $25 worth of naphtha (valuing it at ten cents a gallon, which is rather high) would be 19,872.5 cubic feet of 64.5 candle gas, or 5,178.1 cubic feet more gas of richer quality than a ton of Albertite. By the use of naphtha, too, a larger amount of gas is obtained from the ordinary caking coal. In enriching with Albertite the coal with which it is mixed is distilled in an iron retort at a comparatively low temperature; while, if naphtha be used, all of the common coal can be carbonized in a clay retort, which is acknowledged by all to be more economical, and all of the gas in the coal can be exhausted, so that about 1,000 cubic feet more can be obtained per ton. The iron retorts are more expensive than the clay, because their first cost is greater, and they do not last as long. In making gas on a large scale, about one-half the number of retorts can be dispensed with, in the use of naphtha as an enricher. The New York Mutual Gas Company, for example, in this way, make as much gas with forty retorts as can be made in the other with eighty; and with the disuse of the extra forty retorts the labor necessary to tend them is dispensed with. The increased yield of the coal by the use of naphtha, referred to just now, is demonstrated by practical experience to be