LEAKAGE.--Broadly speaking, it may be said that the commercial success of any village acetylene-supply--if not that of all large installations-- depends upon the leakage being kept within moderate limits. It follows from what was stated in Chapter VI. about the diffusion of acetylene, that from pipes of equal porosity acetylene and coal-gas will escape at equal rates when the effective pressure in the pipe containing acetylene is double that in the pipe containing coal-gas. The loss of coal-gas by leakage is seldom less than 5 per cent. of the volume passed into the main at the works; and provided a village main delivering acetylene is not unduly long in proportion to the consumption of gas--or, in other words, provided the district through which an acetylene distributing main passes is not too sparsely populated--the loss of acetylene should not exceed the same figure. Caro holds that the loss of gas by leakage from a village installation should be quoted in absolute figures and not as a percentage of the total make as indicated by the works meter, because that total make varies so largely at different periods of the year, while the factors which determine the magnitude of the leakage are always identical; and therefore whereas the actual loss of gas remains the same, it is represented to be more serious in the summer than in the winter. Such argument is perfectly sound, but the method of returning leakage as a percentage of the make has been employed in the coal-gas industry for many years, and as it does not appear to have led to any misunderstanding or inconvenience, there is no particular reason for departing from the usual practice in the case of acetylene where the conditions as to uniform leakage and irregular make are strictly analogous.