This invention rendered it no longer necessary for the gas to carry the constituents which contributed to luminosity, among which was benzol. With the mantle they are superfluous: in fact are deleterious. What is required is a gas rich in the constituents contributing to heat. Coal-gas, or as it is more familiarly called, town-gas, is rich in these two essentials. They are hydrogen and methane or marsh-gas. When burned under suitable conditions they are capable of giving off intense heat, and the higher the degree of incandescence to which the rare earths entering into the composition of the mantle can be raised, the more brilliant the illumination. Consequently the time has arrived when the standardization of gas according to luminous power should be thrown overboard in favour of one based upon calorific value. This was introduced to a certain degree as a temporary expedient during the war, but it should now be made rigid. Signs of awakening to the true state of affairs are apparent. The research committee appointed to investigate this question has recommended that gas should be sold according to its calorific value, and that all gas-consuming appliances should be adapted to the new order of things. Should legislation be passed endorsing these recommendations it will be possible for further huge quantities of benzol to be recovered from our coal, or rather the gas derived from the volume of coal annually absorbed for gas production. It is the benzol and toluene which impart the luminous intensity to the gas, but which are unnecessary for the production of heat. At the present moment the quantity of benzol reclaimed from the coal absorbed by the gas-works is approximately 21,000,000 gallons a year--a fraction of what it might be. We may safely assume that of the 270,000,000 tons of coal we draw from our collieries every year, at least 160,000,000 tons are capable of such treatment as will enable the volatile liquid fuel to be recovered. Upon the basis of two gallons per ton of coal this would represent 320,000,000 gallons of benzol, of which huge quantity all but 41,000,000 gallons are being lost under contemporary conditions. The value of this spirit at the moment may be set down at approximately 2s.--50 cents--per gallon. Thus we are deliberately throwing away £27,900,000--$139,500,000--a year. It is being permitted to vanish into thin air. This figure serves to bring home what the losses arising from the neglect of waste really represent, and also reveals our extraordinary lack of imagination and enterprise.