Chapter X: Carburetted Acetylene

Now that atmospheric or Bunsen burners for the consumption of acetylene for use in lighting by the incandescent system and in heating have been so much improved that they seem to be within measurable reach of a state of perfection, there appears to be but little use at the present time for a modified or diluted acetylene which formerly seemed likely to be valuable for heating and certain other purposes. Nevertheless, the facts relating to this so-called carburetted acetylene are in no way traversed by its failure to establish itself as an active competitor with simple acetylene for heating purposes, and since it is conceivable that the advantages which from the theoretical standpoint the carburetted gas undoubtedly possesses in certain directions may ultimately lead to its practical utilisation for special purposes, it has been deemed expedient to continue to give in this work an account of the principles underlying the production and application of carburetted acetylene.

It has already been explained that acetylene is comparatively a less efficient heating agent than it is an illuminating material, because, per unit of volume, its calorific power is not so much greater than that of coal-gas as is its illuminating capacity. It has also been shown that the high upper explosive limit of mixtures of acetylene and air--a limit so much higher than the corresponding figure with coal-gas and other gaseous fuels--renders its employment in atmospheric burners (either for lighting or for heating) somewhat troublesome, or dependent upon considerable skill in the design of the apparatus. If, therefore, either the upper explosive limit of acetylene could be reduced, or its calorific value increased (or both), by mixing with it some other gas or vapour which should not seriously affect its price and convenience as a self-luminous illuminant, acetylene would compare more favourably with coal-gas in its ready applicability to the most various purposes. Such a method has been suggested by Heil, and has been found successful on the Continent. It consists in adding to the acetylene a certain proportion of the vapour of a volatile hydrocarbon, so as to prepare what is called "carburetted acetylene." In all respects the method of making carburetted acetylene is identical with that of making "air-gas," which was outlined in Chapter I., viz., the acetylene coming from an ordinary generating plant is led over or through a mass of petroleum spirit, or other similar product, in a vessel which exposes the proper amount of superficial area to the passing gas. In all respects save one the character of the product is similar to that of air-gas, _i.e._, it is a mixture of a permanent gas with a vapour; the vapour may possibly condense in part within the mains if they are exposed to a falling temperature, and if the product is to be led any considerable distance, deposition of liquid may occur (conceivably followed by blockage of the mains) unless the proportion of vapour added to the gas is kept below a point governed by local climatic and similar conditions. But in one most important respect carburetted acetylene is totally different from air-gas: partial precipitation of spirit from air-gas removes more or less of the solitary useful constituent of the material, reducing its practical value, and causing the residue to approach or overpass its lower explosive limit (_cf._