ACETYLENE FOR HEATING AND COOKING.--Since the problem of constructing a trustworthy
atmospheric burner has been solved, acetylene is not only available for use in incandescent lighting, but it can also be employed for heating or cooking purposes, because all boiling, most warming, and some roasting stoves are simply arrangements for utilising the heat of a non-luminous flame in one particular way. With suitable alterations in the dimensions of the burners, apparatus for consuming coal-gas may be imitated and made fit to burn acetylene; and as a matter of fact several firms are now constructing such appliances, which leave little or nothing to be desired. It may perhaps be well to insist upon the elementary point which is so frequently ignored in practice, viz., that no stove, except perhaps a small portable boiling ring, ought ever to be used in an occupied room unless it is connected with a chimney, free from down- draughts, for the products of combustion to escape into the outer air; and also that no chimney, however tall, can cause an up-draught in all states of the weather unless there is free admission of fresh air into the room at the base of the chimney. Still, at the prices for coal, paraffin oil, and calcium carbide which exist in Great Britain, acetylene is not an economical means of providing artificial heat. If a 0.7 cubic foot luminous acetylene burner gives a light of 27 candles, and if ordinary country coal-gas gives light of 12 to 13 candles in a 5-foot burner, one volume of acetylene is equally valuable with 15 or 16 volumes of coal-gas when both are consumed in self-luminous jets; and if, with the mantle, acetylene develops 99 candles per cubic foot, while coal-gas gives in common practice 15 to 20 candles, one volume of acetylene is equally valuable with 5 to 6-1/2 volumes of coal-gas when both are consumed on the incandescent system; whereas, if the acetylene is burnt in a flat flame, and the coal-gas under the mantle, 1 volume of the former is equally efficient with 2 volumes of coal-gas as an artificial illuminant. This last method of comparison being manifestly unfair, acetylene may be said to be at least five times as efficient per unit of volume as coal-gas for the production of light. But from the table given on a later page it appears that as a source of artificial heat, acetylene is only equal to about 2-3 times its volume of ordinary coal-gas. Nevertheless, the domestic advantages of gas firing are very marked; and when a properly constructed stove is properly installed, the hygienic advantages of gas-firing are alone equally conspicuous--for the disfavor with which gas-firing is regarded by many physicians is due to experience gained with apparatus warming principally by convection [Footnote: Radiant heat is high-temperature heat, like the heat emitted by a mass of red-hot coke; convected heat is low-temperature heat, invisible to the eye. Radiant heat heats objects first, and leaves them to warm the air; convected heat is heat applied directly to air, and leaves the air to warm objects afterwards. On all hygienic grounds radiant heat is better than convected heat, but the latter is more economical. By an absurd and confusing custom, that particular warming apparatus (gas, steam, or hot water) which yields practically no radiant heat, and does all its work by convection, is known to the trade as a "radiator."] instead of radiation; or to acquaintance with intrinsically better stoves either not connected to any flues or connected to one deficient in exhausting power. In these circumstances, whenever an installation of acetylene has been laid down for the illumination of a house or district, the merit of convenience may outweigh the defect of extravagance, and the gas may be judiciously employed in a boiling ring, or for warming a bedroom; while, if pecuniary considerations are not paramount, the acetylene may be used for every purpose to which the townsman would apply his cheaper coal-gas.
The difficulty of constructing atmospheric acetylene burners in which the flame would not be likely to strike back to the nipple has already been referred to in connexion with the construction atmospheric burners for incandescent lighting. Owing, however, to the large proportions of the atmospheric burners of boiling rings and stove and in particular to the larger bore of their mixing tube, the risk of the flame striking back is greater with them, than with incandescent lighting burners. The greatest trouble is presented at lighting, and when the pressure of the gas-supply is low. The risk of firing-back when the burner is lighted is avoided in some forms of boiling rings, &c., by providing a loose collar which can be slipped over the air inlets of the Bunsen tube before applying a light to the burner, and slipped clear of them as soon as the burner is alight. Thus at the moment of lighting, the burner is converted temporarily into one of the non-atmospheric type, and after the flame has thus been established at the head or ring of the burner, the internal air-supply is started by removing the loose collar from the air inlets, and the flame is thus made atmospheric. In these conditions it does not travel backwards to the nipple. In other heating burners it is generally necessary to turn on the gas tap a few seconds before applying a light to the burner or ring or stove; the gas streaming through the mixing tube then fills it with acetylene and air mixed in the proper working proportions, and when the light is applied, there is no explosion in the mixing tube, or striking-back of the flame to the nipple.
Single or two-burner gas rings for boiling purposes, or for heating cooking ovens, known as the "La Belle," made by Falk Stadelmann and Co., Ltd., of London, may be used at as low a gas pressure as 2 inches, though they give better results at 3 inches, which is their normal working pressure. The gas-inlet nozzle or nipple of the burner is set within a spherical bulb in which are four air inlets. The mixing tube which is placed at a proper distance in front of the nipple, is proportioned to the rate of flow of the gas and air, and contains a mixing chamber with a baffling pillar to further their admixture. A fine wire gauze insertion serves to prevent striking-back of the flame. A "La Belle" boiling ring consumes at 3 inches pressure about 48 litres or 1.7 cubic feet of acetylene per hour.