Gas Stoves

GAS STOVES. Many kinds of gas-consuming appliances are commonly included under this heading. The main types in general use are the gas-cooker and the gas-fire, and each of these is manu factured in many different forms. Gas-fired water-heaters, radi ators, boilers for central-heating purposes, furnaces and many other gas-consuming contrivances are also employed in houses, offices, factories, hospitals, etc.

The Gas-Cooker.

As usually manufactured, the gas-cooker consists of a gas-heated oven, combined with a hot plate provided with boiling burners, and some form of griller. Many years of experiment have brought the appliances to a high degree of ef ficiency, with the result that they are very freely used. It is estimated that in Great Britain alone there are six to seven million domestic gas-cookers in use. It is claimed for the most modern appliances that with town gas at 9d. per therm (i.e., 1 oo,000 British thermal units), the cooking of a varied menu for a family of six persons may be performed at a cost of less than 4d. per day per person.

Gas-cookers are now frequently made with a very high-grade finish in polished metal and nickel-plated fittings. A specially tough vitreous enamel is used to cover both the interiors and ex teriors, including the hotplate, and a new process has been adopted by which the enamel is applied cold to castings and fired afterwards, instead of being sprayed on to hot metal. Expansion and contraction do not affect these enamels, and stains can be removed easily without damage to their surfaces.

Gas-cooker ovens are now often fixed at a higher level than in the past, in some cases on stands raised about 6 inches from the floor, and in others about 2 feet 4 inches above floor level. When the oven is raised to eye level, the hotplate is fixed on the same stand at the side of the oven instead of above it.

Nearly all gas ovens are internally-heated, combustion taking place inside the chamber in which the food is cooked. This prac tice was investigated on behalf of the Lancet, and the principle declared sound. Externally-heated ovens have, however, been made. In internally-heated ovens one or two bar burners of bunsen type are fixed at the base. When two burner bars are used they are placed at the sides ; when one only is provided it is fixed at the back. The oven has adjustable shelves which make it possible for several articles of food to be cooked at one time.

The metal walls and door are insulated with silicate wool, which is packed between the inner and outer casings. The products of combustion and the vapours arising from the food pass away through an opening, which in some cases is situated at the top of the oven and in others at the bottom.

The thermostat supplied with many gas cooker ovens is pro vided with a revolving knob and pointer, and a numbered dial. By setting the pointer at the figure required for certain cooking processes the cooking is automatically carried out without the necessity of further attention on the part of the user.

The Hotplate.

The bulk of the cooking for the average house hold is done on the hotplate, which consists of two or more boiling burners and a griller, with bars above to support cooking utensils. The boiling burners are of two kinds—the "drilled ring" and the "spreading flame," each of which has merits. In some cases, both types are used in the same hotplate. The "drilled ring" burner is usually regarded as the better for slow work—especially when solid materials are contained in the saucepan—whereas for plain boiling work, such as heating water in a kettle, the "spreading flame" burner can be employed with advantage in thermal effi ciency. The flames can, in either case, be reduced or increased at will to give a large number of variations of heat between the maximum and the minimum.

The common type of hotplate is of "open" form, the cooking vessels being supported above the burners by relatively slender bars or grids so constructed that, while having the necessary strength, they provide the smallest possible surface contact with the flames of the boiling burners. This ensures the utmost economy in gas consumption, because very little heat is conducted away and wasted through the bars, and with gas at 9d. per therm, about 14 pints of water may be boiled for d.

In the "enclosed" type of hotplate, the burners are covered by a metal plate or plates upon which the vessels stand. With this type of hotplate the amount of gas used for heating a single vessel is greater than when open bars are used, as some of the heat which is passed to the plate is conveyed to the adjoining metal, upon whose surface other and slower cooking operations may of course be carried on. The closed hotplate also provides a smooth sur face on which vessels can readily be manipulated. For this reason this type is sometimes preferred for large-scale cooking opera tions. When cookers are made with closed tops, some detachable plates are provided for removal to permit a kettle or other vessel to be placed directly over the burner flame to hasten the process of boiling. Alternatively, one or more solid plates are frequently supplied with the more popular open-top hotplates for use when specially slow cooking processes are required.

In

the kitchens of works' canteens, hotels, hospitals and institu tions, separate appliances are usually provided for the carrying out of the various functions of the domestic gas cooker. Among those in common use for large-scale catering are roasting ovens, table hotplates, fish-fryers, pastry ovens, soup boilers, vegetable steamers, instantaneous water-heaters, Bains Marie, grillers and toasters, hot closets and carving tables, incinerators, refrigerators, and bread-baking ovens of various sizes up to those nearly ioo feet long, through which the loaves pass on a continuous travelling web of iron plates supported by chains.

Gas Fires.—The gas fire fundamentally consists of : (r) A horizontal burner with a number of jets which produce a row of intensely hot but silent flames; (2) What are known as "radiants," superimposed on these jets to become incandescent when the flames burn within them ; (3) A fire-brick back behind the radiants; and (4) A canopy capable of conveying to a chimney or flue all the products of combustion, and of creating the necessary movement of air to ensure good ventilation.

The details of burner design include regulating devices whereby the correct size, character and silence of the gas flame can be readily produced, and what is known as a "duplex" tap, by means of which some flames may be extinguished while the remainder keep burning. The user is thus able to obtain the exact amount of heat required at any given time. The radiants are made of refractory material specially prepared so that the fire will reach 90% of its full heating power in about five minutes from the moment of lighting, and will radiate at its greatest intensity two or three minutes later. This is due partly to the form of the fuel and partly to its composition. The radiant is of skeleton form, within which the flame burns. It is as slender in construction as possible, but sufficiently strong to withstand a fair amount of rough handling without becoming fractured. Some gas fires are con structed to accommodate "radiants" which are so designed as to simulate the appearance of a coal or coke-fire when burning. The result is obtained by the blackening of portions of the radi ants, which are specially made with a backward curve, and by superimposing upon them a layer of solid pieces of refractory material resembling coke. Another type is made to imitate blaz ing logs of wood.

As gas does not produce soot and its products of combustion are of a vaporous character, the flue area necessary is much smaller than that for a coal fire. By the use of what are called "economy" blocks, suitable gas fire flues can be constructed within the thickness of the party or external walls, rendering unnecessary the provision of brick chimney breasts. Gas fires are low in running cost. It is said that with gas at 9d. per therm, a room 12' X 12' may be heated for an hour, with the fire full on, for 'id., the hourly cost being considerably reduced over a period as the room becomes warm.