HYDROGEN AS FUEL.-1. Air required.-Hydrogen combines with the oxygen of the air to form vapor of water, mingled with nitrogen: • Products of Combustion.
Hydrogen, 1. ---...,,..,Air (34.8) Oxygen, 8. -Vapor of water, 9. Nitrogen, 26.8 Nitrogen, 26.8 - 35.8 35.81 lb. hydrogen therefore requires 34.8 lbs. air, while 1 lb. carbon requires only 11.6 lbs.
2. Amount of Heat Produced.-The amount of heat produced from hydrogen is much greater than that from carbon; the caloric from 1 lb. heatino. 60,840 lbs. water 1° F. Part of this is, however, latent in the water-vapor, and must be deducted in calculating intensity of heat, and also heating effect under all ordinary circumstances. This deduction amounts to 9 lbs. water X 965° latent = S6SS°, leaving 52,155° as the effective heating power of 1 lb. hydrogen.
3. Utmost Temperature or Intensity of Heat.-This is less than in the case of carbon, from the high specific heat and greater quantity of the products. We have Vapor of water 9. lbs. Specific heat .8470 Nitrogen 26.8 " CO AA2754 - 35.8 " Mean sp. " .419152,155° on water will be 124,445° on these products; and 124445-- lbs. = 3476°, is the 35.8 utmost possible temperature. I by ii/hcrosoit 10) 5. of Deficiency of Air.—No new product is the result of deficiency of air, as in combustion of carbon; the hydrogen simply escapes unconsumed.
6. of water-vapor present is diminution of intensity and ultimate loss of beat in application, as in the case of carbon.
Temperature of Ignition of Carbon and substances must be them selves heated before they can burn. Hydrogen begins to burn at or below 300°, while carbon requires a red heat (800° to 1000° F.), and even at that temperature burns very slowly. Consequently, where they are combined, as in common coal, the temperature present is often sufficiently high to ignite and consume the hydrogen, while the carbon remains unchanged as cinder, orpasses away as smoke, unconsumed in either case.
All that has been said above of carbon, as to air required, heating power or value, utmost temperature, temperature of ignition, effect of water present, and of excess or deficiency of air, applies, without modification, to one class of fuels—the purely carbon aceous, including anthracite, coke from coal, charcoal from wood and peat, and the cinder orany description of fuel. The incombustible ash must be allowed for in calm lating,heating power or value; and also the volatile bodies—nitrogen, sulphur, etc. the latter of which frequently renders the F. unsuitable for many purposes in the arts and manufactures.
Peat, wood, and coal, with the exception of anthracite, contain hydrogen to an extent rarely exceeding 5 per cent. We have seen that, compared with carbon, hydrogen requires three times as much air, and generates nearly four times as much heat, but produces 20 per cent less intensity of heat, and ignites at a much lower temperature; and the combustion of wood, coal, etc., is in these respects modified according to the proportion of hydrogen present in them.
The following table shows the composition of British coal, as determined by Playfair and De la Beche. Columns 8 to 12 are added to illustrate the process of combustion.
When coal is heated in a retort, it yields volatile hydrocarbons (q.v.), amounting to
20 to 32 per cent of its weight (see column 11). The hydrogen has _robbed the F. of six times its own weight of carbon. When fresh F. is added to live coal in a furnace. the same result ensues; so that in using coal, 50 to 67 per cent of carbon burn on the grate, and 20 to 32 per cent carbon and hydrogen have to be burned in the open space above the F., or escape unconsumed.
The elements of a hydrocarbon are consumed, not simultaneously, but in succession. First, the carbon is separated from the hydrogen in light floating particles, subsequently seen as soot or smoke (if not consumed); then the hydrogen burns, and communicates heat to the carbon particles, which then appear as flame. The color of the flame indi cates the temperature present; and if the temperature is sufficiently high, the carbon of which the flame is composed burns also. producing a further increase of heat. If not, he flame, as it moves onward, cools, .becoming red, dull red, arid, black and smoky, passing away as such. For complete combustion of common coal, we therefore require not only air in sufficient quantity, but also intensity of heat above the fuel. We require a low temperature to separate the carbon from the hydrogen; a higher tempera ture to consume the hydrogen; and a still higher to consume the carbon of the flame. In closed furnaces, such as those of steam-boilers, while the current of air supplied con tinues pretty uniform in quantity, the volatile bodies are evolved almost immediately after fueling; and would require, for the moment, perhaps four times the quantity of air which is passing through. The volatile F. is, in consequence of the want of air, carried off partly unconsumed; and the temperature in such ftn'naces is frequently too low for the ignition of carbon, as may be seen from the color of the flame; the cold boiler having abstracted the heat before' the flame has been subjected to its influence. We refer to the article SMOKE, CONSUMPTION OF, for an account of the plans which have been adopted to secure perfect combustion, and thus prevent smoke. From the principles involved, we should expect most success where the F. is supplied by mech anical arrangements as regularly and uniformly as the air, and in addition, the body of the furnace is protected or removed so far from hoilersurface and other cooling agents as is necessary to maintain a temperature within it sufficient for the thorough ignition of the flame. In house-fires, where the heat is lost if not radiated forward into the room, the cinders should be drawn to the front, and the fresh F. laid into the vacant space behind. The gases rise between the two, and being highly heated, form a sheet of flame above and behind the red-hot F. in front. If, as is commonly done, we throw the fresh F. on the top of the live coal, we interrupt the process of radiation, and the gaseous part of the F. is thrown off rapidly into the cool atmosphere above the grate, and does not take fire until a considerable period has elapsed. To our ordinary fire utensils, we might with advantage add one of a rake shape, suited for drawing for ward the fuel.