pressure The height of the furnace of Seraing from the blast to the mouth was 46 ft. The blast was heated to 212° F., and the was 0.05 mill. of mercury. corresponding height above the furnace, as compared with the other two, the gases have very nearly the same composition. It will be observed that at the The gases from iron-furnaces consuming coal as fuel have been examined at Alfreton, Derbyshire, by Bunsen and Playfair, at nine different levels. Their results were as follows: Height above the 24 ft. 12 ft. 134 ft. 164 ft. 194 ft. 224 ft. 254 ft. 284 ft. 314 ft. blast. 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 The height of the Alfreton furnace from the blast to the mouth was 36 ft. The blast was heated to 626° F., with a pressure of 6.75 inches of mercury. The most appropriate spot for withdrawing the gases from this furnace would be at about 22 ft. above the blast, where the gases have the following composition: The composition by weight corresponding to the above is as The gases evolved from the anthracite furnaces at Ystalyfera were analyzed at two levels by Schafhautel, with the following results: Composition of Gas from Generators.-The gases from generators, being prepared with a special view to their application as fuel, do not vary so much in composition as those from furnaces which can only be withdrawn so as not to interfere with the smelting process. The following is the composition of generator gases: The apparent absence of all carburetted hydrogen in these mixtures of gases, is due to the method of analysis adopted by Ebelmen; these ingredients would probably only enter in small proportion into the mixture, and the above numbers may therefore be employed for all practical purposes in calculating their relative heating values. RELATIVE VALUE OF FUEL. Different kinds of fuel are by no means capable of producing a like amount of heat, and it becomes both interesting and highly important to learn the methods which science has adopted for ascertaining their maximum heating effect. The results obtained from these researches are called the theoretical calorific effect; and in order to ascertain this, it is necessary to know the quantity of heat which a certain amount of fuel is capable of producing, and the time which is required for effecting that object. These two points furnish the idea of what is called heating power. The value of the fuel depends upon its heating power, and its price at the time of consumption; it varies, therefore, in different localities, and can only be relatively fixed. Strictly speaking, the determination of the first point (the quantity of heat) is impossible, as heat cannot be weighed or measured; the quantity of heat, therefore, which a body produces during com bustion, cannot itself be ascertained; but for practical purposes a knowledge of the absolute quantity is not required, it is sufficient to know how much the quantity of heat produced by one kind of fuel exceeds or falls short of that produced by another, the actual quantities produced by each being undetermined. Several methods have been employed at different times to ascertain this relative heating power. The more ancient, purely physical experiments, undertaken by the most distinguished men of science, were all conducted upon the same principle, that of causing the whole quantity of heat (actually unknown) which a burning substance or fuel emits, to act upon a third body, in order to compare the action which the different kinds respectively had upon it. The apparatus by which this was done, is the well-known calorimeter. Lavoisier and Laplace caused the heat evolved in this apparatus to act upon ice, and measured the amount of heat by the quantity of ice that was melted. At a later period, Count Rumford, to whom we are indebted for many experiments upon fuel, used water instead of ice, and measured the quantity of heat by the increase of temperature produced in a given quantity of water. Both methods of determination are in fact the same, the quantity of heat which will melt 1 lb. of ice at 0°, being just sufficient, according to Lavoisier and Laplace, to raise the temperature of as much water (1 lb.) 75° C.; or what is the same thing, to raise 0.75 lb. of water 100° C.* Clement and Desormes have likewise shown, that an equal weight of aqueous vapour, whatever may be its temperature and tension, is always produced by one and the same amount of heat, and consequently always contains that same quantity; and, farther, the quantity of heat which water at 100° C. absorbs (latent heat) in a manner no longer indicated by the thermometer, in order to be converted into vapour, is 5.5 times (according to Rumford, 5.67) sufficient to heat the same weight of water from 0° to 100° C. it is therefore easy to calculate how much water would be converted into vapour by the heat that is required to melt 1 lb. of ice. Rumford's experiments, which only extended to the different kinds of wood, led to the following results: * This number was obtained as the mean of two determinations, which were 73 and 76. From the more recent and accurate experiments of de la Prevostaye and Desains as well as from those of Regnault, it appears that this number must be raised to 79. |