Suppose a current of heated air to issue from an orifice; what data are required in order to estimate the amount of caloric contained in it, as compared with the amount in the same current at atmospheric temperature? The data are1. Its weight; 2. Its specific heat; 3. Its temperature. Example. In one hour 1000 lb. gaseous matter-specific heat 2596, temperature 560-escape. Required the caloric present over that present at a temperature of 60°. == 1000 lb. at 2596 sp. heat 259-6 lb. water at 1-0000 sp. heat, and 259.6 lb. water heated 500° = 129,800 lb. water, heated 1°, which would be the amount of caloric lost in one hour. Suppose, also, that during the same period we had consumed 120 lb. carbon, what is the loss per cent.? Total heat generated, 14,220° x 120 = 1,706,400". 129,800° = 7.6 per cent. In general we may therefore affirm, 1. The loss by heated waste products increases with the temperature at the moment of escape from contact with the body receiving the caloric. In future, it will be convenient to call this the Terminal Temperature." " 2. The loss also increases with the quantity or weight of the waste products. 3. Also with the specific heat. But, as before observed (column 6, Table III.), this element does not vary to any notable extent in burning carbon with varying equivalents of air. Under all circumstances it ranges from 2596 to 2669. But as the subject admits of more rigid calculation, and as we believe the principles involved to be of the highest importance in practice, we have inserted the columns in Table III., immediately succeeding column 14. This latter column contains, for each case, the weight of water, equal in capacity for heat to the whole gaseous products per lb. carbon. For example, the heat which would raise the waste products from 1 lb. carbon, with a draught of 13, 200° temperature, as indicated by a thermometer, would raise 482 lb. water 200°, or 1 lb. water 964 (= 482 x 200), as in the Table. By multiplying column 14 by the degrees of temperature in the escaping gases, we thus obtain the loss for any terminal tem perature in degrees of heat on 1 lb. water per lb. carbon consumed. Now, each lb. carbon generates 14,220°; so that we are able to find the loss of heat per cent. in each case. Each result given in the Table is calculated in the same manner. Terminal temperatures up to 550 may be ascertained by means of a mercurial thermometer. For higher temperatures other means must be employed. A reliable pyrometer for high temperatures is still a desideratum. In most steamboilers working stationary engines, where economy is at all consulted, the mercurial thermometer ought to be sufficient. Although the calculations have rather a formidable appearance in detail, the results may be got at once by a very simple formula. Formula 2.-To find the per-centage of loss of heat by waste products, multiply the terminal temperature by the equivalents of draught. The constant number 4400 is to the product, as the whole caloric, capable of being generated by the carbon, is to the loss. Examples: Terminaltemp. 500°× Draught 13 650° 14.8 per cent. less on 4400°. 300° x do. 18 540°= 12.2 Do. do. These results agree closely with those given in the Table; and if we are correct in our premises so far as known scientific data extend, the principle is of immense importance, and deserves attention. The quantity of carbon consumed, either as coke, charcoal, cinder, &c., does not affect the result. With a terminal temperature of 600° (which is common), and a draught of 2, or twice the air necessary for perfect combustion (which is equally so), the loss cannot but be, at least, 26.7 per cent. of the heat generated, whether from 100 grains or 100 tons of the carbonaceous material. When we bear in mind that anthracite and several other varieties of coal contain 90 to 98 per cent. carbon; that charcoal contains about as much, the volatile ingredients having been expelled; and that even ordinary bituminous coal contains 80 to 90 per cent., about 50 per cent. remaining on the hearth as purely carbonaceous coke or cinder, the extensive application of the formula now given must be very evident. By its aid, many problems which arise in ordinary practice may be solved-at least approximately, or in proportion as we are able to ascertain, with accuracy, the terminal temperature and draught. We give a few examples. Example.-With one draught, we find the terminal temperature from a boiler-furnace to be 1000°. What saving of fuel might be expected by increasing the boiler surface so as to reduce the terminal temperature to 400°? 1000° 1 = 1000 = 22.7 per cent loss. reduced to 400° X 1 = 400 = 9.1 Probable saving, 13.6 per cent. Example.-With 2 draught, which is much more common 1000° x 2 = 2000 45-4 per cent. loss. reduced to 400° x 1 = 400 = 9.1 Probable saving, 36-3 per cent. Example.-With 2 draught, and terminal temperature 600°, what saving might we expect from adopting Green's Fuel Economizer, or any similar apparatus, to absorb and utilize the waste heat by reducing the temperature to 200° ? 600° x 2 = 1200 27.0 per cent. loss. reduced to 200° x 2 = 400 = 9.1 do. Probable saving, 17.9 per cent. Example. With a draught of 1%, the terminal temperature of a reverberatory furnace is found to be 1500°. Required the saving, if the heat were applied to evaporating purposes, and the temperature reduced to 300°? 1500° × 1% = 1800 40.9 per cent. loss. 10 do. Probable saving, 32.7 per cent. (It may perhaps tend to strengthen confidence in this formula to state that, in the writer's experience, 30 to 35 per cent. saving of fuel has been in some cases effected, by simply reducing and regulating draught, without any reduction of the terminal temperature.) 4. Excess of Air as diminishing the effective and increasing the non-effective Caloric in heated Gaseous Currents.— Against diminishing excessive draught, it may be, perhaps, urged, that it will, by raising the initial temperature, also raise the terminal temperature, and so leave us where we were as to economy of fuel. But we shall endeavour to show, that it is absolutely impossible to obtain so much heat from the same fuel in the one case as in the other. Suppose the case of a steam-boiler, steam at 14 lb. pressure. The temperature of the steam and also of the water will be about the same at all points-viz., about 250°. The iron of which the boiler is formed, being the medium through which the heat is communicated, will be somewhat higher in temperature-suppose it 300°. Lastly, suppose this boiler heated by currents of gaseous matter, containing the caloric generated by the combustion of a constant weight of carbon, with varying proportions of air or draught. It is evident that, under all circumstances, the gaseous current, in the case supposed, must retain at least 300° temperature, that being the temperature of the receiving surface of iron. Up to 300°, therefore, the caloric in the current is noneffective; above 300° it is efficient, and capable of being communicated, if the heating or absorbing surface is sufficiently extensive. Referring again to Table III., we find that the waste products, at a terminal temperature of 300°, contain, for varying draughts, the following per-centages of the whole heat generated, which per-centages are, in this case, non-effective. 1 lb. carbon generates heat capable of evaporating 14.75 lb. water. NEW SERIES.-VOL. XI. NO. 1.-JAN. 1860. F The proportion of non-effective to effective rises rapidly, and the loss is absolute and inevitable with these draughts; as the boiler, however extensive its surface, cannot absorb caloric from a current which has fallen to its own temperature. The last column shows the diminishing effect as to the quantity of water raised into steam. We have reason to believe that 5 to 10 equivalents of air are admitted, very frequently, in one way or another; and, if so, the waste of fuel, or rather of heat, cannot be less than we have stated; it may be more from the action of other causes. For practical guidance, we will express the principle involved, in a formula. Formula 3.-To find the proportion of caloric which is noneffective in the use of carbonaceous fuel, multiply the temperature of the body or surface to which the heat is applied by the equivalents of draught. 4400 is to the product as the whole caloric capable of being generated is to the proportion that is non-effective. This formula differs from the last in one respect only: it gives the minimum loss, supposing our arrangements are most complete, and that all the heat is absorbed which can possibly be; while formula 2 gives the actual loss as determined from the temperature at which the products actually escape, which |