sugar-tree and the other of beech, were thoroughly ignited and laid upon a board. In two minutes the "fire went out" of both these coals. 2. A wooden pill-box of the largest size was filled with sifted ashes, and an oak coal weighing seven grains was barely buried in them. In thirty-five minutes the box was very warm all over; and at this time I surrounded it with cold ashes. In twenty minutes more, the ashes within and immediately around the box were uncomfortably hot. 3. I renewed the second experiment, with the exception of not wholly covering the box. The edge was left exposed, to ascertain whether it would not act as a vent to the accumulating caloric. In half an hour I examined the coal, and found it extinct and the ashes cold. The coal in this case was of beech. 4. This beech coal lighted at one corner, was placed on a cone of sifted ashes, as in the first experiment, and in twenty minutes it was thoroughly ignited. I now pressed a cylinder of paste-board perpendicularly into the ashes, so as to include the coal and most of the heated ashes. The upper edge of the cylinder was left uncovered. I did not examine the coal for an hour; it was at that time not consumed but dead, and the ashes were entirely cold. 5. I built a cone of a quart of pale ashes, and deposited eight or ten dead coals some distance apart, near the base and remote from the surface; at the apex I buried a live coal as before. In three quarters of an hour, stiff paper or a splinter of wood thrust into the centre of the heap took fire; and on demolishing the pile, I found that the heat had descended to the coals below, and ignited them; indeed they were partially consumed, and the whole interior of the base of the cone was extremely hot. 6. A wooden box ten inches deep and eleven inches square, was filled with unsifted ashes as cold as an exposure of several weeks in winter could make thein. A pint of hot ashes was thrown upon the middle of the surface and left uncovered. In eight hours all the central portion of the ashes was hot enough to fire wood thrust into it, and two sides of the box were incalescent. In twenty-three hours the bottom of the box was quite warm, the top of the ashes cool, and the sides of the box were becoming cool. A stick plunged to the bottom of the ashes, was drawn out ignited or burnt at the end, but not even charred above it. In thirty hours the bottom of the box was almost insupportably hot; and the upper half of the ashes retained but little heat. In thirty-six hours, the temperature of the ashes being much reduced, I emptied the box, and found the bottom of it on the inside near the middle converted to coal, one of the sides considerably charred, and another browned by the heat. Coals were found in different parts of the ashes, but I believe they were confined to those portions through which the heat did not travel. The ashes used in the foregoing and the subsequent experiments, were derived from the mixed combustion of hickory, beech, sugartree, oak, and a few other kinds of wood; and the sieve employed Z consisted of twenty-four by thirty-two interstices to the square inch. To what cause could I attribute the augmentation of heat and its downward course, which the preceding instances exhibit? The plausible answer was carbon. There, said the spirit of conjecture, was the fire, burning its way into the ashes, and leaving successive portions of them to cool after it had consumed the combustible matter out of them; travelling downward like the Goth's descent upon Rome, into regions where its fierceness could be fed. There, too, was the gray colour of the ashes, produced, said conjecture, by the admixture of fine carbonaceous particles with the pure white cineritious matter. To prove that the proper colour of wood ashes is white, there lay the beautiful specimen with gossamer lightness upon the hearth, the residue of the undisturbed combustion of a solitary ember; showing the delicate fibrous structure of the original wood; with open avenues on every side, and a thousand apertures within for the free admission of atmospheric oxygen to every atom of carbon; the carbon thus affianced to oxygen had escaped into the air, leaving its white mansion unshaded by its presence. And how could I better account for the various shades of gray which ashes present, than by supposing them to arise from the various proportions of the black powder intermixed? And then, there were the uniform results of repeated trials by fire, in which something escaped out of the contents of the crucible; and what could this be but carbon? Such was the language of imagination before experiment had fully uttered its voice. To strengthen these conclusions, I applied myself to other evidences; but these, to my disappointment, instead of supporting, kicked against my imaginings. 7. Selecting magnesia as an article possessing physical properties somewhat similar to those of ashes, I erected a cone of this material, and at the summit buried a partially ignited coal. In a few minutes I was surprised to find the whole coal was alive with fire. Shortly afterwards the magnesia beneath the coal became ignited, and the bottom of the heap almost intolerably hot. 8. Guided by the specific gravity and the compressibility of the substances employed, I repeated the experiment with pulverized chalk instead of magnesia. The chalk soon became red hot beneath the coal, and the base of the heap heated beyond endurance. Thus discovering that these alkaline earths possessed the same heat-preserving properties as ashes, and that the same downward centralizing tendency of caloric was shown in all, I was led to the conclusion that the heat eliminated and diffused in the sifted ashes was the result of the combustion of the single coal buried in them; and considering their low conducting and radiating power, it appeared probable that the amount of heat apparent was not very far from the absolute quantity generated during the combustion. In every instance, while the central parts of the cones were red hot, the exterior of the ashes, except at the apex, was cold throughout the experiment. The caloric is evolved faster than it is diffused, and of course it accumulates within a small sphere near the coal to an ig niting temperature; combustible matter lying at the circumference of this sphere would ignite and generate another ball of fire, and this produce another, and so on indefinitely, or while the last ignited spheres reached new combustible matter. In this manner I conceive the caloric travelled in the fifth and sixth experiments, and I see no reason why it should not under similar circumstances circulate through a bed of ashes spread over the whole earth. Satisfying myself in this manner that the presence of pulverulent charcoal was not essential to the phenomenon in question, I submitted other powders to similar trials. 9. Fine sand, scorified wood ashes, anhydrous sulphate of lime, common earth, all thoroughly dried, and the earth and sulphate reduced to subtle powders, were severally made the tenements of a fully ignited coal; but in spite of all the persuasion I could command, the coal refused to be buried alive in such sepulchres as these; almost as soon as it was decently interred it expired. During my inquiries into this subject, I was induced to compare the physical and other properties of various powders. Omitting my tables of their specific gravity, porosity, &c., as incomplete, I give the other results below. The substances were dried at a high temperature, and passed through the same sieve; the force used in ascertaining the compressibility was sixty pounds. The gravity was determined by weighing a given measure, compression or jar. without The sand could be shaken into a less space than it could be pressed by the force employed. Conductibility.-I selected neat paper pill-boxes of uniform size, colour, &c., and filled them evenly and without jarring, with the several powders tested. On the centre of the surface, I carefully placed very small squares of tinfoil supporting a particle of phosphorus. Thus prepared, the boxes were at the same instant care fully set upon an equally heated metallic plate, and the time of fusion and of deflagration noted. I give, in the subjoined table, the average results of several trials, in seconds: Ashes. | Scorif. ashes. | Chalk. Sand. ¡Coal. Earth. Gypsum. Sugar. 125.242 | 123.293 125 242 77:420 182.300 154.314 218.407 Magnesia. When fused, the phosphorus assumed a hemispherical form, and delicate vivid lines shot like lightning from the margin apparently across the semiglobules, and continued thus to play in the most lively manner from various points in rapid succession until inflammation ensued. This pretty miniature pyrotechny can only be seen in the dark. Hygrometric Power of Wood Ashes:-One hundred grains of dried ashes were lightly spread over an area of sixty square inches, and were exposed with due caution in the shade for twenty-four hours, when the noon temperature was 62°, and the air clear and calm. In this time they gained no weight; continued exposure for seventy-two hours enabled them to gain 55 of a grain. But when the temperature was near the freezing point at noon, they frequently gained in eight to twenty-four hours from 66 to 1.66 of a grain. A fine sponge was converted into a sensitive hygrometer by saturating it with a solution of carbonate of potash, and drying it at 170°. Thus prepared the sponge gained from thirteen to forty-four per cent. more than the ashes, and it assisted me in making out the following deductions from eighteen experiments on the hygrometric properties of ashes. 1. They absorb atmospheric vapour more rapidly at a low than at a high temperature. 2. They do not cease to act hygrometrically at a temperature considerably below the freezing point. 3. The range of per centage of increase is from 0 to 1.66. 4. Different parcels of ashes possess different degrees of hygrometric power. This is owing perhaps to the varying quantity of potash present. Carbonaceous Dust in Ashes.-It became interesting to ascertain how much, if any carbon, in a pulverised state, existed in ashes. For this purpose I employed sundry rather rude methods, now to be mentioned. 1. By pouring a sufficient quantity of suphuric acid on sifted ashes, to moisten them, much caloric was disengaged, and a white paste formed, in which black particles were very obvious. These particles washed and crushed between the teeth, produced the peculiar sensation of breaking charcoal. On diluting this paste with a large quantity of water, a milky mixture (sulphate of lime) was obtained, in which the black particles rapidly subsided. All the black sediment, however, was not coal. 2. One thousand grains of sifted ashes were stirred in a large quantity of water, and allowed to subside. In a short time the insoluble parts settled at the bottom, and most of the coal with them, very few particles of it floating on the water. Hence the porosity of the coal must have been sufficiently destroyed to render the fragments specifically heavier than this fluid. 3. The washed ashes used in the foregoing experiments, were examined by a microscope, and particles of coal clearly seen in them. Specimens of well burnt and sifted ashes from the stove, exhibited the same appearance. 4. Several hundred grains of sifted ashes were treated with nitric acid, and after long digestion, the residue was washed, dried, and weighed; the quantity was six per cent. of the original weight of the ashes. Under the microscope this residue was found to consist of particles of coal, a greater proportion of black vitrified grains, and transparent particles which scratched glass, and appeared to have undergone partial fusion. 5. One hundred grains of sifted ashes were in like manner submitted to the action of hydrochloric acid. On diluting the solution with water, a black matter was immediately deposited with gray particles beneath it. The black sediment, washed and dried, assumed a black-brown colour, and weighed a fraction over six grains. This powder scintillated in the blaze of a candle like coal-dust; under the action of the blowpipe it became gray, but the principal part remained unconsumed. Having by these means convinced myself of the presence of coaldust in ashes, it followed that an ordinary fire did not always consume all the carbon of wood; and to arrive at an approximation to the degree of heat necessary to burn it out of ashes, I tried the next experiments. 6. Sifted ashes were pressed firmly into a crucible, and to expel moisture I subjected them to a temperature of at least 440° for an hour. The temperature was ascertained by the fusion of tin. The ashes were then weighed, and subjected to a red heat for half an hour. On weighing again, there was no appreciable loss. Sulphuric acid and the microscope detected, as before, particles of coal in these crucibulated ashes. 7. Most of the ashes of the last experiment were placed loosely in the crucible, and again heated to redness for half an hour. The result was as before: no loss of weight. 8. Intimately mixing thirteen grains of coal-dust with four hundred and sixty-seven grains of the crucibulated ashes of the seventh experiment, and pressing them together, they were heated to redness for a considerable time. In this case there could be no doubt of the presence of carbon; yet after cooling, the mixture weighed just four hundred and eighty grains, and consequently had suffered no ponderable loss. 9. I now placed the crucible as it came from the furnace in the eighth experiment in a smith's forge, and heated it to incandescence for several minutes. At this heat the ashes lost nine grains, leaving at least four grains of the adventitious carbon unconsumed. 10. Four hundred and eighty grains of sifted ashes, hot from the stove, were put into the crucible, and exposed to the highest heat of a smith's forge for twenty minutes. On cooling, they weighed only four hundred and thirty-one grains, having sustained a loss of forty-nine grains! The ashes in the middle of the surface were gray, but all other parts throughout were bluish brown, or blackish and brown. The mass was porous, considerably contracted, and cracked through the centre nearly to the bottom of the crucible; it crumbled under considerable pressure, but retained its form in water, yielding up its soluble parts without falling to pieces. |