The charge of Arson^[602] may occasionally become the subject of scientific research, and the accused individual receive an honourable acquittal at the hands of the chemical philosopher; by whose interposition, the conflagration, unjustly imputed to malice, may be proved to have originated from a spontaneous process of decomposition.

Spontaneous Combustion may be defined, an inflammation occasioned by the re-action of different bodies upon each other, at the ordinary heat of the atmosphere, without the contact or approach of any other body previously raised to a high temperature. This definition necessarily excludes that class of substances which evolve gaseous matter of a highly inflammable nature, but which requires the approach of an ignited body to kindle it.

The subject of spontaneous combustion has attracted the attention of many very eminent chemists, and an extensive series of experiments has been instituted in several different countries for its complete investigation, the results of which have thrown considerable light upon the causes which operate in the production of the phenomenon, as well as upon the nature of the substances most liable to such an accension, and the particular circumstances which are essential to its occurrence. The following may be considered as the principal sources from which it may originate, viz.

I. Friction.

II. Fermentation of Vegetable and Animal Substances, as that of hay, oatmeal, roasted bran, coffee, &c. rags in paper-mills, &c.

III. Chemical Action. Accension of oils, by various animal, vegetable, and mineral substances; accension of vegetable matter by concentrated acids; ignition of lime by the affusion of water; ignition of pyrites.

We shall proceed to consider these subjects more in detail.

1. Friction. The kindling of machinery, when not sufficiently greased, from the friction of its various parts, has occurred too frequently to require much illustration, although the immediate cause of the phenomenon involves in its consideration so many recondite points in the theory of Caloric, as at present to elude our attempts at explanation; we must therefore rest upon it as an ultimate fact, and be satisfied with availing ourselves of the advantages to which a knowledge of it may conduce. The original inhabitants of the New World, throughout the whole extent from Patagonia to Greenland, procured fire by rubbing pieces of hard and dry wood against each other, until they emitted sparks, or kindled into flame; some of the people to the north of California produced the same effect by inserting a kind of pivot in the hole of a very thick plank, and causing it to revolve with extreme rapidity: this fact will explain how immense forests have been consumed, from the violent friction of the branches against each other by the wind.

II. Fermentation of Vegetable and Animal Substances. In order to establish the process of fermentation, the presence of water appears indispensable; we accordingly find that in all the cases of spontaneous combustion which have originated from this source, the substances have either been in themselves imbued with moisture, or they have possessed the power of absorbing a considerable portion of water from the atmosphere. The firing of hay, when stacked in too moist a condition, is a striking exemplification of this fact; the same circumstance occurs from great accumulations of turf, flax, and hemp, heaps of linen rags in paper-mills, &c. provided a sufficient portion of moisture be present to excite the process of fermentation, and the consequent evolution of heat. Oatmeal, from the extreme avidity with which it imbibes water,^[603] and the heat which is generated by the absorption of it, is necessarily liable to spontaneous combustion; the following well authenticated case^[604] may serve as an illustration of this fact: “A gentleman removed with his family from Glasgow to Largs, in May last, and shut up his house, which was not re-opened until the end of August; the house stands on the side of a steep declivity, so that the kitchen which is in the back part, though sunk considerably below the level of the street, is entirely above ground, and is well lighted and ventilated. In an opening of the wall, near the kitchen fire-place, originally intended it is supposed for an oven, there was placed a wooden barrel bound with iron hoops, and filled with oatmeal. This meal, which had heated during the absence of the family, at last caught fire, and was totally consumed, together with the barrel which contained it, nothing remaining but the iron hoops and a few pieces of charcoal.” In some cases torrefaction increases the propensity of vegetable substances to spontaneous combustion; coffee, roasted French beans, lentils, &c. are of this description. Some years ago a great fire broke out in the village of Nauslitz, which is said to have been occasioned by the application of roasted bran to the necks of some cattle in a wooden cow-house; in consequence of which, M. Rude an apothecary at Bautzen, instituted some experiments, by which he found that if rye-bran, roasted until it acquires the colour of coffee, be wrapped up in a linen cloth, it will in a short time take fire. Montet relates^[605] that animal substances may also, under certain circumstances of decomposition, kindle into flame; and he tells us that he had himself witnessed the spontaneous accension of a dunghill. We do not believe that the phosphoric appearances that so frequently accompany the process of putrefaction, especially that of fish, are ever connected with actual combustion. Woollen stuffs are said to have taken fire spontaneously; it is related for instance that the article manufactured at Cevennes, and which bears the name of “Emperor’s Stuff,” has thus kindled of itself, and burnt to coal; we are, however, very doubtful whether such a material is liable to this process, unless it be impregnated with oily matter; and this doubt will receive considerable strength from the facts which we shall hereafter enumerate.

III. Chemical Action. This proves a very frequent cause of spontaneous combustion; and there is perhaps no substance that has so frequently performed the part of an incendiary as fixed oil, especially when of a drying nature, which with its various accomplices from the animal, vegetable, and mineral kingdoms, has in darkness and secresy consigned ships, houses, and manufactories to the flames. The following interesting occurrence is related in the Edinburgh Philosophical Journal: About twenty-five pieces of cloth, each of which contained nearly thirty ells, were deposited upon wooden planks in a cellar at Lyons, on the eighth of July, 1815, in order to conceal them from the armies which then over-ran France; in the manufacture of the cloth 25lbs of oil were used for a quintal of wool, and the cloth was quite greasy, each piece weighing from 80lbs to 90lbs; the cellar had an opening to the north, which was carefully shut up with dung, and the door was concealed by bundles of vine-props, which freely admitted the air; on the morning of the 4th of August an intolerable stench was perceived, and the person who entered the cellar was surrounded by a thick smoke, which he could not support; a short time afterwards he re-entered with precaution, holding a stable lanthorn in his hand, and he was astonished to perceive a shapeless glutinous mass, apparently in a state of putrefaction; he then removed the dung from the openings, and as soon as a circulation of air was established, the cloth instantly took fire. In another corner of the cellar lay a heap of stuffs which had been ungreased and prepared for the fuller, but they had suffered no change. In this case the agency of the oil was sufficiently evident. In June, 1781, a similar occurrence happened at a wool-combers in a manufacturing town in Germany, where a heap of wool-combings, piled up in a close warehouse seldom aired, took fire spontaneously; this wool had been, by little and little, brought into the warehouse, and from want of room, been piled up very high and trodden down; that this combed wool, to which rape oil mixed with butter had been added in the combing, burnt of itself, was sworn to by many witnesses; one of whom affirmed that ten years preceding a similar fire had happened among the flocks of wool at a clothiers, who had put them into a cask, where they were rammed down hard for facility of carriage, and that this wool burnt from within outwards, and became quite a cinder. Cotton goods, in which linseed oil had been spilt, have burnt in a similar manner, and there is reason to attribute to an accident of this kind the recent loss of a merchant-vessel homeward bound from the East Indies. Many years since, several fires broke out at very short intervals, in a rope-walk, and in some wooden houses in St. Petersburgh; in none of which instances could the slightest suspicion of wilful firing be entertained; there was lying in the rope-walk, where the cables for the navy are made, a great quantity of hemp, amongst which a considerable portion of oil had been carelessly spilt, and the article was accordingly declared to have been spoilt; in consequence of which it was purchased at a low price, and being heaped up together, it had given rise to the conflagration; the inferior inhabitants had also purchased parcels of this spoilt hemp, for closing the chinks, and caulking the windows of their houses, a fact which offered an easy explanation of the origin of the fires that occurred amongst the houses. It was moreover reported that at the above-mentioned rope-walk coils of cable had been frequently discovered so hot, that the people were obliged to separate them to prevent farther danger. In the year 1757, as Montet reports, sail-cloth, smeared with oil and ochre, took fire in a magazine at Brest. In the spring of 1780, a fire was discovered on board a frigate lying in the road off Cronstadt, which, had it not been timely extinguished, would have endangered the whole fleet. After the most severe scrutiny no cause of the fire was to be found, and strong surmises existed that some wicked incendiary had occasioned it. In the month of August in the same year, a fire broke out at the hemp magazine in St. Petersburgh, by which several hundred thousand poods^[606] of hemp and flax were consumed; the walls of this magazine are of brick, the floors of stone, and the rafters and covering of iron; it moreover stands alone on an island in the Neva, on which, as well as on board the ships lying in the river, no fire is permitted. In the same year a fire was discovered in a vaulted shop of a furrier; it merits notice that in these shops, which are all vaulted, neither fire nor candle are ever allowed, and the doors are all composed of iron: at length the cause of the conflagration was discovered; it appeared that on the evening previous to the fire the furrier had purchased a roll of new cere cloth, (an article much in use for covering tables, counters, &c.) and had left it in his vault, where it was discovered almost consumed. After these several instances of spontaneous combustion, we shall relate the celebrated case which led to a satisfactory explanation of their origin, and induced the philosophers of different countries to confirm the Russian Report by an extensive series of well devised experiments. In the night of the 21st of April, 1781, a fire was seen on board the frigate Maria which lay at anchor, with several other ships, in the road off the island of Cronstadt; the fire was, however, soon extinguished, but the severest examination failed in extorting any satisfactory explanation of the manner in which it had arisen; the garrison were threatened with a scrutiny that should cost them dear, and were placed under circumstances of the most cruel suspense; in the midst of this confusion, the wisdom of the Empress gave a turn to the affair, and, in the following order to Count Chernichet, pointed out an effectual method to be pursued by the Commissioners of Inquiry. “When we perceived, by the report you have delivered in of the examination into the accident that happened on board the frigate Maria, that, in the cabin where the fire broke out, there were found parcels of matting tied together with packthread, in which the soot of burnt fir-wood had been mixed with oil, for the purpose of painting the ship’s bottom, it came into our mind that at the fire which happened last year at the hemp warehouses, the following cause, amongst others, was assigned; that the fire might have proceeded from the hemp being bound up in greasy mats, or even from such mats having lain near the hemp; therefore neglect not to guide your farther inquiries by this remark.”

As it appeared upon juridical inquiry that, in the ship’s cabin where the smoke first appeared, there lay a bundle of matting containing Russian lamp-black prepared from fir-soot, moistened with hemp-oil varnish, which was perceived to have ignited sparks at the time of the extinction of the fire, the Russian Admiralty gave orders to institute various experiments with a view to discover whether such a mixture, folded up in a mat, would kindle spontaneously; a number of experiments was accordingly performed, and the result established the fact beyond the reach of controversy. The Russian Admiralty having thus satisfied the public with respect to the self-enkindling property of this compound, transmitted an account of their investigation to the Imperial Academy of Sciences, at whose desire M. Georgi repeated the experiments, by which he not only confirmed the report of the Admiralty, but extended the information which it contained, and deduced an important generalization of its views.

It sometimes happens that in boiling flowers and herbs in oil, which occurs in several pharmaceutic operations, these herbs after being taken out, dried, and pressed, inflame spontaneously; care therefore should be taken, when such substances are thrown aside, that they are not heaped up near other combustible bodies.

Amongst the mineral substances capable of exciting the inflammation of oils, an ore of Manganese, known by the name of the Black Wad of Derbyshire, holds a distinguished place; when this substance is pulverised, and moistened with a little linseed oil, it will in the space of an hour take fire, and become red hot, like burning small-coal; it is supposed that the Pantheon, in Oxford-street, was destroyed by the inflammation of a compound of Derbyshire wad and oil, used in painting the scenery.

In these cases of combustion, oxygen seems to act an important part, and by combining with the hydrogen of oil to excite a chemical action which may be considered the immediate cause of the phenomenon. Saw-dust, and other vegetable matter, has been occasionally excited into flame by the action of the concentrated mineral acids; we have been lately informed by Mr. Parkes, that a fire took place some years since in his chemical manufactory, in consequence of the leakage from a carboy of nitric acid. Several instances are also on record of fires having been occasioned by the sudden slacking of quicklime; Theophrastus relates an instance of a ship which was loaded in part with linen, and in part with quicklime, having been set on fire by water that was accidentally thrown over the latter, and that the vessel was in consequence entirely consumed. In the Journal de la Haute Saone there is an account of the burning of a barn, one of the partitions of which being wood had caught fire from a quantity of quicklime, intended for the repair of the premises, having been carelessly thrown against it. In this country a similar accident happened in the last winter at Edmonton, near London; the flood, consequent upon a heavy fall of rain, made its way among the quicklime in a bricklayer’s premises, which took fire and were burnt.

There still remains for notice another source of spontaneous burning,—the ignition of Pyrites, and that of cinders from the furnaces of glass-works, from exposure to air and moisture; it was in this manner that the ship Ajax was supposed to have been consumed, from the spontaneous combustion of coal, abounding in Pyrites.