is suddenly developed, and consumes the body in a few hours. 12. Those parts not reached by the fire, are affected by gangrene. 13. A putrid degeneration ensues, which causes gangrene. 14. The residue of this combustion is composed of greasy cinders, and an

unctuous matter.

Professor Jameson observes, in substance, upon this interesting question: "we are of opinion that, in some subjects, and chiefly in women, there exists a general condition of the body, which, conjoined with the extreme debility occasioned by age, a life of little activity, and the abuse of spirituous liquors, may give rise to a spontaneous combustion. But we are far from considering as the material cause of this combustion, either alcohol, or hydrogen, or a superabundance of fat. If alcohol plays a prominent part in this combustion, it is by contributing to its production: that is to say, it produces, along with the other causes mentioned, the degeneration of which we have spoken, which gives rise to new products of a highly combustible nature, the reaction of which determines the combustion of the body."

A curious case of the combustion of both hands only, in which the patient recovered, is related in the Medical Journal, 1830.

CHARCOAL.

Why do various woods afford different quantities of

charcoal?

Because of their different durability; those most abundant in charcoal and earthy matter are the most permanent; while those that contain the largest portion of the gaseous elements are the most perishable. Among British trees, the chestnut and oak are the most permanent, and the chestnut affords rather more charcoal than the oak.

The beams of the theatre at Herculaneum were converted into charcoal by the lava which overflowed

that city; and during the lapse of seventeen hundred years the charcoal has remained as entire as if it had been formed but yesterday; and it will probably continue so to the end of the world. The incorruptibility of charcoal was known in the most ancient times: the famous temple at Ephesus was built upon wooden piles, which have been charred on the outside, to preserve them.-Watson's Chemical Essays.

A new process for manufacturing charcoal, is to fill all the interstices in the heap of wood to be charred, with powdered charcoal; the product is equal in quality. The effect is produced by preventing much of the access of air which occurs in the ordinary method. The volume of charcoal is increased a tenth, and its weight a tenth.-Bulletin Universel, 1830.

Professor Silliman, in his Journal, (1830) says, that in the United States, wood is charred in brick-kilns, with openings at the top and sides, under regulation; and the charcoal thus obtained is exceedingly good, and more abundant than by the old mode of burning.

Wood has also been charred at low temperatures. Thus, on making extracts, in wooden vessels, with steam of very moderate pressure, all the apparent effects of burning may be produced; but the carbonization of the wood is not so complete as by flame. This fact is practically illustrated in the Philosophical Magazine, 1830.

The application of charcoal to various purposes of domestic economy has been already noticed in Part 1 of the present work.*

Why does heated charcoal produce combustion?

Because the mutual cohesion of its particles is so weakened, that is, the particles are so repelled and separated from each other, that their attraction for the oxygen in the air around is allowed to operate, and

*See DOMESTIC SCIENCE, p. 6.

they combine with that oxygen, so as to produce the above phenomenon.

Why does charcoal increase in weight on exposure to the air after burning?

Because it is a very hygrometric substance, and therefore absorbs air and moisture in considerable quantity.-Brande.

Why do sailors at sea throw pieces of burnt biscuit in bad water?

Because it serves as charcoal in destroying the putrid flavour of the water, and rendering it comparatively fresh.

Why does fresh charred wood, or charcoal, improve the flavour of spirits?

Because it destroys the essential oil, or empyreumatic flavour which the spirit may have contracted in distillation.

GUNPOWDER.

Why do mixed nitre, sulphur, and charcoal, or gunpowder, explode with heat; whereas, while cold, they may be mixed together most intimately without any change?

Because, by the change of temperature, and the consequently altered relative attractions of the different substances, a new chemical arrangement of them takes place with the intense combustion and expansion which constitute the explosion.

The proportions of the ingredients of gunpowder vary, The following are those usually employedCommon Shooting Shooting Miners Powder. Powder.

Powder.

Powder.

The latter contains the smallest quantity of saltpetre, as it requires less quickness or strength. The ingredients are perfectly mixed, moistened, beaten into a

cake, which is afterwards broken up, granulated, dried, and for the finest powder, polished by attrition. -Brande.

Why is iron excluded from powder works?

Because it is liable to cause sparks by a blow. Brass and copper have been recommended in its place; but Col. Aubert has remarked that brass can inflame powder, and has made experiments on the subject before a committee, the result of which is as follows:-Inflammation of the powder takes place when the blow is given by iron against iron; iron against brass; brass against brass: iron against marble; lead against lead, or against wood, when the blow is produced by a leaden ball shot from a fire-arm. As yet, powder has not been inflamed by the blow of an iron hammer against lead or wood.-Bulletin Universel.

Why is steam likely to supersede gunpowder in the discharge of artillery?

Because the elastic force of high-pressure steam having much greater range than that of gunpowder, is infinitely better calculated for projectiles, independently of any saving of expense. It is estimated by Mr. Perkins, that the projectile force of steam is ten times greater than that of gunpowder, in throwing a ball to a given distance.

Why do "Prometheans" suddenly inflame on pres

sure?

Because they consist of small glass bulbs, filled with concentrated sulphuric acid, hermetically sealed, and surrounded with a mixture of inflammable materials, amongst which the chlorate of potash forms one; and the whole being again inclosed or surrounded with paper, also rendered still more inflammable by means of resinous matters. Upon pinching the end containing the glass bulb, between the jaws of a pair of pliers, the bulb breaks, and the sulphuric acid instantly kindles the surrounding materials.

VOLCANIC FIRE.

Why are volcanoes produced?

Because, according to the most recently observed phenomena, they "depend upon the oxidation of the metals of the earths upon an extensive scale, in immense subterranean cavities, to which water or atmospheric air may occasionally have access. The subterranean thunder heard at great distances under Vesuvius, prior to an eruption, indicates the vast extent of these cavities; and the existence of a subterranean communication between the Solfatarra and Vesuvius, is established by the fact that whenever the latter is in an active state, the former is comparatively tranquil. In confirmation of these views, the author remarks, that almost all the volcanoes of considerable magnitude in the old world, are in the vicinity of the sea; and in those where the sea is more distant, as in the volcanoes of South America, the water may be supplied from great subterranean lakes; for Humboldt states that some of them throw up quantities of fish.”

The phenomena observed by the author afford a sufficient refutation of all the ancient hypotheses, in which volcanic fires were ascribed to such chemical causes as the combustion of mineral coal, or the action of sulphur upon iron; and are perfectly consistent. The author acknowledges, however, that the hypothesis of the nucleus of the globe being composed of matter liquified by heat, offers a still more simple solution of the phenomena of volcanic fires.-Sir H. Davy, Philosophical Transactions.

On these phenomena, Baron Humboldt says, "Observations made in all countries, in mines and caves, prove that, even at a small depth, the earth's heat is much superior to the temperature of the surrounding atmosphere. A fact so remarkable, and elicited from observations made in almost every part of the globe,