(From the Hebrew term aesh). Fire. Bacon, Boyle, Newton, and their followers, consider lire not as an element but as an adventitious property, resulting from the intestine motion of the smaller particles of matter; and this opinion has been lately revived by Count Rumford and Mr. Davy. On the other hand, Homberg, Boerhaave, Lemery, Lavoisier, and Black, consider fire as a material principle or element. The motion of friction or percussion undoubtedly generates or elicits heat; and, if the supposition of the mere vibration of parts could adequately account for the effects, it would be more simple than to suppose a material substance endued with peculiar properties; for it is still an hypothesis, since we cannot show the existence of fire without combination, and all reasoning by analogy promises very little elucidation of a subject which can only be prosecuted by experimental research. So far as experiment has extended, the result is in favour of the existence of fire as a distinct body. The reality of fire seems evident, by the power we possess of increasing or diminishing it. In the living human body, whatever increases the quantity of crassamentum in the blood, increases the degree of heat also; as an animal diet, aromatics, sometimes iron, and the mineral acids; but nitre, crude sal ammoniac, carbonic acid gas, seem to diminish it, or at least prevent its evolution. In physics, fire is understood to be that subtile invisible cause by which bodies are expanded or enlarged in bulk, and become hot to the touch; fluids rarefied or converted into vapour; solid bodies fluid, and either dissipated, melted into glass, or scorified. It seems, likewise, to be the chief agent in nature on which animal and vegetable life depend; and without which it does not appear that nature could itself subsist for a single moment. See Caloric.
It has been doubted whether light is a modification of heat or a distinct principle. The greater number of facts show it to be distinct, and it has been lately supposed from induction, that they are antagonising principles repelling each other. See Lumen.
Many distempers have been named ignis, or fire, but principally the causus, or burning fever, which Hippocrates often calls fire.
Ignis Ca 'Lidus. A hot fire. A violent inflammation hath been called a gangrene when about to degenerate into it; and has hence received the name of ignis calidus.
ignis frigidus. A cold fire. A sphacelus; because the parts affected become cold as the surrounding air.
ignis persicus. ignis sacer. ignis sancti Antonii. See Erysipelas and Herpes exedens.
ignis sylvaticus. See Impetigines.
Ignis is also a name of several medicines, as argen-tum vivum; the essential oil that swims on the top of distilled waters, etc.
The chemists use fire in different modes in performing their operations; whence their ignis sapientium, or heat of horse dung.
ignis reverberatorius. A reverberatory fire is made in a furnace covered with a dome, that the heat or the flame may be reverberated on the vessels immediately exposed to it.
ignis rotae, or fire for fusion. Red hot coals, surrounding the vessel in which the matter is contained.
The chemists formerly regulated their fire by different degrees: the first was scarcely to be perceived; the second was when the heat was manifest, but not sufficient to give pain; the third, when the heat was painful; the fourth, when sufficient to' destroy the body; and fifth, when the heat would cause gold to evaporate in fumes. Boerhaave was the first who regulated the heat of fires by means of a thermometer; and when the degrees of heat are mentioned in his writings, they are to be understood according to Fahrenheit's scale.
We have since learnt to regulate the higher degrees of heat, by means of Mr. Wedgewood's thermometer, which enables us to ascertain degrees of temperature so high as 32277° of Fahrenheit, could his scale be extended so far; but, in electrical and galvanic experiments, we seem to experience a greater degree, since we can produce greater effects than can be attained by any fire; but perhaps some of the power must be attributed to the momentum.
On the contrary side, at 1500° of Fahrenheit, it is supposed no heat exists; but this is necessarily hypothetical, for it cannot be ascertained by experiment.
Ignis vivens., See Circulatum.
Ignis volaticls. See Impetigines.