« PreviousContinue »
air, smoke, &c. They are sometimes supplied with air from the natural action of the fire, which rare. fies the air about the ignited fuel ; and the rarefied air becoming specifically lighter, ascends into the chimney, whilst the colder, and consequently heavier air, is forced by the atmosphere to enter at the lower part of the furnace. Some furnaces are supplied with air by means of bellows; and those are applied for forging iron, or for reducing metals from the ore, which is called smelting. Hence the furnaces derive their various names, and are called simple, or open furnaces, reverberatory furnaces, wind, or air furnaces, blast furnaces, forges, smelting furnaces, 8c.
A very useful kind of furnace, for many purposes, is that invented by Dr. Black, of Edinburgh, represented in Fig. 6. It consists of a cylindrical or elliptical body of sheet-iron, coated within with a mixture of loam and clay. The aperture A at top is closed occasionally with an iron saucer full of sand, which forms a sand-bath ; B is the door of the fire-place, and C is the ash-pit register, which slides so as to admit more or less air. Dis an iron tube which goes into the chimney of the room, to carry off the smoke.
Blow-pipes are used for directing the flame of a candle or lamp against any bit of ore or other substance required to be examined. They ought to have a bulb upon the middle of their stem, to contain the moisture that is formed from the breath. See Fig. 7.
The blow-pipe contrived by Dr. Black, of a conical form, represented in Fig. 8., is very convenient; a, is the nozzle.
When a solid substance, in powder or otherwise,
is left for a certain time in a fluid, and the mixture is kept exposed to a slow degree of heat, the process is called digestion.
When one substance, which has an affinity to another, is inixed with as much of that other substance as its affinity will enable it to hold in combination, then the former substance is said to be saturated, or the mixture to have attained the point of saturation. If the mixture contain a greater proportion of either substance, then that mixture is said to contain an excess of it, or to be surcharged. The same thing must be understood of the compounds of more than two substances.
The dry way of performing chemical operations is when strong degrees of heat are used, and the humid way is when fuid solvents are used.
Combustion is when a body is burned with the assistance of respirable air.
Deflagration is when the combustion is attended with little explosions or cracklings.
Detonation is a pretty loud report.
OF THE NOMENCLATURE OF CHEMISTRY.
One of the chief improvements which have been made in modern chemistry has been the invention of names for the compound substances, which express the elements which enter into their composition, as well as the proportions in which those elements are combined. By this the memory
is much assisted, in recollecting the nature of the great variety of substances, and to which the ancient chemists gave arbitrary and frequently unappropriate appellations.
When the simple substances, oxygen, chlorine, and iodine, which are supporters of combustion, enter into combination with each other, or with the other elementary bodies, they form combinations that are divided into two classes. In one class the substances are not acid, and their names have their termination in ide, as oxide of chlorine, oxide of nitrogen, chloride of sulphur, iodide of iron, &c. When these supporters of combustion enter into combination with a body in more than one proportion forming oxides, the terminations, ous and ic, are employed. Thus nitrogen, with the smallest proportion of oxygen, forms the nitrous oxide; and, with a large proportion, it makes the nitric oxide.
When the metals combine with oxygen in one proportion only, the compounds are called simply oxides of the metals. Formerly the compound of a metal with oxygen was called a calx, as the calx of tin, now the oxide of tin; and the process of combining a metal with oxygen was called calcination, now oxigenation.
Sometimes oxygen can enter into combination with a metal so as to form oxides in more than one proportion, and then a syllable is prefixed to the term oxide to denote that proportion; the smallest quantity of oxygen forms the protoxide of the metal, the second quantity of oxygen makes the deutoxide, and the third, the tritoxide ; and, farther, the term peroxide is applied to that oxide of the metal that contains the greatest proportion of oxygen with which it is known to combine. The same syllables are prefixed to chlorides and iodides.
An oxide combined with water is called a Audrat.
When an acid is formed by the union of a simple body with oxygen, it derives its name from that
body; as the sulphuric acid, which is formed of sulphur and oxygen; the carbonic acid, which is formed of carbon and oxygen.
Sometimes oxygen will unite in several proportions with a simple body, so as to form different acids; then the acid which is the most oxygenated, has its termination in ic; and that which is the least oxygenated, in ous. Thus sulphur forms two acids; when it unites to the least proportion of oxygen capable of making an acid, it forms the sulphureous acid, and with a larger proportion of oxygen it makes the sulphuric acid.
Hydrogen, like oxygen, combines with a certain number of simple substances, and with them forms compounds, some of which are acid, and others are not.
To distinguish the acids formed by hy. drogen, from those formed by oxygen, the former are designated by the word hydro, as the hydro. chloric acid, hydro-fluoric acid.
Products, not acid, formed by hydrogen and a simple substance, if solid, are called hydruret : if gaseous, the name of the simple substance terminated in ed is prefixed to that of hydrogen gas; as carburetted, or phosphoretted hydrogen gas.
When chlorine, sulphur, phosphorus, and carbon, unite to each other, or to another simple body, the compound has also its termination in uret, as chloruret of phosphorus, and of iron, sulphuret of iodine, phosphuret of lime, carburet of iron, &c. Neutral salts, or substances pioduced by the union of acids and alkalis, are denominated from the names of the acids and alkalis of which they are composed. The salts produced by the acid whose names end in ous have their terminations in ite ; thus sulphurous acid and potash form sulphite of potash : salts produced by acids ending in ic have their termination in atę : thus sulphuric acid and potash form sulphate of potash, and so of all the rest.
The terms, bi-sulphuret, bi-phosphoret, bi-sulphate, &c. denote that these compounds contain twice as much sulphur, phosphorus, sulphuric acid, &c, as the sulphuret, phosphoret, sulphate, &c.
Caloric, or the matter of heat, is generally considered as a peculiar elementary substance. It cannot be ascertained to have any weight, a body when heated not being heavier than before,
A distinction is made between caloric, or the matter of heat, and the word heat when considered as a sensation. The sensation of heat, or sensible heat, is the effect produced upon our organs by the motion of caloric disengaged from the surrounding bodies. When we touch a cold substance, the caloric, which exists in unequal quantities in different bodies, but which always tends to be in equilibrio in all bodies, passes out of the hand into the body, which feels cold, because at the time there was less free caloric in the substance than in the hand ; and as we have lost heat, we feel the sensation of cold: cold being, not any thing positive, but merely the want of heat. The contrary happens when we touch a warm body; the caloric then in passing into the hand, gives the sensation of warmth. If the hand and the body touched be of the same temperature, or very nearly so, we receive no impression either of heat or cold, because there is no motion of caloric.
By free caloric, we mean that which is not combined with any other body. But, as caloric has a