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a gentle heat in close rooms, and thus forms flowers of sulphur.

If sulphur be exposed to heat it will soon fuse, and, by continuing the fusion for some time, it will become thick and tenacious. If worked between the fingers under water in this state, it acquires a consistency like wax, and may be employed for taking impressions from seals or gems. This change in the sulphur has been ascribed to oxydation; but the same effect takes place if the sulphur be kept in fusion without access of air.

Sulphur becomes electric by friction, and then exhibits negative electricity. It is soluble in oils. It does not combine with charcoal, but unites to phosphorus by means of heat. Sulphur and iron have a great attraction for each other. If a bar of iron be heated to whiteness, and then touched with a roll of sulphur, the two bodies combine and drop down together in a fluid state, forming sulphuret of iron. Sulphur also unites to potash and to soda, by melting them together in a crucible : by this liverbrown substances are formed, called sulphurets of potash or of soda, which are soluble in water.

Sulphur is a highly inflammable body, burning with a pale blue flame. Put some threads, dipped in sulphur, into a vessel floating in water. Set fire to them, and cover the whole with an inverted glass. The threads will continue to burn for some time, and the receiver will be filled with a dense white vapour. This vapour is the sulphurous acid, formed by the union of the sulphur and the oxygen during the combustion. It is absorbed by the water which will ascend in the receiver.

Let the whole then be left till the vessel is become again transparent. If the water be exam

ined, it will have a suffocating odour and an acid taste.

Sulphurous acid, or the vapour of burning-sulphur, has been found very useful for destroying the infection of clothes and small uninhabited places, and for fumigating letters from contagious places. It is used in dyeing, and for whitening straw and silk.

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This acid is composed of sulphur and oxygen, and contains a greater proportion of sulphurous acid.

This acid is the same with that commonly known by the name of Oil of Vitriol. It was so called originally, because it was procured from green vitriol; now called sulphate of iron.

Common oil of vitriol has strong acid properties. It is of an oily consistence, and has usually a brown tinge, from impurities. It is inodorous, and about twice as heavy as water. It is highly corrosive, acting strongly on vegetable and animal substances.

It attracts water very strongly, and cannot be entirely separated from it by any known process. When exposed to the air, it attracts the watery vapour in the atmosphere, so as to increase rapidly in weight, which will be doubled in a month. If mixed with cold water, it suddenly becomes extremely hot, even more so than boiling water; and on this account, when it is necessary to dilute it. with water, this should be performed very gradually.

Sulphuric acid is now made by burning sulphur mixed with nitre, in close chambers, entirely lined

with lead, on the floor of which a thin layer of water is put. The combustion of the nitre furnishes oxygen to the sulphur, and the sulphuric acid is condensed in the water. It is in this manner that the common oil of vitriol is made: but it then contains many impurities; when freed from these, it is colourless.

If sulphuric acid be heated in contact with a combustible body, as charcoal or mercury, it loses part of its oxygen, and is then converted into sulphureous acid gas, which must be collected over mercury, as it is absorbable by water.

CARBON.

This elementary body is widely diffused throughout nature. Common charcoal consists of it, mixed with a small quantity of foreign matter. The purest variety of charcoal is lamp black.

Carbon exists as a constituent principle in all vegetable and animal matters, and remains fixed, after all the volatile parts have been carried off, during the process of combustion.

Charcoal is very nearly the same, from whatever it has been procured. It is always black and brittle, and exhibits the fibrous structure of the wood. It is not at all liable to change, and hence wood is sometimes charred on the outside, when driven into the ground for piles, and similar uses.

The diamond, a substance so very different in appearance, has been found by experiment to be only crystallized carbon. Diamonds are found only in Asia and Brazil, and always in the alluvial soil. Diamond is the hardest body, and can only be cut

by its own powder. When found in the earth, they are crystallized, but are usually rough, having lost the angles of their crystals by attrition. They may be cleaved or split, and are then cut with fàcets for jewellery. They are of various colours. The diamond was long thought to be an incombustible body, but it is now known to be capable of being burnt; and by its union with oxygen, it forms carbonic acid. But although we know that diamond is only carbon, no attempts to crystallize carbon, and thus to make diamonds, have succeeded. Art cannot always imitate the processes of nature, even when the materials she has used are known.

Carbon and Oxygen.

Carbon unites to oxygen in two proportions. We shall first consider the most common one :

Carbonic Acid. If charcoal be burnt, it combines with the oxygen of the atmosphere, and thus forms an acid, which, however, cannot be condensed into the liquid form, but is always aërial. Carbonic acid exists in great abundance in nature, combined with mineral bodies, chiefly lime. All limestones are formed of carbonic acid in a fixed state, united to lime. Hence this gas was at first called fixed air, which name is still sometimes used.

It may be procured from limestone or marble, in the following manner: put a quantity of broken pieces of marble or chalk into a retort, and add to it some sulphuric acid, diluted with six times its weight of water; a brisk effervescence will ensue,

and the carbonic acid gas will be disengaged, and may be collected in the pneumatic apparatus. In this process the sulphuric acid severs the lime, leaving the carbonic acid free, which escapes in the gaseous form.

Carbonic acid gas cannot support flame, as may be seen by plunging a lighted taper into a vessel of it: it will be instantly extinguished.

It is fatal to animal life: a small animal confined in it would die in a few minutes.

Its taste is sour: and it is capable of being absorbed by water. Water so impregnated has an acidulous taste, and reddens vegetable blues. Many mineral waters owe their qualities to this gas, which is contained in them, and they may be imitated by impregnating water with carbonic acid gas. Agitation and pressure promotes the absorption ; and in this manner the artificial soda water is made.

During the process of fermentation, this gas is disengaged, and yeast is carbonic acid enveloped in a viscous substance. If a lighted candle be plunged into the upper part of a cask containing fermenting liquor, it will be extinguished, the apparently empty part of the vessel being filled with carbonic acid gas.

This gas is heavier than common air ; hence, when disengaged, it occupies the lowest situation. It may be poured from one vessel into another, which makes a pretty experiment. Fill a vessel with this gas, and then, having placed a bit of lighted paper in the bottom of an empty tumbler,

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into the tumbler upon the taper: the flame will be extinguished : here the gas will be invisible, but its presence is thus manifested.

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