WHAT is a SIMPLE substance?

Those bodies which have never yet been decomposed, nor formed by art, are called simple substances.

How many simple substances are there?

Very lately the simple substances were said to amount to about 50b in number; but since the truly interesting and very important discoveries of Sir Humphry Davy, it is scarcely possible to say what substances are not compound bodies.

The most minute particles into which any substance can be divided similar to each other, and to the substance of which they are parts, are termed the integrant particles: thus the smallest atom of powdered marble is still marble; but if the lime, the carbon, the oxygen and the hydrogen of this marble be separated, we shall then have the elementary or constituent particles.

Suppose a little common salt were reduced to powder, even though it be ground as fine as could be effected by art, still every single particle, however minute, would consist of a particle of soda and a particle of muriatic acid; common salt being a compound body incapable of decomposition by mechanical means. But if we take a piece of sulphur, and pulverize that in the same way, every particle will be a homogeneous body, sulphur being one of the simple substances.

If these substances were all capable of combining, the compounds formed by them would amount to many thousands; but several of them cannot be united by any means we know of.

Can you enumerate what are now deemed simple substances?

All the simple substances that we are acquainted with are; light, caloric, oxygen, the metals, some of the earths, and the simple combustibles, carbon and hydrogena.

Is it well ascertained that these are all simple substances?

It is extremely probable that some of these bodies may be compound; but as no mode has yet been discovered of decompounding any of them, it will be more conducive to science, to consider them, for the present, as simple undecomposable bodies".

Having already examined the nature of all these

a If we omit the earths and alkalies (and there is abundant reason to believe that these are compound bodies) most of the simple substances are combustible, or bear some relation to combustion, either as products or supporters of combustion. Light and caloric are evolved during combustion; oxygen is the principal agent of combustion; and hydrogen, nitrogen, sulphur, phosphorus, carbon, and the metals, are the subjects, or the true instruments, of this process.

b It is curious that most of those substances which were thought by the old chemists to be the elements of all other bodies, are found by our improved methods of experiment to be more or less compounded; while, of those which were formerly ranked among the class of compounds, there are a great number that are really not decomposable, and can only be placed among the simple bodies. Air, fire, water, and earth were by the ancients called the elements of the globe: modern chemistry has demonstrated, that the three first of these are really compound bodies; and there is reason to believe that the earths are also compound. On the other hand, sulphur, phosphorus, carbon, and the metals, which we call simple substances, were supposed formerly to be compounds.

Oxymuriatic acid has lately been added to the list of simple Substances. See page 182.

substances, except the combustibles, we shall now enter upon the consideration of that class of bodies. -Endeavour, therefore, to enumerate the simple

COMBUSTIBLES.

Besides the metals there are four simple combustibles, viz. hydrogen, sulphur, phosphorus, and

carbon.

Why are these substances called SIMPLE combustibles?

They are called simple because we have no proof that they are compounded: whereas oil, spirit of wine, wax, tallow, and other combustible bodies, are well known to consist of two ingredients at the least Þ.

It will be necessary to examine each of these substances separately:-therefore, what is the nature of HYDROGEN?

Hydrogen is the basis of what has been generally called inflammable air, and is one of the

The metals ought to have been included in this chapter, with the other simple combustibles; but as several of their properties are so very different from the four substances now described, it was thought most advisable to treat of them separately.

For the nature of the compound combustibles, consult the chapter on Combustion.

Mr. Cavendish was the first person who examined hydrogen gas and pointed out its nature. This was in the year 1766. Dr. Black then suggested the propriety of applying it to the inflation of air-balloons; and Mr. Cavallo was the first who put it in practice. This gas is about twelve times lighter than atmospheric air.

d Like all other combustibles, hydrogen will not burn unless in contact with atmospheric air, or some substance that contains oxygen. If a portion of atmospheric air be mixed with this gas, and fire be applied, it will explode with violence. It is related of Pilatre de Rosier, that, having mixed one part of common air

component parts of water; but it cannot be exhibited in a separate state. We therefore know

with nine parts of hydrogen gas, and drawn the mixture into his lungs, it caught fire by accident as he respired it, and the whole of the gas exploded in his mouth and nearly deprived him of life. The shock was so violent, that at first he thought the whole of his teeth had been driven out, but fortunately he received no lasting injury whatever. Being myself engaged some years ago in a process in which a large quantity of hydrogen gas was evolved, and having incautiously brought a lighted candle too near the apparatus, the whole exploded with a tremendous crash; and several 12-gallon glass receivers were shattered into ten thousand pieces, and driven in all directions about the laboratory. Such accidents should be noticed in every elementary chemical work, in order to inspire the young pupil with caution when operating on such substances.

a Hydrogen is the inost inflammable substance we are acquainted with; that is, it combines with more oxygen than any other body, and occasions more heat by its combustion. It may be remarked that OXYGEN is mild when in the proportion of 22 per cent. in atmospheric air, and highly corrosive in the proportion of 70 per cent in nitric acid; or even in that of 40 per cent. in sulphuric acid:-How is it then, that it is found in the ratio of 85 per cent. in water, and that this compound, compared with the others, should be perfectly mild and inuocent? Instances of a similar accommodation of the elementary substances have been adduced; and though we cannot comprehend the nature of their operation, we can perceive that the ultimate end of the Creator is our convenience and happiness. See pages 60, 61, and 183. Most oxidized substances, when taken internally, act perceptibly on the system; yet water, the most oxidized of all others, has comparatively little influence, because its oxygen is so forcibly retained by the hydrogen. Had the affinity of hydrogen for oxygen been as feeble as that of nitrogen and oxygen, what is now the most salubrious beverage would have operated as a corrosive poison.

Berthollet has shown that at all temperatures there is a greater disposition in hydrogen than in carbon to combine with oxygen. Chemical Statics, vol. i. 244.

Oil, tallow, wax, &c., used for producing light, do all acquire their power of burning with flame, from the hydrogen, which is a component part of all these substances.

A mixture of oxygen and hydrogen gases produces the most powerful heat yet known. This may be shown by preparing a bladder full of each of these airs, and forcing some out of each into a common tube connected with both, and throwing a stream of the mixed gases on burning charcoal,

it only in combination with other substances, or in the gaseous form, that is, with calorica.

In what other compounds is hydrogen an ingredient?

Hydrogen gas may be combined with water, sulphur, phosphorus, or with carbon.

What is the nature of the compound of hydrogen and water?

Water may be made, by pressure, to absorb a considerable portion of hydrogen gas. It is called hydrogenated water, and is said to be useful in medicine b.

What is the nature of the compound of hydrogen and sulphur?

Sulphur dissolved in this gas forms sulphuretted hydrogen gas, which is a very fetid elastic

or on any other substance in the act of combustion. These bladders should each be furnished with a small metallic pipe and stop-cock, and the tube connecting with both should have a very small orifice, in order that a regular stream of the commixed gas may be thrown upon the burning substance. In performing this experiment all solid vessels should be discarded, for fear of an accident by explosion. When bladders are used no damage can arise, even if such an accident should happen.

a From some late experiments there is reason to suspect that hydrogen gas may be a metal in the aërial form. See Philos. Trans. for 1808.

b Hydrogen gas is slightly absorbable by water, but by pressure water may be made to absorb near a third of its bulk of it. It is said that water, thus impregnated, is useful in inflammatory fevers and other complaints which require similar treatment.

To obtain sulphuretted hydrogen gas, melt together in a crucible three parts by weight of iron filings and one of sulphur, reduce the mass to powder, and put it with a little water into a glass vessel with two mouths: lute one end of a crooked glass tube into one of these mouths, and let the extremity of the tube pass under a glass jar in a pneumatic trough, the jar