In proportion as the combustion proceeds, water is deposited in the internal surface of the vessel; the quantity of this water gradually increases, and it unites itself into large drops, which run down the sides of the vessel, and are collected in the bottom of it.

In making this experiment, proper means were taken to ascertain the weight of the gases employed. Before the experiment, the vessel was weighed; and, by weighing it after the operation, the weight of the water that had been formed was obtained. Here, then, is a double proof; on the one hand, the weight of each of the gases employed; and, on the other, the weight of the water formed; and these two quantities were found to be equal within a two hundredth part. It was thus found that 85 parts by weight of oxygen, and 15 parts also by weight of hydrogen, are required to compose 100 parts of water.

These phenomena of the decomposition and recomposition of water are continually effected before our eyes, by the temperature of the atmosphere, and the agency of compound affinities. It is this decomposition which gives rise, at least in a certain degree, to the phenomena of spirituous fermentation, to those of putrefaction, and to those of vegetation.

Pure water is perfectly transparent, and has no taste nor smell. It is not liable to change. It can absorb a variety of gases; and when exposed to the atmosphere, it always contains a small quantity of common air, which may be separated by boiling, or by the air-pump. Rain-water is the purest which we see in nature; but, for delicate chemical processes, it is distilled in glass vessels. Spring-water generally holds some salts in solution, which gives it various properties.

Hydrogen gas combines with several simple bodies, constituting, with them, peculiar and distinct gases.

Hydrogen and Carbon.

Hydrogen gas unites to carbon, and forms, with it, Hydro-carbonate gas. Of this there are two kinds, according to the quantity of carbon which they contain.

Light Hydro-Carbonate. -This is frequently seen rising from stagnant ponds, when stirred. It may also be procured by passing the vapour of water over red hot charcoal. It burns with a pale blue flame. It is also called Light carbureted Hydrogen. It is contained very abundantly in many coal mines, where it is disengaged from fissures in the strata, often in great quantities; which are called by the miners blowers. When it has accumulated in any part of the mine, it forms an explosive compound, by its admixture with the common air: and when the miners approach it with lighted candles or lamps, it inflames with a tremendous explosion, killing the workmen and destroying the works. Indeed, nothing can be more terrible than such accidents; and there is reason to think that they have happened more frequently than is generally known. The body of miners are, therefore, infinitely indebted to Sir Humphry Davy for his invention of the Safety-lamp, an instrument which they can carry lighted into an explosive mixture, without any danger of setting fire to it. This gas is called the Fire-damp by the miners.

Bi-carbureted Hydrogen. This gas contains

twice as much carbon as the last. It is heavier than it, and is also called the Heavy hydro-carbonate. It burns with a bright white flame, like that of the best wax candles. It has been called the olefiant gas, because, when mixed with chlorine in an exhausted vessel, or over water, a peculiar fluid was formed, resembling a thick oil, but which has been termed by Dr. Thomson, Chloric ether.

Bi-carbureted hydrogen may be procured by heating, in a retort, four parts of sulphuric and of one alkohol; when the mixture boils the gas

comes over.

Gas Illumination. The carbureted hydrogen gases are now extensively employed for the purpose of giving light. When coal is put into an iron retort placed in a furnace, an inflammable gas is given out, which is a mixture of the two abovementioned species of hydro-carbonate, together with small quantities of carbonic acid gas, carbonic oxide, sulphureted hydrogen, tar, ammonia, and water. These last substances are separated by passing the gas through a mixture of quicklime and water; and the purified gas then passes into the gasometer, from which it is distributed by means of pipes. The coal that has been thus acted upon, being deprived of its volatile principle, is converted into coke.

The kind of coal, fittest for the production of good gas, is that which contains most bitumen and least sulphur.

Messrs. J. and P. Taylor have lately taken out a patent for the production of carbureted hydrogen gas from oil. The oil is decomposed by suffering it to drop into a bent iron tube, laid through a. furnace. The oil is separated into charcoal and

bi-carbureted hydrogen, the flame of which much exceeds in whiteness and brilliancy that of coal gas, which is a mixture of the two species of hydrocarbonates. Another material advantage in the use of the oil gas is, that it is not mixed with the impurities of coal gas, many of which are highly injurious to health, and to the furniture of houses. From experiments it appears that the coal gas does not contain above 10 per cent. of bi-carbureted hydrogen; while the oil gas consists almost entirely of it.

Sulphureted Hydrogen Gas.

This is a combination of hydrogen gas with sulphur. It has an extremely fetid odour. It is inflammable. It cannot support life nor combustion: indeed, it is highly deleterious. Water can absorb it, and acquires its peculiar smell. The mineral waters of Harrowgate and Aix-la-Chapelle owe their properties chiefly to this gas.

Sulphureted hydrogen gas has the property of causing metallic oxides to re-approach the metallic state; the hydrogen of the gas attracting the oxygen. If a piece of paper, dipped in a solution of acetite of lead, be exposed to this gas, it instantly becomes blackened. If letters be written with the solution of lead, they will be invisible when dry, but will become black on exposing them to sulphureted hydrogen.

It has also acid properties. It unites with the alkalis and the earths, forming compounds called Hydro-sulphurets.

This gas affords an exception to the doctrine of Lavoisier, that oxygen was the only acidifying principle; for in it there is no oxygen, yet it performs

the most important functions of an acid, reddening vegetable blues, and combining with alkalis. The hydro-sulphurets are formed by passing a stream of this gas through solutions of the alkalis.

Phosphorated Hydrogen Gas.

This gas consists of hydrogen and phosphorus. It is so combustible that it inflames by mere contact of atmospheric air. It has a very disagreeable smell, like that of putrid fish.

To procure it artificially, put one part of phosphorus and ten of a concentrated solution of potass, into a glass retort, and apply a gentle heat. When the mixture boils, the gas will come over, and may be collected in the pneumatic apparatus.

In preparing this gas, the body of the retort should be filled as nearly as possible with the mixture, otherwise the first portion of the gas, finding atmospheric air in the retort, inflames, a vacuum is produced, and the water is forced up into the retort, endangering the bursting of it.

If the bubbles of air which are formed in the retort are suffered to escape into the atmosphere, they will inflame instantly with a slight explosion; at the same time a beautiful dense white circular ring of smoke rises, and gradually enlarges as it ascends.

This gas may be made to burn under the surface of water. Put into a deep glass some phosphuret of lime, and half the quantity of oxy-muriate of potass fill the vessel with water. Procure a longnecked glass funnel and plunge it into the vessel, putting it down to the bottom. Take some con