wish to be free from disease. One man breathes into his lungs at each inspiration about 230 cubic inches of air, or one gallon. In the delicate cells of the lungs the air gives up its oxygen to the blood, receiving, in turn, carbonic acid and water, foul with waste matter which the blood has picked up in its circulation through the body. Should we rebreathe it into our lungs, the blood will leave the lungs, not bearing invigorating oxygen, but refuse matter to obstruct the whole system. Without oxygen the muscles become inactive, the heart acts slowly, food is undigested, brain is clogged, and at last such fatal results as were manifested in the "Black Hole of Calcutta" implore us not to be stingy or afraid of "God's blessing,"—pure air.

4. Having examined slightly the constituent parts of the atmosphere, let us briefly examine the principal gases met with in coal-mining.

Carbonic-Acid Gas.

Symbol, CO2. Equivalent, 22. Specific gravity, 1.53.

One cubic foot of the gas at 32° F., and barometer at 30", weighs 0.12845 of a pound.

This gas is composed of carbon and oxygen. Miners have given it several names, such as "stythe," "chokedamp," "black-damp," and "after-damp." This gas is

always produced when compounds containing carbon are burnt in air or oxygen. It may be produced by treating limestone or marble with hydrochloric or sulphuric acids. The occluded gases in all coal contain carbonic acid. Carbonic acid is considered poisonous, on account of the many deaths which have resulted from burning charcoal and carbonaceous materials in places where there was a deficiency of ventilation, and by reason of the fatal nature of after-damp of explosions in coal-mines. Its specific gravity is 1.524; so that it is a little more than one and a half times as heavy as air. It lodges near the floor of places in which it is evolved when little more than mutual diffusion is

going on. Owing to its great density, it may be poured from one vessel to another. It is the only gas, except nitrogen, which is evolved by most bituminous coals; and, when it is given off in quantity, active ventilation is required to carry it off.

Le Blanc, and many other chemists, affirm that air containing more than five parts in a thousand is injurious to breathe. Mr. J. W. Thomas of England, while not asserting that it is not injurious, says, that "in levels and seams of semi-bituminous and bituminous coals in South Wales, in part or wholly worked to the dip, with scanty ventilation in some particular spots, through the non-completion of air-splits, or conveyances, men often

work in an atmosphere containing from two to five per cent of this gas for hours." Be that as it may, the system, uninspired by the energizing oxygen, is sensitive to cold. The pale cheek, the lustreless eye, the languid step, shortness of breath, speak but too plainly of oxygen starvation. "In such a soil, catarrh, scrofula, miners' asthma, and consumption run riot."

Miners call the carbonic acid produced by the explosion of fire-damp, "after-damp." They fear it almost as much as fire-damp, as it instantly destroys the lives of all who may have escaped the flames of the explosion. This property of carbonic acid, of choking or smothering, has of late years been made use of for putting out fires in coal-mines. In one case, an English mine which had been burning twenty years was smothered by pouring into it eight billion cubic feet of carbonic acid, and then closing it up for one month. At the end of the month the mine was opened, and found to be ready for the resumption of labor.

When found alone in a mine, carbonic acid is not considered as dangerous as fire-damp, since it will not burn. Carbonic acid, at the ordinary temperature and pressure, is a gas. It solidifies when subjected to great pressure; but, as soon as the pressure is removed, it returns to the gaseous state: therefore the term " car bonic acid" is applied as well to the gas as to the acid.

Carbonic Oxide.

Symbol, CO. Equivalent, 14. Specific gravity, 0.9674.

5. One cubic foot of the gas at 32° F., and barometer of 30′′, weighs 0.078305 of a pound.

This gas is sometimes called "white-damp." From experiments made by Dr. Meyer and J. W. Thomas, it was found, that, during every explosion, large quantities of this gas were formed, and that the fatal effects of the after-damp are in a great measure due to its presence. Carbonic oxide is an odorless and colorless gas, incapable of supporting the combustion of other bodies, but is itself an inflammable gas. It possesses very poisonous properties, which act powerfully on the blood and nervous system, producing, when inhaled in very small quantities, a most unpleasant sensation, followed quickly by headache, and disinclination to move, prostration and inactivity: if continued to be breathed, asphyxia follows, and death soon results. Air containing only one-half per cent of this gas would prove fatal, if inspired for any length of time. Mr. Thomas advocates oxygen and induced artificial breathing, for those who are overcome by this gas, in preference to the administration of alcoholic stimulants.

pain, the body passing Whatever position the

This gas is narcotic, and, when breathed in a concentrated form, would produce no instantly into a state of coma. victim assumed, in that position he would be found. dead, unless moved by some other means. "Carbonic acid, and the nitrogen left after an explosion, would be fatal in their effects; but very often men have succumbed to supposed after-damp, while their lamps burned well. The presence of carbonic acid and nitrogen will not account for the result or phenomena.'

SULPHURETTED HYDROGEN.

Symbol, SH2. Equivalent, 17. Specific gravity, 1.178.

6. One cubic foot of the gas at 32° F. and barometer of 30", weighs 0.09492 of a pound.

This gas, although not common, is met with sometimes in mines. It is colorless, but easily distinguished by its peculiar smell, that of rotten eggs. It may be prepared by treating sulphide of iron with dilute sulphuric acid. The composition of sulphuretted hydrogen is,