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which the gas is generally burnt calculated for anything but to do the greatest amount of injury to the persons using it. Some forms of gas-light, such as the sun burners and the ventilating globe light, are comparatively free from defect in these respects, but I have never seen the latter used save in one or two private houses, and the former are almost entirely confined to offices and public buildings.

I have experienced some difficulty in obtaining the quantity of air consumed by the ordinary bat's-wing or fish-tail burner when lighted. But taking the Argand burner using 5 ft. of gas per hour, and 45 ft. of common air in the same time, as a standard, and knowing that the common burners burn from 2 to 6 ft. per hour, according to size and pressure, I think I shall be safe in calculating the average consumption of gas by the common burners at 4 cubic ft. per hour, and the amount of air at 36 cubic ft.

per hour.

Now a room 25 ft. long by 16 ft. broad, and 10 ft. 6 in. high, will contain 4,200 cubic ft. of air, but a deduction must be made for

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furniture, etc., of at least 10 per cent., leaving 3,780 cubic ft., or say 3,800, as the net qnantity of air in the room.

Such a room will require at least three gas burners to light it, and these, as we

will consume 108 cubic ft. of air per hour, rendering it absolutely unfit for breathing by depriving it of its necessary proportion of oxygen.

Ordinary candles do not vitiate more than 11 cubic ft. of air per hour, per candle.

As the chief constituents of coal gas are carbon and hydrogen, so the principal results of its combustion are carbonic acid and water. This water, in the form of vapor saturates the air of the room, which has a greater capacity for moisture when warm than when cold. This may be readily seen if, in a close warm room, we examine the windows, where the moisture will be found condensed, and perhaps running down the glass in streams.

The same effect will be produced by placing a glass bottle filled with cold water on the table, the moisture will settle thickly upon it like dew upon the grass on a clear night.

The reason is this. The air cooled by contact with the cold glass is no longer able to sustain the moisture, and the latter is therefore precipitated in the form of dew.

(C.) The third cause I have mentioned is the presence of living beings in the room. Let us now consider the effect of this.

Man's body is a furnace, a slow combustion furnace if you will, but still a furnace, and the waste from this human furnace is precisely the same as that from any other furnace, viz., carbonic acid and water. To quote the words of Professor Tyndall : “In the animal body the carbon and hydrogen of the vegetable are again brought into contact with the oxygen from which they had been divorced, and which is now supplied by the lungs. Re-union takes place, and animal heat is the result. Save as regards intensity, there is no difference between the combustion that goes on within us, and that of an ordinary fire.” We see then of what vital consequence is the

presof oxygen

in the atmosphere. Without it fires and lights will not burn, vur food will not digest, and the blood

ence

remains unpurified, as is shown by the pale faces and purple lips of people living in close warm rooms. These are the forerunners of certain death to persons deprived of the life-sustaining oxygen.

Atmospheric air consists of a mixture of several gases, for though it is commonly said to be formed of oxygen and nitrogen in proportion of 21 volumes of the former to 79 of the latter, in each 100, yet several other gases are mixed with these. The composition of air varies with its situation. Thus, inland air is not of precisely the same composition as that near the sea coast, where there is said to be a greater proportion of ozone. On rocky mountains there is more carbonic acid than is found in the valleys.

The quantity of air required by a man varies with the state of his body. Thus a man at hard work or violent exercise may require even five times as much air as the same man when asleep.

This amount of air has been variously estimated, but I think we may safely take the following calculation by Box to be cor

rect. He states that an ordinary man takes 20 respirations per minute, of the capacity of 40 cubic in. each, thus vitiating 28 cubic ft.

per

hour. Added to this, there is the quantity of air' saturated by the moisture evolved to be considered. A.coording to Dumas this quantity in the form of vapor equals .0836 of a pound of water per hour, which is sufficient to half saturate, for air should not be more than half saturated to be pleasant-187 cubic ft. of air at 62 deg. Fahr.

We thus see that to be in good health a man must have 215 cubic ft. of air per hour for his own use. Sick persons require very much more than this.

(D.) There is one more source of contamination of the air of our houses, which often forces itself unpleasantly upon our notice. I mean the foul gases which escape from drains and water-closets. It is not too much to say that if architect and builder always did their duty, no foul air from any drain or closet ought over to enter a house, and that the negligence of one and the ignorance, or worse, of the other, must be

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