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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 correct. He states that an ordinary man takes 20 respirations per minute, of the capacity of 40 cubic inches each, thus vitiating 28 cubic feet per hour. Added to this there is the quantity of air saturated by the moisture evolved to be considered. According to Dumas this quantity in the form of vapour 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 feet of air at 62° F.

We thus see that to be in good health a man must have 215 cubic feet 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

from drains and waterclosets. 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 ever to enter a house, and that the negligence of one and the ignorance, or worse, of the other, must be charged with a greater destruction of human life and with causing more disease every year than has been produced by the bloodiest battle recorded in history.

It is impossible to estimate correctly the air contaminated from this source, but I hope to shew how such contamination may be avoided.

A a summary of results we see, that in a room of the net cubic capacity of 3,800 feet, having a fire burning, inhabited, by say six persons, and lighted by three gas lights, there will be req ired every hour, so that the inmates may be healthy, 1,694, or say 1,700 cubic feet of fresh air at 60° F.

But air expands ago, or 0.00204, of its volume for every degree F it is heated, it is obvious from this, that assuming the temperature of the outer air to be 32° F, we shall not require to admit so much cold air into the room by about 100 cubic feet, but exit must be provided for the full quantity.

Professor Tyndall gives the following table of expansion of gases for an increase of temperature equal to 1° F:Hydrogen

0.00203 Carbonic Acid... 0.00206 Air

0.00204 Protoxide of Nitrogen 0:00207 Carbonic Oxide 0.00204 Sulphurous Acid 0.00217

...

...

...

...

...

con

We see from this that gases obey the almost universal law, and expand with increased heat. Upon this fact is built the whole system of thermo-ventilation, and upon its due appreciation depends success in this particular branch; for it follows that as gases expand so are their densities decreased, and they are lifted upwards by the heavier air without; rising, not because they are light, but because the outer air is colder and consequently heavier.

The following is a table of specific gravities of gases taken from the experiments and researches of Regnault and others. Atmospheric air being 1 : Air ... 1.00000 Carbonic Oxide

0.9727 Hydrogen Gas

0.06926 Protoxide of Nitrogen 1:5252 Oxygen Gas ... 1.10563 Sulphurous Acid

2.2464 1•11100 Sulphuretted Hydrogen 1:1710 Nitrogen Gas

0.97137 Vapour of Water ... 0.6235 Carbonic Acid

1.52901 This table shews us how varied are the densities of different gases. Thus, while hydrogen is more than 14 times lighter than air, sulphurous acid is about 24 times heavier.

There is another property of gases which merits our sideration besides that of density, and this is the power they have of mixing with one another.

The gases which compose common air for instance, are not chemically combined to form any new substance; they exist each one of them just as if the others were not present. When we consider this, and the fact that they are of different densities, it would fill us with astonishment that they do not settle, as it were, away from one another, the heavier oxygen falling to the ground, and the lighter nitrogen ascending to the clouds, did we not know of this law of combination, which is called the law of diffusion of gases. Professor Graham expresses this law by saying that the diffusive power varies inversely as the square root of the density of the gas itself.

A simple but beautiful experiment of the Professor's illustrates the law.

I have stated that in the room before mentioned we require at certain times, and all works should be calculated for the greatest possible duty they may have to perform, space for 1,600 cubic feet of fresh air to enter, and for 1,700 feet to leave, the room every hour.

I am aware that any proposal to admit cold air into a room will meet with opposition, and were houses built uponprinciples worthy of our civilization it might easily be avoided. I think, however that, with proper means, the possible evil may be so reduced as to be practically unfelt. I am also now treating of existing houses which could not well be rebuilt or altered.

I would propose that in such houses where the want of ventilation is felt the openings for admission of fresh air should be made as near the floor of each room as possible. For it will be seen from what has gone before, that the cold air will, on entering, be heavier than that in the room, which it will gradually force upwards and out through the foul air exit channels.

Many people will probably say, “Oh what a draught there would be to one's legs and feet.” Doubtless if a good sized hole be cut through the wall, say directly opposite the fireplace, and you shut the door and stand between the opening and the fire, very likely you would feel rather cool about the inferior extremities. But I do not propose a thing of this kind.

The fire must have its own separate supply which should be given by means of a pipe leading through the hearth stone, as is sometimes done now, with the opening facing the fire, which latter, as it constantly acts the part of a pump, will take care to get its own allowance from the nearest source.

We have therefore only the forcing power of the difference in weight, between columns of air, of equal height, but of the different densities due to difference of temperature between the external air and that in the room. This difference I have assumed to be 30°.

This forcing power will cause the air to enter the room with a velocity equal to that which would be acquired by a body falling a distance equal to the difference in height between a column of air 10'6" high at 62°, in the case I have assumed, and the same air at 32".

This difference will be equal to :643 of a foot, and the speed of the entering current will, by the rule for falling bodies, be 6.43 feet per second.

Assuming that all the air enters through one opening, then about 8 square inches would be sufficient. It will be obvious, however, that it is not advisable to admit air at so high a velocity as this, nor would one inlet be so efficient as several.

I would propose then, for existing rooms, that the inlets should be made in the side walls, near floor, and in as many different sides of the room as its situation will allow. That these be made larger towards the room, and that they should be enclosed by metal gratings made ornamental on the outer and inner faces. The sketch marked A will show generally what I mean.

There is one point to which I would call your particular attention, and this is the fine wire gauze screen shewn just behind the ornamental front. This serves a very

useful

purpose, for it screens and breaks up the entering current of air, preventing all drafts, and, if the openings have sufficient area,

allowing the incoming air to mingle so gently with that now in the room, that its presence is not felt save in a pleasant way.

I attach great importance to this screen, and to the size of the openings.

We must now proceed to consider the best position for the exit.

I think a little consideration will shew us that the heated chimney affords the best possible means under the circumstances. By causing the foul air to escape into the chimney we increase the ventilating power very considerably. We have no longer to deal with the small difference before mentioned, but may calculate upon the whole height of the chimney, above the opening, through which the foul air enters it, and have the difference between this column of air highly heated as it is, and that of another of the density of the outer air as the force at our disposal.

Care must be exercised in the choice of a valve to close this opening against down draft. The best which has come under my notice is formed of a series of leaves or flaps of mica enclosed in a metal case. The flaps are very light, and, being hung from the top, are absolutely secure against return currents. The front may be made as ornamental as can be desired.

The heated and spent air from the gas light should be conveyed away immediately when possible.

The ornamental flower which is commonly placed in the centre of the room may be pierced through. The opening thus formed being boxed in between the joists with thin sheet metal connected with a tube for conveying the waste gases into the chimney or outer air.

The register of the fire grate will form a regulator, by closing or opening which the draught through the escape valve may be increased or diminished.

Exercise of proper skill and judgment in the form and placing of the inlets, and in the construction of the exit, will insure comfortable ventilation in rooms built with no special provision for it.

The tube which supplies the fire should have a valve to close it, so that when necessary the whole pumping power of the fire may be applied to sucking in fresh air through the room.

I will now refer to the last source of contamination mentioned above, viz., foul drains and water-closets.

Any unpleasantness from the former will commonly arise from faulty design, or malconstruction. A drain is ill designed which passes under any portion of the house, unless no other way is possible. Also where-no provision is made for ventilating, and where it is not of ample size.

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