given in an able treaties on this subject by Dr. John S. Billings, and printed in the Sanitary Engineer, October 18, and November 1, 1880. This would give the general public a more thorough knowledge of the subject than a hundred pages of explanatory notes.

There is one feature of house building which appears to be governed by no system or rule, and that is the mode of constructing chimneys.

Investigation of chimneys in a score of houses closely contiguous will show scarcely two alike, of the same dimensions. They appear to be constructed according to the caprice or fancy of the builder. Probably not one chimney builder in fifty or one hundred can give any methodical or scientific reason for his method of putting up a chimney. It is no marvel then that we have smoking chimneys and chimneys that draw the wrong way. The tendency is to make them too small, doubtless, from the increased use of stoves. Chimneys may be too large as well as too small. If too large the probabilities are there will not be heated air enough provided for it, and down drafts will be the result.

Upon this subject I quote from Dr. Billings:

"The shape of a flue should be as nearly round or square as the size of the walls and joints will admit. The circle is the best form because it gives the greatest area in proportion to the perimeter, or surface producing friction, and the square is next. If a flue is rectangular, (as most chimneys are) with one diameter not more than four inches (the width of one brick) the friction will be great, and if such a flue be so placed that one of its long sides is parallel to a surface of the wall which is exposed to cold air there will be a great loss of heat. For flues to carry the product of combustion, without reference to ventilation of ordinary dwellings, for each room if built in the usual way should be about one foot square, or for common bedrooms 9x12 inches. If lined with smooth pipes or cement they may be nine inches in diameter."

Fredgold's rule for chimneys for steam boilers is a follows: "The arc of a chimney in inches for a low pressure steam engine, when above ten horse power should be 112 times the horse power of the engine divided by the square root of the height of the chimney in feet."

Milne's rule is: The square root of the height of the chimney multiplied by the square of its internal diameter at the top or narrowest part in feet is equal to twice the nominal horse power for the chimney. By horse power herein is meant that a cubic foot of water at 60° evaporated to steam is equal to one nominal horse power.

The judges at the Centennial defined a horse power to be equal to the evaporation of thirty pounds of water from a temperature of 212°.

As a cubic foot of water weighs a little over sixty-pounds, this standard requires less than half the fuel needed for the former, taking the older estimates used by Fredgold allowing eight pounds of coal per hour per horse power, and three hundred cubic feet of air for the combustion of each pound of coal, and we have for a forty horse power boiler about thirty cubic feet of gases per second to dispose of. Allowing five feet per second in the flue, a flue having an area of six square feet would be necessary. Another rule is for the ordinary horizontal flue boilers, that the chimney should be from sixty to eighty feet high, and have an area equal to half the square of the diameter of one of the tubes multiplied by the number of

tubes. In such a boiler, fifteen feet of boiler surface is reckoned as one horse power.

To remedy smoking chimneys, see that each has its own sufficient supply of air from without, and that one does not draw against another flue.

To illustrate, in one of the large public buildings in Washington were several rooms freely communicating with each other, and each having an open grate. On building the fire in No. 1, the draft was excellent; in No. 2, not so good; in No. 3, bad, while in No. 4 the draft was was all down the chimney. The chimney doctor put in an appearance with his patent backaction flue persuader, and applied one to the flue of No. 4, thus raising it three feet, and it worked well, but No. 3. smoked like a tar kiln. That was also doctored when Nos. 1 and 2 smoked; these were also fitted with a persuader, thus making all the flues of equal height and the result was they became as at the start, and the process of doctoring had to be done over.

VENTILATION OF CELLARS.

It is frequently desirable to ventilate cellars to remove heat or moisture. John P. Hawkins, Commissary of Subsistence of the U. S. Army, gives the following plan :

"When the outer air is warmer than the air of the cellar and it is desired to remove moisture or impure air, advantage should be taken of dry wind from a favorable direction. As about three to four o'clock in the morning it is generally the coldest this would be the most favorable time in warm seasons. Though simple openings at the top, opposite each other, might be sufficient for ventilation they will not arrest light. Tubes are therefore necessary. The inlet tubes should extend to the bottom of the cellar, with a close fitting cap at that end, for opening or closing. The upper end should extend horizontally with a hopper-shaped mouth, which can be turned so as to catch the wind from different directions. The outlet tubes should be placed at the top of the cellar wall and not extend beyond the inner face. The outer end should extend upward and be provided with caps also. Both tubes may be fitted with cowls and vanes so as to turn the wind. All other openings to the cellar should be closed. The number of tubes necessary will depend on the size of the cellar, but they should not be less than ten inches in diameter each. Galvanized sheet iron is a good material for tubes, or they could be made of boards cemented with paint lead. If an outlet tube were carried up through the roof it would be better. A chimney flue from the cellar to the roof is a good outlet. The cooler the inlet current of air the more rapid the removal of moisture. To illustrate: If the outer air at a temperature of zero, and raised therein to 60°, be admitted to a cellar, it would absorb and carry off about five Troy grains of moisture per cubic foot; if raised to 100° it would absorb and carry off nineteen grains per cubic foot."

VENTILATION OF PRIVIES.

I do not know that I can add anything to the excellent method recommended by our civil engineer, Mr. Loring, for the ventilation of privies, as

they are to be found generally in the State. On general principles I would say they should be located as far from dwellings, or habited buildings, as possible, and under no circumstances should they be placed within six feet of any dwelling or school building. The practice of placing privy vaults within the walls of a dwelling should be abolished. If, however, a vault must be placed contiguous to a dwelling it should be outside the walls of the dwelling, and from the vault to the roof it should be entirely separate. Ventilating flues should be placed from the vault to the highest point of the dwelling of an area of not less than thirty-six square inches, and increased with the size of the vault. Its lower end should open into the vault at the highest point at which the gases will have access to it. The flue should be made of galvanized iron or other metal, as the heat of the sun acting on it will create an upward draft inside the flue It should be provided with a cap to prevent down drafts. The building over the vault should be provi ded with ventilation by lattice blinds. Every seat should have a cover, which could be kept closed.

School privies should be not less than fifteen feet distant from the building. The farther off the better. They may be connected with the building by a covered passage-way. It is usual to construct school privies double, with the seats back to back. The partition at the back should also be double and reach to the roof, with a proper space between to serve as a ventilator.

Outlets may be made in the roof, into flues extending upward, sufficiently high to carry the gases above the roof of the school building.

Each apartment should be ventilated by lattice blinds. The building should not be less than ten feet high to the cornice, and the flues should reach the height of the school building.

VENTILATION OF SEWERS.

The admission of gas from the sewer into a habited dwelling is to saturate the same with poisoned air. To quote from Sir Edward Philbrick : "The risks we incur by breathing sewer gas are too serious to be laughed at or whistled over. Common sense should teach us that an ounce of prevention is worth a pound of cure."

Following this idea, Charles F. Wingate, before a conference of the State Board of Health of New York, said: "The proper method to secure a free atmospheric current through house drains is by supplying foot ventilation close to the trap on the main drain."

This method is also indorsed by Hellyer in his work, "The Plumber and Sanitary Houses," in which he says: "The advantages of this second air pipe, or foot ventilation, are greater than will be conceded, except by those who have proved its value. A practical test of eight years upon soil pipes and slop sink waste pipes has resulted in every case with the utmost satisfaction. This air pipe at the foot of the soil pipe is extremely valuable, for by this means a constant change of air is taking place throughout the entire length of a pipe to render it wholesome and prevent any air becoming stagnant in any part of the pipe; for when the soil pipe is not in use, this second air pipe at its foot acts as an air inlet."

A

Fig. 8.

This plan is well illustrated by Fig. 8, for the use of which I am indebted to the courtesy of the Durham House Drainage Company, of New York, which also illustrates a most admirable and safe system of house drainage. The heavy or dark lines show a system of wrought iron pipes, with steam and gas-tight joints, precluding any escape of sewer air into the dwelling. There is an apparent error in the plan, evidently that of the plumber. The pipe A., from the bowl of the closet, should either go into a heated flue or be carried through the roof, independently, with a constantly burning gas jet inside of it, to insure draft up the pipe.

The following requirements for house drains have been adopted by the best authorities of this country, and in several of the large cities:

"Every house drain should have an inlet for fresh air, entering at a point inside the main trap and carried to a convenient location out of doors, not too near windows.

"A trap should be placed upon every main drain to disconnect the house from the sewer or cesspool.

"In places liable to unusual pressure from the sewer it should be a double trap, with vent between the two traps running up full size above the roof; or, where the pressure from the sewer is only occasional, and the rigor of

the climate will permit, the vent may be carried to the sidewalk or area at a safe distance from the windows.

"If the first trap is forced the gas can gain easier exit through this pipe than through the second trap.

"Every vertical soil, or waste pipe, should be extended at least full size through the roof. No trap should be placed at the foot of vertical soil pipes to impede circulation.

"Traps should be placed under all sinks, basins, baths, wash-trays, water-closets, etc., and as near to these fixtures as possible.

"All traps under fixtures, wherever practical, should be separately ventilated to guard against siphonage. Such pipes should not be inserted into a soil pipe below where any drainage enters it. In some cases it is preferable to carry it to outer air independently. Rain-water leaders should not be used as soil pipes, and when connected with house drains the joints should be made gas and water tight to prevent drain air entering the windows. No safe waste should connect with any drain, but it should be carried independently down to a point where its discharge would indicate the existence of a leak or overflow above.

"No waste from a refrigerator should connect with a drain."

The essential points of sewer ventilation are summed up by Mr. Latham in his book on Sanitary Engineering, as follows:

1. That the system should be simple in operation, not liable to get out of order, and independent of uncertain mechanic contrivances.

2. That it should admit of expulsion of all sewer air, and the supply of fresh air at all periods.

3. That the escaping gases shall be so diluted with atmospheric air as to be rendered harmless, or that they shall be "destroyed or arrested.”

4. That the system shall not impede natural ventilation.

5. That it shall not be costly in execution or maintenance.

VENTILATION OF SCHOOL-HOUSES.

It has been variously estimated by different authorities that in early childhood from one-fifth to one-fourth of all the blood in the body is directed to the brain. The whole mass of blood traverses the entire body about once a minute.

The wonderful activity of the circulation may be better appreciated by estimates proportioned to greater lengths of time. It will appear, then, that the heart contracts more than four thousand times an hour, and that as each contraction sends forward four and two-fifths ounces of blood, over one thousand pounds of this fluid pass through the heart every hour.

When the blood has completed one tour of the system it necessarily passes through the lungs before beginning another. This route is intimately connected with the purification of the blood. It is by this means the blood absorbs oxygen from the air, and parts with carbonic acid and other noxious elements.

Oxygen is the agent of nutrition to all the tissues; it is the great inciter of all vital changes, and its presence is indispensable to life and growth. If the blood passing through the lungs does not there obtain a supply of oxygen it takes back to the brain and other tissues carbonic acid instead,