proper state of repair and cleanliness. The apportioning of accommodation to the means of the inmates is an important social problem which is slowly being solved on economic principles, but which is quite outside the scope of the present work. We cannot altogether avoid moral and social considerations in estimating the proper amount of house accommodation. From a purely sanitary point of view, there is no reason why adult males and females might not sleep in the same apartments; but it is manifest that, as sanitary and moral conditions are closely connected, it is impossible to meet sanitary requirements without at the same time. providing the necessary safeguards for morality.

1

Each family should have at least two rooms-a bed-room and living-room; the latter must be used as a kitchen when the tenement consists of but two rooms. It is impossible for healthy conditions to exist in a single room used for all purposes of eating, drinking, sleeping, and cooking. Two rooms will, however, only afford accommodation at the outside for a married couple with one or two small children. When children grow up, it is absolutely necessary, to secure decency and morality, that the sexes should be separated. Thus, if there are adult children of but one sex, two bedrooms will become necessary-one for the parents and small children, the other for the adult children. If there are adult children of both sexes, then three bed-rooms are necessary, and the tenement must be increased to a total of four rooms. The sleeping and living accommodation per room must be commensurate with the number of inhabitants, as will be pointed out in the remarks on ventilation we shall make.

WATER-CLOSETS- -HOUSE DRAINS.

Water-closets should be placed in a return building, or built out from the house, and ought to be thoroughly ventilated by windows, etc., and capable of being shut off completely from the house. The soil-pipe running from the

R

pan should be fully four inches in diameter, and the water supply abundant. One gallon of water is a reasonable quantity with which to flush the pan once. The soil-pipe must be well trapped-preferably with S traps, rather than with the old D form-and then should run directly into the drain. It has been well said, that there are a few simple sanitary rules that can never be transgressed without the infliction of evil, and these rules are:-Whatever pattern of drain pipes be chosen, they should be securely and tightly laid, and in such a manner as to facilitate the removal of waste with all possible speed to a sewer or cesspool. The drain-pipes should run outside, and not through the house, if possible. Well-fitted drain-pipes should be alone used when it is absolutely necessary for the sewage to pass through the house, and then the best form of drainpipe is made with the "Jennings," which admits of opening at intervals for the removal of obstructions and thorough cleansing, without disturbing the drain generally. This is accomplished by having a length in every ten or twelve feet, made of two semi-cylinders, flanged, so as to lie close, and make a good jointed tube with cement; but yet capable of separation, so that the upper half-cylinder may be removed temporarily, to permit the cleansing of the drain.

Over much trapping of drains should be avoided, but a syphon trap before the drain delivers into the main sewer is usually advisable, in order to check the return of sewer gas.

The possible entrance of the foul air of sewers into a house must be carefully guarded against, and especially when, as in autumn and winter, doors and windows are closed, and fires are burning. Sewer gas may enter a house in any of the following ways:

"1. It may find admission through the trap of the water-closet when no ventilation has been provided for the soil-pipe of the closet itself. 2. It may enter through defective joints or fissures in the soil-pipe, such defects being the result of bad workmanship, of accident, or decay.

3. Through any pipe that is in direct communication with the sewer, which is for the purpose of conveying away waste of any kind, such as housemaid's sinks, butler's pantry sinks, ordinary kitchen sinks, all baths which communicate directly with the sewer. 4. Through any pipe which is used as an overflow from wash-basins, baths, cisterns, etc. 5. Through the catch-water tray which is placed beneath the usual pan in all expensive water-closets. 6. Through rainwaterpipes communicating directly with the sewer, when they open in enclosed positions or near to open windows. 7. Catchwater drains, which generally exist in cellars and areas under cover, and which are supposed to be trapped by a bell-trap."

All waste water-pipes which deliver into the soil-pipe should be trapped, defective workmanship remedied, and, above all, the soil-pipe ventilated. A good mode of sewer ventilating is to solder to the soil-pipe from the water-closet a leaden tube, about an inch or an inch and a-half in diameter, which is then carried outside the house, and connected with an iron gas-pipe of rather greater diameter, which is carefully jointed, and carried at least two or three feet beyond the eaves of the house. The connexion of the leaden ventilating tube with the soil-pipe should be made in the upper part of the syphon, and just beyond (i.e., on the sewer side of) the closet-trap. If two closets are placed one over the other, and delivering into the same soil-pipe, ventilation of the kind we have just mentioned is absolutely necessary, else the flow from the upper closet will untrap the lower one, and permit the free escape of sewer gas into the house. If a bath be placed at the top of a house, a sudden rush of waste water from it, and down the soil-pipe, will also probably have the effect of untrapping the closets delivering into the same tube, unless they are ventilated.

It is scarcely necessary to point out that when there are no water-closets, and privies alone are used, the latter should be placed as far from the house and from any pump-well as possible, and should be cleaned out frequently.

244

CHAPTER XXI.

AIR AND VENTILATION.

ATMOSPHERIC AIR.-Constituents-a Mechanical Mixture-Reciprocal Action of Animals and Plants upon it-Percentage Composition— Impurities. Ozone. Sulphuretted Hydrogen, etc. Proportion of Carbonic Acid-its Estimation-Pettenkofer's Process-Dr. Angus Smith's Simple Plan. Cubic Air Space required per Head-Principles of Ventilation-Dr. de Chaumont's Conclusions-Effect of Illuminating Materials-Hints on Ventilation.

As an introduction to the subject of ventilation, we may here most conveniently offer a few remarks on atmospheric air. The atmosphere we breathe in large open spaces is liable to singularly little change in the proportions of its chief constituents-oxygen, nitrogen, and carbon dioxide, or carbonic acid. This remarkable regularity in composition of a merely mechanical mixture of gases is due chiefly to the reciprocal action of animals and plants upon it, to the operation of the law of diffusion of gases, and to the influence of air currents. Animals inhale nitrogen and oxygen, but expire nitrogen, carbon dioxide, a little residual oxygen, and aqueous vapour. Plants, on the other hand, inspire carbon dioxide, and, under the influence of sun-light, separate the carbon from it and exhale the oxygen in the gaseous form. Other influences are at work to charge the air with carbonic acid; for example, processes of combustion of heat-producing and of illuminating materials, and the eremacausis or slow decay of organic matters of various kinds; but the effect of vegetation is yet amply sufficient to prevent the gradual accumulation of impurity in the atmosphere.

Air is never absolutely free from carbonic acid in nature, and usually contains about 04 per cent.; but, when artificially purified from this and other bodies presently to be noticed, the gaseous residue has the following mean composition by weight and by volume :

:

As the result of numerous analyses of air collected at various points upon the earth, it may be stated that the variations in the proportions of oxygen are within th per cent. by volume, except in tropical countries, where, owing to some hitherto undetermined cause, the oxygen may suddenly drop to 20.3 per cent. The impurities met with in atmospheric air are the floating solid particles—so beautifully seen in Tyndall's tube, or when a beam of sunlight passes through the air—and the gaseous or vaporous bodies: carbonic acid, ammonia, aqueous vapour, and, occasionally, carbonic oxide, marsh gas and other hydrocarbons, sulphur dioxide, or "sulphurous acid," sulphuretted hydrogen, oxides of nitrogen, chlorine, ozone, and "organic emanations" from the lungs and skins of men and animals.

Ozone-so named on account of its peculiar smell—is a very active modification of oxygen, and is produced whenever an electric discharge takes place through air. The most important facts in the chemical history of this curious body, and, indeed, the positive proof of its identity, have been made known to us by the researches of a most distinguished Irish chemist, Dr. Andrews, of Belfast, though it was essentially discovered by Schönbein, in 1840. We possess a very delicate test for this ozone in paper saturated with a mixture of iodide of potassium and starch. When paper so prepared is acted on by ozone, iodine is liberated and its separation evidenced by the strong brown or blue colour developed. It has been long known that when this prepared paper is exposed to pure country air it is quickly discoloured, but it remained for Dr. Andrews to prove that this effect is really due to ozone. Now, it is found that this atmospheric ozone is rarely present in the