The Home Medical Library Volume V Part 11

_Street Paving_ serves a double sanitary purpose. It prevents street refuse and sewage from penetrating the ground and contaminating the surface soil, and it acts as a barrier to the free ascension of deleterious ground air.[12]

_Tree Planting_ serves as a factor in absorbing the ground moisture and in oxidizing organic impurities.

_The Proper Construction of the House_ has for its purpose the prevention of the entrance of ground moisture and air inside the house by building the foundations and cellar in such a manner as to entirely cut off communication between the ground and the dwelling. This is accomplished by putting under the foundation a solid bed of concrete, and under the foundation walls damp-proof courses.

The following are the methods recommended by the New York City Tenement House Department for the water-proofing and damp-proofing of foundation walls and cellars:

_Water-proofing and Damp-proofing of Foundation Walls._--"There shall be built in with the foundation walls, at a level of six (6) inches below the finished floor level, a course of damp-proofing consisting of not less than two (2) ply of tarred felt (not less than fifteen (15) pounds weight per one hundred (100) square feet), and one (1) ply of burlap, laid in alternate layers, having the burlap placed between the felt, and all laid in hot, heavy coal-tar pitch, or liquid asphalt, and projecting six (6) inches inside and six (6) inches outside of the walls.

"There shall be constructed on the outside surface of the walls a water-proofing lapping on to the damp-proof course in the foundation walls and extending up to the soil level. This water-proofing shall consist of not less than two (2) ply of tarred felt (of weight specified above), laid in hot, heavy coal-tar pitch, or liquid asphalt, finished with a flow of hot pitch of the same character. This water-proofing to be well stuck to the damp course in the foundation walls. The layers of felt must break joints."

_Water-proofing and Damp-proofing of Cellar Floors._--"There shall be laid, above a suitable bed of rough concrete, a course of water-proofing consisting of not less than three (3) ply of tarred felt (not less than fifteen (15) pounds weight per one hundred (100) square feet), laid in hot, heavy coal-tar pitch, or liquid asphalt, finished with a flow of hot pitch of the same character. The felt is to be laid so that each layer laps two-thirds of its width over the layer immediately below, the contact surface being thoroughly coated with the hot pitch over its entire area before placing the upper layer. The water-proofing course must be properly lapped on and secured to the damp course in the foundation walls."

Other methods of damp-proofing foundations and cellars consist in the use of slate or sheet lead instead of tar and tarred paper. An additional means of preventing water and dampness from coming into houses has been proposed in the so-called "dry areas," which are open s.p.a.ces four to eight feet wide between the house proper and the surrounding ground, the open s.p.a.ces running as deep as the foundation, if possible. The dry areas are certainly a good preventive against dampness coming from the sides of the house.

[Ill.u.s.tration: FIG. 4.

CONCRETE FOUNDATION AND DAMP-PROOF COURSE.]

_Subsoil Drainage._--By subsoil drainage is meant the reducing of the level of the ground water by draining all subsoil water into certain water courses, either artificial or natural. Subsoil drainage is not a modern discovery, as it was used in many ancient lands, and was extensively employed in ancient Rome, the valleys and suburbs of which would have been uninhabitable but for the draining of the marshes by the so-called "_cloacae_" or drains, which lowered the ground-water level of the low parts of the city and made them fit to build upon.

The drains for the conduction of subsoil water are placed at a certain depth, with a fall toward the exit. The materials for the drain are either stone and gravel trenches, or, better, porous earthenware pipes or ordinary drain tile. The drains must not be impermeable or closed, and sewers are not to be used for drainage purposes. Sometimes open, V-shaped pipes are laid under the regular sewers, if these are at the proper depth.

By subsoil drainage it is possible to lower the level of ground water wherever it is near or at the surface, as in swamps, marsh, and other lands, and prepare lands previously uninhabitable for healthy sites.

FOOTNOTES:

[10] Humus is vegetable mold; swamp muck; peat; etc.--EDITOR.

[11] A leak in a gas main, allowing the gas to penetrate the soil, will destroy trees, shrubbery, or any other vegetation with which it comes in contact.--EDITOR.

[12] Town and village paving plans will benefit by knowledge of the recent satisfactory experience of New York City authorities in paving with wood blocks soaked in a preparation of creosote and resin. As compared with the other two general cla.s.ses of paving, granite blocks, and asphalt, these wood blocks are now considered superior.

The granite blocks are now nearly discarded in New York because of their permeability, expense, and noise, being now used for heavy traffic only.

Asphalt is noiseless and impermeable (thereby serving the "double sanitary purpose" mentioned by Dr. Price).

But the wood possesses these qualities, and has in addition the advantage of inexpensiveness, since it is more durable, not cracking at winter cold and melting under summer heat like the asphalt; and there is but slight cost for repairs, which are easily made by taking out the separate blocks.

These "creo-resinate" wood blocks, recently used on lower Broadway, Park Place, and the congested side streets, are giving admirable results.--EDITOR.

CHAPTER II

=Ventilation=

=Definition.=--The air within an uninhabited room does not differ from that without. If the room is occupied by one or more individuals, however, then the air in the room soon deteriorates, until the impurities therein reach a certain degree incompatible with health.

This is due to the fact that with each breath a certain quant.i.ty of CO2, organic impurities, and aqueous vapor is exhaled; and these products of respiration soon surcharge the air until it is rendered impure and unfit for breathing. In order to render the air pure in such a room, and make life possible, it is necessary to change the air by withdrawing the impure, and subst.i.tuting pure air from the outside.

This is _ventilation_.

_Ventilation_, therefore, is the maintenance of the air in a confined s.p.a.ce in a condition conducive to health; in other words, "ventilation is the replacing of the impure air in a confined s.p.a.ce by pure air from the outside."

=Quant.i.ty of Air Required.=--What do we regard as impure air? What is the index of impurity? How much air is required to render pure an air in a given s.p.a.ce, in a given time, for a given number of people? How often can the change be safely made, and how? These are the problems of ventilation.

An increase in the quant.i.ty of CO2 [carbon dioxide gas], and a proportionate increase of organic impurities, are the results of respiratory vitiation of the air; and it has been agreed to regard the relative quant.i.ty of CO2 as the standard of impurity, its increase serving as an index of the condition of the air. The normal quant.i.ty of CO2 in the air is 0.04 per cent, or 4 volumes in 10,000; and it has been determined that whenever the CO2 reaches 0.06 per cent, or 6 parts per 10,000, the maximum of air vitiation is reached--a point beyond which the breathing of the air becomes dangerous to health.

We therefore know that an increase of 2 volumes of CO2 in 10,000 of air const.i.tutes the maximum of admissible impurity; the difference between 0.04 per cent and 0.06 per cent. Now, a healthy average adult at rest exhales in one hour 0.6 cubic foot of CO2. Having determined these two factors--the amount of CO2 exhaled in one hour and the maximum of admissible impurity--we can find by dividing 0.6 by 0.0002 (or 0.02 per cent) the number of cubic feet of air needed for one hour,==3,000.

Therefore, a room with a s.p.a.ce of 3,000 cubic feet, occupied by one average adult at rest, will not reach its maximum of impurity (that is, the air in such a room will not be in need of a change) before one hour has elapsed.

The relative quant.i.ty of fresh air needed will differ for adults at work and at rest, for children, women, etc.; it will also differ according to the illuminant employed, whether oil, candle, gas, etc.--an ordinary 3-foot gas-burner requiring 1,800 cubic feet of air in one hour.

It is not necessary, however, to have 3,000 cubic feet of s.p.a.ce for each individual in a room, for the air in the latter can safely be changed at least three times within one hour, thus reducing the air s.p.a.ce needed to about 1,000 cubic feet. This change of air or ventilation of a room can be accomplished by mechanical means oftener than three times in an hour, but a natural change of more than three times in an hour will ordinarily create too strong a current of air, and may cause draughts and chills dangerous to health.

In determining the cubic s.p.a.ce needed, the height of the room as well as the floor s.p.a.ce must be taken into consideration. As a rule the height of a room ought to be in proportion to the floor s.p.a.ce, and in ordinary rooms should not exceed fourteen feet, as a height beyond that is of very little advantage.[13]

=Forces of Ventilation.=--We now come to the question of the various modes by which change in the air of a room is possible. Ventilation is natural or artificial according to whether artificial or mechanical devices are or are not used. Natural ventilation is only possible because our buildings and houses, their material and construction, are such that numerous apertures and crevices are left for air to come in; for it is evident that if a room were hermetically air-tight, no natural ventilation would be possible.

The properties of air which render both natural and artificial ventilation possible are diffusion, motion, and gravity. These three forces are the natural agents of ventilation.

There is a constant diffusion of gases taking place in the air; this diffusion takes place even through stone and through brick walls. The more porous the material of which the building is constructed, the more readily does diffusion take place. Dampness, plastering, painting, and papering of walls diminish diffusion, however.

The second force in ventilation is the motion of air or winds. This is the most powerful agent of ventilation, for even a slight, imperceptible wind, traveling about two miles an hour, is capable, when the windows and doors of a room are open, of changing the air of a room 528 times in one hour. Air pa.s.ses also through brick and stone walls. The objections to winds as a sole mode of ventilation are their inconstancy and irregularity. When the wind is very slight its ventilating influence is very small; on the other hand, when the wind is strong it cannot be utilized as a means of ventilation on account of the air currents being too strong and capable of exerting deleterious effects on health.

The third, the most constant and reliable, and, in fact, princ.i.p.al agent of ventilation is the specific gravity of the air, and the variations in the gravity and consequent pressure which are results of the variations in temperature, humidity, etc. Whenever air is warmer in one place than in another, the warmer air being lighter and the colder air outside being heavier, the latter exerts pressure upon the air in the room, causing the lighter air in the room to escape and be displaced by the heavier air from the outside, thus changing the air in the room. This mode of ventilation is always constant and at work, as the very presence of living beings in the room warms the air therein, thus causing a difference from the outside air and effecting change of air from the outside to the inside of the room.

=Methods of Ventilation.=--The application of these principles of ventilation is said to be accomplished in a natural or an artificial way, according as mechanical means to utilize the forces and properties of air are used or not. But in reality natural ventilation can hardly be said to exist, since dwellings are so constructed as to guard against exposure and changes of temperature, and are usually equipped with numerous appliances for promoting change of air.

Windows, doors, fireplaces, chimneys, shafts, courts, etc., are all artificial methods of securing ventilation, although we usually regard them as means of natural ventilation.

=Natural Ventilation.=--The means employed for applying the properties of diffusion are the materials of construction. A porous material being favorable for diffusion, some such material is placed in several places within the wall, thus favoring change of air. Imperfect carpenter work is also a help, as the cracks and openings left are favorable for the escape and entrance of air.

Wind, or the motion of air, is utilized either directly, through windows, doors, and other openings; or indirectly, by producing a partial vacuum in pa.s.sing over chimneys and shafts, causing suction of the air in them, and the consequent withdrawal of the air from the rooms.

The opening of windows and doors is possible only in warm weather; and as ventilation becomes a problem only in temperate and cold weather, the opening of windows and doors cannot very well be utilized without causing colds, etc. Various methods have therefore been proposed for using windows for the purposes of ventilation without producing forcible currents of air.

The part of the window best fitted for the introduction of air is the s.p.a.ce between the two sashes, where they meet. The ingress of air is made possible whenever the lower sash is raised or the upper one is lowered. In order to prevent cold air from without entering through the openings thus made, it has been proposed by Hinkes Bird to fit a block of wood in the lower opening; or else, as in Dr. Keen's arrangement, a piece of paper or cloth is used to cover the s.p.a.ce left by the lifting or lowering of either or both sashes. Louvers or inclined panes or parts of these may also be used. Parts or entire window panes are sometimes wholly removed and replaced by tubes or perforated pieces of zinc, so that air may come in through the apertures. Again, apertures for inlets and outlets may be made directly in the walls of the rooms. These openings are filled in with porous bricks or with specially made bricks (like Ellison's conical bricks), or boxes provided with several openings. A very useful apparatus of this kind is the so-called Sheringham valve, which consists of an iron box fitted into the wall, the front of the box facing the room having an iron valve hinged along its lower edge, and so constructed that it can be opened or be closed at will to let a current of air pa.s.s upward. Another very good apparatus of this kind is the Tobin ventilator, consisting of horizontal tubes let through the walls, the outer ends open to the air, but the inner ends projecting into the room, where they are joined by vertical tubes carried up five feet or more from the floor, thus allowing the outside air to enter upwardly into the room. This plan is also adapted for filtering and cleaning the incoming air by placing cloth or other material across the lumen of the horizontal tubes to intercept dust, etc. McKinnell's ventilator is also a useful method of ventilation, especially of underground rooms.

[Ill.u.s.tration: FIG. 5.

HINKES BIRD WINDOW. (TAYLOR.)]

[Ill.u.s.tration: FIG. 6.

ELLISON'S AIR INLETS. (KNIGHT.)]

[Ill.u.s.tration: FIG. 7.