Fig. 35.Fig. 35.THE FIELD MUSHROOM.(Agaricus Campestris.)An edible variety; very common.
THE FIELD MUSHROOM.
(Agaricus Campestris.)
An edible variety; very common.
2. Horse Mushroom(Agaricus Arvensis).—This species may be considered with the foregoing, but it differs in being considerably larger (measuring four to ten inches across) and in having a more shiny cap, of a white or brown hue. The ring about the stem is noticeably wider and thicker, and is composed of two distinct layers. The gills are white at first, turning darkbrown comparatively late, and the stem is a little hollow as it matures. In some localities it is more common than thecampestrisin fields and pastures, while in other places it is found only in rich gardens, about hot beds, or in cold frames. It is not distinguished from thecampestrisby market people, but is often sold with the latter.
Fig. 36.Fig. 36.THE HORSE MUSHROOM.(Agaricus Arvensis.)This variety is edible.
THE HORSE MUSHROOM.
(Agaricus Arvensis.)
This variety is edible.
3. Shaggy Mane, Ink Cap, or Horsetail Fungus(Coprinus Comatus).—This mushroom possesses the most marked characteristics of any of the edible species; it would seem impossible to mistake its identity from written descriptions and illustrations. It is considered by many superior in flavor to thecampestris.
The top or cap does not expand in this mushroom, until it begins to turn black, but remains folded down about the stem like a closed umbrella. Mature specimens are usually three to five, occasionally from eight to ten, inches high. The stem is hollow. The inside of the cap or gills and the stem are snow white. The outer surface of the cap, which is white in young plants, becomes of a faint, yellow-brown or tawny color in mature specimens, and also darker at the top. Delicate scales often rolled up at their lower ends are seen on the exterior of the cap, more readily in mature mushrooms, hence the name "shaggy mane." There is a ring around the stem at the lower margin of the cap, and it is so loosely attached to either the cap or stem that it sometimes drops down to the base of the latter.
The most salient feature of shaggy mane is the change which occurs when it is about a day old; it turns black and dissolves away into an inky fluid, whence the other common name "ink cap." The mushroom should not be eaten when in this condition. The ink cap is usually found growing in autumn, rarely in summer, in richer earth than the common mushroom. One finds it in heaps of street scrapings, by roadsides, in rich lawns, in soils filled with decomposing wood and in low, shaded, moist grounds.
Fig. 37.Fig. 37.THE HORSE-TAIL FUNGUS.(Coprinus Comatus.)Edible; cut shows entire plant and section.
THE HORSE-TAIL FUNGUS.
(Coprinus Comatus.)
Edible; cut shows entire plant and section.
4. Fairy-ring Mushroom(Marasmius Oreades).—This species usually grows on lawns, in clusters which form an imperfect circle or crescent. The ring increases in size each year as new fungi grow on the outside, while old ones toward the center of the circle perish. This mushroom is small and slender, and rarely exceeds two inches in breadth. The cap and the tough and tubular stem are buff, and the gills, few in number and bulging out in the middle, are of a lighter shade of the same color. There is no ring about the stem. Several crops of the fairy-ring mushroom are produced all through the season, but the most prolific growth appears after the late fall rains. There are other fungi forming rings, some of which are poisonous, and they may not be easily distinguished from the edible species; hence great care is essential in gathering them. The under surface of the cap is brown or blackish in the mature plants of poisonous species.
Fig. 38.Fig. 38.THE FAIRY-RING MUSHROOM.(Marasmius Oreades.)An edible variety.
THE FAIRY-RING MUSHROOM.
(Marasmius Oreades.)
An edible variety.
5. Edible Puffball(Lycoperdon Cyathiforme).—Ediblepuffballs grow in open pastures, and on lawns and grassplots, often forming rings. They are spherical in form, generally from one and a half to two inches, occasionally six inches, in diameter, broad and somewhat flattened at the top, and tapering at the base, white or brown outside. They often present an irregularly checkered appearance, owing to the fact that the white interior shows between the dark raised parts. Theinterior is at first pure white and of solid consistency, but later becomes softer and yellowish, and then contains an amber-colored juice. After the puffball has matured, the contents change into a brown, dustlike mass, and the top falls off; and it is then inedible. All varieties of puffball with a pure white interior are harmless, if eaten before becoming crumbly and powdery. There is only one species thought to be poisonous, and that has a yellow-brown exterior, while the interior is purple-black, marbled with white.
Fig. 39.Fig. 39.THE EDIBLE PUFFBALL.(Lycoperdon Cyathiforme.)Upper illustration shows entire plant; lower, a section.
THE EDIBLE PUFFBALL.
(Lycoperdon Cyathiforme.)
Upper illustration shows entire plant; lower, a section.
To escape eating poisonous mushrooms do not gather the buttons, and be suspicious of those growing in woods and shady spots that show any bright hue, or have a scaly or dotted cap, or white gills.[9]By so doing the following species will be avoided.
Fly Amanita(Amanita Muscaria).—Infusions of this mushroom made by boiling in water are used to kill flies. This species grows in woods and shady places, by roadsides, and along the borders of fields, and is much commoner than thecampestrisin some localities. It prefers a poor, gravelly soil, and is found in summer.
The stem is hollow and its gills are white. Thecap is variously colored, white, orange, yellow, or even brilliant red, and dotted over with corklike particles or warty scales which are easily rubbed off. There is a large, drooping collar about the upper part of the hollow, white stem, and the latter is scaly below with a bulbous enlargement at its base.
The young mushrooms, or buttons, do not exhibit the dotted cap, and the bulbous scaly base may be left in the ground when the mushroom is picked. Thefly amanitais usually larger than the common mushroom.
Fig. 40.Fig. 40.A POISONOUS FUNGUS.(Amanita Muscaria.)The Fly Agaric.
A POISONOUS FUNGUS.
(Amanita Muscaria.)
The Fly Agaric.
Death Cup or Deadly Agaric(Amanita Phalloides).—This species is more fatal in its effects than the preceding. Its salient feature is a bulbous base surmounted and surrounded by a collar or cup out of which the stem grows. This is often buried beneath the ground, however, so that it may escape notice. The gills and stem are white like the preceding, but the cap is usually not dotted but glossy, white, greenish, or yellow. There is also a broad, noticeable ring about the stem, as in thefly amanita. This mushroom frequents moist, shady spots, also along the borders of fields. It occurs singly, and rarely in fields or pastures.
Fig. 41.Fig. 41.THE DEADLY AGARIC.(Amanita Phalloides.)This variety is very poisonous.
THE DEADLY AGARIC.
(Amanita Phalloides.)
This variety is very poisonous.
FOOTNOTES:[9]The shaggy mane has white gills, but its other features are characteristic.
[9]The shaggy mane has white gills, but its other features are characteristic.
[9]The shaggy mane has white gills, but its other features are characteristic.
Part IIITHE HOUSE AND GROUNDSBYGEORGE M. PRICE
THE HOUSE AND GROUNDS
BY
GEORGE M. PRICE
We beg to tender grateful acknowledgment to author and publisher for the use of Dr. George M. Price's valuable articles on sanitation. The following extracts are taken from Dr. Price's "Handbook on Sanitation," published by John Wiley & Son, and are covered by copyright.
Soil and Sites
Definition.—By the term "soil" we mean the superficial layer of the earth, a result of the geological disintegration of the primitive rock by the action of the elements upon it and of the decay of vegetable and animal life.
Composition.—Soil consists of solids, water, and air.
Solids.—The solid constituents of the soil are inorganic and organic in character.
The inorganic constituents are the various minerals and elements found alone, or in combination, in the earth, such as silica, aluminum, calcium, iron, carbon, sodium, chlorine, potassium, etc.
The characteristics of the soil depend upon its constituents, and upon the predominance of one or the other of its composing elements. The nature of the soil also depends upon its physical properties. When the disintegrated rock consists of quite large particles, the soil is called agravel soil. Asandy soilis one in which the particles are very small.Sandstoneis consolidated sand.Clayis soil consisting principally ofaluminum silicate; inchalk, soft calcium carbonate predominates.
The organic constituents of the soil are the result of vegetable and animal growth and decomposition in the soil.
Ground Water.—Ground water is that continuous body or sheet of water formed by the complete filling and saturation of the soil to a certain level by rain water; it is that stratum of subterranean lakes and rivers, filled up with alluvium, which we reach at a higher or lower level when we dig wells.
The level of the ground water depends upon the underlying strata, and also upon the movements of the subterranean water bed. The relative position of the impermeable underlying strata varies in its distance from the surface soil. In marshy land the ground water is at the surface; in other places it can be reached only by deep borings. The source of the ground water is the rainfall, part of which drains into the porous soil until it reaches an impermeable stratum, where it collects.
The movements of the ground water are in two directions—horizontal and vertical. The horizontal or lateral movement is toward the seas and adjacent water courses, and is determined by hydrostatic laws and topographical relations. The vertical motion of the ground water is to and from the surface, and is due to the amount of rainfall, the pressure of tides, and water courses into which the ground water drains. Thevertical variations of the ground water determine the distance of its surface level from the soil surface, and are divided into a persistently low-water level, about fifteen feet from the surface; a persistently high-water level, about five feet from the surface, and a fluctuating level, sometimes high, sometimes low.
Ground Air.—Except in the hardest granite rocks and in soil completely filled with water the interstices of the soil are filled with a continuation of atmospheric air, the amount depending on the degree of porosity of the soil. The nature of the ground air differs from that of the atmosphere only as it is influenced by its location. The principal constituents of the air—nitrogen, oxygen, and carbonic acid—are also found in the ground air, but in the latter the relative quantities of O and CO2are different.
AVERAGE COMPOSITION OF ATMOSPHERIC AIR IN 100 VOLUMES
AVERAGE COMPOSITION OF GROUND AIR
Of course, these quantities are not constant, but vary in different soils, and at different depths, times, etc. The greater quantity of CO2in ground air is due to the process of oxidation and decomposition taking placein the soil. Ground air also contains a large quantity of bacterial and other organic matter found in the soil.
Ground air is in constant motion, its movements depending upon a great many factors, some among these being the winds and movements of the atmospheric air, the temperature of the soil, the surface temperature, the pressure from the ground water from below, and surface and rain water from above, etc.
Ground Moisture.—The interstices of the soil above the ground-water level are filled with aironly, when the soil is absolutely dry; but as such a soil is very rare, all soils being more or less damp, soil usually contains a mixture of air and water, or what is calledground moisture.
Ground moisture is derived partly from the evaporation of the ground water and its capillary absorption by the surface soil, and partly by the retention of water from rains upon the surface. The power of the soil to absorb and retain moisture varies according to the physical and chemical, as well as the thermal, properties of the soil.
Loose sand may hold about 2 gallons of water per cubic foot; granite takes up about 4 per cent of moisture; chalk about 15 per cent; clay about 20 per cent; sandy loam 33 to 35 per cent; humus[10]about 40 per cent.
Ground Temperature.—The temperature of the soil is due to the direct rays of the sun, the physicochemical changes in its interior, and to the internal heat of the earth.
The ground temperature varies according to the annual and diurnal changes of the external temperature; also according to the character of the soil, its color, composition, depth, degree of organic oxidation, ground-water level, and degree of dampness. In hot weather the surface soil is cooler, and the subsurface soil still more so, than the surrounding air; in cold weather the opposite is the case. The contact of the cool soil with the warm surface air on summer evenings is what produces the condensation of air moisture which we call dew.
Bacteria.—Quite a large number of bacteria are found in the soil, especially near the surface, where chemical and organic changes are most active. From 200,000 to 1,000,000 bacteria have been found in 1 c.c. of earth. The ground bacteria are divided into two groups—saprophytic and pathogenic. The saprophytic bacteria are the bacteria of decay, putrefaction, and fermentation. It is to their benevolent action that vegetable and animaldébrisis decomposed, oxidized, and reduced to its elements. To these bacteria the soil owes its self-purifying capacity and the faculty of disintegrating animal and vegetabledébris.
The pathogenic bacteria are either those formed during the process of organic decay, and which, introduced into the human system, are capable of producing various diseases, or those which become lodged in thesoil through the contamination of the latter by ground water and air, and which find in the soil a favorable lodging ground, until forced out of the soil by the movements of the ground water and air.
Contamination of the Soil.—The natural capacity of the soil to decompose and reduce organic matter is sometimes taxed to its utmost by the introduction into the soil of extraneous matters in quantities which the soil is unable to oxidize in a given period. This is called contamination or pollution of soil, and is due: (1) to surface pollution by refuse, garbage, animal and human excreta; (2) to interment of dead bodies of beasts and men; (3) to the introduction of foreign deleterious gases, etc.[11]
Pollution by Surface Refuse and Sewage.—This occurs where a large number of people congregate, as in cities, towns, etc., and very seriously contaminates the ground by the surcharge of the surface soil with sewage matter, saturating the ground with it, polluting the ground water from which the drinking water is derived, and increasing the putrefactive changes taking place in the soil. Here the pathogenic bacteria abound, and, by multiplying, exert a very marked influence upon the health by the possible spread of infectious diseases. Sewage pollution of the soils and of the source of water supply is a matter of grave importance, and is one of the chief factors of high mortality in cities and towns.
Interment of Bodies.—The second cause of soil contamination is also of great importance. Owing to the intense physicochemical and organic changes taking place within the soil, all dead animal matter interred therein is easily disposed of in a certain time, being reduced to the primary constituents, viz., ammonia, nitrous acid, carbonic acid, sulphureted and carbureted hydrogen, etc. But whenever the number of interred bodies is too great, and the products of decomposition are allowed to accumulate to a very great degree, until the capacity of the soil to absorb and oxidize them is overtaxed, the soil, and the air and water therein, are polluted by the noxious poisons produced by the processes of decomposition.
Introduction of Various Foreign Materials and Gases.—In cities and towns various pipes are laid in the ground for conducting certain substances, as illuminating gas, fuel, coal gas, etc.; the pipes at times are defective, allowing leakage therefrom, and permitting the saturation of the soil with poisonous gases which are frequently drawn up by the various currents of ground air into the open air and adjacent dwellings.
Influence of the Soil on Health.—The intimate relations existing between the soil upon which we live and our health, and the marked influence of the soil on the life and well-being of man, have been recognized from time immemorial.
The influence of the soil upon health is due to: (1) the physical and chemical character of the soil; (2) the ground-water level and degree of dampness; (3) the organic impurities and contamination of the soil.
The physical and chemical nature of the soil, irrespective of its water, moisture, and air, has been regarded by some authorities as having an effect on the health, growth, and constitution of man. The peculiar disease called cretinism, as well as goitre, has been attributed to a predominance of certain chemicals in the soil.
The ground-water level is of great importance to the well-being of man. Professor Pettenkofer claimed that a persistently low water level (about fifteen feet from the surface) is healthy, the mortality being the lowest in such places; a persistently high ground-water level (about five feet from the surface) is unhealthy; and a fluctuating level, varying from high to low, is the most unhealthy, and is dangerous to life and health. Many authorities have sought to demonstrate the intimate relations between a high water level in the soil and various diseases.
A damp soil, viz., a soil wherein the ground moisture is very great and persistent, has been found inimical to the health of the inhabitants, predisposing them to various diseases by the direct effects of the dampness itself, and by the greater proneness of damp ground to become contaminated with various pathogenic bacteria and organisms which may be drawn into the dwellings by the movements of the ground air. As a rule, there is very little to hinder the ground air from penetrating the dwellings of man, air being drawn in through cellars by changes in temperature, and by the artificial heating of houses.
The organic impurities and bacteria found in the soil are especially abundant in large cities, and are a cause of the evil influence of soil upon health. The impurities are allowed to drain into the ground, to pollute the ground water and the source of water supply, and to poison the ground air, loading it with bacteria and products of putrefaction, thus contaminating the air and water so necessary to life.
Diseases Due to Soil.—A great many diseases have been thought to be due to the influence of the soil. An ætiological relation had been sought between soil and the following diseases: malaria, paroxysmal fevers, tuberculosis, neuralgias, cholera, yellow fever, bubonic plague, typhoid, dysentery, goitre and cretinism, tetanus, anthrax, malignant Œdema, septicæmia, etc.
Sites.—From what we have already learned about the soil, it is evident that it is a matter of great importance as to where the site for a human habitation is selected, for upon the proper selection of the site depend the health, well-being, and longevity of the inhabitants. The requisite characteristics of a healthy site for dwellings are: a dry, porous, permeable soil; a low and nonfluctuating ground-water level, and asoil retaining very little dampness, free from organic impurities, and the ground water of which is well drained into distant water courses, while its ground air is uncontaminated by pathogenic bacteria. Exposure to sunlight, and free circulation of air, are also requisite.
According to Parkes, the soils in the order of their fitness for building purposes are as follows: (1) primitive rock; (2) gravel, with pervious soil; (3) sandstone; (4) limestone; (5) sandstone, with impervious subsoil; (6) clays and marls; (7) marshy land, and (8) made soils.
It is very seldom, however, that a soil can be secured having all the requisites of a healthy site. In smaller places, as well as in cities, commercial and other reasons frequently compel the acquisition of and building upon a site not fit for the purpose; it then becomes a sanitary problem how to remedy the defects and make the soil suitable for habitation.
Prevention of the Bad Effects of the Soil on Health.—The methods taught by sanitary science to improve a defective soil and to prepare a healthy site are the following:
Street Pavingserves a double sanitary purpose. It prevents street refuse and sewage from penetrating the ground and contaminating the surface soil, and itacts as a barrier to the free ascension of deleterious ground air.[12]
Tree Plantingserves as a factor in absorbing the ground moisture and in oxidizing organic impurities.
The Proper Construction of the Househas 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 thewater-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-tarpitch, 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 spaces four to eight feet wide between the house proper and the surrounding ground, the open spaces 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.
Fig. 4.Fig. 4.CONCRETE FOUNDATION AND DAMP-PROOF COURSE.
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 "cloacæ" 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 classes 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.
[10]Humus is vegetable mold; swamp muck; peat; etc.—Editor.
[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.
[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 classes 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.
[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 classes 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.
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 quantity 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 substituting pure air from the outside. This isventilation.
Ventilation, therefore, is the maintenance of the air in a confined space in a condition conducive to health; in other words, "ventilation is the replacing of the impure air in a confined space by pure air from the outside."
Quantity 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 space, 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 quantity 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 quantity of CO2as the standard of impurity, its increase serving as an index of the condition of the air. The normal quantity of CO2in the air is 0.04 per cent, or 4 volumes in 10,000; and it has been determined that whenever the CO2reaches 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 CO2in 10,000 of air constitutes 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 CO2exhaled 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 space 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 quantity 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 space 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 space 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 space needed, the height of the room as well as the floor space must be taken into consideration. As a rule the height of a room ought to be in proportion to the floor space, 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 orartificial 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 passes 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 beutilized 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, principal 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 passing 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 space between the two sashes, where they meet. The ingress of air is made possible whenever the lower sash is raised or the upperone 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 space 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 panesare 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 pass 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 innerends 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.
Fig. 5.Fig. 5.HINKES BIRD WINDOW. (Taylor.)
HINKES BIRD WINDOW. (Taylor.)
Fig. 6.Fig. 6.ELLISON'S AIR INLETS. (Knight.)
ELLISON'S AIR INLETS. (Knight.)
Fig. 7.Fig. 7.SHERINGHAM VALVE. (Taylor.)
SHERINGHAM VALVE. (Taylor.)
Fig. 8.Fig. 8.THE TOBIN VENTILATOR. (Knight.)
THE TOBIN VENTILATOR. (Knight.)