The Home Medical Library Volume V Part 13

[Ill.u.s.tration: FIG. 13.

A GALTON GRATE. (TRACY.)]

=Stoves.=--Stoves are closed receptacles in which fuel is burned, and the heat produced is radiated toward the persons, etc., near them, and also conducted, through the iron or other materials of which the stoves are made, to surrounding objects. In stoves seventy-five per cent of the fuel burned is utilized. They are made of brick, tile, and cast or wrought iron.

Brick stoves, and stoves made of tile, are extensively used in some European countries, as Russia, Germany, Sweden, etc.; they are made of slow-conducting material, and give a very equable, efficient, and cheap heat, although their ventilating power is very small.

Iron is used very extensively because it is a very good conductor of heat, and can be made into very convenient forms. Iron stoves, however, often become superheated, dry up, and sometimes burn the air around them, and produce certain deleterious gases during combustion.

When the fire is confined in a clay fire box, and the stove is not overheated, a good supply of fresh air being provided and a vessel of water placed on the stove to reduce the dryness of the air, iron stoves are quite efficient.

=Hot-air Warming.=--In small houses the warming of the various rooms and halls can be accomplished by placing the stove or furnace in the cellar, heating a large quant.i.ty of air and conveying it through proper tubes to the rooms and places to be warmed. The points to be observed in a proper and efficient hot-air heating system are the following:

(1) The furnace must be of a proper size in proportion to the area of s.p.a.ce to be warmed. (2) The joints and parts of the furnace must be gas-tight. (3) The furnace should be placed on the cold side of the house, and provision made to prevent cellar air from being drawn up into the cold-air box of the furnace. (4) The air for the supply of the furnace must be gotten from outside, and the source must be pure, above the ground level, and free from contamination of any kind.[16]

(5) The cold-air box and ducts must be clean, protected against the entrance of vermin, etc., and easily cleaned. (6) The air should not be overheated. (7) The hot-air flues or tubes must be short, direct, circular, and covered with asbestos or some other non-conducting material.

[Ill.u.s.tration: FIG. 14.

A HOT-AIR FURNACE.

The cold air from outside comes to the COLD-AIR INTAKE through the cold-air duct, enters the furnace from beneath, and is heated by pa.s.sing around the FIRE POT and the annular combustion chamber above.

It then goes through pipes to the various registers throughout the house. The coal is burnt in the fire pot, the gases are consumed in the combustion chamber above, while the heat eventually pa.s.ses into the SMOKE FLUE. The WATER PAN supplies moisture to the air.]

=Hot-water System.=--The principles of hot-water heating are very simple. Given a circuit of pipes filled with water, on heating the lower part of the circuit the water, becoming warmer, will rise, circulate, and heat the pipes in which it is contained, thus warming the air in contact with the pipes. The lower part of the circuit of pipe begins in the furnace or heater, and the other parts of the circuit are conducted through the various rooms and halls throughout the house to the uppermost story. The pipes need not be straight all through; hence, to secure a larger area for heating, they are convoluted within the furnace, and also in the rooms, where the convoluted pipes are called _radiators_. The water may be warmed by the low- or high-pressure system; in the latter, pipes of small diameter may be employed; while in the former, pipes of a large diameter will be required. The character, etc., of the boilers, furnace, pipes, etc., cannot be gone into here.

=Steam-heating System.=--The principle of steam heating does not differ from that of the hot-water system. Here the pressure is greater and steam is employed instead of water. The steam gives a greater degree of heat, but the pipes must be stronger and able to withstand the pressure. There are also combinations of steam and hot-water heating. For large houses either steam or hot-water heating is the best means of warming, and, if properly constructed and cared for, quite healthy.[17]

FOOTNOTES:

[16] Great care should be taken that the air box is not placed in contaminated soil or where it may become filled with stagnant or polluted water.--EDITOR.

[17] See Chapter XI for practical notes on cost of installation of these three conveyed systems--hot-air, hot-water, and steam.--EDITOR.

CHAPTER IV

=Disposal of Sewage=

=Waste Products.=--There is a large amount of waste products in human and social economy. The products of combustion, such as ashes, cinders, etc.; the products of street sweepings and waste from houses, as dust, rubbish, paper, etc.; the waste from various trades; the waste from kitchens, e. g., sc.r.a.ps of food, etc.; the waste water from the cleansing processes of individuals, domestic animals, clothing, etc.; and, finally, the excreta--urine and faeces--of man and animals; all these are waste products that cannot be left undisposed of, more especially in cities, and wherever a large number of people congregate. All waste products are cla.s.sified into three distinct groups: (1) refuse, (2) garbage, and (3) sewage.

The amount of _refuse_ and _garbage_ in cities is quite considerable; in Manhattan, alone, the dry refuse amounts to 1,000,000 tons a year, and that of garbage to 175,000 tons per year. A large percentage of the dry refuse and garbage is valuable from a commercial standpoint, and could be utilized, with proper facilities for collection and separation. The disposal of refuse and garbage has not as yet been satisfactorily dealt with. The modes of waste disposal in the United States are: (1) dumping into the sea; (2) filling in made land, or plowing into lands; (3) cremation and (4) reduction by various processes, and the products utilized.

=Sewage.=--By sewage we mean the waste and effete human matter and excreta--the urine and faeces of human beings and the urine of domestic animals (the faeces of horses, etc., has great commercial value, and is usually collected separately and disposed of for fertilizing purposes).

The amount of excreta per person has been estimated (Frankland) as 3 ounces of solid and 40 ounces of fluid per day, or about 30 tons of solid and 100,000 gallons of fluid for each 1,000 persons per year.

In spa.r.s.ely populated districts the removal and ultimate disposal of sewage presents no difficulties; it is returned to the soil, which, as we know, is capable of purifying, disintegrating, and a.s.similating quite a large amount of organic matter. But when the number of inhabitants to the square mile increases, and the population becomes as dense as it is in some towns and cities, the disposal of the human waste products becomes a question of vast importance, and the proper, as well as the immediate and final, disposal of sewage becomes a serious sanitary problem.

It is evident that sewage must be removed in a thorough manner, otherwise it would endanger the lives and health of the people.

The dangers of sewage to health are:

(1) From its offensive odors, which, while not always directly dangerous to health, often produce headaches, nausea, etc.

(2) The organic matter contained in sewage decomposes and eliminates gases and other products of decomposition.

(3) Sewage may contain a large number of pathogenic bacteria (typhoid, dysentery, cholera, etc.).

(4) Contamination of the soil, ground water, and air by percolation of sewage.

The problem of sewage disposal is twofold: (1) immediate, viz., the need of not allowing sewage to remain too long on the premises, and its immediate removal beyond the limits of the city; and (2) the final disposition of the sewage, after its removal from the cities, etc.

=Modes of Ultimate Disposal of Sewage.=--The chief const.i.tuents of sewage are organic matter, mineral salts, nitrogenous substances, potash, and phosphoric acid. Fresh-mixed excrement.i.tious matter has an acid reaction, but within twelve to twenty hours it becomes alkaline, because of the free ammonia formed in it. Sewage rapidly decomposes, evolving organic and fetid matters, ammonium sulphide, sulphureted and carbureted hydrogen, etc., besides teeming with animal and bacterial life. A great many of the substances contained in sewage are valuable as fertilizers of soil.

The systems of final disposal of sewage are as follows:

(1) Discharge into seas, lakes, and rivers.

(2) Cremation.

(3) Physical and chemical precipitation.

(4) Intermittent filtration.

(5) Land irrigation.

(6) "Bacterial" methods.

_Discharge into Waters._--The easiest way to dispose of sewage is to let it flow into the sea or other running water course. The objections to sewage discharging into the rivers and lakes near cities, and especially such lakes and rivers as supply water to the munic.i.p.alities, are obvious. But as water can purify a great amount of sewage, this method is still in vogue in certain places, although it is to be hoped that it will in the near future be superseded by more proper methods. The objection against discharging into seas is the operation of the tides, which cause a backflow and overflow of sewage from the pipes. This backflow is remedied by the following methods: (1) providing tidal flap valves, permitting the outflow of sewage, but preventing the inflow of sea water; (2) discharging the sewage intermittently, only during low tide; and (3) providing a constant outflow by means of steam-power pressure.

_Cremation._--Another method of getting rid of the sewage without attempting to utilize it is by cremation. The liquid portion of the sewage is allowed to drain and discharge into water courses, and the more or less solid residues are collected and cremated in suitable crematories.

_Precipitation._--This method consists in separating the solid matters from the sewage by precipitation by physical or chemical processes, the liquid being allowed to drain into rivers and other waters, and the precipitated solids utilized for certain purposes. The precipitation is done either by straining the sewage, collecting it into tanks, and letting it subside, when the liquid is drawn off and the solids remain at the bottom of the tanks, a rather unsatisfactory method; or, by chemical processes, precipitating the sewage by chemical means, and utilizing the products of such precipitation. The chemical agents by which precipitation is accomplished are many and various; among them are lime, alum, iron perchloride, phosphates, etc.

_Intermittent Filtration._--Sewage may be purified mechanically and chemically by method of intermittent filtration by pa.s.sing it through filter beds of gravel, sand, c.o.ke, cinders, or any such materials.

Intermittent filtration has pa.s.sed beyond the experimental stage and has been adopted already by a number of cities where such a method of sewage disposal seems to answer all purposes.

_Land Irrigation._--In this method the organic and other useful portions of sewage are utilized for irrigating land, to improve garden and other vegetable growths by feeding the plants with the organic products of animal excretion. Flat land, with a gentle slope, is best suited for irrigation. The quant.i.ty of sewage disposed of will depend on the character of the soil, its porosity, the time of the year, temperature, intermittency of irrigation, etc. As a rule, one acre of land is sufficient to dispose of the sewage of 100 to 150 people.

_Bacterial Methods._--The other biological methods, or the so-called "bacterial" sewage treatment, are but modifications of the filtration and irrigation methods of sewage disposal. Properly speaking the bacterial purification of sewage is the scientific application of the knowledge gained by the study of bacterial life and its action upon sewage.

In intermittent filtration the sewage is pa.s.sed through filter beds of sands, etc., upon which filter beds the whole burden of the purification of the sewage rests. In the bacterial methods the work of purification is divided between the septic tanks where the sewage is first let into and where it undergoes the action of the anaerobic bacteria, and from these septic tanks the sewage is run to the contact beds of c.o.ke and cinders to further undergo the action of the aerobic bacteria, after the action of which the nitrified sewage is in a proper form to be utilized for fertilization of land, etc. The septic tanks are but a modification of the common cesspool, and are constructed of masonry, brick, and concrete.

There are a number of special applications of the bacterial methods of sewage treatment, into which we cannot go here.

=Sewage Disposal in the United States.=--According to its location, position, etc., each city in the United States has its own method of final disposition of sewage. Either one or the other, or a combination of two of the above methods, is used.

The following cities discharge their sewage into the sea: Portland, Salem, Lynn, Gloucester, Boston, Providence, New York, Baltimore, Charleston, and Savannah.

The following cities discharge their sewage into rivers and lakes: Philadelphia, Cincinnati, St. Louis, Albany, Minneapolis, St. Paul, Was.h.i.+ngton, Buffalo, Detroit, Richmond, Chicago, Milwaukee, and Cleveland.