Page:The American Cyclopædia (1879) Volume XVI.djvu/472

452 WARMING AND VENTILATION cub. ft. a minute. Open combustion in a room contaminates the air in the same way. A pound of mineral coal requires 120 cub. ft. of air to burn it, although if the combustion is properly conducted the contaminated air is steadily withdrawn. But in illumination the products of combustion are accumulated with- in the room. A candle (six to the pound) will consume one third of the oxygen from 10 cub. ft. of air per hour; while an oil lamp, with large burner, will change in the same way 70 cub. ft. per hour. A cubic foot of coal gas consumes from 2 to 2J cub. ft. of oxygen, and produces from 1 to 2 cub. ft. of carbonic acid. Thus every cubic foot of gas burned imparts to the atmosphere 1 cub. ft. of carbonic acid, and charges 100 cub. ft. of it with 1 per cent, of this noxious gas. Besides these sources of impurity, subtile streams of effete organic mat- ter are constantly exhaling into the air from the lungs and skin of every living animal. The current from the ventilator of a crowded room has an insufferably nauseous odor, and if passed through pure water quickly renders it putrescent. Thus, morbid, organic poisons, so subtile and minute as to elude chemical de- tection, may be engendered in the confined air of over-crowded rooms, and become the germs of fever and pestilence. A frequent cause of deterioration of the air in close apartments is the withdrawal of its moisture by heating. While the other ingredients of the atmosphere are constant, its moisture depends upon tem- perature. At zero a cubic foot of air will hold 18 grain of watery vapor ; at 82 it will con- tain 2-35 grs.; at 50, 4-24; at 100, 19-12; and as the temperature goes still higher, the capacity for moisture rapidly increases. When air is saturated at a given temperature, it will receive no more moisture unless the heat be increased ; while if its temperature falls, a por- tion of its water is precipitated. (See DEW.) In the open atmosphere, where the air is in contact with the moist earth, evaporation and precipitation take place with the rising and falling temperature, but usually within normal or healthful limits. But if air is heated without the requisite addition of moisture, its constitu- tion is disturbed, and it becomes injurious. Air saturated with moisture at the freezing point, and then heated in a room to 100, has but one eighth its necessary quantity of moisture, and the deficiency represents its drying or parching influence upon the lungs and skin. From tainted air follows tainted blood. Oxygen, the con- sumer of effete matter and purifier of the sys- tem, is withheld, and, the carbonic acid already in the air offering a barrier to its exhalation from the lungs, the vital current is encumbered with the noxious products of bodily waste. Under these circumstances it is supposed the blood may become a ready prepared soil for the seeds of infection. Atmospheric malaria may be powerless upon a perfectly healthy system, while it would find ready lodgment in a constitution which bad air, by lowering the tone and depressing the vital powers, had predisposed to epidemic disease. Because it requires a given quantity of carbonic acid in the air to produce immediately injurious ef- fects, it does not follow that a much lower proportion does not seriously impair the con- stitutional energies, and especially the power of resisting disease. Many a case of disease proves fatal on account of an unperceived de- pression of the sufferer's strength by contin- ued exposure to an atmosphere impure from bodily exhalations. That vitiated air produces intellectual stupor, depression of the feelings, headache, and predisposition to take cold, is proved by very slight observation ; and upon few things is enlightened medical experience more unanimous than that it either causes or greatly aggravates the most malignant diseases, such as fevers, inflammations, infantine mala- dies, cholera, scrofula, and consumption. The first question in practical ventilation relates to the amount of fresh air that requires to be sup- plied to occupied rooms ; and as the air of such rooms cannot be maintained in absolute purity, the problem is, what is the limit of impurity that may bo held consistent with the main- tenance of health? Authorities are agreed that the amount of carbonic acid in air tainted by respiration may be accepted as a fair index to the proportion of other and accompanying impurities, so that the question is, how much carbonic acid may be tolerated in respirablo air? Parkes, Pettenkofer, Angus Smith, and De Chaumont, agree that the permissible amount of carbonic acid in respired air should not be more than double its normal amount, or '8 per 1,000 volumes. Dr. Parkes main- tains that perfect ventilation should keep the proportion down to -6 per 1,000; but that, while it is impossible to prove that a propor- tion of even '8 per 1,000 volumes produces immediately injurious effects, yet when it rises as high as 1 per 1,000, that is, one tenth of one per cent., the accumulative influence is palpably injurious. If the maximum impu- rity allowed is - 8 per 1,000 volumes, the ex- halation of carbonic acid by breathing would require a supply of 1,500 cub. ft. of pure air per hour, or at the rate of 25 cub. ft. per minute for each person. If the carbonic acid generated by illumination is taken into ac- count, the supply of fresh air would of course require to be greater. The rapid exchange of air involves the difficulty of currents, and this depends much upon the cubical space of the apartment. It is important to avoid per- ceptible draughts ; and if the room be small and the ventilation thorough, the currents are liable to be injurious. Thus with our standard supply of 1,500 cub. ft. an hour, if the apart- ment has a space of 250 cub. ft., its air must be renewed six times in an hour, while if there is a space of 750 cub. ft., it will re- quire renewal but twice in an hour. Prof. Pettenkofer of Munich has shown that the air in a chamber of 424 cub. ft. (8 ft. high, 8 ft.