VENTILATION. This word liter ally signifies fanning or blowing. In domestic economy, it is the art of con• veying currents of fresh air through close apartments or confined places, so as to maintain the atmosphere in a state of purity.
Atmospheric air consists of two ingre dients, oxygen and azote, blended toge ther in the proportion of one part by measure of the former to four of the lat When these proportions are altered, air becomes unfit to respiration; and when the oxygen is withdrawn or con sumed, it is rendered altogether incapa ble of supporting animal life or combus tion. But there are operations both of nature and art continually going forward in which the oxygen of the atmosphere is consumed, and gaseous products evolv ed which are destructive of life. Thus, in the act of respiration, a certain portion of the oxygen contained in the air inhal ed into the lungs is converted into car bonic acid, a substance which acts as a narcotic poison ; and hence, in a confin ed apartment, air is soon rendered, by breathing alone, not merely incapable of maintaining life, but highly destructive of it, in consequence of the evolution of a deleterious gas. In like manner, oxy gen is consumed, and carbonic acid evolved, in the process of combustion ; and the burning of a pan of charcoal in a close room is known to be a certain means of extinguishing life.
Although a decomposition and deteri oration of air is thus continually going for ward, nature has by various means pro vided so effectually for the restoration of the two constituent gases, that in what ever part of the world, and at whatever height in the atmosphere, air is taken, it is found, when chemically examined, to contain azote and oxygen in exactly the same proportions.
Quantity of air required for Ventilation. If the question were solely how to com mand a sufficient supply of fresh air, it would be easily solved ; but as in our climates the temperature of the external atmosphere is in winter generally very much lower than is necessary for comfort, we have at the same time to provide for the maintenance of an artificial tempera ture in our apartments, by allowing the air to enter no faster than it can be warm ed. One of the first points, therefore, to be considered, is the amount of the supply of fresh air which an individual requires for comfort and health. This,
however, is a point on which, by reason of the great variety of circumstances con cerned, it is extremely difficult to arrive at any satisfactory conclusion.
Dr. Henry estimates that an adult per son makes, on the average, 20 inspira tions per minute, and draws into his lungs at each inspiration 20 cubic inches of air. Peclet allows 40 cubic inches for each inspiration. Taking the mean of the two estimates, we have 600 cubic inches expired per minute. But, accord ing to Dr. Arnott, air expelled from She lungs is found to vitiate, so as to render unfit for respiration twelve times its own bulk of pure air ; hence, the quan tity of air spoiled every minute by the respiration of an adult, is 7200 cubic inches, or rather more than 4 cubic feet. Dr. Arnott, however, supposes the waste to be only half of this quantity. But there are several other causes of deterio ration besides the production of carbonic acid from the lungs : the effluvia and va por of animal matter exuded from the whole surface of the body is not less in jurious than carbonic acid ; and, accord ing to M. Seguin, in a temperature of 60°, about 31 cubic feet of air per minute is charged with animal vapor transmitted through the skin of an adult, and ren dered unfit for respiration. When arti ficial lights are used, a further allowance must be made for the waste by combus tion. Besides, air is required for various other purposes than those which have now been mentioned. It acts as a cooling power, and hence the supply requisite for comfort depends on its temperature. It likewise serves to carry off moisture from the skin, and therefore its state as to dryness or humidity must be con sidered. Dr. D. B. Reid found, from observations on a number of persons as sembled in an experimental room, that not less than 10 cubic feet per minute should be allowed to each individual on the average, at an agreeable temperature ; but that, to maintain the atmosphere in all its purity, a much larger supply would at times be desirable. On the whole, therefore, we may conclude that 10 cubic feet of fresh air per minute, for each in dividual, is the smallest allowance that should be made in order to ensure health ful ventilation.