Air, water, and food from a sanitary standpoint . es added to the air which is in the rooms will also be re-moved with the carbon dioxide. From nearly all points of view, carbon dioxide is an indi-cator of the efficiency of ventilation, especially if combinedwith observations of temperature and moisture. It is an in-dicator also readily understood and accepted by the public. The principles of ventilation may be readily illustrated toa class by means of simple apparatus. Such an apparatus,using candles and designed to illustrate the section of anordinarv room, is shown in Fig. I. In testing the
Air, water, and food from a sanitary standpoint . es added to the air which is in the rooms will also be re-moved with the carbon dioxide. From nearly all points of view, carbon dioxide is an indi-cator of the efficiency of ventilation, especially if combinedwith observations of temperature and moisture. It is an in-dicator also readily understood and accepted by the public. The principles of ventilation may be readily illustrated toa class by means of simple apparatus. Such an apparatus,using candles and designed to illustrate the section of anordinarv room, is shown in Fig. I. In testing the efficiency of ventilation of any room or AIR: THE PROBLEM OF VENTILATION. 25 building, it is necessary to determine first the direction of theair-currents, for there can be no ventilation without the architect who designed the building, or the engineerwho advised the architect, is responsible, then the chemisthas only to follow directions in taking the samples; but fre-quently the chemist, as well as the sanitary engineer, is called. Fig. 1.—Apparatus to Illustrate the Principles of Ventilation. upon to make tests of rooms and buildings of which no plansare available. In the examination of such rooms, then, the position offlues or conduits, both inlets and outlets, which were intendedto convey air or which serve without such intention, shouldfirst be located. Possible avenues of ingress and egress bymeans of loose windows, cracks around doors, etc., are to beconsidered. When there is great difference of temperaturebetween outer and inner air, these allow of quite rapid changeof air. Some means of rendering visible these currents is de-sirable, such as smouldering paper, magnesium powder, orfumes of ammonium chloride. 26 AIR, WATER, AND FOOD. When the direction and intensity of these air-currentshave been determined, the places from which the air-samplesare to be taken may be chosen. It will be evident in whatpart of the room stagnation occurs and where eddies are
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