HEATING AND VENTILATION. 6117 HEATING AND VENTILATION. regulate the temperature rather than the air- supply of the building. Later the necessity of securing a supply of fresh air in mines served to call attention to the necessity of ventilation independent of heating. In the si.Kteenth centurv' (ieorg Agricola (q.v.) wrote a treatise, Dc lie iletallica, in which he describes the methods em- ployed to ventilate the mines of Saxony and Bohemia. In France ventilation was formerly studied chiefly from the standpoint of securing a fresh- air supply for hospitals. In IS43, according to Pecht, there was but one hospital in France hav- ing a regular ventilating apparatus. In 1853 two systems were tried in the construction of the Hospital Lariboisi&re, one of aspiration, the other of inflation. Both were unsatisfactory be- cause neither of them supplied a sufficient quan- tity of fresh air. In Germany, as in France, the early history of ventilation is connected with hospital construction. In England attempts at securing a fresh-air supply began much earlier, and consisted in repeated attempts to secure ventilation for the English Houses of Parliament. In 1660 Sir Christopher Wren made the first at- tempt, and the history of the subsequent efl'orts made would lie an epitome of the advance of the science of ventilation. In 1S.56 the General Board of Health of England appointed a commis- sion to inquire into the best methods of warming and ventilating dwellings. About the same time, owing to the heavy losses by sickness in the Crimean War. the question of barracks-room ven- tilation was under discussion. In the United States, as in England, the early attempts at ventilation were directed toward securing fresh air for the meeting-places of legis- lative a.ssemblies, the first report on the subject having been made on April 2, 1849. Ventilation has for its object the maintenance of a pure-air supply indoors. This can be ef- fected only by the' removal of foul air and the introduction of an equal amount of pure air. Unfortunately, the fact that these two processes go together is often overlooked. Considered from the standpoint of the air in the room, ventila- tion removes or dilutes such impurities as have been introduced by man, regulates the moisture, cools the air, and may be instrumental in warm ing it. although the latter, properly speaking, pertains to heating. Ventilation has no effect on the quality of the air introduced. Therefore, it alone can give no better air than that sur- rounding the building to be ventilated. It is sometimes practicable to remove dist from the fresh-air supply, in case dust cannot lie avoided, by filtering the air through cotton cloth or fibre, or through fine meshes of wire. The moisture of the air-supply may be lessened by drying, and air which is too dry may be moistened by spraying with water. The chief impurities in the air of houses and public assembly rooms ai-e those thrown off by the lungs and skin. Next in im- portance are the gaseous products of the combus- tion of oil and gas for lighting, and of these two substances and coal when used for heating. Dust, also, is found everywhere, some being due to the processes already mentioned, some being brought in on the feet and clothes, or blown in through doors and windows, while large quantities of it are due to the wear and tear of clothing, carpets, and the like. In shops and factories the air is tontamiuated in most of the ways already men- tioned., some of which, like dust, may be intensi- fied many fold. In addition, the air of manufac- tories is liable to be made impure by the gases given off by Lhe chemicals employed or produced, or by the decomposition of organic matter. The number of hours in a day during which a room is occupied, as well as the number of occupants in proportion to the cubical contents of the room, has a mo.-t direct bearing upon the vitia- tion of the air and the means to be employed to rectify it. Thus, dwellings of the better class have some of their rooms eonlimiously occupied for one-half the day. and still other rooms for the remaining half, the air-space to each person being large. Churches may be crowded, but gen- erally only for one to two hours at a time. School buildings, legislative assemblies, and factories may be crowded for hours together, then as com- pletely emptied as churches. Hospital wards are liable to be fully and continuously occupied, in addition to which there are various well-known special ways of contaminating the air of hospi- tals. Wherever rooms are used intermittently, it is generally possible to give them a thorough airing by throwing the windows wide open; but, beneficial as this may be, its efl'ect is not per- manent, and, with the best of intentions, it is quite sure to be neglected, particularly in cold weather. Even in the summer time the ventila- tion of crowded assembly halls and hospitals cannot be left with safety to the interchange of air diie to open windows, since the air may be stagnant outdoors as well as in. In capacious dwelling-houses, with walls, doors, and windows not too tight, the natural interchange between the inner and outer air may suffice during a large part of cold weather, while open doors and windows will give as much fresh air in summer as it is practicable to provide; but there will be times in cool weather when even these favorable conditions will be lacking. It is pretty clearly shown by the foregoing that v'entilation should be made an essential fea- ture in the design and use of pi-aetically all classes of buildings in which people live, work, are instructed, or amused. The quantity of air to be supplied and removed, and the proper means of doing both, can be best understood after considering in more detail the nature and amoiuit of the chief impurities which it is desired to avoid. The vital principle of air is oxygen. Nor- mal air contains about 211.0 per cent., in volume, of ox-ygen, 79 per cent, of nitrogen and argon, and 0.1 per cent, of other substances, including some 0.03 or 0.04 per cent, of carbonic acid (carbon dioxide). After having been passed through the lungs the oxygen has been diminished to IG per cent., and carbonic acid has been in- creased to 4.4 per cent, of the total volume, the nitrogen rising slightly to some 70. .5 per cent. This exhaled air is rapidly dift'used throughout the room, so unless the room is crowded the per- centage of total oxygen is not greatly diminished for some time. With the reduction in the oxygen conies a change in the gaseous pressure in the lungs, as well as a lowerincr of the amount of the vital principle of the air-supply, both of which cause serious disturbances when carried far. .ssociated with the diminished oxygen there is also an increase in watery vapor, in the efTete and putrescible organic contents of the air. and possibly in the number of harmful bacteria
