ON THE CONDITIONS OF HEALTH IN SCHOOLS. 459 



that tlie allowance of air for each person should not be less than 2,000 

 cubic feet per hour, and to giving an indication of the I'easons which lead 

 them to this recommendation. 



They regard as ideal ventilation the condition of things which would 

 be given by general perflation on a day when the natural temperature of 

 the air is 62° or 63° F. In practice the air supplied must be confined if it 

 is to be warmed ; cold walls and windows also disturb the simplicity of 

 the arrangement. 



The Committee have no evidence to show what amount of air would 

 be supplied under the conditions of ideal ventilation above mentioned ; it 

 would probably be far larger than the amount supplied by ventilating 

 systems in practical use, and the estimates of the quantity of air required 

 are based upon other considerations. 



The most common basis of calculation starts from de Chaumont's 

 estimate of the amount necessaiy to pi'event any disagreeable smell or 

 feeling of closeness being perceived by a person coming from the outside 

 air directly into the room. This, again, has been interpreted by various 

 authorities in terms of the excess of carbonic acid in the air of the room 

 over that in the outside air. In taking samples of air for analysis regard 

 must be paid to the proportion of carbonic acid poasibly being varied in 

 different parts of the room, and as far as possible the average proportion 

 should be ascertained. Different authorities fix the limit of ' respiratory 

 impurity ' from this point of view as that indicated by 2 per 10,000 (which 

 corresponds to a supply of about 3,000 cubic feet of air per hour for adults 

 and somewhat less for children during continuous occupation) to 6 per 

 10,000 (for which a supply of 1,000 cubic feet of air per hour would be 

 sufficient). 



Bacteriological tests of air have been made, but no quantitative 

 statements as to the amount of air required have been based upon the 

 I'esults. 



Another basis of computation is the amount of air necessary to remove 

 the ' heat of combustion ' of the persons in the room, It has been calcu- 

 lated that this heat is sufficient in an adult to raise the temperature of 

 3,000 cubic feet of air per hour by 5° F. ; and, generally speaking, it is by 

 the warming of the air through omission of heat from their bodies that the 

 individuals in an occupied room dispose of their waste products and supply 

 themselves with their share of the fresh air which is delivered to the room. 

 It is clear that it is desirable to remove this heat by removing the air 

 which has been fouled. To remove the heat by conduction through walls 

 and windows while retaining the impurities is not a satisfactory means of 

 maintaining a suitable average temperature, and it should be avoided as 

 far. as- "possible. Restricting the air-supply implies a correspondingly 

 greater increase of its temperature by the occupants themselves during 

 its passage through the room, and is on that account objectionable ; and for 

 the same mean or final temperature it implies a proportionately colder 

 supply and consequently more appreciable draughts. Thus 1,000 cubic 

 feet would be warmed 15° per hour by an occupant, and to keep air in a 

 room until it has been warmed 15° F. by the occupants would at least 

 produce discomfort. The 1,000 cubic feet per hour supply must on this 

 account be regarded as too small. It will probably be allowed, for 

 example, that if air were supplied to a room at 63° F. everyone would 

 wish it removed before it had been raised to 70° F. by the inmates them- 

 selves. Upon this basis of calculation here put forward 2,000 cubic feet 



