f 



I 



The Principles of Ventilation. 219 



by respiration alone, its amount is proportional to the amount of 

 organic matter present, and this latter, owing to its prompt decomposi- 

 tion, is decidedly injurious. 



The amount of carbonic acid present in the atmosphere can be 

 easily determined, while the reverse is true for the organic impurities. 

 A very simple method of determining whether a room contains more 

 than the maximum allowed of carbonic acid is given by Dr. Angus 

 , Smith as follows : Fill a clean bottle, holding ten and one-half fluid 

 I ounces, with the air to be tested, then pour in one-half ounce of clear 

 lime-water and shake it up with the air; if more than about six vol- 

 umes of carbonic acid to 10,000 of air is present, a turbidity will be 

 produced, due to the formation of carbonate of lime. 



2. A second requirement is that the amount of moisture shall be 

 no more than about fifty per cent, of saturation. When this limit is 

 exceeded, the air is with difficulty prevented from acquiring and retain- 

 ing an odor due to organic particles, since these seem to acqufre a 

 coating of moisture and adhere pertinaciously to clothing and furni- 

 ture. Moreover, moist air prevents the proper and healthful excretion 

 of perspiration. Very much less than fifty per cent, of saturation 

 causes a disagreeable feeling of dryness. 



3. It is desirable that the temperature of the air should bo kepc. as 

 nearly as possible, at 70° Fah. in dwellings and about 68' Fah. in 

 schools, churches and public halls. 



4. Xo draughts must be perceptible. This condition requires that 

 there shall be no general movement of air faster than two feet per 

 second. To sum up the requirements, then: 



1. Carbonic acid must be kept down to six vols, per 10,000. 



2. Moisture must not exceed fifty i)er cent, of saturation. 



3. The temperature must be maintained at about 70'. 



4. The air in the room shall not move faster than two feet per 

 second. 



IV. Modes of Ventilatixg. 

 The various modes of ventilation may be divided into two great 

 classes : 



A. Natural ventilation. 



B. Artificial ventilation. 



By natural ventilation, I mean all processes which do not call for 

 the application of force in any form, save that supplied by ordinary 

 natural operations; and by artificial ventilation, those means which 

 involve special appliances requiring the employment of force. There 

 are two forms of natural ventilation: 



1. Perflation. 



