624 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Rooms warmed by furnaces, open fire-places, or by air that 

 passes through coils of steam or hot water pipes, arc usually well 

 supplied with fresh air. 



Apartments warmed by air-tight coal or wood stoves, or by 

 steam coils and radiators, should have especial arrangements for 

 supplying fresh air ; without such special arrangements these 

 rooms are unfit for habitation. 



However large and pure the supply of air is to any apartment, 

 and however it may be warmed, it will still be oppressive and 

 unhealthy if moisture is not added, iu proportion to the rise in 

 temperature that the air undergoes while being conveyed from out 

 of doors to the places where it is to be breathed. 



The very important fact that air, at a low temperature, can con- 

 tain but a small amount of moisture in comparison to that it should 

 coiitaiu if raised to a high temperature, is usually entirely over- 

 looked; and the furnace or steam-heating apparatus is said to dry 

 the air. 



Let the air of a warm room be ever so dry, it will be found 

 upon analysis that a cubic foot of it contains more moisture than a 

 cubic foot of the out of door air, having absorbed this excess from 

 the walls, furniture, &c. of the room. 



The only remedy for a dry atmosphere is to cause vapor to be 

 thrown into it ; that is, we must have a large surface of hot water 

 so exposed that its vapor will be taken up by the air. 



The amount of vapor required depends upon the temperature of 

 the out of door air. When the temperature of the external air is 

 zero, about four and one-half grains of vapor must be added per 

 cubic foot of air, to make it healthy to breathe at a temperature 

 of 68°. When the temperature of the external air is 40°, only 

 about two grains of vapor is required to make it healthy. 



It makes no diflerence how the temperature is raised, moisture 

 must be added. Nature almost invariably follows this rule ; her 

 exceptions have created the deserts of Asia and Africa. 



The hygrodeik will show at a glance the amount of nioisture 

 already in the air, and also what must be added to or taken from 

 it to render it healthy and pleasant. 



Temperature. 

 It will be found, upon investigation, that scarcely two persons 

 will agree upon the temperature at which the air of a room should 

 be maintained for comfort ; one will keep his room at 65°, while 



