1821.] Causes of Calorific Capacity, Latent Heat, fyc. 381 



they can be but of little value, however great, or however splen- 

 did, unless they conduce to the comfort, or add to the conve- 

 nience and benefit of mankind. 



From this corollary, a curious method presents itself of drying 

 a room with cold water. For if a large vessel of water below the 

 temperature at which the vapour of the atmosphere in the room 

 would be sensibly deposited, be brought into the room, the water 

 would rapidly condense all the vapour which contributes to make 

 its elasticity in a vacuum more than the proper tension of vapour 

 at the temperature of the water. If, therefore, the tempera- 

 ture of the water be sufficiently low, a very considerable part of 

 the vapour may be condensed, and the room rendered apparently 

 very dry. Such a method as this is familiar to philosophers, but 

 they have not yet succeeded to bring the effects to mathematical 

 rules. The thing, however, is very easy. Let t be the tension 

 of vapour corresponding to the temperature of the room, t' the 

 same thing corresponding to the temperature at which sensible 

 deposition commences, and r" the tension of vapour at the tem- 

 perature of the water. Then, by this cor. the humidity of the 



air is -, and the humidity after the water has condensed all it 

 can — . The effect of the water, is, therefore. . If r" be 



T T 



less than t', the water contributes to dry the room ; if t" = t', 

 it produces no effect ; but if t" exceed t', it tends to make it 

 damper. 



Do not these views present us with a simple efficacious method 

 of rendering the air of a room where there is a large company 

 more healthy by condensing the noxious vapours as they ascend 

 on a current of cold water, or on a surface of broken ice near 

 the ceiling ? By either of these methods, but especially the 

 last, the air of a room, if the ice he placed in different parts before 

 the company enter, may be preserved wholesome where the party 

 is large without any sensible inconvenience or offence. The ice, 

 if in large pieces, will take a very considerable time to liquefy, 

 and the condensations from the exterior of the vessels may be 

 caught and prevented from falling on the company in reservoirs 

 of obvious contrivance beneath. 



A method first, I believe, proposed by Dr. Franklin, has, within 

 these few years, been practised of heating rooms with air that 

 has passed through a warm tube. Such a method is very simple, 

 uud, perhaps, not very insalubrious, provided the pipe be not too 

 hot, and the air come from a dry and healthy region ; but if the 

 pipe derive its air from a damp atmosphere, or a low humid 

 situation, it is fraught with much inconvenience and mischief. 

 I recollect hearing some of my friends in Bristol, who had rooms 

 heated this way, with pipes receiving their air from near the 

 liver, complain much of an unpleasant dampness the heated air 

 brought with it, while another gentlemen, ofconsiderable science, 



