oct. — mar. 1859-60.] Rooms in Tropical Climates. 323 



in the room, will be warmed up and rise to the higher parts, where 

 an exit may be conveniently afforded by the opening of an upper 

 sash of a window. Then, as the air expired from the lungs of 

 persons likewise rises in a room, from the high temperature more 

 than balancing the greater specific gravity of the gas, this will be 

 carried away also in the general upward stream ; and thus a per- 

 son placed in the room will never have to breathe the same air 

 twice over, a long-sought desideratum in ventilation, and the room 

 will be constantly filled, at least towards its lower parts, with the 

 coldest and freshest air which the machine can supply. 



Fig. 2 is a vertical section of a room so sunk in the ground, 

 and supplied with cold air by a pipe coming from the cooler, the 

 arrows showing the course of the air in passing through the room, 

 and out at last through the window. 



This is all that is required for the complete cooling and venti- 

 lation of the majority of rooms in India ; but in some, as we hint- 

 ed above, additional means are needed for the purpose of drying 

 the cold air. 



A method of effecting this without heating the air, is by expos- 

 ing it to metallic surfaces at a lower temperature, when the 

 moisture in the air will be condensed and deposited on the cold 

 metal. This may be brought about by passing the air, after its 

 escape from under the spring valve of the cooler, through another 

 worm of pipe in a tub where the water is kept always at a slightly 

 lower temperature than the air, either by having a second pump 

 compressing other air more than the first, and then allowing it to 

 bubble through the water of the drying tub, or by dissolving in it 

 continually large quantities of saltpetre and sal ammoniac, one of 

 the most useful of freezing mixtures, as the salts, on evaporation, 

 recrystallize separately ; and the same stock may therefore be used 

 over and over again indefinitely ; besides which they are both 

 found in great abundance in India. It is only necessary to have 

 a person occasionally to throw the salts into the tub ; and draw- 

 ing off the saturated water, expose it to the evaporating influence 

 of the sun and the wind, or, in default of those, to a fire. 



In fig. 3, a representation of the dryer of the cool and expanded 

 air is given. It is merely a thin copper tube, open at both ends, 

 and immersed as to its middle in a tub of water, to which the re- 

 Voi,. xx. o. s. Vol. vii. n. s. 



