the Laws of Evaporation and Absorption. 287 



capacity for absorption decreases according to a geometrical pro- 

 gression. 



It will be hereafter seen that a similar law applies to the solu- 

 tion of absorbent salts. 



It was further determined that, the strength of the acid being 

 constant, the amount of absorption in equal times varies (approxi- 

 mately) inversely as the depth of the liquid from the edge of the 

 vessel in which it is placed. 



Other things being the same, the rate of absorption increases 

 with the temperature. It was also found that the rate of absorp- 

 tion, other things being the same, increases with the decrease of 

 the atmospheric pressure. 



Absorption of moisture by solutions of chloride of sodium from 

 an atmosphere saturated with the vapour of water. 



In this case 2824 grains of a saturated solution of the salt 

 were successively diluted with 1000 grains of water, the diameter 

 of the vessel exposed to the humid air of the receiver being 6 

 inches : thus the second solution contained 2824 grains of the 

 saturated, or first solution, with the addition of 1000 grains of 

 water ; the third solution contained 3824 grains of the last solu- 

 tion, with the addition of 1000 grains of water ; and so on to the 

 other solutions. The results of experiment were as follows : — 



In twenty-four hours, the first, second, third, and fourth solu- 

 tions respectively absorbed 25, 15*4, 90, 6'0 and 4*1 grains of 

 moisture. 



Now these results are approximately expressed by the formula 

 g=25 x '6k, 

 where k= T -£ ul5 of the weight of the water added to the saturated 

 solution. 



It will be seen that this law of absorption is similar to that 

 determined for sulphuric acid. It appears, therefore, that the 

 rate of absorption has a determinate atomic relation. 



Spontaneous evaporation of moisture from different surfaces ex- 

 posed to the atmosphere. 



It has been shown in one of the foregoing papers, that the 

 evaporation from absorbents saturated with moisture is for the 

 most part uniform, the temperature and hygrometric state of the 

 air being constant. 



1. The rate of evaporation of moisture from damp porous sub- 

 stances, of the same material, is proportional to the extent of the 

 surface presented to the air, without regard to the relative thick- 

 nesses of the substances. 



Thus two pieces of calico, presenting 150 square inches of 

 surface, but the one folded double whilst the other was single, 



