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XLIX. Experimental Researches on the Laws of Absorption of 



Liquids by Porous Substances. By Thomas Tate, Esq.* 



[With a Plate] 



THE ascent of liquids in porous substances has hitherto been 

 regarded by physicists as similar to, if not identical with, 

 the ascent of liquids m capillary tubes ; but the following re- 

 searches show that the former phenomena are regulated by pe- 

 culiar and distinctive laws. I was first led to this inquiry by 

 observing the large portion of water which had been evaporated, 

 in the course of a day, from a vase of flowers. Vegetable and 

 animal life are, no doubt, intimately connected with the laws 

 regulating the absorption of liquids by porous substances. 



The following general laws have been derived from the results 

 of these experiments. 



In an atmosphere saturated with the vapour of the liquid, 



(1) The rate of diffusion varies inversely as the space through 

 which the liquid of absorption has moved. 



(2) The rate of diffusion, at equal distances from the surface 

 of the liquid with which the absorbent is in contact, is equal in 

 all directions, that is to say, the rate of diffusion is independent 

 of the force of gravity. 



(3) The rate of diffusion, other things being the same, in- 

 creases with the temperature. 



(4) The liquid diffuses itself equally over the surface of the 

 absorbent ; that is, the weight of the liquid absorbed by a unit 

 of surface is everywhere the same. 



(5) In equal times the force of absorption performs the same 

 amount of work or dynamic effect. 



(6) If an absorbent, saturated with moisture, be exposed to a 

 dry atmosphere, the evaporation goes on for the most part uni- 

 formly. And so on to other laws, which will be hereafter 

 illustrated. 



1. Rate of diffusion of liquids through absorbents in an atmo- 

 sphere saturated with the vapour of the liquid. 



The absorbents employed in these experiments were strips of 

 unsized paper, calico, linen, &c, of various thicknesses and 

 texture, and also thin columns of plaster of Paris. The liquids 

 used were distilled water, turpentine, linseed oil, alcohol, solu- 

 tions of starch, together with solutions of different salts, &c. 

 The line formed by the liquid in its ascent on the strips of un- 

 sized paper is so distinct and sharply defined as to enable us to 

 determine, with the greatest precision, the distance of this line 

 from the level surface of the liquid. The strips of paper, calico, 

 * Communicated by the Author. 



