Laws of Absorption of Liquids by Porous Substances. 509 



indicated by the thermometer, rose to (36 0, 5, giving a maximum 

 rise of 10 o, 5 due to the heat evolved by absorption. 



This change of specific heat, which always takes place during 

 the process of absorption, is doubtless indicative of chemical 

 action. 



It may be worthy of remark, that an absorbent may be used 

 again and again, with distilled water, without suffering any 

 change in its power of absorption. 



The following experiments were made to determine a statical 

 measure of the force of absorption in different porous substances. 



Experiment XV. 



By means of the apparatus represented in the annexed dia- 

 gram, the effect of the force of absorption in elevating a column 

 of liquid may be strikingly ex- 

 hibited. ABCDa bent tube, 

 open at both extremities, having 

 the portion ABC considerably 

 wider than the other portion 

 CDK; the portion A B con- 

 tains mercury, and that of B C 

 water; FG a piece of dry 

 calico, having a narrow strip, 

 m n, proceeding from it, insert- 

 ed through the mercury in con- 

 tact with the water B C ; the 

 extremity K of the tube C D is 

 inserted in a vessel E, contain- 

 ing water. As the absorbent, 

 F G, draws the liquid from B C, 

 the water rises in the tube K C 

 in opposition to gravity. If the diameter of the tube C D be 

 T ^ths of an inch, the water will have risen in the tube K C to 

 the height of about 9 inches in the course of six hours, the air 

 being in an average state of dryness ; and when the air is un- 

 usually warm and dry, to a much greater height in that time. 

 The effect is simply due to the force of absorption, there being 

 no endosmose connected with the phenomenon. 



The following form of this apparatus enables us to measure the 

 force of absorption by the fall of a column of mercury. 



L E D C a small bent tube proceeding from a wide tube or 

 cup L P, ground at the top, which is covered by a plate, P K, 

 of polished slate, having one or more small 'perforations, 0, 

 through it; FG an absorbent placed upon the plate. The 

 bent portion LEDC contains mercury, and the cup, L P, is 

 filled with water. As the liquid diffuses itself through the pores 



rD 



