132 Mr. T. Tate's Experimental Researches on Absorption. 



were obtained for fine sand, wood, and other porous sub- 

 stances. 



A sector of unsized paper was placed on the absorbent tube, 

 first with its surface in a horizontal position, and second with its 

 surface bent vertically downwards,, In the first case, the num- 

 bers of minutes corresponding to successive equal quantities of 

 absorption were 20, 20, 21, 21-5, 22, 23, 232, 23*4; whereas in 

 the second case the times for the same amount of absorption 

 were 18, 18, 19, 19, 20, 20«5, 21, 21. 



In like manner a sector of calico, in four folds, was placed on 

 the absorbent tube : in the horizontal position one-half of a cubic 

 inch of water was absorbed in 95 minutes, whereas in the vertical 

 position the same volume of water was absorbed in 87 minutes. 



This experiment shows that the rate of absorption is slightly 

 affected by the gravity of the liquid absorbed. When water is 

 diffused from a central point in the surface of the absorbent (as 

 in Exp. 5, Phil. Mag. vol. xx. p. 500), the rate of diffusion 

 (within certain limits of range) in an upward direction is the 

 same, or practically the same, as it is in the horizontal direction. 

 But it appears from the foregoing experiment that, when the 

 upward and downward currents are divided, the effect of the 

 gravity of the liquid becomes appreciable. Within short distances 

 of the central point of diffusion, the force arising from the gra- 

 vity of the liquid absorbed is exceedingly small as compared with 

 the force of absorption ; but as the former is an accumulative 

 force, whilst the latter is a constant force acting against a conti- 

 nually increasing resistance, the effects of the gravity of the 

 liquid at length become appreciable. The law of absorption, 

 therefore, given in the article above referred to, must only be 

 accepted with these limitations. 



2. The rate of absorption (in the case of substances composed 

 of loose material) is not much affected by a reduction of the pres- 

 sure of the liquid on the absorbent. 



Thus an experiment was made with a calico absorbent under 

 different pressures : viz., first, when the pressures on both sides 

 of the absorbent were the same, that is, equal to that of the 

 atmosphere; and second, when the pressure of the liquid on the 

 under side of the absorbent was less than the atmospheric pres- 

 sure on the upper side by the pressure of a column of water 7 

 inches high. For equal volumes of water absorbed, the times in 

 the two cases were 13'5 minutes and 16 minutes respectively. 



3. The rate of absorption increases with the diameter of the 

 liquid circle in contact with the surface of the absorbent ; also, 

 in the case of sheets of paper and textile fabrics, it increases 

 with the number of the sheets, or with the thickness of the 

 material placed in contact with the liquid. 



