Laws of Absorption of Liquids by Porous Substances. 61 
Beat cece | Geral Seas 
liquid, seconds, descent, h 
h. ts wu. u= 303° 
agen eit abe e 
105 a - 
93 «(«| (8 2 = 
8 5 03 S 
Be | gag oo Ph ae 
o8 174 * ny 
25 225 * e 
45:1. 986 pelea ae 
Biol Lapa yior|. > - Pain a 
25 «(| (G6 aa 
Bee gape ah FT | 
The results of this experiment show that, for the first nine 
units of descent, the velocity of discharge varies almost exactly 
as the height of the column of liquid. For the last two units, 
the rate of discharge considerably exceeded that which the for- 
mula v= = would give, showing that the effect of the absorb- 
ent power of the filter greatly exceeded that which would be due 
to the pressure alone. 
This experiment was repeated with little or no variation in 
the results. 
Similar results were obtained from filters formed of plugs of 
different sorts of soft porous material ; also from a filter formed 
of fine sea-sand laid upon a perforated plate. 
The followmg experiment was made to determine the variation 
of the rate of filtration due to increase of temperature. 
Experiment XX. 
The liquid used in this experiment was distilled water, and 
the filters were those employed in Experiments XVI. and XIX. 
With the charcoal filter under a constant pressure, the time 
required to discharge one cubic inch of liquid at 52° tempera- 
ture was 114 seconds; whereas at the temperature of 90° it only 
required 65 seconds. In this case an increase of 38° of tem- 
perature increased the rate of discharge 12 times; that is, the 
