62 Mr. T. Tate’s Hxperimental Researches on the 
rate of discharge was nearly doubled by the addition of 38° of 
temperature. ; 
With the sponge-filter the following results were obtained :— 
Time in seconds to discharge 1] eubic inches of water. 
At 50°, At 80°. At 90°. At 100°, 
420" 286" 246" 204! 
Here an increase of temperature from 50° to 90° caused the 
rate of discharge to be increased ]:707 times, a result nearly 
coinciding with that determined for the charcoal filter. At 100° 
temperature the rate of discharge is a little more than double the 
rate at 50°. These results further show that, for equal volumes 
of discharge, the decrements of time are for the most part propor- 
tional to the increments of temperature. 
The following experiment was made to determine the rates of 
filtration of different liquids as compared with that of water. 
Experiment XX1. 
The filter used in this experiment was charcoal; and the 
liquids compared were distilled water, and three different solu- 
tions of carbonate of soda. Solution No. 1 contained 2 per cent. 
of carbonate of soda; No. 2 contained 4 per cent.; and No. 3 
contained 8 per cent.; that is to say, the per-centage of the salt 
in these different solutions were in the geometrical progression 
2,4, 8. The discharge in each case was produced under the 
pressure of a column of 9:2 inches of the liquid. 
Time in minutes to discharge 
one cubic inch of the liquids. 
Water .fieit ets. 27 o= Zo 1S 
Now 2 2.  P87=17%8 x 108" nega 
Occ: nick alts Aderd) CRUG Rao sa ae 
IN Ops veins « larga ere aoe 
Here it will be observed that the rates of discharge are very 
nearly in geometrical progression. This property of filtration is 
analogous to that of absorption, as shown in connexion with ex- 
periments XI.and XII. Thus it appears that the chemical com- 
position of aliquid affects its relative rate of filtration. 
In general the rate of filtration or filtrativeness of a liquid 
seems to depend mainly upon its viscosity, and not so much 
upon its specific gravity. Alcohol, oils, &c., which have a less 
specific gravity than water, have a low rate of filtration. Solu- 
tions of sugar and starch, even when much diluted, have very 
low rates of filtration as compared with that of water; whilst 
diluted acids and weak solutions of alkaline salts, for the most 
part, have a rate of filtration nearly equal to that of water. In 
rc Se 
