ME. T. GEAHAM ON LIQTJID DIEFUSION APPLIED TO ANALYSIS. 
187 
of a litre of the liquid to be diffused was carefully conveyed to the bottom of the jar 
by means of a fine pipette. The whole fluid column then measured 127 millimetres 
(5 inches) in height. So much as five or six minutes of time were occupied in emptying 
the pipette at the bottom of the jar, and extremely little disturbance was occasioned in 
the superincumbent water, as could be distinctly seen when the liquid introduced by 
the pipette was coloured. The jar was then left undisturbed, to allow diffusion to pro- 
ceed ; the experiments being always conducted in an apartment of constant, or nearly 
constant temperature. When a certain time had elapsed, the diffusion was interrupted 
by drawing off the hquid from the top, by means of a small siphon, slowly and delibe- 
rately as the liquid had been first introduced, in portions of 50 cubic centimetres, or 
one-sixteenth of the whole volume. The open end of the short limb of the siphon was 
kept in contact with the surface of the liquid in the jar, and the portion of liquid drawn 
off was received in a graduated measure. By evaporating each fraction separately, the 
quantity of salt which had risen into equal sections of the liquid column was ascertained. 
From the bottom of two jars, A and B for instance, a 10 per cent, solution of chloride 
of sodium was diffused for a period of fourteen days. The whole quantity of salt present 
in each jar was 10 grammes, which was found at the end to be distributed as follows in 
the different sectional strata of fluid, numbering them from the top downwards : — 
In the first or highest stratum, 0T03 and 0T05 gramme of salt in A and B respect- 
ively; in the second stratum, 0T33 and 0T25 ; in the third stratum, 0T65 and 0T58; 
in the fourth stratum, 0'204 and 0T93; in the fifth stratum, 0’273 and 0’260; in the 
sixth stratum, 0‘348 and 0‘332 ; in the seventh stratum, 0‘440 and 0’418 ; in the eighth 
stratum, 0*545 and 0*525 ; in the ninth stratum, 0*657 and 0*652 ; in the tenth stratum, 
0*786 and 0*747; in the eleventh stratum, 0*887 and 0*875; in the twelfth stratum, 
0*994 and 0*984 ; in the thirteenth stratum, 1*080 and 1*1 00 ; in the fourteenth stratum, 
1*176 and 1*198 ; in the fifteenth and sixteenth strata together, 2*209 and 2*324 grammes. 
With differences so moderate in amount between corresponding strata in the two expe- 
riments, this method of observing diffusion may claim a considerable degree of pre- 
cision. 
In similar experiments made at the same time and temperature with sugar, gum- 
arabic and tannin of nut-galls, the final distribution of each substance was different in 
each case, and the results may be placed together in illustration of unequal diffusibility, 
as exhibited by this method of observation. Two experiments were made on each sub- 
stance, as with chloride of sodium, but the mean result only need be stated. 
2 D 2 
