188 
ME. T. GEAHAM ON LIQIND DIEFUSION APPLIED TO ANALYSIS. 
Table I. — Diffusion of 10 per cent, solutions (10 grammes of substance in 100 cub. cent, 
of fluid) into pure water, after fourteen days, at 10° (50° Fahe.). 
Number of stratum 
(from above downwards). 
Chloride of sodium. 
Sugar. 
Q-um, 
Tannin. 
1 
•104 
•005 
•003 
•003 
2 
•129 
•008 
•003 
•003 
3 
•162 
•012 
•003 
•004 
4 
•198 
•016 
•004 
•003 
5 
•267 
•030 
•003 
•005 
6 
•340 
•059 
•004 
•007 
7 
•429 
•102 
•006 
•017 
8 
•535 
•180 
•031 
•031 
9 
•654 
•305 
•097 
•069 
10 
•766 
•495 
•215 
•145 
11 
•881 
•740 
•407 
•288 
12 
•991 
1-075 
•734 
•556 
13 
i-ogo 
1-435 
1-157 
1-050 
14 
1-187 
1-758 
1-731 
1-719 
15 and l6 
2-266 
3*783 
5-601 
6-097 
9-999 
10-003 
9-999 
9-997 
The superimposed column of water being 111 millimetres (4-38 inches) in hoight, 
the chloride of sodium, it will be observed, has diffused in sensible quantity to the top, 
and could have risen higher; the upper layer being found to contain 0T04 gramme of 
salt, or 1 per cent, of the whole quantity present. The apex of the diffusion column of 
sugar appears to have just reached the top of the liquid in the fourteen days of the experi- 
ment, for ‘005 gramme only of that substance is found in the first stratum, followed by 
•008, -012, '016, and '080 in the following strata. Again, no gum appears to be carried 
by difiusion higher than the seventh stratum (2 2 inches), which stratum contains *006 
gramme, followed by 'OSl gramme in the eighth stratum. The minute quantities of 
substance shown in the first to the sixth stratum, and which do not altogether exceed 
•020 gramme, are no doubt the result of accidental dispersion, arising probably from a 
movement of the upper fluid occasioned by slight inequalities of temperature. The 
difiusion of tannin is even less advanced than that of gum ; but the former numbers are 
apparently influenced by a partial decomposition, to which tannin is known to be liable, 
and which gives rise to new and more highly difiusible substances. 
Experiments continued, like those last described, for a constant time, do not exhibit 
the exact relative difiusibilities, although these could be obtained by proceeding to 
ascertain, by repeated trial, the various times required to bring about a similar distribu- 
tion and equal amount of difiusion in all the salts. The numbers observed, however, 
may afford data for the deduction of the relative difiusibilities by calculation. 
A particular advantage of the new method is the means which it affords of ascertain- 
ing the absolute rate or velocity of difiusion. It becomes possible to state the distance 
which a salt travels per second in terms of the metre. It is easy to see that such a 
constant must enter into all the chronic phenomena of physiology, and that it holds a 
place in vital science not unlike the time of the falling of heavy bodies in the physics of 
