ME. T. GEAHAM ON LIQUID DIFFUSION APPLIED TO ANALYSIS. 
201 
The rate of diffusion in water alone, without the septum, would have been doubled by 
an equal rise of temperature instead of being increased one-third only as above. 
The small glass bell-jar (fig. 3) formerly used as an osmometer, was conveniently 
Fig. S.—Bulb Dialyser. 
applied to dialytic experiments. Two sizes of the bulb were employed, 3T4 and 4’44 
inches in diameter respectively, and of which the dialytic septa possessed an area very 
nearly of y-^dth and g^dth of a square metre (15’6 and 7’8 square inches). With 100 
cub. cents, of fluid in the osmometer (the volume usually employed), the septum of the 
smaller instrument was covered to a depth of about 20 millimetres (0-8 inch), and the 
septum of the larger to a depth of 10 millimetres (0’4 inch). The thinner the stratum, 
the more exhaustive the difiusion in a given time. It is generally unadvisable to cover 
the septum deeper than 10 or 12 millimetres (half an inch), where a considerable diffu- 
sion is desired within tsventy-four hours. The following practical observations may be 
found useful in applying the dialyser to actual cases of analysis. They refer to the 
parchment-paper septum, which is much the most convenient for use. 
With a 2 per cent, solution of chloride of sodium, containing 2 grammes of the salt, 
and covering a septum of nearly O'Ol square metre (15’6 square inches) in area, to a 
depth of 10 millimetres, the salt which diffused in five hours amounted to 0'75 gramme, 
and in twenty-four hours to 1’657 gramme, leaving behind 0‘343 gramme, or 17T per 
cent, of the original salt. The following experiments, made with the same osmometer 
and solution, show the effect of reducing the volume of liquid placed in the dialyser. 
The proportion of salt which diffused out in twenty-four hours was — 
From 100 cub. cents, of solution 86 per cent. 
From 50 cub. cents, of solution 92 per cent. 
From 25 cub. cents, of solution 96 per cent. 
In all cases the volume of water outside into which the salt escaped was ample, being 
from five to ten times greater than the volume of fluid placed in the dialyser, and it was 
changed during the continuance of the experiment. A much less volume of external 
water suffices, pro-vided it is changed at intervals of a few hours. The temperature was 
MDCCCLXI. 2 F 
