218 
ME. T. fiEAHAM ON LIQUID DIEEUSION APPLIED TO ANALYSIS. 
four times greater than the volume of organic fluid in the dialyser. The water of the 
basin is generally found to remain colourless after the lapse of twenty-four hours, and 
after being concentrated by evaporation, it admits of the application of the proper 
reagents to precipitate and remove a metal from solution. One-half to three-fourths of 
the crystalloidal and difiiisible constituents of the organic fluid will generally be found 
in the water of the basin. 
In the few illustrative experiments which follow, the 4-inch bulb dialyser, having an 
area of 16 square inches, or about j^odth part of a square metre, was generally made 
use of (fig. 3, p. 201). The volume of liquid placed in the bulb was 50 cubic centi- 
metres, and accordingly covered the dialyser to a depth of 5 millimetres, or about 0'2 
mch. The outer volume of water (in the jar) was not less than 1 litre, or twenty times 
the volume of the solution on the dialyser. 
1. A solution of arsenious acid, in pure water, was first placed on the dialyser, the 
water containing 0’5 per cent, of arsenious acid, or 0’25 gramme of that substance, for 
twenty-four hours. The dialyser being then removed, the outer fluid was concentrated 
by heat, and then precipitated by sulphuretted hydrogen. It gave 0‘300 gramme of 
tersulpliide of arsenic, equivalent to 0‘241 gramme of arsenious acid. It appears, then, 
that about 95 per cent, of the arsenious acid had diffused from the dialyser into the 
water-jar in twenty-four hours. 
2. Water, with one-fourth of its volume of fluid egg albumen and 0’25 gramme, or 
0'5 per cent, of arsenious acid, was now placed on the dialyser as before. The difiiisate 
gave, with sulphuretted hydrogen, after being acidulated with hydrochloric acid, 0-267 
gramme of ter sulphide of arsenic, equivalent to 0-214 gramrne of arsenious acid. 
3. The water contained 10 per cent, of gum-arabic and 1 per cent, arsenious acid, the 
latter amomiting to 0-5 gramme. From the diffusate was derived 0-505 gramme of ter- 
sulphide of arsenic, equivalent to 0-406 gramme of arsenious acid. The dialyser still 
gave out arsenious acid when immersed for a second day in water. The outer fluid 
contained no gum. 
It may be added that a similar 1 per cent, solution of arsenious acid, without the gum, 
gave a diffusate of 0-45 gramme arsenious acid in the same time, that is, nine-tenths of 
the whole acid. 
4. A solution in hot water of 1 per cent, isinglass and 0-5 per cent, of arsenious acid 
(0-25 gi’amme), formed a jelly upon the dialyser on cooling. The diffusate from this 
jelly gave 0-260 tersulphide of arsenic, equivalent to 0-209 arsenious acid, with no gela- 
tine. The escape of the arsenious acid appears then to have been slightly retarded by 
the fixing of the gelatinous solution. This is probably due to the arrest of mechanical 
movement within the gelatinous stratum, and not to any sensible impediment offered by 
the jelly to diffusion. 
In another experiment, similar to the last, but continued for four days instead of 
twenty-four hours, the tersulphide of arsenic weighed 0-320 gramme, equivalent to 
0-257 arsenious acid. 
