Mr. T. Graham on Liquid Diffusion applied to Analysis. 373 



dialyser is then floated in a basin containing a volume of water 

 about 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 diffusible con- 

 stituents 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 

 xxroth part of a square metre, was generally made use of (figs. 3 & 4, 

 pp. 291, 292). The volume of liquid placed in the bulb was 50 

 cubic centimetres, and accordingly covered the dialyser to a depth 

 of 5 millimetres, or about 0*2 inch. 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 concen- 

 trated by heat, and then precipitated by sulphuretted hydrogen. 

 It gave 0*300 gramme of tersulphide 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 diffusate gave, with sul- 

 phuretted hydrogen, after being acidulated with hydrochloric 

 acid, 0*267 gramme of tersulphide of arsenic, equivalent to 0*214 

 gramme of arsenious acid. 



3. The water contained 10 per cent, of gum-arabic and 1 per 

 cent, arsenious acid, the latter amounting to 0*5 gramme. From 

 the diffusate was derived 0*505 gramme of tersulphide 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 gramme), 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 gelatine. The escape of the arsenious acid appears then to 



