374 Mr. T. Graham on Liquid Diffusion applied to Analysis, 



have been slightly retarded by the fixing of the gelatinous solu- 

 tion. This is probably due to the arrest of mechanical move- 

 ment 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 tersulphidc of arsenic 

 weighed 0*320 gramme, equivalent to 0*257 arsenious acid. 



5. A quantity of white of egg, amounting to 50 grammes, to 

 which 0*01 gramme of arsenious acid in solution had been added, 

 was coagulated by heat. The solid mass was then cut up into 

 small pieces and placed on the dialyser, mixed with 50 grammes 

 of water; after the usual period of twenty-four hours, the dif- 

 fusate gave 0*01 gramme of tersulphide of arsenic, equivalent to 

 0*008 gramme arsenious acid. Here, of the mass upon the dia- 

 lyser, the arsenious acid formed only — -L— -th part; yet four- 

 fifths of it are recovered. 



6. One hundred grammes of milk, charged with * th 

 part of arsenious acid (0*01 gramme), and forming a 'stratum on 

 the dialyser of 10 millimetres, gave a diffusate which yielded 

 0*010 tersulphide of arsenic, equivalent to 0*008 gramme of 

 arsenious acid. The outer liquid was colourless, and gave no 

 indication of caseine, but it contained, of course, the salts and the 

 sugar of the milk. 



7. The same experiment was repeated with sized writing- 

 paper as the septum, applied to the same bulb. The result 

 was a slight increase in the quantity of arsenious acid recovered. 



It appears, then, that arsenious acid separates on the dialyser 

 from gum, from gelatine, albumen, fluid or coagulated, and from 

 caseine, and is obtained in a solution fit for the application of 

 reagents. 



8. Half a litre of dark-coloured porter, with 0*05 gramme of 

 arsenious acid added ( * th part of arsenious acid) was 

 placed on a hoop dialyser, 8 inches in diameter, and the whole 

 floated in an earthenware basin containing 2 or 3 litres of water. 

 After twenty-four hours the latter fluid had acquired a slight 

 tinge of yellow. It yielded, when concentrated and precipitated 

 by sulphuretted hydrogen, upwards of one-half of the original 

 arsenious acid in a fit state for examination. 



9. In a similar experiment on 200 grammes of defibrinated 

 blood charged with 40 1 QQ th part of arsenious acid (0*05 gramme), 

 and placed on a similar dialyser to the last for twenty-four hours, 

 the diffusate of arsenious acid was recovered with the same facility, 

 and appeared to be equally considerable. 



10. Animal intestines, charged with the usual minute propor- 

 tion of arsenious acid, were cut into small pieces and digested in 



