108 Mr. Hume's Remarks on his Test for Arsenic, 



the application of a spirit lamp the solution was matle to 

 boil, when the oxide became entirely (.iissolvcd. A- the 

 vessel with its contents had been previously weighed, any 

 deficiency by the operation of boiling was easily rcnii;ii < d, 

 ^y adding to the fluid, when cold, more distilled water to 

 complete the 5000 grains, being the original weight of the 

 solution. 



Fifty grains of this solution, containing -~o^^ of a grain 

 of arsenic, were further diluted with 500 grains of distilled 

 water, and to this the test-liquor was applied bv means of 

 a small strip of glass. Another 50 grains of the solution 

 was treated in the same way with 1000; — a third with 

 1500, and so on, progressively, in the same ratio, until I 

 had arrived ai 5000 grains of the distilled water. At this 

 point I deemed it but fair to stop, being perfectly assured 

 of the efficacy of the test in anv case that can possibly re- 

 quire its aid, since the proportion of the arsenic to the 

 water was in the last experiment as about one to 500,000, 

 a degree of nicety to which I had never expected to attain. 



1 must observe, that, in proportion to the degree of di- 

 lution more or less time should be allowed for the effect to 

 become perceptible ; for, in the last experiment the test did 

 not act till some minutes had elapsed, and then the fluid 

 became slightly tinged without losing its transparency, 

 appearing more like very dilute white wme and water. In 

 the course of some hours, perhaps 12, an evident dark' 

 coloured precipitate had assembled at the bottom, a sure 

 indication of the presence of arsenic; for all these precipi- 

 tates, even the beautiful yellow, lose their first colour and 

 become dark ; setting aside all hopes of our converting 

 them into pigments. 



I prefer cylindrical glass- vessels to watch-glasses for such 

 experiments ; and where verv minute portions of arsenic 

 are to be made manifest by the^e means, it is prudent to 

 place a similar vessel, filled with distilled water, near to the 

 first, so that b) contrasting the contents of these two ves- 

 sels the slightest change will be more conspicuous. 



I have now, it is presumed, confirmed my claim to the 

 arsen'cal test by m£ans of silver, and brought into notice 

 what must be considered as an acceptable improvement in 

 chemistry and its dependent science, metallurgy : it will 

 likewise afford to British juries a more sure guide to their 

 decisions, in all such criminal cases where the existence of 

 arsenic must be ascertained, by calling for the evidence of 

 this test J and hence,, the laws of our country in the ad- 

 ministration 



