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



Dissolve a few grains, say ten, of the nitrate of silver 

 called lunar caustic, in about nine or ten times its weight 

 of distilled water; to this add, by a drop at a time, a solu- 

 tion of ammonia till a precipitate is formed. Continue to 

 add the ammonia, now and then shaking the bottle, till the 

 precipitate shall be taken up and the solution again become 

 transparent, or nearly so, as the ammonia need not be in 

 great excess, if in any ; for, solution of ammonia being 

 lighter than water, the superfluous portion would remain on 

 the surface of any fluid to which this test-liquor may be 

 applied, — a circumstance not noticed by other analysts. 



Here we have one simple liquid, which, if kept in a 

 phial with a glaes stopper, will not easily spoil, and may 

 be always at hand. Its application is also equally simple ; 

 for nothing more is required than to dip a piece of glass 

 into this liquor, and apply it to the solution containing ar- 

 senic. Should the material suspected to contain arsenic 

 be of a dry nature, such as a mixture of sugar, meal, bread, 

 meat, or any other kind of fond, let some boiling water he 

 poured upon the suspected substance, and filtrate thesolulion 

 through paper. The strip of glass may be procured at any 

 glazier's shop; but, if not at hand, a few drops of the test 

 From the phial mav be put in, as there is here not so much 

 uncertainty from an excess of alkali, nor even of the test- 

 liquor itself. 



In the 2d volume of " Medico-chirurgical Transactions," 

 there is a " Case of Recovery from Arsenic," by Dr. Rogtt, 

 in which mv test of silver was employed with great advan- 

 tage. The whole chemical part of this paper is, however, de - 

 scribed in such a way, that whoever reads the *' case" 

 would readily believe that Dr. Marcet, and not I, had 

 originally projected this most delicate test ; especially when 

 my pretensions are «o pointedlv censured and slurred over 

 by Dr. R. who has indted condescended to quote, though 

 not accurately, mv letter to you. 



In that paper Dr. Rdoet has ushered in my own process for 

 detecting arsenic wiih arnmnnia and nitrate of silver ; but this 

 is described as altogether a vew test, to which no reader 

 would suppose Ihad the least claim. On the present occasion 

 I shall make but few remarks upon the injustice done me by 

 this ffentleman's publication ; but it is evident that my own 

 observations upon the test by means of silver, are placed in 

 the Medico-chiriirgical Transactions as original matter; as 

 well as the remarks I made on some of the peculiar and 

 reciprocal habitudes of white oxide of arsenic, the arsenical 

 acid, and nitrate of silver, which are all derived from the 



three 



