308 iJATURE AND DETECTION OF METALLIC POISONS, 



process re- two reagents, which, I think, will not only be found free from 

 commended, (j^g objections applicable to those already mentioned, but ap- 

 peared to combiije most of the advantages requisite in opera- 

 Tvv» tests pro- tions of such extreme delicacy. The reagents employed were 

 posed. ji^g acetate of copper, aad oxyacetate of iron. For the pre- 



paration of them it is merely necessary to decompose oxysul- 

 phate of iron, and sulphate of copper, by acetate of lead, ad- 

 ding the latter until a turbidness ceases to appear. The result- 

 ing mixtures should contain as little of the original ingredients 

 in combination as possible ; particularly the iron test, since an 

 excess of the oxysulphate, as was observed in our experiments, 

 suspends the action of the acetate, and prevents its combination 

 with the arsenic. The presence of acetate of lead is objection- 

 able from its causing a precipitate with arsenic, which cannot 

 be distinguished by the eye from sulphate of lead. When the 

 two acetates are properly prepared, they combine with arsenic 

 with considerable facility ; tbat of iron producing a bright 

 orange yellow deposit, and that of copper, green. The de- 

 composition, however, especially of the former, does not ap- 

 pear to be complete till they have been suffered to stand a few 

 Advantages in seconds. One of the great advantages attending these reagents 



the use of these jg that their action is independent of the use of alkali, which, 

 tests. . , ^ ^ ^ , . . .^ , 



in the two former processes, irom the precipitate uniformly 



occasioned by its presence, throws considerable uncertainty 

 over the results of an experiment ; and where the mixtures are 

 coloured, as will always be the case, in a greater or less degree, 

 in examining the contents of the stomach, must rob these 

 methods of the whole of their value. With the tests here 

 recommended, the colour of the compounds produced is not of 

 that primary importance ; for, since almost all their combina- 

 tions, particularly those of copper, are soluble in water, except 

 the one produced by an union with the white oxide of arsenic, 

 the appearance of any precipitate may, without much risk, be 

 Oftl th- *'^^^*'''^'^ ^^ ^^*^ presence of this metal. Of the two, experience 



acetate of cop- has confirmed us in a preference of the acetate of copper, 

 per prefer- partly from its more sensible action on arsenical mixtures, and 

 in some measure, also, from' the easier mode of its preparation, 

 p . As the oxyacetate of iron, however, may sometimes be occa- 



of the oxya- sionally resorted to, in order to afford additional evidence of the 

 cetate of iron, accuracy of an experiment, it may be necessary to add, as a 



farther 



