_e._ _Sulphuretted hydrogen._ This is a very delicate test for arsenic, producing with its solution a beautiful golden coloured liquor, which, after a short time, lets fall a precipitate, and which will take place sooner if a small quantity of acetic acid be added. By this re-agent so small a quantity as 1/100000 may be detected in solution. The test, however, is not, says _Dr. Bostock_, sufficiently discriminative to be depended upon alone; since _tartarized antimony_ and some other bodies, will produce phenomena that may be mistaken for the effects of arsenic. It has, however, the merit of not being affected by _tannin_, and may therefore be conveniently employed for precipitating arsenious acid, when dissolved in tea. _f._ _Lime water_ produces with the solution of arsenic a beautiful white precipitate of _arsenite of lime_, which easily dissolves in an excess of arsenious acid. The precipitates occasioned by the foregoing reagents, should be carefully collected, and treated with _black flux_, in a glass tube, for the purpose of obtaining the metallic sublimate, as above described. We cannot quit this part of our subject without directing the reader’s attention to the chemical evidence given by _Dr. Addington_, on the trial of _Mary Blandy_ (_see Appendix, p._ 241) to prove that arsenic was contained in a powder with which she was supposed to have poisoned her father. To those in the least acquainted with the habitudes of arsenious acid, it must be evident, that no one of the appearances described by _Dr. Addington_ indicates the presence of arsenic;[258] and his evidence is only to be reconciled upon the supposition that, instead of the arsenic itself, he, in this case, detected the foreign substances with which it had been adulterated; thus it has been before stated that _white arsenic_, as sold by the druggists, is often adulterated with _sulphate of lime_; and the decomposition of this substance by the _sub-carbonate of ammonia_ (“_Spirit of sal-ammoniac_”) or by the _sub-carbonate of potass_ (“_Lixivium of tartar_”) would occasion the precipitation of a white substance, as stated in the evidence; it is however difficult to account for the “considerable precipitation of a lightish coloured substance” by muriatic acid (_spirit of salt_) by the presence of any impurity likely to be contained in the arsenic, or in the water employed for its solution. If any lime were present, it would probably give “white glittering crystals” of sulphate of lime, by the addition of sulphuric acid (_spirits of vitriol_). The only plausible evidence of the presence of arsenic in the suspected powder is “the alliaceous smell and white flowers” which _Dr. Addington_ describes as occurring when it was thrown on red hot iron; it must however be confessed, that from the fallacy of the other experiments, it is even impossible to place any confidence in those last mentioned.