On the Genumenefs and Purity of Drugs and Mcdicinet. iga 



III. 



On the Genuinenefs and Purity of Drugs and Medicines. By Mr, Fbid. Accvm. 



( Continued from page 36.^ 



METALS AND METALLIC SUBSTANCES. 



Mercury, ^ickftlver. — ^Ph. L. 



JL HE property which mercury poflefles of readily uniting with mod of the metals, with- 

 out fufFering any material change in its obvious properties, induces fraudulent dealers to 

 adulterate this article with lead, tin, &c. If thefe metals are prefent in any confiderable 

 quantity, the mercury will have a dull afpe£t, and will not run freely into round globules, 

 but when gently moved, it forms vermicular ftriae, ar tears. When agitated in a bottle, 

 it foon becomes black, the lead and tin becoming oxidated, and may thus be feparated, as 

 has been noticed in the Phllofophical Journal I. But as thefe metals arc fo eafily dete£ted, 

 and can only be added in a comparatively fmalF quantity, the dealers in this article have 

 recourfe to other pradlices. It is a faft, that bifmuth and zinc remarkably lavor the union 

 of lead with this metallic fluid, and that even tin may then be added in a confiderable 

 quantity. As It is impoffible to free mercury from thefe metals completely by a mere 

 agitation, recourfe muft be had to diflillation ; and even then the mercury cannot be ob- 

 tained peifeCily pure, unlefs the procefs be very carefully managed. 



Mercury free from any admixture fliould be totally volatile, when gently heated to the 

 boiling point. In order to deteft the prefence of lead, one part muft be boiled for a few 

 minutes with twelve parts of eleftric acid. The fluid is then to be decanted, and examined 

 by means of fuiphuric acid. If the fmaller quantity of lead be prefent, a few drops of this 

 acid will render the fluid turbid, and a white precipitate will be feparated. One hundred 

 grains of this precipitate, well waflied and dried, contains 72 parts of metal, and 28 of 

 acid ; the quantity of lead contained in a given quantity of mercury, may thus be accurately, 

 afcertained. But the minuteft quantity of lead in the greateft quantity of mercury, can 

 only be detected by diflblving the mercury in nitric acid, and then mixing this folution 

 with water faturated with fulphurated hydrogenous gas. Dark brown clouds will imme- 

 diately appear, and a precipitate of the fame colour will be depofited, if the fluid is fuf- 

 fered to reft undifturbed for a day or two, one part of lead may thus be feparated from 

 15260 parts, of mercury. The admixture of bifmuth is detefted in a fimilar manner, by 

 pouring the nitrous folution into diftilled water ; a white precipitate will appear if this 

 metal be prefent. Tin is manifefted in the ufual manner, by a weak nitro-muriatic folu- 

 tion of gold ; and zinc, like the reft of the metals, may be feparated by expofing the 



mercury to heat. 



Siueet ■ 



