AQTION OP PLATIKA AND MIRCUftY. 1^5 



Tijey diflblved one hundred and fi(ty grains of platina wHh by adding hydro- 

 four hundred and fifty of mercury, and added a ''■t)lutIon of [^'P^^^^J°'^»5» 

 hydrofulphuret of potafti. They obtained a precipitate which, tion 5 

 at firft, was black, afterwards gray; but the whole became 

 black by being flirred. To be certain that all the metal was 

 precipitated, they added an excefs of fulphuret of polafli, and 

 perceived that a part of the precipitate was re-diflblved. The 

 liquor was then filtered, and to that part of it, which contained 

 the re-diflblved precipitate, an acid was added. From this pro- — but they ob* 

 cefs they obtained a yellow precipitate weighing ninety- one *^^^^^^^^°P*^^*' 

 grains j and fifty grains of this expofed to a ilrong heat, left 

 three-eights of a grain of platina. Tliey obtained no palIa-< 

 dium from that part of the precipitate which had not been 

 re-diflblved 5 and the refult of the experimont was poraplete 

 failure. 



I (liall not make any obfervalion upon the ifliie of this 

 procefs, fince, in this cafe, the beft condudied is but too liable 

 to be unfuccefsful, and that without any apparent fault in the 

 operator. But as it has been given as a repetition of one of 

 mine, it may not be fruitlefs to examine how far the repetition 

 was exad. 



I had pafled a current of fulphu retted hydrogen gas through They did not 

 a mixed folution of platina and mercury, by which means they the auJho^j^\x» 

 were precipitated together. My objedl was fo intimately toperiment. He 

 combine fulphur with thefe metals, that when expofed to heat,*^^^^'^ \he^"ad(icd 

 they might (if I may be allowed the expreflion) be in chemical an alkali j 

 contact with it at the moment of their nafcent metallic fiale ; 

 and as a low temperature fuffices, as well to reduce thole 

 metals, as to combine palladium with fulphur, 1 hoped that 

 thofe effeds might be produced before the total diffipalion of 

 the mercury. Plow far my expectation was fulfilled has been 

 Hated in my former paper. 



The fulphuretted hydrogen gas which Meflrs, Rofe apd — and this laft 

 Gehlen prelented to thofe metals was combined with potafti. notoniron 

 Now, in the courfe of docimaiiic ledlures annually delivered mercury j 

 by M. Vauquelin at the Ecole des Mines in Paris, when he was 

 ProfelTor at that eftabiifliment, it was his conftant cufiom to 

 exhibit an experiment to prove that mercury, precipitated from 

 its folution by many of the alkaline and earthy hydrofulphurets, 

 w^s rediiTolved by adding an excefs of them. 



