Experiments on Platlna. 51 



property of ftalning : in a word, it has as much luftre as the 

 beft Ensilii]) pencils *. 



That the allay by this method may be exa£l, the graphite, 

 when heated by the blowpipe, ought to exhale no fulphurous 

 odour; for, if this odour is perceived, it indicates that it ftill 

 contains metal not dillblved. I mult however obferve, that 

 during the folution the platina appears to be reduced to a 

 bl:4ck powder; or, rather, a powder is detached which rcTcm- 

 bles galena coarfely pulverized. 



This powder, which is as heavy as platina, accumulates 

 at the bottom of the retort : after the folution of the grains 

 of the metal, it ftill retains for a long time the fame 

 appearance; and it is only by renewing the nitro-mu- 

 riatic acid that it difappears entirely, leiving nothing in its 

 place but graphite. The nature of this powder will be feeii 

 hereafter. 



X. Obfervat'ions on Solutions of Platina. 



To free thefe folutions from the nitric acid employed in 

 excefs to oxygenate the muriatic acid, they muft be con- 

 centrated till they acquii*e the confiftence of honey. The 

 fuperabundant muriatic acid, becoming oxygenated in its 

 turn at the expenfe of the remaining nitric acid, acquires 

 the quality of oxygenated muriatic gas combined with nitrous 

 gas. 



The faline mafs which remains is of a dark brown colour: 

 it diflblvcs in warm water if the deliccation has not been too 

 llrong; for in that (.afe the part which relifts folution is a 

 brown muriate containing lefs acid, in which platina, iron 

 and copper are re-found, and from which the muriatic acid 

 cannot be feparated even by fcveral wafliings. In regard to 

 the liquid folution, it is merely a muriate ; for, when decom- 

 pofcd by means of potafh, nothing is produced but muriate 

 of potafli and a little fulphate. It has an aftringent tafte, 

 hut without any of ihofe metallic favours which are fo dif- 

 agrecable in all lohitions of lilver, copper, &c. 



If the folution in this Itate be treated with potafli, the 

 faline precipitates common to all folutions of platina will 

 be obtained, but not an atom of nitrate will be obtained by 

 evaporation; from which it may be inferred, that the nitric 

 acid of folutions not concentrated has no part in precipita- 

 tions of this kind. It will be fcen, in the courfc of this paper, 

 that the (lightell vcliige of this acid is not found in the pre- 



• On fufin>4 crude pl.Tinn witli oxygen gas, a black fhining fcale forms 

 on the outfidc of tlic glolnilc, v.'lilcli may be feparated by the haiiiincr. 

 Thii is frcquemly fouiid w foil tbt- finc^ers. — Edit. 



D z cipitates 



