f RECIPITATION OFPLATINA, SSS 



wfed with fuccefs, for gilding poliftied (leel with gold; per- 

 haps it may be worth knowing, that a very fimilar procefs 

 may be performed with platina. That metal, in a ftate of 

 folution, is taken up from the acid by agitation with ether, in 

 tlie way that gold is, though certainly with lels avidity. The 

 ethereal folution of plat ina afforded by this procefs, is,Tike 

 that of gold, depofitedon the furface of poliHied iron, or fteel, and coats iron or 

 forming a coat of defence from ruft. It is perhaps a fad of 

 equal importance, that the furface of poliihed brafs is coated 

 with platina by the fame operation that fleel is; namely, by and alfo brafs, 

 plunging the brafs for an inftant into the ethereal Iblution, 

 As far as I know, thefe fads have not hitherto been noticed : 

 on the contrary, authors highly refpedable, Iiave from ingeni- 

 ous and well conduded experiments, been led to conclufions 

 very oppoifite to thole I have advanced. Dr. Lewis, to whofe Dr. Lewis's ex- 

 genius and induflry the arts are much indebted, fays, " go^^ contra^ e£a -^ 

 is the only one of the knou'n metals which the ether takes 

 from acids; and hence this fluid affords a read)^ method of 

 diftinguifliing gold, contained in acid folutions." The fame 

 author gives the following experiment. ** Sulphuric ether 

 was poured into a folution of .platina, and into a compofitioii 

 of platina and gold. The vials were ftopt and fliaken, the 

 ether received no colour from the folution of platina, but be- 

 came infiantly yellow from that of the platina and gold.*' 

 The only way in which I can account for thefe refults, lb con* 

 trary to my experience, is by fuppofing that the platina with 

 which Dr. Lewis made his experiments, was not fo pure as 

 that with which we are now furnifhed. What I ufed was probably Secaufc 

 part of an excellent malleable bar, its fpecifk gravity I do .^'^ ^'^^"* ^^ 

 not exadly know, I am inclined to think it was quite pure. 

 The ether was furniihed by my friend Mr. Hume, whom I 

 am again happy to thank for his kind and able affiftance. 

 The ethereal folution of platina is of a beautiful pale yellow 

 colour, does not at all ftain the hand, and is precipitated by 

 volatile alcali. The precipitate I have not examined. It may 

 be fulminating, and I have no relifli for explofions. The coat 

 of platina on fieel is of a dull white? colour. I have no doubt The platina 

 of its proving quite as good a defence from rufl, as the coat f^f '"^ ^\^^L 

 of gold. It is, however, by no means fo beautiful; for which gold. 

 reafon a preference will probably be given to the lafl named 

 Bielal. I have ufed both ihe gold and platina in coating 



diilerent 



