538 Suits, PrtclpU.itts and Amalgam cf Platina, 



The alkalis precipitated (though with tlifTiculty) from the aqueous folutions a fmaU 

 quantity of yellow powder, refcmblin^ Naples-yellow. 1 fuppofe, however, that this pre- 

 cipitate was compofed of cryftals, though none could be difcerned with the magnifier : 

 and it did not appear to be foluble in water; for the nitrous acid, by remaining upon it- 

 for forty-eight hours, did not appear to have afTeiflcd it in the lead. The light yellow pre- 

 cipitate which is obtained by vegetable alkali, after fal-ammoniac has thrown down the 

 whole of the brick- coloured precipitate, was feparated by the fdter, and fubmitted without 

 edulcoration to the aflion of nitrous acid in the proportion of nearly half an ounce of the 

 acid to one dram of the precipitate, in conical veffels, fuch, for example, as a wine-glafs, 

 in which the precipitate occupied the fmalleftpofliblc fpace, and the acid covered it a finger's 

 depth, and prcfented a confiderable furface to the air. In three or four days the acid takes 

 up more orlefs, according to the temperature, and alTumcs the confiftence of a jelly, at firfl 

 yellow, but afterwards of a chryfolite green more or lefs confident, but always in a certain 

 •legree moid. Before the blow-pipe this jelly becomes converted into a black fubftancc, 

 probably the impcrfe£t oxide of platina. This experiment appeared furprlfing to me at firft ; 

 but I reco!le£led that MargrafF, by detonating faltpetre upon platina, and then wafliing and 

 filtering, had likewife obtained a jelly which may have been of the fame nature as mine. I 

 mud obferve that I fatisfied myfelf in the mod convincing manner, that the acid and alkali 

 1 made ufc of were abfolutely pure, and that the platina alone, that is to fay in the metallic 

 date, did not convert the nitrous acid into a jelly. 



Urine, whether frefli or putrid, precipitates platina in the form of a fupcr-compound 

 fait at the fame time that a grey yellow precipitate is formed, which is neither faline nor 

 foiuble in water. Part of this precipitate is formed a few moments after the urine is poured 

 into the folution of platina : the fait is formed afterwards. In order to obtain this fait, it is 

 necefTary that the folution of platina fhould be very concentrated, and carry with it an 

 abundant portion of the fird precipitate. I have not yet attempted to didolve this fait in 

 boiling water, but I think it would exhibit a very beautiful topaz-yellow -, for fome of the 

 crydals, when obferved in the microfcope, were femi-tranfparent, and had not the red co- 

 lour of the fait precipitated by the muriate of ammoniac. With refped to the grey-yellow 

 precipitate, I fuppofe it to bephofphate of iron contaminated with fome foreign fubdance, 

 and perhaps mixed with a fmall quantity of the precipitate of platina. 



When urint is poured into a folution of the red fait in water, a beautiful lemon-yellow 



precipitate is formed, and the grey matter afterwards falls down flowly. This may per- 

 haps afford a new method of feparating iron from platina, if this grey precipitate (hould ia 



fail prove to be the phofphate of iron. 



II. On the Amalgam of Platina. 



REFLECTING on the facility with which the fuper-compound falls of platina are re- 

 duced in the fire, I thought that an amalgam of platina might perhaps be obtained by tritu- 

 rating thefe falts with mercury. To afcertain this, I took a dram of the orange-coloured 

 fait of platina, and triturated it with an equal weight of mercury in a mortar of chalcedony. 

 7 ■ la 



