4QQ PHILOSOPHICAL TEANSACTIONS. [aNNO 1754. 



or appearance, whether urged with an intense fire, or cemented for many hours 

 in a weaker one. '2. Platina was injected into melted borax, and urged with an 

 intense fire for several hours, without undergoing any alteration. Nor had 

 black, flux, common salt, pure fixed alkaline salts, or caustic alkalies, any sen- 

 sible effect. 3. Vitreous matters were no more powerful than the saline. Pla- 

 tina was kept in strong fires, for several hours, with common green glass, with 

 glass of antimony, and with glass of lead, without seeming to be in the least 

 acted on by either. 4. Platina was likewise stratified with plaster of Paris, a 

 powerful flux for the most difficultly-fusible metallic body hitherto known, 

 forged iron ; as also with quicklime, and with calcined flint ; with as little effect 

 as in the former trials. 



Exper. 7. — Nitre, which reduces all the known metallic bodies, except gold 

 and silver, into a calx, was mixed with an equal weight of platina, the mixture 

 injected into a strongly ignited crucible, and the fire kept up for a considerable 

 time ; no deflagration happened ; and the platina, freed from the salt by re- 

 peated ablutions with water, proved of the same weight and appearance as 

 at first.* 



Exper. 8. — 1. An ounce of platina was spread on twice its weight of sulphur, 

 with which some powdered charcoal had been previously mixed to prevent its 

 becoming fluid in the fire so as to suffer the platina to subside. The crucible, 

 having another with a hole in the bottom inverted into its mouth, was kept in a 

 cementing furnace for several hours ; when the sulphur was found to have en- 

 tirely exhaled, leaving the platina separable from the charcoal by washing, with- 

 out alteration or diminution. '2. We likewise varied the experiment, injecting 

 repeatedly pieces of sulphur on platina strongly heated ; and constantly found 

 that pure sulphur had no more effect on this mineral, than on gold itself. 3. 

 As fixed alkaline salts enable sulphur to dissolve gold ; platina was exposed to the 

 fire with a mixture of sulphur and alkali, called hepar sulphuris. After a consi- 

 derable heat had been continued for some time, and the matter occasionally 

 stirred, very little of the platina was found remaining in its proper form ; the 

 greatest part being taken up by the sulphureo-saline mixture, so as to dissolve 

 along with it in water. 



General Remarks. — It appears, from the foregoing experiments and observa- 

 tions, 1 . That probably this mineral is originally found in large, hard masses, 

 composed of true platina, a substance similar to the black Virginia sand, and an- 

 other ferruginous matter of the emery kind, some spar, and particles of gold. 

 1. That these masses are, not without great labour, reduced into small grains, 

 which are afterwards ground with mercury, in order to extract the gold. 3. 



* SeeTenuant on the Action of Nitre on Gold and Platina in the Phil. Trans, for 1797. 



