300 PHILOSOPHICAL TRANSACTIONS. [aNNO 1754. 



heat, for several hours, the liquors remained uncoloured, the platina unaltered, 

 and undiminished. The heat was afterwards increased, and the liquors kept 

 strongly boiling till they had totally exhaled, without occasioning any sensible 

 change in the platina. 2. Three ounces of a mixture of 2 parts decrepitated 

 sea-salt, and 3 parts of vitriol highly calcined, were pressed smooth into a cru- 

 cible ; an ounce of platina spread evenly on the surface, and covered with some 

 more of the mixture ; the crucible closely luted, and kept in a moderate red 

 heat for several hours. On examining it when cold, the saline mixture was 

 found to have melted, and formed a smooth, uniform lump. The platina, which 

 had sunk to the bottom, being separated from the mixture by washing, proved 

 of the same appearance as at first, though a little deficient in weight. 3. The 

 experiment was repeated with what is called the regal cement, a less fusible 

 mixture, composed of common salt and colcothar each one part, and 4 parts of 

 powdered red bricks. An oz. of platina, surrounded, as above, with 6 oz. of 

 this composition, and cemented in a close-luted crucible with a red heat, for 20 

 hourSj'was still found unaltered in appearance, though there was some deficiency, 

 as before, in the weight. 



Remark. — The marine acid, when thus detained in the fire by the combina- 

 tion of other bodies, till strongly heated, and then set at liberty in the form of 

 fume, dissolves or corrodes all the known metallic substances, gold alone ex- 

 cepted. As the platina, in these experiments, retained its original polished 

 surface, without any mark of corrosion ; it was presumed, that this mineral 

 likewise had resisted the marine fumes ; and that the deficiency was owing to 

 some of the smaller grains having been washed oft', along with the ponderous 

 colcothar or metallic matter of the vitriol ; an accident not easily avoided. 



4. Platina was therefore treated with mercury-sublimate, a combination of the 

 highly-concentrated marine acid with a volatile substance, which in a proper de- 

 gree of heat it readily forsakes, to unite with other metallic bodies. An oz. of 

 platina was spread on 3 oz. of powdered sublimate ; the glass covered, and set in 

 sand : after a moderate fire for some hours, the sublimate was found to have 

 entirely arisen, Jeaving the platina of its original weight, as well as appearance. 

 5. Fifty grains of a mixture of one part of platina and 2 of gold, well nealed, 

 and cautiously hammered into a thin plate, were surrounded with regal cement, 

 the vessel covered, closely luted, and kept for a considerable time in a red heat. 

 On examining the metal, it was found to retain the whiteness and brittleness, 

 which gold constantly receives from so large a proportion of platina ; and to have 

 lost in weight about 4- gr. or -i^j- part. 



Remark. — The loss here appears to have proceeded, not from the platina, but 

 from alloy in the gold employed, which was above standard, but not perfectly 

 fine : for the metal cemented a second time, with fresh mixture, sufitred no 



