VOL. XLVm.] PHILOSOPHICAL TRANSACTIONS. 501 



further diminution. If the marine acid were capable of dissolving platina, in- 

 stead of -rh-s-^ nearly ^ would have been exeded. This experiment therefore 

 determines, with certainty, the resistance of platina to the marine fumes ; and 

 that the regal cement, so called from its being supposed to purify gold from all 

 heterogeneous metallic matters, is incapable of separating platina from it.* •' 



Exper. 3. — Platina ivilh the Nitrous Acid. 1. Spirit of nitre diluted with 

 water, proof aqua fortis, and the strong nitrous spirit, were digested separately, 

 with -J- their weight of platina, in a gentle heat, for several hours. During the 

 digestion, some bubbles were observed, as if a solution was beginning ; but the 

 liquors acquired no colour ; and the platina, washed and dried, was found to 

 have neither altered its appearance, nor lost of its weight. The fire being after- 

 wards increased, and the acid spirits kept strongly boiling till they had entirely 

 evaporated, no change could be observed in the platina. 2. Platina was like- 

 wise treated with nitrous mixtures, by processes similar to those in which it had 

 been exposed to the marine fumes. After cementation for many hours, in a red 

 heat, with a mixture of 3 parts calcined vitriol, and 2 of melted nitre, the grains 

 were recovered not only unaltered, but without any deficiency in weight. 



Remark. — From these experiments it is plain, that platina, equally with gold, re- 

 sists the force of the vitriolic, marine, and nitrous acids, though applied in such a 

 manner, as to be capable of perfectly dissolving all other known metallic bodies. 



Exper. A. — Platina ivith Aqua Regia. 1. Aqua regia,-}- which perfectly dis- 

 solved gold, poured on platina, began to act on it in the cold, and, by the as- 

 sistance of a moderate heat, slowly dissolved it ; acquiring at first a yellow 

 colour, which deepened by degrees, as the menstruum became more saturated, 

 into a dark brownish red. A few drops of the saturated solution tinged a large 

 quantity of water of a fine golden colour. 2. The experiment was several times 

 repeated with different aqua; regiae, made by dissolving sea-salt and sal ammoniac, 

 separately, in 4 times their weight of aqua fortis ; and by abstracting the nitrous 

 spirit from the same proportion of each of the salts. With all these menstrua 

 the solution seemed to succeed equally. 



3. In order to determine the quantity of menstruum necessary for the solu- 

 tion ; 3 oz. of an extremely strong aqua regia, diluted with water, were poured 

 on one oz. of platina, in a retort, to which was adapted a recipient. A gentle 

 heat being applied, the menstruum acted violently, and red fumes arose in abun- 

 dance. When about \ of the liquor had come over, the action was scarcely, if 

 at all, sensible, though the fire was considerably raised. The distilled liquor, 

 which appeared of a light redish colour, being poured back again into the retort, 



• When these experiments were made, the marine acid in its oxygenized state (oxymuriatic acid) 

 was unknown. The metal of platina, called phtinum, is soluble in that preparation of the marine 

 acid. t Termed in the New Chemical Nomenclature, nitromuriatic acid. 



