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regal cement, the crucible covered and luted, and kept fortwenty hours in a red heat. On examining the metal, itwas found to retain the whiteness and brittlenefs, whichgold constantly receives from so large a proportion of pla-tina, and to have lost in weight about half a grain, or onehundredth part. This loss proceeded perhaps from alloyin the gold employed, which was above standard, but notperfectly fine, or perhaps from the dissolution of some ofthe heterogeneous parts of the platina, but by no meansfrom the platina itself; for the same plate, cemented againwith fresh mixture for the same length of time, suffered nofurther diminution. If the marine acid was capable ofcorroding the platina, the corrosion would have continuedin the second process, and instead of a hundredth part,near a third part would have been eaten out. This ex-periment therefore determines with certainty the residenceof platina to the marine fumes; and that the regal cement,so called from its being supposed to purify gold from allheterogeneous metallic bodies, is incapable of separatingplatina from it.

6.There are circumstances in which gold itself is dissolvedby the pure marine acid ; as when it has been melted withtin, and the mixture beaten into powder and calcined; orwhen it has been reduced into the form of a calx by preci-pitation from other menstrua. Platina calcined with tin,and some of the precipitates of platina of which an accountwill be given in the next section, were digested in spirit ofsalt, with a moderate heat, for several hours : the reddishyellow colour which the menstruum acquired, shewed thata part of the platina was dissolved, though it seemed todissolve somewhat more difficultly, and more sparingly,than gold treated in the same manner.

III. Platina