VOL. XLVm.] PHILOSOPHICAL TRANSACTIONS. -197 



longer attracted. In other respects there was no sensible alteration. 2. An oz. of 

 platina was urged with a strong sea coal fire, in a blast-furnace, for above an 

 hour : the heat was so vehement, that the black-lead crucible vitrified, and the slip 

 of Windsor brick, which covered it, melted and ran down. The grains of platina 

 were found superficially cohering into a lump, of the figure of the bottom oi the 

 crucible, of a brighter colour than at first. On a slight blow, they readily fell 

 asunder again, and seemed not to have altered their shape. 3. In several repe- 

 titions of the experiment, the platina began to cohere in a moderate white heat : 

 the grains were at this time very easily separable, and seemed to cohere the more 

 strongly in proportion as the heat was raised. In the most intense fires, which 

 the common vessels could not long support, the platina did not melt, or soften, 

 or alter its figure, or lose sensibly of its weight. The colour was constantly 

 brightened by a strong heat, and generally rendered dusky by a small one : on 

 quenching it, when violently heated, in cold water, the grains, which composed 

 the internal part of the lump, acquired a violet or purple colour. 



Exper. 3. — 1 . As the power of fire on metallic, as well as earthy substances, is 

 remarkably promoted by the immediate contact of fuel, and the impulse of air on 

 the subject ; platina was exposed to its action in those circumstances. A cru- 

 cible, having a bed of charcoal in it, was laid on its side, in a good blast-lur- 

 nace, with its mouth towards the nose of the bellows ; and 4 ounces of platina 

 spread on the charcoal. The fire was vehemently urged for above an hour, 

 during which an intense white flame passed through the crucible, and issued at 

 an aperture made for that purpose. The crucible was vitrified : the grains of 

 platina only superficially cohered, and became brighter, as in the preceding ex- 

 periment, without seeming to have softened or altered their shape. 2. The ex- 

 periment was several times repeated, and varied : once, common salt was thrown 

 on the fuel before the crucible, and its fumes strongly impelled on the platina : 

 some platina was likewise placed before the nose of the bellows in violently-ex- 

 cited sea-coal fires, so strong as almost instantly to melt off a piece of the end of 

 a forged iron rod, without effect ; except that once there were a very few globu- 

 lar drops, about the size of very small shot : these broke easily on the anvil, and 

 looked, both internally and externally, like platina. 



Remark. — It is probable, that the fusion here was owing to sotne accidental 

 admixture, possibly iron : for the unmelted grains, exposed afterwards to a fire 

 rather more intense, suffered no sensible alteration. 



Exper. Q. — Platina was likewise exposed to the fire in conjunction with se- 

 veral substances, which are found to promote the fusion of other bodies, or to 

 occasion considerable alterations in them. 1. Platina mingled with powdered 

 charcoal, with compositions of charcoal, soot, common salt, and wood ashes, 

 substances employed for changing iron into steel ; suffered no change in weight 



VOL. X. 3 S 



