8 Dr. Wollaston o« a Method of renJeriugPlatina malleahle. 



to be finally purified by cupellation, in an open crucible, with 

 borax and a little nitre. The sulphuret is then to be roasted, 

 at a low red heat, on a flat brick, and pressed, when reduced 

 to a pasty consistence, into a square or oblong and perfectly 

 flat cake. It is again to be roasted very patiently, at a low 

 red heat, until it becomes spongy on the surface. During this 

 process, sulphur flies off in the state of sulphurous acid, espe- 

 cially at those moments when the heat is allowed occasionally 

 to subside. The ingot is then to be cooled ; and when quite 

 cold, is to be tapped with a light hammer, in order to condense 

 and beat down the spongy excrescences on its surface. The 

 alternate roastings and tappings (or gentle hammerings) re- 

 quire the utmost patience and perseverance, before the cake 

 can be brought to bear hard blows : but it may, by these means, 

 at length be made so flat and square, as to bear being passed 

 through the flatting-mill, and so laminated to any required de- 

 gree of thinness. 



Thus prepared, it is always brittle, while hot ; possibly, 

 from its still containing a small remnant of sulphur. I have 

 also fused some palladium p^r se, without using sulphur; but 

 I have always found it, when treated in this way, so hard and 

 difficult to manage, that 1 greatly prefer the former process. 



To obtain the oxide of osmium in a pure, solid, and cry- 

 stallized state, I grind together, and introduce, when ground, 

 into a' cold crucible, 3 parts by weight of the pulverulent ore 

 of iridium, and 1 part of nitre. The crucible is to be heated 

 to a good i"ed in an open fire, until the ingredients are re- 

 duced to a pasty state ; when osmic fumes will be found to 

 arise from it. The soluble parts of the mixture are then to 

 be dissolved in the smallest quantity of water necessary for the 

 purpose, and the liquor, thus obtained, is to be mixed, in a 

 retort, with so much sulphuric acid, diluted with its weight of 

 water, as is equivalent to the potash contained in the nitre em- 

 ployed ; but no inconvenience will result from using an excess 

 of sulphuric acid. By distilling rapidly into a clean receiver, for 

 so long a time as the osmic fumes continue to come over, the 

 oxide will be collected in the form of a white crust on the sides 

 of the receiver ; and there melting, it will run down in drops 

 beneath the watery solution, forming a fluid flattened globule 

 at the bottom. When the receiver has become quite cold, the 

 oxide will become solid and crystallize. One such operation 

 has yielded 30 grains of the crystallized oxide, besides a strong 

 aqueous solution of it. 



II. An 



