rendering Platina malleable. 105 



sulphur, and each cake of the sulphuret, after being fused, is 

 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 Halting-mill, and so laminated to any 

 required degree 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 per se, without using sulphur ; but I 

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

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



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

 tallized 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 red in an open fire, until the ingredients are reduced 

 to a pasty state, when osmic fumes will be found to arise 

 from it. The soluble parts of the mixture are then to be dis- 

 solved in the smallest quantity of water necessary for the pur- 

 pose, 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 employed ; 

 but no inconvenience will result from using an excess of sul- 

 phuric 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 



