

rendering Platina malleable. 99 



The gray product of platina, when turned out of the cru- 

 cible, if prepared with due caution, will be found lightly co- 

 herent, and must then be rubbed between the hands of the 

 operator, in order to procure, by the gentlest means, as much as 

 can possibly be so obtained of metallic powder, so fine as to 

 pass through a fine lawn sieve. The coarser parts are then to 

 be ground in a wooden bowl with a wooden pestle, but on no 

 account with any harder material, capable of burnishing the 

 particles of platina* ; since every degree of burnishing will 

 prevent the particles from cohering in the further stages of the 

 process. Since the whole will require to be well washed in 

 clean water, the operator, in the later stages of grinding, will 

 find his work much facilitated by the addition of water, in order 

 to remove the finer portions, as soon as they are sufficiently 

 reduced to be suspended in it. 



Those who would view this subject scientifically should here 

 consider, that as platina cannot be fused by the utmost heat 

 of our furnaces, and consequently cannot be freed, like other 

 metals, from its impurities, during igneous fusion, by fluxes, 

 nor be rendered homogeneous by liquefaction, the mechanical 

 diffusion through water should here be made to answer, as far 

 as may be, the purposes of melting ; in allowing earthy matters 

 to come to the surface by their superior lightness, and in 

 making the solvent powers of water effect, as far as possible, 

 the purifying powers of borax and other fluxes in removing 

 soluble oxides. 



By repeated washing, shaking, and decanting, the finer parts 

 of the gray powder of platina may be obtained as pure f as 



* The following experiment will prove the necessity of attending to this 

 precaution : — if a wire of platina be divided with a sharp tool in a slant- 

 ing direction, and, being then heated to redness, be struck upon an anvil 

 with a hammer, so as to force into contact the two newly-divided sur- 

 faces, they will become firmly welded together ; but if the surfaces have 

 previously been burnished with any hard substance, the welding will be 

 effected, if at all, with very great difficulty. 



When the powder of platina has been over-heated in decomposing the 

 ammonio- muriate, or has been burnished in the grinding, I have in vain 

 endeavoured to give it a welding surface, by steeping it in a solution of 

 sal-ammoniac in nitric acid. 



t Sulphuric acid, digested upon the gray powder of platina, thus pu- 

 rified, extracted less than j^ th part of iron. 



H2 



