6 Dr. Wollaston on a Method 



essential to expose the cake to the most intense heat that a 

 wind-furnace can be made to receive, more intense than the 

 platina can well be required to bear imder any subsequent 

 treatment; so that all impurities may be totally driven off, 

 which any lower temperature might otherwise render volatile. 

 The furnace is to be fed with Staffordshire coke, and the ac- 

 tion of the fire is to be continued for about twenty minutes 

 from the time of lighting it, a breathing heat being maintained 

 during the last four or five minutes. 



The cake is now to be removed from the furnace, and being 

 placed upright upon an anvil, is to be struck, while hot, on 

 the top, with a heavy hammer, so as at one heating effectually 

 to close the metal. If in this process of forging, the cylinder 

 should become bent, it should on no account be hammered on 

 the side, by which treatment it would be cracked irremediably; 

 but must be sti-aightened by blows upon the extremities, dex- 

 terously directed, so as to reduce to a straight line the parts 

 which project. 



The work of the operator is now so far complete, that the 

 ingot of platina may be reduced, by the processes of heating 

 and forging, like that of any other metal, to any form that may 

 be required. After forging, the ingot is to be cleaned from 

 the ferruginous scales which its surface is apt to contract in 

 the fire, by smearing over its surface with a moistened mix- 

 ture of equal parts by measure of crystallized boi'ax and com- 

 mon salt of tartar, which, when in fusion, is a ready solvent 

 of such impurities*, and then exposing it, upon a platina tray, 

 under an inverted pot, to the heat of a wind-furnace. The 

 ingot on being taken out of the furnace, is immediately to be 

 plunged into dilute sulphuric acid, which in the course of a 

 few hours will entirely dissolve the flux adhering to the sur- 

 face. The ingot may then be flattened into leaf, drawn into 

 wire, or submitted to any of the processes of which the most 

 ductile metals are capable. 



The perfection of the methods above described, for giving 



* The chemist will find this flux very serviceable for removing from his 

 crucible or other vessels of platina those ferruginous scales with which, 

 after long iise,"and particularly after being strongly heateii in a coal or coke 

 fire, they become incrusted. In the analysis of earthy minerals, I have 

 been in the habit of using a similar flux, composed of 2 parts by weight of 

 crystallized carbonate of soda, and 1 of crystallized borax, well ground to- 

 gether. It has the advantage of not acting, like caustic alkali, upon the 

 platina crucible, and is a powerful solvent of jargon and many other minerals, 

 which yield with difficulty to other fluxes. If the mineral to be operated 

 on requires oxidation, in order to decompose it, a little nitre or nitrate of 

 soda may be added. 



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