30 On the Action of 



lamp-black was then hollowed out to the shape of the cru- 

 cible as far as one-third from the bottom, leaving that much 

 filled with the compressed materials ; this lining, which 

 adhered strongly to the sides of the crucible, was made ex- 

 (remelv thin in order not to obstruct the passage of caloric. 

 A cylindrical piece of wood, as a pencil, was then forced into 

 the centre of the thick mass of lamp-black at the bottom, 

 and the diameter of this rod was determined by the quantity 

 of metal to be fused, or varied according to other circum- 

 stances at pleasure. In general the axis of the cylindrical 

 hole was about three or four times the diameter of the basis. 

 After withdrawing the rod, the crucible was about half filled 

 with borax. Upon this was placed the metal to be fused ; 

 and if it had been before melted into a cylindrical form, the 

 axis of the metallic cylinder was placed horizontally, and 

 'vas of course perpendicular to the axis of the cylindrical 

 excavation at the bottom of the cover. More borax was 

 then added to cover the piece of metal, and another quan- 

 tity of lamp-black was prcsssed hard over the whole in order' 

 to keep it tight together. An earthen cover was finally 

 luted to 'the crucible, and in this state it was exposed to heat 

 in a forge, in which, upon another occasion, I had, in the 

 presence of Messrs. Hatchett, Howard, Davy, and others, 

 completely melted a Hessian crucible lined and prepared in 

 the same manner. The fuel which I used was the patent 

 coke of Messrs. Davcy and Sawyer. In the present expe- 

 riments I moderated the heat so as not materially to injure 

 the crucible, and, upon taking it out of the fire, the lining 

 was generally found so compact and so firm that it remained 

 in a solid mass after the crucible was broken. When the 

 metallic cylinder occupied the space at the bottom, it was 

 natural to suppose that it had been fuse*! ; because in no 

 other state but that of liquidity could it have run into the 

 mould. In order, however, to prevent all objections, I had 

 the precaution to make the hole of a different diameter from 

 the metallic cylinder, and to observe whether the necessary 

 change in the shape of the latter ensued. If, after such a 

 test, repeated as often as required, I perceived that the metal 

 did not vary in its specific gravity, I thought myself autho- 

 rized to conclude that it was exempt from air. 



M. Richtcr says that he had hoped to have put himself in 

 possession of a considerable piece of palladium by repeat- 

 mg, with minute accuracy, the process which I had recom- 

 mended as the best. He precipitated a mixed solution of 

 platina and mercury by a solution of green sulphate of iron ; 

 and, after varying the subsequent operations, to which he 



submitted 



