102 Dr. Wollaston on a Method of 



elevation. This expression, at an elevation of 5°, becomes 

 nearly 60 x power, and at an elevation of 1°, becomes nearly 

 300 x power; and when the lever becomes horizontal, the 

 multiplier of the power becomes quasi infinite. This expla- 

 nation will be sufficient to show the mechanical advantage with 

 which, by means of this press, the weight of the operator, 

 acting on the end of the lever, will be made to bear against 

 the area of the section of the barrel, a circle little more than 

 an inch in diameter. 



After compression, which is to be carried to the utmost limit 

 possible, the stopper at the extremity being taken out, the cake 

 of platina will easily be removed, owing to the conical form of 

 the barrel ; and being now so hard and firm that it may be 

 handled without danger of breaking, it is to be placed upon a 

 charcoal fire, and there heated to redness, in order to drive off 

 moisture, burn off grease, and give to it a firmer degree of 

 cohesion. 



The cake is next to be heated in a wind -furnace ; and for 

 this purpose is to be raised upon an earthen stand about 

 2\ inches above the grate of the furnace, the stand being 

 strown over with a layer of clean quartzose sand, on which 

 the cake is to be placed, standing upright on one of its ends. 

 It is then to be covered with an inverted cylindrical pot, of the 

 most refractory crucible ware, resting at its open end upon the 

 layer of sand ; and care is to be taken that the sides of the 

 pot do not touch the cake. 



To prevent the blistering of the platina by heat, which is the 

 usual defect of this metal in its manufactured state, it is essen- 

 tial 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 under any subsequent treatment; 

 so that all impurities may be totally driven off, which any 

 lower temperature might otherwise render volatile. The fur- 

 nace is to be fed with Staffordshire coke, and the action 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 



