Dr. WoUaston on a Method 



barrel without cavities, and with uniformity, — a uniformity to 

 be rendered perfect by subsequent pressure. In order, how- 

 ever, to guard effectually against cavities, the barrel may be 

 weighed after filling it, and the actual weight of its contents 

 being thus ascertained, may be compared with that weight of 

 platina and water which it is known by estimate that the barrel 

 ought to contain *. A circular piece of soft paper first, and 

 then of woollen cloth, being laid upon the surface, allow the 

 water to pass, during partial compression by the force of the 

 hand with a wooden plug. A circular plate of copper is then 

 placed upon the top, and thus sufficient consistency is given 

 to the contents to allow of the barrel being laid horizontally 

 in a forcible press. 



The press which I have generally used for this purpose, 

 consists of a flat iron bar AB, set edgeways, and screwed down 



by a hook E, near its middle, where it would otherwise be 



* From the mean weight of the ingots ohtained in previous operations, 



it is known that the barrel described in the text ought to contain 16 ounces 



troy of dry platina powder. The weight of the contents of the barrel 



, « sp- grav. of platina — 1 . , - . , - 



= lb ounces X . . ,. h the weight of a cubic inch of 



sp. grav. of platina " 



20-25 

 water x capacity of the barrel in cubic inches = 16 ounces X 1- "526 



21-25 

 ounces x 7"0.") = 189575 ounces troy. Should the contents of the barrel 

 weigh materially less than this estimated weight, there must be a want of 

 uniformity in the disposition of the powder within the barrel. 



liable 



