WRITINGS OF JAMES SMITHSON. 77 



The mean is 140.17 from 100 of silver. 

 If we suppose 100 of silver to form 107.5 of oxide, we 

 shall have 



Oxide of silver - - 107.50 



Acid of arsenic - - 32.67 



Consequently 1 of acid of arsenic will produce 4.29 of 

 arseniate of silver ; 1 of white oxide of arsenic, 4.97 ; and 

 1 of arsenic, 6.56. 



Of Mercury. 



All the oxides and saline compounds of mercury laid in 

 a drop of marine acid on gold vyith a bit of tin, quickly 

 amalgamate the gold. 



A particle of corrosive sublimate, or a drop of a solution 

 of it, may be thus tried. The addition of marine acid is 

 not required in this case. 



Quantities of mercury may be rendered evident in this 

 way which could not be so by any other means. 



This method will exhibit the mercury in cinnabar. It 

 must be previously boiled with sulphuric acid in the platina 

 spoon to convert it into sulphate. 



Cinnabar heated in solution of potash on gold amalga- 

 mates it. 



A most minute quantity of metallic mercury may be dis- 

 covered in a powder by placing it in nitric acid on gold, 

 drying, and adding muriatic acid and tin. 



A trial I made to discover mercury in common, salt by 

 the present method was not successful, owing, perhaps, to 

 the smallness of the quantity, which I employed. 

 I am, sir, yours, &c., 



James Smithson. 



