€d and enfeebled in colour by the addition of sulphat of 
lime, formed by the union of the lime of the whiting to 
the sulphuric acid of the blue vitriol. This is what is 
called Sanders’ blue : a corruption I presume of cendres 
blues* 
3dly, When the refiners dissolve together in aqua fortis 
a mixture of copper and silver, they separate the silver by 
adding a solution of common salt ; the acid of common 
salt unites with the silver, and the alkali of common salt 
unites with that portion of the aqua fortis which held the 
silver in solution. The liquor now contains nitrat of cop- 
per and nitrat of soda. The copper may be thrown down, 
either by a solution of pearl or potash, or by whiting™ 
In this latter case, the whiting does not mix with and con- 
taminate the colour of the precipitate, as the nitrat of lime 
is soluble in water. 
These precipitates when washed, form the various 
shades of green and blue Verditer, used by the paper 
stainers. 
In all these cases, the precipitate is a carbonat of cop- 
per : different shades may also be procured, by using 
pure lime, and pure or caustic potash. (Soap boiler’s 
Ley.) 
Mr Hatchet? s brown prussiat of copper. 
On the utility of Prussiat of Copper as a pigment . By 
Charles Hatchett , j E sq. F. R. S. 
The accidental discovery made by Diesbach of the 
pigment called Berlin or Prussian blue, about the year 
1710, and which afterwards was published by W oodward 
in the Philosophical Transactions for 1724, was soon 
adopted by artists and manufacturers, so that in a short 
time the great utility of this colour was completely estab- 
lished : it is therefore remarkable, that but little attention 
has been subsequently paid to the colorific properties of 
the other metallic prussiates. 
