[ 445 ] 
Of the CHEMICAL MANUFACTURES fcEPENDAN? UP- 
on lr on, viz. green copperas : ink: Prussian 
blue : colcothar, grocus martis, 
COPPERAS. 
Green copperas : sulphat of iron ; is procured three 
ways, viz. from pyrites : from the precipitation of copper* 
water : from solution of iron directly in sulphuric acid. 
First method. Pyrites, or sulphuretted iron, is found 
frequently in great abundance in strata of argillaceous 
shist ; in England particularly, in the stratum superincum* 
bent upon coah 
“ The sulphuric acid dissolves iron, and forms the well 
known salt Sulphat of iron ; Green vitriol ; Green coppe * 
fas ; or Sal martis . The greater quantity of this salt 
which is used in manufactures of various kinds* particu* 
larly in dying black, is not prepared from the direct com- 
bination of its ingredients, but from various kinds of na- 
tive sulphats of iron, or pyrites, after they have Undergone 
spontaneous oxygenation by long exposure to air. Green 
vitriol is prepared in many counties in England ; the first 
manufacture of the kind was undertaken in the reign of 
queen Elizabeth, at Deptford, where it is still carried on. 
It is likewise made largely in Northumberland and Dur- 
ham. The method of manufacture is simple, and scarce- 
ly differs now from what it was more than a century ago 
as described by Col walk 55 
The following is the process actually ill use, 
“ The usual mode of manufacturing copperas on the 
* rivers Tyre and Wear, is by exposing iron pyrites (there 
called brasses) which are found in the collieries, to the 
44 influence of the atmosphere. For this purpose a situa* 
lion is chosen inclining towards the river, of a natural 
4 4 strong clay. After the soil is taken off, gutters are cut 
* £ in different directions, and wells of about 5 or six feet 
3 J. » 
