GREEN VITRIOL. 139 
within; and externally of yellowish grey, or blackish 
colour. 
Sal-ammoniac is applied to many useful purposes. 
Occasionally it is used in medicine. A considerable 
portion of it is consumed by dyers, to give brightness 
to some of their colours. It is also employed in the 
assay of metals, to discover the presence of iron ; and 
having the property of rendering lead brittle, is some- 
times used in the manufacture of shot. By copper- 
smiths and tinners it is used for cleansing the surface of 
the metals which they are about to cover with tin. In 
certain manufactories sal-ammoniac is mixed with to- 
bacco, to give that article, or the snuff that is made from 
it, additional stimulant properties. Sal-ammoniac dis- 
solved in nitric acid (30) forms the fluid named aqua- 
regia, which is employed in the solution of gold. 
ORDER II. METALLIC SALTS. 
SALTS OF IRON. 
208. GREEN VITRIOL, IRON VITRIOL, or 
COPPERAS, is a mineral salt formed on a decomposition of 
pyrites (236) by the moisture of the atmosphere. It is also called 
SULPHAT OF IRON. 
Its colour is bright green, and its taste very astringent ; a 
solution of it in water dropped on oak lark instantly produces 
a Hack spot. 
Although copperas is occasionally found in grottoes, 
caverns, the galleries of mines, and other places ; yet, 
being much in request by dyers, tanners, and the manu- 
facturers of ink, it is artificially prepared from pyrites. 
This mineral being moistened and exposed to the air, 
a crust is formed upon it, which is afterwards dissolved 
in water; and from this the crystals of vitriol are ob- 
tained by evaporation. 
