WHITE VITRIOL. HI 
over a fire till all the fluid particles are dissipated, and 
the vitriol alone is left. 
Blue vitriol is used by artists and manufacturers in 
various ways. It is employed in dyeing: and enters 
into the composition of black colours, to which it gives 
depth and solidity. Blue feathers are stained by plung- 
ing them into a hot solution of it. The beautiful grass- 
green colour of the shops, called mineral gree?i, is made 
from blue vitriol ; and fowling-pieces and tea-urns are 
browned by washing them with a preparation of it. 
SALTS OF ZINC. 
210. WHITE VITRIOL, arSULPHAT OF ZINC, is 
a whitish, yellowish, or greenish white salt, formed by a com" 
lination of sine (241) with sulphuric acid (24). 
Although the white vitriol that is used in commerce 
is chiefly an artificial preparation, this salt sometimes 
occurs in a natural state, in mineral repositories that 
contain blende (241) ; and it appears to be formed by a 
decomposition of that ore. It is found at Holywell, in 
Flintshire, and in some parts of Cornwall. 
When white vitriol is artificially prepared, the blende 
is roasted, and thrown, while red hot, into a vessel filled 
with water ; in which it is allowed to remain about 
eighteen hours. This process is repeated several times ; 
and, after the solution has become clear, it is removed 
into leaden vessels, and the water is evaporated by 
means of heat. On cooling, it crystallizes. After this 
the crystals are melted in a copper vessel, and the sur- 
face of the solution is skimmed with a hair sieve. It is 
then poured into a wooden vessel, and stirred till it be- 
comes cool, and acquires a sufficient degree of con- 
sistence, when it is formed into loaves for sale. In this 
state it has the appearance and colour of refined sugar. 
White vitriol is chiefly manufactured in Germany. 
It is used in medicine ; and is employed in great 
quantities by varnishers, to make their oil varnishes 
dry more readily than they otherwise would. A fine 
white colour, called zinc-white, which is more durable 
