144 COMMON SULPHUR. 
composition of gunpowder (206). Its readiness of 
taking fire is the reason of its being employed in the 
making of matches. Sulphur gives a blue colour to ar- 
tificial fireworks. Its vapour is used for the whitening 
of silk and wool, and also for the bleaching of straw 
used for making ladies' hats. 
Modellers employ sulphur to make moulds for various 
kinds of casts; and artists are enabled, by means of it, 
to take sharp and beautiful impressions of medals 
and engraved stones. The mode of doing this is very 
simple. The sulphur is put into an earthen vessel called 
a crucible, and placed on a hot fire. It soon melts ; 
and if kept some time over the fire, becomes thick and 
dark-coloured. When poured into water in this state, 
it is as soft as wax. It may now be easily worked be- 
tween the fingers into any given form : and, if pressed 
upon a seal or engraved stone, will be found to retain a 
perfect impression of it. It is this property of sulphur 
of which Mr. Tassie, of Leicester-fields, London, has 
availed himself, to furnish extremely elegant impressions 
of many antique gems. 
Sulphur was much used by the ancients in medicine; 
and it is now occasionally administered both as an ex- 
ternal and internal remedy. The compounds formed 
from it are employed to considerable extent in various 
processes of dyeing and calico printing. Many of the 
mineral waters, those, for instance, of Harrowgate (299) 
and MofFat (300), are indebted to sulphur for their 
most valuable qualities. 
This substance has the property of becoming electric 
by rubbing. On exposure to a gentle heat, it melts ; but 
if the heat be increased, it is entirely consumed, and 
passes off in vapour. When ignited, and the combus- 
tion is slow, it burns with a suffocating and acid fume, 
and blue flame; but when the combustion is quick it 
burns with a white and vivid flame. If exposed to a 
sudden, though gentle heat, by holding it, for instance, 
in a hand when that is warm, it will sometimes break in 
pieces with a crackling noise. 
