g 
h 
FLINT. 55 
that state, is thrown into cold water. It is then of a 
white colour, and capable, without difficulty, of being 
reduced to powder, either in a mortar or by a mill. 
After this powder has been passed through fine sieves, 
some aqua fortis is poured upon it, to dissolve any 
particles of iron which it may have acquired in the 
rinding. The powder is then several times washed in 
ot water, and afterwards dried for use. The glass that 
is manufactured from this substance is perfectly trans- 
parent and faultless. 
Glass is made by mixing sand, or prepared flint, with 
a certain proportion of soda (200) or potash (205); and 
exposing these substances, in a furnace, to a violent 
heat. When they are in a perfectly fluid state, part of 
the melted matter is taken out at the end of a long 
hollow tube. This is done by dipping the tube into it, 
and turning it about until a sufficient quantity is taken 
up ; the workman, at each turn, rolling it gently upon 
a piece of iron, to unite it more intimately. He then 
blows through the tube tiii the melted mass, at the ex*- 
tremity, swells like a bubble ; after which he rolls it 
again on a smooth surface to polish it, and repeats the 
blowing until the glass i brought as nearly to the siae 
and form of the vessel required, as he thinks necessary. 
If he be forming a common bottle, the melted matter 
at the end of the tube is put into a mould of the exact 
size and shape of the body of a bottle ; and the neck is 
formed by drawing out the ductile glass at the upper 
extremity. 
If he be making a vessel with a large or wide orifice, 
the glass, in its melted state, is opened and widened 
with an iron tool; after which, being again heated, .it 
is whirled about with a circular motion, and, by the 
centrifugal force thus produced, is extended to the size 
required. Should a handle, foot, or any thing of similar 
kind be required, that is made separately, and stuck on, 
in its melted state. 
Window glass is made in a similar manner, except 
that the mass at the end of a tube is formed into, a, 
