m 
Art of making Gun-Flints. 
The silex pyromachus is sometimes too moist when ta- 
ken out of the quarry. It requires to be dried ; but if by 
too long exposure to the air or the wind it loses a certain 
portion of humidity which is often very perceptible when 
it is recent, it can then no longer be broken into gun- 
flints, as its fracture is less easy. The workmen careful- 
ly reject all those which have lost this favourable degree 
of moisture. Perhaps they might be restored by keeping 
them in a damp place, or covering them with earth, and 
by these means at least they might succeed in preserving 
those intended to be worked up in winter. 
When the fragments are thrown upon a red hot plate 
of iron, it flies and cracks, and becomes opaque. When 
projected in powder upon nitre in fusion, it gives a few 
sparks with slight inflammation and detonation. 
When calcined in a test, it loses one &50th part of its 
weight, increases in bulk, becomes extremely white, and 
so brittle as to be almost friable. In this state it resem- 
bles the finest porcelain biscuit. 
When distilled in a retort by strong heat, it affords a 
little carbonic acid gas, and a quantity of water amount- 
ing to &00 parts of the weight before indicated as its spe- 
cific gravity ; but gives no sign of the combustible matter 
which in the preceding experiment caused the nitre to de- 
tonate. 
This water, which appears essential to all the flints, 
and may be called their radical water, is the cause of 
their transparency. Exposure to air by drying them, 
renders them opaque ; so that they may be considered as 
imperfect hydrophanes ; for they do not again absorb, but 
with difficulty the water necessary to their transparence. 
This water also contributes to the connexion of their in- 
tegrant particles, whence their fracture becomes more 
equal, and is harsh when they have lost it. These flints 
when recently dug up even afford an aqueous vapour 
