PYR 
Flint genus. Its colour is dark blood red, 
which, when held between the eye and the 
light, falls strongly into yellow. It occurs 
in angular grains, which are imbedded, but 
never crystallized ; it is completely transpa- 
rent and hard ; specific gravity about 3.8. 
It is composed of 
Silica 40.00 
Alumina 28.50 
Magnesia 10.00 
Lime 3.50 
Oxideof iron 16.50 
• manganese 0.S5 
98.75 
Loss 1.25 
100 
It is found in many parts of Germany ; 
also in Fifeshire in .Scotland, in the sand of 
the sea-shore. It is employed in almost 
every kind of jewelry, and generally set in 
gold foil. The very small grains are pow- 
dered, and used in the stead of emery in 
cutting softer stones. This was formerly 
considered as a variety of the garnet, and 
denominated the Bohemian garnet, from its 
occurring in that country in great beauty 
and perfection. Werner has given the title 
to a distinct species, on account of its co- 
lour, transparency, and want of crystalliza- 
tion. 
PYROPHORUS, in chemistry, a com- 
pound substance, which takes fire on the 
admission of the atmospheric air. It is pre- 
pared by exposing to heat in an jron pot, 
three parts of alum, with one part of flour ; 
the mixture liquifies, and is to be stirred 
constantly till the whole becomes grey, and 
easily reducible to powder while hot. 
The coarse powder is put into a coated 
phial, so as nearly to fill it ; the mouth of 
the phial is stopped with a small plug of 
clay, and is placed in a crucible, and sur- 
rounded with sand up to the neck. The 
crucible is heated to redness, until a blue 
flame appears at the mouth of the phial ; 
when this has continued ten minutes, the 
crucible is removed from the fire, and the 
phial, when sufficiently cold, is accurately 
stopped. This substance inflames in at- 
mospheric air ; in a moist atmosphere, the 
inflammation is much more speedy, and, in 
a dry air, it can scarcely take place. It 
burns also very brilliantly in oxygen gas, in 
nitrous gas, and in oxy muriatic acid .gas; 
jand is inflamed by the, sulphuric and nitric 
acids. See Alum. 
PYROSTRIA, in botany, a genus of the 
PYR 
Tetrandria Motiogynia class and order. 
Natural order of Rubiacem, Jussieu. Ge- 
neric character : calyx very small, four- 
toothed; corolla bell-shaped, five-cleft, to- 
mentose in the throat ; stamina four ; pistils 
one ; stigma capitate ; pericarpium drupe, 
pear-shaped, inferior, small, eight-streaked ; 
nuts eight, one-seeded. There is but one 
species, viz. P. salicifolia, a native of the 
island of Mauritius. 
PYROTECHNY, is, properly speaking, 
the science which teaches the management 
_ and application of fire in divers operations ; 
but in a more limited sense, and as it is com- 
monly used, it refers chiefly to the compo- 
sition, structure, and use of artificial fire- 
works. The ingredients are, 1. saltpetre, 
purified for the purpose ; 2. sulphur, and 3. 
charcoal. Gunpowder is likewise used in 
the composition of fire-works, being first 
ground, or as it is technically termed, mealed. 
Camphor and gum-benzoin are employed gs 
ingredients in odoriferous fire-works. The 
proportions of the materials differ very 
much in different fire-works, and the ut- 
most care and precaution are necessary in 
the working them to a state fit for use, and 
then in the mixing. In this work we can- 
not enter on the subject with a sufficient 
degree of minuteness to teach the method 
of making of fire-works, and shall therefore 
content ourselves with a brief notice of the 
proportions of the materials in some of the 
more common, and more interesting articles 
in use. 
The charges for sky-rockets are made of 
saltpetre, four pounds ; brimstone, one 
pound ; and charcoal one pound and a half ; 
or by another direction, saltpetre, four 
pounds ; brimstone, one pound and a half ; 
charcoal, twelve ounces ; and meal-powder, 
two ounces. These proportions vary again 
according to the size of the rocket ; in 
rockets of four ounces, mealed-powder, 
saltpetre, and charcoal, are used in the pro- 
portions of 10 : 2 and 1; but in very 
large rockets the proportions are saltpetre, 
four ; mealed-powder and sulphur one each. 
When stai-s are wanted, camphor, alcohol, 
antimony, and other ingredients are re- 
quired according as the stars are to be blue, 
white, &c. In some cases gold and silver 
rain is required ; then brass dust, steel-dust, 
saw-dust, &c. enter into the composition ; 
hence the varieties may be almost indefinite. < 
With respect to colour, sulphur gives a 
blue, camphor a white or pale colour, salt- 
petre a clear white yellow, sal-ammoniac a 
green, antimony a reddish, rosin a copper 
