P Y R 
P Y R 
«2« I* Y R 
alteration in length of metal bars, bv ad- 
va n 'ing the point of a micrometer-screw, 
till it sensibly stopped against the end oi the 
bar to be measured. This screw, being small 
an 1 very lightly hung, was capable of agree- 
ment within the three or four-thousandth 
part of an inch. On this general principle 
-hlr. Smeaton contrived his pyrometer, in 
which the measures are determined by the 
contact of a piece of metal with the point of 
3 micrometer-screw. 
The following table shews how much a 
foot in length of each metal grows longer by 
an increase of heat corresponding to 180° 
ot Fahrenheit’s thermometer, or to the dif- 
ference between freezing and boiling water, 
expressed in parts of which the unit is equal 
to the 10,000th part of an inch. 
1 • White glass barometer-tube, - 100 
2. Martial regulus of antimony, - 130 
3. Blistered steel, - 138 
4- Hard steel, - - - - 147 
3 . I ron, - - - - - 151 
6. Bismuth, - - - - 1(37 
7. Copper hammered, - - 204 
8. Copper eight parts, with tin one 218 
9- Cast brass, - 225 
10. Brass sixteen parts, with tin one, 229 
1 1 • Brass-wire, - 232 
!§• Speculum-metal, - - 232 
1 3. Spelter-solder, viz. brass two parts, 
zinc one, - - - 247 
14. Fine pewter, - 274 
15. Grain tin, - - - . 298 
16. Soft solder, viz lead two, tin one, 301 
17. Zinc eight parts, with tin one, a 
little hammered, - - 323 
IS. Lead, ... - 344 
19. Zinc or spelter, - - 353 
20. Zinc hammered half an inch per 
foot, 373 
BYROPS, a mineral found in Bohemia, 
which was formerly distinguished by the name 
of Bohemian garnet. It is never found 
crystallized, but only in round or angular 
fragments, usually small. Colour deep red, 
which passes to orange when the mineral is 
exposed to the sun. It is ve'y hard ; the 
specific gravity is from 3.7 to 3.9. Fracture 
conchoidal and very brilliant. It is compos- 
ed of 
40.00 silica 
28.50 alumina 
10.00 magnesia 
3.50 lime 
16.50 oxide of iron 
0.25 oxide of manganese. 
98.75 
PYROPIIORUS, a substance which has 
the property of catching fire whenever it is 
exposed to the open air. See Sulphats. 
PY ROSTR1A, a genus of the tetrandria 
nionogynia class and order. The cal. is four- 
toothed ; cor. bell-shaped ; nuts eight, one- 
seeded. There is one species, a small tree 
of Mauritius. 
PYROTECHNY, the art of fire, or a 
science which teaches the management and 
application of fire in several operations. But 
the term is more particularly used to denote 
the doctrine of artificial fireworks. 
Of ingredients and compositions. 
1 . Saltpetre is the principal ingredient in 
fire-works ; but will not answer so well when 
Soul and gross as when purified from its 
crude and earthy parts, which greatly retard 
its velocity ; when, therefore, any quantity 
of ii re-works are to be made, it should be 
examined ; for if it is not well cleansed, am! 
of a good sort, your works will not have their 
proper effect ; neither will it agree with the 
standing proportions of compositions. 
To refine it, put into a copper, or any 
other vessel, 100 lb. of rough nitre with 1*4 
gallons of clean water ; let it boil gently halt 
an hour, and as it boils take off the scum ; 
then stir it, and before it settles put it into 
your filtring-bags, which must be hung on 
a rack, with glazed earthen pans under them, 
in which must be sticks laid across for the 
crystalsdo adhere to : it must stand in the 
pans two or three days to shoot; then take 
out the crystals, and let them dry. The 
water that remains in the pans boil again an 
hour, and strain it into the pans as before, 
and the saltpetre will be quite clear and 
transparent ; if, not, it wants more refining ; 
to do which proceed as usual, till it is well 
cleansed of all its earthy parts. 
N. B. Those who do not clmse to procure 
their saltpetre by the above method, may 
buy it ready-done, which for fire-works in 
general will answer. 
To pulverise saltpetre. Take a copper 
kettle, whose bottom must be spherical, and 
put into it 141b. of refined saltpetre, with 2 
quarts or five pints of clean water : then put 
the kettle on a slow fire, and when the salt- 
petre is dissolved, if any impurities arise, 
skim them off, and keep constantly stirring it 
with two large spatulas, till all the water ex- 
hales ; and when done enough, it will appear 
like white sand, as fine as Hour ; but if it 
should boil too fast, take the kettle off the 
fire, and set it on some wet sand, which will 
prevent the nitre from sticking to the kettle. 
When you have pulverised a quantity of salt- 
petre, be careful to keep it in a dry place. 
2. Sulphur is one of the principal ingredi- 
ents in gunpowder, and almost in all com- 
positions of fire-works; and therefore great 
care must 1 be taken of its being good, and 
brought to the highest perfection. To know 
when sulphur is good, you are to observe 
that it is of a high yellow ; and if, when held 
in one’s hand, it crackles and bounces, it is 
a sign that it is fresh and good : but as the 
method of reducing brimstone to a powder is 
very troublesome, it is better to buy the 
flour ready-made, which is done in large 
quantities, and in great perfection ; though 
when a grand collection of tire-works is to be 
made, the strongest and best sulphur is the 
lump-brimstone well ground. 
3. Charcoal for tire-works must always be 
soft and well burnt, which may be bought 
ready-done. 
4. See Gunpowder in the order of the 
alphabet. It is mealed or ground in mortars, 
&c. 
5. Camphor may be had in the shops ; and 
is of two kinds, differing in regard to the 
degree of their purity, and distinguished by 
the name of rough and refined. Refined 
camphor must be chosen of a perfectly clean 
white colour, very bright and pellucid, of the 
same smell and taste with the rough, but 
more acrid and pungent. 
6. Benjamin is one of the ingredients in 
odoriferous fire-works, when reduced to a fine 
flour ; which may be done by putting into 
a deep and narrow earthen pot between three 
and tour ounces of benjamin grossly pound- 
ed; cover the- pot with paper, which tie 
very closely round the edge ; then set the 
pot on a slow fire, and once in an hour take 
oft the paper, and you will find some flour 
sticking to it, which return again in the pot ; 
this you must continue till the flour appears 
white and fine. There is also an oil of ben- 
jamin, which is sometimes drawn from the 
dregs of the flour ; it affords a very good 
scent, and may be used in wet compositions. 
7. Spur-fire. As the beauty of this compo- 
sition cannot be seen at so great a distance 
as brilliant fire, it has a better effect in a 
room than in the open air, and may be fired 
in a chamber without any danger: it is of 
so innocent a nature, that, though with an 
improper phrase, it may be called a cold 
fire; and so extraordinary is the fire pro- 
duced from" this composition, that, if well 
made, the sparks will not burn a handker- 
chief when held in the midst of them ; you 
may hold them in your hand while burning, 
with as much safety as a candle ; and if you 
put your hand within a foot of the moutii of 
the case, you will feel the sparks like drops 
of rain. When any of these spur-fires are 
fired singly, they are called artificial flow er- 
pots; but some of them placed round a 
transparent pyramid of paper, and' fired in a 
large room, make a very pretty appear- 
ance. 
The composition consists of saltpetre 41b, 
Soz., sulphur 2 lb. and lamp-black 1 lb. 8 oz. ; 
or, saltpetre, 1 lb., sulphur 4 lb. and lamp-black 
quarts. This composition is very difficult to 
mix. The saltpetre and brimstone must be 
first sifted together, and then put into a 
marble mortar, and the lamp-black with 
them, with you work down by degrees with a 
wooden pestle, till all the ingredients appear 
of one colour, which will be something 
greyish, but very wear black: then drive a 
little into a case for trial, and fire it in a 
dark place ; and if the sparks, which are 
called stars, or pinks, come out in clusters, 
and afterwards spread well without any other 
sparks, it is a sign of its being good,* other- 
wise not ; for if any drossy sparks appear, 
and the stars not full, it ‘is then not mixed 
enough ; but if the pinks are very small, and 
soon break, it is a sign that you have rubbed 
it too much. The reason of its being called 
spur-fire, is because the sparks it yields have 
a great resemblance to the rowel of a spur. 
8. To prepare cast iron for gerbes, white 
fountains, and Chinese fire. Cast iron being 
of so hard a nature as not to be cut by a file, 
we are obliged to reduce it into grains, 
though somewhat difficult to perform ; but 
if we consider what beautiful sparks this 
sort of iron yields, no pains should be spared 
to granulate such an essential material : to 
do which, get at an iron-foundry some thin 
pieces. of iron, such as generally run over 
the mould at the time of casting; then have 
a square block made of cast iron, and an 
iron square hammer about four pounds weight ; 
then, having covered the floor with cloth or 
something to catch the beatings, lav the thin 
pieces of iron on the block, and beat them 
with the hammer till reduced into small 
grains ; which afterwards searee with a very 
fine sieve, to separate the fine dust, which is 
sometimes used in small cases of brilliant fire 
instead of steel-dust ; and when you have got 
