GUNPOWDER. 
and white. Then put the crystals into a dry 
kettle over a moderate tire, which gradually 
increase till it begins to smoke, evaporate, 
lose its humidity, and grow very white: it 
must be kept continually stirring with a ladle, 
lest it should return to its former figure, by 
which its greasiness would be taken away; 
after that, so much water is to be poured into 
the kettle as will cover the nitre; and when 
it is dissolved, and reduced to the consistency 
of a thick liquor, it must be continually stir- 
red with a ladle till all the moisture is again 
evaporated, and it is reduced to a dry and 
"white meal. 
The like regard is to be had to tine sul- 
phur ; choosing that which is in large lumps, 
clear and perfectly yellow ; not very hard, 
nor compact, but porous; not yet too much 
shining ; and if, when set on lire, it freely 
burns all away, it is a sign of its goodness ; 
so likewise, if it is pressed between the two 
iron plates that are hot enough to make it 
run, and in the running appear yellow, and 
that which remains of a reddish colour, it is 
then lit for the purpose. But in case it is 
foul, it may be purified in this manner ; melt 
the sulphur in a large iron ladle or pot, over 
a very gentle coal-fire, well kindled, but not 
flaming; then scum oft' all that rises on the 
top, and swims upon the sulphur ; take it 
presently after from the fire, and strain it 
through a double linen cloth, letting it pass 
leisurely ; so will it be pure, the gross matter 
remaining behind in the cloth. 
For the charcoal, the third ingredient, such 
should be chosen as is large, clear, and free 
from knots, well burnt, and cleaving. The 
charcoal of light woods is mostly preferred, 
as of willow, and that of the branches or 
twigs of a moderate thickness, as of an inch 
or two in diameter. Dogwood is now much 
esteemed for this purpose. And a method 
of charring the wood in a large iron cylinder 
has lately been recommended, and indeed 
proved, as yielding better charcoal than for- 
merly. 
The charcoal not only concurs with the 
sulphur in supplying the inflammable matter, 
which causes the' detonation of the nitre, but 
also greatly adds to the explosive power of it 
by the quantity of carbonic acid gas, ex- 
pelled during its combustion. 
These three ingredients, in their purest 
state, being procured, long experience has 
shewn that they are then to be mixed to- 
gether in the proportion before-mentioned, 
to have the best effect. 
But it is not the due proportion of the ma- 
terials only, which is necessary to the making 
of good powder; another circumstance, not 
less essential, is the mixing them well to- 
gether; if this is not effectually done, some 
parts of the composition will have too much 
nitre in them, and others too" little; and in 
either case there will be a defect of strength 
in the powder. 
After the materials have been, reduced to 
fine dust, they are mixed together, and moist- 
ened with water, or vinegar, or urine, or 
spirit of wine, Ac. and then beaten together 
with wooden pestles for 24 hours, either by 
hand, or by mills, and afterwards pressed into 
a hard, firm, and solid cake. When dry, it 
is grained or corned, which is done by break- 
ing the cake of powder into small pieces, and 
so running it through a sieve ; by which 
means the grams may have any size given 
them, according to the nature of the sieve 
employed, either finer or coarser ; and thus 
also the dust is separated from the grains, 
and again mixed with other manufacturing 
powder, or worked up into cakes again. 
Powder is smoothed, or glazed, as it is 
called, for small arms, by the following ope- 
ration: a hollow cylinder or cask is mounted 
on an axis, turned by a wheel; this cask is 
half-filled with powder, and turned for six 
hours ; and thus by the mutual friction of the 
grains of powder it is smoothed, or glazed. 
The fine mealy part, thus separated or worn 
off from the rest, is again granulated. 
The nature, effects, 4'C. of powder. When 
the powder is separated as above, if the least 
spark is struck upon it from a steel and flint, 
the whole will immediately inflame, and 
burst out with extreme violence. The effect 
is not hard to account for : the charcoal part 
of the grain upon which the spark falls, 
catching fire like tinder, the sulphur and nitre 
are readily melted, and the former also 
breaks into flame ; the contiguous grains at 
the same time undergoing the same fate. 
'I’he explosion of gunpowder therefore 
arises from the violent action, by which all 
the mixture being quickly and vehemently 
heated, is rarefied and converted into gas 
and vapour; which vapour, by the violence 
of that action becoming so hot as to shine, 
appears in the form of a flame. 
To understand the force of gunpowder, it 
must be considered that, whether it is fired in 
a vacuum or in air, it produces by its explosion 
permanently elastic fluids. It also appears 
from experiment, that the elasticity or pres- 
sure of the fluids produced by the firing of 
gunpowder is, exteris paribus, directly as its 
density. 
To determine the elasticity and quantity 
of the elastic fluids produced from the ex- 
plosion of a given quantity of gunpowder, 
Mr. Robins premises, that the elasticity of 
the fluids increases -by heat, and diminishes 
by cold, in the same manner as that of the 
air; and that the density of this fluid, and 
consequently its weight, are the same w ith the 
weight of an equal bulk of air, having the 
same elasticity and the same temperature. 
From these principles, and from the experi- 
ments by which they are established, he con- 
cludes that the fluid produced by the firing 
of gunpowder is nearly three-tenths of the 
weight of the generating powder itself; and 
that the volume or bulk of this air or fluid, 
when expanded to the rarity of common at- 
mospheric air, is about 244 times the bulk of 
the powder.. 
Hence it appears, that any quantity of 
powder fired in any confined space, which it 
adequately fills, exerts at the instant of its 
explosion against the sides of the vessel con- 
taining it, and the bodies it impels before it, 
a force at least 244 times greater than the 
elasticity of common air, or, which is the 
same thing, than the pressure of the atmo- 
sphere ; and this without considering the 
great addition arising from the violent de- 
gree of heat with which it is endued at that 
time ; the quantity of which augmentation 
is the next head of Mr. Robins’s enquiry. 
He determines that the elasticity of the air 
is augmented in a proportion somewhat 
greater than that of 4 to 1, when heated to 
8S7 
the extremist heat of red-hot iron ; and sup- 
posing that the flame of fired gunpowder is 
not of a less degree of heat, increasing the 
former number a little more than four times,,, 
makes nearly 1000 ; which shews that the 
elasticity of the flame, at the moment of ex- 
plosion, is about 1000 times stronger than the 
elasticity of common air, or than the pressure 
of the atmosphere. But, from the height of 
the barometer, it is known that the pressure 
of tiie atmosphere upon every square inch, 
is on a medium l4|lb. ; and therefore 
1000 times this, or 147501b. is the force or 
pressure of the flame of gunpowder, at the 
moment of explosion, upon a square inch, 
which is very nearly equivalent to six. tons 
and a half. 
This great force, however, diminishes as. 
the fluid dilates itself, and in that proportion, 
viz. in proportion to the space it occupies,, 
it being only half the strength when it occu- 
pies a double space, one-third the strength 
when triple the space, and so on. 
Mr. Robins farther supposes the degree of 
heat above-mentioned to be a kind of me- 
dium heat ; but that in the case of large quan- 
tities of powder the heat will be higher, and 
in very small quantities lower ; and that 
therefore in the former case the force will 
be somewhat more, and in the latter some- 
what less, than 1000 times the force of the 
atmosphere. 
He farther found that the strength of pow- 
der is the same in all variations in the den- 
sity of the atmosphere,, but that the mois- 
ture of the air has a great effect upon it ; for 
the same quantity which in a dry season.' 
would discharge a bullet with a velocity of- 
1700 feet in one second, will not in damp 
weather give it a velocity of more than 12 
or 1300 feet in a second, or even less, if the 
powder is bad., and negligently kept. Farther, 
as there is a certain quantity of water which,, 
when mixed with powder, will prevent its 
firing at all, it cannot be doubted that every 
degree of moisture must abate the violence 
of the' explosion ; and hence the effects of 
damp powder are not difficult to account for. 
It is to be observed, that the moisture im- 
bibed by powder does not render it less ac- 
tive when dried again. Indeed, if powder is 
exposed to very great damps without any- 
caution, or when common salt abounds in 
it, as often happens through negligence in 
refining the nitre, in such cases the moisture 
it imbibes may perhaps be sufficient to dis- 
solve some part of the nitre ; which is a per- 
manent damage that no drying can retrieve. 
But when tolerable care is taken in preserving 
powder, and the nitre it is composed of has 
been well purged from common salt, it will 
retain its force for a long time; and it is said 
that powder has been known to have bee»» 
preserved for 50 years without any apparent, 
damage from its age. 
The velocity of expansion of the flame of 
gunpowder, when fired in a piece of artillery, 
without either bullet or other body before it, 
is prodigiously great,, viz. 7000 feet per se- 
cond, or upwards, as appears from the ex- 
periments of Mr. Robins. But Mr. Bernou- 
illi and Mr. Euler suspect it is still much 
greater.. Perhaps, indeed, it may net be 
less, at the moment of explosion, than four- 
times as much. 
It is this prodigious celerity of expansion: 
of the flame of fired gunpowder, which is its 
