35. We now have to enter upon the most difficult part of the manufacture
of Roman candles. This is the regulation of the charges of powder which
are to blow the stars into the air. These are so small, and necessarily
so, that unless their quantity be very accurately measured you are very
likely to spoil the performance of the whole. The following table will
give you _an approximate_ idea of the quantity that each charge should
contain; but so much depends upon the _quality_ of the gunpowder which
you employ, that it is impossible to give you anything more than an
approximation:—
For the 1st star 3 grains.
„ 2nd „ 4 „
„ 3rd „ 4 „
„ 4th „ 5 „
„ 5th „ 5 „
„ 6th „ 6 „
„ 7th „ 6 „
„ 8th „ 7 „
„ 9th „ 8 „
„ 10th „ 30 „
Gunpowder exerts more or less force in its combustion in proportion as
it meets with more or less resistance. It is in accordance with this
principle that those charges of gunpowder which are at or near the lower
end of the Roman-candle case, are obliged to be much smaller than those
placed nearer its mouth. If it were not so, and all the charges were
alike, when the combustion reached a certain point the case would be
burst. You must modify the quantities given in the above table until you
produce the greatest and best effect with the greatest economy of power.
I think that the five first charges will not require to be altered much.
I have given charges for _ten_ stars. You need not, of course, put so
many into the case; but you should not put in less than _eight_. All
must depend in this matter upon the quantity of composition which you
like to use in the intervals between the stars. _Only be sure to keep
the two last charges of gunpowder always the same, and do not place the
two last stars too near the mouth of the case._ The reason why these
rules must be observed is that the force of the charges of gunpowder
which lie near the mouth of the case is so soon spent, that if the stars
are too near the mouth of the Roman candle they will do little more than
fall out of the case, instead of being blown to their proper height. The
first star means, not that one which is fired first from the Roman
candle, _but that which is first put into it_.
Your best plan for measuring the charges of powder is to have some small
scoops or ladles made of very thin sheet-brass, of the same shape as
that used in filling rockets, and capable of holding exactly the right
charge of powder for each star. This is the only plan that I am aware of
for insuring with any accuracy the various quantities.
Now, having your stars primed, as directed above, with quick-match, your
clay rammed firmly into the lower end of the case, and your composition
ready moistened for use, you must cut some _thin_ touch-paper into
squares of an inch in size. Next you must be provided with a round stick
with a flat end, which will pass easily into the case from one end to
the other, not shorter than _eighteen inches_. Your materials and
apparatus are now complete.
First put into the case the first charge of gunpowder, and take care
that this finds its way to the bottom of the case; drop in next the
first star, _with its priming upwards_. Take care also that the star
lies directly upon the charge of powder. Now, by means of another brass
scoop made to hold the proper quantity of composition, put into the case
half the quantity that is to be rammed between the first and second
stars. You must then press this into its place by means of your
ramming-stick. This can be done with the hand, without any mallet. The
weight of a mallet would break the star beneath. Remember always to ram
in the composition which is to form the interval between the stars _in
two quantities_. If you attempt to ram it all in at once it will not be
sufficiently consolidated, and its combustion will be too rapid. The
quantity of composition must depend entirely upon your own taste. I
generally put in as much, in two quantities, as will rise about an inch
in height in the case; it will not do to put in less.
Then upon the top of this composition put one of the square pieces of
thin touch-paper. This may be rammed down in the same manner in which a
gun-wadding is driven upon the top of the charge. The object of this
little piece of touch-paper is to prevent the charge of powder which is
above it from disturbing in its explosion the composition which is below
it. This I have always found it most effectually does, and allows,
moreover, of the use of a rather stronger charge of powder, than could
be employed without it. Having put this in flatly, measure out your
second charge of powder, and put upon the top of it your second star,
then another half-charge of composition, then the remaining half-charge,
then another piece of thin touch-paper, and so on till the case is
filled. _The last charge of powder should not be less than two inches
below the mouth of the case._ The Roman candles should always begin with
composition in their burning.