5. Now supposing your cases to be thoroughly dry and ready to be
charged, the next thing that we must consider is the composition with
which they are to be filled. Judging from the effect produced by rockets
prepared by different makers, I should imagine that the formulas for
their compositions are of almost endless variety. Some seem to prefer a
very quick composition, which will raise the rocket to a great elevation
in a very short time; others, one which will produce a large and rich
tail of sparks not ascending so fast or so high. In my opinion, the mean
between these two extremes is decidedly preferable: that which I aim at
in rocket manufacture is to produce a very high, but not a very rapid,
ascent; and when this my object has been properly gained, I have never
had any fault to find with the tail of sparks which is thrown out. I may
say, without any exaggeration, that I have experimented upon several
hundreds of different compositions, varying first one ingredient and
then another, increasing or decreasing them by very gradual steps, until
I have come to the conclusion that the two following are the only ones
worth retaining. But it must be remembered that it is not enough to have
a good formula or two in order to be successful, for much will depend
upon _the manner in which_, and _the care with which_, these are made
up:—
No. 1.
Nitre 16 parts.
Sulphur 4 „
Charcoal 8 to 9 „
This, I believe, is a very old formula, and, provided the charcoal be
properly prepared, may be found very useful and effective. I used this
receipt for a long time, and thought it incapable of improvement, until,
from a wish to try the effect of the addition of a little meal-powder, I
came by chance upon the following, which I do not think can be
surpassed:—
No. 2.
Nitre 16 parts.
Sulphur 3 „
Meal-powder 4 „
Charcoal 8 „
Now let me tell you that the success of rocket compositions depends upon
two things—the intimate union of their ingredients, and the fineness or
coarseness of the charcoal. Such charcoal as you can procure at a
chemist’s ready pounded will be of no use whatever to you, for it is in
far too fine a state of subdivision. You will require a much coarser
charcoal for the most part, and one not of the same coarseness or
fineness throughout. If you could make a mixture containing charcoal of
three different degrees of fineness—the first moderately fine, the next
in pieces of the size of grains of ordinary sporting gunpowder, and the
third of the size of large poppy seeds—and take equal parts of each of
these three you will find that you have a mixture very serviceable for
rocket purposes. But you can procure of Mr. Darby, whom I have mentioned
before, a mixed charcoal which will save you the trouble of sifting. I
recommend you, however, to use no charcoal that will not pass readily
through your 20-mesh mixer, for your object is not to have your charcoal
in large pieces, but to have a certain proportion of it coarser than the
rest. You will find that the larger your proportion of coarse charcoal
is, the slower your composition will be, and, within certain limits, the
more fine charcoal you employ, the quicker it will be. Now, as the
sparks produced by coarse charcoal remain visible in the air much longer
and are much larger, than those produced by fine charcoal, I think it
advisable to employ a good proportion of the coarse and in order to make
up the strength that the composition loses by this plan, I take a
smaller proportion of sulphur, as you will see by comparing formulas
Nos. 1 and 2, and at the same time add a certain quantity of
meal-powder. All these ingredients may be procured of Mr. Darby. The
mode of mixing them is as follows:—Weigh out your quantities of nitre,
sulphur, and meal-powder, mix them well together, and pass them through
your 40-mesh sifter. This you will have no difficulty in doing, because
the condition in which you purchase them is one of fine powder; your
meal-powder especially cannot be too finely sifted for this purpose. You
will find it a great convenience to add to this mixture a few drops of
methylated spirits of wine or gin—a very slight quantity will suffice to
render it less dusty—but you must bear in mind that whenever either of
these liquids is employed, the composition will be sure to rust the
steel spindle around which it is driven, unless you take the precaution
of rubbing it over with a little oil or grease after using and before
putting it away. Next add your charcoal. Stir the whole together, and
pass the mixture two or three times through your 20-mesh mixer; by this
means it will be thoroughly incorporated and fit for use.