1. In the first place, some are indispensable. The scales that I use are
of a very common make, with copper pans capable of holding about four
ounces of nitre. These I have always found very convenient, and they are
by no means expensive to buy; but I should think there is hardly a house
where such a pair would not be found ready to hand. I use also, for
purposes in which more delicacy and exactness is required, a pair of
grain scales such as are employed by the apothecary. It is very
important, particularly in the preparation of coloured fire
compositions, to be very exact in weighing out those ingredients which
enter sparingly into the formulas, for a little more or less of these
will often change entirely the character of the composition.
And now let me say a few words upon the subject of _weights_. The old
books on pyrotechny did their best to confuse their readers in many
ways, but in none more successfully than the following:—They insisted on
giving their formulas in _weight_. For instance, they would tell you to
mix together 3½ oz. of one ingredient, 2 dwt. of another, 1 scruple of
another.
Now the ordinary way in making up such a receipt would be by employing
one weight out of three distinct tables, for the ounce usually employed
in commerce is the avoirdupois ounce; the pennyweight is only found in a
table used for weighing precious metals and precious stones; the scruple
only in a table used by a compounder of medicines. Now I intend to avoid
all confusion of this kind by the simple plan of giving my formulas in
_parts_ and not in weights. For instance, in writing down the formula
for gunpowder, I should put it in the following manner:—
Nitre 70 parts.
Sulphur 15 „
Charcoal 15 „
So that, whether you take it in grains or in tons, the formula is
equally intelligible, and you get at one glance a true idea of the
relative proportions of the ingredients. But, although I mean to keep
weights out of my formulas, we cannot dispense with them in our work.
Now, if you would save yourself much trouble and inconvenience, procure,
in addition to your ordinary grain weights, a 2-oz., a 1-oz. and a ½ oz.
_troy_ weight. This ounce contains precisely the same number of grains
as eight of your apothecary’s drachms and as twenty-four of your
apothecary’s scruples—that is 480 gr., whereas the avoirdupois ounce
contains only 437½ gr. And by this means you will avoid much confusion
and save much time in your calculations; because you will have all your
smaller weights convenient aliquot parts of the greater; and, if I
mistake not, you will find these extra weights very handy for other than
pyrotechnic purposes.
Next, I wish to caution you against an injudicious employment of the
pestle and mortar. These auxiliaries are not intended for any other
purpose but the reduction to powder of lumps, crystals, &c.; they are
never properly used for _incorporating_ ingredients. _Large_ quantities
of pyrotechnic compositions are always _mixed_ in a sieve; _small_
quantities are best mixed by stirring them about with a spatula upon a
piece of paper. A pestle and mortar is a species of apparatus which I
rarely use, for I procure my various salts, &c., in the form in which
they are ready for use, and I strongly recommend you to do the same,
feeling that you will soon be convinced of the convenience of such a
plan. Remember, too, to keep your powdered ingredients in well-corked or
stoppered bottles, for the reason that some of them are very
deliquescent, and are utterly unfit for pyrotechnic purposes except when
perfectly dry. The four following things, however—nitre, sulphur,
charcoal, and meal-powder—which are not subject to injury from a slight
exposure to the air, and which will be required in larger quantities
than other things, I always keep in tin canisters, such as are made to
hold a pound of coffee. A piece of sheet copper about six inches long,
bent into the form of a shallow boat or scoop, will be found useful in
taking these things out of their canisters to be put into the scales and
weighed.