SCALES AND WEIGHTS.

1. In the first place, some are indispensable. The scales that 12I 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 „

13So 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 14subject 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.