PROOF OF MERCHANT’S POWDER.
The following are the different proofs merchant’s powder is subjected to:—
Lots of 100 barrels are sent in, marked with the number of the lot and the maker’s name on the head of each barrel. 25 per cent. of these are unheaded in the examining house; the Proof Officer then—
If dusty.
First, takes a bowl out of each barrel, and holding it about three feet above, pours it out quickly; should there be a good deal of dust, it is satisfactorily shown by this means.
Firmness.
Secondly, it is handled and pressed between the fingers, to test the firmness of its grain; Size of grain.and should there appear to be any great difference in the proportions of different sizes to that laid down as a standard, it is sifted and compared accordingly, being rejected should the quantities fall short or exceed the sample in any great degree.
Density.
Thirdly, a barrel or two are selected, and the powder poured into a hopper, under which is placed a box very carefully constructed, so as to hold exactly a cubic foot. A slide is now withdrawn at the bottom of the hopper, and the powder allowed to run into the box in a continuous even stream until it is piled up; the hopper is then removed, and the powder struck off with a straight edge, level with the top of the box. The weight is now carefully taken, that of the latter being subtracted; should this not amount to 55lbs. it is rejected, as not being of sufficient density.
Strength by range.
Fourthly, samples are taken from every barrel, and lot for the firing proof.
Firing Proof.—An average of nine rounds of sample Waltham Abbey powder is taken, three rounds being respectively fired at the beginning, middle, and end of the proof, from the same kind of mortar before mentioned, with a charge of 2oz. An average of three rounds of each lot of the merchant’s powder is also taken; should it fall short by more than 1 in 20, it is rejected.
Purity by flashing.
Fifthly, to ascertain if any residuum or ash is left after ignition, about half an ounce is burned on a clean glass plate, and fired with a hot iron. The explosion should be sharp, and produce a sudden concussion in the air; and the force and power of this concussion should be judged by that of known good quality. Few sparks should fly off, nor should white beads or globules appear, as it would be a sure indication, as we have before explained, of insufficient incorporation. It is also subjected to a second proof.
Purity by weight after exposure to damp.
Second proof.—A sample of 1lb. from each lot, carefully weighed up, and a similar sample of the comparison powder, is exposed for three weeks in a box perforated with holes (called a damp chest), to the action of the atmosphere. This box is placed under cover, so that it is sheltered from the wet, but that the moisture can get to it. If, at the end of this time, there is a greater proportion of difference in range between them than one-twentieth, it is rejected. The pounds are also very carefully weighed up again, to ascertain the comparative absorption of moisture. This is called the hygrometric test.