LEAD-SHOT. The origin of most of the imperfections in the manufacture of lead-shot is the too rapid cooling of the spherules by their being dropped too hot into the water, whereby their surfaces form a solid crust, while their interior re i mains fluid, and, in its subsequent con cretion, shrinks, so as to produce the ir regularities of the shot.
The patent shot towers obviate this evil, by exposing the fused spherules after they pass through the cullender, to a large body of air during their descent into the water tub placed on the ground. The greatest erection of this kind is pro bably at Villach, in Carinthia, being 240 Vienna, or 249 English feet high.
The quantity of arsenic added to the mass of melted lead, varies according to the quality of this metal • the harder and less ductile the lead is, the more arsenic must be added. About 3 pounds of either white arsenic or orpiment is enough for one thousand parts of soft lead, and about 8 for the coarser kinds. The latter are employed preferably for shot, as they are cheaper and answer sufficiently well. The arsenical alloy is made either by in troducing some of this substance at each melting, or by making a quantity of the compound considerably stronger at once, and adding a certain portion of this to each charge of lead. If the particles of the shot appear tens-shaped, it is a proof that the proportion of arsenic has been too great ; but if they are flattened upon one side, if they are hollowed in their middle, called etTpim g by the workman, or drag with a tad behind them, the pro portion of arsenic is too small.
The following is the process prescribed by the patentees, Ackerman and Martin. Melt a ton of soft lead, and sprinkle round its sides, in the iron pot, about two shovelfuls full of wood ashes, taking care to leave the centre clear ; then put into the middle about 40 pounds of arsenic, to form a rich alloy with the lead. Cover the pot with an iron lid, and lute the joints quickly with loam or mortar, to confine the arsenical vapors, keeping up a mode rate fire to maintain the mixture fluid for three or four hours ; after which skim carefully, and run the alloy into moulds to form ingots or pigs. The composition thus made is to be put in the proportion of one pig or ingot into 1000 pounds of melted ordinary lead. When the whole is well combined, take a perforated skim mer and let a few drops of it fall from some height into a tub of water. If they do not appear globular, some more arseni cal alloy must be added.
Lead which contains a good deal of pewter or tin must be rejected, because it tends to produce elongated drops or tails.