The drained mass is now to be dissolved, by adding to „it 50 per cent. of pure water at 212". This solution is next to be placed in shallow leaden vessels in a cool place, in order to allow the nitre to crystallize, which very soon takes place. During the crystallization the solution is frequently agitated, to prevent the crystals from being too large. It is an object to have the prisms not thicker than needles, in order to profnote their more speedy desicca tion, previous to its being reduced to powder, for mixing with the sulphur and charcoal. As the crystals are deposit ed, they are removed into baskets to drain. They are ultimately placed in wicker wooden vats with double bot toms, the superior bottom being perforated, so as to allow the water to drain through into the cavity below. This nitre is deemed sufficiently pure for making gunpowder.(*) The choice of the sulphur for making gunpowder, is easy to those who are experienced. It should be of a lively yellow colour. Its specific gravity should not be great.
It should appear porous, but not shining. When a bit or it is burned upon a piece of clean glass or porcelain, it should leave no residuum.
If it does not answer these characters, it should be melt ed at a low heat, and skimmed from time to time. II' this is not sufficient, it should be sublimed at the lowest pos sible heat. The sulphur which is extracted from pyrites is never sufficiently pure for this purpose. That from Italy and Sicily, which is naturally sublimed by the heat of volcanos, is the most pure.
In the choice of charcoal, it was once deemed an object even to make use of peculiar kinds of wood ; but now any kind of wood properly charred is employed. The charcoal which is formed during the distillation of the pyrolignic acid is now generally preferred.
Having pointed out the proper materials, it will now be necessary to spew the manner of intimately mixing them together ; for certainly we cannot with propriety call gun powder a compound. Since that sort of contiguity essen tial to their readily exploding depends upon mechanical and not chemical union, it will not be wondered that gunpowder should differ so much in its qualities even with the best proportions. All the explosive chemical com pounds, such as ftilminating gold and silver, are uniform in their effects, because their formation is the result of chemical union.
The first-business in preparing gunpowder is, to pound the materials separately and pass them through fine sieves. Then for 100 pounds of powder, weigh 75.4 nitre, 11.8
sulphur, and 12.8 charcoal. These powders are to be in timately mingled, till the mass assumes a uniform colour ; that is, till no specks of yellow, white, or black appear ; for the nitre, after its crystals have been dried and powdered, becomes as white as flour. Water is now to be added, and the. mass agitated till it assumes the form of a stiff but kneadable paste. In this state it has been formerly knead ed or beaten in mills, called turning mills. This apparatus consists of large mortars, with pistons, or stompers of lignum vim. These are still worked in some manufactories, but in the works of government they are laid aside, on account of the danger arising from the heat of percussion. The machine substituted for this seems much better. It con sists of a large stone in the form of a grindstone, which is made to roll upon its edge in the circumference of a circle. A vertical shaft turns' in the centre of the circle. A hori zontal shaft works in the centre of the stone, the height of which is equal to the radius of the circle, in the peri phery of which the stone is to roll, the end of this horizontal shaft being fastened into the vertical shaft. It will be evi dent that, when the latter turns round, the rolling stone will go round just as a cart wheel is carried round by drawing the cart forward. The edge is a little rounded on the face, and works in a circular bed or trough, con taining the paste to be worked or kneaded. The stone now goes round upon the paste, squeezing it flat. The point of contact is constantly preceded by a scraper, which goes round with the stone, and which constantly turns the paste, previously flattened, into the track of the stone, so that a new surface is always presented to its action. The size of this apparatus is sufficient to work from 50 to 60 pounds at once. It is driven by a steam engime, a water wheel, or by horses.
The paste being sufficiently worked, which cannot be too much, is now sent to the corning house, where a se parate mill is used for forming the paste into corns or grains.
This process is performed in sieves with parchment bot toms, perforated with holes. These sieves are placed upon a revolving horizontal plane. The paste, in a certain state of dryness, is put into the sieves, and a piece of lignum vita in the shape of an oblate spheroid laid upon it. A rota tory motion is given to the spheroid at the time the sieves are revolving. This forces the paste in small grains through the holes in the parchment, which is received below.