An instrument to test the comparative strength of different kinds of gunpowder is yet a desideratum in projectile science; and we cannot doubt that such an instrument will be produced, when the importance of the granulation of gunpowder is more generally known and appreciated.
The charcoal formerly used was made in the common way, by pits, which must have been seen by almost every one. The method is now to distil the wood in cast-iron cylinders, extracting the pyroligneous acid, &c., by heating them red hot, and allowing all other volatile matter to evaporate, the charcoal only being retained in the cylinder or retorts; hence arises the name cylinder gunpowder. The best charcoal for sporting powders is the black dog wood; Government use willow and alder. Any charcoal does for common powders. Charcoal is ground in the same way as the nitre. Sulphur is purified simply by fusing, and when in that state, skimming off the impurities: it is cooled and pulverised in the same way as the other two ingredients. The three ingredients, after being carefully weighed in their due proportions, are sifted into a large trough, and well mixed together by the hands. They are then conveyed to the powder mill. This is a large circular trough, having a smooth iron bed, in which two millstones, secured to a horizontal axis, revolve, traversing each other, and making nine or ten revolutions in a minute. The powder is mixed with a small quantity of water put on the bed of the mill, and there kept subject to the pressure of the stones; and if we calculate the weight of the two millstones at six tons, it follows that in four or five hours’ incorporation on this bed, it subjects the ingredients to the action of full 10,000 tons. It is this long-continued grinding, compounding, and blending together of the mixture, that alone renders it useful and good. After this intimate mixing, it is conveyed away in the shape of mill-cake, and firmly pressed between plates of copper. Bramah’s press has been introduced of late years—we should say with a good deal of improvement to the powder, as will be shown hereafter—and by its means the mass is more compressed and in thinner cakes. It is then broken into small pieces with wooden mallets, and taken to the corning-house, where it is granulated, “by putting it into sieves, the bottoms of which are made of bullocks’ hides, prepared like parchment, and perforated with holes about two-tenths of an inch in diameter; from twenty to thirty of these sieves are secured to a large frame, moving on an eccentric axis, or crank, of six inches throw; two pieces of lignum vitæ, six inches in diameter, and two inches or more in thickness, are placed on the broken press-cakes in each sieve. The machinery being then put in rapid motion, the discs of lignum vitæ (called balls) pressing upon the powder, and striking against the sides of the sieves, force it through the apertures, in grains of various sizes, on to the floor, from whence it is removed, and again sifted through finer sieves of wire, to separate the dust and classify the grain. One man works two sieves at a time, by turning a handle and eccentric crank; the sieves being fixed to a frame, which is suspended over a bin by four ropes from the ceiling.”
The grains afterwards undergo a process of glazing, by friction against each other, in barrels containing nearly 200 lbs., making forty revolutions in a minute, and lasting several hours, according to the fancy of the purchaser. This part of the business we entirely disagree with, as injurious to the quick and certain ignition. Gunpowder is finally dried by an artificial temperature of 140° Fahrenheit, which is suffered gradually to decline. The last process is sifting it clear of dust, and then packing it in canisters or otherwise.
The utility of the process of granulation results from the impossibility of firing mealed powder sufficiently simultaneously to effect an explosion; and also from the fact that gunpowder, in a mass, does not explode. Fire a solid piece of mill-cake, and it does not flash off like unto granulated powder, but burns gradually, though with an extreme fury, until the whole is consumed. This arises from its density, the compression in the press; it also teaches us one fact, that to be of the greatest service, the time each grain should occupy in burning should be proportioned to the size of the gun for which it is required; since it is clear that the explosion of a heap of gunpowder is but the rapid combustion of all its parts. This action, as is well known, is so rapid, even in a large quantity of powder, that it appears to be a sudden and simultaneous burst of flame; though philosophically and actually it is not so.
Fine grain, when unconfined, explodes quicker than large, or is sooner burnt out, and consequently generates more force in the same period of time; but when it comes to large quantities, its very quickness is detrimental to its force, by condensing the air around the exterior of the mass of fluid which thus constrains its bound. In small quantities, the proportion of condensation is not so apparent, and hence the reason why greater velocities can be obtained with small arms than with cannon.
There exists a diversity of opinion in regard to the strength or projectile force of gunpowder. Dr. Ure remarks—“If we inquire how the maximum gaseous volume is to be produced from the chemical reaction of the elements of nitre on charcoal and sulphur, we shall find it to be by the generation of carbonic oxide and sulphurous acid, with the disengagement of nitrogen. This will lead us to the following proportions of these constituents:
| Hydrogen 1. | Per Cent. | ||||
|---|---|---|---|---|---|
| 1 | prime | equivalent of | nitre | 102 | 75·00 |
| 1 | „ | „ | sulphur | 16 | 11·77 |
| 3 | „ | „ | charcoal | 18 | 13·23 |
| 136 | 100·00 | ||||
“The nitre contains five primes of oxygen, of which three combining with the three of charcoal, will furnish three of carbonic oxide gas, while the remaining two will convert the one prime of sulphur into sulphurous acid gas. The single prime of nitrogen is therefore, in this view, disengaged alone.
“The gaseous volume, in this supposition, evolved from 136 grains of gunpowder, equivalent in bulk to 751⁄2 grains of water, or to three-tenths of a cubic inch, will be, at the atmospheric temperature, as follows:—
| Grains. | Cubic Inches. | |
|---|---|---|
| Carbonic oxide | 42 | 141·6 |
| Sulphurous acid | 32 | 47·2 |
| Nitrogen | 14 | 47·4 |
| 236·2 | ||