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5-7ths of the pressure. On the amount of pressure the cake receives mainly depends the quickness of the finished powder. Indeed it depends entirely on it if the meal, before pressing, contains a uniform quantity of moisture, and if the cake is broken up into grains of uniform size and shape. The highly-explosive mill-cake may be converted by great pressure into a substance so hard and compact that when ignited it takes a perceptible time to consume. Most of the difficulties experienced in obtaining uniform results in powder-making arise in the operation of pressing. As at present practised, the pressure is maintained till a block is forced a certain distance into the press-box, containing the layers of powder between the plates. Hence unless exactly the same quantity of material is placed in the box each time, and unless it contains exactly the same amount of moisture, the resulting press-cake will vary both in density and hardness. Were small quantities only handled at a time, or were the substances not affected by atmospheric change, the difficulties to be overcome would be trifling. But when quantities varying in weight from 600 to 800 lbs., and containing varying amounts of moisture, are pressed at once, it is impossible to guarantee uniform results, having due regard to rapidity and facility of manufacture.
A piece of press-cake burns comparatively slowly; that is, the time of burning is appreciable, and no instantaneous flash is produced. But it must not be inferred from this that the danger of accidents in pressing is thereby lessened, or that there is less risk of life in the operation than in others. On the contrary, accidents in press-houses, particularly when the powder is under pressure, are not uncommon, and are the most violent of all explosions connected with the manufacture of gunpowder. Of twenty great explosions which happened in powder-works between May, 1858, and December, 1867, putting the frequent minor explosions of incorporating mills out of the question, no fewer than four originated in press-houses, viz., one at Messrs. Curtis and Harvey's, at Hounslow, in 1859; another at the Ballincollig Works in 1861; a third at Messrs. Sharp's factory at Chilworth, in 1864; and the fourth at the Ewell Works in 1865, entailing a total loss of life of sixteen persons. It is often difficult in the cases of great explosions, where generally two or three buildings are exploded successively, leaving not a stone behind, to ascer tain which was the first. The cases, however, of the four presses mentioned appear to be free from all doubt of this kind.
The quantity of gunpowder allowed to be at one time in a press-house is restricted by the Act of Parliament to 20 cwt.; and of this quantity only one-half is to be subjected to pressure at a time. The wording of the Act is too plain to be evaded.
The quantity of gunpowder to be subjected to pressure at one time in any press-house shall not exceed ten hundred weight.'
And again :
The quantity to be at any one time in any press-house. . . . shall not exceed twice the quantities hereby allowed to be subjected to pressure.'
The object of restricting the quantities is, however, entirely defeated, inasmuch as no rules are laid down regarding the distances that press-houses must be from other powder buildings. A fraction of the quantity allowed would, if exploded, inevitably destroy the lives of all persons in the houses at the time; and unless some restrictions are enforced respecting the distances of adjacent buildings, the object of the clause in the Act, viz., to prevent the non-ignition of these, is of course defeated, as sad experience but too frequently proves.
The quantity of powder to be submitted to the next operation in the manufacture, viz., 'corning' or 'granulating,' is also restricted. Twelve hundredweight is the maximum that may be operated on, and not more than twice that quantity is to be in the building where the process is carried out. But there is the same silence in the Act as to the distances of granulating houses from other buildings containing powder; and the legal enactments intended to secure the safety of the workmen are thus rendered null and void.
The 'corning' or 'granulating' process is that in which the hard slate-like press-cake is broken up into the grains of various sizes required by the manufacturer. The former term is derived from the old corning machines with shaking frames;' and the latter from the improved granulating machine, the invention of Sir William Congreve. But in most cases where the new machines have superseded the old, the older term is still retained. The old-fashioned machine consists of a large frame of wood suspended from the roof by ropes, and put in motion by a crank underneath. On this are fixed a number of sieves, having double bottoms of strong parchment, the holes in the lower being smaller than those in the upper. Into each is thrown a quantity of press-cake and two cheese-shaped discs of lignum vitæ ; and the machine being started, the frame oscillates round, creating a hideous din, and throwing out clouds of powder-dust. The discs shaking about in the sieves break the cake to pieces, and the grains pass through the first parchment and are retained on the second, the dust falling through to the floor, whence it is shovelled up after the corning is complete. The whole process is as clumsy and dangerous a one as could well be devised. The granulating machine of Congreve is, on the contrary, a safe and simple one. It consists essentially of three, sometimes four
pairs of toothed bronze rollers, arranged in a slanting direction consecutively, one above the other, and having slanting rectangular sieves leading from under each pair to the top of the next. Underneath the whole is a long slanting frame, containing parallel screens covered with wire gauze of various sizes of mesh, with a board underneath all to retain the dust. The press-cake is carried up to the top pair of rollers on an endless band, and passing between them is broken up into grains, which fall on the first sloping sieve, and pass through it if small enough; or, if not, are carried on to the next pair of rollers, and so on. The grains which pass fall on the upper screen of the long frame, which, along with the sieves, are kept in a continual state of vibration by the action of the machine. There are generally three tiers of screens, each leading down to wooden boxes which receives the finished grains of various sizes, which, if too large, are sent through the machine again, and, if too small, are sent back to the incorporating mills to be reworked for an hour or so. The machine is self-supplying and self-working, so that after filling a large hopper with press-cake the workmen can retire to an out-house protected by a strong traverse, and start the machine, which, when the hopper is empty, rings a bell to show when the work is finished.
To judge from the large proportion of accidents which take place in corning-houses, the process would appear to be a specially dangerous one. Of the twenty accidents in nine years previously referred to, no less than nine originated in corning or granulating-houses, an average of one per annum. This appears to be a very large average, and a very terrible one when the great loss of life and property entailed is taken into account. At the Battle Works in 1860 a corning-house exploded, killing one man; the same year another exploded at the Melfort Works in Argyleshire, killing six; in 1863, at the Ewell Works in Surrey, another followed, exploding also a glazing-house, and killing three; and in December the same year, the great explosion at the Kames Works in Argyleshire, originating in a granulatinghouse, took place, in which seven of the unfortunate workmen were instantly killed, and eight others terribly burnt and injured. This was perhaps one of the worst explosions in a powder factory on record. The flame was communicated from the granulating-house, in succession, to a press-house distant 150 yards, to a glazing-house distant 100 yards from the press-house, then to a dusting-house 200 yards distant from the press-house, then to a double press-house about 200 yards distant from the last, and finally to a glazing-house at the same distance. Some of these exploded almost simultaneously with the granulatinghouse; but from the others the workmen managed to get clear
before the explosion, escaping with a few burns and wounds from falling timbers.
The other explosions of granulating-houses were, one at the Faversham Works in 1864, in which two men were killed; an old-fashioned corning-house at the Roslin Works near Edinburgh, in 1866, one man killed ; a granulating-house at the Melfort Works in the same year, in which three men lost their lives; and two others in December last year, one at the Blackbeck Works near Ambleside, killing three of the workmen, and the other at Faversham which exploded also a double press-house and a charge-magazine, and sacrificed the lives of eleven people. The total loss of life in these nine explosions was therefore thirtyseven killed; the number of burnt, maimed, and disfigured is not stated. This grievous loss of life is the more to be deplored, because there is no reason why breaking the press-cake into grain should be one whit more dangerous than any other operation in powder-making. At some well regulated factories the granulating operation is considered a perfectly safe one, and moreover the machines are constructed in such a way that the presence of a workman when they are in motion is not required. The real cause of the frequency of the disasters appears to be that if there is carelessness or want of precaution anywhere, whether in not sufficiently eliminating all chance of dirt or grit entering the powder at any stage, or even any of the ingredients before mixing; or in the method of handling or working the powder by the men themselves; the granulating-house is the place where such carelessness will be most sure to tell. The accidental presence of gritty particles may ignite the powder by friction in the machine itself; but the great cause of danger would appear to be the large quantity of powder-dust caused by the granulating or corning process which coats every part of the building, roof, walls, and floor thickly. The risk of explosion is so great, caused by men walking about in this building, when great care is not exercised, that the floors are covered with leather secured with copper nails, and the shoes worn by the men not only contain no iron, but are never suffered to touch anything from which gritty particles may be taken up. The wonder is, not that the old-fashioned corning-houses did explode, but that they ever lasted a week without exploding. In these the whole of the dust was allowed to fall on the floor, in a sort of pen, into which the workmen afterwards stepped and shovelled it up with wooden shovels, tipped with copper. There is reason to believe that in some cases the workmen are not supplied with shoes at all; that the boards are not covered with hides; and that they are sometimes secured with iron nails. The explosion when it does come,
as come it must, destroys all traces of these enormities; and juries on the inquest are not supposed to know anything of the precautions requisite in powder-making, and are generally satisfied with the report of the manager or foreman that 'every precaution was observed.' The Gunpowder Act is totally silent on all matters relating to the dress of the workmen, and the regulations to be observed by them. In well regulated establishments, where every possible precaution' as to the cleanness of the floor, shoes, &c., is taken, no powder is allowed to touch the floor. Any that does is damped and swept up with the dust, and the sweepings go to the extracting pot, to yield the saltpetre contained in them.
The powder when granulated is termed 'foul grain,' being rough, angular, and full of dust. The next operation it goes through, dusting,' has for its object the entire removal of the dust, to prepare the powder for glazing and stove drying. To effect this a quantity of the dusty foul grain is placed in a 'reel,' which is a long cylindrical frame of wood, covered with canvas or silk of different fineness of mesh, according to the kind of powder operated on; and the reel being made to revolve at a tolerable speed for some hours, the dust becomes shaken through the canvas or silk covering. Glazing' is a similar operation, a wooden barrel or churn' taking the place of the reel, a few hours' churning in which will impart a fine glaze to the powder grains from their friction against each other. A little black lead greatly assists the operation; but this, being really an impurity, must be sparingly used. In one Government powder alone, that introduced for the Armstrong guns, and which has since been adopted for all cannon charges, is it employed, with the express intention of causing a possible retardation in the speed of combustion of the several grains, and the brilliancy which it imparts to the finished powder is very marked.
Some powders being of a tenderer grain require special arrangements for dusting, to prevent the grains being broken and adding to the dust already present. Such is specially the case with the Government small-arm powder, which is the softest and least dense of all powders, and requires no less than five and a half hours' churning' in the barrels to acquire anything like a polish; and at least three separate dustings to render it free of dust.
The Gunpowder Act is pleasantly vague as to the quantity of gunpowder which may be kept in a dusting-house :—
The quantity to be at any one time in any drying or dusting-house shall not be more than is necessary for the immediate supply and work of such house.'-Act 23 and 24 Vict., cap. 139, p. 1262.
This practically leaves the quantity of powder to the discretion of the manufacturer; and it is a common practice to accu