proved, a superior method.

The pulverized sulphur was placed in barrels or cylinders, with hollow axles, which were made to revolve slowly by machinery; there were ledges on the interior which caused the sulphur to be lifted and poured over as the cylinders revolved; a light current of air was blown through each, entering the hollow axle at one end, and passing out through the axle at the other end, which led into an adjoining room; there the impalpable sulphur dust was deposited, much finer than by the usual bolting process.

Adjoining this Refinery was the department in which charcoal was made and pulverized. Charcoal for gunpowder has to be made of a porous fine-grained wood, having very little ashes when burned; willow is generally preferred, and was used at first in the Powder Works, but the exigencies of the war taking away those who would ordinarily have supplied it, rendered it impracticable to procure a sufficient quantity. Recourse was had to the cotton wood, which was abundant; on trial its charcoal was found fully equal to that of the willow for the purpose, and was, thereafter always used.

Charcoal for gunpowder must be made by what is termed the distilling process; that is, the wood must be heated in iron retorts to the proper degree, to have it of the best quality and free from sand or grit. For this purpose cast iron cylinders, or retorts, six feet long and four feet in diameter were used, placed over furnaces, each having one end solid and the other with a movable cover; into these were run the slip cylinders, which contained the kiln dried cotton wood, split up into sticks about one and a half inches in diameter, and entirely filling it.

The slip cylinders were charged with the wood in an outside apartment, their covers put on, then readily moved by cranes to the retorts, into which they were pushed; the covers of which were then luted with clay and closely applied. The bottoms of the retorts being perforated, permitted the escape of the vapors and gases into the furnaces beneath, where inflaming, they supplied mainly the heat required in the operation. In about two hours the slip cylinders were withdrawn from the retorts and moved by the cranes over, and lowered into the cast iron coolers beneath the floor; these had water from the canal circulating around them; the covers being then put [p16] on to exclude the air, the mass of charcoal was rapidly cooled. As soon as a slip cylinder was removed from a retort a freshly charged one would take its place, and thus the process was continued. The slip cylinders were taken out of the coolers in succession by the cranes, and swung over a long and broad table upon which their contents were dropped; here the sticks of charcoal were separately examined and the imperfect rejected. The charcoal was then placed in pulverizing barrels with bronze balls, which revolving by machinery, soon reduced it more or less to a fine powder; it was then bolted, and with the sulphur and saltpetre taken to the weighing house. Here the three materials were arranged into sixty pounds charges, by mingling forty-five pounds of saltpetre, nine pounds of charcoal and six pounds of sulphur, which was then moistened and ready for incorporation.

Reflecting over the processes for making gunpowder, it suggested itself that the chemical reactions would necessarily have the most favorable conditions, when there should be the most intimate approximation of the component molecules. That, as the charcoal by its combustion with the oxygen of the saltpetre, supplied the expanded gases which produced the explosive force, it was of the first consideration that there should be the most perfect mixture practicable between these two ingredients. Under the microscope a fine particle of charcoal was seen to be a mass of carbon penetrated by numerous pores, hence it became necessary to completely fill these minute pores with the saltpetre to have the best condition. This might be accomplished by the usual processes, as the charge is kept moistened when stamped or rolled, but as it will not answer to have the mass wet during the incorporating operation, only moist or damp, the completion of the process was necessarily delayed. If this mass of material could be made into a semi-liquid condition by the action of steam, the hot solution of saltpetre would speedily penetrate the minute pores of the charcoal, and thus the desired end would be rapidly attained.

Accordingly, the following process was devised: The moistened sixty pounds charges, roughly mixed and moistened with water, were introduced into horizontal cylinders of sheet copper thirty inches long by eighteen inches in diameter. These cylinders revolved slowly on a common axis, consisting of a heavy brass tube three inches in diameter, perforated with holes. High pressure [p17] steam was introduced through the tube raising the temperature to the boiling point while the water produced by condensation, added to that originally used to moisten the materials, reduced them to a semi-liquid slush, which was run out of the cylinders after about eight minutes rotation. On cooling, this mud became a damp solid cake, the saltpetre which in the state of boiling hot saturated solution had entered the minutest pores of the charcoal, now crystallizing. The cake as produced was transferred to the incorporating mills, and under the five ton rollers was in an hour brought to the condition of finished mill cake, ready to be cooled and granulated, while without the steaming process, four hours incorporation in the mills had previously been necessary to produce powder of the same first-class character. The capacity of the work of the mills was thus practically quadrupled, the thorough saturation of the charcoal with saltpetre being accomplished by the steaming, while it remained for the rollers merely to complete the incorporation of the whole mass and give the required density to the mill cake.

The Incorporating Mills, twelve in number, extended along the canal beyond the Refinery building and further back from its bank, having the Laboratory between the two; they were two hundred and ninety-six feet long. This separation was for safety, as they worked explosive material. The walls were massive, being four to ten feet thick, the horizontal section of each being that of a huge mortar of seventeen feet wide by twenty-four feet long; the height of the walls was twenty-eight feet; they faced alternately in opposite directions, so that an explosion of one would not be communicated to those adjoining.

The fronts were constructed of light wood and glass, and the roofs of sheet zinc, so that but slight resistance would be offered, upwards and outwards, to the explosive force. A wing wall, nearly as high as the main walls, and three feet thick, extended outwards from the centre of the exterior back wall of each mill twenty feet, to guard still further against the effects of an explosion. Behind these the powder-makers stood, for safety, while starting or stopping the motion of the ponderous rollers. This was done by means of a long lever, which threw in or out of gear the friction arrangement, which worked each set beneath the floor, in the thick archway which extended from end to end beneath the mills. It has already been stated that this archway contained the great iron shaft [p18] which imparted motion to all the mills, and which derived its own from the large steam engine, which was located above, in the centre apartments separating the mills into two divisions.

In