The rams are worked by means of a hydraulic accumulator, loaded so as to give a pressure of 1000 lb. on each punch in the mould plate. From 10 to 20 seconds generally suffices to give the density required.
There are other varieties of machines used for this purpose which are self-feeding, but they are liable to clog with powder meal, and therefore are best used with grain powder.
Granulated powder contains much dust, and the grain itself is not in a condition to be made use of as powder, being rough and porous on the surface, and very angular in shape. It is freed from duet by placing it in revolving reels, and then glazed by causing the grains to rub against each other in revolving wooden barrels, Fig. 616.
On leaving the reels or glazing barrel, the powder requires only to he stove dried to be fit for use.
Stoving is effected in large chambers, heated with steam pipes. Gloom stoves or drying rooms, having a large metal dome built into one wall, under which a fire was made, were formerly used. The present steam stoves consist of large chambers having an arrangement of steam pipes running along the floor, and provided with double doors, which can be closely shut, and with ventilators at top and bottom, which can be closed or opened from with out, so as to increase or lower the internal temperature. The temperature is maintained at 52°-54° (125°-130° F.). The stove is fitted with wooden racks, on which are placed the trays, either of sheet copper, or of wood, with a canvas bottom for containing the powder.
The powder is generally 24 hrs. in the stove altogether, being put in one morning and with drawn the next, but does not actually get more than 18 hours of the full temperature, as the heat of the chamber must be lowered, to admit of the workmen remaining in it when putting in or with drawing the trays which hold the powder.
Density is the most im portant quality of gun powder, and must be most accurately determined, which can only be done by means of the mercury densimeter.
The deneimeter, Figs.
617, 618, consists of a baro meter tube m, supported on a stout metal stand, and having a cook d at the bottom by which it can be closed or opened. Attached to the top of the
tube is a flexible tube communicating with an air-pump, bymeans of which the air can be exhausted from the tube. A glass globe A fitted with metal collars e el, on which again are screwed other collars provided with stop-cocks f g, can be attached to the bottom of the barometer tube by means of a closely fitting screw. The lower collar of this globe is provided with a nozzle h which dips into an iron bowl filled with mercury i. If, then, the lower cock g be kept closed and the other ones opened, the air can be exhausted from the barometer tube and globe; and the lower cock being then opened, the mercury rushes in, rises up till it fills the globe, and continues to rise in the tube till it has attained the same height from the surface of the mercury left in the bowl as the column in an ordinary barometer stands at the time.
In taking the density of a sample of powder, the air is first exhausted from the tube and globe, and the mercury allowed to fill them. The upper and lower cocks of the globe are then closed, the nozzle is taken off, and the globe unscrewed from the barometer tube and weighed. This weight, the weight of the globe filled with mercury, is registered.
The globe is then emptied, and a definite weight of the powder, generally 100 grammes, is introduced into the globe. The globe is then attached to the barometer tube as before, the air exhausted, and the mercury allowed to enter and rise in the tube as before. The stop-cocks attached to the globe are provided with diaphragms, the upper one of chamois leather, the lower one of fine wire gauze, to prevent any particle of powder being carried out of the globe. As soon as the mercury has risen to the proper height, the stop-cocks attached to the globe are again closed, the nozzle unscrewed, and the globe taken off and weighed. The second weight, the weight of the globe full of mercury, added to the weight of the powder, and less the weight of the volume of mercury displaced by it, is also registered.