the case of discs and cubes in built-up charges.  A general view of the press is given in Fig. 19.  The gun-cotton in a container is placed on a cradle fixed at an angle to the press.  The mould is swivelled round, and the charge pushed into it with a rammer, and it is then swivelled back into position.  The mould is made up of a number of wedge pieces which close circumferentially on the enclosed mass, which is also subjected to end pressure.  Holes are provided for the escape of water.

[Illustration:  FIG. 19.—­A 4-CWT.  BLOCK OF GUN-COTTON BEING TAKEN FROM HYDRAULIC PRESS.]

The Waltham Abbey Process.—­At the Royal Gunpowder Factory, Waltham Abbey, the manufacture of gun-cotton has been carried out for many years.  The process used differs but little from that used at Stowmarket.  The cotton used is of a good quality, it is sorted and picked over to remove foreign matters, &c., and is then cut up by a kind of guillotine into 2-inch lengths.  It is then dried in the following manner.  The cotton is placed upon an endless band, which conducts it to the stove, or drying closet, a chamber heated by means of hot air and steam traps to about 180 deg.  F.; it falls upon a second endless band, placed below the first; it travels back again the whole length of the stove, and so on until delivered into a receptacle at the bottom of the farther end, where it is kept dry until required for use.  The speed at which the cotton travels is 6 feet per minute, and as the length of the band travelled amounts to 126 feet, the operation of drying takes twenty-one minutes.  One and a quarter lb. are weighed out and placed in a tin box; a truck, fitted to receive a number of these boxes, carries it along a tramway to a cool room, where it is allowed to cool.

Dipping.—­Mixed acids are used in the proportion of 1 to 3, specific gravity nitric acid 1.52, and sulphuric acid 1.84.  The dipping tank is made of cast iron, and holds 220 lbs. of mixed acids, and is surrounded on three sides by a water space in order to keep it cool.  The mixed acids are stored in iron tanks behind the dipping tanks, and are allowed to cool before use.  During the nitration, the temperature of the mixed acids is kept at 70 deg.  F., and the cotton is dipped in quantities of 1-1/2 lb. at a time.  It is put into a tin shoot at the back of the dipping tank, and raked into the acids by means of a rabble.  It remains in the acids for five or six minutes, and is then removed to a grating at the back, pressed and removed.  After each charge of cotton is removed from the tank, about 14 lbs. of fresh mixed acids are added, to replace amount removed by charge.  The charge now weighs, with the acids retained by it, 15 lbs.; it is now placed in the pots, and left to steep for at least twenty-four hours, the temperature being kept as low as possible, to prevent the formation of soluble cotton, and also prevent firing.  The proportion of soluble formed is likely to be higher in hot weather than cold.  The pots must be covered to prevent the absorption of moisture from the air, or the accidental entrance of water, which would cause decomposition, and consequent fuming off, through the heat generated by the action of the water upon the strong acids.