When the jelly in the tanks has become semi-transparent and the cotton has entirely dissolved, the mixture should be transferred to the mixing machine. The mixing machines are specially designed for this work, and are built in iron, with steel or bronze kneading- and mixing-blades, according to requirements. A suitable machine for the purpose is that known as the Nito-Universal Incorporator, shown in Fig. 30, which has been specially constructed by Messrs Werner, Pfleiderer, & Perkins, Ltd., after many years' experience in the mixing of explosive materials, and is now almost exclusively adopted in both Government and private factories. Mr George M'Roberts'[A] mixing machine, however, which is shown in Fig. 31, is still used in some factories for dynamite jelly. [Footnote A: See _Jour. Soc. Chem. Ind._, 1890, 267.] If it is intended to make gelignite, or gelatine dynamite, it is at this point that the proper proportions of wood-pulp[A] and potassium nitrate should be added, and the whole well mixed for at least half an hour, until the various ingredients are thoroughly incorporated. [Footnote A: Most of the wood-pulp used in England is obtained from pine-trees, but poplar, lime, birch, and beech wood are also used. It is chiefly imported as wood-pulp. The pulp is prepared as follows:--The bark and roots are first removed, and the logs then sawn into boards, from which the knots are removed. The pieces of wood are afterwards put through a machine which breaks them up into small pieces about an inch long, which are then crushed between rollers. These fragments are finally boiled with a solution of sodium bisulphite, under a pressure of about 90 lbs. per square inch, the duration of the boiling being from ten to twelve hours. Sulphurous acid has also been used. Pine-wood yields about 45 per cent. and birch about 40 per cent. of pulp when treated by this process. The pulp is afterwards bleached and washed, &c. Birch. Beech. Lime. Pine. Poplar. Cellulose 55.52 45.47 53.09 56.99 62.77 per cent. Resin 1.14 0.41 3.93 0.97 1.37 " Aqueous extract 2.65 2.47 3.56 1.26 2.88 " Water 12.48 12.57 10.10 13.87 12.10 " Lignine 28.21 39.14 29.32 26.91 20.88 "] The following analysis of woods is by Dr H. Mueller:--These mixing machines can either be turned by hand, or a shaft can be brought into the house and the machine worked by means of a belt at twenty to thirty revolutions per minute. The bearings should be kept constantly greased and examined, and the explosive mixture carefully excluded. When the gelatine mixture has been thoroughly incorporated, and neither particles of nitrate or wood meal can be detected in the mass, it should be transferred to wooden boxes and carried away to the cartridge-making machines to be worked up into cartridges.