general heating of the mass, and the consequent evaporation of the camphor.  When kept in the air bath at 135 deg.  C., celluloid decomposes quickly.  In an experiment (made by M. Berthelot) in a closed vessel at 135 deg.  C., and the density of the charge being 0.4, it ended in exploding, developing a pressure of 3,000 kilos.  A large package of celluloid combs also exploded in the guard’s van on one of the German railways a few years ago.  Although it is not an explosive under ordinary circumstances, or even with a powerful detonator, considerable care should be exercised in its manufacture.

The Manufacture of Gun-Cotton.—­The method used for the manufacture of gun-cotton is that of Abel (Spec.  No. 1102, 20. 4. 65).  It was worked out chiefly at Stowmarket[A] and Waltham Abbey,[B] but has in the course of time undergone several alterations.  These modifications have taken place, however, chiefly upon the Continent, and relate more to the apparatus and machinery used than to any alteration in the process itself.  The form of cellulose used is cotton-waste,[C] which consists of the clippings and waste material from cotton mills.  After it has been cleaned and purified from grease, oil, and other fatty substances by treatment with alkaline solutions, it is carefully picked over, and every piece of coloured cotton rag or string carefully removed.  The next operation to which it is submitted has for its object the opening up of the material.  For this purpose it is put through a carding machine, and afterwards through a cutting machine, whereby it is reduced to a state suitable for its subsequent treatment with acids, that is, it has been cut into short lengths, and the fibres opened up and separated from one another.

[Footnote A:  The New Explosive Co.  Works.]

[Footnote B:  Royal Gunpowder Factory.]

[Footnote C:  Costs from L10 to L25 a ton.  In his description of the “Preparation of Cotton-waste for the Manufacture of Smokeless Powder,” A. Hertzog states that the German military authorities require a cotton which when thrown into water sinks in two minutes; when nitrated, does not disintegrate; when treated with ether, yields only 0.9 per cent. of fat; and containing only traces of chlorine, lime, magnesia, iron, sulphuric acid, and phosphoric acid.  If the cotton is very greasy, it must be first boiled with soda-lye under pressure, washed, bleached with chlorine, washed, treated with sulphuric acid or HCl, again washed, centrifugated, and dried; if very greasy indeed a preliminary treatment with lime-water is desirable.  See also “Inspection of Cotton-Waste for Use in the Manufacture of Gun-cotton,” by C.E.  Munro, Jour.  Am.  Chem.  Soc., 1895, 17, 783.]