The interior of this apparatus is filled with nitric acid, cotton wool is introduced, the acid fumes exhausted through earthenware pipes, and the remainder of the acid removed by the centrifugal machine; the nitrated material is then washed, teazed in teazing machines, again washed, neutralised with calcium carbonate, again centrifugalised, and dried. Since drying in drying stoves is a great source of danger of explosion, dehydration is effected with alcohol, and the gun cotton intended for the production of smokeless powder carried directly to the gelatinising vessels (see Smokeless Powder). Gun cotton, apart from its use for smokeless powder, is pressed in prisms and used for charging torpedoes and sea mines. _Collodion cotton_ is a partially nitrated cellulose. It is prepared generally in the same way as gun cotton, except that it is treated with a more dilute acid. It is soluble (in contradistinction to gun cotton) in alcohol-ether, and the solution is known as collodion (as used in surgery, photography, and to impregnate incandescent gas mantles). Mixed with camphor and heated collodion forms celluloid. In Chardonnet’s method for making artificial silk collodion is used by forcing it through fine glass tubes and drawing and spinning it. The alcohol-ether vapours are carried away by fans and the spun material is de-nitrated by ammonium sulphide. _Smokeless powder_ is a gun cotton powder—that is gun cotton the explosive power of which is utilised by bringing it into a gelatinous condition. This is effected by gelatinising the gun cotton with alcohol-ether or acetone (sometimes with addition of camphor, resin, &c.). A doughy, pasty mass results, which is then rolled, washed, dried, and pressed into rods. Nobel’s nitroleum (artillery powder) consists half of nitro-glycerin and half of collodion cotton. In the production of gun cotton and collodion cotton the workers are affected and endangered by nitric and nitrous fumes unless the nitrating apparatus is completely airtight. Erosion of the incisor teeth is general, but use of the new nitrating apparatus, especially of the nitrating centrifugal machines already described, has greatly diminished the evil. In making collodion, celluloid and artificial silk, in addition to the risks referred to in the production of gun cotton, the vapour from the solvents, ether, alcohol, acetone, acetic-ether, and camphor, comes into consideration, but there is no account of such poisoning in the literature of the subject. Other explosives which belong to the aromatic series are described in the chapter on Tar Derivatives, especially picric acid. PHOSPHORUS AND PHOSPHORUS MATCHES