July 29, 1909] 



NA TURE 



145 



guncotton, still in the same physical condition as the 

 cotton waste from which it had been produced, was re- 

 duced to a fine state of division in a beating-engine. The 

 effect of this important modification was to remove the last 

 traces of " free acid " and of unstable bodies, so that 

 the prolonged washing; in cold water could be dispensed 

 with, and, at the same time, a much more stable product 

 obtained. 



Cotton fibre is of a tubular structure, and so long as 

 these tubes exist in long lengths the impurities in the 

 interior of the tubes, derived from the evaporated juices of 

 the cotton plant, and more or less affected by the nitration 

 process, are extremely difticult of removal. Not only is 

 the cotton in the form of long tubular fibres, but these 

 fibres are themselves matted and entwined to such an 

 extent that the former process of washing in running 

 water even failed to remove impurities from amongst the 

 bundles of fibre. 



The operation of pulping introduced by Abel breaks up 

 both the bundles of fibre and the fibres themselves, re- 

 ducing the latter to short lengths or destroying them 

 altogether by crushing. In this fine state of division the 

 removal of impurities is much more readily effected by 

 washing. 



The manufacture of guncotton by the von Lenk-Abel 

 process was commenced in this country about 1S65. 

 Foreign countries took It up in quick succession, and the 

 process was the one universally followed for the next forty 

 years. Some modifications of the nitration process were 

 made towards the end of that period, in one case in the 

 direction of dipping larger charges of cotton waste, and 

 of allowing them to remain in the original acid mixture 

 until nitration was completed, and then transferring the 

 whole contents of the nitrating pan into the acid centri- 

 fugal ; in another case the nitration process was actually 

 carried out in the centrifugal itself. 



In 1905, however, an entirely new system of nitration, 

 hereafter referred to as the "displacement process," was 

 invented by Messrs. Thomson, of the Royal Gunpowder 

 Factory, and this process has been perfected and has 

 entirely replaced the pot system of nitration there, and at 

 Nobel's Explosives Factory at Ardeer, in Scotland. It is 

 also being adopted at other factories both in this country 

 and abroad. 



The nitration of the cotton waste is carried out in 

 shallow, circular earthenware pans. These pans are 

 group' d together and worked in sets of four. The bottom 

 of the pan slopes downwards to a central hole, connected 

 by suitable pipes and cocks to a pipe supplying the 

 nitrating acid, and to other pipes through which the 

 waste acid is removed on completion of nitration. The 

 pans are covered with aluminium hoods connected to an 

 exhaust fan, for carrying off fumes. 



Nitrating acid is then run in up to a definite mark, and 

 a charge of 20 lb. of dry. cotton waste is immersed in 

 the acid in each pan In small quantities at a time. An 

 aluminium fork is used for the purpose. When the 

 vharge of cotton waste has been dipped,* perforated earthen- 

 ware plates are placed on the top of it to keep it all 

 under the surface of the acid; a film of cold water is run 

 on to the surface of the plate? and serves as a seal to 

 prevent fumes getting' into the room, and the aluminium 

 hoods are removed. The cotton waste remains soaking 

 in the acid for two and a half hours ; at the expiration 

 of that time Its conversion to guncotton is complete. The 

 cock leading to the waste acid pipe is then opened, and 

 t,he waste acid allowed to flow away from the guncotton 

 at a definite rate, whilst cold water is allowed to flow on 

 to the top of the perforated plates at an equal rate. The 

 water follows up the acid through the guncotton without 

 any appreciable mixing of the water and the acid taking 

 place, and when the whole of the acid has been displaced 

 in this way the water is allowed to drain away from the 

 guncotton, which is then ready for the final purification 

 process. This system of manufacture possesses many 

 advantages over the systems which it is superseding. Fore- 

 most among them are : — 



(i) Decreased cost of manufacture, due to the facts that 

 for a given output very much less labour is required ; 

 that the plant is both very cheap and very durable : that 

 no DOwer is required to work it ; that less acid is lost 

 in the washing processes : and that, owing to the absence 



NO. 2074, VOL. 81 1 



of fumes and spilt acid, the cost of maintenance of the 

 buildmgs is reduced. 



(2) Increased safety so far as personnel is concerned, 

 because there is no escape or splashing about of acid, 

 which in the old processes was a fruitful source of acid 

 burns, and also because decompositions, which used to 

 take place both in the digesting pots and In the acid 

 centrifugals, with the consequent evolution of poisonous 

 oxides of nitrogen, no longer occur. 



(3) A better guncotton is obtained. It Is freer from un- 

 converted cotton, and as the whole of the nitration and 

 preliminary washing operations are carried out in earthen- 

 ware receptacles, It is freer from mineral Impurities. 



(4) An increased yield to the extent of about 7 per cent, 

 is realised. 



The manufacture of guncotton was not commenced at 

 the Royal Gunpowder Factory, Waltham Abbey, until the 

 year 1S72. Shortly after that date an Improvement was 

 made in the purification process. It consisted in subjecting 

 the guncotton, while still in the waste form, to a series 

 of steam boilings in large wooden vats. In the early days 

 of this process boilings of long duration were used 

 throughout. Later, a system was introduced in which a 

 large number of short boilings at the commencement was 

 followed by a couple of final long boilings. With the 

 introduction of the displacement process of nitration, a 

 thorough investigation of the chemistry of the boiling 

 process was undertaken at Waltham Abbey, and as a 

 result it was ascertained that a more rapid purification 

 was eftected by means of two long boilings, each of twelve 

 hours' duration, followed by a series of very much shorter 

 ones. 



It is very probable that the displacement system of 

 nitration is itself responsible for the reduction in the 

 amount of boiling required to produce a stable guncotton. 

 Although there is no appreciable amount of mixing taking 

 place between the displacing water and the waste acid, 

 still, mixing at the surface of contact does occur to a 

 slight extent, sufficient to produce a distinct rise of 

 temperature. The zone of warm acid liquid produced 

 passes very slowlv through the whole of the guncotton, 

 removing In Its course various Impurities. The purifying 

 action of this liquid is no doubt due to the fact that It 

 possesses strong oxidising and solvent properties. 



The pulping process introduced by Abel is still universally 

 employed, and although its value from a purification point 

 of view is no longer of such great importance now that 

 guncotton Is boiled as it was in the early days of cold- 

 water washing, it is, undoubtedly, still of use in effecting 

 a final purification of the guncotton. 



In the beating-engine the mechanical process of reducing 

 the guncotton to a pulp is effected, but no actual removal 

 of impurities takes place, because the water is not changed 

 during the operation. The impurities still present in the 

 guncotton at this stage are both mechanical and chemical. 

 The mechanical impurities consist chiefly of particles of 

 metal of various kinds, sand and fine grit, wood and 

 similar substances, introduced originally In the cotton 

 waste and during the processes of manufacture. _ The 

 chemical impurities are bodies produced by the action of 

 the nitrating acid on bodies other than cellulose ; they are 

 not entirely removed in the boiling process, but are_ set 

 free in the pulping. To remove the mechanical impurities 

 the guncotton pulp, in a large volume of water, is at 

 Waltham .'\bbey run from the beaters over flannel laid 

 on long shallow troughs, the troughs having pockets with 

 baflle plates at intervals. The rough surface of the flannel 

 retains the fine particles of grit, &c., and the larger 

 particles settle in the pockets or grit-traps. In the last 

 pocket an electromagnet is inserted to remove iron or 

 steel particles which may have escaped retention in the 

 grit-traps. 



The guncotton thus freed from mechanical impurities 

 runs into large oval iron tanks called " poachers," where 

 it receives several cold-water washings. The contents of 

 the poacher are agitated by means of a power-driven 

 wooden paddle-wheel, and then allowed to settle. The 

 washing water containing the impurities is drawn off from 

 the surface of the guncotton by means of a large skimmer, 

 in order that not only impurities in solution may be 

 removed, but also any light solid impurities in suspen- 

 sion. 



