TO CORRESPONDENTS.

Poverty Bay Standard, Volume X, Issue 1126, 18 August 1882, Page 2

TO CORRESPONDENTS.

[COX'TISI'ED FROM OCR LAST.] “Late Royat. Engineer” is informed as follows in reply to questions : — GUN COTTON. The process proposed by Profc or Abel, F.R.S., and nov<- adopted in E l 4 nd, in the preparation of gun cotton, of submitting the gun cotton fibre to the pulping process and afterwards converting the pulp into sheets or moulded masses to ivh-'ch perfect compactness and a high den.lty con'd lie given without difficulty, by me." .s of mechanical appliances, has been attended with most advantageous results, not only by increasing its efficiency as an explosive agent, but also with regard to its stability and facility, and cheapness of manufacture, instead of the raw cotton of high quality and long staple which it had been previously necessary to use in carrying out the Austrian system, any description of cotton can now be used, and the waste cuttings (such as are used for cleaning machinery) are as now suitable for the manufacture of gun cotton as any other description. The cotton, after being very carefully dried is immersed in small quantities at a time in a cold mixture composed of three parts by weight of sulphuric acid, specific gravity 1.85, and one part of nitric acid, specific gravity 1.5, and moved about for a few- minutes, then removed, gently pressed, and placed in stone jars in a cool place and allowed to remain for about 24 hours in contact with about ten times its weight of the mixed acids, to ensure a complete conversion into gun-cotton, it is then raised two or three times in a large volume of water, the water being extracted as completely as possible between raising by means of centrifugal apparatus ; it is then transferred to a rag engine of the kind ordinarily used in producing pulp for paper making. Here it is not only reduced to the state of fine division necessary for its subsequent conversion into homogeneous compressed masses, but it also undergoes at the same time a most searching purification, which is continued in a still more complete manner in the next operation, tho pulp being transferred to what is termed a 11 poaching’' machine where it is beaten about, so as to remain uniformly suspended in a large volume of warm water, continuously renewed, and rendered slightly alkaline at the close of the operation, This washing generally lasts about 48 hours. When tlio pulp is completely purified it is converted into compact masses of tho desired form and density, by means of a moulding process and hydraulic pressure ranging from tour to six tons on the square inch. During these processes, the gun-cotton, being wet, Is absolutely uninflammable. The final drying of the masses is carried on very rapidly and safely upon hot plates whkli are freely open to the air at the sides. Compressed gun-ootton though not liable to explode when stored In small quantities, should, when stored DRY in large quantities, be treated with the same precautions as gunpowder. It Is not injured by the damp. It can either bo exploded instantaneously, or with any required degree of velocity by simply varying the mechanical arrangements under which it Is used. Instantaneous combustion in mines or submarine explosions; slow combustion when manageable powder is required. If the first is required the gun-cotton must be confined in a perfectly close receptacle i if the latter, the cotton should be opened out mechanically, in which state it can be made to aot more slowly than gunpowder. But the necessity of confining either gunpowder or gun-cotton iu strong receptacles, for the purpose of developing their explosive force, is greatly reduced when detonating fuses are used as exploding agents, and is indeed, entirely dispensed with in tho case of charges fired under water. Thus if thin glass, or a waterproof bag Is used in conjunction with a detonating fuze, the effect produced will be as great as that of a charge fired in a strong iron receptacle by the ordinary method. The effect of gun-cotton in submarine explosions is equal to that obtained with four times the weight in gunpowder. 8001bs. of gunpowder would not produce more result than 1501bs. of compressed gun-cotton (being fired by detonation) as now manufactured. The depth in feet at which a given charge of gun-cotton can be used with the greatest effect may be roug’ ly taken as the square root of the charge, in gunpowder, in pounds. Wet gun-cotton can be used in torpedo's with nearly equal destructive effect to that of dry cotton. Gun-cotton yarn steeped in saltpetre, and covered with a coating of India-rubber, makes an excellent fuze j the combustion is rapid, being about 30ft. per second. Gun-cotton explodes at a comparatively low temperature varying between 280° and 325° Fahrenheit.

[The foregoing answers to “Late Royal Engineer’s” enquiry in our issue of the 12th hist., are condensed from “The Manual of Gunnery for Her Majesty’s Fleet,” which, we believe to be the best authority extant upon the subject referred to, being the joint work of some of the most distinguished officers of both services, aided by eminent professors of Chemistry.—Ed. P.B.S.]