GUN-COTTON 757; 



' 7. After the lapse of forty-eight hours, the acid is separated from the gun-cotton, 

 as completely as possible, by mechanical moans (. e., by means of the centrifugal 

 extractors). The expressed acids are not employed again. 



. ' 8. The hanks aro then drenched with water, singly, as rapidly as possible ; they 

 are afterwards washed by hand till no longer acid to the taste, and are afterwards 

 placed in crates or perforated boxes, and kept immersed in flowing water for about 

 three weeks. 



' 9. At the expiration of that time, the water is separated mechanically from tho 

 gun-cotton, and the moist skeins are boiled for fifteen minutes in a solution of potassic 

 carbonate (of specific gravity 1 '02). When the alkaline liquor has been expressed, 

 the skeins are once more immersed, in flowing water, for a few days. The finished 

 gun-cotton, is then dried by exposure to air. 



. ' 10. It is afterwards allowed to soak for about one hour in a cold solution of sodic 

 silicate (of specific gravity 1-072). The liquid is then expressed from tho hanks in 

 the usual manner ; after which they are allowed to dry thoroughly, again washed, for 

 five or six hours, in running water, and finally by hand. The thorough desiccation 

 of the gun-cotton then completes its manufacture. 



' The employment of the cotton in the form of hanks of loosely-spun yarn, instead 

 of simply in the loose carded condition, considerably facilitates its conversion and 

 purification. The proper impregnation of the cotton by the acids is more rapidly 

 accomplished with the hanks ; such manipulations as attend the separation of the 

 main quantity of acid from the converted material, and its first rapid and complete 

 immersion (while still saturated with the concentrated acids) into water, and aro 

 much more readily carried out with the cotton in the spun form ; and, again, the 

 exposure of the latter to the full purifying effects of a current of water, is much more 

 simply and perfectly effected than if carded cotton be used, while the mechanical loss 

 of wool and of gun-cotton, in the several operations of washing and expressing, is 

 much reduced.' ... 



Professor Abel perfedtly satisfied himself of the advantages 'just 'pointed out, by 

 operating upon considerable quantities of carded cotton wool. 'In these experiments 

 it was found impracticable, moreover, : except by application of very powerful pres- 

 sure, to reduce the proportion of the acid which the wool retained after immersion 

 (and which had to be left in contact with it, as prescribed) below that of fourteen parts 

 to one of cotton ; whereas with the yarn there is no difficulty in reducing the quan- 

 tity, by moderate pressure, to ten parts, or even lower. The consumption of acid is 

 therefore economized by using the cotton in a spun form. 



' The preparation of the mixture of nitric and sulphuric acids, as directed by Von 

 Lenk, involves no important point of novelty. The necessity of employing the mixture 

 cold, and therefore of either submitting it to refrigeration before use, or of preparing 

 a stock of the mixture some time before it was required, was well known to the earlier 

 operators. 1 



In the treatment of the cotton with the mixed acids, the following precautions, 

 namely, the immersion of uniform quantities <5f the" perfectly dry cotton in the bath of 

 acid, the adherence to a fixed proportion in weight between the cotton and the acid 

 uith which it is left in contact, and the regular "replacement 'of the acids removed 

 from the bath at each successive immersion of the Cotton; by a corresponding quantity 

 of fresh mixture, combine to exert ' no tfnimpbrtant influence* upon the uniformity of 

 the product. That such is the cdse has been established by manufacturing experi- 

 ments. For example, on one occasion 'some* hanks of 'cotton were immersed in the 

 bath of acids without addition 1 to ttie latter, of the Quantity of fresh acid proportionate 

 to the amount removed in the previous operation of immersion. The resulting pro- 

 duct, which was in all other respects treated as usual, exhibited a decided difference, 

 both in its composition and its explosive powers, when compared with gun-cotton 

 previously produced, strictly according to rule, in the same bath of acids.' 



Effects of heat upon gun-cotton. The behaviour of gun-cotton under exposure, 



1 An observation made by Bechamp, in his Papers on Pyroxylin, that the production of a soluble 

 or insoluble product was determined simply by conditions of temperature when the conversion was 

 effected by means of sulphuric acid and saltpetre, induced me to ascertain by experiment whether 

 the solubility, in alcohol and ether, of the product obtained with the employment of the prescribed 

 mixture of nitric and sulphuric acids, increased, if the temperature of the latter was raised to about 

 70 C. That temperature was fixed upon for the experiment as being the average of the freshly-pre- 

 pared mixture of nitric and sulphuric acids, usually employed for producing gun-cotton for photo- 

 graphic purposes, and which, in experiments instituted, furnished soluble gun-cotton, yielding 

 transparent collodion. The products obtained by the action of the warm mixture upon the cotton 

 wool exhibited no difference as regards its insolubility from the ordinary products furnished by the 

 cold mixture. Neither was insoluble gun-cotton rendered at all soluble by being submitted to treat- 

 ment with the warm mixture. Hadow has shown that a more dilute mixture of acids, which when 

 cold, furnishes an almost insoluble product, will, if employed at a temperature of 55 C., yield 

 perfectly soluble gnn-cotton, giving a fluid transparent collodion. 



