MR. ABEL'S RESEARCHES OX GUN-COTTON. 277 



A careful examination of products of manufacture, prepared by continuing the contact 

 of the acids with the gun-cotton for only one-half of the usual period (twenty-four hours), 

 failed to indicate any diiference between them and products obtained by the full period 

 of immersion ; on the other hand, a prolongation of the immersion to seventy-two hours 

 did not furnish results more closely in accordance with theoretical demands than the 

 ordinary treatment. 



It was found, by experiments with several hundred pounds of spun cotton, that a con- 

 siderable increase beyond the prescribed proportion of acid left in contact with the gun- 

 cotton (eighteen or twenty parts instead of ten parts to one of cotton) furnished products 

 which differed from those obtained by a strict adherence to Lenk's directions, only in 

 containing somewhat smaller proportions of foreign matters than products in the manu- 

 facture of which ten parts of acid had been used. 



The heat resulting from the chemical action of the nitric acid upon the cotton, and 

 from the union of the acids with the liberated water, is considerable ; it is therefore 

 quite as important that the bath of acid in which repeated immersions are effected should 

 be kept cool by being surrounded with cold water, as that the acid mixture should in 

 the first instance be perfectly cold. Moreover, the precaution which Von Lenk adopts 

 (excepting in cold weather) of keeping the closed vessels, in which the gun-cotton 

 remains for forty-eight hours in contact vdth the acids, surrounded by cold water, is also 

 very essential ; for otherwise the accumulation of heat by the contents of the vessel, in 

 consequence of the gradual conversion of some portions of the cotton, after its removal 

 from the bath, may occasionally become sufficiently considerable to establish a destructive 

 action of the acids upon the gun-cotton. 



There can be no question as. regards the necessity of employing some method, such as 

 that adopted by Von Lenk, for rendering as sudden and complete as possible the first 

 immersion into water of the gun-cotton which is still saturated with acids (though these 

 have been separated from it as far as possible by means of a centrifugal extractor) ; for 

 if the hanks are simply thrown or dipped into water, the heat generated by the gradual 

 penetration of the latter into the compact mass of gun-cotton, saturated with concen- 

 trated acids, suffices to establish in some parts a destructive action of the latter upon the 

 gun-cotton, which is rendered evident by the disengagement of nitrous vapours, and 

 which, though it is very speedily checked, as the acid becomes largely diluted by water, 

 may give rise to the production of small quantities of substances of comparatively 

 unstable character, not removed from the gun-cotton by the subsequent purification, 

 The most effectual plan of rapidly diluting the acid in the gun-cotton is to throw the 

 skeins just removed from the extractor singly into a cascade of water, whereby the instan- 

 taneous penetration of the mass of cotton by a large body of water is accomplished with 

 ease and certainty. 



The subsequent continuous immersion of the gun-cotton for at least three weeks in a 

 stream of water, as directed by Von Lenk, is unnecessarily long, as the gun-cotton is 

 afterwards still subjected to treatment with an alkaline water, and to a final washing. 



MDCCCIAVI. 2 Q 



