of -preparing and employing Gun-cotton, 539 



means of ascertaining the influence which they may exert is to 

 compare their respective products. This we have done within the 

 last three months, with the cooperation of M. Faucher, Assistant 

 Commissioner of Gunpowder, and of M. Chapoteaut, assistant to 

 one of us. 



Before describing our comparative experiments, we must men- 

 tion a last modification which General von Lenk has introduced 

 into the manufacture of Austrian gun-cotton. 



It is regarding the use of soluble glass, with a view to close 

 the fibres of cotton by the precipitation of silicate to retard the 

 disengagement of gas, and then to eliminate the traces of acid 

 which might be there. (The words in italics are extracted from a 

 note of General von Lenk.) 



This preparation is applied by arranging the gun-cotton in a 

 rotatory apparatus, into which leads a pipe pouring upon it solu- 

 tion of glass of 12° Baume. The gun-cotton thus treated is 

 dried and left for a sufficiently long time to allow the carbonic 

 acid of the atmosphere to unite with the soda of the glass, which 

 causes the precipitation of silica. The carbonate of soda being 

 removed by washing, the insoluble silicate remains as a sort of 

 sheath, adhering to the fibres of the cotton, which thus increases 

 about 2 per cent, in weight. 



Here is a difference between the two methods; soluble glass 

 has never been used in France; but we shall show in describing 

 our experiments that this modification has not the importance 

 ascribed to it by General von Lenk. 



Our experiments have been made upon three series of pyro- 

 xyles. 



In the first we class the large number of specimens which 

 have been prepared and examined in the laboratory, principally 

 with a view to determine the quantity of pyroxyle produced by 

 a given weight of cotton, by varying the quantity of the mixture, 

 its proportion, and the duration of the impregnation. 



The second series comprises three specimens of the Lenk 

 manufacture : one which General Lenk has presented as a spe- 

 cimen of the Hirtenberg manufacture ; another which came 

 from London, the product of a private manufactory in England 

 on the model of that of Hirtenberg ; the third, which has been 

 prepared under our own eyes, by the method of General von 

 Lenk. 



We may observe that this third specimen was immersed in a 

 current of water for four days instead of for six weeks, and sili- 

 cate of soda was not used. In our view an immersion of four 

 days was sufficient to remove all trace of acids. The washing 

 with water was followed by a washing with potash; we even 

 think that it might have been abridged without the least incon- 



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