288 ME. ABEL'S RESEAECHES ON GUN-COTTON. 



sible, by repeated digestion and washing, from matters soluble in ether and alcohol ; 

 and, in calculating the results, allowance was made for the mineral constituents of the 

 gun-cotton operated upon. 



Carbon determinations. Method I. — ^The gun-cotton yam was cut into small pieces, 

 dried, and the fragments introduced singly into a very long combustion-tube, each 

 portion being separated from the next by about 5 centimetres of oxide of copper. 

 When the tube had received the entire quantity to be burned, about 15 centimetres of 

 the anterior portion were filled with oxide of copper, and the remainder (about 20 cen- 

 timetres) with porous fragments of reduced copper. The potassa-apparatus, used for 

 absorbing carbonic acid, had a small chloride-of-calcium tube attached to it, which was 

 weighed together with the apparatus, before and after the combustion. Although the 

 greatest care was taken to proceed as slowly as possible with the heating of those portions 

 of the tube containing the gun-cotton, the successful completion of the operation was a 

 matter of great uncertainty, as the explosive combustion of some small portion of the 

 gun-cotton would very frequently throw the surrounding oxide of copper fonvard, thus 

 closing the necessary passage in the front part of the tube. This method was therefore 

 abandoned after about two dozen experiments had been made, of which only four were 

 brought to a satisfactory termination. The results of these were as follows : — 



Substance employed. Carbon found. 



I. 0-2219 grm. 23-71 per cent. 



II. 0-3204 „ 24-00 



III. 0-3790 „ 24-26 



IV. 0-1996 „ 24-12 



Mean 24-02 per cent. 



Method II. — The weighed substance was saturated with distilled water, and the latter 

 removed as far as possible by pressure. The moist yarn was then cut into eight or ten 

 pieces and introduced separately into one end of a long coftibustion-tube open at both 

 extremities, and divided in the centre by a plug of asbestos. The shorter portion of the 

 tube contained only the fragments of gun-cotton placed at distances of about 12 milli- 

 metres from each other ; the longer portion was previously filled with long layers of 

 oxide of copper, oxidized copper turnings, and porous reduced copper. This part of 

 the tube was connected with a desiccating apparatus, to which were attached the potassa- 

 bulbs with the small weighed chloride-of-calcium tube, fixed on to the outer limb. The 

 extremity of that part of the combustion-tube which contained the gun-cotton was con- 

 nected vdth an arrangement for passing an easily regulated current of pure dry air 

 through the apparatus. The two portions of the tube were separated in the furnace by 

 a screen. When the front part of the tube had been raised to a full red heat (at which 

 it was maintained throughout the operation), the pieces of gun-cotton were consecutively 

 made to undergo slow combustion, the portion nearest the asbestos plug being first 

 heated, and the resulting gases and aqueous vapours being carried forvi^ard by the slow- 

 current of air continuously passed through the apparatus. This passage of air served 



