Mr. W. Crmn on the Composition of Gun-Cot ton. 429 



from the common air introduced with the gun-cotton, and a 

 minute portion also, which is always accidentally entangled 

 between the mercury and the glass. Its oxygen is absorbed 

 by the mercury, when in the state of nitrous acid. 



In one experiment — 



6-02 grs. of gun-cotton = 5*978, after being dried over 

 sulphuric acid in vacuo, and = 



5'964' grs., after deducting ashes, produced 



5-513 cubic inches of gas, bar. 30 in., therm. 60°, of which 



0-08 was left by sulphate of iron. 



S"433 cubic inches, therefore, were deutoxide of nitrogen, = 



1'746 grs. NOj, which represent 



3-143 grs. of nitric acid, or 52-70 per cent. 

 Another experiment gave 52*68 per cent. 



The gun-cotton prepared by a single immersion gave only 

 51*42 per cent, of nitric acid. 



Carbon in Gim-Cotton. — Having failed to obtain good results 

 by burning this substance with oxideof copper, I used chromate 

 of lead, precipitated from the nitrate, and heated to redness. 

 I employed for the combustion an apparatus which I used 

 many years ago for the analj'sis of indigo, and I still find it 

 very convenient for substances which do not require a strong 

 red heat. It consists of a tube of hard glass, eight inches long 

 and three-eighths of an inch in diameter; the gases from which 

 are led by a small bent tube under the receiver in a mercurial 

 trough. 



1 inch at the closed end of the tube is filled with 8 grains 

 chlorate of potash, ground with chromate of lead. 



4i inches are filled with chromate of lead, among which is 

 ground to powder 3 grains of the gun-cotton. 



li inch contains chromate of lead that has been used to wash 

 out the mortar. 



A glass plug separates these materials from the perforated 

 cork which joins the two tubes. The materials are gradually 

 heated with broad-wicked spirit-lamps. Carbonic acid comes 

 over, mixed, when in the receiver, with nitric oxide and the 

 azote of the apparatus ; and when all the gun-cotton is con- 

 sumed, the lamps are extended to the chlorate of potash. The 

 oxygen gas thus liberated, which in other cases is useful to 

 consume carbonaceous matter that may have escaped the 

 chromate, expels in this case all remains of carbonic acid, and 

 passing itself into the receiver, mixes tliere with the nitric oxide, 

 and causes its entire absorption by the mercury. Oxygen and 

 azote are then the only gases left along with the carbonic acid, 

 and as those are not absorbable, an addition of half a cubic 

 inch of solution of caustic soda indicates exactly the quantity 

 of carbonic acid present. 



