166 Mr. Crum on the Analysis of Nitrates, and on Explosive Cotton. 



second time, and for twenty-four hours, in the same mixture of acids, but 

 without yielding any greater quantity of nitric acid. 



An immersion of one hour in nitric acid alone gave a better result. It 

 lost in weight by this second process 0*47 per cent. It was little altered 

 in fcppeara&oe, but after being dried in the open air, it lost in the air- 

 pump only 069 per cent., instead of 1*33, as in the former case. It is 

 this substance of which I will now relate the analysis. 



Ashes in Gun-Cotton. — Sixteen grains of gun-cotton were dissolved 

 in nitric acid. The solution being evaporated by degrees, and burnt to 

 ashes, left 0*035 gr. of a reddish ash, or 022 per cent. 



Nitric Acid in Gun-Cotton. — In this process the same apparatus is 

 employed as for nitrate of potash. About six grains of the gun-cotton, 

 containing a known quantity of water, is collected into a ball — squeezed 

 between the finger and thumb to free it as much as possible from air — 

 and let up into the jar, over the mercurial trough. 125 grains of sulphuric 

 acid are added to it. Nitric acid is liberated, and, being acted upon by 

 the mercury, produces nitric oxide. After one hour, when about three- 

 fourths of the whole gas has been evolved, and the gun-cotton is entirely 

 dissolved, fifty grains of water are added. In another hour the increase 

 of gas ceases ; in a few hours more its boundary is noted, then treated with 

 sulphate of iron, and the residue measured. It consists of azote 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 grains of gun-cotton=5*978, after being dried over sulphuric acid 



in vacuo, and= 

 5'964 grains, 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. 



5 '433 cubic inches, therefore, were deutoxide of nitrogen = 

 1*746 grains N0 2 , which represent 

 3*143 grains 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 Gun-Cotton. — Having failed to obtain good results by 

 burning this substance with oxide of 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 analysis 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 ijiches 



