[ 4.26 ] 



LXVI. On a Method for the Analysis of Bodies containing 

 Nitric Acid, and its application to Explosive Cotton. By 

 Walter Crum, F.R.S.* 



\ T the first meeting oftlie present Session of the Philoso- 

 ■^^ phical Society, I gave an account of some experimental in- 

 quiries into the nature of gun-cotton, a body whose composition 

 was then little known. I had at that time chiefly occupied my- 

 self with its nitrous contents, and described a method by which 

 some approximation could be made to a quantitative result for 

 nitric acid. On resuming the subject, I found that much was 

 wanting to render the method a rigorously accurate one; and 

 I shall now relate what I have since done to simplify and 

 complete it. I shall first, however, give an account of its 

 application to nitrate of potash, — a body of known composi- 

 tion, and easily obtained in a state of purity, — to which I had 

 recourse as a means of proving the accuracy of the method, 

 and detecting any fallacy to which it might be liable. 



Nitric Acid in Nitrate of Potash. — The salt 1 employed 

 was purified by repeated crystallization, and fused at little more 

 than its melting heat. A glass jar, eight inches long and an 

 inch and a quarter in diameter, is filled with, and inverted 

 over mercury. A single lump of the fused nitrate, weighing 

 about six grains, is let up into it, and afterwards fifty grains 

 of water. As soon as the nitrate is dissolved, 125 grains of 

 sulphuric acid, ascertained to be free from nitric acid, are 

 added. By the action of the mercury upon the liberated nitric 

 acid, deutoxide of nitrogen soon begins to be evolved, and 

 usually in about two hours, without the application of heat, 

 the whole of the nitric acid is converted into that gas. Occa- 

 sional agitation is necessary, and it is easily performed by 

 giving a jerking horizontal motion to the upper part of the jar. 

 The surface of the sulphuric acid is then marked, and three- 

 fourths of a cubic inch of solution of sulphate of iron, recently 

 boiled, let up into the jar. The gas is rapidly absorbed, ex- 

 cept a small portion at last, which must be left several hours 

 to the action of the solution, or be well agitated in a smaller 

 tube with a fresh portion of it. No correction of the nitric 

 oxide has to be made for moisture ; for the mixture of acid and 

 water which I employed, as I ascertained by direct experiment, 

 has no perceptible force of vapour. In one experiment, 



5*40 grains nitrate of potash yielded 



4'97.5 cubic inches of gas, at 60^ Fahr., and bar. 30 inches. 



The residue not absorbable by sulphate of iron, was 



* Read before the Philosophical Society of Glasgow, April 14, 1847, and 

 communicated by tlie Author. 



