58 FARADAY 



the atmosphere; and I have known of cases of cotton-mills 

 being fired as if with gunpowder through the very finely 

 divided particles of cotton being diffused through the atmos- 

 phere in the mill, when it has sometimes happened that a 

 flame has caught these raised particles, and it has run from 

 one end of the mill to the other and blown it up. That, then, 

 is on account of the affinity which the cotton has for the 

 oxygen; but suppose I set fire to this piece of cotton which 

 is rolled up tightly; it does not go on burning, because I 

 have limited the supply of oxygen, and the inside is pre- 

 vented from having access to the oxygen, just as it was in 

 the case of the lead by the oxide. But here is some cotton 

 which has been imbued with oxygen in a certain manner. 

 I need not trouble you now with the way it is prepared; 

 it is called gun-cotton ( 20 ). See how that burns [setting 

 fire to a piece] ; it is very different from the other, because 

 the oxygen which must be present in its proper amount is 

 put there beforehand. And I have here some pieces of 

 paper which are prepared like the gun-cotton ( a ), and im- 

 bued with bodies containing oxygen. Here is some which 

 has been soaked in nitrate of strontia : you will see the beau- 

 tiful red color of its flame; and here is another which I 

 think contains baryta, which gives that fine green light; and 

 I have here some more which has been soaked in nitrate of 

 copper: it does not burn quite so brightly, but still very 

 beautifully. In all these cases the combustion goes on inde- 

 pendent of the oxygen of the atmosphere. And here we have 

 some gunpowder put into a case, in order to show that it is 

 capable of burning under water. You know that we put it 

 into a gun, shutting off the atmosphere with shot, and yet the 

 oxygen which it contains supplies the particles with that 

 without which chemical action could not proceed. Now I 

 have a vessel of water here, and am going to make the 

 experiment of putting this fuse under the water, and you 



80 Gun-cotton is made by immersing cotton-wool in a mixture of sulphuric 

 acid and the strongest nitric acid or of sulphuric acid and nitrate of potash. 



a Paper prepared like gun-cotton. It should be bibulous paper, and must 

 be soaked for ten minutes in a mixture of ten parts, by measure, of oil of 

 Titriol with five parts of strong fuming nitric acid. The paper must after- 

 ward be thoroughly washed with warm distilled water, and then carefully 

 dried at a gentle heat. The paper is then saturated with chlorate of 

 strontia, or chlorate of baryta, or nitrate of copper, by immersion in * 

 warm solution of these salts. (See Chemical News, vol. i., p. 36.) 



