100 CHEMICAL AFFINITY. 



[setting fire to a piece] ; it is very different from 

 the other, because the oxygen that must be 

 present in its proper amount is put there before- 

 hand. And I have here some pieces of paper 

 which are prepared like the gun-cotton ( a2 ), and 

 imbued with bodies containing oxygen. Here 

 is some which has been soaked in nitrate of 

 strontia you will see the beautiful red colour 

 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 ex- 

 periment of putting this fuse under the water, 

 and you will see whether that water can extin- 

 guish it ; here it is burning out of the water, 



