40 Transactions of the 



decomiiosed cliloride and bromide of niti'Ogen, being all gaseous, 

 expand much more, and so produce a louder report, and do more 

 damage. 



When we turn our attention to gun-cotton and its allied sub- 

 stances, we see that their explosive properties are owing to a 

 different cause than mere distcnion of atoms, as is the case in 

 iodide of nitrogen, for it is the oxygen which they contain, ready 

 to be liberated at any time from the nitrogen, that directly on 

 being set free forms new gaseous products, occupying a much 

 greater bulk. 



Since oxygen is formed in such great quantities from the sub- 

 stance itself, there is no need, as in the combustion of paper, wood, 

 &c., for the presence of tlie oxygen of the air. So gun-cotton, like 

 gunpowder, can be burnt in a closed space free from air, or in an 

 atmosphere incapable of acting on it, as nitrogen, or carbonic acid. 

 {Experiment) 



Nitroglycerine, which is glycerine with three atoms of its 

 hydrogen replaced by three molecules of the radicle NOo, is used 

 for blasting rocks, and is ignited by an iron wire passing through 

 it, when enclosed in a strong case, and connected at each end with 

 a copper wire from either pole of a voltaic battery. This iron 

 wire, being a less perfect conductor of electricity than the copper 

 wire, causes some of the electricity to be transformed into a 

 different kind of energy, viz., heat, and the nitroglycerine is ignited 

 and explodes. 



Gun-cotton, as its name implies, has lately come into use for 

 guns and cannons as a substitute for gunpowder. 



Gun-cotton is manufactured on a large scale by acting on cotton- 

 wool (previously cleansed from grease by boiling with soda) with 

 a mixture of strong nitric and sulphuric acids : the sulphuric acid 

 is necessary for taking up all the superfluous water of the nitric 

 acid, and tlms the cotton-wool is kept continually exposed to the 

 nitric acid in its strongest form, when deprived of its water. After 

 a certain time, from a quarter to half an hour, the cotton-wool has 

 taken i>p as much NOo as it can, and is converted into the highest 

 form of gun-cotton : I say the highest form, because there are 

 many lower nitrous compounds of cotton, or cellulose, which 

 mixed together constitute collodion, a substance used in jihoto- 

 graphy, and soluble in a mixture of alcohol and ether, whilst the 

 highest form of nitrocellulose (represented by [ds H.j (NOj);, Ou]) 

 is quite insoluble in the mixture. {E^nperiment.) 



The gun-cotton is next washed well in a stream of running 

 water, pulled to pieces, and thrown on to the cooper hooks of a 

 centrifugal machine, where by an action like that of drying a mop 

 by twirling it round, the gun-cotton parts with most of its mois- 



