NITROGEN BODIES OF MODERN CHEMISTRY. 211 



snlplinrons smoke which renders approach impossible, as torexami)k^ iu 

 mines. ParticiUarly when common gunpowder is used for fracturing' rocks, 

 when experimental bkistings are made with closed shafts, after the ex- 

 plosion the air is irrespirahle, the ventilating shaft must act for a long 

 time before the place can be entered. This inconvenience is avoided ] >,v 

 the use of gun-cotton. I take this opportunity to indicate how we may 

 easily and intiillibly recognize a nitrogen body. It is merely necessary 

 to i)roduce its explosion in a partially closed space ; the space becomes 

 filled with weak nitrous acid vapor. For nitrous acid we have a very 

 reliable reagent, the sulphate of iron. Of course the experiment should 

 be made with a very small quantity of the cotton, as othervrise the ex- 

 jilosion would be too violent ; it would act in all directions, and prove 

 its fracturing force on the vessel. I beg here to repeat that the explo- 

 sion of such bodies consists in the sudden liberation of confined gases. 

 There is an instantaneous iiroduction of gas occupying a hundred-fold 

 the space of the cotton, a gas of high temperature and great elasticity. 

 Such gases iu a spherical space act in all directions ; therefore they act 

 not merely lengthwise of the. tube but against the sides of it also. Now, 

 if the action is on a scale not large enough to overcome the cohesion of 

 the sides of the vessel, the gas has time to escape upwards; but if the 

 action is so intense that its lateral components are sufQcienj] to overcome 

 the cohesion of the containing vessel, the fracturing force takes effect, 

 the vessel is shattered. Y/e must therefore use only a very small 

 quantity in our experiment. 



Nitrous acid changes the color of sulphate of iron to brown. We are 

 not to expect a conspicuous change of color, observe, because most of 

 the vapor escapes, only a small proportion remaining. Still there is 

 enough to prove that we have to do with a nitrogen compound. 



The slowly burning form of gun-cotton is called collodion-cotton. 

 This modification of gun-cotton, which is not so rapidly consumed, but 

 gradually burns out, is not used to propel projectiles, but it has other 

 and very valuable uses. This allotropic form of gun-cotton is obtained 

 by mixing English sulphuric acid with nitrate of potash and heating 

 the mixture to 50°. The nitrate of potash is decomposed, and the result 

 is bi-sulphate of potash and concentrated monohydrous nitric acid. 

 When it is all dissolved we immerse in this liquid at 50° cotton well 

 separated and dried, just as much as will lie in the liquid without pres- 

 sure and be entirely covered, and we let it remain at this temperature, 

 carefully watching it, from half an hour to an hour. The heat must rise 

 no higher, for if it does the mass begins to develop red vapors, the cot- 

 ton is in a tumuK, and presently nothing is left but oxalic acid. The 

 red vapor is a signal to lower the temperature. When this is all done 

 the cotton must be picked apart, rinsed in cold water, and dried ; and 

 thus we have cotton which does not explode well, but which dissolves 

 in alcohol and ether, while good gun-cotton will not so dissolve. Cot- 

 ton prepared at freezing temperature is insoluble in alcohol and ether, 



