MECHANICS AND USEFUL AE.TS. 89 



a little of this substance, and then to expose this to a moderately 

 violent blow, in order to show its explosive nature. 



One of the most recently-discovered and curious of these explo- 

 sive organic bodies is the nitrate of diazobenzol, obtained by the 

 action of nitrous acid at a low temperature upon aniline. This sub- 

 stance expledes at least as violently as iodide of nitrogen and fulmi- 

 nate of silver, if exposed to a heat approaching that of boiling 

 water; it is, however, far less sensitive to friction than those two 

 bodies. Similarly explosive substances have been quite recently 

 obtained by Dr. Hoffmann from derivatives of the interesting and 

 important base, rosaniline, the salts of which furnish some of the 

 most beautiful of the colors now obtained from aniline. 



Explosions are most readily produced by establishing chemical 

 action between certain substances greatly opposed to each other in 

 their properties, and brought together in an intimate state of mix- 

 ture. The substances applicable to the production of such mixtures 

 are, on the one hand, bodies remarkable for their great affinity for 

 oxygen, and, on the other, compounds containing that element in 

 abundance, and partly or entirely in a loose state of combination. 

 To the first class belong the elements carbon, sulphur, and phospho- 

 rus, and compounds of the last two with readily oxidizable metals. 

 The second class includes a few of the higher metallic oxides, such 

 as the higher oxides of manganese and lead, and combinations of met- 

 als with nitric, chloric, and perchloric acids. Mixtures produced 

 with these two classes of bodies readily ignite, or afford explosions, 

 either upon the direct application of heat, or by submitting them to 

 friction, percussion, or concussion : and, in a few instances, by estab- 

 lishing chemical action in a small portion of the mixture, with the 

 aid of some other compound. These explosive mixtures vary greatly 

 in the ease with which chemical action is established in them, and in 

 the rapidity and violence of their transformation ; their properties 

 are naturally regulated by the chemical and physical characters of 

 their constituents, and by the degree of intimacy of their mixture. 



The variation in their explosive properties, and the great extent 

 to which the characters of any particular mixture may be modified, 

 are very important elements in their application to practical pur- 

 poses ; while the comparatively instantaneous nature of the decompo- 

 sition of explosive compounds, and the facility with which it is 

 brought about, present very great, and in many cases insuperable 

 obstacles to their employment as explosive agents. 



A very slight examination into the effects of fulminate of mercury 

 and of gunpowder, employed under the same circumstances, will 

 illustrate the difference in the effects produced by substances which 

 explode with different rapidity. Let me first compare the rate of com- 

 bustion of those two substances. Here is a small train of fulminate 

 of mercury, and here is a similar train of gunpowder. You observe 

 that the flame travels much more rapidly along the train of fulminate 

 than along the gunpowder. This difference will prepare you to 

 believe that the effect of the two when confined in vessels must be 

 different. Here are the fragments produced by the explosion, in a 

 small shell, of 100 grains of fulminate of mercury; a number (amount- 

 ing to one-seventh of the weight of the shell) were, however, so small 



8* 



