THE ATMOSPHERE AS AiV ANVIL. 221 



caustic potash. My assistant will pour some nitric acid into a solution 

 of caustic potash, and you will soon see crystals of saltpetre appear, 

 shooting out from the sides of the dish, whose image we have pro- 

 jected on the screen. In a similar way we can prepare nitro-glycerine, 

 by pouring glycerine in a fine stream into very strong nitric acid, ren- 

 dered more active by being mixed with sulphuric acid — oil of vitriol. 



" We could easily make the experiment, but you could see nothing. 

 There is no apparent change, and it is a remarkable fact that, when 

 pure, nitro-glycerine resembles, externally, very closely glycerine it- 

 self, and, like it, is a colorless, oily fluid — the reddish-yellow color of 

 the commercial article being due to impurities. As soon as the chem- 

 ical change is ended, the nitro-glycerine must be very carefully washed 

 with water, until all adhering acid has been removed. The material 

 thus obtained has most singular qualities, and not the least unex- 

 pected of these is its stability under ordinary conditions. After the 

 terrible accidents that have happened, it would, perhaps, be rash to 

 say that it did not readily explode ; but I can assure you that it is not 

 an easy matter to explode pure nitro-glycerine. It is not nearly so 

 explosive as gunpowder, and I am told that the flame of an ordinary 

 match can be quenched in it without danger, although I confess that 

 I should be unwilling to try the experiment. Still, there can be no 

 doubt that, under ordinary circumstances, a small flame will not ignite 

 it. My knowledge of the matter is derived from Prof. Hill, of the 

 Torpedo Station, at !N'ewport, who has studied very carefully the prep- 

 aration and application of the material. He is of opinion that most 

 of the accidents which have given to nitro-glycerine such an unfortu- 

 nate notoriety have been caused by the use of an impure article, and 

 that proper care in its preparation would greatly lessen the danger 

 attending its use. Nitro-glycerine is usually exploded, not by the 

 direct application of heat, but by a sudden and violent concussion, 

 which is obtained by firing in contact with it a fuse of some fulminat- 

 ing powder. The efiects of this explosion are as peculiar as the meth- 

 od by which it is obtained, and I can best illustrate the subject by 

 describing an experiment with nitro-glycerine which I witnessed my- 

 self at the Torpedo Station a few months since. 



*' It is so inconvenient to handle liquid nitro-glycerine that it is 

 now usual to mix it with some inert and impalpable powder, and the 

 names dualine and dynamite have been given to different mixtures of 

 this kind ; but in both of these the powder merely acts as a sponge. 

 In the experiment referred to, a canister holding less than a pound of 

 dynamite, and only a few ounces of nitro-glycerine, was placed on the 

 top of a large bowlder-rock, weighing two or three tons. In order 

 that you may fully appreciate the conditions, I repeat that this tin 

 case was simply laid on the top of the bowlder, and not confined in 

 any way. The nitro-glycerine was then exploded by an appropriate 

 fuse fired from a distance by electricity. The report was not louder 



