Page:Popular Science Monthly Volume 56.djvu/316

302 classified under the heads of physical mixtures like gunpowder, or chemical compounds like nitroglycerin, and they owe their development of energy to the fact that, like gunpowder, they are mixtures in which combustible substances such as charcoal are mixed with supporters of combustion such as niter; or that, like chloride of nitrogen, they are chemical compounds, the formation of whose molecules is attended with the absorption of heat; or that, like gun cotton, they are chemical compounds whose molecules contain both the combustible and the supporter of combustion, and whose formation from their elements is attended with the absorption of heat; while occupying a middle place between the gunpowder and the



gun-cotton class, and possessing also to some degree the properties of the nitrogen-chloride class, are the nitro-substitution explosives, of which melinite, emmonsite, lyddite, and joveite furnish conspicuous examples.

It may lead to a clearer understanding of what is said regarding the applications of explosives to dwell briefly on the methods by which some of them are produced, since, although the raw material in each case is different and the details of the operations vary, the underlying principles of the methods are the same, and a good example is found in the military gun cotton as made by the Abel process at the United States Naval Torpedo Station.