It might be interesting to note that the charcoal employed for military and sporting powder is made from dog-wood, while for inferior grades of powder willow and alder are used.
Explosive Compounds of the Nitro-Substitution Class and Nitric-Derivative Class. The two explosives of these classes which are generally known are gun-cotton and nitro-glycerine, with special preparations made from them, such as dynamite, blasting gelatine, etc.
Gun-Cotton. Gun-cotton is made by treating suitably prepared cotton with a mixture of one part by weight of nitric acid and three parts sulphuric acid. The immersion lasts 48 hours, the temperature being maintained at 60 deg. F. The cotton is then subjected to a thorough and prolonged washing, after which it is carried through various processes to prepare it for use. The cellulose of the cotton has thus been converted into tri-nitro cellulose. By varying the strength of the acids different degrees of nitration may be obtained. Gun-cotton is extensively used for military purposes.
Gun-cotton differs but slightly in appearance from ordinary cotton. It has a harsh feel and is less flexible than common cotton. It becomes highly electrified when rubbed between the fingers and appears luminous when rubbed in the dark. It is entirely insoluble in hot or cold water, but dissolves in a mixture of ether and ammonia. It will rarely take up more than two per cent. of moisture from the atmosphere. It is insensible to pressure, percussion or friction, unless closely confined or firmly compressed. It burns with a flash, but without explosion if brought into contact with burning or incandescent bodies. Wet gun-cotton will not burn or explode. Its ignition temperature is 360 degrees F. Pure gun-cotton will undergo no spontaneous decomposition and is the safest explosive known. Although it will not explode when wet, it may be detonated in this condition by a Mercury Fulminate Detonator with a small initial charge of dry gun-cotton in contact with it.
Nitro-Glycerine. Nitro-glycerine is a nitric ether, or specifically a glyceryl tri-nitrate. Different degrees of nitration yield the mono-di- and tri-nitro glycerine, respectively; the latter being the nitro-glycerine of commerce. It is made by treating an exceedingly pure quality of glycerine with a mixture of nitric and sulphuric acids, the proportions commonly adopted being 3 parts of nitric acid, 5 parts of sulphuric acid, and from 1 to 1.15 parts of glycerine. The glycerine is added very slowly and with constant stirring. The agitation of the mixture is now usually accomplished by compressed air.
When made from the purest ingredients, nitro-glycerine is an oily looking fluid, as clear and transparent as water. When freshly made it is whitish and opaque, but on standing it clears. The specific gravity at normal temperature is about 1.6 deg. F., when frozen 1.735 deg. F. Nitro-glycerine dissolves in alcohol, ether, methyl-alcohol, benzine, etc. Freshly made, opaque nitro-glycerine freezes at from 2.2 deg. F. to 7.6 deg. F., while the transparent, or clear, product freezes at from 39.2 deg. F. to 37.4 deg. F. In its frozen state it is less sensitive to shock or concussion than when it is in liquid. It may be completely evaporated when at a temperature of 158 deg. F. Its ignition temperature or firing point is 356 deg. F. Exposed to a temperature of 365 deg. F. it boils with evolution of vapors; at 381.2 deg. F. it volatilizes slowly; at 392 deg. F. it evaporates rapidly; at 422.6 deg. F. it detonates violently. From this point its behavior changes, passing through temperatures at which it explodes with constantly lessening violence until, at a dark, cherry-red heat, it assumes a spheroidal state and fails to explode. This applies to small quantities only. When gradually heated it is certain to explode at 356 deg. F.
Picric Acid. When coal tar is subjected to a fractional distillation the portion which comes over up to a temperature of 170 deg. C. is called “light oil” and contains all the compounds of low boiling paint contained in tar, and from this several of our most valuable explosives can be obtained. When these light oils have distilled over the next fraction, or “middle oil,” yields phenol or carbolic acid, a body which nitrated gives picric acid, which is the basis of the French high explosive “melinite” and the English “lyddite.”
Picric acid consists of a very strong nitric acid and carbolic acid, and is a very high explosive. It was introduced by Turpin, who mixed it with collodium and called it “melinite,” by which name it is known in the French Service. It forms with metals a class of salts (picrates). The potassium salts were suggested as a bursting charge for shells nearly fifty years ago. Sprengel and, later, Turpin, employed the acid itself as an explosive. It was possible to get a great weight of explosive into small space, as the acid could be melted and poured into the shell in a molten condition. Picric acid is a very safe explosive, but has the drawback of acting on metals, forming “picrates,” some of which are more sensitive to disturbing influences than the acid itself.
Lyddite. Lyddite consists of melted solidified picric acid, and has the same disadvantage of forming “picrates” when in contact with metal, making it necessary to varnish the interior of shells when used in them. Experience with lyddite shells shows them to be very erratic, due to the fact that they require a very powerful detonator, the use of which is very dangerous, as they may cause a premature explosion.