Dynamite (Gr. dynamis, 'strength') is produced by the admixture of nitro-glycerine with a siliceous infusorial earth known under the German name as kieselguhr. Nitro-glycerine, which can be prepared in small quantities by dropping glycerine into a mixture of strong nitric and sulphuric acids, the temperature being kept as low as possible, was discovered by Sobrero in 1846, but it was not till nearly twenty years later that the experiments of Alfred Nobel, who combined it with the absorbent inert earth just mentioned, placed the new substance on a basis of practical and commercial importance.
How important were the results of Alfred Nobel's investigations, and how extended an application in industrial undertakings this class of explosive has obtained, may be judged from the fact that whereas about 1870 the total world's output of dynamite was computed not to exceed 11 tons, in 1889 the annual production of nitro-glycerine compounds was reckoned to be no less than 12,000 tons. For the properties of nitro-glycerine, see that article.
Kieselguhr is the mineral remains of a species of algae (see DIATOMS); the stem consisted chiefly of silica, and when the organic portions of the moss decayed, the tubular siliceous stem remained, retaining its shape. Beds of kieselguhr, underlying peat, are found in many countries; the principal formations in Europe being in Great Britain (especially Aberdeenshire—that of Skye not being sufficiently absorbent), Germany, and Norway.
The raw kieselguhr, after calcination in a specially designed kiln to remove water and organic substance, is ground and sifted, and finally contains about 98 per cent. of pure silica with traces of lime and iron. In the early days of dynamite many substances were employed for admixture with nitro-glycerine, such as charcoal, sawdust, brick-dust, paper, rags, &c., before kieselguhr was finally adopted.
Dynamite, which has a reddish-brown colour, consists of 1 part of kieselguhr to 3 parts of nitro-glycerine, and has a specific gravity varying from 1.59 to 1.65. Dynamite burns with a yellowish flame, and in small quantities without danger; but explodes with great violence when fired by a detonating fuse. The freezing-point is about 40° F., but this is liable to fluctuate. Like nitro-glycerine, dynamite is more difficult to explode when frozen. The time of explosion of a dynamite cartridge has been calculated to occupy only the 24,000th part of a second; a fact which explains the violent nature of its action. Dynamite is much employed in breaking up boulders and the heavier metal-castings, also in agricultural operations for removing the roots of trees. Under water it loses only 6 per cent. of its power, and is consequently greatly in requisition for subaqueous operations. Loose tamping, such as sand or water, is found to be amply sufficient, and in many instances boreholes can be dispensed with altogether, the dynamite being simply laid on the surface of the bodies to be blasted, and covered with sand or clay. For quarrying purposes, dynamite possesses too great shattering power, and gunpowder, though about double the quantity and some three times the number of boreholes are found necessary, is more generally employed.
The principal dynamite-works in Great Britain are those founded by the Nobels at Ardeer, near Stevenston, Ayrshire, in 1873. The manufacture is carried on under the supervision of H.M. inspectors of explosives, who pay periodical visits, and test the raw materials, a system which, if adding to the cost of production, forms an authoritative guarantee of the article produced. The various processes are carried on in isolated wooden buildings, about 20 yards from each other, and surrounded by massive banks of earth. Nitric and sulphuric acids having been mixed, the temperature being maintained as low as possible by cold water and compressed air, the acids are run into a large leaden tank and further cooled, when glycerine is injected by means of compressed air. This process, being one of considerable danger, has to be closely watched; but on 8th May 1884 an explosion cost ten women's lives. The nitro-glycerine now formed is drawn off and washed in an alkaline solution to remove any acidity, and is then incorporated with the kieselguhr in the proportion of 1 to 3. Cartridges, about 1 inch to inch diameter by 3 inches long, are then made up by female labour, wrapped in vegetable parchment, and packed in boxes covered with water-proof oil-paper, with instructions and cautions printed on them in different languages. Government regulations, both as to the storage and transport of dynamite, are stringent and restrictive.
For the pneumatic dynamite gun, patented in 1883, and adapted specially for harbour defence, see CANNON; it is rather an apparatus for discharging torpedoes than a gun. The so-called 'dynamite cruiser' Vesuvius of the United States navy was built in 1888-89 to carry three pneumatic guns. In 1888, too, a United States naval lieutenant invented a dynamite shell which can be discharged from any ordinary breech-loading gun, fired with gunpowder. The shell is lined with asbestos cloth, and partitioned so as to contain a number of pellets of dynamite, each wrapped in paraffined paper. Dynamite has unhappily been turned effectively to merely destructive uses. At Bremerhaven (q.v.) a dynamite infernal machine exploded prematurely in 1875. In 1883-85, plotters belonging to extreme sections of Irish malcontents in America arranged a series of dynamite explosions intended to strike terror through the length and breadth of Great Britain. Those outrages include attempts to blow up the Glasgow gas-works, the Parliament House at Quebec; and, in London, the Local Government Offices, four railway stations, Scotland Yard (the police headquarters), and, on the same day, the House of Commons, Westminster Hall, and the Tower. They caused great destruction of property, and injured many people; but happily only two lives were lost—the lives of two of the dynamiters themselves, who were blown to atoms in trying from a boat to blow up London Bridge. Between January 1882 and November 1885, twenty-five of their confederates were brought to justice, and sentenced, most of them to life imprisonment. See ANARCHISM, CHICAGO, SANTANDER.