~Dynamite.~--Dynamite consists of nitro-glycerine either absorbed by some porous material, or mixed with some other substance or substances which are either explosives or merely inert materials. Among the porous substances used is kieselguhr, a silicious earth which consists chiefly of the skeletons of various species of diatoms. This earth occurs in beds chiefly in Hanover, Sweden, and Scotland. The best quality for the purpose of manufacturing dynamite is that which contains the largest quantity of the long tubular _bacillariae_, and less of the round and lancet-shaped forms, such as _pleurosigmata_ and _diclyochae_, as the tube-shaped diatoms absorb the nitro-glycerine better, and it becomes packed into the centre of the silicious skeleton of the diatoms, the skeleton acting as a kind of tamping, and increasing the intensity of the explosion. Dynamites are classified by the late Colonel Cundill, R.A., in his "Dictionary of Explosives" as follows:-- 1. Dynamites with an inert base, acting merely as an absorbent. 2. Dynamites with an active base, i.e., an explosive base. No. 2 may be again divided into three minor classes, which contain as base-- (_a._) Charcoal. (_b._) Gunpowder or other nitrate, or chlorate mixture. (_c._) Gun-cotton or other nitro compound (nitro-benzol, &c.). The first of these, viz., charcoal, was one of the first absorbents for nitro-glycerine ever used; the second is represented by the well-known Atlas powder; and the last includes the well-known and largely used gelatine compounds, viz., gelignite and gelatine dynamite, and also tonite No. 3, &c. In the year 1867 Nobel produced dynamite by absorbing the nitro-glycerine in an inert substance, forming a plastic mass. In his patent he says: "This invention relates to the use of nitro-glycerine in an altered condition, which renders it far more practical and safe for use. The altered condition of the nitro-glycerine is effected by causing it to be absorbed in porous unexplosive substances, such as charcoal, silica, paper, or similar materials, whereby it is converted into a powder, which I call dynamite, or Nobel's safety powder. By the absorption of the nitro- glycerine in some porous substance it acquires the property of being in a high degree insensible to shocks, and it can also be burned over a fire without exploding." Ordinary dynamite consists of a mixture of 75 per cent. of nitro-glycerine and 25 per cent. of kieselguhr. The guhr as imported (Messrs A. Haake & Co. are the chief importers) contains from 20 to 30 per cent. of water and organic matter. The water may be very easily estimated by drying a weighed quantity in a platinum crucible at 100 deg. C. for some time and re-weighing, and the organic matter by igniting the residue strongly over a Bunsen burner. Before the guhr can be used for making dynamite it must be calcined, in order not only to get rid of moisture, but also the organic matter.