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 _bacillariæ_, and less of the round and lancet-shaped
forms, such as _pleurosigmata_ and _diclyochæ_, 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