_Improved Form of Jacobi's fuze._--The section shown in Fig. 17 is an improved form of the chemical fuze, invented by Professor Jacobi, and used by the Russians in their land and sea mines during the Crimean war (1854-5). It consisted of a small glass tube _a_, containing sulphuric acid, enclosed in a lead cylinder _b_. A mixture of chlorate of potash and white sugar surrounds the tube and holds it in position; _c_ is a primer filled with mealed powder in connection with the charge of the mine. The action of this fuze is as follows:--On a vessel striking against the lead cylinder _b_, it is crushed in, breaking the glass tube containing the sulphuric acid, and thus causes it (acid) to flow into the mixture of chlorate of potash and white sugar, producing fire, which by means of the primer _c_, passes into the charge, and explodes the mine. [Illustration: MECHANICAL FUZES. PLATE V.] _Defect of Chemical Fuze._--The defect of the chemical fuze just described is its slow rate of ignition when compared to gunpowder. This may be remedied by adding a small quantity of sulphuret of antimony or perro cyanide of potassium. Both the Turks and the Germans employed, as a mode of ignition for their mechanical submarine mines, the chemical fuze described above, with but slight modifications in the shape of the lead cylinder and manner of fixing the fuze into the torpedo case. Mechanical fuzes, both percussion and chemical, which require a blow to effect their ignition, are to a certain extent defective when applied to submarine mechanical mines (which are always buoyant ones) in so far that a hostile vessel passing over ground supposed to be defended by torpedoes of any description, would do so at as slow a rate of speed as it would be possible to proceed at, and would, under those circumstances, _push away_ rather than strike a buoyant mine, with which she might come in contact. During the American civil war and the Russo-Turkish war, especially in the former, there are several instances on record of vessels passing over buoyant mechanical mines unharmed, whilst similar vessels have afterwards been destroyed by those self-same mines; and the only cause for such apparent inconsistency being the above-mentioned one, viz., the pushing rather than striking effect produced on a buoyant mine by a vessel under weigh proceeding at a very slow speed, or merely drifting with the current.