_Percussion and Chemical Fuzes._--Many forms of this mode of mechanical ignition have been from time to time devised, of which the following are the most important ones:-- _Sensitive Fuze._--It consists of an inner cylinder _a_, _a_, Fig. 15, of composition metal, 1-1/2" diameter, and 2-1/2" long, having a thread cut on its outside, and a bouching _b_, 2-1/4" diameter and 2" long with a sexagonal projection _c_, for applying a wrench, also with an external and internal thread. The upper end of the inner cylinder _a_, is solid for 1", and is perforated by three holes _d_, _d_, _d_, in each of which a percussion primer is placed _e_, _e_. A piece of thin, soft and well annealed copper _f_ is soldered to the upper end of the bouching _b_, to keep moisture from the primers, and is so thin that a slight blow will crush without breaking it. A safety cap can be screwed on to the external thread above the projection _c_. _Rain's Detonating Composition._--The detonating composition employed in this and many other forms of percussion fuzes by the Confederates, etc., consisted of a combination of fulminate of mercury and ground glass, and was invented by, and is named after, General Rains, Chief of the Torpedo Bureau, at Richmond, during the Civil War (1861-5). So sensitive was this composition that seven pounds pressure, applied to the head of one of the primers, would explode it. When required for use the internal cylinder _a_, containing the primers _e_, _e_, is screwed up until contact between them and the copper cap _f_ is secured. _McEvoy's Percussion Fuze._--Fig. 16 represents a longitudinal section, full size, of the mechanical percussion fuze, used by Captain McEvoy in connection with his drifting torpedo, which latter will be hereafter described. _a_ is a piece of metal, having an external and internal thread, and a projection _b_, to which is applied the spanner for screwing it into the torpedo case. This piece _a_ is hollow at its upper end, and is closed by means of a thin copper dome _c_, which is soldered to it. Screwed into the piece _a_ is the plug, or nipple _d_, with a hole through it from end to end, it is rammed full of mealed powder, and then a fine hole is drilled through the composition. A cavity _e_ at the head of the plug, or nipple _d_, is filled with a fulminating substance. A spiral spring _f_, encircles the plug _d_, on which a cap _g_ rests; _h_ is a needle in this cap. The action of this fuze will be readily understood from the plan of the fuze at Fig. 16. A safety cap is provided, which fits into the slots _i_, _i_, and is fixed there by means of a set screw.