whole work from a safe standpoint. The roof, or one side of the building, should be of glass, so as to give the explosion a direction. ~Trench's Fire-extinguishing Compound~ is manufactured by the Cotton Powder Company at Faversham, and is the invention of Mr George Trench, F.C.S., the manager of the Company. The object of the invention is to surround the cartridges of tonite, when used in coal mines, with a fire- extinguishing compound. If a charge of tonite, dynamite, or gelatine dynamite is put inside a few ounces of this mixture, and then fired, not the least trace of flame can be observed, and experiments appear to show that there is no flame at all. The compound consists of sawdust impregnated with a mixture of alum and chlorides of sodium and ammonia. Fig. 22 shows the manner of placing the tonite cartridge in the paper bag, and surrounding it with the fire-extinguishing compound, _aa_. The attachment of the fuse and detonator is also shown. [Illustration: FIG. 22.--TRENCH'S FIRE-EXTINGUISHING CARTRIDGE.] The following report (taken from the _Faversham News_, 22nd Oct. 1887) of experiments conducted in the presence of several scientific and mining men will show its value:--"A large wrought-iron tank, of 45 cubic feet capacity, had been sunk level with the ground in the middle of the yard; to this tank the gas had been laid on, for a purpose that will be explained later on. The charges were fired by means of electricity, a small dynamo firing machine being placed from 30 to 40 yards away from the 'mine.'" Operations were commenced by the top of the tank being covered over and plastered down in order to make it air-tight; then a sufficient quantity of coal gas was placed in it to make it highly inflammable and explosive, the quantity being ascertained by a meter which had been fixed specially for the purpose. Whilst the gas was being injected the cartridge was prepared.