78. TO MAKE THE COMMON FULMINATING POWDERS.--Grind and mix intimately, three parts of nitrate of potass, with two of sub-carbonate of potass, and one of sulphur. If half a drachm of this compound be placed on a shovel, and held over a gentle fire, it will soon explode with a loud report. It is not, however, attended with any danger. If two grains of chlorate of potass in powder and one of sulphur be mixed together, and wrapped in a piece of strong paper, and the paper be then struck with a hammer, it will also explode with detonation. This experiment may require some caution. _Note._--The percussion powder, such as is used for priming the patent percussion rifles, is composed of chlorate of potass, and flour of sulphur, with a trifling proportion of charcoal and loaf sugar, being made into a paste or dough with alcohol,--then grained and dried. 79. TO MAKE THE MERCURIAL FULMINATING POWDER.--Dissolve half an ounce of mercury in three ounces of nitric acid, assisting the solution by a gentle heat. When the solution is cold, pour it upon an equal quantity of strong alcohol previously introduced into a flask, and apply a moderate heat till effervescence is excited. (Do not forget that the mercurial solution must be poured upon the alcohol, and not the alcohol upon the solution.) A white fume will soon begin to undulate on the surface of the liquor, and flow through the neck of the flask, and a white powder will be gradually precipitated. As soon as any precipitate ceases to fall, quickly pour the contents of the flask on a filter; wash the powder with pure water, and cautiously dry it by a heat not exceeding that of boiling water. The immediate washing the powder is material, because it is liable to the re-action of the nitric acid; and while any of that acid adheres to it, it is very subject to be decomposed by the action of light. This powder, if very pure and nicely made, explodes by percussion, or a moderate degree of heat. _Experiment._--Place one-fourth of a grain of this powder, between the ends of two slips of paste-board, and paste, or bind them firmly together;--hold the ends of the slips over the flame of a candle, and as soon as it becomes warm, it will explode with a loud report. This composition is less dangerous than the fulminating compounds of gold or silver, as it never explodes spontaneously; but yet it cannot be handled with too much caution. _Note._--The silver powder, or fulminating silver, with which torpedoes and waterloo crackers are charged, is prepared in a similar manner; pure silver being dissolved instead of mercury, but it is too dangerous to be trifled with.