make meal or grind coffee.  It should then be wrapped up to a piece of canvas, or a skin, and pressed, with as heavy a pressure as can be obtained, to condense it.  Next, the cake is squeezed and worked against a sieve made of parchment, in which the holes have been burnt with a red-hot wire, and through which the cake is squeezed in grains.  These grains are now put into a box, which is well shaken about, and in this way the grains run each other smooth.  The fine dust that is then found mixed with the grains, must be winnowed away; lastly the grains are dried.

Recapitulation.—­1.  Pound the ingredients separately. @.  Mix them. 3.  Add a little water, and knead the mass. 4.  Press it. 5.  Rub the mass through a sieve. 6.  Shake up the grains in a box. 7.  Get rid of the dust. 8.  Dry the grains.

The ingredients should be used as pure as they can be obtained.  For making a few charges of coarse powder, the sieve may be dispensed with:  in this case, roll the dough into long pieces of the thickness of a pin; lay several of these side by side, and mince the whole into small grains; dust with powder, to prevent their sticking together:  and then proceed as already described.

To procure good Charcoal.—­Light woods that give a porous charcoal, are the best;—­as poplar, alder, lime, horse-chestnut, willow, hazel-nut, and elder.  It should be made with the greatest care, and used as soon as possible afterwards:  it is the most important ingredient in gunpowder.

Sulphur.—­The lumps must be melted over a gentle fire; the pot should then be put in a heap of hot sand, to give the impurities time to settle, before it cools into a mass.  When this has taken place, the bottom part must be broken off and put aside as unfit for making gunpowder, and the top part alone used.  Flower of sulphur is quite pure.

Saltpetre.—­Dissolve the saltpetre that you wish to purify, in an equal measure of boiling water; a cupful of one to a cupful of the other.  Strain this solution, and, letting it cool gradually, somewhat less than three-fourths of the nitre will separate in regular crystals.  Saltpetre exists in the ashes of many plants, of which tobacco is one; it is also found copiously on the ground in many places, in saltpans, or simply as an effloresence.  Rubbish, such as old mud huts, and mortar, generally abounds with it. (It is made by the action of the air on the potash contained in the earths.) The taste, which is that of gunpowder, is the best test of its presence.  To extract it, pour hot water on the mass, then evaporate and purify, as mentioned above.

Rocket Composition consists of gunpowder 16 parts, by Weight; charcoal, 3 parts.  Or, in other words, of nitre, 16 parts; charcoal 7 parts; sulphur, 4 parts.  It must not be forgotten that when rockets are charged with the composition, a hollow tube must be left down their middle.

Blue Fire.—­4 parts gunpowder meal; 2 parts nitre, 3 parts sulphur; 3 parts zinc.