cartridge, having a small hole through it, communicating with the powder below; lay upon this, half an ounce of fine gun powder, and fold the paper down upon it from all sides, cementing the folds firmly with glue, thus giving the end of the cartridge a conical form. Then bore a hole about two thirds of the length of the cartridge from the choke with a gimblet or bit. Fill this hole (which must be as large as the choke, but tapering towards the other end) with fine gun powder, to the choke, and fill the choke with the compound, the outside of which may be moistened a little, the better to keep it in its place. Finish the others in the same manner, and keep them in a warm dry place till used. They are then to be lashed firmly to the end of a light pine rod, with the choke towards the opposite end. The length of the rod, should be about nine times that of the cartridge. The rocket then being elevated by the rod, and being ignited at the choke, the compound inside burning intensely, acts upon the air, and causes it to ascend. The cartridges for fire wheels, are prepared in the same manner, but are generally smaller; and instead of being lashed to a rod, they are lashed to the arms of a wheel, in such manner, that a violent rotary motion is produced by their combustion. 85. TO PRODUCE DETONATING BALLOONS.--Moisten and compress a bladder till no air remains in it, and tie the neck of it upon a perforated cork; set the cork in a flask containing the materials for producing hydrogen gas (see 9.) Thus convey into the bladder a quantity of the gas, and then remove the cork to another flask, containing two or three ounces of black oxide of manganese, moistened with sulphuric acid, sufficient to form with it a soft paste; apply the heat of a lamp, and oxygen gas will be evolved, and will also rise through the neck of the flask; in this manner, convey into the bladder, nearly half as much oxygen gas, as it previously contained of hydrogen. Then tie the stem of a tobacco-pipe in the neck of the bladder, and dip the bowl of the pipe in a solution of soap in water, (soap-suds) and compress the bladder a little, so as to swell a bubble from the bowl of the pipe;--shake off the bubble, which being lighter than atmospheric air will naturally rise, or float horizontally in the air. If the flame of a candle be brought in contact with one of these balloons, or floating bubbles, it will explode with a violent detonation, resembling the report of a pistol. If this compound gas be forced into the water, so as to form several bubbles on the surface, and flame be then applied to them, a volley of explosions will be the result. Caution is requisite in these experiments, that the fire be not communicated to the bladder, as such an explosion might not be safe.