[2] Potash, or the vegetable alkali, is generally obtained from wood-ashes; but sometimes from the tartar, or from the lees of wine: what is used in England is generally imported from the north, where there is an abundance of wood, to allow of its being burnt for this purpose.
This Nitrate of Potash exists in a natural state, but is generally in very small quantities. It is found at the surface of the ground in some parts of Persia and the East Indies, and is mostly united with a kind of yellowish marl, which they dig from the cliffs on the sides of hills, exposed to the northern and eastern winds.
[3] Alumine, or clay; it is found of various degrees of purity, and mixed with a variety of other earths.
[4] This is Lime combined with sulphuric acid; it is called Gypsum, plaster of Paris, plaster-stone, or selenite. It is very abundant in some parts of England, and the hills near Paris are chiefly composed of it.
[5] From pyr, fire, and lignum, wood; the acid obtained from the partial combustion of wood; this acid is used in calico printing as mordants for dark-coloured patterns.
[6] The name given by chemists to the pure part of charcoal. It is said to be present in almost all combustible bodies, and is of itself entirely of that nature. When charcoal is burnt, its carbon unites with the oxygen of the air, and so much heat as to give it a gaseous form, and constitutes carbonic acid gas, or fixed air. The same gas is also obtained by the combustion of the diamond, proving that this precious and costly article is carbon or charcoal, in a very indurated state, and assuming a determinate form. It was not till lately that the diamond was proved to be combustible; but by means of the blow-pipe, and a stream of oxygen gas, it may be, to speak in common language, wholly consumed. The air that is extricated during the combustion, is carbonic acid gas, proving the diamond to have been chiefly, if not wholly, composed of carbon.
Long before this fact respecting the diamond was ascertained, Sir Isaac Newton, reasoning from its great refracting power, declared it to be his opinion, that it was one of the most combustible of bodies. Modern discoveries have now proved the fact; and it affords us an admirable instance of the acumen of that great Philosopher.
Popular Chemical Essays.
[7] The force by which this wheel revolves is very remarkable, as it unites in itself those two adverse forces which have been the subject of so much mathematical controversy, namely, the centrifugal and centripetal: it may appear like trifling with science to observe these forces in this simple production, but that they do exist in it is not less evident: for from the revolutions of the ignited particles of the composition the former is produced, and from the nature and well known properties of the evolute curve, cæteris paribus, the latter is produced.
The Evolute and Involute Curves are possessed with many remarkable properties, which it would be no difficult task to unfold, but as it could be of no practical use to the Pyrotechnist, we shall leave it to such of our Mathematical readers as are able to appreciate the pleasure which such investigations afford. And for their assistance we refer them to the excellent writings of Hutton, Simson, Maclaurin, &c. And to Sect. 4, Book 2, Newton’s Principia, where they will find the subject beautifully illustrated.