The discovery of _gunpowder_ has completely changed the modern art of war. The earliest notice that has occurred respecting the use of this article in Europe is, that it was employed in the wars of Germany, somewhat before the year 1373. It is said, however, to have been known in China long anterior to that period. Its component parts are nitre, charcoal, and sulphur, in the proportion of seventy─six, fifteen, and nine parts, in every hundred. These ingredients are first reduced to a fine powder separately, and then mixed with water, so as to form a thick paste. After this has dried a little, it is placed upon a kind of sieve full of small holes, through which it is forced. By this process it is divided into grains, the size of which depend of course upon the size of the holes through which it has been squeezed. It afterwards undergoes some other operations before it is ready for use. Nitre is frequently administered in medicine; and it is used very extensively in different arts. A mixture of equal parts of nitre and tartar, burned together in a crucible, forms what is called _white flux_, which is used for melting and reducing different kinds of metallic substances. And a mixture of one part of nitre and two parts of tartar burned in the same manner forms what is called _black flux_. Nitre possesses antiseptic qualities in a considerable degree, whence it is much used, in conjunction with common salt and bay salt, for the preserving of animal food from putrefaction. _Aqua─fortis_, or _nitric acid_ (30) as it is denominated by chemists, is prepared from this mineral. The mode of obtaining it in large manufactories is by distilling a mixture of nitre and clay in glass or stone retorts, each capable of containing seventy or eighty pounds’ weight of this mixture. But the acid thus procured being weak and impure, chemists, for nicer purposes, generally prepare it by distilling, in a glass apparatus, a proportion of three parts of nitre and one of sulphuric acid (24). The uses of aqua─fortis are various and important. All kinds of metals, except gold and platina, are capable of being dissolved in it. Hence, among other uses, it is employed by dyers, for dissolving tin, and forming with madder a scarlet colour; and, by hatters, for dissolving mercury (228) for some processes in the preparation of hats. Jewellers use it for several purposes. AMMONIA FAMILY. 207. _SAL─AMMONIAC, or MURIAT OF AMMONIA, is a salt compounded of ammonia and muriatic acid (22). It is occasionally found in a state of powder, sometimes in a massive form, and sometimes in very irregularly shaped crystals, the primitive form of which is an octohedron (Pl II, Fig. 5). It is, however, more frequently an artificial production from the soot of burned animal matter._