Ammonia is, in many respects, a peculiar substance, and much might be id of its composition and chemical relations to other bodies. Our purpose is, however, in the present article, to give only a brtef and popular account of its manufacture on an extensive scale, and to say something of its important applications in the arts. Ammonia has been long known under various names, aqua causlica, spirits of hartshorn, sal volatile, and lastly, ammo-nia,from Ammonium, a district in Africa,taldng its name from the Temple of Jupiter Ammon, the salts of ammonia having been formerly obtained there. The production of ammonia is now very large and necessarily so, as the already large demand for it in the various arts is constantly increasing. Ammonia has been made by the direct combination of the gases which compose it, namely, nitrogen and hydrogen, but this method has never been made profitable in its manufacture. It is most cheaply and extensively obtained as a collateral product in other manufactures. It is one of the by-products in the distillation of coal in gas works, and also in the manufacture of boneblack. It has also been made under- patent process, which consists in distilling a mixture of two parts of guano with one part of lime, or other caustic alkali, the gaseous ammonia being conducted into water Avhich is thus saturated with it, forming a commercial aqua ammonia. Several other patents have been granted on processes for manufacturing ammonia. One of these is a method for extracting ammonia from gas water. The gas water is put into a retort with slaked lime, and distillation performed as in the guano process. An improvement was made and patented, 1838, for the production of ammoniacal liquor from gas water, which was a great advance on the old methods, as it enabled the product to be obtained in a concentrated form. One of the mostT=ecent 0]jrces of supply has been found in the boracic acid manufactories of Italy,v-ihich formerly allo\ved enormous quantities to be wasted. It is now estimated that over one milBon pounds of ammoniacal salts are produced by these establishmeiits. In the beetnroot sugar manufacture, large quantities of sulphate of ammonia are allowed to go to ivaste. Ammonia has been proposed as a means of generating motive power, but the experiments hitherto tried in this field have not proved very successful, though the liberation of this gas Irom its salts, in a close vessel, may be made to generate an enormous pressure, and its ready absorption by cold water renders the application of the condenser perfectly easy. Oneof the obstacles met with in these attempts has been the difficulty of constructing cheap machines out of materials which are not chemically acted upon by this gas, but it still seems to us that the method might be advantageously applied to the generation of motive power under circumstances where steam is not admissible. We do not, however, believe it can be \vorked as economically as steam for many of the purposes for \vhich it has been proposed. Machines for man-'dfaeturing ice,ploying liquid ammonia, have been constructed, on the principle, that ivhen liquids expand into gase-s, they absorb heat from surrounding bodies. The same principle has, however, been more cheaply applied in the use of volatile hydrocarbons as a substitute for the liquefied ammonia. The details of these different machines are, of course, dissimilar, but the general principle of their operation is the same. To specify the widely extended and various uses to which this substance is applied in the arts,would compel us to greatly lengthen this article. Suffice it to say, that it is one of those essentials to the present status of the industry of the world, the absence of which would be felt scarcely less than soda or sulphuric acid.