This substance is placed by agricultural chemists at the head of all fertilizers. Guano derives its chief value from its presence, as it contains over 60 per cent. of it. Could it be obtained cheap in the state of a salt, like the muriate (salammoniac,) a valuable and cheap substitute for guano could be made artificially. But it is a dear substance, and farmers cannot afford to buy it. There appears, however, to be some prospect of obtaining a cheap supply, as it is stated that “ Prof. Gale, of the Patent Office, has recently received some crude sal- ammonia, brought from Chincha (whether the Peruvian valley or not we cannot say,) which has recently been discovered in a vein like that of metallic ore, and in quantities suffici ent to render it an article of commerce.” We hope this information is true, but the quanti ty may be as moderate as that now found in all volcanic regions. Ammonia is a compound of two gases, viz. , nitrogen and hydrogen.— They do not combine directly in their gase ous state, but if a great number of electric sparks be passed through a mixture of them, especially if acid vapors are present, a combi nation takes place, and a third body—ammo nia— (NH3) is formed. It is always found in the rains of thunder storms, hence it is conclu ded that the lightning is an active agent in its formation—it is the marryingminister. These two gases, however readily combine in a na scent state ; a piece of iron rusting in the air is aimost constantly giving rise to a small por tion of ammonia. The moisture which co vers the iron dissolves the atmospheric air; the oxygen of this air unites with the iron to form the rust—oxide—and the pellicle of oxide constitutes with the metal, a voltaic element strong enough to decompose water. The oxygen thus set at liberty unites with a new quantity of iron, and the nascent hydro gen of the water finding nitrogen in solution in the moisture, unites with it and forms am monia. When zinc is dissolved in dilute nitric acid, the liquid is found to contain a marked quan tity of the nitrate of ammonia. In the solution of the zinc in the dilute acid, hydrogen gas is set free and nitrate of oxide of zinc is formed, but if zinc is treated with concentrated nitric acid, the zinc is oxidated at the expense of a portion of the nitric acid, and as a mixture of hydrogen and nitrogen is separated, these two gases meeting in the liquid in a nascent state (act of evolution) unite and form ammo nia. A notable quantity of ammonia is there fore found in the liquid. It is the case with other gases beside nitrogen and hydJ)gen, that although they do not readily combine when brought together in their distinct gaseous state, yet do so freely when simultaneously set at liberty in the same solution. Animal matters burned under exclusion from the air, give off a considerable quantity of the carbonate ofammonia. This is dissolved in hy drochloric acid, and produces the salammoniac of commerce. Ammonia is obtained in a gase ous form by mixing powdered salammoniac with about an equal quantity of dry slacked lime, and heating it in a retort having a bent tube. The gas is abundantly discharged, and may be collected in the c'l1lmon way over mercury in a trough. Ammonia is a colorleSil gas of a very pungent odor, causing tears to flow freely. It is a powerful alkali, and neu tralizes strong acids, such as sulphuric, 'c.— In water it is very soluble, and being mixed with it, is called aqua-ammonia. Under a pressure 01 five atmospheres, it becomes li quid ; it extinguishes the light of a candle, and does not burn under ordinary circumstances ; if breathed undiluted it is fatal to life.— It is very volatile as a liquid, and is employed to give that plflgent odor to what are termed smelling salts. The produ cing of tears which is a peculiarity of onions, is attributable to ammonia. In the destruc tive distillation of bituminous coal in ma king gas, a quantity is produced which has all to be removed, for it detracts from its illuminating properties. . This is done by u. water cooler—a vessel through which the gas passes before it goes into the retain ing tanks and pipes for distribution. It would be wpll for agricultural chemists to devote their attention to the artificial production of a cheap ammoniacal salt, as the Lobos Islands, are not yet free proparty for all the world.