France, Church of Mousseau, 5-3/8 per cent.
" Cavern of Fouquières, 3-1/2 "
U. States, Tennessee, dirt of caves, 0.86 "
Ceylon, Cave of Memoora, 3-1/10 "
Upper Bengal, Tirhoot, earth simply, 1-6/10 "
Patree in Guzerat, best sweepings, 8-7/10 "
In each case the salt is mixed saltpetres.
Artificial.
France, 100 lbs. earth from
plantations afford 8 to 9 oz.
Hungary and Sweden, from
the same, 1/2 to 2-3/10 per cent.
It may be calculated that the flesh of animals, free from bone, carefully decomposed, will afford ninety-five pounds of saltpetre for one thousand pounds thus consumed.
In the manufacture of saltpetre, the earths, whether naturally or artificially impregnated, are mixed with the ashes from burnt wood, or salts of potash, so that this base may take the place of all others, and produce long prisms of potash saltpetre.
In this country there are numerous caves of great extent in Kentucky, Tennessee, and Missouri, from which saltpetre has been manufactured. Under the most favorable conditions of abundance of labor, obtainable at a low price, potash saltpetre can be made at a cost about one-fourth greater than the average price of India saltpetre, and those sources of supply are the best natural deposits known on this side of the Rocky Mountains. Where there is an insufficient supply of manure in a country, resort to the artificial production of saltpetre is simply a robbery committed on the resources of the agriculturists, and it is only during the pressure of a great struggle like that of the wars of Napoleon, that the conversion into saltpetre of materials which can become food for the community would be permitted.
Hitherto, in peaceful times, our supply of saltpetre has come from India through commercial channels; but twice within a few years this course of trade has been interrupted by the British Government, and the price of a necessary article has been greatly enhanced,—leading reflecting minds to the inquiry after other sources whence to draw the quantity required for an increasing consumption. On the boundary between Peru and Chili, in South Peru, about forty miles from the ports of Conception and Iquique, is a depression in the general surface of a saline desert, where a bed of soda saltpetre, about two and a half feet thick and one hundred and fifty miles long, exists. The salt is massive, and, occurring in a rainless climate, it is dry, and contains about sixty per cent. of pure soda saltpetre. In Brazil, on the San Francisco, the same salt is found extending sixty or seventy miles,—and again near the town of Pilao Arcado, the beds being about two hundred and forty miles from Bahia, but at present inaccessible for want of roads. The Peruvian native saltpetre is rudely refined in the desert, and then transported on the backs of mules to the shipping-port. As found in commerce, it is less impure than India saltpetre; and it might be usefully substituted for the latter in the manufacture of gunpowder, were it less deliquescent in damp atmospheres. For chemical purposes it now replaces India saltpetre, but the larger consumption is perhaps as a fertilizer of land, in the cool and humid climate of England, the low price it bears in the market permitting this consumption.
We have found that the various saltpetres of natural production, or those obtained in artificial arrangements, are converted by the use of potash salts into potash saltpetre, and among the products so changed is natural soda saltpetre. Now to us in this country, so near the sources of abundant supply of soda saltpetre, this substitution becomes a matter of great interest. We possess and can produce the alkaline salt of potash in almost unlimited quantity, and, excepting for some special purposes, it is consumed for its alkaline energy alone. When soda saltpetre in proper proportion is dissolved and thus mixed with potash salt, an exchange of bases takes place, and no loss of alkaline energy follows. The soda in a quite pure state is eliminated from the soda saltpetre, and will serve for the manufactures of glass and soap; while the potash, taking the oxygen compound of the soda saltpetre, produces, as a final result, a pure and beautiful prismatic saltpetre, most economically and abundantly.
Instead of working on a hundred pounds of earth to obtain at most eight or nine pounds of saltpetre, a hundred pounds of soda saltpetre will afford more than one hundred and nine pounds of potash saltpetre, when skilfully treated. Here, then, we have, by simple chemical treatment of an imported, but very cheap salt, a result constituting a source of abundant supply of potash saltpetre, without the loss of the agent concerned in the transformation.