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