NITRATE OP SODA.

49

was first brought over to this country, some few yearsago, it was proposed to substitute it for the nitrate ofpotash in the manufacture of gunpowder and for thepreparation of nitric acid. It was, however, foundthat it possessed the property of attracting moisturefrom the air; and hence being always more or less damp,it could not be used by the gunpowder-makers. Whenfirst imported its price was low, and it was accordinglyadvantageously substituted for the more expensivenitrate of potash in the manufacture of nitric acid;but as the price of nitrate of soda soon rose, it was nolonger found profitable to use it for this manufacture,and now almost the only purpose for which it is em-ployed is as a manure. It appears to resemble thenitrate of potash in its effects on growing plants, andlike it to exert considerable influence on the fertility ofcertain kinds of land.

143. The “soda” of commerce is, as will be readilysupposed, not the pure alkali soda, but is a carbonate,and, like the carbonate of potash, possessed of consider-able caustic properties. It was formerly for the mostpart procured by burning sea-weed, the ashes of whichcontain a large quantity of carbonate of soda, and im-mense quantities of sea-weed were annually collectedand burnt for the purpose of obtaining weed-ash, kelp,or barilla, as the crude salt was called. Of late years,however, means have been discovered of obtaining thecarbonate of soda by decomposing common salt; fromwhich it is now manufactured so cheaply, that it has