On Nitrate of Soda. 



359 



as dung, soot, sulphate of ammonia ; secondly, vegetable or 

 animal organized substances, as seaweed or wool, which class 

 was represented at Rothampstead by rape-cake ; lastly, mineral 

 combinations of nitric acid. Now, undoubtedly we could not 

 be certain beforehand that such compounds with nitric acid would 

 act on plants in the same manner as the former two, which 

 contain nitrogen, either in ammonia, or in organic matter capable 

 of producing ammonia. But facts prove that the nitrates, not- 

 withstanding the acid form of their nitrogen, are no exception to 

 the great law. For we have no less than three nitrates which 

 act as fertilizers ; first, nitrate of potash, the original saltpetre, 

 used as manure partially a few years ago in this country. Its 

 advantages are also known, as Professor Johnston acquaints us, 

 to the hereditary gardeners of Bengal. 



*' The districts of Chaprah, Tirhoot, and Shahabad, near Patna, where a 

 large proportion of the saltpetre sent from Bengal is produced, are considered 

 the most fertile in Bengal, producing two, and sometimes three crops yearly. 

 The natives of these districts, particularly a class called Quircas (hereditary 

 gardeners), who cultivate the best land and produce the best crops, are in the 

 habit of irrigating their fields with w^ater from wells so strongly impregnated 

 with saltpetre and other salts as to be brackish. . . . Grain-crops also grow 

 most luxuriantly on lands yielding saltpetre, where there is enough of rain 

 within a week or two after the seed is sovvn ; but if a drought follow the sowing, 

 and continue for three weehs or a month ^ the leaf becomes yellov:, and the crop 

 fails." ^ 



Thus the soil, it appears, is sometimes naturally fertilized by 

 saltpetre ; and since even this natural endowment occasionally 

 proves prejudicial, we may learn to be more merciful if the 

 means theoretically proposed by philosophers be not exempt 

 from every shade of objection, nor safe from every accident of 

 our varying climate. Secondly, the mortar of old walls is known 

 to have a manuring power far beyond any virtue of the lime 

 contained in it ; now this mortar is in France the principal source 

 of saltpetre, which is obtained by steeping the rubbish, and de- 

 composing with potash the nitrates of lime and magnesia found 

 dissolved in the steep-water. The nitrate of these earths also 

 must therefore act as a fertilizer. Lastly, the activity of the soda- 

 nitrate has been shown repeatedly in this Journal. 



We may assume, therefore, that nitrates, notwithstanding their 

 special form, fall under the general law of nitrogenous manures, 

 and may proceed to compare cubic nitre with guano, as is natural 

 from their similarity of application for top-dressing corn as well 

 as from the probable competition in commerce between these 

 two manures as sources of nitrogen. We find then chemically 

 that the new nitre, though costing about half the price, contains 

 more nitrogen by one-sixth than saltpetre, but, though costing 



* Lectures on Agricultural Chemistry, p. 281. 

 VOL. XIII. 2 B 



