BY SALINE MANURES. 313 



are used in agriculture are those of ammonia, potash and so- 

 da. Nitrate of ammonia is formed in fermenting dung 

 heaps, but is rarely applied artificially. 



Nitrate of potash, or nitre, is composed of 54 parts, by 

 weight, of nitric acid (aquafortis) and 47 of potassa. This 

 substance has long been a celebrated saline manure. Its 

 effects are not only powerfiil but permanent. Upon what 

 does its utility depend ? In order to answer this inquiry, 

 we have only to refer to principles already suggested. 



Every 100 lbs. of nitre contain about 46 of potash. This 

 acts only upon the vegetable matters of the soil, and is proba- 

 bly let loose from its combination, by growing plants (by ca- 

 talysis). We have already noticed the influence of potash 

 upon peat. 200 lbs. of nitre would furnish potash sufficient to 

 decompose one cord of peat or muck. The action of the acid 

 is more complicated. It contains 40 parts of oxygen and 14 

 of nitrogen. It may therefore be decomposed, and yield nitro- 

 gen and oxygen to the vegetable products, p. 16#/ But its 

 oxygen probably acts both upon the vegetable matter and the 

 silicates. By its action on the humus, a part is rendered 

 soluble, and carbonic acid is formed, which acts upon the 

 silicates, and liberates their alkalies. If the above is a true 

 representation of the changes which take place, it proves that 

 nitre is a most valuable substance to be applied to the soil. 

 Experiment has shown that 100 or 150 lbs. of nitre, per acre, 

 will produce the most gratifying results. It may be spread, 

 or mixed with the manures. 



Nitrate of soda is nitric acid combined with soda, in the 

 proportion of 54 parts of the former to 31 of the latter. Its 

 action is precisely similar to nitre. The soda acts upon veg- 

 etable matter, and the acid indirectly upon the silicates. The 

 quantity applied may be about 100 or 150 lbs. to the acre, 

 spread broad-cast, or mixed with the manures. 



The above substances, including nitrate of ammonia, are 

 the food of vegetables, and hence are properly classed as ma- 



