1323. Nitric acid, as might be expected from its composition, is a very powerful manure when combined with some alkaline base. Nitric acid is never found in its free or uncombined state, but always in combination with some base; being a very powerful acid, it is easy to understand that as soon as formed it seizes upon some base to combine with, and forms a neutral salt. The commonest salts containing nitric acid, or nitrates, as they are called, are the nitrates of potash, soda, and lime, which are found native abundantly in different places. Of the salts thus formed, nitrate of soda appears to be the most powerful as a manure. Its effects, however, are to produce a great abundance of leaves, which are of an intensely deep green; but it does not appear to have so good an effect in producing either seeds or fruits. Nitrate of potash has been found to make plants grow luxuriantly when dissolved in water.