882 ALKALINE SILICATES. 



nitric acid, or which, in consequence of the subst<ances 

 they contain, are constantly forming nitrates. On 

 soils neither containing nitrates nor other alkaline 

 salts, they appear to produce very beneficial results. 

 It has been found that wheat manured with alkaline 

 nitrates, contains more gluten and albumen than 

 wheat grown in land not so manured. 



902. These remarks apply equally to nitrate of 

 soda and nitrate of potash ; at least similar effects 

 are produced by the two salts, as far as regards the 

 increased formation of gluten and albumen. Nitrate 

 of soda contains weight for weight more nitrogen than 

 does the nitrate of potash. It is not known in how 

 far soda is able to replace potash, or whether it is 

 indifferent which of the two alkalies is supplied to 

 plants. 



903. Silicates of potash and soda have also been 

 proposed and partially employed as manures. These 

 salts are easily made by melting together sand and 

 carbonate of potash or soda (262); it was supposed 

 that they would be particularly valuable for corn and 

 grass crops, as these plants contain a considerable 

 quantity of silica, but the result of trials hitherto 

 made with these compounds has been such as to 

 render it probable that the silica which they contained 

 produced much less effect than the alkali. It appears 

 that almost all soils contain silica in a soluble form ; 

 and consequently that plants are always able to ob- 

 tain as much silica as they require, from the soil, 

 except in very rare cases. 



