254 FERTILIZERS. 



Silicate of Potash. Glass is a silicate of potash ; but the compounds of silica and potash 

 are not well understood. Silica in its ordinary state is nearly insoluble ; it becomes soluble by 

 union with potash, the solubility increasing with every addition of the alkali. Silicate of potash 

 exists in rocks, and also in soils in a state of minute division. In distilled water the natural 

 silicates of the soil are also nearly insoluble ; but the carbonic acid of rain water and the water 

 of soils are competent to effect a solution, and which fits this compound for the use of the 

 vegetable kingdom. Silicate of potash is required by all indigenous plants, as they contain a 

 great amount in their stems, and by which they acquire strength. The grasses and grains, 

 without silex in their composition, would be unable to rise upward and withstand the wiiids. 

 This compound exists also in the husk of grains ; it is necessary for protection against insects, 

 and to preserve the vitality of the seed. One of the defects of a soil for the production of the 

 cereals is the absence of this salt. The defect will be observed in the weak straw, and its early 

 prostration after rains and winds. Silicate of potash, it is evident, requires to be mixed with 

 other fertilizer&in order to secure a profitable investment. A mixture of the following kind 

 has been used with success : sulphate of ammonia seven pounds ; silicate of potash, sulphate 

 of soda, bones dissolved in muriatic acid, fourteen pounds each. This amount was applied to 

 one-eighth of an acre of oats. The weight of the crop, when cut, amounted to 1600 pounds. 

 The amount of grain was sixty-five bushels and five pounds. Sulphate of ammonia applied to 

 the same crop, of the same area, gave 1108 pounds ; and in grain fifty-two bushels and eighteen 

 pounds. A mixture of the substances detailed, it will be. observed, furnishes many of the 

 necessary substances required by the cereals. When it is in the power of the farmer to com- 

 pose artificial fertilizers, it is necessary to consider, first, what his particular crop requires in the 

 shape of food, and then, if possible, make the mixture to supply its special wants. 



4. Soda and its salts. 



The salts of soda being, generally, cheaper than the salts of potash, have been more frequently 

 employed as fertilizers. Soda, however, is not seen to be so essential to vegetation as potash. 

 The great repository of soda is the ocean. Soda is abundant in the mineral kingdom. 



Carbonate of Soda. It is the soda of commerce : it is manufactured from common salt ; 

 marine plants is another source. It becomes dry in the air, or loses a portion of water. Car- 

 bonate of soda acts upon the soil, and promotes vegetation directly by furnishing the proper 

 food ; and in the next place, it operates indirectly by its effect upon the constituents of the 

 soil, dissolving the silicates. We may suppose, therefore, that both carbonate of soda and 

 potash will act favorably upon the wheat crop and other grains, by supplying directly the ne- 

 cessary food, and by giving to the plant also dissolved silica, or the soluble silicate of soda or 

 potash, as one or the other has been employed. We have little reason to doubt but that acids, 

 in combination with their bases, are decomposed, and it becomes one of the sources of carbon. 

 The cereals do not seem fitted to acquire their carbon from the atmosphere ; and it does not ap- 

 pear that it is necessary they should, inasmuch as there is such an ample storehouse in the soil. 



Johnston remarks that the carbonate of soda is applicable to meadow lands overgrown with 



