SODA COMPOUNDS. Ill 



important part in the changes which occur in the interior 

 of plants, although its direct agency in this direction has 

 not hitherto been distinctly understood. 



TARTRATES AND CITRATES OF POTASH, exist in many 

 fruits; the citrates abound in the citrus class of fruits, 

 oranges, lemons, shaddocks, and limes; and the tartrates 

 in grapes. These salts are easily decomposed by heat as 

 the oxalate of potash is, leaving carbonate of potash. Few 

 experiments have been made in regard to these compounds 

 of potash; probably because of the slight difference between 

 them and the carbonate and the ease with which they can 

 be interchanged in the process of growth of plants. 



SODIUM AND ITS COMPOUNDS. 



Sodium is never found uncombined and of necessity has 

 no relation to vegetation. It is of some interest however 

 as being the base of various compounds which are inti- 

 mately connected with the growth of plants. Like potas- 

 sium it is a soft silvery white metal, light enough to float 

 upon water, and like it will oxidize and burn on contact 

 with this fluid. It is produced from soda in precisely the 

 same manner. Its compounds are first 



CHLORIDE OF SODIUM, or common salt. This substance 

 is universally diffused. It forms 2| per cent, of the weight 

 of the ocean and is found more or loss in all soils ; it also 

 exists as a rock in enormous beds among the strata of the 

 earth's crust, some of these being considerably over a thou- 

 sand feet in thickness. It forms a portion of the substance 

 of all plants and animals, and hence is of great interest to 

 farmers, as being a most important manure for crops ; for 

 which purpose it has been used from the earliest ages. It 

 consists of sodium and chlorine. It is so well known that 

 its properties need no further consideration at this time. 



SODA, is the oxide of sodium, and resembles very strongly 

 the corresponding oxide of potassium ; although its proper- 

 ties are not so strongly marked. It is extremely caustic 

 and absorbs moisture from the air. The sodium compounds 

 seem to be everywhere diffused, being found everywhere, 



