CARBONATES OF POTASSA, MAGNESIA, ETC. 45 



Origin and Discharge of Carbonate of Soda. This sub- 

 stance is not introduced into the body as carbonate of soda, 

 but is formed, as is the carbonate of lime in part, by a de- 

 composition of the malates, tartrates, etc., which exist in 

 fruits. It is discharged occasionally in the urine of the hu- 

 man subject, and a great part of it is decomposed in the 

 lungs by the action of pneumic acid, setting free carbonic 

 acid, which is discharged in the expired air. 



Carbonate of Potassa, KO, CO 2 . 



This salt exists particularly in herbivorous animals. It 

 is found in the human subject when subjected to a vegetable 

 diet. Under the heads of function, origin, and discharge, 

 what has been said with regard to the carbonate of soda will 

 apply to the carbonate of potash. 



Carbonate of Magnesia, MgO, CO 2 HO, and Bicarbonate of 

 Soda, NaO, CO 2 + HO, CO,. 1 



It is most convenient to take up these two salts in con- 

 nection with the other carbonates, though they are put at the 

 end of the list of inorganic substances, as the least important. 

 We know very little about them, chemically or physiologi- 

 cally. Traces of carbonate of magnesia have been found 

 in the blood of man, and it exists normally in considerable 

 quantity in the urine of herbivora. In the human subject 

 it is discharged in the sebaceous matter. 



Liebig has merely indicated the presence of bicarbonate 

 of soda in the blood. 



Phosphate of Magnesia, 3 MgO, P0 5 + 7 HO ; Phosphate 

 of Soda (neutral), 3 NaO, PO 5 ; and Phosphate of Potassa, 

 2 KO, P0 5 . 



1 Formula of Graham, op. cit. t p. 389. 



