INORGANIC ELEMENTS. 1 9 



The alkali salts of the three classes are readily soluble in 

 water. The secondary and tertiary phosphates are mostly in- 

 soluble, those of the alkali metals excepted. Secondary phos- 

 phates are converted into pyrophosphates by heat and the 

 primary phosphates into metaphosphates. To most indica- 

 tors the primary phosphates show acid behavior, while the sec- 

 ondary phosphates are feebly alkaline. The soluble tertiary 

 phosphates are strongly alkaline. The action on different 

 indicators must be remembered in attempting to estimate the 

 acidity or alkalinity of urine. 



The phosphates furnished us in various animal and vege- 

 table foods are mainly those of calcium and potassium, but it 

 is likely that the larger part of the phosphorus utilized in the 

 body is combined in relatively complex organic compounds, 

 the lecithins and nucleins, for example, which yield phosphoric 

 acid and phosphate in the final oxidation. We find therefore 

 the tertiary calcium and magnesium phosphates, Ca 3 (PO 4 ) 2 

 and Mg 3 (PO 4 ) 2 in bones. Acid calcium phosphate of the 

 formula Ca(H 2 PO 4 ) 2 occurs in some of the body fluids, and 

 is an important urinary excretion. The phosphate CaHPO 4 

 may sometimes be deposited from the urine. Secondary po- 

 tassium phosphate, K 2 HPO 4 , is a constituent of all animal 

 cell structures, possibly in soluble form, but possibly, also, in 

 organic combination. The muscular juice is rich in alkali 

 phosphates. 



Chlorides. Chlorine is found in the body as sodium 

 chloride and potassium chloride, also as free hydrochloric acid 

 in the gastric juice. In our foodstuffs it comes to us mainly 

 as sodium chloride, but this by double decomposition may 

 give rise to the potassium chloride later: 



K 2 C0 3 + 2NaCl = 2KC1 + Na 2 CO 3 . 



In the gastric and pancreatic juices and in the blood sodium 

 chloride is more abundant than potassium chloride, but the 

 latter is in excess in the cell structures. Chlorine is utilized 

 in the animal body only as it is found in the metallic com- 



