SALTS. 83 



is converted into sodium biphosphate, or, as it is sometimes called, 

 " acid sodium phosphate," which gives to the urine its acid 

 reaction. In this fluid are discharged daily 4.5 grams of the 

 alkaline phosphates and the sodium biphosphate. 



Sulphates. Sodium sulphate (Na.,S0 4 ) and potassium sulphate 

 (K 2 SO 4 ) are found in the blood, lymph, aqueous humor, milk, 

 saliva, mucus, perspiration, urine, and feces. Their quantity is 

 small, however, except in the urine, by which fluid they are dis- 

 charged daily to the amount of 4 grams. 



Source of Sulphates. These sulphates are taken in as part of 

 the solid food we eat and also in the water we drink. They are 

 present in flesh, in eggs, in the cereals, and in other animal and 

 vegetable foods. Drinking-Avater often contains these sulphates, 

 and calcium sulphate as well. Sulphates are undoubtedly formed 

 to some extent within the body. In discussing the constitution 

 of the albuminous ingredients of the food it will be seen that one 

 of their elements is' sulphur. Some of this sulphur becomes 

 oxidized, forming sulphuric acid, which, being a stronger acid 

 than carbonic, displaces it from the carbonates and unites with 

 the alkaline bases, forming sulphates. 



Carbonates. Sodium carbonate (Na 2 CO 3 ), sodium bicarbonate 

 (NaHCO s ), and potassium carbonate (K 2 CO 3 ) are salts which are 

 known as the " alkaline carbonates," and are intimately associated 

 with the alkaline phosphates. 



Source of Carbonates. These salts are, to some extent, intro- 

 duced with the food, but are principally formed by the decom- 

 position of the salts of the vegetable acids. In fruits, such as 

 apples and cherries, and in vegetables, such as potatoes and carrots, 

 are found malic, tartaric, and citric acids, united with sodium and 

 potassium to form malates, tartrates, and citrates of sodium and 

 potassium. When these fruits or vegetables are eaten, these salts 

 are taken up by the blood, and while in the blood the organic acids 

 are decomposed, and the bases uniting with carbonic acid, alkaline 

 carbonates are formed, which are discharged in the urine. This 

 accounts for the fact that after eating sufficient of such fruits or 

 vegetables the urine becomes alkaline. 



Office of Carbonates. The alkalinity of the blood and of other 

 alkaline fluids is, as has been stated, only partially due to the 

 alkaline phosphates. In causing this reaction the alkaline car- 

 bonates have a share. In the blood of flesh-eating animals the 

 phosphates are more abundant, this being due to the predominance 

 of phosphates in muscular tissue, while in that of the herbivora 

 the carbonates are in excess of the phosphates. Remembering, 

 then, what has been said of the formation of the carbonates from 

 the salts in fruits and vegetables, this difference in the blood is 

 readily understood. In human blood there are both phosphates 

 and carbonates to account for its alkalinity. 



