ELEMENTS OF COMPOSITION. 61 



PHOSPHATE OF SODIUM, Na 2 HP0 4 , and NaHJPO 4 . 



Like potassium, to be alluded to presently, sodium forms three combina- 

 tions with phosphoric acid, namely, basic phosphate of sodium, Na 3 P0 4 ; 

 neutral phosphate of sodium, with two atoms of base, Na. 2 HP0 4 ; and an 

 acid salt with one atom of base NaH 2 P0 4 . The first of these probably 

 does not occur in the system, so that we have only to deal with the two 

 last. Of these the neutral salt is the most common. 



Phosphate of sodium is widely met with throughout the body. It has 

 been found in the blood, the milk, the bile, the urine, and in the tissues. 

 It is, perhaps, the bearer of the carbonic acid of respiration, and is, pro- 

 bably, the solvent for many matters, as, for instance, casein and uric acid. 

 It probably plays an important part, also, in the formation of tissues, 

 which is not yet fully understood. 



SULPHATE OP SODIUM, ETa a S0 4 . 



Like the sulphates of the alkalies generally, this salt is found in animal 

 fluids, especially in urine, and in* the excrements. In some of the most 

 important secretions, however, it is not met with, as, for instance, in the 

 gastric juice, the bile, and the milk. Like other sulphates, it cannot be 

 said to possess any histogenic properties, but rather those of a decomposi- 

 tion product, the sulphur of the protein compounds and allied substances, 

 forming sulphuric acid by oxidation, and displacing the carbonic acid of 

 the soda salt. 



In confirmation of what we have just stated, the facts may be adduced 

 first, that sulphates introduced into the body are rapidly excreted, and 

 on the other hand, that after an abundant fleshy diet their amount in the 

 urine increases (Lehmann) ; secondly, that the sulphur of taurin, as 

 already mentioned (see above, p. 49), is set free under the action of. 

 ferments in the form of sulphurous acid which becomes subsequently con- 

 verted into sulphuric acid by oxidation (Buchner). 



44. 

 Potassium Compounds. 



These are of subordinate importance in the human economy, which 

 fact may to a certain extent depend upon the nature of our food. Among 

 the vegetable feeders, however, the serum of the blood still shows a pre- 

 ponderance of soda salts, and soda is also the base in their bile. But in 

 many other portions of the system we find the most remarkable prepon- 

 derance of potassium salts over those of sodium. 



CHLORIDE OP POTASSIUM, KC1 . 



This compound is found together with common salt in animal fluids; in 

 smaller quantity in man than in phytophagous animals. Its amount in 

 the blood cells is however large (C. Schmidt], and in the juice of muscle 

 it replaces chloride of sodium (Liebig). , 



CARBONATE OF POTASSIUM, K 2 C0 3 . 



Probably occurs with carbonate of sodium in some of the animal fluids, 

 and in the urine of vegetable feeders in all probability as bicarbonate, 

 KHC0 3 . 



PHOSPHATE OF POTASSIUM, KH 2 P0 4 , or K,HP0 4 . 



It is not yet decided in what form of combination with potassium ordi- 



