596 THE URINE [CH. XXXIX. 



The ethereal sulphates just mentioned form about a tenth of the 

 total sulphates. They are combinations of sulphuric acid with 

 organic radicals, and the greater part of them originate from putre- 

 factive changes in the intestine. The chief of these ethereal 

 sulphates are phenyl sulphate of potassium and indoxyl sulphate of 

 potassium. The latter originates from the indole formed in the 

 intestine, and as it yields indigo when treated with certain reagents 

 it is sometimes called indican. The indican of urine, however, is 

 not the same thing as the indican of plants, which is a glucoside. 

 Both yield indigo, but there the resemblance ceases. 



The formation of these sulphates is somewhat important; the 

 aromatic substances liberated by putrefactive processes in the 

 intestine are poisonous, but their conversion into ethereal sulphates 

 renders them harmless. 



The equation representing the formation of potassium phenyl-sulphate is as 

 follows : 



C 6 H 5 OH + S0 2 = S0 2 < 65 + H 2 0. 



[Phenol.] [Potassium [Potassium [Water.] 



hydrogen phenyl-sulphate.] 

 sulphate.] 



Indole (C 8 H 7 N) on absorption is converted into indoxyl : 



C.OH : CH 



The equation representing the formation of potassium indoxyl-sulphate is as 

 follows : 



C 8 H 7 NO + SO := S0 2 < 8e + H 2 0. 



[Indoxyl.] [Potassium [Potassium [Water.] 



hydrogen indoxyl-sulphate.] 



sulphate.] 



Carbonates. Carbonates and bicarbonates of sodium, calcium, 

 magnesium, and ammonium are only present in alkaline urine. 

 They arise from the carbonates of the food, or from vegetable acids 

 (malic, tartaric, etc.) in the food. They are, therefore, found in the 

 urine of herbivora and vegetarians, whose urine is thus rendered 

 alkaline. Urine containing carbonates becomes, like saliva, cloudy 

 on standing, the precipitate consisting of calcium carbonate, and 

 also phosphates. 



Phosphates. Two classes of phosphates occur in normal urine : 



(1) Alkaline phosphates that is, phosphates of sodium (abundant) 

 and potassium (scanty). 



(2) Earthy phosphates that is, phosphates of calcium (abundant) 

 and magnesium (scanty). 



The composition of the phosphates in urine is liable to variation. 

 In acid urine the acidity is due to the acid salts. The chief are : 



Sodium dihydrogen phosphate, NaH 9 P0 4 , and calcium dihydrogen 

 phosphate, Ca(H 2 P0 4 ) 2 . 



