URINE. 297 



sometimes called conjugate sulphuric acid. The greater part of 

 the sulphur is eliminated in the oxidized form but the absolute per- 

 centage of sulphur excreted as the preformed, ethereal or loosely 

 combined type depends upon the total quantity of sulphur present, 

 i. e., there is no definite ratio between the three forms of sulphur 

 which will apply under all conditions. The preformed sulphuric 

 acid may be precipitated directly from acidified urine with BaCl 2 , 

 whereas the ethereal sulphuric acid must undergo a preliminary 

 boiling in the presence of a mineral acid before it can be so precipi- 

 tated. 



The sulphuric acid excreted by the urine arises principally from 

 the oxidation of protein material within the body; a relatively small 

 amount is due to ingested sulphates. Under normal conditions 

 about 2.5 grams of sulphuric acid is eliminated daily. Since the 

 sulphuric acid content of the urine has, for the most part, a protein 

 origin and since one of the most important constituents of the pro- 

 tein molecule is nitrogen, it would be reasonable to suppose that a 

 fairly definite ratio might exist betwen the excretion of these two 

 elements. However, when we appreciate that the percentage con- 

 tent of N and S present in different proteins is subject to rather 

 wide variations, the fixing of a ratio which will express the exact 

 relation existing between these two substances, as they appear in the 

 urine as end-products of protein metabolism, is practically im- 

 possible. It has been suggested that the ratio 5:1 expresses this 

 relation in a general way. 



Pathologically, the excretion of sulphuric acid by the urine is in- 

 creased in acute fevers and in all other diseases marked by a stimu- 

 lated metabolism, whereas a decrease in the sulphuric acid excretion 

 is observed in those diseases which are accompanied by a loss of 

 appetite and a diminished metabolic activity. 



EXPERIMENTS. 



1. Detection of Inorganic Sulphuric Acid. Place about 10 c.c. 

 of urine in a test-tube, acidify with acetic acid and add some barium 

 chloride solution. A white precipitate of barium sulphate forms. 



2. Detection of Ethereal Sulphuric Acid. Filter off the 

 barium sulphate precipitate formed in the above experiment, add 

 i c.c. of hydrochloric acid and a little barium chloride solution to 

 the filtrate and heat the mixture to boiling for 1-2 minutes. Note 

 the appearance of a turbidity due to the presence of sulphuric acid 



