422 PHYSIOLOGICAL CHEMISTRY 



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 precipitated. 



The sulphuric acid excreted in the urine arises principally from 

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

 amount is due to ingested sulphates. Under nprmal conditions about 

 2.5 grams of sulphuric acid (SO 3) are eliminated daily, about 75-95 per 

 cent of this being in the form of sulphates. About 90 per cent of this 

 sulphate excretion is in the form of inorganic sulphate and 10 per cent as 

 ethereal sulphates. 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 protein molecule is nitrogen, it would be reasonable 

 to suppose that a fairly definite ratio might exist between the excretion 

 of these two elements. However, when we appreciate that the per- 

 centage content 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 elements as they appear in the urine 

 as end-products of protein metabolism is practically impossible. It 

 has been suggested that the ratio 5 : i 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 stimulated 

 metabolism, whereas a decrease in the sulphuric acid excretion is ob- 

 served 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 sul- 

 phuric acid which has been separated from the ethereal sulphates and has com- 

 bined with the barium of the BaCl 2 to form BaSO 4 . 



3. Detection of Unoxidized or Neutral Sulphur. Place about 10 c.c. of urine 

 in a test-tube, introduce a small piece of zinc, add sufficient hydrochloric acid 

 to cause a gentle evolution of hydrogen, and over the mouth of the tube place a 



