CH. XII.] ETHEREAL SULPHATES. 285 



NOTE. Any alkaline phosphate, Na 2 HPO 4 , present in the urine is precipi- 

 tated by BaClj as BaHPO 4 . The acid phosphates remain in solution as 

 Ba(H 2 PO 4 ) 2 . On the addition of the alkaline baryta mixture, the acid phos- 

 phate is converted into the insoluble alkaline phosphates of barium. li no 

 precipitate is produced when the baryta-mixture is added, there are no acid 

 phosphates present in the sample of urine. 



Since the acidity of a sample of urine varies almost directly with the 

 amount of acid phosphates present, as determined by the above method, it is 

 generally held that the acidity of urine is mainly due to the presence of these 

 acid phosphates. 



331. Treat 10 cc. of urine with a few drops of strong hydro- 

 chloric acid, and about 3 cc. of a solution of barium chloride. A 

 precipitate of barium sulphate is produced as an opaque milkiness. 

 If the precipitate is thick the sulphates are in excess. (The hydro- 

 chloric acid is added to prevent the precipitation of phosphates.) 



332. To demonstrate the presence of ethereal sulphates. 



To urine add an equal bulk of baryta mixture (two parts of baryta 

 water to one part of a 10 per cent, solution of barium nitrate). A 

 precipitate is formed consisting of the phosphates and the ordinary 

 inorganic sulphates. Filter till quite clear. To the nitrate add a 

 third of its volume of strong hydrochloric acid, boil in a beaker for 

 five minutes, and allow to stand. A faint white cloud of barium 

 sulphate is formed, indicating the presence of ethereal sulphates in 

 the urine. 



NOTES. i. The ethereal sulphates form soluble barium^salts, but are 

 hydrolysed to sulphuric acid by heating with an acid. 



c 6 H 5 - o _ 



_^SO 2 + H 2 O=C 6 H 6 .OH + H a So 4 . 



HO Phenol. 



Phenyl-sulphuric acid. 



The sulphuric acid thus formed is converted into bariiim sulphate by the 

 excess of barium present. 



2. The solution becomes very dark in colour on boiling with the strong 

 acid, owing to the action of the latter on the aromatic chromogenic substances 

 in the urine. 



3. Ethereal sulphates can be prepared as follows: warm 10 drops of 

 absolute alcohol with 5 drops of concentrated sulphuric acid in a test-tube. 

 Cool and make alkaline with 5 per cent. soda. Add 10 per cent, barium 

 chloride as long as a precipitate continues to be formed. Boil and filter. 

 The filtrate con tarns barium ethyl sulphate. Add one-half volume of concen- 

 trated hydrochloric acid and boi!. A precipitate of barium sulphate is 

 formed. 



