264 PRACTICAL PHYSIOLOGY 



/N\ 

 it is gently boiling, then run in from a burette a standard I ,-TJ J solution 



of uranium acetate (1 c.c. of ^j- uran. acet. 1 ^ 0-00355 grm. P 2 5 ) 



until a drop of the boiling mixture placed on a drop of potassium 

 ferrocyanide on a white glazed tile gives an immediate brown colour 

 due to the formation of uranium ferrocyanide, thus indicating that 

 there is now an excess of uranium present. In taking out drops for 

 testing care must be taken to see that the glass rod employed does 

 not come in contact with the mouth of the burette and get con- 

 taminated with uranium solution, otherwise erroneous results will 

 be obtained : 



N 

 c.c. uran. acetate used X 0-00355=grms.P 2 5 in25(or50) c.c. 



Cochineal added to the mixture in basin may be used as indicator 

 in place of the ferrocyanide. End reaction is change of red colour 

 to green. (See also p. 288.) 



Sulphates. Sulphur is excreted in three forms in the urine as 

 (a) preformed (inorganic) sulphates, (b) ethereal sulphates, and (c) 

 neutral sulphur. The bulk of the excretion is in the form of 

 inorganic sulphate. 



EXPERIMENT III. Add about 2 c.c. HC1 to 10 c.c. urine in a 

 test tube and then an excess of barium chloride solution. A white 

 precipitate of barium sulphate forms. Filter off this precipitate 

 and boil the clear filtrate. A further precipitation of barium sul- 

 phate should take place due to the decomposition of ethereal 

 sulphates by the hydrochloric acid. (See also p. 289.) 



Metabolism. One of the results of Folin's investigations on metabolism 

 has been to show the significance of determinations of sulphates in the urine. 

 The total sulphur in the urine is, like the nitrogen, distributed among several 

 substances, which are divided into three groups the inorganic sulphates, the 

 ethereal sulphates, and the neutral sulphur compounds. The inorganic 

 sulphates are mainly those of sodium ; the ethereal sulphates are compounds 

 of phenol, cresol, scatoxyl, andindoxyl, with sulphuric acid and potassium (see 

 p. 238), and the neutral sulphur compounds are organic compounds in which 

 the sulphur is an integral part of the molecule. Cystin, when present, belongs 

 to this group. When the relative amounts of SO 3 excreted in the above- 

 mentioned three forms are calculated as percentages of the total SO 3 excretion, 

 it is found that the inorganic sulphates on a protein-poor diet behave like 

 urea-nitrogen, i.e. become less both in absolute amount and in relative 

 percentage ; that the neutral sulphur under the same conditions behaves like 

 creatinin-nitrogen, i.e. remains constant in absolute amount, whereas the 

 percentage rises, and that the ethereal sulphate excretion behaves like that of 

 ammonia-nitrogen, i.e. becomes somewhat less in absolute amount, but that 

 the percentage rises. 



These facts are clearly shown in the following table, which is an extension of 

 that on page 254. 



1 j-Q uranium acetate, 21-3 grm. ur. acet. dissolved in water and made up 

 to 1 litre. 



