PRACTICAL EXERCISES 479 



P ? O 5 ) is now run in from a burette, until a drop of the urine gives, 

 with a drop of potassium ferrocyanide solution, on a porcelain slab, 

 a brown colour. Uranium acetate may be used instead of uranium 

 nitrate, but the latter keeps best. When uranium acetate is employed 

 it is not necessary to add the sodium acetate mixture. 



5. Sulphates (i) Qualitative Test. Add to urine a drop of hydro- 

 chloric acid and then a few drops of barium chloride. A white pre- 

 cipitate comes down, showing that inorganic sulphates are present. 

 The hydrochloric acid prevents precipitation of the phosphates. 



(2) Quantitative Estimation of the Sulphates (Inorganic and 

 Ethereal). Add to 50 c.c. of albumin -free urine in a 200 -c.c. 

 Erlenmeyer flask 5 c.c. of a 4 per cent, potassium chlorate solution 

 and 5 c.c. of strong hydrochloric acid, and boil the mixture to break 

 up the ethereal sulphates. In five to ten minutes it becomes per- 

 fectly colourless. While it continues to boil, 25 c.c. of a 10 per 

 cent, solution of barium chloride are added by drops, at such a 

 rate that it takes about five minutes to add this quantity. The 

 flask is now put on the water-bath for one-half to one hour, till the 

 precipitate has settled. Then filter through an ash-free filter. 

 Wash the precipitate on the filter for half an hour with hot water. 

 During the first twenty minutes of the washing, at intervals of a 

 few minutes, substitute hot 5 per cent, ammonium chloride solution 

 for the water. At the end of the half-hour's washing, as soon as 

 the water Jhas run through the filter, fold up the latter and press it 

 gently between dry filter-papers to remove a portion of the water. 

 Then place the filter in a weighed porcelain crucible. Pour into 

 the crucible 3 or 4 c.c. of alcohol, and ignite it, to dry and partially 

 burn the filter-paper. Then incinerate till all the carbon is burned 

 off, cool, and weigh. From the weight of the barium sulphate, 

 the sulphuric acid in 50 c.c. of urine is easily calculated (SO 4 in 

 i gramme of barium sulphate, 0-41187 gramme) (Folin). 



(3) Quantitative Estimation of the Sulphuric Acid united with Aromatic 

 Bodies (Aromatic or Ethereal Sulphates). Put 200 c.c. of the same 

 urine as used in (2) into a beaker. Add 100 c.c. of 10 per cent, 

 barium chloride solution in the cold. Let stand for twenty-four 

 hours. Then decant off the clear supernatant liquid, and filter it. 

 Measure 150 c.c. of the clear filtrate, corresponding to 100 c.c. of 

 the urine, into a 4OO-c.c. Erlenmeyer flask. Add 10 or 15 c.c. of con- 

 centrated hydrochloric acid, and 10 to 15 c.c. of 4 per cent, potassium 

 chlorate. Heat the mixture to boiling, and proceed as in (2). 

 From the weight of the barium sulphate, the ethereal sulphuric 

 acid in 100 c.c. of urine can be calculated. Deducting this from 

 the quantity per 100 c.c. of urine obtained in (2), we get the^amount 

 of inorganic sulphuric acid per 100 c.c. (Folin). 



6. Indoxyl (contained in the urine as indican, the potassium salt 

 of indoxyl-sulphuric acid) can be oxidized into indigo, and so 

 detected and estimated. 



A Qualitative test is the following : Ten c.c. of horse's urine is 

 mixed with 10 c.c. of Obermayer's reagent (pure concentrated 

 hydrochloric acid containing 2 to 4 parts of ferric chloride in 1,000), 

 and shaken well for a minute or two ; a bluish colour appears if, as 

 is generally the case, indoxyl is present, indigo (C 10 H 10 N 2 O 2 ) being 

 formed by the oxidizing action of the ferric chloride on the indoxyl, 

 the compound of which with sulphuric acid has been broken up by 

 the hydrochloric acid. The urine must be free from albumin . In per- 

 forming the test in human urine, which contains a smaller quantity 



