PRACTICAL EXERCISES 517 



phosphoric acid. As soon as there is more uranium in the solution than 

 is required to combine with all the phosphoric acid, a brown colour is 

 given with potassium ferrocyanide, due to the formation of uranium 

 ferrocyanide. In carrying out the method, 5 c.c. of a mixture of acetic 

 acid and sodium acetate (there are 10 grammes of sodium acetate and 

 10 grammes of glacial acetic acid in 100 c.c. of the mixture) are added 

 to 50 c.c. of urine, which is then heated in a beaker on the water-bath 

 almost to boiling. The standard uranium solution (which contains 

 35-5 grammes of uranium nitrate in the litre, and I c.c. of which corre- 

 sponds to 0-005 gramme PaO 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 2OO-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 sul- 

 phates. In five to ten minutes it becomes perfectly 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 has 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 400-0. c. 

 Erlenmeyer flask. Add 10 or 15 c.c. of concentrated 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 sul- 

 phate, 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. (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 



