52 4 EXCRETION 



acid. A similar red colour is given by dextrose, but not unless the 

 solution is heated. 



Quantitative Estimation of Creatinin by Folin's Method. It depends 

 upon the comparison of the colour which* creatinin gives with picric 

 acid in an alkaline solution with that of a standard solution of potassium 

 bichromate. Ten c.c. of urine is measured into a 500 c.c. measuring- 

 flask; 15 c.c. of a saturated picric acid solution (containing about 

 12 grammes per litre) and 5 c.c. of a 10 per cent, solution of sodium 

 hydroxide are added. The mixture is allowed to stand for five minutes. 

 Then water is added up to the 500 c.c. mark, and the flask shaken to 

 mix uniformly. Samples of the liquid are then at once compared 

 colorimetrically with a half-normal solution of potassium bichromate 

 containing 24-55 grammes per litre. The colour of the urine does not 

 introduce a sensible error on account of the great dilution". For exact 

 work the comparison must be made with a good colorimeter. It has 

 been found experimentally that, when to milligrammes of creatinin 

 are present in 500 c.c. of a solution made as described, a layer of the 

 solution 8-1 millimetres in thickness has the same depth of tint as 8 milli- 

 metres of the bichromate solution. Suppose it takes 9 millimetres ol 

 the urine-picrate solution to equal 8 millimetres of the bichromate, 



O. j 



then the 10 c.c. of urine contains 10 x =9-0 milligrammes of 



creatinin. 



12. Hippuric Acid. From horse's or cow's urine hippuric acid is 

 prepared by evaporating to a small bulk, and adding strong hydrochloric 

 acid. The crystalline precipitate is washed with cold water, then 

 dissolved in hot water, and filtered hot. Hippuric acid separates out 

 from the filtrate in the cold in the form of long four-sided prisms with 

 pyramidal ends. Heated dry in a test-tube, the crystals melt, and 

 benzoic acid and oily drops of benzonitrile, a substance with a smell 

 like that of oil of bitter almonds, are formed. 



ABNORMAL SUBSTANCES IN URINE. 



13. Proteins (i) Qualitative Tests. (a) Boil and add a few drops 

 of nitric acid. A precipitate on boiling, increased or not affected by 

 the acid, shows the presence of coagnlable proteins (serum-albumin or 

 globulin). A precipitate of earthy phosphates sometimes forms on 

 boiling. It is distinguished from a precipitate of proteins by dissolving 

 on the addition of acid. 



(b) Heller's Test. Put some nitric acid in a test-tube. Pour care- 

 fully on to the surface of the acid a little urine. A white ring at the 

 junction of the liquids indicates the presence of albumin or globulin. 

 If much albumose is present, a white precipitate, which disappears on 

 heating, may be formed. When this test is performed with undiluted 

 urine, uric acid may be precipitated and cause a brown colour at the 

 junction. A similar ring may be found in the absence of proteins when 

 the test is made on the urine of a patient who has been taking copaiba. 

 In very concentrated urine a white ring of nitrate of urea may be 

 formed. A coloured ring is frequently seen, owing to the oxidation of 

 certain chromogens of urine. 



(c) Filter some urine, and add to the filtrate its own volume of acetic 

 acid. A precipitate may indicate mucin or nucleo -albumin. If any is 

 formed, filter ft off, and add to the filtrate a few drops of potassium 

 ferrocyanide. A white precipitate shows the presence of proteins. 



(d) Test for Globulin in Urine. Serum-globulin probably never 



