PRACTICAL EXERCISES 431 



colourize the copper solution, it rarely causes so much reduction that 

 a yellow or red precipitate is formed, as is the case in diabetic urine. 

 Glycuronic acid, which is said to occur even in normal urine in very 

 slight traces, and which appears in considerable amount after the 

 administration of chloroform, chloral, nitro-toluol and other sub- 

 stances, also reduces cupric salts, as does alcapton or homogentisinic 

 acid, a substance found in rare cases in disease. If less than 0*5 

 per cent, of sugar is present in the urine, no precipitate of cuprous 

 oxide will be formed till the urine is cooled. The test may also be 

 performed with Fehling's solution. 



(b) Phenyl-hydrazine Test. This test depends upon the fact that 

 phenyl-hydrazine forms with sugars such as glucose, maltose, isomal- 

 tose, etc., but not with cane-sugar, characteristic crystalline substances 

 (phenyl-glucosazone, phenyl-maltosazone, etc.) which can be recog- 

 nised under the microscope, and are distinguished from each 

 other by melting at different temperatures. Phenyl-glucosazone 

 (C 18 H 2? N 4 O 4 ) melts at 205 C. To perform the test for glucose in 

 the urine, proceed thus : Put 5 c.c. of urine in a test tube, add 

 T decigramme of hydrochlorate of phenyl-hydrazine and 2 deci- 

 grammes of sodium acetate. Heat the test-tube in a boiling water- 

 bath for half an hour. Then cool at the tap and examine the 

 deposit under the microscope for the yellow osazone crystals 

 (Plate IV., 3). Sometimes the osazone precipitate is amorphous. 

 Lest this should be the case the precipitate, if no crystals can be 

 seen, must be dissolved in hot alcohol. The solution is then diluted 

 with water and the alcohol boiled off, when the osazone, if any be 

 present, will crystallize out. Very minute traces of sugar can be 

 detected in this way (as little as o'i per cent, in urine). Often in 

 normal urine yellow crystals are deposited during the first fifteen 

 minutes' heating. They must not be mistaken for glucosazone. 

 They probably consist of a compound of glycuronic acid and phenyl- 

 hydrazine. They are changed as the heating goes on into an 

 amorphous brownish-yellow precipitate (Abel). 



(c] The Yeast Test is an important confirmatory test for distin- 

 guishing the fermentable sugars from other reducing substances, but it 

 is not very delicate, and will with difficulty detect sugar when less than 

 o'5 per cent, is present. It can be performed thus : A little yeast 

 (the tablets of compressed yeast do very well) is added to a test-tube 

 half filled with urine. The test-tube is then filled up with mercury, 

 closed with the thumb, and inverted over a dish containing mercury. 

 The dish may be placed on the top of a water-bath whose temperature 

 is about 40 C After twenty-four hours the sugar will have been 

 broken up into alcohol and carbon dioxide. The latter will have 

 collected above the mercury in the test-tube, and the former will be 

 present in the urine. The tests for sugar will either be negative or 

 will be less distinct than before. A control test-tube containing 

 water and yeast should also be set up, as impurities in the yeast 

 sometimes yield a small amount of carbon dioxide. 



(2) Quantitative Estimation of Sugar in Urine. (a) Volumetrically , 

 the sugar can be estimated by titration with Fehling's solution. As 

 this does not keep well, two solutions containing its ingredients 



