350 PHYSIOLOGICAL CHEMISTRY 



them. For differentiating among the various carbohydrates, 

 the methods employed are those already familiar to the student 

 from his study of the carbohydrates. 



With samples of the carbohydrate urine furnished perform 

 the following tests: 



REDUCTION TESTS. Albumin or globulin must be removed if 

 'present by acidifying slightly with acetic acid, boiling and 

 filtering. 



54. Qualitative Test. Perform the Fehling test. The test is 

 subject to two sources of error : unless the liquid is boiled the test 

 is not sensitive; if boiled, other substances such as uric acid, 

 creatinine, mucin, pentoses, glycuronic acids, lactose, or a reduc- 

 ing agent used in the preservation of the urine, such as chloro- 

 form or formaldehyde may give a reduction. 



55. Perform the Benedict test. 



Quantitative Estimation of Sugar. The quantitative esti- 

 mation of sugar in urine is attended by some difficulty, and a 

 variety of methods have been proposed. Only two titration 

 methods will be included here, first the Fehling method, because 

 it is the standard method upon which most later and more ac- 

 curate methods are based, and second Benedict's method, which 

 is perhaps the best for general use, all things considered. 



56. Fehling Method. The Fehling test may be made quan- 

 titative by making up the copper sulphate solution accurately. 

 A given amount of dextrose will reduce a definite amount of 

 copper. As long as copper sulphate remains unreduced the 

 solution will have a blue color. A measured volume of Feh- 

 ling 's solution may thus be titrated with the dextrose urine 

 until the color has completely disappeared. From the volume 

 of urine necessary to reduce the given volume of Fehling 's 

 solution, the amount of dextrose in the urine may be calculated. 



The quantitative Fehling solution is made up of such a 

 strength that 10 c.c. of the copper solution (20 c.c. of the 

 mixed Fehling 's) will be reduced by 0.1 gm. glucose or 0.134 

 gm. lactose. 



