28 PHYSIOLOGICAL CHEMISTRY 



Second Modification. 1 Benedict has further modified his solution and has 

 succeeded in obtaining one which does not deteriorate upon long standing. 2 

 The following is the procedure for the detection of glucose in solution : To 5 c.c. 

 of the reagent in a test-tube add 8 (not more) drops of the solution under exam- 

 ination. Boil the mixture vigorously for from one to two minutes and then allow 

 the fluid to cool spontaneously. In the presence of dextrose the entire body of 

 the solution will be filled with a precipitate, which may be red, yellow or green in 

 color, depending upon the amount of sugar present. If no glucose is present, the 

 solution will remain perfectly clear. (If urine is being tested, it may show a very 

 faint turbidity, due to precipitated urates.) 



Even very small quantities of glucose (o. i per cent) yield precipitates 

 of surprising bulk with this reagent, and the positive reaction for glucose 

 is the filling of the entire body of the solution with a precipitate, so that 

 the solution becomes opaque. Since amount rather than color of the 

 precipitate is made the basis of this test, it may be applied even for the 

 detection of small quantities of glucose, as readily in artificial light as in 

 daylight. Chloroform does not interfere with this test nor do uric acid 

 or creatinine interfere to such an extent as in the case of Fehling's test. 



Mercuric Oxide Reduction Test (Cramer). 3 This test depends on 

 the reduction of mercuric oxide in a weakly alkaline solution, with the 

 formation of metallic mercury. The degree of alkalinity is an important 

 factor, as the test becomes more sensitive but less specific the greater 

 the alkalinity of the reagent. 



For the detection of reducing sugar in aqueous solution proceed as follows : 

 Introduce 3 c.c. of Cramer's "2.5 reagent" into a test-tube 4 and heat to boiling. 

 The solution remains clear, but turns slightly yellow. Add 3 c.c. of the sugar 

 solution and again heat to boiling. Remove the tube from the flame and note 

 that the mixture becomes turbid, darkens, and that on standing a precipitate 

 of finely divided mercury settles to the bottom of the tube. 



1 Benedict: Jour. Am. Med. Ass'n, 57, 1193, 1911. 



2 Benedict's new solution has the following composition: 



Copper sulphate 17.3 grams. 



Sodium citrate 173 . o grams. 



Sodium carbonate (anhydrous) 100.0 grams. 



Distilled water to make i liter. 



With the aid of heat dissolve the sodium citrate and carbonate in about 600 c.c of water. 

 Pour (through a folded filter paper if necessary) into a glass graduate and make up to 850 c.c. 

 Dissolve the copper sulphate in about 100 c.c. of water and make up to 150 c.c. Pour the 

 carbonate-citrate solution into a large beaker or casserole and add the copper sulphate solu- 

 tion slowly, with constant stirring. The mixed solution is ready for use and does not dete- 

 riorate upon long standing. 



3 Cramer: Bioch. Jour., 9, 156, 1915. 



4 Cramer's " 2.5 Reagent." 0.4 gram mercuric oxide (red or yellow) and 6 grams potas- 

 sium iodide are dissolved in 100 c.c. water. This solution is weakly alkaline. The alka- 

 linity must now be adjusted so that 10 c.c. of the reagent are neutralized by 2.5 c.c. of 

 N/io acid, using phenolphthalein as indicator. This is done by titrating 10 c.c. of the 

 reagent with N/io acid and, after the alkalinity of the reagent has thus been determined, 

 adding the requisite amount of N/io acid or alkali to the bulk of the reagent. The reagent 

 is a clear colorless solution which turns slightly yellow on heating and becomes colorless 

 again on cooling. It must remain clear on boiling. 



