CARBOHYDRATES 27 



nation. Boil the mixture vigorously for two minutes and then allow the fluid 

 to cool spontaneously (Do not hasten cooling by immersion in cold water). 

 In the presence of dextrose the entire body of the solution will be filled with a 

 colloidal precipitate, which may be red, yellow or green in color, depending 

 upon the amount of sugar present. In the presence of over 0.2-0.3 per cent 

 of glucose the precipitate will form quickly. 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 precipi- 

 tates 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. 



(d) Folin-McEllroy Test. 1 To 5 c.c. of the reagent 2 in a test tube add 

 5-8 drops of urine (never add more than 0.5 c.c.) and boil for 1-2 minutes or 

 heat in a beaker of boiling water for 3 minutes. If more than the normal traces 

 of sugar be present the hot solution will be filled with a colloidal (greenish- 

 yellow or reddish) precipitate as in Benedict's test. Because of the sensitiveness 

 of this test, when working with urine only a distinctly positive test obtained with 

 the solution still hot is to be regarded as positive. 



(e) Bismuth Reduction Test (Nylander). To 5 c.c. of sugar solution in a test- 

 tube add one-tenth its volume of Nylander's reagent 3 and heat for five minutes 

 in a boiling water-bath. 4 The solution will darken if reducing ugaris^>resent, 

 and upon standing for a few moments a black color will appear. 



This color is due to the precipitation of bismuth. If the test is made 

 on urine containing albumin this must be removed, by boiling and 

 filtering, before applying the test, since with albumin a similar change of 

 color is produced. Glucose when present to the extent of 0.08 per cent 

 may be easily detected by this reaction (Rabe 6 claims that o.oi per cent 

 sugar may be so detected). Uric acid and creatinine which interfere 



1 Folin and McEllroy: Jour. BioL Chem., 33, 513, 1918. 



2 Folin-McEllroy Reagent. It has been shown that alkaline phosphates may be used 

 in [place of tartrates or citrates to hold cupric hydroxide in solution. This reagent is 

 based on that principle. Dissolve 100 g. of sodium pyrophosphate, 30 g. of disodium phos- 

 phate and 50 g. of dry sodium carbonate in approximately i liter of water by the aid of 

 a little heat. Dissolve separately 13 g. of copper sulphate in about 200 c.c. of water. 

 Pour the copper sulphate solution into the phosphate-carbonate solution and shake. 



3 Nylander's reagent is prepared by digesting 2 grams of bismuth subnitrate and 4 grams 

 of Rochelle salt in 100 c.c. of a 10 per cent potassium hydroxide solution. The reagent is 

 then cooled and filtered. 



4 Hammarsten suggests that the mixture should be boiled 2-5 minutes (according to the 

 sugar content) over a free flame and the tube then permitted to stand 5 minutes before 

 drawing conclusions. 



6 Rabe: Apoth. Ztg., 29, 554, 1914. 



