420 PHYSIOLOGICAL CHEMISTRY 



after 30 seconds acidify with a few drops of acetic acid. Hold the tube over 

 ordinary print. If the urine is normal, a slight but distinct turbidity remains 

 but the print is clearly readable. If sugar is present in the urine above the nor- 

 mal concentration, the contents of the tube darken and on standing a finely di- 

 vided precipitate of mercury settles to the bottom of the tube. The amount of 

 the precipitate depends upon the concentration of reducing sugar in the urine. 



It is claimed that this test is free from fallacies inherent in Fehling's 

 test as the result of the reducing action of uric acid and creatinine. 

 The test is said to be more sensitive than Fehling's test or the bismuth 

 reduction tests, and is particularly suitable for the examination of 

 urines in which the amount of sugar present exceeds the normal amount 

 only slightly. 



If the reagent be made more alkaline than indicated, it ceases to be 

 specific for reducing sugars. 



(f) Bismuth Reduction Test (Boettger). To 5 c.c. of urine in a test-tube add 

 i c.c. of KOH or NaOH and a very small amount of bismuth subnitrate, and boil. 

 The solution will gradually darken and finally assume a black color due to reduced 

 bismuth. If the test is made with 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 (bismuth sulphide) . 



(g) Bismuth Reduction Test (Nylander). To 5 c.c. of urine in a test-tube 

 add one-tenth its volume of Nylander's reagent 1 and heat for five minutes 

 in a boiling water-bath. 2 The mixture will darken if reducing sugar is present 

 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 3 claims that 

 o.oi per cent may be so detected). Uric acid and creatinine which 

 interfere with the Fehling test do not interfere with the Nylander's 

 reaction. It is claimed by Bechold that the bismuth reduction tests 

 give a negative reaction with solutions containing sugar when mercuric 

 chloride or chloroform is present. Other observers 4 have failed to 

 verify the inhibitory action of the mercuric chloride and have shown 

 that the inhibitory influence of chloroform may be overcome by raising 



1 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. 



2 Hammarsten suggests that the solution be boiled for 2-5 minutes (according to the 

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

 drawing conclusions. 



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



4 Rehfuss and Hawk: Jour. Biol. Chem., 7, 267, 1910; also Zeidlitz: Upsala Lakdre- 

 foren Forh. t N. F., n, 1906. 



