3O PHYSIOLOGICAL CHEMISTRY. 



yield precipitates of surprising bulk with this reagent, and the posi- 

 tive reaction for dextrose 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 quan- 

 tities of dextrose, as readily in artificial light as in daylight. 



(d) Boettger's Test. To 5 c.c. of sugar solution 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 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 (bismuth sulphide). 



(e) Nylander's Test (Aknen's Test). To 5 c.c. of sugar solu- 

 tion 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 solution 

 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. Dextrose when present to the extent of 0.08 per cent. 

 may be detected by this reaction. It is claimed by Bechold that 

 Nylander's and Boettger's tests give a negative reaction with 

 solutions containing sugar when mercuric chloride or chloroform 

 is present. Other observers have failed to verify the inhibitory 

 action of mercuric chloride and have shown that the inhibitory in- 

 fluence of chloroform may be overcome by raising the tempera- 

 ture of the urine to the boiling-point for a period of five minutes 

 previous to making the test. Urines rich in indican, uroerythrin 

 or hcematoporphyrin, as well as urines excreted a'fter the inges- 

 tion of large amounts of certain medicinal substances, may give 

 a darkening of Nylander's reagent similar to that of a true sugar 

 reaction. 



According to Rustin and Otto the addition of PtCl 4 increases 

 the delicacy of Nylander's reaction. They claim that this pro- 



1 Nylander's reagent is prepared by digesting 2 grams of bismuth subnitrate 

 and d grams of Rochelle salt in TOO c.c. of a 10 per cent potassium hydroxide 

 solution. The reagent is then cooled and filtered. 



2 Hammarsten suggests that the mixture should be boiled 2-5 minutes (accord- 

 ing 10 the sugar content) over a free flame and the tube then permitted to stand 

 5 minutes before drawing conclusions. 



