CARBOHYDRATES. 



cedure causes the sugar to be converted quantitatively. No quan- 

 titative method has yet been devised, however, based upon this 

 principle. 



A positive Nylander or Boettger test is probably due to the fol- 

 lowing reactions: 



(a) Bi(OH) 2 N0 3 



KN0 



FIG. 2. 



(b) 2Bi(OH) 3 30 = Bi 2 + 3H 2 0. 



10. Fermentation Test. " Rub up " in a mortar about 20 

 c.c. of the sugar solution with a small piece of compressed yeast. 

 Transfer the mixture to a saccharometer 



(shown in Fig. 2) and stand it aside in a 

 warm place for about twelve hours. If 

 the sugar is fermentable, alcoholic fermen- 

 tation will occur and carbon dioxide will 

 collect as a gas in the upper portion of the 

 tube. On the completion of fermentation 

 introduce a little potassium hydroxide solu- 

 tion into the graduated portion by means 

 of a bent pipette, place the thumb tightly 

 over the opening in the apparatus and in- 

 vert the saccharometer. Explain the result. 



11. Barfoed's Test. Place about 5 c.c. 

 of -Barfoed's solution 1 in a test-tube and 

 heat to boiling. Add dextrose solution 

 slowly, a few drops at a time, heating after 

 each addition. Reduction is indicated by 

 the formation of a red precipitate. If 

 the precipitate does not form upon continued 



boiling allow the tube to stand a few minutes and examine. Sodium 

 chloride interferes with the reaction (Welker). 



Barfoed's test is not a specific test for dextrose as is frequently 

 stated, but simply serves to detect monosaccharides. Disac- 

 charides will also respond to the test, according to Hinkel and 

 Sherman, if the sugar solution is boiled sufficiently long, in contact 

 with the reagent, to hydrolyze the disaccharide through the action 

 of the acetic acid present in the Barfoed's solution. 



12. Formation of Caramel. Gently heat a small amount of 



1 Barfoed's solution is prepared as follows : Dissolve 4.5 grams of neutral, 

 crystallized cupric acetate in 100 c.c. of water and add 0.12 c.c. of 50 per cent 

 acetic acid. 



EINHORN SACCHAROMETER. 



