CARBOHYDRATES 31 



reduction test, but differs from Fehling's and other reduction tests in 

 that the reduction is brought about in an acid solution. It is unsuited 

 for the detection of sugar in urine. 



12. Fermentation Test. "Rub up" hi a mortar about 20 c.c. of the sugar solu- 

 tion with a small piece of compressed yeast. Transfer the mixture to a sacchar- 

 ometer (shown hi Fig. 3) and stand it aside hi a warm place for about twelve 

 hours. If the sugar is fermentable, alcoholic fermentation will occur and carbon 

 dioxide will collect as a gas in the upper portion of the tube (see Fig. 4). 

 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 invert the saccharometer. Re- 

 membering that KOH has the power to absorb 

 CO 2 how do you explain the result? 1 



13. Formation of Caramel. Gently heat a 

 small amount of pulverized dextrose in a test-tube. 

 After the sugar has melted and turned brown, allow 

 the tube to cool, add water and warm. The color- 

 ing matter produced is known as caramel. 



FIG. 3. EINHORN SACCHAROMETER. 



FIG. 4. ILLUSTRATING DIFFERENT STAGES 

 IN FERMENTATION. 



14. Demonstration of Optical Activity. A demonstration of the use of the 

 polariscope, by the instructor, each student being required to take readings and 

 compute the "specific rotation." 



USE OF THE POLARISCOPE 



For a detailed description of the different forms of polariscopes, the 

 method of manipulation and the principles involved, the student is 

 referred to any standard text-book of physics. A brief description fol- 

 lows: An ordinary ray of light vibrates in every direction. If such a 



1 The findings of Neuberg and associates 2 indicate that the liberation of carbon di- 

 oxide by yeast is not necessarily a criterion of the presence of sugar. The presence of 

 an enzyme called carboxylase has been demonstrated in yeast which has the power of 

 splitting off CO 2 from the carboxyl group of amino- and other aliphatic acids. 



2 Neuberg and Associates: Biochem. Zeitsch., 31, 170; 32, 323; 36, (60, 68, 76), 1911. 



