114 ORGANIC AGRICULTURAL CHEMISTRY 



sugar. Also the three-carbon sugar glycerose, which may be 

 made from glycerol, condenses and yields fructose. As fructose 

 may be converted into glucose, we may say that both of the 

 hexose monosaccharoses have been synthesized in the labora- 

 tory. There is pretty general belief that this formaldehyde 

 synthesis of glucose and fructose represents part of the process 

 by which carbohydrates are photo-synthesized in green plants. 



Galactose, C6H12O6 



Galactose, the third monosaccharose hexose sugar, may be 

 simply mentioned. It is obtained together with glucose when 

 milk sugar is hydrolyzed by enzymes or acids. It is dextro- 

 rotatory and ferments with yeast zymase. It has not been found 

 free in either plants or animals, but occurs in combination in 

 certain glucosides, especially one known as cerebron found in the 

 brain. In plants it occurs also as polysaccharose derivatives 

 known as galactans. These latter will be referred to again. 



EXPERIMENT STUDY XXII 



Hexoses 



(i) Examine for general properties, such as solubility in water and 

 in alcohol, taste, etc., {a) Glucose or dextrose ; {b) Fructose or levu- 

 lose. 



(2) To 5 c.c. Fehling's solution add about i c.c. of glucose solution. 

 Warm. Notice reduction of the copper sulphate to red CU2O. Allow 

 to settle. If a blue color remains, add a little more sugar solution 

 and repeat until all copper sulphate has been reduced. 



(3) Repeat the Fehling's solution test with a solution of levulose. 



(4) Perform Experiment XX, 3, with both glucose and fructose. 



(5) To 5 c.c. of ammoniacal silver nitrate solution add a little glu- 

 cose solution and warm in hot water. Notice formation of silver 

 mirror due to the reduction of the silver solution. 



(6) Make up a i.o per cent solution of glucose. Mix this solution 

 with 1.0 g. yeast and fill a Fermentation tube with the mixture. Allow 

 to stand 24 hours, and determine the amount of CO2 evolved. This 

 fermentation tube is a form of clinical apparatus known as a Sac- 



