CH. XXV.] 



SUGARS 



389 



saccharide group undergo a corresponding condensation, we get what 

 are called poly saccharifies. 



C 6 H 12 6 = = (C G H 10 5 ) + H 2 0. 



The polysaccharides are starch, glycogen, various dextrins, cellu- 

 lose, and gums. We may, therefore, arrange the important carbo- 

 hydrates of the hexose family in a tabular form as follows : 



The + and signs in the above list indicate that the substances 

 to which they are prefixed are dextro- and levo-rotatory respectively 

 as regards polarised light. (See Polarimeter, p. 404.) The formulae 

 given above are merely empirical ; the quantity n in the starch group 

 is variable and often large. The following are the chief facts in 

 relation to each of the principal carbohydrates. 



Dextrose or Grape Sugar. This carbohydrate is found in fruits, 

 honey, and in minute quantities in the blood and numerous tissues, 

 organs, and fluids of the body. It is the form of sugar found in large 

 quantities in the blood and urine in the disease known as diabetes. 



Dextrose is soluble in hot and cold water and in alcohol. It is 

 crystalline, but not so sweet as cane sugar. When heated with strong 

 potash certain complex acids are formed which have a yellow or 

 brown colour. This constitutes Moore's test for sugar. In alkaline solu- 

 tions dextrose reduces salts of silver, bismuth, mercury, and copper. 

 The reduction of cupric to cuprous salts constitutes Trommer's test, 

 which is performed as follows : put a few drops of copper sulphate 

 into a test-tube, then solution of dextrose, and then strong caustic 

 potash. On adding the potash a precipitate is first formed which 

 dissolves, forming a blue solution. On boiling this a yellow or red 

 precipitate (cuprous hydrate or oxide) forms. 



On boiling a solution of dextrose with an alkaline solution of 

 picric acid, a dark red opaque solution due to reduction to picramic 

 acid is produced. 



Another important property of grape sugar is that under the 

 influence of yeast it is converted into alcohol and carbonic acid 



Dextrose may be estimated by the fermentation test, by the polari- 



