CH. XXV.] CARBOHYDRATES. 3 8 7 



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 

 (C 6 H 12 6 =2C 2 H 6 0+ 2 C0 2 ). 



Dextrose may be estimated by the fermentation test, by the 

 polarimeter, and by the use of Fehling's solution. The last 

 method is the most important: it rests on the same principles as 

 Trommer's test, and we shall study it in connection with diabetic 

 urine. 



Levulose. When cane sugar is treated with dilute mineral 

 acids it undergoes a process known as inversion i.e., it takes up 

 water and is converted into equal parts of dextrose and levulose. 

 The previously dextro-rotatory solution of cane sugar then 

 becomes levo-rotatory, the levo-rotatory power of the levulose 

 being greater" than the dextro-rotatory power of the dextrose 

 formed. Hence the term inversion. Similar hydrolytic changes 

 are produced by certain ferments, such as the invert ferment of 

 the intestinal juice. 



Pure levulose can be crystallised, but so great is the difficulty 

 of obtaining crystals of it that one of its names was uncrystallis- 

 able sugar. Small quantities of levulose have been found in 

 blood, urine, and muscle. It has been recommended as an article 

 of diet in diabetes in place of ordinary sugar ; in this disease it 

 does not appear to have the harmful eft'ect that other sugars 

 produce. Levulose gives the same general reactions as dextrose. 



Galactose is formed by the action of dilute mineral acids 

 or inverting ferments on lactose. It resembles dextrose in its 

 action on polarised light, in reducing cupric salts in Trommer's 

 test, and in being directly fermentable with yeast. When 

 nx ii Used by means of nitric acid it yields an acid called mucic 

 acid (C 6 H 10 O 8 ), which is only slightly soluble in water. Dextrose 

 when treated in this way yields an isomeric acid i.e., an acid 

 with the same empirical formula, called saccharic acid, which is 

 very soluble in water. 



Cane Sugar is generally distributed in the vegetable kingdom, 

 but especially in the juices of the sugar cane, beetroot, mallow, 

 and sugar maple. It is a substance of great importance as a 

 food. It undergoes inversion in the alimentary canal. It is 

 crystalline, and dextro-rotatory. With Trommer's test it gives 

 a blue solution, but no reduction occurs in boiling. After 

 inversion it is, of course, strongly reducing. 



Inversion may be accomplished by boiling with dilute mineral 



c c 2 



