76 HOW CROPS GROW. 



water. Observe that the saccharose and dextrin suffer no alteration for 

 a long time, while the glucose and molasses shortly cause the separation 

 of suboxide of copper. 



EXP. 32. Heat to boiling a little white cane-sugar with 30 e. c. of 

 water, and 3 drops of strong sulphuric acid, in a glass or porcelain dish, 

 for 15 minutes, supplying the waste of water as needful, and test the 

 liquid as in the last Exp. It will be found that this treatment trans- 

 forms saccharose into glucose, (and levulose.) 



Tfie quaittit itive estimation of the sugars and of starch is commonly 

 based upon the reaction just described. For this purpose the alkaline 

 copper solution is made of a known strength by dissolving a given weight 

 of sulphate of copper, etc., in a given volume of water, and the glucose, 

 or levulose, or a mixture of both, being likewise made to a known vol 

 ume of solution, it is allowed to flow slowly from a graduated tube into 

 a measured portion of warm copper solution, until the blue color is dis 

 charged. Experiment has demonstrated that one part of glucose or 

 of levulose reduces 2.205 + parts of oxide of copper. Starch and sac 

 charose are first converted into glucose and levulose, by heating with an 

 acid, and then examined in the same manner. For the details required 

 / to ensure accuracy, consult Fresenius (Juant&ttive Analysis. 



As already stated, cane-sugar, by long boiling of its 

 / aqueous solution, and under the influence of hot dilute 

 acids (Exp. 32) and yeast, loses its property of ready crys- 

 V tallization, and is converted into levulose and glucose. 



According to Dubrunfaut, two molecules of cane-sugar take up the 

 elements of two molecules, (5.26 per cent,) of water, yielding a mixture 

 of equal parts of levulose and glucose. This change is expressed In 

 chemical symbols as follows : 



2 (C ia H 22 ()) + 2 H 2 O = C, a H 24 O 13 + C 12 H 24 O ia 

 Cane-sugar. Water. Levulone. Gliicose. 



The alterability of saccharose on heating its solutions 

 occasions a loss of one-third to one-half of what is really 

 contained in cane-juice, and is one reason that solid sugar 

 is obtained from the sorghum with such difficulty. Mo 

 lasses, sorghum syrup, and honey, usually contain all three 

 of these sugars. In molasses, both the saccharose and 

 glucose are hindered from crystallization by the levulose, 

 and by saline matters derived from the cane-juice. 



Honey-dew, that sometimes falls in viscid drops from 

 the leaves of the lime and other trees, is essentially a mix- 



