62 THE CARBOHYDRATES 



solution of different concentrations heated for varying periods 

 and examined periodically after cooling. 



Maltose gives an osazone characterized by dense rosettes of 

 lemon yellow crystals, which are broader and larger than those 

 obtained with dextrose and levulose ; the crystals may, how- 

 ever, take several weeks for their formation. 



Dextrose and levulose may be distinguished by the fact 

 that methylphenylhydrazine gives a crystalline osazone with 

 levulose and not with dextrose. It is to be noted that the 

 methylphenylhydrazine must be very pure. 



LEVULOSE OR FRUCTOSE. 



Levulose occurs in most sweet fruits and in honey, together 

 with both cane sugar and dextrose, but usually in excess of 

 the latter two. It is formed in equal quantity with dextrose 

 by the hydrolysis of cane sugar, but being more strongly laevo- 

 rotatory than dextrose is dextro-rotatory, the resulting mixture 

 turns the plane of polarized light to the left, whereas the 

 original cane sugar is dextro-rotatory ; the resulting mixture 

 is accordingly known as invert sugar and the process by which 

 this change is produced is called inversion. 



The separation of pure levulose from invert sugar on a 

 small scale is not easy to carry out, but the operation is per- 

 formed on a large scale by making use of the fact that on 

 treating invert sugar with milk of lime the levulose is converted 

 into an insoluble calcium compound, which may be filtered 

 ofif and purified, while the glucose remains in solution. The 

 easiest means of preparing levulose in the laboratory is to 

 hydrolyse inulin by boiling I part of this substance with 5 

 parts of "5 per cent sulphuric acid* for one hour; the acid is 

 then removed by means of barium carbonate, and the solution, 

 after being treated with animal charcoal and filtered, is eva- 

 porated at a low temperature to a thin syrup. The latter is 

 then crystallized from alcohol after sowing with a crystal of 

 pure levulose. A modification of this method is employed 

 for the manufacture of pure levulose. f 



* Diill {" Chem. Zeit.," 1895, 19, 216) recommends the use of oxalic acid ; see 

 also Wiechmann : "Z. d. Vereins Deut. Zuckerind.," 1891, 41, 331. 

 t Cf. Stein : " Proc. Internal. Confer. Sugar Ind.," April, 1908. 



