124 THE CARBOHYDRATES 



Detection. 



There are no rapidly performed characteristic tests for 

 rafRnose. 



The only really rehable method of identifying it is to 

 isolate the substance by precipitating the strontium compound 

 in alcoholic solution, filtering off the precipitate and decom- 

 posing it by a current of carbon dioxide. The resulting 

 solution is then evaporated and the residue extracted with 

 alcohol to remove sucrose and other sugars which are more 

 soluble in alcohol than raffinose. The pure substance should 

 be identified by its crystalline form and optical properties. 



Another way of identifying raffinose * is to add to the 

 solution a little decoction of fresh yeast, to act as nutriment, 

 and then to sterilize the solution ; a pure culture of top fer- 

 mentation yeast is then added to the solution and the fermen- 

 tation is allowed to proceed in a thermostat at 31° ; when 

 it is completed, the solution is boiled with animal charcoal, 

 filtered, and evaporated to a syrup ; the latter is then, while 

 still hot, poured into hot alcohol and on cooling it is filtered ; 

 the filtrate is then precipitated by mixing with l| vols, of 

 ether. After twenty-four hours the supernatant liquid is 

 poured off and the residual syrup, which consists of melibiose, 

 is converted into its osazone which is characterized by its 

 crystalline form and melting-point, 1 78-1 79°. f 



Finally, Neuberg % has proposed making use of emulsin for 

 the identification of raffinose. 



MELECITOSE. C^^Yi^^O^^, 2H,0. 



This is a sugar which occurs in the sap of Larix europcea, 

 in Persian manna, and especially in the manna exuded from 

 the twigs and needles of Pseudotsuga Douglasii ; it crystallizes 

 with two molecules of water in rhombic prisms, and is dextro- 

 rotatory (au =+ 83°). It does not reduce Fehling's solution, 

 and on hydrolysis yields first a molecule of glucose and a disac- 

 charide — turanose, C12H22O11 — which subsequently itself breaks 



* Bau : loc. cit., 1897, 21, 185. f I<i' 1902, 26, 69. 



X Neuberg : " Biochem. Zeit.," 1907, 3, 519 and 535. 



