238 A. I. KINGEK AND EMIL J. BAUMANN 



If the motlier liquid from tlio methyl glucoside be concentrated to a 

 syrup and allowed to stand for several weeks, P-methyl glucoside will crys- 

 tallize out. It can be more readily obtained from this mother liquid by 

 treating it with yeast, which hydrolyzes the a, but not the P-form, to 

 glucose, and this in turn is converted to ethyl alcohol and carbon dioxid. 

 (^-methyl glucoside crystallizes with one half molecule of water of crystal- 

 lization, arid melts at 108 C. Its specific rotation is 32. 



By boiling with acids both methyl glucosides are converted into glucose 

 and methyl alcohol. o-Methyl glucoside is also hydrolyzed by maltase, an 

 enzyme of yeast, but (3-methyl glucoside is not. Emulsin, an enzyme found 

 in bitter almonds, decomposes the (5-methyl glucoside, but not the a-form. 

 This is a splendid illustration of the specificity of biochemical reactions. 



Mannose. d-Mannose occurs free in some plants, but usually it is 

 found as an anhydride condensation product called Mannan. tt It is 

 most readily prepared from the vegetable ivory nut by hydrolysis with 

 dilute hydrochloric acid, neutralizing the acid and converting the man- 

 nose to the very insoluble, characteristic mannose hydrazone, from which 

 mannose is obtained in the usual way. A not uncommon form in which 

 mannose also occurs in nature is as the alcohol mannitol. Mannose can 

 be obtained from mannitol by oxidation. This was the method by which 

 it was first prepared (Fischer and Hirschberger) and only later was it 

 identified with the natural product. On the other hand, d-mannitol may 

 be prepared by reduction of d-mannose with sodium amalgam. 



In general behavior, mannose is quite similar to d-glucose. It forms 

 the same phenyl osazone, exhibits mutarotation and has similar solubilities. 

 It forms rhombic crystals, melting at 132 C. 



Galactose. d-Galactose is rarely found free in nature. When found, 

 it is often the result of special conditions. For example, Lippmann dis- 

 covered galactose as a crystalline efflorescense in ivy berries after a sharp 

 frost the first of the autumn. Usually galactose occurs combined with 

 sugars and with other substances as galactosides. It is most commonly 

 found combined with glucose, as lactose in milk, and with sucrose in the 

 trisaccharide raffinose, in beets. 



+ H 2 



lactose d-glucose d-galactose 



C 18 H 32 1(i + 2H 2 - CH 12 C + C n H 12 6 + C 6 H 12 6 

 Kaifinose d-Fructose d-Galactose d-Glucose 



It is interesting to observe that the amount of raffinose found in the beet 

 is increased when the plant is subjected to a sudden frost. 



From alga*, lichens and mosses, mucilages can be obtained that yield 



'Polymers of] the sugars are given the name of the sugar with the ending an. 

 Thus common starch is a glucosan. 



