MAN NOSE 67 



salt. Filter once more, and evaporate the filtrate almost to 

 dryness, and acidify with nitric acid ; the precipitate is pure 

 mucic acid. 



MANNOSE. 



Mannose may be obtained by the hydrolysis of a form of 

 mannane contained in salep mucilage (Orchis Morid] and from 

 several other so-called hemi-celluloses contained in peas, 

 coffee beans, date stones, etc. It is most conveniently prepared 

 by the hydrolysis of the hemi-cellulose contained in ivory 

 nuts, the fruits of Phytelephas macrocarpa ; turnings from these 

 seeds,* obtained in the manufacture of vegetable ivory buttons, 

 are heated over a water bath for six hours with twice their 

 weight of 6 per cent hydrochloric acid. After filtering, the 

 solution is boiled with animal charcoal, neutralized and preci- 

 pitated with phenylhydrazine acetate ; the sugar may be iso- 

 lated from the resulting phenylhydrazone by decomposing it 

 with concentrated hydrochloric acid in the cold. 



Mannose when dry is a hard crumbling substance, which, 

 however, deliquesces and is readily soluble in water ; it is only 

 slightly soluble in hot alcohol and is insoluble in ether. It is 

 dextro-rotatory, [a] D 20 = + 14*36 in 10 per cent solution, and 

 is readily fermentable by yeast 



Detection. 



1. Mannose is most readily detected and estimated by 

 means of its phenylhydrazone, which is almost insoluble in 

 water, and forms almost at once on adding phenylhydrazine 

 acetate to an aqueous solution of the sugar ; the phenylhydra- 

 zone is soluble in a very large volume of boiling water, and 

 separates in fine prisms from the solution on cooling. These 

 crystals melt at 195-200. 



An excess of phenylhydrazine converts mannose into 

 glucosazone, which is identical with the substance obtained 

 under similar conditions from both glucose and levulose. 



2. Mannose reduces Fehling's solution, I c.c. = 4*307 mg. 

 mannose. 



* Fischer and Hirschberger : " Ber. deut. chem. Gesells.," 1889, 22, 3218. 



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