io6 THE CARBOHYDRATES 



MANNOSE. 



Occurrence. 



There is no record of the free occurrence of mannose in 

 plants ; in its polymerized or polysaccharide form, however, 

 it is widely distributed as a constituent of the so-called 

 hemicelluloses contained in the cell walls of the seeds of peas, 

 coffee, date, etc. It is also a constituent of salep mucilage 

 [Orchis Morio). 



Preparation. 



Mannose may be prepared by the hydrolysis of the hemi- 

 cellulose contained in the endosperm of ivory nuts, Phytelcphas 

 macrocarpa, which are extensively used in the manufacture 

 of vegetable ivory buttons. The turnings are added to ten 

 times their weight of boiling i per cent caustic soda and allowed 

 to stand for half an hour with occasional stirring. The 

 liquor is then decanted off and the residue washed with water 

 and dried ; 500 grams of this material are mixed with an 

 equal weight of 75 per cent sulphuric acid and allowed to 

 stand for twenty-four hours. The resulting substance is dis- 

 solved in water, diluted to 5-5 litres, and then boiled for 

 two and a half hours. The solution is neutralized with barium 

 carbonate paste and filtered through a thin layer of animal 

 charcoal. The last traces of barium are removed by the 

 careful addition of dilute sulphuric acid and filtering. The 

 filtrate is concentrated over a boiling water bath until it 

 contains 87-88 per cent of total solids ; it is then mixed with 

 an equal volume of glacial acetic acid, seeded with a few 

 crystals of mannose and then frozen. On allowing the mass 

 to thaw slowly in a refrigerator, the mannose will crystallize 

 out.* 



Properties. 



Mannose has a sweet taste ; when dry, it is a hard crumbling 

 substance, which, however, deliquesces and is readily soluble 

 in water ; it is only slightly soluble in hot alcohol and is 



* Clark : "J. Biol. Chem.," 1922, 52, i. Patterson: "J. Chem. 

 Soc," 1923, 123, 1139. 



