MALTOSE. PENTOSES. 21 



being liquid, can be pressed out of the fruit-sugar compound, 

 which can then be decomposed, the fruit-sugar being set free, by 

 the addition of oxalic acid as long as a precipitate is produced. 

 Filter and obtain the fructose by the evaporation of the filtrate. 



MALTOSE (MALT-SUGAE: C^H^O^, H 2 0). 



41. Boil a small lump of starch with 25 cubic centi- 

 meters of water, cool it to nearly body temperature, and 

 add an aqueous extract of ground malt, made at the same 

 temperature. Observe that the mixture becomes thinner 

 and that finally a sample is not turned blue by iodin. Then 

 test for the maltose with phenyl-hydrazin as in the glucose 

 reactions. Try also Trommels test or Fehling's test. It 

 responds to all. 



42. PREPARATION OF PURE MALTOSE. One hundred grammes 

 of starch are to be mixed with 500 cubic centimeters of cold water 

 as thoroughly as possible, then heated on a water-bath until it 

 makes a paste. Make a watery extract of malt at 40 C. from 6 

 or 7 grammes of dry malt. When the starch-paste has cooled 

 down to 60 or 70, add the malt-extract and keep it at this tem- 

 perature for an hour. When the starch has been converted to 

 maltose the liquid becomes thin and watery. Then boil, filter, 

 and evaporate to a syrup upon the water-bath. Dissolve the 

 maltose from the residue with small portions of 90-per-cent. 

 alcohol. Distill the alcohol off from this solution, and evaporate 

 to. a syrup. Let this stand until it crystallizes. This may be 

 hastened by the addition of a little crystallized maltose, which 

 can be prepared by evaporating a few drops of the solution in a 

 thin layer on a piece of glass. It may be purified by recrystal- 

 lizing from methyl alcohol. 



PENTOSES. 



43. Normally but small amounts of the pentoses are found in 

 the urine and these doubtless originate mostly in certain vegetable 

 foods. In pathological conditions they may be more abundant. 



