III.] 



THE CARBOHYDRATES. 



23 



(/.) Preparation of Maltose. — Take i part of potato-starch and make it 

 into a paste with 10 of water. Digest the paste with a filtered extract of 

 low-dried malt (200 grams to i litre of water) for an hour at 57-60' C, filter, 

 evaporate, precipitate the dextrin with alcohol, concentrate the filtrate to a 

 syrup, and allow the maltose to crystallise. 



11. Estimation of Maltose.— (i.) Determine its reducing power 

 on 10 cc. of Feliling's solution (see "Urine"). 



(ii.) Convert it into dextrose by boiling (J an hour) 50 cc. of tlie 

 solution with i cc. of H^SO^. Cool and bring the solution to the 

 original volume (50 cc.) by adding water. Again determine its 

 reducing power by Fehhng's solution. If a: = cc. of maltose 

 solution necessary to reduce 10 cc. of Feliling's solution, then as 



Flo. 7.— Crystals of Maltose. 



Fig. 8.— Crystals of Phenyl- Maltosazone, x 120. 



the respective reducing powers of glucose and maltose are as 2 : 3 



2X 



— = cc. of dextrose solution necessary for the same purpose. As 



10 cc. of Fehling correspond to o 05 grms. dextrose, the strength 

 of the maltose solution can easily be calculated. 



12. VII. Lactose (Milk-Sugar), Ci.,H220ii + H20 (see "xAlilk"). 



(a.) Note its whiteness and hardness. It is not so sweet as 

 cane-sugar. Microscopically it occurs in rhombic prisms (fig 9). 



(/>.) It is less soluble in water than cane- or grape-sugar, and 

 insoluble in alcohol. 



{('.) Heat its solution carefully with sulphuric acid = chars 

 slowly. 



{d}j Add excess of caustic soda, and a few drops of copper 

 sulphate solution, and heat = yellow or red precipitate (like 

 dextrose). 



(e.) Test with Fehling's solution = reduction like dextrose, but its 

 reducing power is not so great as dextrose. It requires 10 parts of 

 lactose to reduce the amount of Fehling's solution that will be re- 

 duced by 7 of dextrose. 



