METHODS OF ESTIMATING CARBOHYDRATES 51 



entirely by the following modification of Young's well- 

 known method for the preparation of alcohols and other 

 liquids in the anhydrous state. Young distils the alcohol, 

 containing a little water, with benzene, through his 

 evaporator stillhead with eight or more sections. *At 

 first a turbid ternary mixture of constant boiling-point 

 comes over at 64-85. This contains almost all the 

 water, a large percentage of benzene, and some alcohol. 

 Then the temperature rises to about 68, and the 

 last traces of water are removed as a little of the 

 ternary mixture passes over, together with a small 

 quantity of a binary mixture of alcohol and benzene. At 

 68-25 the distillate is the pure binary mixture of constant 

 boiling-point. Finally the temperature rises to 78-3, the 

 boiling-point of the pure alcohol; or if benzene has been 

 added in excess it rises to 80-2, the boiling-point of pure 

 benzene. To obtain anhydrous fructose, for example, it is 

 only necessary to add some of the powdered solid to the 

 distillation flask. This is dissolved by hot alcohol (99 per 

 cent.), and is then distilled from a water-bath with benzene. 

 If the quantities have been suitably chosen, by reference to 

 Young's " Fractional Distillation," at the end of the dis- 

 tillation anhydrous fructose remains partly as a solid and 

 partly in solution in hot alcohol. The alcohol can be 

 readily removed in a vacuum desiccator. In some cases 

 it is preferable to have benzene in excess, so that at the 

 end the solid is dissolved or suspended in the liquid. With 

 a substance which remains suspended in alcohol, such as 

 starch or cellulose, the method is equally applicable. Its 

 use over a more extended range of substances is being 

 examined. It is of course desirable to test the anhydrous 

 nature of the products by carrying out moisture deter- 

 minations in the usual manner by drying over phosphorus 

 pentoxide in vacuo. 



