STARCH 401 



Description. From whatever source starch is obtained it forms 

 either a fine white powder, or angular or columnar masses easily 

 reducible to powder. It is inodorous and quite insoluble in water, 

 to which it should impart not more than a faintly acid (wheat and 



6> 



FIG. 219. Wheat Starch. Magnified 300 diam. (Tschirch.) 



potato starches) or faintly alkaline (maize and rice starches) reaction. 

 It leaves, when incinerated, only traces of ash. Boiled with water and 

 cooled it gives a cloudy, more or less gelatinous mixture, which is 

 coloured deep blue by solution of iodine. Air-dry starch usually 

 retains from 12 to 16 per cent, of moisture. 



FIG. 220. Maize Starch. Magnified 300 

 diam. (Tschirch.) 



Although the different varieties of starch show certain differences 

 in the temperature at which they gelatinise, the chief means of dis- 

 tinguishing them and ascertaining their freedom from admixture lies 

 in the examination with the microscope. 



Wheat starch consists of large and small grains mixed together, 

 with few intermediate in size ; the former are lenticular in shape and 

 sometimes marked with faint concentric rings. The hilum is central 

 but not conspicuous. The larger of the large grains average about 30 to 



26 



