48 PRACTICAL AGRICULTURAL CHEMISTRY [130-132 



Cereal and Leguminous Foods 



130. The most important cereal and leguminous foods 

 are wheat, barley, oats, maize, peas, and beans. These focds 

 should be tested for their main constituents, viz. water, oil, 

 albuminoids, and carbohydrates, by the methods described 

 in paragraphs 108, 109, no, and m; noting at the same 

 time the relatively large quantities of albuminoids in peas, 

 and beans, and of carbohydrates in wheat, barley, oats, 

 and maize. Wheat differs from other foods in containing 

 a nitrogenous substance, called gluten, which gives wheaten 

 flour the peculiar property of kneading with water. All the 

 cereals contain large quantities of starch. 



131. Starch in Flour. — The test for starch has already 

 been given (116). Wet a little flour with water so as to make 

 a thin cream. Boil a little water in a test-tube, and when 

 it is boiling briskly add a drop of the cream, then boil for a 

 few seconds. Cool the liquid by allowing a current of cold 

 water to flow from a tap round the outside of the test-tube, 

 and when quite cold add a drop of iodine solution. An 

 immediate deep-blue coloration indicates the presence of 

 starch. The colour will appear almost black, but if a drop 

 of the dark liquid be mixed with a large quantity of water 

 it will be seen that it really is of a dark-blue colour. 



132. Gluten in Wheaten Flour.— Mix a handful 

 of wheaten flour with enough water to form a stiff paste. 

 Knead it well in the fingers, then wrap it up in a small 

 piece of muslin and hold it in a gentle stream of water from 

 a tap, kneading it all the time. The starch will be gradually 

 washed away through the muslin, leaving a dark-coloured 

 indiarubber-like mass. This is gluten, which gives a mixture 

 of flour and water its peculiar adhesiveness. 



