40 SEEDS AND SEEDLINGS. 



68. Wheaten Flour, made from the grains (seeds) of 

 Wheat, makes very convenient material to examine and test 

 for starch and proteids. 



* (a) Take a tablespoonful of wheaten flour and enclose it in a piece of 

 muslin. Hold it under a tap of gently running water and work the 

 flour about by constant squeezing. Catch the whitened water as it 

 flows away from the flour. In a little time the water passes off clear. 

 Keep working it for a little longer time, then open the muslin and 

 discover a mass of sticky material : this is gluten. Let the muddy 

 water settle, then pour off the liquid and keep the sediment. The 

 sediment is starch ; it forms a large proportion of the flour. 



* (6) Put a small bit of gluten on the end of a mounted needle, and 

 hold it over the flame of a spirit-lamp ; it burns, then turns black. 

 Rub the charred mass on white paper ; it leaves a mark of charcoal 

 (carbon). 



* (c) Mix a little of the gluten with soda-lime, place the mixture in a 

 test-tube, and heat by means of a spirit-lamp. As the gluten decom- 

 poses, ammoniacal fumes are given off, thus proving the presence of 

 nitrogen in the gluten. 



(d) Put a little of the gluten into a test-tube containing a weak 

 solution of caustic potash. Shake well : the gluten dissolves. 



(e) Put another bit of gluten into a small quantity of strong nitric 

 acid in a test-tube or watch-glass. Heat. Note the yellow coloration, 

 which deepens to orange if ammonia solution be gradually added. Add 

 the ammonia solution very cautiously with a glass tube, as the action 

 between the acid and the ammonia is a violent one. 



(/) Place a little of the sticky gluten in a test-tube and warm it. 

 Notice that the heat causes it to solidify. 



* (g) Take a little of the milky liquid from the basin. The milkiness 

 is due to starch granules. Boil it : this makes it go clear. Cool the 

 clear liquid, and add a few drops of solution of iodine. A deep blue 

 colour proves the presence of starch. Note that the blue colour 

 disappears on heating ; does it reappear on cooling ? 



69. Oils. Many plants store up food in the form of oil. 

 Oils are compounds made up of carbon, hydrogen, and oxygen, 

 the oxygen present being insufficient to combine with all the 

 hydrogen and form water. Chemically they are compounds 

 of "fatty" acids with glycerine. Most vegetable oils are 

 obtained from seeds, e.g. mustard, sunflower, linseed, castor oil. 



Oily seeds usually contain little or no starch, and vice 

 versa. 



* Remove the coats from dry seeds of Sunflower, Cress, Mustard, Castor 

 Oil ; fold the seeds in blotting-paper and crush between two flat stones 

 and note the greasy stain produced, which dissolves in ether or alcohol. 



