SUBSTANCES AND PROPERTIES 



oblong in shape. These are pieces of a third substance, felspar 

 (Fig. 5). All the particles in the granite belong to one or other 

 of these three kinds. The chemist, then, studies the specific 

 properties, such as the hardnesses and the crystalline forms of 

 various parts of the specimen and seeks to state or describe the 

 nature of the specimen in terms of the substances he finds 

 in it. 



A Third Illustration. When flour is examined by the chem- 

 ist, it appears to the eye to be all alike. Under the microscope, 

 even, all he can learn is that it consists largely of grains, which 

 have the characteristic appearance of grains of starch (see Fig. 

 99, p. 399). He places some flour on a square piece of cheese- 

 cloth and encloses it by tying with a thread (Fig. 6). On knead- 

 ing the little bag in a vessel of water, the water becomes milky. 

 When the milky water stands, 

 the white material settles to the 

 bottom, the water can be poured 

 off, and the deposit can be dried. 

 This white substance, when boiled 

 with water, gives an almost clear 

 liquid which jellies on cooling. 

 This is another property of starch. 

 A little tincture of iodine (solu- 

 tion of iodine in alcohol), dropped on a part of the starch, 

 causes the latter to turn blue. This is a very characteristic 

 property of (and therefore test for) starch. When the bag of 

 flour is kneaded persistently in water which is frequently changed, 

 the material finally ceases to render the water milky. The starch 

 has all been washed out. When the bag is now opened, a sticky 

 material is found in it. This is called gluten. 



The chemist therefore finds that flour contains starch and 

 gluten. He learns this by separating these two different sub- 

 stances. 



FIG. 5. 



FIG. 6. 



