PLANT LIFE. CELLULOSE, STARCH AND SUGAR 399 



a small orifice into alcohol, the cellulose is reprecipitated in the 

 form of a thread. By carbonizing, this is made into filaments 

 for incandescent electric lamps. 



Cellulose is solubl?. also in a solution of cupric hydroxide in 

 excess of ammonium hydroxide, and is reprecipitated by dilute 

 sulphuric acid. Paper or cotton goods can be passed through 

 first one and then the other of these liquids, and so receive a tough, 

 waterproof surface. Artificial silk is made by pressing the solu- 

 tion through dies into the precipitant. It can be dyed to any 

 desired tint, and is at least as brilliant in appearance as the natural 

 article. Its strength, however, does not equal that of the natural 

 silk fibre, especially when wet. 



Cotton, when dipped in concentrated sodium hydroxide solu- 

 tion, and then stretched while drying to prevent the shrinkage 

 which otherwise occurs, acquires a brilliant luster and is used in 

 enormous quantities under the name of mercerized cotton. 



Finally, mercerized cotton, or wood pulp treated with caustic 

 soda, combines with carbon disulphide to give viscose. Viscose 

 dissolves in water, and decomposes in solution giving a plastic 

 form of cellulose. This can be rolled into transparent sheets, 

 made into caps for bottles, moulded into any form, or pressed 

 through dies into solutions of salts of ammonium to give an- 

 other form of artificial silk. 



Starch (CeHioOs)*. Starch is found in plants in little colorless 

 granules of various rounded shapes (Fig. 99) which may readily 

 be seen under the microscope. These 

 granules are massed in large numbers in 

 the ears of wheat and oats, in the tubers 

 of potatoes, in the grains of maize 

 (corn) and in peas and beans. Even 

 in the leaves they can be seen, im- 

 mediately after the plant has been ex- 

 posed to sunlight. They gradually disappear from the leaves 



