192 THE CONSTITUENTS OF PLANTS. IX. 



weight of carbon disulphide, CS 2 , a substance is produced after 

 three or four hours which will dissolve in water on standing. 



This cellulose thiocarbonate, CSg a 6l 5n ' spontaneously de- 



composes, especially in contact with a large amount of water, 

 giving a jelly or coagulum. Heating also effects the coagula- 

 tion. This product lends itself to many useful applications 

 and is employed commercially under the name of " Viscose." 



By the action of nitric acid, or better, a mixture of nitric and 

 sulphuric acids, cellulose is converted into various nitro-deriva- 

 tives or nitrates, some of which are of great value in the arts. 



Gun-cotton is chiefly cellulose hexa-nitrate C 12 H 14 (NO 3 ) G 4 , 

 and is valued for its explosive properties. Pyroxylin or collo- 

 dion is mainly tetra-nitrate, C 12 Hi ( ;(NO 8 ) 4 (i , and penta-nitrate, 

 C 12 H 15 (N0 8 ) 5 O S . These substances are soluble in ether and 

 alcohol and are then known as collodion. This is employed in 

 surgery and photography, also in the manufacture of celluloid, 

 which is a mixture of nitrocellulose and camphor. 



Parchment paper is obtained by immersing ordinary unsized 

 paper in sulphuric acid and then washing it with water. It 

 closely resembles true parchment in strength and apparently 

 has the outer part of its cellulose altered into a substance 

 known as amylouL A similar change is produced by zinc 

 chloride solution, and since amyloid is, like starch, coloured 

 blue by iodine, a solution of iodine in concentrated zinc 

 chloride forms a useful reagent for the identification of cellu- 

 lose. 



By the action of sulphuric acid cellulose is eventually con- 

 verted into dextrin and dextrose. 



B. THE SUGARS. 



(a) The Glucoses, Hexo-monoses, or Hexoscs, C 6 H 12 O 6 . 



The hexoses occur widely distributed in the vegetable king- 

 dom, being found in the free state (as in ripe fruits) or in 

 combination with organic acids as glucosides. 



They are produced by the hydrolysis (i.e., the addition of the 

 elements of water), of the di-saccharoses, polysaccharides, or 

 of the glucosides. The hydrolysis is usually effected by 



