C A RBOH YDRA TES 67 



soluble in water to a gelatinous consistency, and dextro- 

 rotatory. They can also be made from starch by roasting 

 it in ovens with about 0.2 per cent, nitric acid to 1 10°- 170° 

 C, and dissolving out the so-called Dextrin or British Gum, 

 which is used in the textile industries for thickening colors, 

 as mucilage on stamps, envelopes, etc. 



On boiling starch with mineral acids such as hydrochloric 

 or sulphuric, the same hydrolytic changes take place except 

 that maltose is still further changed into dextrose. 



Commercial starch is prepared from corn by grinding 

 and separating the starch from the other material by gravity 

 in water; from potatoes by scraping or pulping, filtering 

 off the fiber, and washing to separate the starch. It is used 

 for a great variety of purposes, such as for food in pud- 

 dings, for laundry work, for sizing in paper and textiles, 

 for cosmetics, etc. 



58. Cellulose— (C 6 Hio0 8 )i (n greater than 200). The 

 graphic formula is not well understood, but the following 

 has been assigned to it as the unit group which occurs a 

 large number of times: 



H O— H H O— H H O— H H O— H 



\ / \ / \ / • \ / 



C C H H— O C- -C H 



/ \ / \/ \ / 



o=c c c c 



\ / \ / \ 



C C C C H 



/ \ / \ / \ / \ 



H O— H H O— H H O— H H O— H 



Cellulose comprises about one-half of the dry matter of 

 plants. 1 It forms their framework, being the chief con- 

 stituent of cell-walls and supporting fibers. Usually it 

 occurs in combination, either weakly chemical or physical, 



1 Different plant materials contain the following approximate amount 

 of cellulose: 



Per cent. 



Wood 60 



Straw 40 



Seeds (including husks) 15 



Roots 10 



