122 



LECTURES ON 



Fig. 5. 



lulose or gun cotton. By the continued action of oxydizing agents 

 it ]is converted into that series of brown bodies known under the 



name of Humus, or finally into 

 oxalic and carbonic acid. 



Next to cellulose, starch (fig. 5) 

 is the most abundant vegetable 

 body. It usually occurs as micro- 

 scopic grains, which for many spe- 

 cies of plants possess a character- 

 istic form and size, being some- 

 times angular as in maize,but most 

 often oval or spherical as in the 

 other grains, the potato, &c. 



Starch is insoluble in and un- 

 affected by cold water; in hot 

 water it swells up and forms a 

 translucent jelly, and in this 

 state is employed for stiffening 

 linen. 

 Starch is always enclosed in the cells of the plant as seen in the ac- 

 companying figure G, and is exceedingly 

 abundant, existing not only in the grains 

 and esculent roots, but also in the trunks 

 of trees, especially the sago-palm, and 

 throughout nearly the whole tissue of the 

 higher orders of plants. 



Inulin closely resembles starch in 

 many points, appearing to replace that 

 body in the roots of the artichoke, elecam- 

 pane, dahlia, dandelion, and other com- 

 posite plants. It occurs in the form of small 

 round transparent grains, which dissolve 

 easily in boiling water, and mostly sepa- 

 rate again as the water cools. Unlike 

 starch, inulin exists in a liquid form in 

 the roots above named, and separates in grains from the clear 

 pressed juice when this is kept some time. The juice of the dahlia 

 tuber becomes a semi-solid white mass in this way, after reposing 12 

 hours from the separation of 8 per cent, of this interesting substance, 

 ( ' Bouchardat. ) 



Dextrin is a colorless transparent body, soluble in water, and 

 it appears universally distributed in the juices of plants, though 

 existing in but small amount compared with the previously de- 

 scribed proximate principles. The solution of an impure and arti- 

 ficially prepared dextrin, called British gum, is largely employed in 

 calico printing, as a substitute for the more expensive natural gums, 

 and closely resembles them in its adhesive properties. It is an un- 



interesting observation, that a solution of oxyd of copper in ammonia dissolves cellulose 

 to a clear liquid, from which the cellulose may again be thrown down by an acid. 



