PART II. 



VEGETABLE SUBSTANCES 



METHODS OF RECOGNIZING THEM. 



[The reader is requested to consult the principal literature in the first 

 section, under the different reagents.] 



CELLULOSE. 



Pure cellulose is colored violet by chlor-iodide of 

 zinc, blue by iodine and sulphuric acid, and brown, 

 or yellowish brown, or even yellow, by an aqueous 

 or alcoholic solution of iodine. On the addition 

 of water to membranes which have been dried 

 after treatment with iodine, they often become 

 clear blue. Young cellulose frequently colors blue 

 with iodine and sulphuric acid, only after treatment 

 with hydrochloric acid, or after being compressed 

 strongly under the cover-glass. 1 



The cellulose of the seeds of Paeonia colors 

 blue in iodine dissolved in iodide of potassium. 



l Richter: Sitzb. wien. Akad., 1881, Bd. LXXXIII. 



75 



