2i6 THE CARBOHYDRATES 



I "" ~l 



-CH . (CHOH 



O 



-CH O CH . (CHOH) 2 . CH . CH . CH . CH^OH 



(CHOH) 2 O 



CH O CH . (CHOH) 2 . CH . CH . CH^OH 



I 



-O- 



I CH 



CHjOH 

 On the other hand, Karrer * favours a disaccharide basis, 

 such as — 



i — ^ 1 



CH,OH . CH . CH . (CHOH), . CH 

 I A 



O o 



CH— (CH0H)2 . CH . CH . CHj.OH 



I o-J 



but much work remains to be done before a final decision is 

 possible. 



MICROCHEMICAL REACTIONS. 



1. With a dilute solution of iodine a yellow coloration 

 results. 



2. After staining well with iodine, the addition of strong 

 sulphuric acid causes the cellulose walls to swell considerably 

 and to turn blue. 



3. Chlorzinc iodide causes swelling, accompanied by the 

 assumption of a blue colour. 



4. Calcium chloride iodine solution turns pure cellulose 

 dull pink to violet without swelling. 



Zimmermann gives the following directions for making 

 this reagent. A concentrated solution of calcium chloride is 

 made, and for each 10 c.c. of this solution there is added 

 •5 gram of potassium iodide and -i gram of iodine. The 

 mixture is then gently heated and filtered through glass-wool. 



5. Pure cellulose is easily soluble in cuprammonia. 



LIGNIFIED MEMBRANES. 



Wood, for the most part, is the material used in the study 

 of lignified tissues, and is best employed as a source of hgnin 

 and associated substances. It is well, therefore, to recall to 

 * Karrer and Smirnoff : " Helv. Chim. Acta," 1922, 5, 187. 



