84 HOW CROPS GROW. 



digesting it with cold dilute chlorhydric acid, precipitat- 

 ing and washing with alcohol. Thus obtained, it had all 

 the characters ascribed to pectin. Its centesimal com- 

 position, however, corresponded nearly with that assigned 

 by Fremy to pectic acid, and differs somewhat from that 

 given by this chemist for pectin, as is seen from the sub- 

 joined figures : 



Pbctin. Pectic add. Grouverfs pectin. 



C 32 H 48 O 32 C 16 H 22 O 15 



Carbon 40.67 42.29 42.95 



Hydrogen 5.08 4.84 5.44 



Oxygen 54.25 52.87 51.61 



100.00 100.00 100.00 



From the best analyses and from analogy with cellulose 

 it is probable that pectose has the same composition as 

 pectin, or differs from it only by a few molecules of water. 

 If we subtract the water, which in the formula? (p. 83) is 

 separated by + from the remaining symbol, we see that 

 the proportions of Carbon, Hydrogen, and Oxygen are the 

 same in all these bodies, and correspond to the formula 

 C 8 H 10 O 7 . This nearness of composition assists in com- 

 prehending the ease with which the transformations of 

 pectose into the other members of the group are effected. 



Relations of the Cellulose and Pectose Groups. It was 

 formerly thought that the . pectin bodies are convertible 

 into sugar by the prolonged action of acids. Fremy has 

 shown that this is not the case. 



Sacc, (Ann. Ch. et Phys., 25,' 218,) and Porter, (Ami. 

 Ch. et Pharm., 71, 115,) have investigated a body having 

 the properties and nearly the composition of pectic acid, 

 which is produced by the action of nitric acid on wood. 



Divers, (Jour. Chem. Soc., 1863, p. 91,) has observed 

 a substance having the essential characters of pectic acid 

 among the products of the spontaneous decomposition of 

 nitrocellulose, (gun cotton.) 



It is probable, though not yet fairly demonstrated, 



