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: 
Pectin. Peetic acid.  Growven’s pectin. 
C; 32 Hus Ose Cys Hoe Ors 
Carbon ....... «.- 40.67 42,29 42.95 
Hydrogen......... 5.08 4,84 5,44 
OXY Bes ivicesswee's 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 formule (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,H,, O,. 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 Celhidose 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. 
Sace, (Ann. Ch. et Phys., 25, 218,) and Porter, (Ann. 
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, 
