THE SKELETON OF THE PLANT 47 
from cellulose convert it into pectine, or into pectic acid, 
the former being soluble in water, the latter in alkalies. 
The cell-wall can be shown to contain the two constituents 
by the action of Schweizer’s reagent, which, when used 
with proper precautions, dissolves out the cellulose and 
leaves the framework of the cell apparently unaltered ; 
it consists then, however, not of pure pectose, but of a 
compound of pectic acid with some of the copper of the 
reagent. 
Pectine swells up and dissolves in water, forming a 
viscous liquid which soon becomes a jelly. It exists in 
considerable quantity in many ripe fruits and in some 
mucilages. It gives no precipitate with the neutral acetate 
of lead, but is thrown down by the basic acetate in the form 
of white flocculi. If it is boiled for some hours in water, it 
is converted into parapectine, which is precipitated by 
neutral lead acetate. Further boiling with dilute acids 
converts it into metapectine, which can be precipitated by 
barium chloride. 
The acid series shows peculiarities similar to those of the 
neutral one. Its most insoluble member is pectic acid, which 
will not dissolve in water, alcohol, or acids ; it forms soluble 
pectates with alkalies, and insoluble ones with the metals 
of the alkaline earths, of which calcic pectate ig the most 
widely distributed. It dissolves in solutions of alkaline 
salts, such as the carbonates of sodium and potassium, 
alkaline phosphates and most organic ammoniacal salts, 
forming with them double salts which gelatinise more or 
less freely with water. Its solution in alkaline carbonates 
is mucilaginous, but when ammonic oxalate is the solvent 
it is perfectly limpid. 
The member at the other end of the series is metapectic 
acid, a body with an acid reaction, freely soluble in water 
and forming soluble salts with all bases, especially those of 
calcium and barium, which precipitate pectic acid. Meta- 
pectates are coloured yellow when they are warmed with an 
excess of alkali. This body and its compounds are probably 
