THE VOLATILE PART OF PLANTS. R38 
which remains in insoluble combination with oxide of 
copper. 
Metapectic acid.—By too iong boiling, by prolonged contact 
with acids or alkalies, and by decay, the pectic and pectosic acids, as well 
as pectin, are transformed into still another substance, viz., metapectie 
acd, which, according to Fremy, is a very soluble body of quite sour 
taste. It is the last product of the transformation of the bodies of this 
group with which we are acquainted. It exists, according to Fremy, in 
beet-molasses and decayed fruits. 
Exp. 35.—Stew a handful of sound cranberries, covered with water. 
just long enough to make them soft. Observe the speedy solution of 
the firm pect>se. Strain through muslin. The juice contains soluble 
pectin, which n.ay be precipitated from a small portion by alcohol. 
Keep the remaining juice heated to near the boiling point in a water 
bath, (i. e., by immersing the vessel containing it in a larger one of boil- 
ing water.) After a time, which is variable according to the condition of 
the fruit, and must be ascertained by trial, the juice on cooling or stand- 
ing solidifies to a jelly, that dissolves on warming, and reappears again 
on cooling—Fremy’s pectosic acid. By further heating, the juice may. 
form a jelly which is permanent when hot—pectie acid—and on still 
fonger exposure to the same temperature, this jelly may dissolve again, 
by passing into Fremy’s metapectic acid, which alcohol does not precip- 
itate. 
Other ripe fruits, as quinces, strawberries, peaches, grapes, apples, etc., 
may be employed for this experiment, but in any case the time required 
for the juice to run through these changes cannot be predicted safely, 
and the student may easily fail in attempting to follow them. 
Chemical composition of the Pectose group.—Our know!l- 
edge on this point is very imperfect. Pectose itself, hav- 
ing never been obtained pure, has not been analysed. The 
other bodies of this group have been examined, but, owing 
to the difficulty of obtaining them in a state of purity, the 
results of different observers are discordant. 
The formule of Fremy are as follows: 
Pectose, unknown. 
Pectin, Ceo Hay Ons + 4 Hy oO 
Pectosie acid, Cg H» Oy + 144 H,O 
Pectic acid, Cis Hao Ox, =e H, O 
Metapectic acid, Cs Hy O, + 2H,O 
Grouven, (2éer Salzmiinder Bericht, p. 470,) has prepar- 
ed pectin on the large scale from beet-root cake, (remaining 
after the juice was expressed for sugar manufacture,) b* 
