136 CHEMICAL AGENTS IN DEFECATION. 
cane of the tropics. But its employment on the plauta- 
tions was attended with difficulty, inasmuch as it was 
deemed necessary to heat the juice to the boiling point in 
a deep tank, and then to allow it a long period of rest be- 
fore the precipitation of the alumina and the impurities 
with which it was combined could fully take place. The 
loss of time in the heating of the juice, and in the slow 
precipitation, together with the difficulty of separating 
from the bulky sediment the portion of juice in immediate 
contact with it by any means that could conveniently be 
applied, were obstacles which were generally thought to 
outweigh the advantages derived from its use. 
While alumina is one of the most energetic decolor- 
izers known, not excepting even animal charcoal, it does 
not remove from cane juice by ordinary precipitation some 
impurities of another kind. These are feculancies very 
abundant in sorghum juice for which the alumina possesses 
little or no attraction—and which do not naturally separate 
by heat—glutinous and gummy matter are also present in 
considerable quantities. And if these are permitted to 
remain until the syrup becomes more dense by evaporation, 
they cannot afterward be entirely separated, and they im- 
pair the quality of the syrup not only by reason of the 
viscidity which they impart to it, and by the destruction 
of a portion of the sugar through the chemical changes 
which they produce when assisted by heat, but also by the 
precipitation upon the bottom of the pans of a peculiar 
gummy sediment which, adhering to them, forms, with earthy 
matters, the hard scale so common where the defecation 
has been imperfect. This differs from ordinary lime scale 
not only in its composition, but also in its liability to burn 
at once upon the bottom of the pan. 
For the removal of this class of impurities, at this stage 
of tne evaportion, no means that I have employed can be 
