ADVANTAGES OF THIS MODE. 137 
compared to albumen, assisted by a very small but definite pro- 
portion of tannic acid. Albumen,in small quantity, is always 
present in sorghum juice, and by its coagulability at a tem- 
perature below the builing point it assists considerably in 
its clarification, and is suggestive of the effeets which it is 
capable of producing when added in sufficient quantity. 
But the quamtity naturally incorporated with the other 
impurities above mentioned is too smail to effect the re- 
moval of but a part of them, and this effect even is produced 
only when the juice has been previously neutralized, for it 
is not coagulable in juice containing an excess of acid. 
If we compare the results of defecation by means of 
alumina, albumen, and tannin separately, we find that each 
has a peculiar attraction for certain substances, and that 
neither used singly nor in any way combined in pairs, are 
they capable of accomplishing the work of the three com- 
bined in the proper proportions. They unite together, 
and with the substances that they are designed to remove 
from the juice, in the insoluble form, and all are carried 
away. Separately they would act in a different way. The 
alumina being an earthy substance, when used alone, carries 
down the coloring matters with which it unites and de- 
posits them as a sediment in a liquid at rest. The tannic 
and albuminous compounds, on the contrary, rise to the 
surface of the heated juice. YetI find that when suitably 
combined, all three and the associated impurities rise to 
the surface—the superior buoyancy of the albumen, especi- 
ally, overcoming the tendency of the alumina to sink and 
bringing ft up along with it. Each minute particle of the 
alumina is a center of attraction for the coloring matter 
in the fluid around it, which it seizes upon and forcibly 
retains. When the juice is admitted into the evaporating 
pan, the tannin and albumen are dissolved, and the alumina 
is suspended in the liquid. The juice becomes almost im- 
12* 
