8 BULLETIN 1025, U. S. DEPARTMENT OF AGRICULTURE. 
distinctive flavor.” The results obtained by the Bureau of Plant Industry with 
a large number of apple and grape juices indicate that carbon has too much 
effect upon flavor to permit its use with apple juices or with any but the more 
strongly flavored grape juices. 
(4) The various carbons differ materially in the degree of transparency 
which it is possible to produce in a given juice by their use. In part, these 
differences are due to differences in adsorbing surface presented by equal 
weights of material ground to unequal degrees of fineness, but in part they are 
specific differences due to differences in porosity, in ash content, or to other 
factors not controllable by separation of the samples into particles of like 
size by screening. The results indicate that the character and amount of ash 
in a given carbon may have considerable significance in determining the 
efficiency of the carbon in the removal of colloidal material of the nature here 
dealt with, namely, pectins and gums. A certain sample of animal charcoal, 
when prepared for use in the usual manner by poeta with hydrochloric acid 
and washing free of acid with water (20, p. 22; 31, p. 88), gave a clearer, 
more brilliant product than any other carbon. When this charcoal was sub-.-- 
jected to exhaustive treatment in order to remove salts as completely as pos- 
sible, its clarifying efficiency was reduced practically to the level of other 
carbons. This, of course, suggested that it may be possible to improve the 
efficiency of carbons for the particular purpose here aimed .at by preliminary 
chemical treatment, but the fact that carbons are not well adapted to the 
purpose in other respects made it appear inadvisable to follow up the suggestion, 
especially since Zerban and his associates (34, 36, 37) already have under 
investigation the broader problem of the particular property or constituent of 
carbons which gives them clarifying power. 
(5) The removal of pectins and gums by carbon is very incomplete in the 
case of apple and grape juices, as Zerban (34) has shown to be the case in 
cane juices. Consequently, the pasteurization of juices clarified with carbon 
is followed by the formation of a considerable precipitate unless such juices 
have been subjected to preliminary pasteurization followed by the removal 
of the heat-coagulable material prior to treatment with carbon. This double 
pasteurization is to be avoided if possible, as it materially increases the labor 
and cost of handling, while at the same time increasing the loss of flavor. 
(6) Considerable difficulty is encountered in dealing with viscous juices 
after the addition of carbon, even when subjected to preliminary pasteuriza- 
tion, as a result of the fact that a portion of the added carbon forms a per- 
sistent suspension in the liquid. This can not be removed by any of the usual 
methods of filtration, and when juices so treated are pasteurized and stored 
there is a slow deposition of carbon upon the sides and bottom of the con- 
tainers. Gore (14) encountered this difficulty and found ‘it necessary to add 
diatomaceous (“ infusorial”’) earth and to filter in order to remove the carbon. 
His process as applied to the more difficult juices consequently involved a pre- 
liminary treatment with infusorial earth and filtration, treatment with earbon, 
a second treatment with earth, and a second filtration. As some time must be 
allowed to permit sedimentation after each step in the treatment, the process 
is laborious and requires rather careful temperature control to prevent fer- 
mentation. The repeated handling necessarily involves a greater danger of 
infection with mold spores and increases the difficulty of securing perfect pas- 
teurization. 
In view of the many serious saat encountered in the use of 
carbon and the decided denaturing effects upon color and flavor of 
all but the most strongly flavored and deeply colored juices, it 
