6 BULLETIN 1025, U. S. DEPARTMENT OF AGRICULTURE. 
method useless for fruit juices. The same objections apply to the 
use of such materials as fish glue, egg albumen, milk, casein, and 
blood; the precipitation obtained with these substances is due to re- 
ae with tannin or the pods present, or both, with consequent 
alteration of flavor. 
As the work of La Marca (/6) upon the effects of clarifying agents 
on the chemical composition of wines has shown, perceptible altera- 
tion in flavor as well as in chemical composition of the wine results 
from the employment: of such materials, which led La Marca to 
advise strongly against their use by wine makers. 
A rather careful study carried on in the laboratory of the Bureau 
of Plant Industry has yielded results showing conclusively that the 
use of any of the nitrogenous materials previously mentioned as a 
clarifying agent for unfermented fruit juices is highly inadvisable. — 
The viscosity of most juices is sufficiently high to make the subsi-. 
dence of the precipitate extremely slow and incomplete. All the sub- 
stances used are complex protein mixtures containing constituents 
which are to some degree soluble in the juice, and the introduction of 
such sources of nitrogen makes the liquid a better medium for the 
erowth of molds. The alteration of flavor produced by the loss of 
tannin and the introduction of foreign material is perceptible in all 
juices and amounts to denaturation in the case of the more delicately 
flavored ones. For these reasons the use of such methods with un- 
fermented juices is ineffective and injurious. 
CLARIFICATION BY THE USE OF INERT ADSORBING AGENTS. 
The third group of methods for clarifying colloidal solutions or 
suspensions is that employing chemically inert solids as adsorbing 
agents. Methods of clarifying wine and vinegar and some other 
liquids by means of such materials as fuller’s earth and Spanish clay 
have been developed empirically and have been in use for long 
periods, while the use of carbons in decolorizing cane juice has been 
discussed in the literature, according to Zerban (34), since 1785; but 
it is only very recently that much attention has been devoted to the 
study of solid adsorbents for clarifying fruit juices. 
CARBONS AS CLARIFYING AGENTS FOR FRUIT JUICES. 
The studies of solid adsorbents made in the laboratory of the Bu- 
reau of Plant Industry began in 1918 with a study of a considerable 
number of carbons, which included, with others, samples of a number 
of special filtering carbons stpplied by American manufacturers and 
various samples of purified animal charcoals obtained through chemi- 
cal supply houses. The work included the treatment of a large num- 
ber of apple and grape juices, immediately after pressing or after 
