6 BULLETIN 1010, U. S. DEPARTMENT OE AGRICULTURE. 
centage of earth used. Seven per cent of earth appears to be the 
most beneficial, but from a practical standpoint 5 or 6 per cent is 
sufficient, since no reduction in red is obtained with higher propor- 
tions. There is a limit, of course, to the proportion of earth which 
may be used in practice. The expense involved would not justify 
the use of more than 6 per cent. The expense lies not only in the cost 
40 
?35 
\» 
X 
r 
</0 
N 5 
Temperature 
T/ME 
/oo° c. 
\ 
%OEEAf?TH YELLOW 
/TED 
O 
z 
4 
7 
/O 
36.0 
304 
Z30 
/30 
/oe 
40 
2/ 
AS 
/ / 
/.o 
^^ 
/?E0 
Peacea/t of Fullers Fa^th 
/o 
Fig. 1.— Relation between the pioportion of fuller's earth used and the extent of the bleaching effected. 
of the earth, but in the additional loss of oil which is entailed by the use 
of the greater quantities and the somewhat greater expense of 
filtering. Fuller's earth generally shows less bleaching efficiency when 
used in laboratory quantities than when used in large-scale opera- 
tions. Hence, the use of a maximum of 5 or 6 per cent of earth, as 
generally practiced in refineries, would seem to be in accordance with 
the results of these tests. 
