PROPERTIES OF THE COLLOIDAL SOIL MATERIAL 
21 
loicls. Little attention, however, has been paid to comparative vol- 
umes of the coagulated materials. Doubtless such comparative vol- 
umes are without much significance in the case of widely different 
sois, but in the case of closely related materials, such as colloids 
isolated from different soils, the volumes of floe may be characteristic 
of the colloidal materials. 
It was not the purpose in these studies to investigate the factors 
influencing the coagulation of the different colloids, but merely to 
coagulate them in a comparable manner so that differences in floc- 
culated volumes would be as nearly as possible characteristic of the 
materials. The procedure was as follows: Sols containing 3 to 5 
grams of solid per liter were prepared from soil colloids that had 
not been air dried after isolation from the soil. Sufficient methylene 
blue to produce rapid flocculation was added to a quantity of the 
sol containing 0.2 gram of solid, and the volume was made to 100 
cubic centimeters. The solutions were well mixed by shaking and 
were poured into graduated tubes of identical dimensions. At the 
end of 24 hours the volumes occupied by the flocculated colloids 
were observed. Preliminary tests were made to determine the quan- 
tity of methylene blue needed to flocculate rapidly each colloid. In 
most cases the methylene blue needed was proportional to the quan- 
tity required for rendering isoelectric the more dilute sols employed 
in the work on cataphoresis (p. 29). 
The volumes occupied by seven soil colloids flocculated by the 
above procedure are given in Table 11. The relation of the volume 
of floe to the number of particles present in the unflocculated sol is 
also shown in columns 3 and 4. 
Table 11. — Volume of -floe and number of particles per gram of colloid 
Kind of colloid 
Volume 
of floe 
per gram 
of colloid 
Number 
of par- 
ticles 
per gram 
divided 
by 10" 
Number particles per gram 
volume flocXIO 12 
Fallon 
Sharkey 
Marshall 
Sassafras 
Huntington. 
Norfolk 
Susquehanna 
Cubic 
centi- 
meters 
128 
110 
58.5 
38.0 
31.5 
31.0 
31.0 
960 
613 
335 
505 
322 
5.3 
8.7 
10.5 
8.8 
16.0 
10.4 
8.5 
The different colloids vary widely in volume of floe, the Fallon 
giving a volume four times as great as the Norfolk or Susquehanna. 
Differences in volume are evidently more or less characteristic of 
the colloids, since it is apparent from column 4 that there is some 
correspondence between volume of floe and number of particles in the 
suspension as determined by the Zsigmondy count method. 
The correspondence between volume of floe and number of particles 
would naturally suggest that the volume is a function of the number 
of particles. It is possible, however, that the numbers of particles in 
the suspensions used for flocculation were not the same as, or pro- 
portional to, the number of particles counted in the dilute sols used to 
