510 
Journal of Agricultural Research 
Vol. XXVIII, No. G 
Table VII .—Effect of surface area on breaking strength of the briquettes 
(a) CALCULATED FROM TABLE V 
Coarse sand.. 
Medium sand. 
Fine sand_ 
Very fine sand 
Silt.... 
Clay_ ... 
Material 
Surface 
area of 
1 gram 
Load per gram of 
briquette 
Observed 
Calculated 
Square 
centimeters 
52 
105 
224 
523 
1,425 
15,685 
Kilograms 
3.8 
4.3 
6.2 
Kilograms 
3.3 
4.8 
7.1 
9.8 
24.6 
61.6 
11 . 
18. 
65.4 
L=0.42 
(ft) CALCULATED FROM TABLE VI 
A... _ 
308 
21.1 
b _ .. ; / v / .. 
625 
43.4 
c. 
3, 495 
71.0 
L=1.66 5»-47 
The above values are all based on a colloidal content of 25 per cent. Suf¬ 
ficient material was not available, particularly in the silt and clay groups, to test 
this relation extensively except in a general way. The value of n was found 
Fig. 6.—Showing the effect of the surface on the breaking strength of briquettes 
to be practically constant as shown above, the variation in strength due to size 
and grading of the material and the amount of colloid present being indicated 
by variation in the value of k . 
THE EFEECT OF THE AMOUNT OF COLLOID 
To determine the effect of the amount of colloid present in a mixture on the 
binding power of the colloid, varying amounts of colloid were mixed with quartz 
flour and also with medium sand. The results of these tests are shown in Table 
VIII. It may be noted from the methods of calculating the load per gram of 
—i © 
