32 
BULLETIN 1179, U. S. DEPARTMENT OF AGRICULTURE. 
Table 17. — Shatter tests on briquets made from mixtures of low-grade and high-grade 
phosphate rock with coke. 
Fresh briquets. 
Air-dried briquets. 
Oven-dried i 
briquets. 
Sample No. 
Weights. 
H 2 0. 
Shattered 
on drop- 
ping to 
cement 
floor. 
Shattered 
on drop- 
ping to 
cement 
floor. 
With- 
stood drop 
on mass 
of similar 
briquets. 
Compres- 
sion test. 
Shattered 
on drop- 
ping to 
cement 
floor. 
With- 
stood drop 
on mass 
of similar 
briquets. 
3-T 
Grams. 
\ 118.5 
} 113.5 
Per cent. 
Feet. 
Feet. 
12 
8 
10 
10 
8 
Feet. 
18 
20 
20 
20 
15 
Pounds 
per sq. in. 
72S 
738 
960 
1,004 
811 
Feet. 
14 
8 
10 
18 
11 
Feet. 
4-T 
12. 00 Yi 
11.90 8 
14.30 ! 10 
20 
7-T 
8-T 
20 
7-T 
} 103.0 
8-T 
20 
15-T 
16-T 
18-T 
19-T 
20-T 
\ 111.6 
I 121.6 
14.35 
11.02 
20+ 
9 
20 
20 
With few exceptions all of the briquets in the air-dried condition 
withstood a drop on a cement floor of from 6 to 8 feet and a drop of 
20 feet or more upon a mass of other briquets. The drying of the 
briquets in an oven increased somewhat the effectiveness of the 
binder, but in actual commercial practice it would scarcely be eco- 
nomically feasible to. put them through a drying process. In charg- 
ing these briquets to a shaft furnace, however, they would never be 
subjected to a drop of over 15 feet upon a mass of similar briquets 
and therefore they would meet all practical requirements. 
Through the courtesy of two commercial firms, briquetted charges 
of several tons were made up with the silica-lime ratio given in the 
preceding tables and protracted tests made on a semicommercial 
scale in a modified form of blast furnace w T hich is described later in 
this bulletin. 
EFFECT OF HIGH TEMPERATURES ON VARIOUS BRIQUETTED 
MIXTURES. 
The results obtained in these larger scale experiments indicated 
that the silica-lime ratio as well as the carbon content of the 
briquetted charge might be advantageously altered to give a some- 
what more rapid evolution of phosphoric acid without sacrificing the 
fluidity of the slag. Accordingly a series of laboratory experiments 
was undertaken to determine the following points: (1) The percent- 
age of coke to incorporate in the briquets for optimum reducing effect ; 
(2) the optimum silica content required for the rapid elimination of 
phosphoric acid and the production of a fluid slag; (3) the most practi- 
cal temperature to employ to effect the decomposition of the phos- 
phate without undue erosion of the refractory lining of the furnace. 
Four batches of briquets were made up of run-of-mine phosphate 
from Tennessee mixed with sufficient sand to give the following ratios 
of silica to lime in the charge— 59: 41, 61 : 39, 63: 37, and 68: 32. The 
amount of coke in the first batch of briquets (having the lowest 
silica content) varied between 12 and 15 per cent of the weight of 
the charge, and in certain briquets bituminous coal was substituted 
