The Deterioration of Jute Materials. 
11 
TABLE 8. 
(Tests made at 70°C.) 
Superphosphate. 
Per Cent, of 
Calcium Carbonate 
added. 
Tensile Strength of jute twine. 
Contact. 
Vapour. 
lbs. 
lbs. 
Nauru 
none 
4 
14 
. 2 
36 
33 
Christmas 
none 
5 
33 
2 
22 
35 
Kosseir 
none 
1 
9 
2 
9 
34 
10 
4 
36 
12 
11 
38 
.Sofaga 
none 
2 
20 
2 
12 
37 
10 
12 
38 
12 
32 
34 
These results are discouraging in that large amounts of calcium car- 
bonate were necessary to afford protection to jute bags when in contact 
with Kosseir and Sofaga superphosphates at high temperatures. Protection 
in the vapour phase was satisfactory with 2% added calcium carbonate. 
(b) Reduction in the Amount of Sulphuric Acid used in Manufacturing 
the Superphosphate. — As it was first thought that the increased acidity of 
the new season’s superphosphate (p. 3) was an important factor in pro- 
moting the damage observed in the 1941/42 season, the effect of using less 
than the customary amount of acid was investigated. Standard tests were 
made on jute twine, using first the usual amount of acid in the manufacture 
of the superphosphate and then 95, 90 and 85% of this amount. The results 
are given in Table 9. 
In each ease the superphosphate was allowed to mature for at least one 
month before testing. 
In no instance does this table indicate any significant difference in the 
damaging effect resulting from variations in the amount of acid used. Fur- 
thermore, the free acidity of the superphosphate was always substantial, 
irrespective of the amount of sulphuric acid used in its preparation. It 
seems that the responsible agent is released in damaging amounts in the 
initial stages of the reaction between the acid and the rock; the reaction 
between the acid and the rock phosphate does not go to completion and 
there is always a residue of free sulphuric or phosphoric acid in the 
superphosphate which decreases slowly with time during storage. The 
residue of unattacked rock in the superphosphate, which is not acted on 
by the remaining acid, does not protect the bags from damaging agents. 
This conclusion is supported by the finding (in Table 4) that rock flour 
was ineffective as a protective agent. 
