442 
Philippine Journal of Science 
1920 
As in the experiments recorded with 0.5 N acid, the corrosion 
of iron with increasing potassium dichromate concentration in 
normal sulphuric acid first increased, then decreased, and finally 
was entirely inhibited. A much greater salt concentration was 
necessary, however, to effect passivity than was required in the 
case of the more dilute acid. These first experiments indicated 
a maximum corrosion rate with a concentration between 25 and 
50 grams of salt per liter, and passivity beyond 50 grams of 
potassium dichromate per liter of acid. To locate these points 
more closely, the experiments explained in Table 3 were per- 
formed. 
Table 3 . — Effect of addition of potassium dichromate on the corrosion of 
iron in normal sulphuric acid. 
As in the preceding experiments, increasing quantities of , 
potassium dichromate decreased the amount of corrosion. With 
additions above 45 grams of salt per liter results became ex- 
ceedingly irregular, and no definite passivifying concentration 
was determined, though passivity was effected in individual cases 
for concentrations as low as 50 grams of salt per liter. 
With 2 N sulphuric acid, the addition of potassium dichromate 
induced no passivity, as shown in Table 4, even when the acid 
solution was saturated with the salt. 
