444 
Philippine Journal of Science 
1920 
salts have little or no effect. This conclusion was corroborated 
by the experiments recorded in Table 6. 
Table 6. — Corrosion of iron in normal sulphuric add. Effect of addition 
of chromium compounds. 
[Addition equivalent to 2.5 grams metal per liter of solution.] 
Loss after — 
Total loss 
Experiment No. 
Addition. 
Weight 
of iron. 
24 hours. 
+25 
hours. 
in 49 
hours. 
61 
None __ 
Grams. 
15.914 
Grams. 
0. 173 
Grams. 
0. 189 
Grams. 
0.362 
62 
Chromium sulphate a. 
15. 972 
0.230 
0. 201 
0.431 
63 
do 
15. 574 
0. 176 
0. 191 
0. 367 
64 
Chromium chloride.. _ 
14.605 
0. 266 
0.266 
0.632 
65 
do 
14.663 
0.365 
0.312 
0.677 
“ Added as chromic hydroxide. 
Chromium chloride showed some accelerate ry effect, but this 
was very slight as compared with the effects noted with chro- 
mates or dichromates. 
DISCUSSION OF RESULTS 
The amount of potassium dichromate necessary to passivity 
iron became progressively greater as the sulphuric acid con- 
centration increased. In half-normal sulphuric acid, iron be- 
came passive with a potassium dichromate concentration above 
19 grams per liter; in normal acid the critical concentration of 
potassium dichromate was above 50 grams ; in twice-normal acid 
iron did not assume the passive state. 
With increasing potassium dichromate concentrations, the 
corrosion in half-normal and in normal acid first increased and 
then gradually decreased. In twice-normal acid the corrosion 
rose to a maximum as in less concentrated acid, but showed 
no decrease. 
The corrosion data in Tables 1, 2, and 4 are shown graph- 
ically in fig. 1. They indicate that, below the concentration 
which effects maximum corrosion, the amount of corrosion is 
proportional to the potassium dichromate concentration. 
The marked inhibition of the corrosion of iron by chromium 
salts, recorded by Watts,® was not confirmed with the sample 
of iron used in the present investigation. This discrepancy may, 
' Loc. cit. 
