16,6 Heise and Clemente: Corrosion of Iron 443 
Table 4. — Effect of addition of potassium, dichromate on the corrosion of 
iron in 2 N sulphuric acid. 
Experiment No. 
Potas- 
sium di- 
chromate 
added. 
Weight 
of iron. 
Loss due 
to corro- 
sion in 21 
hours. 
46.__ 
Grams 
ver liter. 
0 
Grams. 
15. 685 
Grams. 
0. 201 
47 
25 
14. 9'74 
4.314 
48 . _ _ 
25 
14. 998 
4. 408 
49 ’ 
60 
15. 424 
6. 802 
60 
50 
15. 295 
6.727 
51 
76 
15. 510 
6.808 
52 - - — 
75 
14. 633 
6.231 
53 
100 
15. 240 
64 
100 
16. 871 
6.809 
The amount of potassium dichromate added (40 grams) was 
more than would dissolve in 400 cubic centimeters of 2 iV acid, 
indicating that iron could not be passivified in acid saturated 
with potassium dichromate. With additions of more than 20 
grams of the salt, the rate of corrosion no longer increased, 
which Vvould seem to show that, but for the limited solubility 
of potassium dichromate, passivity might have been effected 
even in 2 iV acid. 
Table 5 shows the progressive corrosion of iron in sulphuric 
acid containing potassium chromate and potassium dichromate. 
Table 5. — Corrosion of iron in 10 per cent sulphuric add. Effect of 
potassium chromate and potassium dichromate. 
Experiment 
No. 
Addition. 
Weight 
of iron. 
Loss after— 
Total loss 
in 169 
hours. 
19 hours. 
29 hours. 
48 hours. 
73 hours. 
Grams. 
Grams. 
Grams. 
Grams. 
Grams. 
Grams. 
55 
None 
15. 399 
0.163 
0.204 
0.177 
0.170 
0.714 
56 
do 
15. 762 
0.142 
0.141 
0.159 
0.160 
0.602 
67 
Potassium chromate 
(K2Cr04) 2.5 g 
15.296 
0.387 
0.265 
0. 162 
0.186 
1.000 
58 . - 
do . 
18. 455 
0.611 
0.218 
0.133 
0.192 
1. 164 
59 
Potassium dichromate 
(KsCrsO?) 2.5 g 
15. 807 
0.545 
0.268 
0.146 
0.185 
L144 
60 
18.211 
0.579 
0.226 
0.167 
0.262 
1.234 
The foregoing data show that both chromate and dichromate 
first accelerate corrosion ; but that, after reduction to chromium 
salt has once taken place, the rate of corrosion is very similar 
to that taking place in acid alone, indicating that chromium 
