16,5 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. 
Potas- Loss due} 
: ; sium di- | Weight | to corro- } 
Experiment No. 'chromate) of iron. (sion in 21 
| added. hours. 
Grams 
per liter.| Grams. | Grams. 
Ne a ee er eee 0 | 15.685 | 0.201 
ERC gaan GS ALR go wl Sway te 4 OMIA a OE ERO RiP NB, TE Rt 25 14. 974 4.314 
ers i a es ee ee co eabwcwae 25 14. 998 4.408 
Me ees i re ee oe a ae 50 15. 424 6. 802 
i Rr ee ee ee oaks 50 15. 295 6.727 
a ee Be Hee a oe eee 75 15.510 6. 808 
ee a es ee er ae Se ese 75 14. 633 6.231 
Sy Ba Re EEE ERR SREP Suh Dm OO RLSeRERiGe SEmEene ONES ane 2 SeMaR Dy eee ed 100 15. 240 6. 683 
A ate ae Le aa Sa OUR, epee oa epee GRE eects er ee Ge eer eiege 100 15. 871 6. 809 
The amount of potassium dichromate added (40 grams) was 
more than would dissolve in 400 cubic centimeters of 2 N 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 would seem to show that, but for the limited solubility 
of potassium dichromate, passivity might have been effected 
even in 2 N 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 acid. Effect of 
potassium chromate and potassium dichromate. 
| Loss after— | 
E a Weight . oa loss, 
No. Addition. ie in 169 
Lechctceen hours. 
19 hours.}29 hours.|48 hours.|73 hours. 
————— 
Grams. | Grams. | Grams. | Grams. | Grams, | Grams. 
OB... a 15.399 0.168 0.204 0.177 0.170 | 0.714 
Es SEE Mo ee ee 0.142 0.141 0,159 0.160! 0.602 
We Potassium chromate 
(KeCrO4) 2.5 ¢ -____-- 15. 296 0.387 0.265 0. 162 0.186] 1.000 
ee ee eat ieee FO 18.455| 0.611! 0.218) 0,133! 0.192] 1.154 
OR isiuas Potassium dichromate 
(KeCr207) 2.5 g -___--- 15. 807 0.545 0. 268 0. 146 0.185 | 1.144 
beret eee Risen Mo 18.211! 0.579| 0.226/ 0.167| 0.262| 1.284 
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 
