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 acid. Effect of addition 
of chromium compounds. 
{Addition equivalent to 2.5 grams metal per liter of solution.] 
Loss after— 
aS Total loss. 
Experiment No. Addition. ie «= | om 
24 hours. + : 
hours. 
—— 
Grams. | Grams. | Grams. | Grams. 
ee aes A eae ae 15.914| 0.178| 0.189| 0.862 
PRUE «E'S Say fer epee aan eee Chromium sulphatea_| 15.972 0.230 0.201 | 0.481 
ORs St er ee fib ess os 15.574 0.176 0.191 0,367 
ee ee | eee Chromium chloride.._|__ 14. 605 0.266 0.266 | 0.532 
Oh ee a 14. 563 0.365| 0.812| 0.677 
| eae 
8 Added as chromic hydroxide. 
Chromium chloride showed some acceleratory 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 passivify 
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 corrosio? 
rose to a maximum as in less concentrated acid, but showe 
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 18 
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. 
