440 Philippine Journal of Science 1920 
gests that the protective action heretofore ascribed to chromates may really 
be due solely to the chromium which they contain, and not to the chromate 
as such. 
The stimulative action of potassium chromate and dichromate is in strik- 
ing contrast to the protection afforded by chromium sulphate. Chromealum 
is a much less efficient protective agent per unit of chromium than chro- 
mium sulphate. These experiments indicate the possibility of a revision 
in our ideas of the manner in which chromates protect iron from rusting, 
and may lead to the substitution of chromium salts for the chromates here- 
tofore used to render iron “passive.” 
Among the data accumulated by us, in the course of an ex- 
tensive series of corrosion tests, are results which have direct 
bearing on the question of the effect of the addition of chromium 
compounds on the corrosion of iron in sulphuric acid. Since 
there seems to be no good prospect for the completion of this 
series as originally planned, these rather fragmentary results 
are offered at this time, as of possible interest. 
The series of experiments to be described shows the effect 
on the corrosion of iron in sulphuric acid, (1) of varying con- 
centration of sulphuric acid and of potassium dichromate, and 
(2) of additions of chromium salts. 
EXPERIMENTAL 
The iron used was a sample of very pure commercial sheet 
iron, over 99.8 per cent pure, but containing a very small amount 
of copper. It was cut into strips 10 centimeters long and 2.5 
centimeters wide, cleaned of mill scale by being made the cathode 
in a bath of sulphuric acid,’ dipped in a weak caustic alkali 
solution, scrubbed, rinsed, dried, and kept packed in lime until 
wanted. 
The corrosion tests were made in half-liter, wide-mouthed, 
glass bottles, covered with watch glasses. The sulphuric acid 
used was chemically pure and free from arsenic, 400 cubic centi- 
meter portions of solution being used in each test. All tests 
were performed in a large water bath (covered to avoid any 
disturbing factor due to light) in which the temperature was 
maintained at 28°+1.0° C. 
The following data were obtained: 
* Reed, C. J., Trans. Am. Electrochem. Soc. 11 (1907) 181. 
