Technologic papers of the Bureau of Standards Volume 20-31

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1913 edition. Excerpt: ... to fall away from the test specimen. This seems particularly likely to happen in the case of very impure metals, which often exhibit a more or less honeycombed aspect after long-continued corrosion. Since the efiiciency of corrosion is always determined from the net loss of weight, any particles of iron that might be dislodged in this manner would be charged against the current, and in this way the corrosion efliciency might easily be made to appear larger than 100 per cent. (d) Circulation of the Electrolyte.--It is well known that if the electrolyte surrounding a piece of iron be kept in constant circulation, the amount of self corrosion which results will be greater than if the electrolyte remains practically still. When an electric current flows through an electrolyte it causes a migration of the ions, which may increase the self corrosion of the iron in a marmer analogous to circulation of the electrolyte. Particularly, in the case of an anode there is a tendency for the acid radicals such as Cl, S0,, etc., to concentrate near the anode surface, and it is well known that liquids containing large amounts of these radicals, particularly the chlorine, produce very rapid corrosion of the iron. Here, again, any excess of self corrosion which would be produced would be charged against the electric current, and a high efiiciency of corrosion would result. It is not improbable that any or all of the above-mentioned causes may be operating in certain cases to produce a high efficiency of corrosion. However that may be, it has been definitely established that if a check specimen is embedded in the earth along with the anode the self corrosion will always be much higher than if the check specimen is embedded in the same earth but in a separate vessel....