Table V Rearrioir berccceti ferrous chloride solrrtion und the aqrrcorrs esrracl of a zbrc soap The aqueous estract of the zinc soap had a plr value of J .78 FcC12 so!. bcforc mising pll of Conc. o f Fc in ",, F e I I B . Fclml. PII mixture filtrate 116. I:e/ml. removed 524-0 4.04 4.74 183 '0 30 .z 100.0 4.3s 4.76 20 '0 60 so 9.0 5.07 4.82 2.8 37 .R 5'3 5.17 4 -83 2 .o 26.4
66.0%~ it was concluded that the aqueous extract of a zinc soap was acting heterogeneously, that is, acting as an adsorption inhibitor by interaction with the metallic surface. This conclusion is supported by more recent work in Cambridge which suggests that certain inhibitors, which have prcviously been considered as acting homogeneously, do, in fact, function heterogeneously. If this view can be upheld, it indicates that the classification of anodic inhibitors into prccipitation and adsorption inhibitors is incorrect, and that all inhibitors should be regarded as acting heterogeneously. A paper dealing with this point will be published shortly.
Summary
It has been shown that zinc dust, zinc oxide and lithopone were not capable of rendering water non-corrosive. When ground in linseed-oil the corrosive nature of the water was diminished, but complete inhibition was obtained onlywith zinc linoleate and with one sample of zinc dust. It was concluded that inhibition was brought about by soluble zinc compounds produced by the hydrolysis of zinc soaps, and that the majority of zinc pigments were not efficient inhibitors owing to their inadequate soapforming properties. The mechanism of the inhibition is discussed, and the view is put forward that the soluble zinc compounds are adsorbed on the metal surface, and act as 311 anodic inhibitor.
Acknowledgements
This investigation formed part of a programme of research carried out for the Corrosion Committee of the British Iron and Steel Research Association by the group of investigators associated with Dr. U.R. Evans. The author is indebted to the British Iron and Steel Kesearch Association and to Dr. U. R. Evans for their support and interest, without which the work could not have heen carried out.
The author also wishes to thank Dr. H. Miils of the Imperial Smelting Corporation Ltd., and Mr. A. Pass of Amalgamated Oxides (1939) Ltd., for the supply of materials, and Mr. I;.
Fancutt, Dr. P. \'ormaell and Miss Brasher for their helphl comments on the manuscript.