that with untinned cylinders the copper content of the water decreased with time to a low figure. With tinned cylinders, however, the copper continued to build up to a relatively high value. He considered that Mr. Hunt's work on the metalography of tin coatings offered an explanation of this phenomenon; that a tin coating of poor quality could be responsible for pitting of the under-lying copper and thus cause a continuous build up of copper in the water.

Dr. G. Moir referred to trouble which he had experienced some time ago with pitting along each side of welds in stainless-steel vessels used in brine solutions.

Mr. G. S. Lambert explained how an unstabilised stainless steel would undergo this type of “weld decay” under corrosive conditions. This difficulty has been overcome by using alloy steels stabilised by the addition of small amounts of titanium and columbium. This prevents precipitation of chromium carbide at the grain boundaries.

Mr. I. S. Hunt, in replying to Mr. Wilkinson's remarks, confirmed that a poor-quality tin coating in which the protective eutectic layer was missing or discontinuous could cause excessive solution of the underlying copper such as was described.

In reply to Dr. Moir's remarks Mr. Hunt referred to tests being carried out at the Dominion Laboratory which were showing that even welded stabilized stainless steels were not completely resistant to chloride solutions. In the tests carried out so far, pitting developed in the welds in both acid and alkaline oxygen-saturated brines. This pitting did not develop when the brines were saturated with nitrogen. The work had not yet been carried far enough to determine what were the conditions favouring the development of pits in the weld regions.