RAVAGES OF SEA

New Zealand Herald, Volume LXXIII, Issue 22412, 7 May 1936, Page 8

RAVAGES OF SEA

TIMBER AND METAL many years of research REPORT AT LAST PUBLISHED j [I'ROM OUB OWN CORRESPONDENT] LONDON, April 8 For 19 years experts have been investigating the ravages caused to ti®. ber, metal and concrete structures when immersed in sea water. The Stationery Office publishes the results of this long research. Hundreds of different materials have been exposed, some for 10 years, in many parts of the Empire to the action of sea air -and water. Damage to timber in sea water, the report points ou.t, is mainly caused by ship worms, known to the scientist as teredo. These are molluscs, but differ from mussels and oysters in haying only a small part of the front portion oi their soft bodies covered by shell. Using their shells as chisels they excavate burrows in the wood, taking the sawdust produced into their bodies. Incidentally, ship worms proved disastrous on the fourth voyage of Columbus, whose ships were "pierced with wormholes like i beehive." Impregnating the timber with poisons has been found to W the most satisfactory method of dealing with theij attack. Most Efficient Poison The most efficient poison has been found to be the arsenical compound chloro-dihydro phensarsine, which wai used as a poison gas during the war. The best method of impregnation appears to be to dissolve the poison in creosote and to force it into the timber by an ordinary Bethell process, in which the timber is first placed in a vacuum and the liquid then forced in under pressure. "Incising" the timber with knives before creosoting greatly increases the uniformity of penetration. Another creature which in some situations, the report states, causes even more damage than teredo is limnoria. These creatures, which are allied to shrimps and lobsters, are minute compared with the mollusc borers. They work on the surface of the wood, and Professor Barger states in the report thai really no effective protection against them has yet been revealed by the committee's experiments, though good creosoting seems tp repel them to some extent. *

In the tests of the corrosion of iron and steel, specimen bars of 14 different materials were used. The test specimens were in general 24in. long by 3in. by; 2in. They were despatched for testing to Auckland, Colombo, Halifax, Nova Scotia and Plymouth. Considerable variation was found in the extent and nature of the corrosion at the different observing stations. For example, in the half-tide tests and in the tests above high-water mark, the bars at the Colombo station were most severely attacked. Next in order were those at Plymouth and Halifax, while those at Auckland suffered the least. Addition of Jfickel The investigations show that, on the whole, there is little to choose between wrought iron and mild carbon steels, both being cleaned from scale. With regard to carbon steels exposed witbi&e scale on, those high in sulpjiur and phosphorous proved the leaSs satisfactory. The addition of small percentages of copper was shown to be of some benefit. The addition of chromium appeared beneficial in the tests above high-water mark, but in the half-tide and complete immersion tests it resulted in excessive pitting. The best results were obtained by adding a proportion of nickel to the steel, an addition of 36 per cent, rendering the steel exceptionally resistant under all conditions. Cast irons resisted aerial corrosion well, but in the halftide'and complete immersion tests corrosion was found beneath the surface. The report discusses the protection of iron and steel'by means of paint and other preservatives, and adds that it is desirable to remove all scale before application of paint. This may be accomplished by sand-blasting, picking, or some other method. In the tests above high-water mark and the complete immersion tests additional coats of paint were found to have a beneficial result, but in the half-tide tests the opposite result was obtained.