Prevention of decay in wooden and iron ships.

Scientific American 18, 31.10.1863

The prevention of rot in wooden vessels, and rust in iron steamships, are questions of vast importance to all commercial nations. Efforts to prevent wooden vessels from decaying were made hundreds of years ago; but the case is different with iron steamers, as they are only of recent date. Iron now enters so largely into the construction of steamships — mercantile and marine — that intense interest is manifested in the desire to render them as perfect and durable as possible; especially as this metal is liable to rust or oxidize, and the bottoms of iron vessels so readily become foul in salt water. Much has been done to accomplish the objects desired in both timber and iron ships, and yet the defects in both classes of vessels have not been fully remedied. Perfect success, however, is not improbable; but in order to prevent fruitless toil, so as to secure success by new efforts, a knowledge of what has already been done in this department of the arts is necessary. A mass of very valuable and practical information on this head, has fortunately just been presented in the columns of Mitchell's Steam Shipping Journal, from a contributor who has consulted all the specifications of patents bearing on the subject in the British Patent Office. These we have condensed with remarks as follows: —

In 1739, Alexander Emerton took out a patent for preserving wood from decay, by boiling planks and boards in oil, then coating them with paints containing poisons. In the early part of the present century, several chemists recommended the treating of green timber intended for shipbuilding with decoctions of vegetable poisons, to destroy all insect deposits in the wood. Applications of this character did not prove efficacious in preventing dry rot, and for a long interval afterwards the question seemed to have vanished from the public mind. John Oxford next secured a patent in 1822 to prevent decay in wood and rust in iron, with a compound of tar oil saturated with chlorine gas, and mixed with red and white lead, the carbonate of lime, and a portion of tar. This compound was applied like paint. In 1830, G. G. Bompass secured a patent for the protection of iron from corrosion by galvanic action. He employed an alloy of tin and zinc in connection with the iron. At the same time John Revere obtained a patent for fixing zinc protectors to the studs of chain cables and other iron surfaces exposed to the action of salt water. These galvanic protectors were riveted or soldered to the iron that was to be protected. When a more oxydizable metal, such as zinc, is placed in contact with iron, a galvanic action ensues, the zinc is decomposed, and the iron, being positive, does not oxydize so rapidly as it otherwise would in the same liquid. In 1832 Captain Crawford, R. N., obtained a patent for preserving iron from oxydation by coating it with zinc paint, over which he laid a covering of an alloy of tin and lead. John R. Neilson took out a patent in 1840 for coating iron with copper, and also with an alloy of tin and zinc. According to this invention, the surface of the iron was first scoured bright, then borax in powder was spread thereon, and it was afterwards drawn through a bath containing the molten metal with which it was to be coated. In 1840 Arthur Wall obtained a patent for applying hot muriate of iron to coat the surface of iron and prevent oxydation. In 1841, W. E. Newton secured a patent for the use of silicates of soda and potash (soluble glass) to the surface of iron, to prevent rust; and at the same time, Professor R. Mallet obtained one for coating galvanized iron with a poisonous paint, to render it suitable for exposure in salt water. In the same year E. Morehead also took out a patent for preserving iron, by first tinning it, then covering its surface by immersion in molten zinc. In 1846, Baron Wetterstedt patented a paint for iron, composed of the regulus of antimony and oxide of copper, mixed with tar, naphtha, and oil. C. H. Paris secured a patent in 1849 for coating metals with glass. The iron was first cleaned, gum water applied to its surface, then powdered glass sprinkled upon it; after which it was placed in a furnace and fused, when the glass adhered to the metal.

To protect the bottoms of iron ships, J. Macintosh secured a patent in 1852, for dissolved india-rubber combined with metallic salts. In 1852, Hughes & Firmin took out a patent to be applied to the bottoms of iron vessels, consisting of lampblack, naph tha, and linseed oil: R. M. Glover obtained one in the same year for a paint composed of the arsenite of lead, arsenite of copper, and orpiment; and about the same time T. Murdoch patented white zinc as a paint for iron. In 1853, I. C. Meduros patented the use of mercury as applied to iron, by using a strong solution of corrosive sublimate, in which the iron was immersed until its surface was coated. In 1854 E. Newton patented ground blacklead, pulverized charcoal, and bone black mixed with oil, as a paint for iron; in the same year, F. Ransoms patented a mixture of theground oxides and carbonates of lead and zinc, sulphate of barytes, and soluble silicate of soda applied to iron and wood. In 1856 Bancroft & White patented petroleum as a protective applied to the metal of ships; and in the same year A. F. Mennons patented a composition for iron consisting of clay, animal charcoal, sawdust, and oil; at the same time J. McInnes obtained a patent for coating iron with powdered emery and shellac varnish; R. D. Atkinson patented the coating of iron surfaces with brass in the same year. Armor plates are now being covered with brass at Portsmouth, England, by M. Wielan. A. Reid also secured a patent in 1856 for preventing iron from rusting, by covering the metal with soot, placing it in a suitable furnace, and raising it to a white heat. After being coated, it is asserted that the surface of the iron is covered with a coat impervious to rust. In 1857, G. Bedson pittented an elastic paint for iron, composed of mineral tar, india-rubber, tar oil, and shellac; in the same year F. L. Oudry patented the coating of iron with copper upon an intermediate coating of another metal. In 1858, M. M. Bouchaul & Clanel, of Paris, patented a composition for painting iron, consisting of ochre, lime, and oil; and in the same year Le Comte de Fountainemoreu patented an improved mode of zincing iron. In the following year — 1859 — patents were granted to J. Crawford for a composition consisting of plumbago, arsenic, and lac varnish; also to F. W. Emerson for oxychloride of lead mixed with varnish; also one to J. Meikle for coating iron ships with asphalt. In 1860, patents were issued to M. Allen for gashouse tar applied to the inside of boilers and to ships; to R. Smith, for a mixture of pitch, tar resin, and assafcetida, in turpentine, applied to the bottoms of vessels; and to G. Hallet, for a paint composed of the oxide of antimony and linseed oil. In 1861 John Hay took out a patent for coating the bottoms of iron vessels with black protoxyd of copper ground in linseed oil. This composition has lately been applied to some of the British armorclad vessels. In the same year John Snider, (an American) patented finelypowdered amorphous graphite, mixed with linseed oil and beeswax, for coating ships' bottoms; and in the same year Mallet & Stenhouse patented native oxides of antimony mixed with red lead, as a paint for iron.

The record of these English patents ends here. They seem to cover almost all substances capable of being mixed with oil and varnish to be applied as paints; also the coating of iron with zinc, copper, and tin. Several of these patented compositions are very similar; and it is not a little remarkable that the zinc protectors of John Revere, patented in 1830, have lately been the subject of a patent in France, by Mons. Jean P. Jouvin, chief medical officer of the French Navy, and Professor of Chemistry at the Naval School, Rochefort. The French Goyernment are now making experiments with them on two armorclads. To protect the exterior part of the• hull under water from the adherence of marine shells, Professor Jouvin also applies a paint composed of turpeth mineral (subsulphate of mercury) Prussian blue, and red lead mixed with boiled oil. This poisonous paint must bo applied on the outside of two coats of zinc paint, because the iron would reduce the mercurial paint by direct contact. The most successful method of protecting the bottoms of iron vessels from fouling, appears to consist of a planking of wood extending a little above the water line, countersinking the bolt heads, covering the whole with asphalt and felt as a nonconductor, and then sheathing on the outside with copper.