Harlingen, Stavoren, and Nieuwendam, and afterward in the ports of Nieuwe-Diep and Stavoren. The woods employed were oak, red fir, ordinary fir, and Pinus sylvestris, generally in pieces one metre long by two or even three decimetres square. These blocks were prepared in different ways, and care was taken to place by their side blocks of the same kinds of wood without any preparation as counter-proofs.
The trials made by the commission may be placed under three principal groups:
1. Coatings applied to the surface of wood, or modifications of the surface itself.
2. Impregnation of wood with different substances, which modify the interior as well as the surface of the wood.
3. Employment of exotic woods, other than ordinary woods of construction.
Coatings applied to the Surface of Wood.—The methods belonging to this group, which have been examined by the commission, are the following:
1. Method invented by M. Claasen, and kept secret by the inventor.
2. Metallic paint, invented by M. Claasen and likewise kept secret.
3. Method of M. Brinkerink, consisting of a mixture of Russian talc, coal-tar, resin, sulphur, and finely-powdered glass, applied hot on wood previously roughened by a toothed instrument; this application was two millemetres thick.
4. Method of M. Rijswijk, analogous to the preceding.
5. Paraffine varnish, obtained by the dry distillation of peat, from the factory of MM. Haages & Co., at Amsterdam.
6. Coal-tar, applied cold on the wood in several successive layers, or applied hot on wood whose surface had been previously carbonized. Some pieces were treated as follows: Holes were first bored in them and filled with tar, then plugs were fitted closely to the holes and driven in with sufficient force to make the tar penetrate the wood; other pieces still were painted over with a mixture of tar with sulphuric acid, or sal ammoniac, or turpentine, or linseed-oil.
7. Painting with colors mixed with turpentine and linseed-oil—among others with chrome-green or with verdigris.
8. Singeing or superficial carbonization of the wood.
The pieces of wood thus prepared were placed in the water at the end of May, 1859, and the first examination, made toward the end of September of the same year, showed that neither of these methods afforded any protection from destruction by the teredo. There was one partial exception, and that was the pieces of wood treated according to No. 6; these showed only traces of the teredo here and there. But, at a later examination, in the autumn of 1860, when the wood had been exposed a year and a half, these were also found to be equally severely attacked by the teredo.
The results of these experiments strongly convinced the commission