Page:Popular Science Monthly Volume 13.djvu/571

This page has been validated.
553
THE TEREDO AND ITS DEPREDATIONS.

impregnated with this salt at the establishment of MM. Van der Elst and Smit. The first summer proved that this method would not in the least prevent the wood from being destroyed by the teredo. And the same was true of the following method:

3. Acetate of Lead.—The blocks impregnated with this salt were prepared at the same establishment.

Surprise may be expressed that the commission did not try experiments with corrosive sublimate. It felt that it could dispense with them, as its inefficacy had already been sufficiently established by previous experiments on a large scale at the marine dock-yards at Rotterdam. Experiments with mercurial and arsenical salts were tried, in 1730 and later, but without satisfactory results.

4. Soluble Glass and Chloride of Calcium.—Pieces of oak and red fir were impregnated at the same establishment at Amsterdam, first with a solution of soluble glass (silicate of soda), and afterward with a solution of chloride of calcium; the object of this double impregnation was to produce in the pores of the

PSM V13 D571 Treated and untreated wood exposed to the teredo.jpg
Fig. 15.—This cut was made from a piece of pine-slab, partially creosoted and exposed one season (1877) in the Gulf of Mexico. Only the dark-colored portion on the right side of the block was creosoted for this experiment. The rest of the block, untreated, was entirely riddled by the Teredo navalis, up to the edge of the creosoted portion, but that the destructive marine worm carefully avoided.

wood a silicate of lime. The pieces thus prepared were left in the open air during six months before being placed in the water, in order that the chemical combination might be as complete as possible. These pieces were exposed in the water at Nieuwe-Diep, in March, 1862, and