THE TEREDO AND ITS DEPREDATIONS. 



553 



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 experi- 

 ments with corrosive sublimate. It felt that it could dispense with 

 them, as its inefficacy had already been sufficiently established by pre- 

 vious experiments on a large scale at the marine dock-yards at Rotter- 

 dam. Experiments with mercurial and arsenical salts were tried, in 

 1730 and later, but without satisfactory results. 



4. Soluble Glass and Chlo- 

 ride of Calcium. Pieces of 

 oak and red fir were impreg- 

 nated at the same establish- 

 ment at Amsterdam, first with 

 a solution of soluble glass (sil- 

 icate 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 



Fig. 15. This cut was made from a piece of pine-slab, partially creosoted and exposed one sea- 

 sou (1877) in the Gulf of Mexico. Only the rlark-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 



