BOKING LIFE 153 



of methods which aim at the protection of timber by 

 armour of one kind or another. Metal has been largely 

 used for this, steel or iron sheathing has been employed but 

 found to corrode too quickly, zinc and Muntz metal 

 (an alloy of copper and zinc) also giving indifferent results ; 

 much better are casings of cast iron or copper. The latter 

 is highly poisonous to all forms of life but is expensive and, 

 unfortunately, much sought after by thieves. Vitrified 

 pipe castings have been found to give excellent protection 

 but they, in their turn, suffer from the serious defect that 

 they are easily broken. A great number of patent armours 

 of one kind and another have been put on the market but, 

 though they give initial protection, all break down sooner 

 or later and the wood borers enter. Concrete casings are 

 largely used at the present day, especially in the United 

 States, and they are often very effective but there is always 

 the danger that the concrete will be attacked chemically 

 by the sea water or that it will break away near the base 

 of the pile and so allow borers to effect an entrance there 

 and work their way upwards. An old and very effective 

 method consists of covering the surface of the wood with 

 broad-headed iron nails, known as " scupper-nailing." 

 The rust from the nails spreads and forms a complete 

 coating over the surface and with satisfactory effect. 

 All these methods are more effective with the Crustacean 

 borers than with the Shipworm, since the former can do 

 little damage unless a good deal of the surface is exposed 

 whereas a very small unprotected area will allow com- 

 paratively large numbers of minute larval Shipworms to 

 begin boring, and these may each penetrate into the wood 

 for a depth of a foot or more, according to the particular 

 species. 



The best method of protecting timber against the ravages 

 of the Shipworm is to impregnate it with some poisonous 



