59 



at the linic ol tlie cxpcrimfnt. Whctlu-r the coiuHtioii disclosed will ccintiiuie or not 

 is another matter and must he judged by consideration of other controlling factors 

 and by repeated tests. 



The first information to be secured is that on salinity. If it is found, either Ijy 

 actual test or 1)\' reference to existing recortls, that the salinity is sufficient for borer 

 activity, then test timbers can be exposed to determine their presence and the inten- 

 sity of attack. The information usually desired in connection with piling material 

 is the practical)ility or inipracticahility of un|:>rotected timber, the life to be expected 

 from it, or the extent to which protective measures should be adopted. Since unpro- 

 tected timber will last a year or less under sexere conditions, if protections are to be 

 justified they must be capable of prolonging that life many times. It is therefore 

 obvious that a complete test of ultimate life for a protected type of wood construction 

 is impracticable because of the time required. For this reason the intensity of attack 

 is measured by the effect on unprotected wood and the probable life of protections 

 is judged accordingly, on the basis of data for the protections concerned, such as 

 are presented in this volume. (See p. 177.) 



The test specimen must be exposed under all ccmditions which could normally 

 prevail for a structure at that point. Where Teredo or Bankia are involved the speci- 

 mens should be placed in the water just before their breeding seasons (see p. 190) for 

 the reason that this is the time at which initial attack is made by them. If jilaced in 

 the water after the breeding season there may be no attack until the next year, which 

 will give a negative result until that time and, if not understood, may lead to the 

 incorrect conclusion that borers are not present. The destruction of wood takes 

 place during the period succeeding the breeding season, in which the borers grow to 

 maturity; hence the specimen should remain exposed for at least several months. 

 In the case of Limnoria, which in the mature form is free to move from place to place 

 and apparently breeds throughout the year, attack may occur at any time, if that 

 borer is present in the \icinity or may be conveyed there by driftwood or other 

 agencies, and if salinity is suitable. 



The test specimens should be exposed in the deepest water, beginning near the 

 mud line where the shipworm attack is greatest. Limnoria will be more plentiful 

 near low tide level, but are not likely to be absent at any level, if present in that 

 location. Specimens must be pre\ented from rubbing against other objects because 

 this would hinder borer attack on the abraded surface and, e\-en though they secured 

 a foothold, would reduce their actix'ity lielow that otherwise normal under the given 

 conditions. Instructions for the preparation and installation of test boards will be 

 found in Appendix B. 



