262 TIMBER 



edges of sapwood, decay first, and whilst the top edges are 

 often badly decayed, the lower edges remain quite sound, 

 as the water cannot lie there. 



The reason why the floors and joists in basements, or 

 over cellars, are more liable to decay than the rest of the 

 timber in a building is because they are more subject to 

 damp and moisture and often have not proper air currents 

 round them. 



The joinings of timbers, whether notched or unnotched, 

 or where one timber rests upon another so that wet or 

 damp is liable to lodge, should have a good coat of Stock- 

 holm tar and pitch put on hot ; this is an excellent 

 preservative. 



Some recent German theory goes to show that the 

 calcium bicarbonate arising from the hydrate of lime in 

 mortar is probably the chief cause in the development of 

 spores, as almost without exception the wood nearest to 

 the walls of buildings is first attacked by rot. When 

 fungus has gained access, all visibly affected parts should 

 be cut away, as well as the adjoining and apparently sound 

 timber for several feet round, and the brickwork should be 

 well cleaned and brushed over with creosote or coated with 

 good plaster. 



The most destructive agent with which the engineer has 

 to contend in the case of timber structures erected in sea 

 water is known by the general name of the sea worm. 

 One or other of the several pests known by this name are 

 found in sea water all over the world and cause enormous 

 destruction. 



The Teredo Navalis, often called the " ship worm " from 

 its destructive action on timber ships, as a protection 

 against which they had to be copper sheathed, resembles a 

 long worm, although it is really a mollusc. The animal is 



