120 



THE TIMBERS OF THE WORLD 



the largest sap-ring. It has been customary to divide all the shipments 

 into two sorts, these being described respectively as " thick sap " and 

 " thin sap." In the former the sap rings vary from anything between one 

 inch to more than two-thirds of the tree, but in the latter generally from 

 not more than half an inch to an inch. The heart-wood is of a greenish- 

 black colour, and upon being exposed to light and air grows darker. 

 The sap-wood is a bright light yeUow, in colour very similar to East 

 Indian satinwood. Lignum vitae is one of the hardest and heaviest, 

 as it is one of the most useful of timbers, and for a great many purposes 

 it has been found impossible to produce a substitute. The maintenance 

 of a sufficient store of supply may indeed be said to be a question of 



Forest Railw. 



national importance, for during the war the great demand practically 

 exhausted all the available supplies. There is nothing equal to it for the 

 making of sheaves for blocks, and when employed in this way it wears 

 well and seems aktaost imperishable. Laslett said that he had examined 

 some sheaves after they had been in use for fifty to seventy years, and 

 found them perfectly good and fit for further service. 



Perhaps the most important of the many uses to which it is put is 

 for the bushing of the stern tubes for propeller shafts in aU, even the 

 largest ships. In a private note Mr. S. Woodrow says : " Lignum vitae 

 has been found by long experience to be the best material for this purpose, 

 as, owing to the silky nature of the wood and the oil contained in it 

 acting in conjunction with the water, a natural lubricant is formed." 



