294 TIMBEES AND THEIR USES 



they can easily be carried out by anyone of 

 average ability, it may be well to describe tlie 

 methods in brief, for the benefit of those who 

 are carrying out such tests for the first time. 

 It is usual and convenient to express the moisture 

 content as a percentage on the dry weight of 

 timber. Accurate weighing, on a chemical 

 balance, is an essential to success. 



The timber to be tested is cut into a small 

 block by means of a chisel ; then, by aid of the 

 same tool, the wood block is cut into small 

 pieces and weighed. The test pieces of wood 

 are then put into a drjdng oven which is main- 

 tained at a constant temperature of 200° F. 

 After a period of twenty-four hours or so, the 

 test pieces are removed from the oven and 

 allowed to cool in a desiccator. When cool, 

 the test pieces are weighed and the loss of weight 

 shows the amount of moisture that has been 

 driven off, so that the moisture percentage is 

 easily calciilated from the known data. 



For more accurate determinations the wood 

 should be repeatedly heated in the oven, cooled 

 and weighed tiU the weight is approximately 

 constant, i.e. till all the available moisture has 

 been driven ofi. 



We mentioned that the samples should be 

 prepared with a chisel, for the reason that, by 

 this means, less heat is evolved in the working 



