INTRODUCTION. 



volume — i.e. occupying a definite portion of space — will 

 weigh so much. 



He will then dry the piece of wood, driving off its 

 moisture (water) at a known temperature, and then 

 again weigh it ; here he will pause to note that the 

 weight has diminished considerably — so much water, by 

 weight, has been driven off as vapour, and can be con- 

 densed and compared with his first results. 



He will also note that the dried piece of wood has 

 diminished in volume considerably ; in other words, the 

 wood not only loses weight, but it also shrinks as the 

 water is expelled. 



He will find that the amount of water which can be 

 thus driven off by merely drying the wood, and not 

 charring or burning it, varies according to the kind of 

 wood examined, the age of the tree which yielded it, the 

 season at which the tree was felled, and the part of the 

 stem from which his specimen was selected, and some 

 other circumstances ; it will probably amount to from 

 about 1 8 per cent, to about 52 per cent, of the original 

 weight before drying — say nearly 40 per cent, as 

 an average number. But he will also find that this 

 process of drying takes place in two stages, as it were. 

 Most of the water comes off easily as the temperature 

 rises above that of a hot summer day, or that of a busy 

 kitchen where the stoves are in full working order — say 

 25° to 30° C. ; but there is a smaller proportion of the 

 water which is held very tenaciously in the wood, and 

 cannot be easily driven off until the temperature ascends 

 to perilously near the scorching point, and which must 

 therefore be expelled by keeping the wood at a tem- 

 perature somewhat above that of boiling water — say 

 1 10° C. — for several hours. 



The first lot of easily dissipated water was merely 



