10 TIMBER AND TIMBER TREES. 



out the nails. This brings us to the question of 

 "seasoning." 



Many woods, if they once become air-dry — i.e. de- 

 prived of all the water that the air can take up from 

 them at ordinary temperatures — alter very little in 

 volume or shape in the ordinary course of events ; that 

 is to say, they do not shrink or swell beyond certain 

 limits which can be tolerated in practice. As a matter 

 of fact no wood exists that does not alter its dimensions 

 as the temperature and hygrometric conditions of the 

 atmosphere vary; and all undergo such changes in 

 volume more in directions across the longitudinal axis 

 of the wood than in those which coincide with that axis. 

 " Seasoning " is also necessary because wood is apt to 

 undergo certain deteriorations of very serious nature, 

 unless the excess of moisture is got rid of Consequently 

 the joiner^ cabinet-maker, etc., will assure himself of the 

 fact that wood has been properly seasoned before he 

 employs it for specific purposes. 



4. BY THE CHEMIST. 



Let us now inquire what the chemist has to say to- 

 our piece of wood. 



By means of those two busy handmaids of his — the 

 balance and the fire — we may be sure he can give us 

 some information ; though there may be room for dis- 

 appointment at some of his results, and we stand aghast 

 at the wreck of our object which remains, after he has 

 dissipated its elements by his searching analysis. 



We may assume that he will take a somewhat small 

 piece of the wood, and will weigh it accurately in its- 

 fresh condition ; this piece, having a certain size or 



