290 TIMBERS AND THEIR USES 



drying is likely to give better results by kiln 

 drying than newly felled timber. 



There are various impregnation methods of 

 seasoning, many of them of doubtful utOity. 

 The object of such methods is to replace the 

 sap by some antiseptic substance. Most of the 

 methods of impregnation in general use are 

 named after their discoverers, thus Burnettizing 

 the wood or impregnating it with zinc chloride 

 is due, in the first place, to Sir William Burnett ; 

 Kyanizing, called after its inventor, Kyan, con- 

 sists in impregnation with corrosive subhmate 

 which forms insoluble compounds in the tissues, 

 but the method is expensive and corrosive sub- 

 limate is highly poisonous, 



Powellizing consists in boihng the wood in a 

 sugar solution and then drying at high tempera- 

 tures. This is- one of the • most rapid* of all 

 methods for seasoning wood, and wood so 

 treated may be seasoned within a few days of 

 being felled. 



Other substances commonlyused for chemically 

 seasoning wood are copper sulphate, which 

 renders the wood brittle and is not lasting ; 

 creosote, which is cheap and effective ; carbolic 

 acid, equally efiective but more expensive ; 

 ferric tannate ; borax ; a mixture of iron and 

 copper sulphates with kainite, and various modi- 

 fications which are the subject of patents. 



