12% /Selections. [no. 5, new series, 



The patentees of some of the wood-preserving processes go so 

 far as to state that they are enabled to render wood incombustible 

 or uninflammable, and such statements have tended to lead to the 

 presumption that a thoroughly effective protecting agent should 

 have the power of depriving wood of its combustibility. 



It will be readily understood, however, that even if a piece of 

 wood could be most thoroughly impregnated with a solution of 

 some strength, of matter unalterable, or at any rate only fusible, 

 by continued exposure to heat, the amount of protective material 

 thus deposited in the pores of the wood, although it might be con- 

 sidered to surround each particle of fibre, would not prevent the 

 destructive distillation of the wood by the effect of heat, the result 

 of which would be the disengagement of inflammable vapours from 

 the wood, and its ultimate complete ignition, if maintained for a 

 sufficient period in the vicinity of highly heated or burning matter ; 

 or, if on the other hand, the protective agent employed be conver- 

 tible by heat into vapours possessing the property of extinguish- 

 ing such fire as they may completely surround, such vapours might 

 have the effect of partially or completely extinguishing the fire in 

 a piece of ignited wood, after its removal from the source of heat or 

 fire, but otherwise the volume of vapour generated from the prepa- 

 ration used, would be but slight, as compared with the inflamma- 

 ble vapours evolved from the over-heated wood, and would have 

 no perceptible effect on the combustion of these', while the scorch- 

 ed, or charred, woody fibre would be less efficiently shielded from 

 the effect of flame than by the coating formed from an indestruc- 

 tible preparation. 



It does not therefore appear reasonable to expect more from the 

 most efficient protective coating or impregnating material than — 



1st. That it should considerably retard the ignition of wood, 

 exposed for some length of time to the effect of a high tempera- 

 ture, or of burning matter in its immediate vicinity. 



2nd. That if the vapours which the wood will emit, by con- 

 tinued exposure to heat, become ignited, the flames thus produced 

 shall not readily affect the fibre of the wood, and shall cease almost 

 directly on the removal of the wood from the source of heat ; and 



