3G3 
On Preventing the Decay of Wood . 
perabundance of the oil of turpentine. In this state it 
may, in various ways, be more readily acted on by water 
and air. W e know, that the properties of what are call- 
ed unctuous or fat oils are much changed by the admix- 
ture of the volatile or essential oils. On this principle we 
succeed in getting grease out of woollen cloths by oil of 
turpentine ; but whether the same change is produced on 
the drying oils, I have not learned. 
It appears, then, that these drying oils either by them 
selves, or boiled with metallic oxides, will form a var- 
nish on wood ; but it may be questioned how far the co- 
louring matters, with which they are usually mixed, con- 
tribute to increase their preservative power. I do not, 
however, deny, that they may be serviceable in this and 
other views. They might be supposed to enable the oil 
to lay firmer hold, as it were, on the wood ; and they may 
serve to increase the thickness of the defensive covering. 
The first of these points is of some importance ; for we ob- 
serve that the paint on street doors, which is become 
thick by frequent incrustation, is apt, from the strong in- 
fluence of the summer’s sun, to separate from the polished 
wood beneath, and rise in large blisters ; probably in 
consequence of a greater expansion in the crust itself 
than in the subjacent wood. Mere, therefore, the colour- 
ing matter of the paint fails to produce the desired effect; 
and as to the second end, or that of increasing the thick- 
ness of the covering, that may, probably, be much more 
effectually accomplished than by the mere addition of 
pigments, some of which are capable of chemical decom- 
position, and all are costly. This purpose an ingenious 
artist has of late attempted to answer, by recommending 
an admixture of road-dust; and for that and other means 
of reducing the price of paints, has obtained a premium 
from the London Society of Arts. However just the ge- 
neral principle in this case may be, the application is 
