UG8 On Preventing the Decay of Wood . 
dry, so as to sink deeply into its pores ; and though at 
first they are apparently somewhat greasy when cold, yet 
after some days they make a firm varnish, which does not 
come off on rubbing. When it is required to give beauty 
to the work, colouring matters may either be added to 
the mixture, or afterward applied over it in form of com 
mon paint. Two coats of the composition should always 
be given; and in all compound machinery, the separate 
parts should be so varnished before they are put toge- 
ther ; after which it will be prudent to give a third coat 
ing to the joints, or to any other part which is peculiarly 
exposed to the action of moisture, such as water-shoots, 
flood gates, the beds of carts, the tops of posts and rails, 
and all timber which is near or within the ground. Each 
coat should be dry before the parts are joined, or the last 
coat applied. 
These compositions are equally efficacious in keeping 
iron from decay by rusting. They might also be very 
advantageously employed in rendering water-tight the 
plaister which is used to case the outside of the arches of 
vaults unsheltered by roofs, provided the mortar were 
made perfectly dry, and the covering of the arch brought 
up to an angle, instead of making it follow the form of 
the arch in an elipse or the segment of a circle. 
It is necessary to mention, that compositions made of 
hot oil should for the sake of security be heated in metal- 
lic or glazed earthen vessels in the open air. For when- 
ever oil is brought to the boiling point, or 600° of Fah- 
renheit’s thermometer, the vapour immediately catches 
fire, although not in contact with any flame ; anti though 
a lower degree of temperature than that of boiling should 
be used in this process, it is not always practicable ei- 
ther exactly to regulate the heat, or to prevent the over, 
flowing of the materials, in either of which cases, were 
