66 Procefs to diffalue Copal in Alcohol. 
manner in which the vehicle dried, was one of its adyan- 
tages. But as that circumftance has been objeéted to, and 
in fome cafes really is a difadvantage, I have fince endea- 
voured to remove that obje€tion by the following procefs : 
Put a pint of nut or poppy oil into a large earthen veffel ;. 
make it boil gently upon a flow fire; put in by degrees two. 
ounces of cerufe, and ftir it Setiargite till the whole is dif 
folved. 
Have ready a pint of the copal oil varnifh heated in a fe- 
parate veffel ; pour this by degrees into the hot oil, and ftir 
them together till all the {pirit of turpentine is diflipated ; let. 
it then be fet by till cold, when it will be fit for ufe. 
It is obvious, that, as this is a compound of the copal var- 
nifh with the leaft exeeptionable of the drying oils, it will 
partake of the properties of each of its component parts. It 
gives lefs brightnefs and durability to colours than the varnifh | 
will, but more than oil: but as it certainly may be ufed int 
painting in the fame manner as any other drying oil, and 
gives more brightnefs and durability to colours than they 
can derive from any other oil, it is not unreafonable to ap 
pofe that it will prove ani advantagcous vehicle. 
I have mentioned fpecific quantities of the ingredients 
but it is eafy to fee that the relative proportions may be ya- 
ried according as it is required to dry fafter or flower. It 
mutt be remarked too, that whenever the mixture is to be 
made, both the ingredients fhould be hot; becaufe, if either 
of them 1s cold, the mixture becomes turbid, and a part, 
often the whole of the copal, is precipitated + but this incon- 
venience is avoided by mixing and boiling them together, as 
I have dire&ed. It mut likewife be obferved, that after 
fome time a fpontaneous alteration takes place, which di~ 
minifhes, and at laft deftroys the drying quality of this mix- 
ture: it will therefore be advifable to nf it freth, or at leatt 
not to ufe it after i it has been made more than a month or 
fix weeks, 
XIV, Proce(s 
