ae 
64 Procefi to diffilve Copal i in Spirit of Turpentine. 
folve; though, while in a liquid ftate, it feemed to poflefs alf 
the properties of a gum. 
As the proceffes by which I diffolved the amber and copat 
to make the oil varnifhes, are to be found in many books, 
and as it will be better for artifts to purchafe tian attempt 
to make thofe varnifhes, it can fearcely be thought neceffary 
to aetail thole proceffes here: but, as I believe the methods 
‘by which I diffolved the copal in fpirit of turpentine. and 
fpirit‘ef wine are not known, I fhall now fubjotn them. 
To diffilve Copal in Spirit of Turpentine. 
N.B. Whatever quantity is to be diffolved, fhould be put 
into a glafs veffel capable of containing at leaft four times as 
much, and it fhould be high in proportion to its breadth. 
Reduce two ounces of copal to {mall pieces, and put them 
into a proper veffel. Mix a pint of fpirit of turpentine with 
1-8th of fpirit of fal-ammoniac ; fhake them well together ;- 
put them to the copal; cork the glafs, and tie it over with a 
ftring or wire, making a fmall hole through the cork. Set: 
the glafs in a fand-heat fo regulated as to make the contents 
boil-as quickly as poflible, but fo gently that the bubbles 
may be counted as they rife from the bottom. ‘The fame 
heat muft be kept up exactly till the folution is complete. 
- It requires the moft accurate attention to fucceed in this 
operation. After the fpirits are mixed, they fhould be put to 
the copal, and the neceffary degree of heat be given as foon 
as poffible. It fhould likewife be kept up with the utmoft 
regularity. If the heat abates, or'if the fpirits boil quicker 
than is dire&ted, the folution will immediately ftop, and it 
will afterwards be in vain to proceed with the fame mate- 
rials; but if properly managed, the fpirit of fal-ammonia¢ 
will be feen gradually to defeend from the mixture and attack 
the copal, which fwells and diffelves, except a very fall 
quantity which remains undiffolved. 
It is of much confequence that the veffel fhould not be 
opened till fome time after it has been perfectly cold. It has 
twice happened to me, on uncorking the vefiel when it was 
not warm enough to affect the hand, that the whole of the 
contents were blown with violence againft the cieling. It is 
hikew ife 
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