COPAL, 2$S 



from the rhus copallinum, but it is of an inferior quality to that 

 brought from Guinea and Spanish America. 



The specific gravity of copal varies from 1*045 to 1*139. Mr, 

 Hatchett found it soluble in alkalies and nitric acid, with the usual 

 phenomena. 



Copal varnish used by the English japanners is made as follows. 

 Four parts by weight of copal in powder are put into a glass ma- 

 trass and melted. The liquid is kept boiling till the fumes con- 

 densed upon the point of a tube, thrust into the matrass, drop to 

 the bottom of the liquid without occasioning any hissing noise, as 

 water does. This is a proof that all the water is dissipated, and 

 the copal has been long enough melted. One part of boiling hot 

 linseed oil (previously boiled in a retort without any litharge) is 

 now poured into it, and well mixed. The matrass, if then taken 

 off the fire, and the liquid, while still hot, is mixed with about its 

 own weight of oil of turpentine. The varnish thus made is trans- 

 parent, but it has a tint of yellow, which the japanners endeavour to 

 conceal by giving the white ground on which they apply it a shade 

 of blue. It is with this varnish that the dial plates of clocks are 

 covered, after having been painted white. 



A correspondent in the 17th volume of the Transactions for the 

 Encouragement of Arts, &c. informs us, that copal may be dis- 

 solved in spirit of turpentine by the following process : having 

 prepared a glass vessel, of sufficient capacity to contain at least 

 four times the quantity intended to be dissolved, and which should 

 be high in proportion to its breadth, reduce two ounces of copal to 

 small pieces, and put them into the vessel. Mix a pint of spirit of 

 turpentine with one-eighth of spirit of sal ammoniac ; shake them 

 well together ; pour them on the powder, cork the glass, and tie it 

 over with a string or wire, making a small hole through the cork. 

 Set the glass in a sand heat, so regulated as to make the contents 

 boil as quickly as possible ; but so gently, that the bubbles may be 

 counted as they ascend from the bottom. The same heat must be 

 kept up exactly, till the solution is complete. It requires the most 

 accurate attention to succeed in this operation ; for, if the heat 

 abate, or the spirits boil quicker than is directed, the solution will 

 be impeded, and it will afterwards be in vain to proceed with the 

 same materials ; but, if properly managed, the spirit of sal ammo- 

 niac will be seen gradually to descend from the mixture, and at- 



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