ON COPAL VARNISHES. 157 



and copal which he had thrice attempted in vain to diflblve; 

 and at the fame time fubjeftihg another portion of ray own 

 materials to the fame procefs in every particular : I fucceeded 

 in both inftances : the only difference was that the folution 

 which I produced from the materials which had been tried by 

 my friend was not fo vifcid as that which was obtained from 

 the freih materials. 



As the procefs which I have ufed for fome time pad is dif- Improve*! 

 ferent from and better than that wliich I communicated to the ^'^^ 

 Society, and has been pubiiftied in their Tranfa^ions, I truft 

 you will excufe me for defcribing it here; it is fuch an one as 

 may be fuccefsfully ufed by any perfon upon a common fire, 

 without any danger, and which any man of fcience, or who 

 may chufe to adopt in a large way, may eafily modify fo as to 

 anfwer his purpofe. ' '■' 



Provide aflrong vefTel made of tin or other metal, it fhould Safe and eafy 

 be fhaped like a wine bottle and capable of holding two quarts ; ^ ^.^ j ^^^^l 

 it will be convenient to have a handle ilrongly rivetted to thenifli. 

 neck; the neck fliould be long and have a cork fitted to the 

 mouth, but a notch or fmall hole fliould be made in the cork, 

 that, when the fpirit is expanded by heat, a (mall portion may 

 force its way through the hole, and thus prevent the velfel from 

 burfting. 



Diffolve half an ounce of camphor in a quart of fpirit of tur- 

 pentine, and put it into the vefTel ; take a piece of copal the 

 fize of a large walnut, reduce it to coarfe powder or very 

 fmall pieces ; put tliem into the tin bottle, faften the cork down 

 with a wire, and fet it as quick as poffible upon a fire fo brifk 

 as to make the fpirit boil almoft immediately; then keep it 

 boiling very gently for about an hour, when fo much of the 

 copal will be difTolved as will make a very good varnifli ; or, 

 if the operation has been properly begun, but enough copal 

 has not been diflblved, it may be again put on the fire, and by 

 boiling it (lowly for a longer time, it may be at laft brought to 

 the confiftence defired. 



The rationale of the operation I believe will be nearly as Explanation of 

 follows : copal and camphor have fo firong an affinity for each ti^« procefs j 

 other, that when feparately powdered and th6n rubbed toge- 

 ther, the copal abforbs the camphor, fwells, foftens, and be- 

 comes one coherent mafs; nor when once united do they eafily 



feparate 



