44-S Solution of Copal for Varnijh. 



may be counted as they rife from the bottom ; and continue the fame heat till the folution \i 

 completed. 



Camphor a6ts more powerfully upon copal than any fubftance that I have tried. If copal 

 is finely powdered, and a fmall quantity of dry camphor rubbed with it in the mortar, the 

 whole becomes, in a few minutes, a tough coherent mafs. The procefs above defcribed will 

 diffolve more copal than the menftruum will retain when cold. The moft economical me- 

 thod will, therefore, be to fet the veflel which contains the folution by for a few days ; and 

 when it is perfectly fettled, pour off the clear varnifti, and leave the refiduum for a future 

 operation. 



This is the brighteft folution of copal that 1 have feen ; it is an excellent varnifh for pic- 

 tures, arid may, perhaps, be found to be an improvement in fine Japan works ; as the ftoves 

 ufetl in drying thofc articles may drive off the camphor entirely, and leave the copal pure 

 and colourlefs on the work. 



N.B. Copal will 'diffolve in fplrit of turpentine by the addition of camphor with the fame 

 facility, but not in the fame quantity, as in alcohol. 



At the tim& I determined to lay the preceding papers before the fociety, I conceived that 

 the quick and certain manner in which the vehicle dried was one of its advantages; but as 

 that circumftance' has been objeftcd to, and in fome cafes really is a difad vantage, 1 have 

 fince endeavoured to remove that objediion 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 ccrufe, and ftir it continually till the whole is 

 diffolvcd. 



Have ready a pint of the copal-oil-varnifh heated in a fcparate veffel ; pour this by degrees 

 into the hot oil, and ftir them together till all the fpirit of turpentine is diffipated; let it then 

 be fet by till cold, when it will be for ufe. 



It is obvious that as this is a compound of the copal- varnifh with the lead exceptionable of 

 th; drying oils, it will partake of the properties of each of its component parts. It gives lefs 

 brightncfs and durability to colours than the varnifli will, but more than oil : but as it cer- 

 . tainly may be u fed in painting in the fame manner as any other drying oil, and gives more 

 durability and bri^^htnefs to colours than they can derive from any other oil, it is not unrea- 

 fonable to fuppofe that it will prove an advantageous vehicle. 



I have mentioned fpeclfic quantities of the ingredients ; but it is eafy to fee tliat the relative 



proportions may be varied according as it is required to dry fafter or flower. It muft b« 



remarked too, that wherever the mixture is to be made, "both the ingredients Ihould be hot ; 



becaufe if either of them is Cold, the mixtufe becomes turbid, and a part, often the whole of 



..the copal is precipitated : but this inconvenience is avoided by mixing and "boiling them toge- 



rther.as I have diredled. It muft likewife be obferved, that. after fome time a fpontaneous altera- 



■■tign takes place, which diminiftles, and at laft deftroys, the drying quality of this mixture ; 



: and -it will, therefore, be advifeable to ufe It frefh ; or at leaft not to ufe 'it after it has been 



jjDade more than a month, or fix weeks. 



Analyfis 



