ON COPAL VARNISHES. 151 



falfe membrane with a pair of tweezers, and difcovered be* 

 hind it, the tympanum, quite found and entire, I thought it 

 probable that, in the fecond operation, I had only touched 

 this falfe membrane. I immediately perforated the true one, Repetition of 

 and was furprized (as well as my brother who attended this jJj^j^^P^^^^'^^"^^ 

 operation), to find tliat, although Mr. F. had already learnt fimilgr pheno- 

 again to hear with the right ear, yet the reftoration of his hear* "*^"^« 

 ing in the left, occafioned in him the fame eiFeds of wonder, 

 and of exceffive fenfibiUty to the lead unexpected noife, which 

 he had experienced after the firft operation. This inconveni- 

 ence, however, has not been of longer duration in this ear, 

 than it had been in the other." 



III. 



Zetter from Mr. Timothy Sheldrake, expofing the Errors 

 of M. Tingry refpeding Copal Varnijkes; with fame farther In- 

 J!ru6iions concerning the fame, 



(Received OB, 16, 1804-.) 



To Mr. NICHOLSON. 

 SIR, 



TINGRY, profeflbr of chemiftry, &c. in the academy Tingry in his 

 of Geneva, has publiOied a treatife on the art of making and y^^l^^^^""^ 

 applying varnifhesj with new obfervations and experiments 

 on copal, &c, &c. A tranflation of that work has lately 

 appeared here, and at p. 157 of that tranflation I find the fol- 

 lowing paflage. 



" Mr. Timothy Sheldrake mentions camphor as a medium 

 for difTolving copal in eflfence* and alcohol. He gives alfo an- 

 other procefs, in which ammonia (volatile alcaline fpirit offal 

 ammoniac) in the proportion of an eighth part of the eflence 

 employed, is fubftituted in the room of camphor. 



*' Exper, I, Of the three procefles which he defcribes, I repeated Shel- 

 repeated two: thofe which regard the folution of copal in ef-f" dH^lving^ 

 fence and in alcohol by a mixture of camphor. That with ef- copal in eflence 

 fence did not fUcceed. The author himfelf announces that he ^5/'!,"°'^"*' 



♦ Throughout the book this word islifeil to defcribe what we call 

 fpirit of turpentine. 



always 



