152 



ON COPAL VARNISHES. 



Bor with alcohol. 



He infers that 

 the compounds 

 tnuft be imper- 

 feft and not 

 varnifhes. 



Obfervations 

 in replyt 



Mr. Tingry 

 ought not to 

 have oppofed 

 fpeculation againft 

 faHi, 



always failed, except when he obtained the eflence from apo* 

 Ihecaries hall. It appears that this eflfence had by chance all 

 thofe effential qualities which we endeavour to give it by time, 

 and ftill more fpeedily by the influence of light. 



" Exp. II. The fame experiment repeated with pure alco- 

 hol was attended luith too little fuccefs to make the refult be con- 

 Jtdered as a varnijh. The alcohol appeared milky, and the 

 copal formed at the bottom of the veflel a mafs which did not 

 feem to have decreafed in volume. Next morning the inter- 

 pofed part of the copal, which altered the limpidity of the al- 

 cohol, was precipitated, and adhered to the (ides of the glafs. 

 The procefs I have defcribed for fpirituous tindure of amber 

 would give more hopes of fuccefs without any intermediate 

 fubftance." 



" In regard to the means propofed by the medium of am- 

 monia, the faline nature of that liquid, if the procefi fucceeds, 

 will not admit of the produ6l being placed in the clafs of var- 

 niflies deftined for delicate painting. It is a kind of faponace- 

 ous compound, the ufe of which is not to be recommended in fuch 

 cafes," 



The paflTage above quoted undoubtedly relates to a paper 

 which I communicated feveral years ago to the Society for the 

 Encouragement of Arts, &c. 



This paper was wholly tranfcribed * into fome periodica] 

 publications, and parts of it into others; it may therefore be 

 neceflary to obferve that when reference is made to the original 

 paper, it muft be underftood to mean as it was printed in the 

 Society's Tranfadions, and not to any imperfect extracts that 

 may have been made from it. 



Mr. Tingry (hould have been fenfible of the danger in op- 

 pofing a conje<3ure or opinion purely fpeculative , to what is de- 

 fcribed as a fadl that had been demonjirated by experiment. Since 

 it is more probable that the conjecture fliould be unfounded, or 

 the opinion untrue, than that a man Ihould forfeit his reputation 

 with the public by relating that, as having been demonftrated 

 by experiment, which the perfon who contradicts him fays 

 cannot, in the nature of thjngs be true, even if the procefs 

 Jucceeds : As it is the intention of your valuable Journal to pro- 

 mote the caufe of fcience, and as that caufe will be as etfe6^- 



* Sec our Journal, I, 250. 



ually 



