j 98 ProceJ-s of preparing Verdigris. [Book VI. 



but fcarcely ad: on it in its metallic ftate. It is ar 

 curious circumflance, which has never been fuffi-.- 

 ciently explained, that vegetable acids act more power- 

 fully on copper when cold than when they are heated. 

 Thus pickles, or even lemon juice, may be boiled in, 

 clean copper veffels without danger; and yet, if left 

 for a few hours, when cold, in copper vefiels, they are 

 apt to contract a metallic impregnation fufficient to 

 produce dangerous effects. This fact has by fome 

 chemifts been attributed to the fleams of the boiling 

 fluid keeping off the air, which is thought to affift the 

 actiop of the acids. 



Verdigris is a very beautiful green ruft or calx of 

 copper, much ufed by painters, and prepared in large 

 quantities near Montpelier in France. The procefs 

 for making verdigris was thus defcribed by M. Mon- 

 net, of the Royal Society of Montpelier, about the 

 year ^750. Vine ftalks, well dried in the lun, are 

 Itemed, during eight days, in ftrong wine, and after- 

 wards drained , they are then put into earthen pots, 

 and wine is pouied upon .them; the pots are kept 

 carefully covered. The wine undergoes the acetous 

 fermentation, which in fummer is finiflied in {even or 

 eight days, but requires a longer time in winter, though 

 this operation is always performed in cellars. When 

 the fermentation is fufficiemly advanced, which may 

 be known by obferving the inner fur face of the lids 

 of the pots, which, during the progrefs of the fermen- 

 tation, are continually wet by the mciliure of the rif- 

 ing vapours, the ftalks are to be taken ou; of the pots. 

 The ftalks are by this method impregnated with all 

 the acid of the wine, and the remaining liquor is only 

 a very weak vinegar. The ftalks are now drained 

 Tome time in bafkets, and layers of them are put into 

 earthen pots with plates of Swedifh copper, fo difpofed 



'that 



