I 394 J 



caries. The very air of thefe places abounding 

 with acid, oleaginous, and faline particles, pene- 

 trates and difpofes them to diflblution, even before 

 they are ufed. The mildeft fluids, fuch as nnilk, 

 whey, or even plain water, left to fland in open 

 copper veflels, receive an impregnation of the 

 metal, difcoverable by the volatile alkali. But it 

 is remarkable that the corrofion always begins at 

 the furface, in contadl with the air, and is dif- 

 tinguifhable by leaving a greenifh ring. Such is 

 the power of the air in promoting the a6lion of 

 the menftruum. On this principle, perhaps, may 

 be explained why acid vapours a6t more powerfully 

 on lead and copper than the acids themfelves, con- 

 verting the former more fpeedily into cerufs, the 

 latter into verdegris. 



'■ People generally imagine that the ill efFedls of 

 ^copper are entirely prevented by its being tinned, 

 '''and therefore without hefitation commit to fuch 

 vefTels acid foups, vinegar, lemon-juice, apple- 

 fauce, greens, butter, and other articles equally 

 exceptionable, where they are fometimes fufFered to 

 remain a confiderable time without any fufpicion 

 of danger. But the tin which lines the copper is 

 fo extremely thin that it is foon abraded, or even 

 penetrated by the verdigris, which infinuates itfelf 

 through the pores of the nietal, and at length be- 

 trays 



