1 824 .] Discovery to Copper Vessels usedfor Culinary Purposes. 1 79 



copper were plunged into equal quantities of acetic acid, one of 

 the plates projecting one-third above the fluid, while the other 

 was wholly immersed in it. The blue crystals began to form on 

 the upper part of the first piece of copper long before any effect 

 could be perceived in the plate that was totally immersed. In 

 10 days the two plates were removed, the crystals were dissolved 

 from the one that was partially immersed, when it appeared that 

 the loss of weight in this was at least as considerable as in the 

 plate that had been wholly immersed. 



11. A plate of copper was half immersed in acetic acid satu- 

 rated with potash ; the upper part of the copper was scarcely 

 affected ; it was only slightly tarnished and a few minute crystals 

 formed upon it at a little distance from the level of the fluid ; 

 the fluid remained clear and had acquired a bright blue tinge. 



12. In order to observe how far the action of acetic acid 

 upon tin, when copper is immersed in the same fluid, depends 

 upon the extent of surface, two equal plates of copper were 

 immersed in equal quantities of acetic acid; in one a sheet of 

 tin was applied to the copper of three square inches in extent, 

 in the other of one square inch only ; in ten days they were 

 examined, when the two sheets of tin were found to have lost 

 very nearly the same weight. 



13. In order to observe whether the contact, of tin preserves 

 copper from the action of oil or fat, two plates of copper were 

 smeared with grease, the surface of one of them being half 

 covered with a sheet of tin; nine days elapsed before any effect 

 could be perceived in either of them, at the end of this time a 

 faint shade of green was visible in some parts of the grease on 

 the uncoated copper, and the colour has since continued to 

 increase and to extend itself; no change has taken place on 

 any part of the partially coated copper. 



The practical conclusion that we may draw from the above 

 experiments is sufficiently obvious ; we find that copper is pre- 

 served by tin from the action of acetic acid in the same manner 

 as it is from that of sea water; but that we cannot make use of 

 this principle in vessels intended for culinary purposes, in con- 

 sequence of the volatile nature of the acid. Most of the phe- 

 nomena that were observed might have been anticipated from 

 our previous knowledge with respect to the galvanic action of 

 metals upon each other, and upon the saline solutions in which 

 they are immersed. Such are the increased solubility of both 

 the copper and the tin when placed in the same vessel of acetic 

 acid, and the deposition of the dissolved copper on the surface 

 of the tin ; the greater quantity of the crystallized acetate of 

 copper formed when the half immersed plate of copper had a 

 sheet of tin plunged in the same fluid, and the small quantity 

 of the acetate which was produced when the acid was rendered 

 less volatile by being saturated with potash. 



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