178 Dr. Bostock on the Applicability of Sir H. Davy's [Sept. 



being placed opposite to the copper, or being in contact with it, 

 the quantities of tin dissolved were respectively as the numbers 

 10, 25, and 9. 



7. I next wished to examine the effect of the vapour of acetic 

 acid upon copper ; for this purpose a sheet of polished copper 

 was half immersed in acetic acid, so that an inch of it was 

 above the level of the fluid. In six days the fluid was tinged 

 blue ; the part of the copper in the acid did not appear much 

 affected, and there was a clean bright band of '2 inch above the 

 fluid ; above this was a considerable crust of dark-blue crystals 

 which covered the upper part of the plate, gradually becoming 

 less dense, until towards the top it had the appearance of a thin 

 sprinkling of a fine powder; the colour also gradually changing 

 from a deep blue to a light bluish green. 



8. A plate of copper weighing 76*8 grains was partially 

 immersed in acetic acid, a sheet of tin weighing 6 grains being 

 placed opposite to it, and completely immersed in the fluid. In 

 seven days, the copper, with the adhering crust, had gained in 

 weight -2 grain : it was then immersed in water, so as to dissolve 

 the crust, when it was found to have lost "3 grain, making the 

 whole weight of the crystals '5 grain. The disposition of the 

 crystals was as follows : the part of the copper that was 

 immersed in the acid retained its polished appearance ; at the 

 surface of the fluid was a very fine black line, above this was a 

 space of rather more than ■ 1 inch as bright and clean as the part 

 immersed : above this there was a pretty well defined zone of 

 dark-blue crystals, of nearly "2 inch in breadth, while the 

 remainder of the copper was covered with a greenish, powdery 

 matter, more in quantity near the crystals, and gradually dimi- 

 nishing to the upper edge. 



9. A similar experiment was performed, except that one of 

 the surfaces of the copper was half covered with a sheet of tin, 

 the upper edge of the tin coinciding with the level of the fluid ; 

 the copper weighed 74*5 grains, and the tin 10 grains. After 

 immersion for seven days, the copper had *6 grain of the crys- 

 talline matter adhering to it. The disposition of the crystals on 

 the coated side of the copper was so far similar to that in the 

 last experiment, that there was the clean space of about '1 inch 

 above the fluid, next the zone of dark-blue crystals, like those 

 in iNfo. 8, but more than twice their breadth, while above these 

 crystals the upper part of the copper was nearly clean. Chi the 

 uncoated surface of the copper there was a pretty distinct arch 

 of crystals passing between the two upper corners of the tin, and 

 rising about - 5 inch above the level of the fluid. The tin was 

 considerably eroded, and exhibited much of the moiree appear- 

 ance. 



10. In order to compare the effect of acetic acid upon copper 

 in the liquid state and in that of vapour, two similar plates of 



