176 Dr. Bostuck on the Applicability of Sir H. Davy's [Sept. 



the electro-positive energy of the base is greater. Thus, in the 

 salts with a basis of potash they are feeble, and often only per- 

 ceptible by a momentary start of the mercury when the circuit 

 is completed. In those of soda, ammonia, baryta, strontia, and 

 lime, they are more distinct, while in salts of magnesia, alumina, 

 and the metallic oxides, their influence is still more sensible. 

 On the other hand, under solutions of the pure alkalies and 

 alkaline earths, the mercury remains quite quiescent, or at 

 most is only agitated by feeble and irregular motions, depend- 

 ing on causes not now in contemplation. 



( To be concluded in our next.) 



Article III. 



On the Applicability of Sir H. Davy's Discovery to Copper 

 Vessels employed for Culinary Purposes. By Dr. Bostock, FRS. 



(To the Editors of the Annals of Philosophy.) 



GENTLEMEN, Upper Bedford-place, Aug. 2, 1884. 



The following experiments were undertaken in consequence 

 of a conversation that took place on the subject of Sir H. Davy's 

 interesting discovery of the mode of preserving copper from the 

 action of sea water. The question was proposed, how far the 

 same principle was applicable to the copper vessels that are 

 employed for culinary purposes, whether it be necessary to have 

 their interior surface completely lined with tin, or whether it 

 might not be sufficient to have a portion of it only covered, 

 which might protect the remaining part. 



1. Three discs of copper were immersed in vinegar ; the first, 

 without any addition ; the second, with one of its surfaces 

 covered with a sheet of tin; the third, with a similar sheet of 

 tin immersed in the fluid, but not in contact with the copper. 

 After an interval of five weeks, the fluid belonging to the first 

 disc was of a glaucous colour, and was found, by the action of 

 ammonia and of potash, to contain a considerable quantity of 

 copper dissolved in it. The vinegar in the two other vessels 

 was opaque, and contained a considerable quantity of a light- 

 brown sediment, which appeared to be an impure acetate of tin. 

 The plates of tin were evidently much eroded, and the one 

 which was not in contact with the copper had a coating of 

 copper deposited upon its surface; no copper could be detected 

 in either of the fluids. 



The general fact being thus ascertained, the phenomena were 

 examined with more accuracy. A colourless acetic acid was 

 employed of such strength that 100 grains of it were neutralized 

 by 66 grains of crystallized bicarbonate of potash ; by the test 



