204 Sir H. Davy's additional Experiments 



modes of preventing the chemical action of fluid menstrua, 

 such as saHne solutions, or sea-water containing air, on cop- 

 per, by the contact of more oxidable metals*. 



For some months I have been engaged in a series of new 

 experiments on this subject, so important to the navigation 

 and commerce of the country : and through the liberal and 

 enlightened views of Loi-d Melville and the Lords of the Ad- 

 miralty, who desired the Commissioners of the Navy Board 

 and of the Dock-yards to give me every assistance in their 

 power, and all the facilities which our magnificent naval es- 

 tablishments at Chatham and Portsmouth furnish, I have 

 been enabled to conduct my operations upon a very large 

 scale. 



At this advanced period of the session, it will be impossible 

 for me to give more than a very short notice of experiments 

 which have been tried under a great variety of circumstances, 

 and the details of which would occupy some hours in reading ; 

 but I cannot deprive myself of the pleasure of stating the sa- 

 tisfactory and conclusive nature of the results, many of which 

 have even surpassed my expectations. 



Sheets of copper, defended by from ;j'(jth to yxj'o u^h part of 

 their surface by zinc, malleable and cast iron, have been ex- 

 posed, for many weeks, in the flow of the tide in Portsmouth 

 harbour, and their weights ascertained before and after the ex- 

 periment. Where the metallic protector was from -^^ to yy^, 

 there was no corrosion nor decay of the copper. With smaller 

 quantities, such as from ^^^tOyi^, the copper underwent a loss 

 of weight, which was greater in proportion as the protector 

 was smaller : and as a proof of the universality of the princi- 

 ple, it was found that even joVn^^ P^*^^ ^^ ^^^^ ^^^^ saved a cer- 

 tain proportion of the copper. 



The sheeting of boats and ships protected by the contact 

 of zinc, cast and malleable iron in different proportions, com- 

 pared with those of similar boats and sides of ships unpro- 

 tected, exhibited bright surfaces, whilst the unprotected copper 

 imderwent rapid corrosion, becoming first I'ed, then green, 

 and losing a part of its substance in scales. 



Fortunately, in the course of these experiments, it has been 

 proved that cast iron, the substance which is cheapest and 

 most easily procured, is likewise most fitted for the protec- 

 tion of the copper. It lasts longer than malleable iron or 

 zinc; and the plumbaginous substance which is left by the 

 action of sea-water upon it retains the original form of the 

 iron, and does not impede the electrical action of the remain- 

 ing metal. 



* Phil. Trans. 1824, Part I. or Phil. Mag. vol. Ixiv. p. 30. 



1 had 



