1826.] Presei'vation of Metals hi/ Electro-chemical Means. 255 



before was rapid, is now almost at an end; and a few drops 

 more of the solution of potassa produces a perfect equilibrium ; 

 so that neither of the metals undergoes any change, and the 

 whole system is in a state of perfect repose. By making the 

 fluid in the glass containing the iron still more alkaline, it no 

 longer corrodes ; and the green tint of the sea water shows that 

 the copper is now the positively electrified metal ; and when the 

 solution in the glass containing the iron is strongly alkaline, the 

 copper in the other glass corrodes with great rapidity, and the 

 iron remains in the electro-negative and indestructible state. 



I began this paper by some observations upon the nature of 

 the processes by which copper sheeting is destroyed by sea 

 water, and on the causes by which it is preserved clean, or 

 rendered foul by adhesions of marine vegetables or animals ; I 

 shall conclude it by some further remarks on the same subject, 

 and with some practical infeiences and some theoretical elucida- 

 tions, which naturally arise from the results detailed in the fore- 

 going pages. 



The very first experiment that I made on harbour-boats at 

 Portsmouth, proved that a single mass of iron protected fully 

 and entirely many sheets of copper, whether in waves, tides, or 

 currents, so as to make them negatively electrical, and in such 

 a degree as to occasion the deposition of earthy matter upon 

 them ; but observations on the effects of the single contact of 

 iron upon a number of sheets of copper, where the junctions and 

 nails were covered with rust, and that had been in a ship for 

 some years, showed that the action was weakened in the case 

 of imperfect connexions by distance, and that the sheets near 

 the protector were more defended than those remote from it. 

 Upon this idea I proposed, that when ships, of which the copper 

 sheeting was old and worn, were to be protected, a greater pro- 

 portion of iron should be used, and that if possible it should be 

 more distributed. The first experiment of this kind was tried on 

 the Sammarang, of 28 guns, in March, 1824, and which had 

 been coppered three years before in India. Cast iron, equal in 

 surface to about -^'-^ of that of the copper was applied in four 

 masses, two near the stern, two on the bows. She made a voyage 

 to Nova Scotia, and returned in January, 1825. A false and 

 entirely unfounded statement respecting this vessel was 

 published in most of the newspapers, that the bottom was 

 covered with weeds and barnacles. I was at Portsmouth soon 

 after she was brought into dock : there was not the smallest 

 weed or shell-fish upon the whole of the bottom froui a few feet 

 round the stern protectors to the lead on her bow. Round the 

 stern protectors there was a slight adhesion of rust of iron, and 

 upon this there were some zoophytes of the capillary kind, of an 

 inch and a half or two inches in length, and a number of minute 

 barnacles, both Lepas anatifera and Balanus tintinnabulum. 



