SJX WILLIAM SIEMENS, F,R,S. 309 



attaching to it, viz., that iron ships would foul very quickly. The 

 means hitherto adopted were clearly insufficient as a remedy for 

 til-- I'vil. The poisonous compounds spoken of he thought might 

 be fairly dismissed from their minds as being playthings iu con- 

 nection with a very serious subject. Copper sheathing appeared 

 Very inapplicable, for when in contact with iron it invariably had 

 the effect of corroding it, because the salt water would percolate 

 between the two metals ; and moreover the copper sheathing itself 

 would fail in its purpose from the want of exfoliation of the 

 surface. With regard to the insulation of the two metals by the 

 interposition of a wooden layer, he agreed with Mr. Heed, that the 

 iron would be effectually protected so long as no metallic contact 

 took place. The moisture between the two metals would not be 

 sufficient to set up galvanic action, the battery would be in the 

 condition of an " open " battery, not a " closed " one. There was, 

 however, great difficulty in maintaining perfect separation, because 

 wire, even of T V inch gauge, was sufficient to transmit a consider- 

 able current, and produce a great amount of mischief upon the 

 iron, and it was hardly to be supposed that the two enormous 

 surfaces could be long kept perfectly separated without metallic 

 connection being formed between them. What surprised him, 

 somewhat, on hearing this paper, was the very slow rate of ex- 

 foliation of the zinc. He had himself made experiments on 

 the action of the salt water upon zinc in contact with iron ; and 

 he found the zinc acquired weight up to about three months, 

 but after that period a sensible diminution in weight took 

 place. The author of the paper stated that the amount of the 

 oxidation of the zinc was not more than If oz., or 2 oz., even if 

 the exfoliation was made more active by an increased galvanic 

 action. It would be interesting to ascertain whether there was 

 any increased exfoliation when the ship was in motion. No doubt 

 there would be some increase, but experiment would determine the 

 amount. No doubt, chemically, zinc sheathing would protect the 

 bottom of the vessel entirely, for even if a sheet of the metal were 

 displaced, there would still be the influence of the zinc in contact 

 with the iron. So far, then, the invention appeared to him to be 

 an exceedingly promising one, and one which he thought should 

 certainly be tried seriously by the Admiralty. With regard to the 

 observations of Mr. Reed, he thought he had stated the case very 



