164 PRESERVATION OF METALS USED IN MARINE CONSTRUCTION. 



DISCUSSION. 



Naval Constructor Henry Williams, U. S. N., Member: — Commander 

 Lyon has rendered valuable service in bringing before this Society the question of 

 the corrosion of metals, also in elucidating the electrolytic theory as to its causes 

 and the conditions under which the electrolysis takes place. I believe, however, 

 that few of those present will be willing to accept his statements in toto, for while 

 there is no question that fundamentally he is correct, differences will be drawn as 

 to the conclusions and the interpretation of the various phenomena. 



He treats of a subject that unfortunately has not received much attention 

 from shipbuilders, except in so far as the effects of corrosion have manifested them- 

 selves in necessitating repairs. 



Painting, which is the largest item of expense in the upkeep of ships, is required 

 almost entirely by the necessity for preventing or at least checking corrosion. 

 Commander Lyon states the necessity for proper painting, but unfortunately he 

 places himself in the attitude of regarding the price of a paint as an index of its 

 efficacy. He states also his opinion that the best paint is none too good and should 

 be obtained at any cost. I am unable to agree with his view in these particulars. 

 In my opinion, paint should be selected entirely with a view to its fitness for the 

 purpose for which it is to be used, having in mind always the value of service which 

 it is expected will be rendered. Where it is intended to preserve the metal in inac- 

 cessible locations, it is obvious that within reasonable limits the cost should not be 

 considered in the effort to obtain the most effective paint. On the other hand, if it 

 is a question of painting for decorative effect the exterior surface of a ship in a loca- 

 tion that is easily accessible and that has already a number of coats of paint on it, 

 consideration should be given to the probable time the paint will be expected to 

 last before repainting ,and a cheap paint should be appUed, if that will meet the 

 requirements. However, I wish to emphasize my idea that the price is no index of 

 quality of paint. I think often a cheap paint, properly compounded, has greater 

 merit than the conventional high-grade paints made with linseed oil, turpentine, 

 lead and zinc. 



As regards the question of the use of zinc protectors, Commander Lyon appears 

 to have lost sight of the fact that these zincs are put on for the purpose of protect- 

 ing the ste«l from the electrolytic action produced by copper alloys used in sea 

 chests and propellers. He states his experiments were by way of proving that the 

 zinc had no effect in reducing the corrosion of steel alone. In order to demonstrate 

 this point clearly, I have had prepared two small bars of steel with smaller bars of 

 copper attached. On one of these couples the copper was surrounded by a frame of 

 zinc. All were submerged in salt water, and the conditions may be regarded as 

 exhibiting in an aggravated form the action that takes place continually between 

 the steel of the ship and the copper in under-water fittings, as well as the protective 



