i66 PRESERVATION OF METALS USED IN MARINE CONSTRUCTION. 



regarding the price of a paint as an index of its efficiency nor does he believe that a 

 careful reading of the paper justifies such conclusion. His intent was to lay stress 

 on the use of the proper paint for the service required of it regardless of the cost. 

 If a cheap paint will give better service under a certain condition than a more 

 expensive one then use it by all means, but use the proper paint under any circum- 

 stances. The author believes with the critic that the most effective paint for the 

 purpose is the one to use, but does not agree with him in saying that a cheap paint 

 properly compounded has of necessity greater merit than the standard paints. 

 The author has not lost sight of the fact that zincs are put on for the purpose of 

 protecting the steel from the electroljrtic action produced by copper. He stated 

 on page 152, top Une, that in his experience zincs do not stay in the bottom below sea 

 chest openings (these chests are of composition connected to steel), and that the 

 corrosion around these chests is no more noticeable than that around other similar 

 openings if the steel in the vicinity is properly painted. He knows full well that 

 bare steel connected by good metalUc contact to copper or composition will have 

 its corrosion increased by such contact when immersed in any sea or distilled water 

 at ordinary temperatures. 



Had the constructor carried his test as that he showed for a period of thirty 

 days, he would probably have found that, after the zinc had become covered with 

 zinc oxide, the zinc-protected piece would have been in as bad or worse condition 

 than the unprotected one. The author in his experiments considered this due to the 

 fact that the zinc oxide added to the corrosive effect of the copper. A piece of zinc 

 (rolled for boiler use) and a piece of American ingot iron, in one case, and steel, in 

 another, connected by a copper wire, screwed hard into each, protected the iron 

 and steel for four days; in distilled water by the end of seventeen days the pro- 

 tective effect of the zinc was entirely lost, and at the end of thirty days the steel 

 and iron connected to the zinc had lost more per unit of area than similar pieces 

 of the same irons and steels similarly connected to themselves in the same water. 



If steel is galvanized in such a way that a complete coating, impervious to 

 water, is obtained and the coating is thick enough to stand the corrosion on it as 

 long as the ship lasts, it is a good thing to use. In the present state of galvanizing 

 the above ideal condition is very seldom obtained. The author's chief objection to 

 galvanized fittings and piping on board ship is that when the zinc, is once gone it 

 cannot be renewed and the ship's material is damaged more where it is gone by the 

 presency of zinc oxide than it would have been had the zinc coating not been used. 



The statement of the constructor that the difficulty due to corrosion in salt 

 water piping on U. S. naval vessels have been solved effectually by use of lead- 

 lined piping is seriously questioned. There is the same objection to this method 

 as to that of galvanizing. Unless the piping in all of its parts is perfectly lined 

 more harm than good is done the piping. 



More can be done to prevent corrosion of piping by seeing that the pipes are 

 made of good homogeneous metal, properly heat-treated in the finished product, 

 and then properly fitted, than can ever be done by lining with lead, zinc, or lacquer. 



