PRESERVATION OF METALS USED IN MARINE CONSTRUCTION. 163 



one ten-thousandth normal concentration of alkahne solutions decreased 

 the rate of corrosion of irons and steels slightly below that in distilled water 

 and caused no pitting, while the one one-thousandth and one-hundredth 

 concentrations increased the rate above that and caused very active local 

 corrosion or pitting until the 2.6 per cent normal concentration was reached, 

 when all corrosion stopped. 



Cement washing the plates of drinking water tanks has its advan- 

 tages but the washing must be done with great care, will not stick to paint, 

 and is not durable. It must be watched carefully and renewed frequently. 



The Cumberland Electrical Process appears to be the only way of 

 preserving the interior surfaces of water-carrying pipes and circulating 

 systems. It is on the same principle as the alkaline theory. The potential 

 of the water is raised to a point higher than any point of the system by 

 sending a current from an outside source to it from an easily replaced anode. 

 The current must be at a potential high enough to raise that of the water 

 to the proper point and must be kept on continuously. If the potential 

 of the water drops below that of the metal at any point it will pit or corrode 

 at that point similar to the alkaline solutions. This system will give excellent 

 results when properly installed and properly attended. 



The preservation of copper, composition or iron piping on board 

 ships in the flushing, condenser and refrigerator circulating systems can be 

 maintained by the Cumberland process if run by some electrical source other 

 than the main power system of the vessel. This process has many draw- 

 backs and requires constant attention. Except by making the piping and 

 tubing of the best and most homogeneous metal obtainable, having it properly 

 made and the finished article properly heat treated and fitted, it seems to 

 be the only practicable plan available. It is sure if properly controlled. 



The wrought iron, steel, and other iron manufacturers make many 

 claims for their various materials, claiming maximum durability and resist- 

 ance to rust. In thirty months of continuous testing of these various 

 products it was interesting to note that in many cases one would show much 

 better than another, but by varying solution, temperature, and treatment 

 they could all be made to give practically similar results. 



In waters that are made non-corrosive to iron or steel by alkaline 

 solutions, their metallic contact with copper and other metals lower than 

 iron in the potential series does not start corrosion, nor does the addition 

 of free oxygen. 



These notes and observations are made after thirteen years of active 

 sea service as both an engineer and line officer in the U. S. Navy, and after 

 nearly three years' work on corrosion problems at the U. S. Naval Academy. 

 The writer offers them for whatever of interest they may be to anyone. 



