114 PROF. CRACE-CALVERT ON THE OXIDATION OF IRON. 



salts of lime and magnesia were decomposed, there still 

 remained in the solutions I to 5 per cent, of alkalies or 

 the alkaline carbonates ; and when iron blades were intro- 

 duced into such liquids, they gave the same results as when 

 iron had been dipped partially into an alkaline solution of 

 Manchester water. I would propose, in conclusion, that a 

 certain quantity of soda-ash should be introduced from time 

 to time into the bilge- water of iron ships, as by so doing a 

 great saving would be effected, as it would prevent the 

 rapid destruction of such ships. 



After reading the above paper, Mr. E. Hunt inquired 

 whether I had made experiments to ascertain if the pre- 

 sence of caustic alkalies or their carbonates when mixed 

 with sugar prevented the marked action of that substance 

 on iron. Considering this a most important question to 

 determine, as iron ships are rapidly destroyed when used 

 for conveying sugar from the colonies to this country, 

 I instituted the following series of experiments : — 



Blades of iron were partly immersed in a solution con- 

 taining 10 per cent, of sugar, and in similar solutions to 

 which had been added 2| to 5 percent, of caustic and car- 

 bonate of soda ; after a month the same results were ob- 

 tained with the saccharine as with the aqueous solutions. 

 But as it would be impracticable to use solutions of caustic 

 or carbonated alkalies in the holds of ships laden with sugar, 

 I thought it therefore advisable to try what might be the 

 influence of zinc when attached to iron in preventing its 

 oxidation, and am glad to say that a piece of zinc covering 

 about the fiftieth part of the blade preserves the iron from 

 rusting in that part of the blade immersed in the sugar- 

 solution. The use, therefore, of plates of zinc fixed on the 

 sides of an iron vessel, or, perhaps better, the employment 

 of galvanized iron plates in the construction of ships, de- 

 serves the attention of shipowners. 



