THE CORROSION OF IRON AND OTHER METALS 655 



other cause than to the action of silicic acid present at the 

 glass surface. 



Friend, however, has met the criticism applied to Moody's 

 results in a most ingenious way, by carrying out experiments 

 with the simple apparatus shown in fig. 2, 



The thimble-shaped tube shown within the flask is of iron 

 and can be cooled by circulating water inside it in the manner 

 indicated ; the flask contains strong caustic potash solution 

 and above this air. At the outset, some of the air is expelled 

 or withdrawn and the flask closed by sealing the side-tube at 





Fig. 2. 



its point ; after shaking well, so as to wash down all the surfaces 

 exposed within the flask with alkali, to remove all traces of 

 adherent carbonic acid, the flask is immersed in water at 100° 

 and cold water circulated through the iron thimble ; as the 

 steam condenses on the outer iron surface, this becomes cleansed 

 of alkali ; when the cleansing process is judged to be complete, 

 the flask is set aside. Operating in this way, Friend found that 

 no rusting took place, except on one occasion when a couple 

 of rust spots were formed at the top of the thimble ; as the 

 spots appeared at the same place after the rust had been 

 removed, there can be no doubt that the rusting was due to 

 the presence of "slag" at the point affected. Moody had a 

 similar experience and advisedly used chromic acid as a means 



