244 TOWERS AND TANK'S FOR WATER-WORKS. 



well-known authority upon the manufacture and properties of 

 structural steel in reply to a request for his opinion as to the 

 best protective coating for steel, in which he says that he 

 " knew no more about it than the average engineer. This 

 is equivalent to saying that I know nothing, for there seems 

 to be a radical difference of opinion on this question, and one 

 engineer will claim that one kind of material is the very best 

 thing that can possibly be used, and the next man will claim 

 that it is the very worst. It reminds me of the investigation 

 made by the L. A. W. Bulletin on the ' Best Lubricant for a 

 Bicycle." They published their conclusions, which ran about 

 as follows : 



1. Vaseline is the best lubricant. 



2. Vaseline is no earthly good." 



Considering the immense and increasing amounts of iron 

 and steel used annually as structural materials for marine 

 work, buildings, trusses, bridges and the like, and the limited 

 and conflicting knowledge of the best methods of protection, 

 it is surprising that accidents are not more frequent and seri- 

 ous, and that coroners' juries are not more often called upon 

 to render similar verdicts to that given in investigating a cele- 

 brated bridge-failure and accident, where the jury found th.it 

 " All went in, none came out, and there is nothing to sit on." 



Iron-rust. Although the best methods of preventing 

 corrosion may be involved in uncertainty and dispute, the 

 cause of the destruction of ferric members seems to be fairly 

 well established and it is a generally accepted scientific theory 

 that, primarily, rust or metallic corrosion is the effect of a 

 chemical combination of carbonic acid gas, oxygen, and water 

 with metallic iron, producing ferric oxide or iron-rust which, 

 once affected, continues with great rapidity through both 

 chemical and galvanic action. 



It has been shown by frequent experiment that carbonic 

 acid gas and oxygen, together or separately, will not pro- 



