PAINTING, 247 



steel its effect upon the neighboring bared metal is as strong 

 and continuous as copper would be in its galvanic action. 



Overwhelming testimony and positive evidence have 

 proven the following facts: 



1st. That rust and mill-scale exert a most destructive 

 action upon iron and steel. 



2d. That where moisture and carbonic acid gas accumu- 

 late in considerable quantities, the rapid destruction of ferric 

 bodies follows. 



3d. That rusting, once started, progresses rapidly even 

 under what seems a perfect protective covering. 



4th. That if a covering can be found which will prevent 

 the penetration of moisture, the perfect protection of the 

 metal is assured so long as the covering remains intact. 



In 1882 exhaustive experiments were conducted by author- 

 ity of the British Admiralty, resulting in the following con- 

 clusions : 



(i) That no pitting occured in mild steel when freed from 

 mill-scale; (2) that the loss of weight from corrosion of clean 

 mild steel and clean iron did not differ greatly; and (3) that 

 the action of mill-scale is considerable and continuous, and 

 equal to a similar quantity of copper in its corrosive action 

 due to galvanism. 



In long tunnels in which accumulations of carbonic acid gas 

 and moisture are found, and as exampled by the Arlberg, St. 

 Gothard and Musconetong tunnels, the life of iron or steel 

 work is very brief, and a renewal every few years has been a 

 necessity; in the last of these, it is reported that the 76-lb. 

 steel rail was removed after five years' service and was found 

 to have lost more weight by corrosion than by use. 



The continuous action of rust is clearly shown by a report 

 to the French Naval Office as to the effect of rust upon several 

 torpedo-boats which had never been put into commission, but 

 were laid up undercover and painted at intervals. An inspec- 



