248 TOWERS AND TANKS FOR WATER-WORKS. 



tion showed that the plates under the paint were so corroded 

 that the blow of a testing-hammer was sufficient to puncture 

 them, and that large areas under the paint-film were so affected. 

 This same effect of the continuous action of rust has been ob- 

 served in the repair of numerous bridges and other structures, 

 when the metal was found entirely destroyed under the paint- 

 coating. A large truss-roof that was kept constantly painted 

 having failed, it was found that the metal was simply rotten 

 with rust under the paint, while no appearance of the insta- 

 bility of the structure from this cause was apparent to the eye. 

 The same result is recorded by builders in the case of floor- 

 beams which were practically eaten away below the paint-sur- 

 face. 



A recent investigation by Mr. D. H. Maury, of the elec- 

 trolitic injury to the metal of the Peoria, 111., stand-pipe is of 

 great interest, and is given as follows: 



"On March 30, 1894, the water company's steel stand- 

 pipe on the West Bluff burst, killing one person and injuring 

 15 others, one of whom died later from his injuries. Upon 

 examining the wreck of the stand-pipe, the writer at once 

 noticed a peculiar pitting of the inside of the vertical sheets, 

 and the appearance of these pits was so different from that 

 caused by any ordinary oxidation that he was soon almost 

 positive that they were due to electrolytic action. A similar 

 stand-pipe on the East Bluff was drained, and was found to be 

 similarly pitted. The whole inner surface of the vertical shell 

 appeared to be thickly covered with blisters, resembling in 

 outward appearance the. tubercles sometimes found inside of 

 old cast-iron mains. 



"This blistered covering, which was almost as thin as 

 paper, was composed entirely of oxide of iron, and on brush- 

 ing it away with the finger-tips, the black paint with which 

 the stand-pipe had been originally coated would be found 

 beneath it. 



