THE USE OF IRON. 5 1 



The Change to Steel. The underlying cause for a 

 change so radical as to amount to an industrial revolution, is 

 the appreciation and realization of the commercial and con- 

 structive value of steel, leading to scientific advance constant- 

 ly improving the physical and chemical properties, whilst the 

 increased demand introduced new facilities for reducing the 

 price of the product below that of commercial wrought iron. 

 As has been stated, at this time, of the 992 metallic reservoirs 

 in the United States, 220 are of iron and 292 of steel, 

 leaving 480 undefined. Whilst these records give only a 

 small excess of steel as compared with iron structures, the 

 increased use of steel is more apparent when it is considered 

 that only within the past few years has steel been recognized 

 as a suitable metal for such work. 



Classification of Failures. From the best procurable 

 records amongst the entire number of metallic reservoirs of 

 water-supply plants in this country, there are recorded 54 partial 

 and complete failures and collapses, 17 of which are credited 

 to steel structures, whilst only 7 known to have been built of 

 iron plates have failed. From this it would seem that steel 

 tanks are more liable to collapse than iron ones, but this fact 

 should only be admitted conditionally and after consideration 

 of the causes inducing the failures. 



Of the 17 complete and partial failures attributed to the 

 list of steel tanks, the date of erection and failure shows the 

 majority of them to have been constructed during what might 

 be termed the experimental stage of steel-production, as, for 

 instance, chemical analysis of the steel used in four of these 

 tanks shows a large proportion of phosphorus in one case as 

 high as 0.162$, which would certainly have caused the plate 

 to be rejected at this time, unless its use were dictated by dis- 

 tinctly dishonest conditions. 



Again, a consideration of the circumstances and a study of 

 the prevailing conditions and designs, show three of the re- 



