300 Annual Report of the Council. 



the metal. Originally, steel of a tensile strength of forty 

 tons to the square inch was used, but complete success was 

 not obtained until a milder variety having a tensile strength 

 of thirty to thirty -two tons, with 20% elongation, was adop- 

 ted, whereas now-a-days, in the best practice, engineers are 

 content with a strength of 24 to 28 tons per sq. inch, and 

 an elongation of not less than 20% in a length of ten inches. 

 Steel plates made by the Bessemer or Siemens process, as 

 now used, are not only stronger, but more uniform in quality 

 than iron, they are practically not liable to blistering or 

 lamination as were even the best iron plates, and they are 

 tougher and more ductile and even less liable to deterioration 

 in work than iron plates. In all first-class boiler work steel 

 plates are now practically used to the exclusion of iron. 



When steel was first used, it was found that the plates 

 were seriously damaged by the operation of punching the 

 rivet holes, and, to overcome this difficulty, Adamson in 1862 

 introduced the method of drilling these holes, to avoid 

 distressing the plates. On Mr. Adamson's plan, the plates 

 are bent to their final form, and the holes are drilled through 

 the plates when in the position they will occupy in the 

 finished state. The plates are then taken apart, the 

 burrs formed in drilling removed, and the plates and 

 seams are riveted up. In this way the holes fall quite 

 true and fair when brought together, thus avoiding all 

 such drifting as was customary with punched holes to 

 the detriment of the plate. The holes also being true, 

 each rivet completely fills its hole, and takes up its 

 proper proportion of the stress, whereas in the rough and 

 irregular surfaces of punched holes, some rivets might be 

 taking an undue share of the strain, thus causing rupture at 

 a point below the strength of the seam taken generally. 

 Thus the seam is strengthened and made more reliable, it is 

 less liable to leakage, the material is better utilised, and the 

 work is altogether better and more neatly finished. 



