TEST OF IRON BY MAGNETISM. 



71'J 



:m<l that its outer ond had mado a true weld 



with tin- iron. This was found to In- correct 



on cutting ii|> tlio iron. A, in the figure In-low, 



and the end \i--w A, show tin- nn welded hole 



in the I'.i:-. Into a hole in a If in. round l>ur, 



. in. loiu, there u a- met.'d an iron 



Tlie two were then hammered into each 



other as nnieli as possihlc. Mr. Savby's needle 



d I lie rivet, and his mark, A, hit . 



ly upon its centre. At B and two faults 



di -Covered, and their presence con- 



! in cutting the bar at B and C, as shown 



in the respective sections. A 2 in. square bar 



(L''ig. 18) was brought to him, thickly painted 



Fio. 18. 



over. The needle found out a very great defect, 

 and th\s defect was indicated by a cross-mark. 

 It turned out that Mr. Saxby had hit upon the 

 very centre of an iron plug, which had been 

 driven into a hole drilled in the bar. He was 

 asked by the master-smith of Sheerness to try 

 the weld of a new stud link winch had been 

 put into a chain cable. Externally the weld 



Fio. 19. 



appeared good; the compass in Mr. Saxby's 

 hands soon showed the weld to be unsound. 

 He indicated this spot with a chalk-line, Fig. 



in the sketch, in which the chalk-mark is abo 



indicated. An old mooring-ring, Fig. 20, which 



hail been ivdiic.-d hy tin- -mith down to 28 ID. 



in diameter outride, and which was of 4 in. 



round iron, had been tried in the i:-nal way in 



machine. After withstanding the 



..TV -mall cracks showed themselves, ta 



in the li^nrc. The compass-needle, how- 



20. 



ever, detected still greater faults, as shown by 

 crosses in the dotted sketch, testifying to a flaw 

 that, it was inferred, would probably cause the 

 ring to break somewhere between the 4J in., 

 as marked on the engraving. The ring was 

 then again tried in the testing-machine. It 

 actually broke at the spot indicated by the 

 thick line in the dotted ring. The weld showed 

 itself to be good, but fresh pieces of iron had 

 been placed crosswise in making the weld. 

 This fresh iron had its fibres, or elongated 

 crystals, laid at right angles to those of the 

 ring, as shown in Fig. 21, and it was here that 



Fio. 21. 



the ring gave way. A large paddle crank- 

 shaft a new one, we believe, for the Virago 

 was being turned up in a lathe in one of the 

 shops at Sheerness dockyard. The magnetic 

 test found out a fault near the neck, as indi- 

 cated by a cross in the figure. FL-. --2. The 



19, and on cutting and breaking the line at defective weld, A, was then quite invisible, but 

 that mark, faults were found in it, as shown in turning the metal down to the dotted lino 



