[Illustration: Fig. 52.]
The condition of a boiler can be learned by tapping on the sheets,
rivets, seams, etc., to ascertain whether there are any broken stays,
laminated places, broken rivets, etc.
[Illustration: Fig. A.]
[Illustration: Fig. B.]
Fig. A represents the method of preparing testing pieces of boiler
plate, for the machines prepared specially to measure their elongation
before breaking, and also the number of pounds they will bear
stretching before giving way. Fig. B exhibits the same with reference
to the brace and other =O= iron.