This circular describes a widely-used but controversial invention to avert steam engine explosions. A spindle was inserted into a metal alloy near the hottest part of the boiler. If the temperature reached a certain level, the alloy would melt, and the spindle would release steam. Here the illustrations are accompanied by a detailed key and description, as well as a list of 27 boats built in Pittsburgh which had used the safety guard. 23 more ships are added in manuscript. The inventor was Cadwallader Evans, son of well-known engineer and author Oliver Evans. One in OCLC, at Princeton.
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