Page:Popular Science Monthly Volume 88.djvu/838

 Hanging a Defective Boiler Plug

as a Warning

��A MINIATURE gallows from which hangs a defective fusible plug re- sponsible for a boiler explosion which occurred on board the steamship Jefferson, near Norfolk, Va., on May ii, 1914, is one of the interesting curios on the walls of the office of Secretary Red- f ield, of the Department of Commerce in Washington. It is a grim reminder of a tragedy which cost the lives of eleven men. A small placard above it reads:

"A Murderer! Hung for killing eleven men."

Below it are the words :

"The fusible (?) plug which failed to fuse. From the boiler of the S. S. Jefferson. Boiler exploded. Eleven lives lost."

The plug con- sisted of a threaded brass bushing about an inch and a half in diameter, with hexagonal head. Through the center of the bush- ing runs a plug of fusible metal, which, in this in-

���Impurities of the fusible filling of this plug prevented its blowing out and re- sulted in the loss of eleven lives. So, the plug was hanged as a murderer, in a government bureau

��higher than 2,900 degrees Fahrenheit. Impurities in the fusible metal, which were the cause of its failure to blow out, are easily discernible. In subsequent investigations made by the United States Bureau of Standards ten hundred and fifty fusible plugs were exam- ined. These were from one hundred and five different makers, and about one hundred of them had been in actual use for from four to twelve months. From a study of these plugs the Bureau recommends that the fusible metal itself should pre- ferably be pure tin, because it has been found to be far more reliable and durable. The Bureau further recommends that the tin be as free as possible from zinc and lead.

One of the many types of deteriora- tion of fusible plug fillings observed by the Bureau consists in the formation of a network of mi- nute thread-like cracks or corrosion-

��stance, was defective; it did not blow out when the water in the boiler became low, thereby causing a disastrous explo- sion. When the plug was sawed open lengthwise it was found that most of the original filling had disappeared, only a few traces of it remaining embedded in a dirty, greenish-white mass of tin oxide, which would not melt until heated to a temperature somewhat

��regions, ramifying in all directions. The Bureau found that these penetrated the metal and then broadened out until the filling was largely, or wholly, oxidized and destroyed. The presence of small quantities of zinc in the tin was the main contributing cause of the network type of corrosion. This was proved conclusively by the investigation con- ducted after the disaster.

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