BURGESS AND MERICA: FUSIBLE TIN BOILER PLUGS 4G1 



of Mo, Lo and the calculated Ro were therefore made for each 

 tube, the average change found being 1.1, 9.4 and 8.2 parts per 

 million respectively. 



On the basis of the above new determinations the interna- 

 tional ohm, as- represented by the four mercury standards in 

 December, 1912, was 12.5 millionths smaller than the international 

 ohm as represented by the manganin coils at the same time. 

 England, Germany, Japan, Russia, France, and the United 

 States now have mercury standards of resistance. Comparison 

 of the units defined by the mercury standards of the above 

 countries in 1913 (those of France excepted; dates not being avail- 

 able) indicate a very satisfactory agreement, the average devia- 

 tion of the units of the several countries from the mean being 

 about ± 7 parts per million. 



PHYSICAL CHEMISTRY.— .4 ?z investigation of fusible tin 

 boiler plugs.^ G. K. Burgess and P. D. Merica, Bureau 

 of Standards. 



An investigation of fusible tin boiler plugs has been conducted 

 at the Bureau of Standards to determine what are the types of 

 deterioration to which they are subject in service and to what 

 these various types are due. The function of the fusible tin 

 boiler plug is, as its name indicates, to give warning by the 

 melting of the tin plug and blowing out of the boiler overheat- 

 ing. The attention of the Bureau has, however, been directed 

 to several instances of the failure of such plugs so to operate, and 

 examination showed that the tin in these plugs had become 

 oxidized in service to Sn02, melting above 1600°C. 



About 1050 plugs — including used and new plugs — were ob- 

 tained through the courtesy of the Steamboat-Inspection Serv- 

 ice, and were examined as to design and construction, and con- 

 dition and purity of the tin filling. Of the four classes or types of 

 deterioration noticed in such used plugs, one could be pro- 

 nounced dangerous, and that consisted in the formation of this 



^ To appear as a Technologic Paper of the Bureau of Standards. 



