942 



SCIENCE. 



[N. S. Vol. XIX. No. 495. 



by the resolutions of the committee of the 

 International Bureau of Weights and Meas- 

 ures, dated October 15, 1887. (This scale 

 has now come into world-wide use, and its 

 general adoption in all important scientific 

 and technical work has contributed toward 

 the solution of important questions bearing 

 on the mechanical equivalent of heat and 

 the international electrical units.) 



As primary standards the bureau now 

 has fifteen Tonnelot and Baudin thermom- 

 eters that have been carefully studied at 

 the international bureau and which are 

 now undergoing further intercomparison 

 here. 



As primary standards, in the interval 

 100° to 600° C, Dr. Waidner has had con- 

 structed some specially designed platinum 

 resistance thermometers, both of the com- 

 pensated and potential lead type, together 

 with resistance bridges and other apparatus 

 designed to afford the highest accuracy and 

 convenience in working. He has chosen 

 the platinum resistance thermometer as the 

 primary standard of the bureau because it 

 defines a scale of temperature that is at 

 any time reproducible in any part of the 

 world, and unlike most standard scales, it 

 is not locked up in a few instruments that 

 have been directly compared with the gas 

 thermometer. As secondary and working 

 standards in this interval, 100° C. to 550° 

 C, the bureau has a number of mercury 

 thermometers constructed of French hard 

 glass and of Jena borosilieate (59"') glass. 

 Those intended for work above 300° 0. 

 have the space above the mercury filled 

 .with dry N or COj gas under pressure. 

 These mercurial standards are intercom- 

 pared from time to time and occasionally 

 they will be compared with the platinum 

 resistance thermometers. 



In the interval 0° C. to — 200° C. the 

 standard scale of temperature is again that 

 of the hydrogen-gas thermometer, and here 

 also the platinum resistance thermometer 



serves to define the scale. For work in this 

 range the resistance thermometer is, as be- 

 fore, referred to three known temperatures, 

 viz., melting ice, melting CO,, and the boil- 

 ing point of liquid oxygen. As secondary 

 and working standards in this interval, 

 the bureau has a number of toluene ther- 

 mometers, and copper-constantan thermo- 

 couples; and, in addition, some petroleum- 

 ether and pentane thermometers, for use 

 as low as — 180° C. 



The scope of the testing work in this 

 field, which is rapidly increasing, is already 

 somewhat varied. It includes the certifi- 

 cation of precision thermometers to be used 

 in scientific work, the certification of stand- 

 ards used by some American thermometer 

 makers, of thermometers used in important 

 engineering tests, and of special types of 

 mechanical thermometers used in industrial 

 operations. 



One branch of testing which promises to 

 grow rapidly is the testing of clinical ther- 

 mometers. Special apparatus has, there- 

 fore, been designed and constructed in the 

 instrument shop of the bureau, to enable 

 this work to be carried on with the greatest 

 rapidity and precision. As an illustration 

 of the results attained, it may be noted that 

 600 clinical thermometers can be read, at 

 one temperature, in the space of 30 

 minutes. 



Special facilities have been provided for 

 high temperature testing^ such as the stand- 

 ardization and testing of nearly all kinds 

 of high temperature measuring instru- 

 ments, including thermocouples, platinum 

 resistance thermometers, expansion and 

 optical pyrometers; the determination of 

 the melting points of metals and alloys; 

 the determination of the specific heats and 

 coefficients of expansion at high tempera- 

 ture, etc. 



Some of the apparatus has already been 

 installed for the determination of the 

 calorific value of fuels. 



