TEMPERATURE SCALE. 21 



air). A fortunate circumstance made it possible to send these care- 

 fully calibrated elements to Washington by messenger, which made 

 it certain that they suffered nothing in transit. 



The elements were then further compared in an electric furnace, 

 which will be described below, and the melting points of the same 

 group of metals again determined in our laboratory. The metals 

 used, however, were from other sources than those which had served 

 for the calibration at the Reichsanstalt. When this test was finished, 

 we were able to assure ourselves that, although all the constants in 

 the measuring apparatus thermo-elements, resistances, standard 

 cells, metals, etc. had been changed in the transfer from the Reich- 

 sanstalt to the Geological Survey at Washington, the aggregate error 

 nowhere exceeded i over the entire range from 250 to 1150 . It 

 will be remembered that i was about the accuracy which the stand- 

 ard gas thermometer showed at 1000 . Our thermo-electric system 

 is, therefore, now doubly established (1) by direct comparison and 

 (2) through an independent series of metal melting points upon the 

 gas-thermometer scale of the Reichsanstalt within the limits of error of 

 the latter, and can be verified at any time with the help of two of the 

 elements which have been laid aside for this purpose, or the melting 

 points of the metals. The scale is, therefore, permanent. 



TEMPERATURE SCALE. 



As the introduction of the standard high temperature scale of the 

 Reichsanstalt into this country and its establishment by proper 

 fixed points may be a matter of considerable interest to other 

 investigators, some further details regarding the metals chosen for 

 these fixed points are added here. We tried to find metals which 

 should not only be of the purity necessary for such standards, but 

 which should be easily obtainable in uniform quality. With four of 

 the five metals of the Reichsanstalt series cadmium, zinc, silver, and 

 copper no difficulty was experienced, but we were not able to find 

 satisfactory antimony in this country. This need not prove an 

 obstacle, for the four points mentioned will serve most purposes with- 

 out a fifth, while if the needs of an experiment are so exacting as to 

 require an intermediate melting point, antimony can be imported 

 from Kahlbaum, of Berlin, without great delay or excessive cost, in 

 the same purity as that originally used at the Reichsanstalt. 



The cadmium and zinc in our series were taken from the regular 

 listed chemicals of Eimer & Amend (zinc, " C. P. in sticks ;" " cadmium, 

 metal sticks"). The silver was the well-known test silver of the 



