170 DAY AND SOSMAN: NITROGEN THERMOMETER SCALE 



ings. This series of operations constituted a set of observations 

 as carried out in the tables which follow. Inasmuch as the gas 

 thermometer was brought as close as practicable to the tempera- 

 ture of the points (benzophenone, zinc, etc.) selected as standards, 

 the intermediaty role of the thermoelements was merely that of a 

 transfer agent, in which role the individual properties of the ther- 

 moelements do not appear at all, , provided the wires were origin- 

 ally homogeneous. The danger of contamination of the elements 

 and consequent inhomogeneity is negligible at these temperatures. 

 Even if such contamination had crept in it would have discovered 

 itself in differences between the readings of the three elements 

 with each change in the gradient, of which differences no trace 

 was found. 



By way of providing a strictly rigorous test of the accuracy of 

 the transfer of temperature from gas thermometer bulb to the 

 reference standards and its independence of the intermediary 

 thermoelement, a special arrangement was devised in the case of 

 zinc as follows : A steel bulb was made up with approximately the 

 dimensions of the gas thermometer bulb and suspended in the 

 same position in the nitrate bath. Enclosed in this bulb was the 

 charge of zinc in its graphite crucible. In this crucible the ther- 

 moelement occupied the same position which it occupied in refer- 

 ence to the»gas thermometer bulb, and all other conditions were, 

 of course, identical. The zinc melting points were determined 

 in this way, i.e., in a nitrate bath in which there were no measur- 

 able temperature differences in the region about the melting zinc 

 and with the temperature gradient along the thermoelements 

 identical with that surrounding the gas thermometer bulb itself. 



4. BOILING POINT OF SULFUR 



Finally an attempt was made to establish one temperature in 

 this region from which the intermediary thermoelement should be 

 completely eliminated. The gas thermometer bulb itself was 

 immersed in the vapor of boiling sulfur. For this determination 

 the nitrate bath was replaced by an appropriate sulfur boiling- 

 point apparatus, all other conditions remaining the same. In 

 building this apparatus, the experience of the Bureau of Stand- 



