536 Dr. M. W. Travers and Mr. A. G. C. Gwyer. [Jan. 11, 



accuracy of our determination of the transition point of sodium sulphate 

 on the platinum scale and that of Kichards and Wells on the hydrogen 

 scale. If this result is correct it would appear that since the value 

 1-5 for 3 gives for A 0'329 at 32-38 C., there must be at this tem- 

 perature a difference of 0"08 between the constant pressure air scale 

 and the constant volume hydrogen scale. 



Comparison of the Thermometers at Higher Temperatures. In order to 

 make certain that our thermometer behaved normally at higher 

 temperatures, we repeated the original experiments of Callendar and 

 Griffiths, and obtained the same result. 



The Boiling Point of Naphthalene, Benzophenone and Sulphur on the 

 Platinum Thermometers. The apparatus employed in these experiments 

 was exactly similar to that described by Callendar and Griffiths.* In 

 the case of the two organic substances the top of the glass Meyer tube 

 was closed by a cork, and a bent glass delivery tube served to condense 

 the vapour and conduct the liquid into a receiver. The constancy of 

 the temperature while the substance distilled served as an indication 

 of its purity. 



The naphthalene was first crystallised from absolute alcohol, was 

 then distilled, and subsequently redistilled before each experiment. 

 The benzophenone (Kahlbaum) was dissolved in alcohol, water was 

 added to the hot solution till it appeared cloudy, and then ether was 

 added till it again became clear. On standing large crystals 

 separated, and these were taken, dried in a desiccator, and distilled. 



In the sulphur experiments we sometimes employed pure sulphur, 

 sometimes crude roll sulphur, without observing any difference in the 

 result. 



Naphthalene. Callendar and Griffiths! taking 444-55 for the boiling 

 point of sulphur on the constant pressure air thermometer, measured the 

 boiling point by means of a platinum thermometer, and found the 

 value 217'94. Crafts J measured the boiling point by means of an 

 air thermometer and found 218*06. Recently Jaquerod and Wassmerg 

 have determined the vapour pressure on the scale of a constant 

 volume thermometer, filled with hydrogen at a pressure of 500 mm. 

 at the ice point. Their results for the temperatures corresponding 

 to pressure in the neighbourhood of 760 mm. may be expressed in the 

 form 



T^ = 217-68 + 0-057 (p-760). 



* ' Phil. Trans./ A, 1891, p. 119. 



f Loc. tit. 



I ' Bulletin Soc. Chiin.' [2], vol. 39, p. 282. 



' J. de Chim. PLys.,' vol. 2, p. 52. 



