An instrument for the Comparison of Thermometers. 117 



air can be exhausted from or admitted to this bottle by means 

 of a three-way tap H. Some mercury is placed on the top 



Fir-. 1. 



of the cork C (fig. 2) to prevent the liquid used to form the 

 vapour touching the cork. The liquid is heated by means of 

 a spiral of fine uncovered platinum wire, the terminals being 

 fused into glass tubes which pass down through the mercury 

 and the cork. 



Attempts to boil the liquid in an auxiliary bulb were 

 rendered futile on account of the excessive bumping which 

 took place after the liquid had been boiling for a day or two. 

 The heating by a platinum wire, however, entirely obviates 

 all bumping, and might be of use in determining the boiling- 

 point or in distilling liquids which are inclined to bump, so 

 long as they are not electrolytes. 



The vapour of the boiling liquid rises between the inside 



