454 PROCEEDINGS OP THE AMERICAN ACADEMY. 



portion to their concentration than the less concentrated ones. This is 

 shown by the increasing values in the last column. The hypothesis of 

 ionization predicts the opposite effect. 2 



From these points a curve may be drawn which will enable any one 

 to correct his own thermometer at any point upon repeating the experi- 

 ments in question. 



It may be noted in conclusion that this means of calibrating thermom- 

 eters is theoretically as exact as any other. According to the Phase 

 Rule, in a system composed of two components, hydrochloric acid and 

 water, four conditions must be fixed in order to fix a point. In the 

 present case the four conditions are the pressure, the concentration of 

 the dissolved substance, and the co-existence in equilibrium of two phases, 

 solution and pure ice. 



Summary. 



This paper describes a simple method of calibrating thermometers at 

 temperatures below the freezing point of water by using as standards of 

 comparison the depressions of the freezing point caused by given addi- 

 tions of hydrochloric acid. The data given are for the construction of a 

 curve enabling direct comparisons of a thermometer to be made with a 

 minimum of labor. The method is shown to be both practically and 

 theoretically satisfactory. This paper is preliminary in nature, and does 

 not pretend to give final values, because only a single standardized ther- 

 mometer was used. 



2 It is needless to call attention to the fact tliat many other cases of this kind 

 have been studied in detail by de Coppet, Riidorff, and others, especially in very 

 recent times by Harry C. Jones. 



