CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



A NEW METHOD OF STANDARDIZING THERMOMETERS 



BELOW 0° C. 



By Theodore W. Richards and Frederick G. Jackson. 



Presented December 13, 1905. Received December 8, 1905. 



Witiiin recent years the theory of physical chemistry has been pro- 

 foundly influenced by inferences drawn from the freezing points of 

 aqueous solutions, and many experimenters have contributed data upon 

 this subject. Too often, however, the data are of uncertain value, even 

 when all conceivable precautions have been taken to avoid supercooling 

 and superheating. One cause of the uncertainty is the lack of knowledge 

 concerning the calibration of the thermometers used. Obviously the 

 error of the hundredth of a degree in the thermometer will affect the 

 result by a whole per cent if the fall of temperatm*e caused by the dis- 

 solved substance is a degree ; and such errors are common. The impor- 

 tance of a simple method of calibrating thermometers below the freezing 

 point of water, both for the theory and practice of physical chemistry, 

 is therefore very apparent. The object of the present paper is to describe 

 the practical working of a method which may be easily carried out by 

 any one, a method which has already been suggested by one of us in a 

 previous paper. 1 



Evidently a solution of given concentration of a given substance must 

 freeze always at exactly a given temperature. If, then, the freezing points 

 of a series of solutions of this substance are determined once for all on a 

 given thermometer of known precision, any other thermometer in any 

 part of the world may be compared at these points with the standard 

 thermometer by finding its readings in similar freezing solutions. If the 

 indications of the standard thermometer are plotted in a curve comparing 

 concentration with scale reading, any point on any thermometer may be 



1 T. W. Richards, "The Freezing Points of Dilute Solutions," Journ. Am. 

 Chem. Soc, 25, 297 (1903) ; Zeit. phys. Chem., 44, 570 (1903). 



