CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



THE TRANSITION TEMPERATURE OF SODIC BROMIDE : 

 A NEW FIXED POINT IN THERMOMETRY. 



By Theodore W. Richards and Roger C. Wells. 



Presented December 13, 1905. Received November 29, 1905. 



Introduction. 



Recent work upon the transition temperatures of crystallized salts 

 has shown that many of these transition temperatures are capable of 

 determination with accuracy enough to serve as a means of standard- 

 izing thermometers. 1 A number of such points have been found 

 approximately by Richards and Churchill, and one of these points, 

 namely, the transition of sodic sulphate at 32.383°, has been fixed 

 with great precision in reference to the International Scale by Rich- 

 ards and Wells. 



It is highly desirable that as many such points as possible should be 

 determined with great precision, because they furnish means of deter- 

 mining temperature intervals dependent only upon the procuring of pure 

 materials, and independent of the possession of a standard thermometer. 

 Among the many transition temperatures to be investigated, two espe- 

 cially promised great usefulness, — one, that of sodic bromide, 50.7°, lying 

 about half-way between the freezing and boiling points of water, and 

 therefore capable of testing the middle of the thermometric scale ; and 

 the other, that of sodic chromate, lying at about the ordinary temper- 

 ature of a laboratory. Of these two points, the former is discussed in 

 the present paper, and the latter will soon be discussed in considerable 

 detail in another paper. Both were determined approximately by Rich- 

 ards and Churchill in the paper already cited, but these determinations 

 were only of a crude and preliminary nature, and required careful 

 verification. 



i Richards, Am. Jour, of Science, 6 , 201 (1898) ; Richards and Churchill, These 

 Proceedings, 34, 277 (1899) ; Richards and Wells, ibid., 38, 431 (1902) ; also Zeit. 

 f. phys. Chem., 26, 690 (1898). 



