CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



THE TRANSITION TEMPERATURES OF SODIUM CHROMATE 

 AS CONVENIENT FIXED POINTS IN THERMOMETRY. 



By Theodore William Richabds and George Leslie Kelley. 



Preeented April 12, 1911. Received April 4, 1911 



Introduction. 



In previous papers^ from this laboratory it has been shown that the 

 transition temperature of a crystallized salt is in some cases so easily 

 observed and so constantly maintained as to form a convenient fixed 

 point of reference for the scale of temperature. The cases of sodium 

 sulphate (32.383°) and bromide (50.674°) and manganese chloride 

 (58.089°) have been studied in detail and found to be very satisfactory 

 in these respects. 



Among other substances suggested for this purpose, sodium chromate 

 is especially inviting because two of its transition temperatures are 

 near 20'', a temperature at which it is frequently desirable to verify 

 thermometers. 



The outcome of the work on this salt described in the present paper 

 was entirely satisfactory, and gives promise of great practical usefulness 

 to those who are interested in exact thermometric measurement. 

 Nevertheless, the problem was not so simple as it had at first appeared. 

 The wealth of variety exhibited by the hydrates proved at first to be 

 an embarrassment of riches, and led to some preliminary confusion, 

 which has been happily reduced to order. Moreover, the salt is some- 



^T. W. Richards, Am. J. Sci. (4), 6, 201 (1898); Richards and Churchill, 

 These Proceedings, 34. 277 (1899); Richards and Wells, These Proceed- 

 ings, 41, 435 (1906); Ibid., 38, 431 (1902); Richards and Wrede, These Pro- 

 ceedings, 43, 343 (1907). These five papers are all to be found in full in the 

 Zeitschr. fiir phys. Chem., the references being respectively 26, 690 (1898) ; 

 28, 313 (1899) ; 43, 465 (1903) ; 61, 313 (1908). The work on manganese 

 chloride was finished by Dr. Wrede and one of us at the University of Berlin. 



