178 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



has been reached by the cooling material. Two analysis of the tetra- 

 hydrate showed 30.74 and 30.76 per cent of water, sufficiently close 

 to the theoretical value 30.72. On cooling a solution saturated at 

 63°, it frequently happens that no crystals appear, although upon 

 adding a crystal of the tetrahydrate crystallization at once occurs. 



90 





S 





|4 



80 



70 



60 





30 



15' 20= 25° 



Temperature 



In the accompanying figure the solubilities ^ of sodium chromate in 

 contact with its various hydrates have been plotted for temperatures 

 in the neighborhood of room temperature. Evidently three transitions 

 are possible within a small range. The dekahydrate undergoes transi- 

 tion to the hexahydrate and solution at 19.53°, or into tetrahydrate 

 and solution at 19.99°,^ depending on which of these last-named 

 hydrates is present. A similar transition from hexahydrate to 

 tetrahydrate and solution occurs at 25.9° ±. 



8 Mylius and Funk, Ber. d. ch. Ges., 33, 3689 (1901); also Salkowski, ibid., 

 34, 1948 (1901). These are recorded in Landolt and Bornstein Tabellen (1905), 

 page 5.57. 



^ This is probably the point found by J. L. R. Morgan as approximately 

 19.92°, Zeit. anorg. Chem., 55, 263 (1907). 



