^8 



BRIDGMAN. . 



runs were made, separated by an interval of seven months. The first 

 series of runs gave four points on the transition curve. The acetamide 

 was used without purification for this run; it was placed in the in- 

 verted nickel steel cup under mercury. There was a rather large 

 amount of impurity as shown by the moist appearance of the original 

 material, and the very large amount of rounding of the corners of the 

 melting curve. This rounding w^as so large that it was not possible 

 to make accurate measurements on the upper end of the transition 

 line, near the triple point, and much less to make even rough determi- 

 nations of the melting data. This did not at that time seem a very 



TABLE II. 

 Acetic Acid. 



serious matter, however, since the primary interest of this work was 

 not in measuring more melting curves, and since the transition itself 

 was sharp, showing that the impurity did not form mixed crystals. 

 On working up the data it appeared, however, that there were some 

 very slight indications that there were really three modifications 

 instead of two. If there were three modifications, the volume of one 

 of them must have been so close to one of the others that it was 

 desirable to use as pure material as possible. A second series of runs 

 was accordingly made with material which had been twice crystallized 

 in the thermostat at constant temperature. Large perfe ctly trans 



