596 



BRIDGMAN. 



sure of completion of the reaction. The point at 7000 on the I-II 

 curve is reallv three coincident points, two with falhng pressure, and 

 one with rising pressure, at constant temperature. The pressure 

 Hmits for this point were twice as wide as usual, to ensure completion 



of the reaction. , i • i 



There seems considerable reason to suspect that the high point 

 on the upper end of the line for II-III belongs to another equilibrium 

 line, and that there is a fourth modification. The consistently low 

 points for the corresponding Av bear this out. These points, when 

 compared with the low point on the upper end of the Av curve for I-ll, 

 are too low in proportion to be entirely explained by a partial transi- 

 tion to a thallic salt. This surmise was not verified; results would 

 have been difficult of interpretation because of the known partial 

 change of the thallous nitrate. It was also of no use to try for the 

 usual data with the low pressure apparatus; the low pressure points 

 are always made after the runs at high pressures, and m this- case it 

 was known that the high pressure had at least initiated some sort of a 

 permanent change. It may be mentioned that whatever the transi- 

 tion product, it does not form mixed crystals with TINO3, for the 

 p-t values were unaffected by the discordant Av values, and the tran- 

 sition remained sharp throughout. Under the conditions, the best 

 that I could do with the data was to draw a straight line through 



23456 7 B9 

 Pressure, kgm./cm.' x 10^ 

 Thallium Nitrate 



Figure 9. Thallium Nitrate. The computed heats of transition and the 

 changes of internal energy. 



