POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 85 



up to 3000 kgm. beyond the supposed transition point, that is to 6000 

 kgm. But above 6000 kgm. tiae secondary pressure reaction was a 

 decrease after every increase. 6000 kgm. is above the II-TII line, 

 but no trace of this transition was found on crossing the hne. On 

 relieving pressure to 3500 the rise of pressure continued. On taking 

 the apparatus apart, the CoCle was found to have decomposed, and a 

 good deal of mercury had disappeared. A suffocating gas was ex'olved, 

 probably chlorine. There was, however, no apparent effect on the 

 steel cylinders. This decomposition is an interesting one. It evi- 

 dently was produced by the high temperature and not by the high 

 pressure, for the reaction runs with increase of volume. The effect 

 of pressure would be to prevent the decomposition; this is what 

 occurred at 6000 kgm. Neither did the decomposition occur at the 

 higher pressures of the II-III curve at 177°. The products of the 

 decomposition found their way to all parts of the apparatus, which 

 had to be taken apart and cleaned. The manganin coil had to be 

 carefully cleaned, but recovered its normal resistance. With the 

 second setting up of the apparatus, one point was found on the lower 

 end of the II-III curve, and the other points were found on the I-TI 

 curve, not rising to the temperature of the previous decomposition. 

 The order of points on the I-II curve was 102°, 136°, 86°, 104° and 120°. 

 The first three of these determinations gave consistent values for pres- 

 sure and temperature, and the second and third apparently gave good 

 values for AT. The first point at 102° gave a value for AT impossibly 

 low, as low as the II-III curve. This possibl}^ was due to the transi- 

 tion not having been complete. The fourth and fifth points gave 

 values of the pressures considerably lower than the other points and 

 too high values for AV; evidently the decomposition had begun and 

 was progressing. The decomposition had probably started at 136°, 

 the highest temperature to which the material had been subjected, 

 and then proceeded at an accelerated rate. 



The points at low pressures were determined six months after those 

 at high pressures. Six determinations were made, both at constant 

 temperature and constant pressure. There were difficulties here also. 

 At 77 kgm. there was evidence of decomposition at 90°. This may 

 have begun earlier; the A F value of this attempt was not good. The 

 other attempts by the method of varying pressure at constant tempera- 

 ture gave good results on the I-II curve, but AV on the II-III curve 

 was lower than to be expected from the high pressure points. This 

 might be due in large measure to the extreme slowness of the reaction 

 from below on the II-III curve. Working at low pressures, the pres- 



