POLYMORPHIC TRANSFORMATIONS OF SOLIDS. 81 



An attempt to find the crystalline form of KCIO3 II will be described 

 in another place. 



Seven measurements of the difference of compressibility l:)etween 

 the two phases were made. These all point to the same conclusion; 

 that the difference is very small, probably less than 0.062. This 

 enables us to set upper and lower limits for the diflference of expansion 

 and specific heats. Assuming Aa = 0, we find A/3 = — 0.0622, and if 

 Aa = 0.062, A/3 = -O.OtIo. A value for Aa only 10 % higher than 

 O.O52O would give a positive instead of a negative value for A/3. We 

 conclude that the difference of thermal expansion between the two 

 phases is unusually small, and that possibly, although not certainly, 

 the high pressure phase is the more expansible. Aa and A/3 are so 

 small that the values of ACp are not affected by changes within the 

 limits of error. ACp is nearly constant o^■er the entire range at 

 — 0.024 (= —0.00056 gm. cal. per gm.). Here again is a case where 

 the phase stable at the lower temperature has the higher specific heat. 



PoTASSiuiNi Nitrite. — This substance was Kahlbaum's purest, 

 used without further purification, except drying. After the runs had 

 been made the irregularity of the results led me to take up the question 

 of the purity of the substance with the J. T. Baker Chemical Co., 

 and I learned from them that it is impossible to prepare KXO2 pure 

 commercially. There is always impurity of water and KNO3. The 

 impurity may be fairly large in amount, varying from 10 to 15%. An 

 analyzed sample from the J. T. Baker Chemical Co. contained 89% 

 KNO2. The amount of water was not stated. These results, there- 

 fore, must be taken as merely indicating the order of the effects which 

 may be expected with pure KNO2. It is unfortunate that there was 

 this large amount of impurity, because the results are interesting both 

 because of the direction of curvature of the transition line, and the 

 behavior of the reaction velocity. 



Three fillings of the apparatus were used. With the first, only one 

 point was determined, at 22°. The salt was not dried for this run, and 

 considerable rounding of the corners led to the suspicion that moisture 

 was present. For the second filling of the apparatus, the salt was 

 dried in vacuum over H2SO4 for two days. Five points were found 

 with this filling. For the third filling, the salt was dried in vacuum 

 at 100° for several hours; three points were found with this filling. 

 The different methods of getting rid of the moisture seemed to make 

 no difference; the three runs were in essential agreement. In all three 

 fillings the KNO2 was hammered into a compact mass; the first two 



