800
Vol. 60
NOTES THERMAL EXPANSION OF CRYSTALLINE (239°C.) was first reported by CadyS4 Westrum and Pitzerb demonstrated that the entropy increKHF& BY RICHARD W. FINK^ AND EDGAR F. WESTRUM,J R . ~ ment of the a! --t /3 transformation is nearly twice that involved in fusion, and that because the Received Oclober 8, 1066 bonding is so largely ionic in the (F-H-F)- ion, In a n approach to the study of the behavior of the proton moves in a potential well having a single the (F-H-F)- ion in the soft, translucent, paraffin- minimum in contrast to more typical hydrogen like, high-temperature @) phase of KHF2,the volume bonds with double minimum potential energy increment on transition from the low-temperature functions. The dilatometer is shown in cross-section in (cy) phase was determined. The existence of the beta-phase, stable from 196" to the melting point Figure 1. The sample (J) of KHF2 is trapped within the float (H) machined from solid molybdenum stock. The body is machined from solid monel metal rod and provided with a monel tube of 0.636 cm. uniform bore which is silver-alloy brazed to the body (F) in such a manner that mercury (G) used as the dilatometric fluid does not contact the brazing alloy. The body is sealed with a molybdenum gasket seated by a threaded plug. The meniscus can be located to within about 0.006 cm. by closing an electrical circuit when incipi-
H
J
G
Fig. 1.-Diagram of the molybdenum float dilatometer described in the text. (1) Experimental work performed at the University of California Radiation Laboratory under auspices of the U. 8. Atomio Energy Commission. Preliminary measurementa were made at the University of Michigan. (2) Department of Chemistry, University of Arkansas, Fayetteville. (3) Department of Chemistry, University of Michigan, Ann Arbor. (4) G. H. Cady, J . A m . Chsm. Soc., 6 6 , 1481 (1934). ( 6 ) E. F. Westrum, Jr., and K. 8. Pitzer, ibid., 11, 1940 (1949); J . Chcm. Phya.. 10, 526 (1947).
U Fig. 2.-Techniqne of filling with mercury; prior t o evucuation, the float was loaded with the KHF2 sample.
NOTES
June, 1956
ent contact with the mercury is made by the pointed tungsten rod (D). This rod, which is centered by the glass bead (E), is surrounded by an electrically-insulating sheath of polystyrene (C) and is activated by the shaft (B) which is threaded with a 0.006-em. pitch and which engages two tapped brass blocks (A) mounted rigidly with respect to the body. Preliminary studies revealed that nickel, monel, and stainless steels react with P-KHFZ with evolution of gas. No reaction with molybdenum was observed a t temperatures as high as 260" over periods of several weeks. The glass apparatus depicted in Fig. 2 illustrates the method of filling the dilatometer with mercury. After evacuation of the inverted dilatometer for several days at
