The static dielectric constant of CH 3F and CHF 3 to 468 K and 2000 bar

The static dielectric constant ∊ of methyl fluoride and trifluoromethane was measured between -60 and 195°C and from 50 to 2000 bar. ( _c(CH ₃F)=44.6°C, T_c(CHF ₃)=26.3°C.) The high pressure cell and procedure is described. At 20°C the ∊-values for CH ₃F increase between 50 and 2000 bar from 9.7 to 15.9, and for CHF ₃ between 100 and 2000 bar from 7.2 to 12.7. At 2000 bar ∊=8.0 (195°C) and ∊=5.7 (205°C) are found for CH ₃F and CHF ₃, respectively. Functions for ∊ in dependence of pressure are given for both compounds. Estimated Kirkwood correlation factors g (between 1.0 and 1.2) deviate only moderately from unity.