p, q, T) Measurements and visual observations of the meniscus for isobutane were carried out carefully in the critical region over the range of temperatures: À15 mK 6 (T À T c ) 6 35 mK, and of densities: À7.5 kg AE m À3 6 (q À q c ) 6 7.5 kg AE m À3 by a metal-bellows volumometer with an optical cell. Vapor pressures were also measured at T = (310, 405, 406, 407, and 407.5) K. The critical point of T c and q c was determined by the image analysis of the critical opalescence which is proposed in this study. The critical pressure p c was determined to be the pressure measurement at the critical point. Comparisons of the critical parameters with values given in the literature are presented.

No abstract