Critical parameters for ammonia

(p, ρ, T) measurements and visual observations of the meniscus for ammonia were carried out carefully in the critical region over the range of temperatures: −1 K ⩽ (T − Tc) ⩽ 0.04 K, and of densities: −19 kg · m−3 ⩽ (ρ − ρc) ⩽ 19 kg · m−3 by a metal-bellows volumometer with an optical cell. Vapor pressures were also measured at T = (310, 350, and 400) K. The critical parameters of Tc and ρc were determined based on the results of observation of the critical opalescence. The critical pressure pc was determined from the present measurements at Tc on the vapor pressure curve. Comparisons of the critical parameters with values given in the literature are presented.