Sound velocity has been measured in the liquid Bismuth-Zinc system as
a function of temperature and composition to investigate the propagati
on of ultrasonic waves in a metallic liquid alloy with a miscibility g
ap. The critical point determined from the dependence on temperature o
f the sound velocity is 580+/-3-degrees-C at 17.8+/-0.3 at.% Bi. Above
the critical point, the sound velocity shows a temperature dependence
associated with critical concentration fluctuations.