substantially pure , free flowing , sodium amalgam particles of predetermined composition and controlled particle size are prepared for use as vaporizable fill for high pressure discharge lamp devices , whereby accurately measurable quantities of the sodium amalgam may be introduced into the lamp devices . a process for producing the substantially pure amalgam particles of accurately controlled size includes heating a mixture of sodium and mercury to form a melt , passing the melt through a vibrating discharge nozzle and subjecting the droplets so formed to an inert cooling fluid maintained at a temperature below the solidification point of the amalgam . an apparatus for producing the amalgam particles comprises a vessel to contain an alkali metal amalgam melt , a vibrating discharge nozzle adapted to form the melt into uniformly sized droplets , and a column of inert cooling fluid maintained at a low temperature at which the melt droplets are solidified .