Using successive quartz double distillation system FS-2 which was commercially supplied by Fujiwara Scientific Company, the highest purity of water was obtained in our laboratory routinely. Waters in first and second distillation chamber of this still were changed after 101 distillation. Distillation rate was controlled to 5 l/d(DDW-1) and 10 l/d(DDW-2). Distillation system was settled in semi-clean lab (Lead concentration in the air was about 1 ng/m^3) in Aoyama Gakuin University. DDW-1 and -2 were collected directly from still in 21 polyethylene bottles and were shipped to C. Patterson's Laboratory of California Institute of Technology in U. S. A. for the determination of lead. Lead blanks of reagents and bottles were determined before analysis. The sample water was acidified to 0.1 N HNO_3 and spiked with 30 ng of ^<208>Pb and equilibrated for 3 h at 55℃. Lead was extracted with dithizone-chloroform solution, backextracted to 1 N HNO_3 and dried in Teflon beaker. The lead isotope ratio was measured with a mass spectrometer in Caltech. The lead concentrations were 1.0 (DDW-1) and 0.7 (DDW-2)ng/kg. This water was pure enough for the ultra trace analysis for lead.
