b Air-stable, solid V2(SO& quantitatively reduces perchlorate to chloride upon 5 to 10 minutes' refluxing in 7 to 8M HzS04 in the presence of Os04 as catalyst. The determination is completed by potentiometric titration of the chloride formed or by spectrophotometric measurement of the VO+2 formed. Accuracies of 0.1 to 0.2% are obtained for 0.01-to 3-mmole samples by chloride determination. The spectrophotometric method gives accuracies of 1 to 270, with some interference by V(III) absorption. A correlation between the effectiveness of a metal ion as a reductant for perchlorate and the affinity of the oxidized metal for oxygen is noted. RESENT analytical methods for