15 GC. Solubiltty of Sr°U Denosited in Rains The ahove indirect evidence for the solubility of the 5r90 activity in fallout is confirmed by the analysis ard reasvrenent of the insolubio residues from Chicago rains, The irsoluble residucs from two active Chicago rains, CY, 320 and CL O07 & hO8, initially separated ty filtratin., were fused with NapC03 and dissolved in HCl. Following a fuwaing nitric acid separation of Sr, tho samrles vere reserved for vttrium-990 crovth and milked for the ye activity, Tne results are snovnm in Table 3 tocether with the Sr0 activity or the water soluble fraction, Table 3 * Soivhbility of Sr?° in Rains CT. 320 | oI. Lo7-8 1, Total Sr? Activity in Solution (DPM) 49.2 + 065 29.92 1.5 2. Total Sr?0 Activity in Insoluble Residue (DP!) £0.6 C.7 + 0.4 3, Percent cf Total Activity in Inseluble Residue 21,% 2.2 + O.L% D, Chicaro Fellout History from Rain and 3oil Date The Sr?° data for Thi age rains and Chicago Milksnc-d soils are sumuarized in Figure which gives the approximate total scil burden of Sr7° und its change with time over the three year veriod, January 1953 to Becember 1955, The curve is normalized to the average available Sr7° in six typical Chicarce. iilkshed soils collecte’i on September 29 and 30, 1955, The totai mortaiy fallout in Chicago rains are taken from Tsbles 1 and @ above, ani the method of measurement and data are discussed in the eccommanying section. ‘ilkshed soil data are discussed below. ~ The Chicago NYOO The everage availatle sr? observed fr the same six soils samoles in late September 1953 is also piotted, The i-reement in this case ma; be partly 6