18 ITI. Results for 1955 Chicago ilkshed Samples A. 1955 Chicago iiilkshed Soils Table h summarizes the results obtained for the Chicaco lMilkshed coils collected September 29 and 30, 1955, The availabl2 calcium in crams er square foot was computed from Beltsville anal+rses of available calcium rer unit weicht of sample and total weight and area of sample collected, Stroentium90 analyses sere rade ov the Chicago Sunshine Laboratory. The samrles were taken from the same fields of farms sampled in 1953 and acain in 19S), Farms 43, #6 and #7 had been plowed recently, For each of tiess, 15 nlugs, 3.5 inches in diameter, vere taken to a decth slirchtly greater tna. anvarent plow derth. On farm #7, two sets of samples were taken from alternately snaced holes to »~rovide a check on the reliability of samplin, recently plowed fields. The agreement in the results of the duolicate samnles is very strikinc, The results in dpm per square foot anply to the available strontium-90 (*.e., extractable in normal neutral aymonium acetate) and not necessarily the total strontium-90 deposited per square foot. Although the Chicago rain data indicate that the strontium-90 is derosited in soluble form, it is recelled ‘that 1953 soil samples fused with Hagl03 following s:ecessive °H)AC and HCl extract.cn stioved appreciable residual strontium=90. The average for the first six farms listed in Table NYOO is 970 + 1€0 dom available strontium-90 per square foot, corresponding to about 12 millicuries per square mile for titis area. The Septemoer 30, 1953 average for these sare six soils vas approximately 5 millicuries ner square mile. The increase of 7 millicuries per square nile for the two vear period is in surprisingly good agreement with the total deposition of strontium-90 in Chicago rains over the same time interval (see Figure l),