354 A. N. Winchell— Great Dustfall of 1920. 



Table I. — Analyses of three samples of dustfall at Madison, 

 March 19, 1920. 



(Dried at 105° C.) 



I II III Average 



Si0 2 68.61 66.32 66.66 67.20 



A1 2 3 13.81 13.44 13.89 13.71 



FeO 2.24 2.10 2.17 2.17 



MnO 33 .42 .41 .39 



MgO 1.63 1.71 1.94 1.76 



CaO 1.81 1.83 1.59 1.74 



Na 2 1.64 3.04 1.64 b 2.11 



K 2 2.22 2.11 2.56 2.30 



H 2 0+ (above 105°C) 2.55 3.47 3.63 3.22 



Ti0 2 53 .53 .52 .53 



P 2 5 14 .16 .16 .15 



N 37 .41 .37 .38 



Ignition 5.52 5.66 5.68 5.62 



101.40 101.20 101.22 101.28 

 H 2 0— (below 105° C) 3.23 2.91 2.19 3.11 



a Metallic iron determined and calculated to FeO. 



b Not determined on account of lack of material ; assumed to be the same 

 as in sample I. 



c Includes organic matter and C0 2 , but not H 2 nor N. 



I. Dustfall collected by E. R. Miller from one square meter 

 of surface at 2125 Van Hise Ave., Madison, Wis., 19 March, 1920. 



II. Dustfall collected by W. S. Fuscli from one square yard 

 of surface of ice about 1,000 feet north of Science Hall on Lake 

 Mendota at Madison, Wis., 19 March, 1920. 



III. Dustfall collected -by A. N. Winchell from one square 

 yard of porch roof at 200 Prospect Ave., Madison, Wis., 19 

 March, 1920. 



It was hoped that special tests could be made to measure 

 the tenor of water soluble salts, of organic matter, and of 

 carbon dioxide, 5 but scarcity of material prevented, as 

 it likewise prevented the determination of soda in sample 

 number III. It is our opinion that sample number II 

 is abnormally high in soda for some unknown reason; 

 therefore, we have assumed for purposes of mineral cal- 

 culations that sample III has the same tenor of soda 

 found in sample I. 



5 Sample I showed no visible effervescence when treated with warm HC1, 

 but carbonates can be recognized in small amount in all the Madison samples 

 under microscope. 



