445 
Nov. i, 1924 Dustfall of February 13, 1923 
matter in the other parts, but the per¬ 
centage is very small. 
It may be useful to compare these 
results with similar analyses of other 
dustfalls and of loess from the upper 
Mississippi valley, as shown in Table 
II and in Figure 2. Many other 
mechanical analyses of loess from the 
no doubt that part of it is actually 
present in the ferrous state. The only 
analysis of another American dustfall 
with which this can be compared is 
that of an earlier fall at Madison. As 
only a few satisfactory analyses of 
foreign dustfalls are available, all the 
good ones are included in Table IV. 
Fig. 2—Mechanical composition of dustfalls and of natural soils. The ordinate shows the per cent by 
weight of all sizes smaller than the size indicated by the abscissa. Curves 1 to 5 refer to Table II, 
Other curves from Meinzer, Water Supply Paper 489 
Mississippi Valley could be given, but 
they simply show that it varies con¬ 
siderably in the abundance of the 
various sizes. Increase of examples 
would not modify the main conclusion, 
which is that there is no essential differ¬ 
ence in this respect between the mate¬ 
rial of dustfalls and that composing 
loess. 
CHEMICAL COMPOSITION 
Dr. E. J. Graul, of the Soils Depart¬ 
ment of the University of Wisconsin, 
made a determination of the alkalies in 
the dust. The main analyses were 
carried out in duplicate by Martin 
Tosterud, of the Chemistry Department 
of the University. 3 The results are 
shown in Table ill. It was impossible 
to determine the state of oxidation of 
the iron in the dust because of organic 
matter. The small amount present 
was determined after complete oxida¬ 
tion, and is so reported, but there is 
Table III.— Chemical composition of 
the Madison dustfall of February 13, 
1923 (dried at 105° C.) 
Constituents 
Percentages 
Si02__ 
71.75 
71.70 
71.73 
AI 2 O 3 -__ 
7.84 
7. 85 
7.85 
Fe2C3-_.___ 
FeO... 
} 3.85 
4. 01 
3.93 
MgO.. 
1. 01 
.99 
1.00 
CaO__ 
1.83 
1.82 
1.83 
Na20___ 
1.12 
1.22 
1.17 
K 2 0___ 
2.15 
2.06 
2.11 
H 2 O (above 105° C.)_ 
5.00 
4.89 
4.95 
Ti0 2 .. 
.48 
.49 
.49 
P 2 O 5 _ 
. 17 
.17 
.17 
MnO__ 
.24 
. 17 
.21 
N____ 
.37 
.37 
! .37 
Ignition _ 
3. 57 
3.65 
3.61 
II 2 O (below 105° C.). 
H 2 0 (below 110° C.)_ 
99.38 
1.65 
2.46 
99. 39 
1.66 
2. 45 
99.42 
1.66 
2.46 
« Includes organic matter and CO 2 , but not H 2 O 
nor N. 
3 In order to further this work a grant of funds for chemical analyses was obtained from the research fund 
of the University of Wisconsin. 
