IOWA ACADEMY OF SCIENCE 
131 
number of organisms per cc. was determined. Then College sewage 
was allowed to percolate through these same cylinders filled with 
earth. The results obtained were as follows : 
All plates were plated on the 15th of August and counted on the 
17th. The College sewage had 540,000 bacteria per cc. The College 
water supply, 40 bacteria per cc. The number of organisms found 
m different media in effluent from different soil samples were as 
follows : Sample taken near river, % mile below Power House, 
Litmus lactose agar, 100, 500, and 300 bacteria per cc. Below 
Barneston, about half way to city intake, where the railroad will 
be quite close to the stream, the number of organisms per cc. was 
as follows : 140, 300, and 1,350. Sand and gravel half way between 
Power House and Barneston : Litmus lactose agar, 350, 400, and 300 
bacteria per cc. This although not a crucial test because the experi- 
ment should have been conducted over a longer period^ seems to 
indicate efficient filtration of sewage organisms. The water coming 
through the soil was clear, after the liquid was allowed to percolate 
through for an hour or more. The writer is indebted for the 
mechanical analysis of the soils to Mr. E. B. Watson of the Soils 
Department of Iowa State College. This analysis shows consid- 
erable gravel and sand but a small amount of clay. The point below 
Barneston was 50 feet from the river; sample No. Ill was 20 feet 
from the river. 
REPORT OF MECHANICAL ANALYSTS OF SOIL. 
a 
CM 
Analysis of “Fine Earth,” 
1 Finer Than 2 M. M. 
Soil 
Coarse gravel 
greater than ! 
m. i 
Fine gravel 
2-1 m. m. $ 
Coarse sand 
1-.5 m. m . i 
Medium ssnd 
.5-. 25 m. m. i 
Fine sand 
25-. 1 m. m . 
Very fine sand 
.1-.05 m.m, $ 
Total sand 
2-. 05 m. m. i> 
Silt .05.-005 m. 
m. i 
Clay ,005-m. 
m. i 
o 
EH 
I. 
One half way between 
Barneston and power- 
house 
53.1 
14.03 
16.58 
8.50 
14.24 
8.50 
61.85 
29.55 
7.86 
99.26 
II. 
Below Barneston 
5.9 
1.42 
4.10 
4.70 
32.36 
21.21 
63.81 
30.13 
6.07 
* 
III. 
Just below power house 
61.4 
17.40 
12.79 
5.66 
22.01 
11.74 
69.60 
23.06 
7.34 
t 
* 100 . 01 . tioo.oO. 
Mr. E. B. Watson calls my attention to the results of some work 
carried on by the Bureau of Soils 1 with reference to the absorption 
of organic matter. 
1. Bui. Bureau of Soils, 23:46. 
