244 
IOWA ACADEMY OF SCIENCES. 
plants of the fields to which this is applied will, finally 
incorporate it into their own tissues after it has been decom- 
posed by bacteria. As can be readily seen such a system 
must have several serious disadvantages. First, granting 
that sewage farming will purify the sewage, which no doubt 
can be done to a greater or less extent owing to the imposed 
conditions it is still doubtful whether or not it could be 
carried on successfully in a great majority of cases. In the 
first place the land must be of such a character as to per- 
mit of the irrigation system; secondly, if the sewage were 
applied continuously, it would be disastrous to the crops, 
killing them out as well as preventing the nitrification of 
the sewage by limiting the supply of oxygen to the soil. In 
the third place, the amount of desirable land required would 
in many cases be very expensive if it could be obtained at 
all. Mr. B. S. Brundell, M. Inst. C. E., who has constructed' 
many sewer farms, among them a farm at Dorchester, Eng- 
land, which is one of the most successful from a sanitary 
point of view, wrote as follows: “Sewage if properly ap- 
plied to land may be purified, but the operation is not prof- 
itable. That is to say. sewage farming cannot, save in ex- 
ceptional instances, be made to pay.” Mr. Brundell also 
brings up the additional factor of cold winter weather and 
seriously doubts whether or not the system could be suc- 
cessfully used in cold countries on account of the protracted 
cold winter. A very good short account of the Berlin, Ger- 
many, sewage farm is given by Barwise. 
Chemical precipitation was an effort made on the part 
of some to entirely purify sewage by the addition of chemi- 
cals. The principal precipitants used are lime, iron, alumi- 
num hydrate, alum, and copperas. Although the 
chemicals used for this purpose are almost innumerable, 
results tend to show that only the solid matter in suspen- 
sion is removed, while the sewage is deodorized for the 
time being. Extensive experiments with chemical pre- 
cipitation of sewage were made by Mr. Bibden in England 
as well as by the Massachusetts State Board of Health in 
America under the supervision and charge of Allen Hazen. 
The cost of constructing a plant for the chemical precipi- 
