= 36 
mated (see Oil, Paint and Drug Reporter, ’18 and ’18a) that the sewage 
of ninety-seven cities of more than 50,000 inhabitants, treated by the 
Miles acid process, would yield per year as follows: 
HMentilizer: ae cie ee ice eee 97,393,680 tons 
Ammonia, ; | 'tavan iat so) Gelazis lotta tne 4,869,684 tons 
Greases) ok. ae idah. oeia eases bie earns 25,780,680 tons 
Glycerine: .k evan ee eee ienite eee 1,289,039 tons 
Recovery plants have not been installed, however, because critics of 
the conservation plan maintain that the profits will be less than its 
friends have predicted. As has been true in most other cases, calcula- 
tions of the cost of suitable recovery plants and of the value of recovered 
products have been made with only minor regard to public health, and 
with little reference to the damage which the remaining effluent may do 
to fishes. In correct calculations the value of the recovered products and 
the benefits to public health would both be regarded as credits. The 
dangers or benefits to fisheries from the residual acid effluent of the Miles 
process should also be considered. This effluent is 50 parts per million 
acid. Either sulfuric acid or sulfur dioxide may be used in the process. 
Sulfur dioxide and salts of sulfurous acid (Phelps,’09) are probably 
more toxic to fishes than sulfuric acid and its salts (see Table II1). The 
acid should be neutralized if present in dangerous concentrations, and 
the cost of reducing the acidity of the effluent balanced against fisheries 
protected thereby. 
