

add copper sulphate at frequent intervals in sufficient amount to 
the upper lake, in which the brook has its rise, or else to the brook 
at its source at the outlet of the lake. This suggestion takes for 
granted the unproved and doubtful proposition that dissolved 
copper would be carried from the head of the brook throughout its 
length in sufficient amount to destroy the algae in the intervening 
pools. The copper sulphate method for killing algae has not, to 
my knowledge, been so far tried out for rapidly moving streams, 
such as we have in the Garden brook. It has, however, proven 
singularly efficacious in destroying algae in quiet reservoirs, lakes, 
aquaria, and watercress beds; in keeping water molds from min- 
now boxes; and in destroying bacteria in sewage effluents. 
Intelligently used, copper sulphate is undoubtedly a valuable 
adjunct in protecting bodies of water against excessive growths o 
algae. For several reasons, however, it must be used with ex- 
treme caution. In the first place, certain kinds of fish are readily 
killed by injudicious applications of the poison. Thus, trout have 
been shown to be very susceptible, the limit of safety being placed 
by Kellerman at 0.14 parts of sulphate per million gallons of water. 
The limit of safety for carp is somewhat higher, being placed at 
0.30 parts, and for goldfish at 0.50 parts per million gallons of 
water. The amounts required for the destruction of some algae 
are dangerously near mie amounts which are found also to kill 
fish. For example, Hydrodictyon requires 0.10 parts of copper 
sulphate (or 0.88 of a pound) per million gallons of water; the 
more troublesome blue-green algae require from 0.10 to 0.30 parts 
per million, while some of the more resistant and troublesome 
‘diatoms and green algae require as much as I part (equivalent to 
8.3 pounds) of copper sulphate per million gallons. The pos- 
sibility of injury to some of the higher flowering plants growing 
in the brook must also be taken into careful consideration, espe- 
cially in view of the fact that exposed roots of the willows and 
other plants, which in many places have grown out into the 
stream, lend themselves liable to serious injury from the poison. 
And, finally, the fact cannot be lost sight of that even though the 
copper sulphate method may prove efficacious in killing the algae 
of the Garden brook, the dead and unquestionably unsightly scums 
themselves must afterward be removed in some manner. All of 
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