BY HARDOLPH WASTENEYS. 123 
to the lagoon water during the stagnation period before 
mentioned, a still smaller amount of the salt would be necessary 
on account of the fact that organisms exist to any great 
extent during that period only in the upper 15 feet of water, 
whilst it is probable that the stratification of the water by 
reason of its varying density would help to maintain the solu- 
tion in the upper layers of a sufficient strength and for a 
sufficiently long period to enable it to do its work among the 
algae; and it is to be remembered also that in the surface 
layers of water where the algae are most abundant, the 
solution will in any case owing to the method of applica- 
tion, be for a short period much stronger than one to eight 
million. 
My experiments also proved that when solutions of the 
strength named were used, no copper could be detected in 
the water three days after its addition, although the test 
used would easily have detected the presence of 1 part of 
copper sulphate in 25 million parts of water. As this pro- 
portion is equivalent to 1 part of metallic copper in 100 million 
parts of water, it may be considered I think that all the 
copper is eliminated by precipitation. 
In the majority of these experiments with copper sulphate, 
43 gallons of water were used, the containing vessel being 
glass in nearly every case. Small fish were invariably present, 
and in no case suffered any apparent inconvenience. 
It is impossible here to go into the results obtained 
in these experiments in anything like detail, and it is sufficient 
to state that the results indicate that the method could be 
successfully applied to a water of the type under considera- 
tion, nevertheless although the copper sulphate treatment 
is a most valuable remedy for the unpleasant odours and 
tastes, and might be advantageously applied where no other 
method of purification exists, or in conjunction with other 
methods, it does not remove the colour and dissolved organic 
matter, and only removes one of the causes of colour and 
organic contamination, consequently it cannot be said to 
remove the necessity for filtration. 
In conclusion I may state that nearly every one of the 
methods I have described for the purification of this lagoon 
water yields a product which would be received with delight 
