604 



SCIENCE. 



[N. S. Vol. XXI. No. 538. 



montlis, at least, is so foul that people have 

 to discontinue sprinkling the lawns and in 

 some cases the reservoir can be detected — by 

 the nose — over a half mile away. Now, as 

 this letter says, examinations of an algal- 

 polluted water usually show it to be harm- 

 less so far as man is concerned, but be- 

 cause of the odor and taste it might just 

 as well be poisonous. People can not use 

 it, and for this reason they are frequently 

 driven to use polluted wells and springs, or 

 bottled waters, which by no means are al- 

 w^ays free from disease germs. In this way, 

 epidemics have been known to arise, due to 

 the presence of algae in the city water 

 which, of itself, contained no pathogenic 

 organisms. A problem of so much sani- 

 tary and financial importance has naturally 

 received much attention from water engi- 

 neers and others. However, the recom- 

 mendations usually made of aerating the 

 water or covering the reservoir have been 

 either ineffective or too expensive, and up 

 to within a short time the problem of how 

 to get rid of the bad odors and taste in 

 water has been considered impossible of 

 solution. The principal means of avoid- 

 ing such difficulties has been to abandon 

 the reservoir, create a new system of supply 

 and hope the old condition would not re- 

 turn until the water company or the town 

 could afford to install another plant. Fil- 

 tration offered little or no relief; indeed, 

 filtered water, stored in an open reservoir, 

 is often more subject to algal pollution than 

 any other kind. Consequently, this prob- 

 lem of how to prevent the growth of algae 

 in water for domestic purposes had been 

 practically abandoned as impossible by 

 many of those most closely concerned with 

 water supply work. 



It seemed necessary, therefore, to take 

 up the question along some entirely new 

 line and, consequently, careful investiga- 

 tions were undertaken regarding the life 

 history of the particular organisms con- 



cerned and an attempt was made to find 

 some toxic element which, although fatal 

 to the plants, would yet be absolutely harm- 

 less to man. It is not necessary to consider 

 the large number of substances that were 

 experimented with, but, of course, it was 

 very soon found that the heavy metals were 

 more effective than anything else that could 

 be used on a practical scale. The fatal 

 effect of copper upon algse has been known 

 for a long time and our own experiments 

 seemed to demonstrate that it was more 

 efficient than anything else sufficiently 

 cheap and easily obtained. Therefore, it 

 was decided to carry on experiments on a 

 large scale with this metal alone. 



The three points, of course, necessary in 

 determining a means of destroying algae is 

 that it shall be thoroughly efficient ; that it 

 shall be cheap— for, of course, there must 

 be no limit to the amount of water treated 

 • — and finally it must be harmless to man. 



First, in regard to the efficiency, I will 

 give the result of a few experiments which 

 demonstrate what high dilutions of copper 

 sulphate will do to algae. 



The first opportunity Avhich presented 

 itself for experimenting on a large scale 

 w^as in the cress beds of the South. Here 

 the conditions were such that after the 

 cress had been cut and before the new 

 growth could start, a thick heavj^ mat of 

 algfE would form over the surface of the 

 water sufiicient to prevent the growth, if 

 not entirely smother out the delicate cress 

 plants. Since water cress at that time of 

 the year was worth about $20 a barrel, and 

 the demand was considerably greater than 

 the supply, a large amount of money was 

 being lost in this way, and it seemed worth 

 while to experiment with these beds and 

 see if it would not be possible to extermi- 

 nate the algal growth without destroying 

 the cress. Consequently, a solution of 

 copper sulphate was prepared of a strength 

 of about one to fifty million parts of water, 



