SUMMARY. 43 



COST. 



No definite estimate of the cost of the treatment of a reservoir can 

 be given, because of the special conditions governing each case. It is 

 evident, however, that the maximum cost of material for exterminating 

 algae can not exceed 50 to 60 cents per million gallons, and will often 

 be less than half this amount. The cost for the copper-sulphate 

 destruction of bacteria will be from $5 to $6 per million gallons, and 

 where lime or some soluble hydrate is used in addition the cost would 

 be increased about one-third. The cost of labor necessary to intro- 

 duce these substances will be slight, since two men can usually treat 

 from 10,000,000 to 20,000,000 gallons in less than three hours. 



SUMMARY. 



The importance of maintaining all public water supplies at the 

 highest degree of purity and wholesomeness is too well recognized to 

 require any discussion. 



The disagreeable odors and tastes so often present in drinking water 

 are due almost exclusively to algae, although the economic importance 

 of studying these plants has not been recognized until recent years. 



These algal forms are widely distributed, and reservoirs in many 

 States have been rendered unfit for use by their presence. 



The methods now known for preventing or removing the odors and 

 tastes caused by algae have proved unsatisfactory, either because of 

 prohibitive expense or failure to accomplish result. 



It is therefore desirable that some new, cheap, harmless, and effective 

 method be devised for ridding reservoirs of these pests. 



It has been found that copper sulphate in a dilution so great as to 

 be colorless, tasteless, and harmless to man, is sufficiently toxic to the 

 algae to destroy or prevent their appearance. 



The mode of application makes this method applicable to reservoirs 

 of all kinds, pleasure ponds and lakes, fish ponds, oyster beds, water- 

 cress beds, etc. It is also probable that the method can be used for 

 the destruction of mosquito larvae. 



At ordinary temperatures 1 part of copper sulphate to 100,000 parts 

 of water destroys typhoid and cholera germs in from three to four 

 hours. The ease with which the sulphate can then be eliminated from 

 the water seems to offer a practical method of sterilizing large bodies 

 of water, when this becomes necessary. 



The use of copper sulphate for the prevention of disease is regarded 

 as incidental and is not designed in any way to supplant efficient pre- 

 ventive measures now in use. It is believed, however, that up to this 

 time no such satisfactory means of thoroughly, rapidly, and cheaply 

 sterilizing a reservoir has been known. Since the selective toxicity of 



