EFFECT OF COPPER UPON WATER BACTERIA. 71 



lent example of the results to be expected from incorrect use of copper 

 in connection with slow sand filtration is furnished in Clark's " report. 

 Not onl}^ was copper found in the efiluent of the experimental filter, 

 but Bacillus coli was found in a rather high per cent of the bacterial 

 samples. 



The carbon dioxid content of the Ohio River is a possible explana- 

 tion also of the fact reported by Brown ^ that samples of Ohio River 

 water yielded between 0. 00772 and 0. 00657 grain of metallic copper to the 

 gallon, though Bacillus coli was occasionally present. To use his own 

 words, " It is seen from the work done, as above stated, that the copper 

 is present in an insoluble form and probably as the oxid united with 

 the suspended mineral matter which the water carries. If in this form 

 it would be unable to exert any germicidal power, and, as far as could 

 be determined, this seems to be the case. It was decided that the cop- 

 per was present in a spent condition." As there was no monocarbon- 

 ate alkalinity noted, the Ohio River water at this time doubtless 

 contained some free carbon dioxid, and from the analogy of the labora- 

 tory results it seems fair to assume that Brown's explanation must 

 be supplemented by the theory of the heightened resistance of Bacil- 

 lus coli due to carbon dioxid. 



« Journal New England Water Works Association, vol. 19, 1905, pp. 503-505. 

 & The Purification of Water at Marietta, Ohio. Ofiicial Eeport to Board of Public 

 Service, 1906. 



100— VII 



