70 



MISCELLANEOUS PAPERS. 



The following table shows the various combinations of precipitates 

 tested and the exact results: 



Table XXXII. — Toxicit;/ of combined, precipitates to Bacillus coli} 



Duration of exposure to action of 

 precipitate. 



hour... 

 2 hours. . 

 6 hours . . 

 24 hours . 



Check. 



Copper 

 hydrate. 



Iron 

 livdrate. 



Aluini- I Copper 



num ' and iron 



hvdrate. hydrate. 



Copper 

 and alu- 

 minum 

 hydrate. 



Colonies. 



2,2.30 



675 



465 



165 



Colonies i Colonies. 



3,450 ; 1,7.50 



25 ' 320 



I 15 



■ 1 



tate 



1 Experiment conducted in 100 c.c. Jena glass flasks, each containing 15 mg. of the proper precipi- 

 te. All flasks inoculated with a 2 mm. loop of culture of Bacillus coli received from Prof. Theobald 



Smith. The temperature during this experiment varied from 18° to 22° C 



Table XXXIII. — Toxicity of combined precipitates to Bacillus coli.^ 



Duration of exposure to action of 

 precipitate. 



hour . . 

 2 hour.s. . 

 6 hours.. 

 24 hours. 



Check. 



Copper 

 hydrate. 



Colonies. 



3,350 



305 



350 



200 



Colonies. 



380 







1 







Iron ^l^^i- I Copper | ^^PPer^ 

 i,,7.^,„+^ num I and iron ,-,,,■,,,,,„ 

 hydrate, j^^^^^^^ hyd^te. ; jf^^^j^/^^^^ 



i_j^ 



Colonies. 



1,065 



1,900 



1,350 



850 



Colonies. 



2, 650 



3 



1 



1 



Colonies. 



3,100 



1 











Colonies. 



2,350 



80 











1 Experiment conducted in 100 c.c. Jena glass flasks, each containing 15 mg. of the proper precipi- 

 tate All flasks inoculated with a 2 mm. loop of culture of Bacillus coli received from the Bureau of 

 Animal Industry, isolated from hog. The temperature during this experiment varied Irom 18° to 

 22° C. 



The presence or absence of carbon dioxid is probably important in 

 this connection. If the laborator}- results will hold for tield condi- 

 tions, a copper precipitate or a precipitate of iron and copper will 

 be highl}' toxic to Bacillus coli and Bacillus typhi in a w^ater whose 

 alkalinit}' is chiefly monocarbonate; and, conversely, the action of a cop- 

 per precipitate or a copper-iron precipitate will be reduced if a water 

 contains free carbon dioxid. This is probably the reason that small 

 quantities of copper are toxic" in a mechanical filter using the proper 

 quantities of iron and copper, and gives an additional reason for the 

 advice given by EUms^and Brown nhat before tiltration or distribu- 

 tion of a copper-treated water all free carbon dioxid and part of the 

 semicombined carbon dioxid should be neutralized by caustic lime. 

 Copper treatment of water previous to slow sand filtration should be 

 made under similar conditions, and as this is seldom practicable it is 

 perhaps advisable to limit the use of copper in connection with slow 

 sand filtration to treatment after passing the filter, and before distri- 

 bution the proper quantity of caustic lime may be added. An excel- 



aBul. 76, Bureau of Plant Industry, U. S. Dept. of Agriculture. 



* Journal Xew England Water Works Association, vol. 19, 1905, pp. 496-503. 



<■' Journal New England Water Works Association, vol. 19, 1905, p. 578. 



100— VII 



