70 



MISCELLANEOUS PAPEES. 



The following table shows the various combinations of precipitates 

 tested and the exact results: 



Table XXXII. — Toxicity of comhined precipitates to Bacillus coli.'^ 



Duration of exposure to action of 

 precipitate. 



Check. 



Copper Iron 

 hydrate, hydrate. 



Alumi- 

 num 

 hvdrate. 





hour 



Colonies. 

 : 2, 250 



Colonies. 

 1, 525 



• 



Colonies. 

 645 

 230 

 230 

 230 



Colonies. 



7,750 



1,800 



195 



5 



Colonies. 



3,450 



25 











Colonies. 

 1,750 





; 675 



320 



6 hours 



.... 465 



15 



24 hours 



: 165 



1 









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

 tate. All flasks inoculated Avith 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 jjrecipitates to Bacillus coli.^ 



Duration of exposure to action of 

 precipitate. 



Check. 



Copper 

 hydrate. 



'--:S..asi|i 



hour 



Colonies. 



3,350 



305 



350 



200 



Colonies. 



380 







1 







1 ; 



Colonies. Colonies. Colonies. 1 Colonies. 

 1,065 ! 2,650 3,100 1 2.350 





1,900 3 1 1 



80 





1,350 

 850 



1 

 1 I 



i 







24 hours 











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 Industrv, isolated from hog. The temperature during this experiment varied from 18° to 

 22° C. 



The presence or absence of carbon dioxid is probably important in 

 this connection. If the laboratory results will hold for held condi- 

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

 be higiily toxic to Bacillus coli and Bacillus typld in a water whose 

 alkalinity 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 probabh^ 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 Ellms ^ and Brown ^ that before filtration 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 ma}' be added. An excel- 



« Bui. 76, Bureau of Plant Industry, U. S. Dej)!. of Agriculture. 

 & Journal New England "Water Works Association, vol. 19, 1905, pp. 496-503. 

 ^ Journal New England Water Works Association, vol. 19, 1905, p. 578. 

 100— vn 



