26 



THE POPULAR SCIENCE MONTHLY. 



that natural ice sometimes contains. Nearly all natural water 

 contains considerable numbers of bacteria, many of which are 

 derived from the sewage discharged into some lakes and rivers 

 from which ice is cut. It is commonly believed that water in 







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freezing purines itself from all kinds of contamination, but Dr. 

 T. M. Prudden has shown in this magazine that the truth is other- 

 wise. In his article on Our Ice-supply and its Dangers (Popular 

 Science Monthly for March, 1888) he says: 



A great deal of careful experiment has shown that water in freezing largely 

 expels its coarser visible contaminations, and also that a large proportion of the 



