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
Fig. 3.—Rink of Artifical Ice in Paris.
freezing purines itself from all kinds of contamination, but Dr. T. M. Prudden has shown in this magazine that the truth is otherwise. 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
