1885.] The Removal of Micro- Organisms from Water. 383 



liquefied, the filtered water did not contain in either of two experi- 

 ments any organism whatever. The filter had thus completely steri- 

 lised the water passing through it. 



The rate of filtration was considerably less rapid than in the case 

 of the greensand, being only 0*82 inch per hour. Continuous filtra- 

 tion was then carried on for twelve days, during which time 4"2 litres 

 of water passed through, after which the unfiltered and filtered waters 

 were again examined. 



The unfiltered water contained . . 2792 centres per c.c. 



The filtered „ „ . . No organisms of any kind. 



Thus the efiicacy of the filter remained unimpaired after twelve 

 days' continuous action. 



After acting for one month, 14'6 litres of water having passed 

 through, the waters were again examined. 



The unfiltered water contained. . 1281 centres per c.c. 

 The filtered ,, ,, .. 6958 ,, „ 



Thus at the end of one month the filter was actually delivering 

 water more highly impregnated with organic life than that with which 

 it was supplied. 



Sjpongy Iron. — The filtering power of this material was also examined 

 by means of a similar series of experiments. The rate of filtration 

 at the commencement was 1*84 inches per hour, and the following 

 results were obtained : — 



Unfiltered water contained .... 80 centres per c.c. 

 Filtered „ ,, .... No organisms whatever. 



After twelve days' continuous filtration, 3*6 litres of water having 

 passed through, the following results were obtained : — 



Unfiltered water contained. . 2792 centres per c.c. 

 Filtered „ ,, No organisms whatever. 



Again, at the close of one month's continuous filtration, 9 litres of 

 water having passed through, the examination was repeated : — 



Unfiltered water contained. . 1281 centres per c.c. 

 Filtered „ ,, . . 2 „ ,, 



The column of spougy iron, 6 inches in depth, was thus able to 

 remove all the organisms from the water for upwards of twelve dajs, 

 and even at the end of the month, the water after filtration was 

 almost destitute of organic life. The rate of filtration was, however, 

 greatly diminished in the course of the month during which the filter 

 was in operation. It is worthy of notice that the organisms found 

 in the filtered water were all of the same kind, and caused no lique- 



