Proceedings. 207 



small, and to obtain reliable figures it is necessary to filter a 

 large quantity of it to obtain a moderate quantity of the solid 

 matter so that it can be weighed and examined. On 

 making some experiments with the Berkefeld filter, which 

 is made of Kieselguhr or fossil earth, I found that the 

 smallest of the microbes, or other particles, were arrested, 

 and the water sterilized. I observed that the water was 

 filtered so rapidly that a large quantity could be passed 

 through the filter in a few hours before it began to get 

 blocked up ; thus in one experiment I filtered 36 gallons in 

 6}i hours, whilst only 24 more were filtered during the 

 following 120 hours (five days). The suspended matter 

 was of a black- slimy nature, and on microscopical exami- 

 nation was found to contain bacteria and animalcules, 

 amongst which were diatomacea;, monads, etc. The water 

 contained from 003 to O'l grains, i.e., from yfoths to yWhs 

 of a grain per gallon of total suspended matter, of mineral 

 and of organic origin. Sometimes there was a larger 

 quantity of mineral than organic matter, and sometimes the 

 reverse. The following are the figures obtained from the 

 water examined at my laboratory in Princess Street, 

 Manchester : — 



Grains per Gallon — 1892. 

 g Dec. JO Dec. ib to 31 Oct. 8 Dec. 12 Dec_ 



Total Solid Matter in suspension o'looi o'0386 o'oSgG o"o373 o'o6io 

 Which is composed of : — 



Organic Matter, Combined 



Water, etc o'0357 ... o'0292 0'02i7 0*0395 



Mineral Matter 0-0644 ••• o'o6o4 o'oioa o'02i5 



Totalamountofwater filtered (gals. ) i7'8 3S'o 6075 35-2 20"5 



When a beam of light was passed through the water 

 contained in a large glass globe, before filtration it appeared 

 turbid, the course of the beam of light passing through 

 being well marked ; after filtration, however, the water 

 appeared quite free from turbidity, and the course of the 

 beam of light in the filtered water could not be followed. 



