FILTRATION OF WATER 



15 



That known as the Chamberland " F " is the more permeable, 

 one generally used both for .domestic purposes and for ordinary 

 by aspiration. The less porous and harder bougie, the Cham- 

 berland " B," is only used for nitration under pressure (vide 

 infra), and when manipulating fluids containing exceedingly 

 minute organisms, e.g. the organisms of foot and mouth disease, 

 pleuro-pneumonia, horse-sickness, etc. (vide "Filtrable Viruses" 

 Chap. LXIV.), which pass through the more porous "F" bougies. 



In addition to the Chamberland bougies there are other 

 niters of a similar nature. [The Doulton white-porcelain filter 

 (fig. 10) has been found to be " at least as efficient in the 

 retention of micro-organisms as the best material on the market, 

 viz. the Pasteur-Chamberland filter," and to " excel the latter 

 in its rate of filtration." x ] 



Another filter, Garros', is made of infusorial earth. This, 

 [like Doulton's] filter, has all the essential properties of a 

 Chamberland filter, and both are used in exactly the same 

 way. The Berkefeld bougie is also made of infusorial earth ; 

 it is inferior to the Chamberland " B " in that it wears out 

 more rapidly and does not hold back the smallest organisms ; 

 on the other hand it filters more quickly than, and does not 

 retain dissolved organic matter to the same extent as, the 

 Chamberland filters. For the latter reason it is especially 

 useful for the filtration of albuminous fluids. [But it must be 

 pointed out that recent experiments have shown that the 

 Berkefeld is not a trustworthy filter. 2 ] 



There are several ways in which these unglazed porcelain 

 and similar filters may be used. 



and the 

 filtration 



FIG. 10. Doul- 

 ton's porous por- 

 celain filter with 

 nozzle. 



1. Filtration of water. 



Every laboratory has a filter 

 attached, to a water tap, for the 

 purpose of readily obtaining a supply of sterile 

 water (fig. 11). 



The filter (Chamberland F [or Doulton white]) is 

 contained within a metal cylinder, through the 

 lower end of which it is inserted, and then securely 

 fixed by means of a metal screw-cap, an india- 

 rubber washer intervening ; both the washer and 

 metal cap are perforated to allow the passage of 

 the glazed nozzle. The upper end of the metal 

 cylinder is screwed on to a tap connected with the 

 water main. When the tap is turned on, water 

 runs into the space between the cylinder and the 

 bougie, traverses the bougie, on the surface of 

 which the solid matter in suspension is deposited, 

 filter attached to the water enterg the centra j cavity, and escapes from the 



is shown by the dotted lines m0 uth of the glazed nozzle, 

 and the glazed nozzle is seen 



projecting below. Preparation of the filter. 1. Before putting a filter 



into the metal cylinder it is absolutely necessary to 



ascertain that it has no fissure or flaw in its substance, because unless it be perfect 

 micro-organisms will quickly find their way through it. To determine whether or 



FIG. 11. A porous porcelain 



ter attached to the water 



main : the outline of the filter 



^Journal of Hygiene. 1906, 1909.] 



[ 2 Journal of Hygiene, 1908, 1909.] 



