54 THE DOMESTIC WATER KILTER. 



cylinder, closed at one extremity and having a nipple-shaped 

 open tube composed of glazed porcelain at the other extremity. 

 The unfiltered water surrounds the outer surface of the unglazed 

 porcelain, and passing through this issues as filtered water from 

 the glazed nipple. This candle is composed of such dense 

 porcelain, that enormous pressure is required to force water 

 through it. The candles used for table filters are not so dense, 

 and consequently permit the water to flow through by gravita- 

 tion and capillary attraction. After a time these candles become 

 coated on their outer surface with a film of a slimy nature which 

 impedes the passage of water. This, however, is readily brushed 

 off, and the candle may be boiled to render it absolutely sterile. 

 This form of filter is extensively used in laboratories, and is 

 found to work very well, not only in sterilising water but also 

 the various cultures used for bacteriological purposes. The 

 Pasteur filter, as this is called in France, has been in use in that 

 country since 1886, and has been shown practically and scien- 

 tifically — according to the statement of the vendor — to absolutely 

 arrest all germs of disease in water, and to prevent typhoid 

 fever, cholera, malaria, dysentery, and all other diseases com- 

 municated by water. Drs. Woodhead and Wood state that the 

 " true criterion of an efficient filter is, whether it permits or not 

 of the passage of test organisms, such as cholera and typhoid 

 bacilli which do not readily multiply (if at all) in water, with the 

 filtrate." Water containing in suspension the Staphylococcus 

 pyogenes aureus to the number of 3,000 to 4,000 per c.c. was 

 passed through this filter and the filtrate gave a negative result 

 on the first, second, third and fourth days. Suspensions con- 

 taining from 5,000 to G,000 cholera bacilli to the c.c. and those 

 containing 8,000 to 10,000 typhoid bacilli to the c.c. were also 

 passed through the filter, and gave negative results on the first, 

 second, third and fourth days. Tap water containing 35 to 40 

 micro-organisms per c.c, when passed through these filters was 

 free from the presence of any organism on the first, second, 

 third and fourth days. 



The Berkefeld Filtering Company. — The filtering medium of 

 their filters consists of silicious earth formed into a hollow cylinder, 

 the candles being very similar to the Chamberland Pasteur ones. 

 This filter can be used as a table as well as a pressure filter. 



