46 Transactions Texas Academy of Science. 
Regarding the methods by means of which the filters remove the 
organic matter and bacteria the two systems differ materially. With 
the slow sand (or English) filters purification is brought about by bac- 
terial action within the filter bed itself, the full efficiency of the beds 
not being developed until the particular bacteria that effect this purifi- 
cation have had time to grow and coat the grains of sand composing the 
filter. The mechanical filters, on the other hand, act more as strainers 
and remove the organic matter and bacteria by entanglement within the 
body of the filter. They require to be frequently washed, and for this 
purpose filtered water must be used. This accounts in some measure for 
the greater cost of operation when this method is used. The slow sand 
filtration may be either continuous or intermittent, it being still some- 
what of an open question as to which effects the better results. With 
the slow sand filters the organic matter is decomposed by bacterial action, 
as has been stated, and converted from unstable into stable compounds, 
and it is probable that some, at least, of the bacteria that are found in 
the effluent are of a harmless kind that have grown near the bottom of 
the filter bed. With either method 100 bacteria per cubic centimeter in 
the effluent is not considered high for a first class drinking water. 
Quite recently the sanitary journals have contained notices of a new 
method proposed for the purification of water supplies by the use of 
ozone. The Engineering Record for February 3, 1900, contains the 
translation of a paper read some months ago before the German Asso- 
ciation of Gas and Water Engineers, in which Dr. Th. Weyl, of Char- 
lottenburg, Germany, describes the methods used by him. The Record 
also gives the discussion by engineers present at the meeting. One set 
of experiments was made on a scale of considerable magnitude in which 
water containing varying number of bacteria were treated. One test 
showed a reduction of the bacteria from 84,400 to 371 per cubic centi- 
meter, while the average of fourteen tests given show that less than 1.5 
per cent, of the bacteria remain after ozonation. The water was first 
passed through a species of rough filter to remove the larger pieces of 
suspended organic matter, such as paper, decayed vegetable and animal 
matter, as it was found that the ozone attacked these first and only 
burned up the bacteria after the larger particles of organic matter had 
been destroyed. The water used was taken from the river Spree, and 
contained from 80,000 to 100,000 bacteria per cubic centimeter, and as 
this is far beyond the limit allowable in water from which a drinking 
water supply should be drawn it was mixed with water from the city 
mains before the ozone was added. On February 14, 1900, Dr. George 
A. Soper, of New York City, read a paper before the New England 
Water-works Association upon this subject — the first of the kind to be 
presented in America, though the paper had been printed, in substance, 
