BY HARDOLPH WASTENEYS. Vis: 
material such as the fused mixture of glass and sand, used 
in the Fischer Plaque filter. Filters under this section are 
neatly always operated at extremely rapid rates amounting 
in some cases to 130,000,000 gallons per acre per 24 hours. 
There are methods of filtration which do not come under 
either of these heads, but all the more important processes 
at present in use on a large scale are included. 
As I have already indicated, the water of this lagoon 
is objectionable for a town supply owing to its appearance, 
colour, smell and taste, but apart from these aesthetic con- 
siderations, water of this description is to some people positively 
harmful, causing when imbibed in any quantity various 
stomachic complaints. 
The purification of waters of this class is generally 
consiedred to be one of the difficult problems which Water- 
works Engineers and Chemists have to deal with. 
In the experimental purification of this water, the fol- 
lowing methods have been tested :— 
(a) Plain continuous filtration in filters constructed en- 
tirely of sand, with, of course, underdrains, and in filters whose 
sections consist of layers of sand, ashes and crushed quartz 
of various grades. 
(b) Plain intermittent sand filtration. 
(c) Mechanical filtration, with lime and alum as coaga- 
lants. 
(d) The Anderson Process, which comes under my heading 
of Mechanical Filtration. 
A method of water purification has been tried which, 
strictly speaking comes under neither of the heads mentioned, 
but which may for practical purposes be described as slow, 
downward, intermittent filtration. This ingenious process 
was suggested by Mr. Arthur Morry, of this City, who was at 
that time District Supervisor of Public Works, and in that 
capacity devoted a considerable amount of time and thought 
to the subject of water purification. A combination of this 
process and ordinary sand filtration was also experimented 
with. One more process has been tested, namely, Dr. 
Moore’s method of removing Algae and Bacteria from water 
supplies by means of copper sulphate. 
Continuous SAND FILTRATION. 
Although no less than five different filters have been used 
in this investigation, it is sufficient for the end in view to 
