WATER SUPPLY	347
In choosing a site for a mill too much importance cannot be attached to
the question of water supply, and exhaustive tests must be carried out to ascer-
tain the amount and quality of the supply, having due regard to the immediate
and possible future requirements.
In almost every mill vast quantities of water can, and should, be recovered
for further use. This question is now receiving greater attention than formerly,
and it is a most important one.

STORAGE HOPPER
feed /     Jssam^ jv^^^^^n ^^^^bh^^^«~ drive
CONTROL
VORTEX
MOCER,

[Paterson Engineering Co. Ltd.
fig. 152.—chemical dry feeder, for the accurate addition op chemicals
for water treatment
Broadly speaking, the water has to be recovered from the machine and
returned to the beaters, or to the stuff box at the machine, but there are other
places where a great deal can be recovered.
To take first a rag mill, which uses more water per ton of paper than other
mills. Water is first used in the rag boilers; this is irrecoverable, owing to
the presence of grease, soluble soaps, etc., and it must be passed to settling
tanks if no convenient sewer is available. It should not in any case be returned
to the river.