y increasing in thickness
until the two opposite layers meet and join together. If thinner
blocks are required, the freezing process may be stopped at any time
and the ice removed. In order to detach the ice it is customary to cut
off the supply of cold brine and circulate brine at a higher
temperature through the cells. Ice frozen by either of the above
described methods from ordinary water is more or less opaque, owing to
the air liberated during the freezing process, little bubbles of which
are caught in the ice as it forms, and in order to produce transparent
ice it is necessary that the water should be agitated during the
freezing process in such a way as to permit the air bubbles to escape.
With the can system this is generally accomplished by means of arms
having a vertical or horizontal movement. These arms are either
withdrawn as the ice forms, leaving the block solid, or they are made
to work backward and forward in the center of the moulds, dividing the
block vertically into two pieces. With the cell system agitation is
generally effected by making a communication between the bottom of
each water space and a chamber below, in which a paddle or wood piston
is caused to reciprocate. The movement thus given to the water in the
chamber is communicated to that in the process of being frozen, and
the small bubbles of air are in this way detached and set free. The
ice which first forms on the sides of the moulds or cells is, as a
rule, sufficiently transparent even without agitation. The opacity
increases toward the center, where the opposing layers join, and it
is, therefore, more necessary to agitate toward the end of the
freezing process than at the commencement. As the capacity for holding
air in solution decreases if the temperature of the water is raised,
less agitation is needed in hot than in temperate climates.
Experiments have been made from time to time with the view of
producing transparent ice from distilled water, and so dispensing with
agitation. In this case the cost of distilling the water will have to
be added to the ordinary working expenses.

_Cooling of Liquids._--In breweries, distilleries, butter factories,
and other places where it is desired to have a supply of water or
brine for cooling and other purposes at a comparatively low
temperature, refrigerating machines may be advantageously applied. In
this case the liquid is passed through the refrigerator and then
utilized in any convenient ma