(b) Refrigerate the inside of the thermometer well with powdered dry ice
(solid C02).
The entire Equiphase Cell may be precooled by placing it in the food compartment of an
ordinary refrigerator overnight. Other means of precooling can be used but it is important
to avoid freezing of water in the glass cell. Precooling is not required but will result in
maintaining the ice mantle for a longer period and will require less coolant to form the ice
mantle initially.
CAUTION: Refer to para 2f(1) (a). The glass cell should be held in its container when
the assembly is inverted for draining. This will eliminate the possibility of
the cell's falling from the container.
Prepare powdered dry ice by pulverizing 1/2" to 2" chunks of dry ice in an ice crusher,
grinder, or shaver to produce particles ranging in size from a fine snow to 1/16" diameter.
Pour the dry ice into a plastic funnel held over the top of the thermometer well. Tap
lightly on the side of the funnel to prevent the dry ice from blocking the funnel.
Replenish frequently to keep the well reasonable full of dry ice. Gas evolution,
particularly on first introducing the dry ice into the well, is vigorous and particles will be
suspended in the gas stream. To prevent formation of gas pockets shake the cell gently.
When the glass cell and the insulating jacket are at room temperature, it takes
approximately 15 to 20 minutes to form a large ice mantle. The thickness of the mantle is
not important provided it completely envelopes the well but does not touch the outer wall
of the glass cell. A mantle 3 to 10 mm thick is satisfactory. When the water level in the
glass cell has risen 1/8" to 1/4", a sufficient ice mantle will have formed. (See figure 6)
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