AN APPARATUS FOR AUTOMATICALLY CHANGING THE TEM- 
PERATURE OF A CHAMBER 
George F. Potter 
It has been shown that the injury produced in certain plant tissues by 
freezing is influenced considerably by the rate at which the temperature 
falls during the freezing process.^ In order to obtain a uniform and known 
rate of temperature fall for experiments of this sort, the writer has developed 
an apparatus in which the rate of temperature change is automatically con- 
trolled by clockwork. Any desired rise or fall of temperature can be ob- 
tained, the conditions desired for a ten-hour period being determined and 
recorded in advance. By repeating the experiment without altering the 
adjustments, different lots of tissues may be frozen under duplicate tempera- 
ture conditions. 
A longitudinal section of the freezing chamber, together with end, top, 
and side views of the controlling mechanism are shown in Plate I. De- 
tails of certain portions of the apparatus, as indicated by lettering analogous 
to that used in Plate I, are shown in both front and side view in Plate II. 
The freezer proper consists of three cylindrical galvanized iron cans, placed 
one within the other, riveted together, and packed in a box of sawdust for 
insulation. The freezing mixture is placed in the space between the two 
outside cans (a, Plate I). The innermost can (c, Plate I) is the freezing 
chamber. The intervening space (5, Plate I) is used as an air space to 
prevent too rapid cooling unless temperatures lower than — io° C. are de- 
sired, in which case it is filled with an additional quantity of ice and salt. 
The two outside chambers {a and h, Plate I) are fitted with pipes and stop- 
cocks for drawing off the brine. The opening through these must be 
straight to facilitate removing obstructions. 
The freezing chamber is fitted with a tight galvanized iron cover, to 
the center of which a short section of iron pipe is attached firmly by means of 
an iron collar. All thermometers, recording and control apparatus are 
introduced through this opening. A steel T-bar is securely clamped to the 
iron pipe (section BB, Plate II) and extends from slightly above the top of 
the pipe to within a few inches of the bottom of the chamber. This bar 
serves as a support for both fan shaft and thermostat, and by means of 
clamps holds interchangeable racks to which the experimental materials are 
attached. All three cans are covered by a single galvanized iron cover of 
circular shape insulated with cork board. The iron pipe from the inner 
^ Chandler, W. H. Killing of plant tissue by low temperature. Mo. Agric. Exp. 
Sta. Research Bull. 8: 199-205. 1913. 
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