(a) COMPARISON OF TWO EQUIPHASE CELLS. Since the triple point
temperature of water is a defining standard, an Equiphase Cell can best be
checked for accuracy by comparing it to a second Equiphase Cell. If the
two cells are free from air leak or any other contamination, no temperature
difference between them will be observed. If a temperature difference is
detected, the cell having the lower temperature contains impurities. This is
so because the defining temperature of 0.0100, C is a theoretically
calculated maximum value for the triple point of water.
(b) TEST OF INDIVIDUAL CELL FOR AIR LEAK (See figure 12). Test
for air leak by tilting the Equiphase Cell, holding the seal-off tube down.
If there is no significant air contamination, an audible "click"is heard, and
the bubble trapped in the seal-off tube will diminish in volume by a factor
of three or more as the cell is tilted slowly tofurther compress the bubble.
A 3 to 1 reduction in the volume of the trapped air bubble means that the
freezing point is lowered less than 50 microdegrees, a figure within the
Equiphase Cell guarantee of .0005,C by a factor of 10. In most cases the
reduction in bubble size will be much greater than 3 to 1 (see figure 13).