(b) Principle of Operation. Figures on the dial, 26
through 31, represent inches of mercury, the standard means of
expressing atmospheric pressure. Read the indicating hand, the one
cloest to the dial; it-responds readily to any change in atmospheric
pressure. Use the set hand to note any change in pressure. Position
the set hand directly over the indicating hand. A few hours after
se'tting, not any change in pressure. Position the set hand directly
over the indicating hand. A rise in pressure is indicated by move-
ment of the indicating hand to the right. A fall in pressure is
indicated by movement of the indicating hand to the left.
(16) Desiccating Cabinet.
(a) Description. The desiccating cabinet (27, fig.
1-4) is constructed of stainless steel with glass side panels. A
molded rubber door gasket provides an airtight fit. A set of two
shelf runners are provided to hold a shelf or a tray. The 8 by 9 5/8
inch (20.32 by 22.86 cm by 1.59 cm) tray is constructed of stainless
steel, and the asbestos shelf has twelve 7/8 inch (2.22 cm) holes. A
manual relief valve is located in the upper right-hand corner.
(b) Operating Instructions.
1. To close the door, it may be necessary to force
the door tightly against the jamb before turning handle. Be sure that
the square rods enter the top-and bottom keepers before tightening
Do not turn the handle move than necessary
to seal the door. Balance of movement should
be reserved for future adjustment.
2. Before opening the door, normalize the pres-
sure in the cabinet by opening the manual relief valve.
3. Place a thermometer in the cabinet with heat-
ed samples and note the temperature rise. Do not open the door until
the temperature returns to ambient.
(1) Safety Features.
is provided in the electrical system. This prevents the supply of
power to all electrical circuits except the exhaust fan for 10
minutes after the unit is connected to the external power source.
Therefore, a 10 minute air-purge, which removes any accumulation of
explosive or toxic fumes, must take place before any operations can
(b) Automatic Gas Alarm. A combustible-gas-mixture
alarm system for the detection of an accumulation of combustible gas
is also provided in the laboratory. When a dangerous accumulation of