Tank Lid 
The lid is built separately from the tank proper, 
though of similar construction as to insulation (fig. 
5). On it are two shock-mounted 1/20-hp motors 
connected by V-belt drive to two shafts, each passing 
into the tank through Micarta insulating inserts 12 
inches in diameter. A stainless steel four-bladed pro- 
peller is mounted on each shaft at diagonal corners 
of the tank to provide thorough cross-stirring of the 
tank liquid. Apertures in the lid are provided for 
a standard platinum resistance thermometer and for 
the thermostat sensing element. Two apertures are 
also provided for inserting leads for any other ele- 
ment that may be undergoing calibration. 
A motor and its accessory drive are mounted on 
the tank lid to permit reversing the thermometer rack 
with the lid closed. A motor is also provided for in- 
dexing the rack so that the thermometers may be 
read successively at the telescope. This latter drive 
includes a solenoid-controlled disengaging lock to 
enable the rack to be reversed. 
STIRRING 
MOTOR 
STIRRING 
SHAFT 
LEAD FOR 
RESISTANCE 
THERMOMETER 
LEAD FOR 
THERMOSTAT 
APERTURE FOR 
NSERTING LEADS 
RAISING AND 
LOWERING CABLE 
The under edge of the lid is fitted with a round 
soft rubber strip to form a seal between it and the 
upper lip of the tank proper, which is of '%2-inch 
Micarta. As can be seen, all controls are mounted 
on the lid of the tank, so that the only apertures 
beneath the surface of the liquid are those necessary 
for liquid transfer. 
The lid is raised and lowered by four 5/32-inch 
stainless-steel cables, one attached to each corner, 
passing over a pulley mounted on top of each up- 
right and down through its center. The cable is led 
by another pulley to two doubly grooved spiral 
drums mounted on the bottom of the tank, each of 
the two drums handling two of the cables. One drum 
is mounted on each end of the shaft of a reduction 
gear driven through a friction-slip clutch by a 1/6- 
hp motor. The direction of rotation of the motor is 
reversed for raising or lowering the lid. Limit switches 
are mounted at the top and bottom of the lid’s 
travel to prevent overrunning. Sets of rollers at each 
corner guide the lid and maintain it in strict align- 
ment with the four supporting uprights. 
MOTOR FOR 
INDEXING RACK 
MOTOR FOR 
REVERSING RACK 
STIRRING 
SHAFT 
STIRRING MOTOR 
RAISING AND 
LOWERING CABLE 
NEGATOR 
CONSTANT-TENSION 
SPRINGS 
Figure 5. Tank lid. 
