Figure 7.
Schematic drawings of the NBS gas thermometer gas-bulb assembly and the capillary temperature-profile measurement system used with the stirred-liquid thermostat baths. The upper portion of the figure, reprinted from reference 21, shows the gas bulb and capillary with their protective casings. Sliding seal H allowed for the difference in thermal expansion between the capillary and its protective case. The drawing also shows the location of Pt wires welded to the capillary to form Pt vs. (Pt+10 Wt% Rh) thermocouple thermometers A1-A12 and B1, used to determine the temperature distribution along the capillary. The lower portion of the figure shows details of the gas thermometer construction in the region of the connection between the gas bulb GB and the capillary C, both made of Pt-Rh alloys. The capillary protection tube PT and the gas-bulb protective casing IC were made of Inconel alloy. AI denotes an alumina collar used to insulate the bulb electrically from the case and to create a gap CP between them. The gap, known as the counterpressure space, was filled with 4He gas held at the gas-bulb pressure. Both the bulb and case were constructed by welding, using the heliarc technique.