Chapter 5 Measurement of Atmospheric Pressure

clearance enough to rattle, allowing for expansion.(10) Inspecting the barometerAfter disassembly, cleaning, and reassembly of the barometer, check the outer tube for mercurydrops. Stand the barometer upside down and leave overnight to check for mercury leakage.If mercury leakage is found, readjust the screws.If there is no leakage, turn the barometer back to a vertical setting and inspect the degreeof vacuum. It can be judged by a metallic sound like a click when mercury comes in contactwith the top of the glass tube. When this sound is heard in the same way as beforedisassembly, the degree of vacuum is satisfactory.If two barometers are available, compare their index errors before cleaning. Comparethem again after cleaning to make sure that there is no change in the index error.21