The
mercury barometer is located in the laboratory on the far right wall next
to the computer lab, under the clock. It is kept in a locked wooden
box on the wall. It will be unlocked for you before you get to lab.
In the very bottom of the barometer is a pool of Mercury, which supplies the column with Mercury.
Notice that the Mercury meniscus, concave down, is opposite
of water, which is concave up. When reading pressure on the barometer
the top of the meniscus needs to be level with the index line, which extends
from the bottom of the sliding metal plate. Adjust the knob on the
side until the bottom of the sliding metal plate sits atop the Mercury
meniscus.
After the sliding metal plate is lined up with the meniscus,
it is time to take a reading. Notice that the index line is lined
up in between 700 mmHg and 800 mmHg.
A closer look shows that the index line is between 758
and 759, so our pressure measures 758.X mmHg. Use the Vernier scale
to find out how many tenths of a mmHg are in the measurement by finding
the line on the Vernier that lines up exactly with a line on the main scale.
In this case the 6 on the Vernier scale lines up exactly with the main
scale, so the complete reading is 758.6 mmHg.
