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chemical formula is CH3COC2H5.
melt. To change the physical state of a material from a solid to a liquid. A material melts when it absorbs
enough heat to change from a solid into a liquid.
melting point. The temperature at which a material changes from a solid into a liquid because of the heat it
has absorbed.
mendelevium. A radioactive chemical element in the actinide series. Mendelevium’s symbol is Md, and its
atomic number is 101. Mendelevium is made by bombarding lighter elements with light nuclei accelerated
in cyclotrons.
meniscus. The shape of the top of a column of liquid caused by surface tension. Water wets the inside of a
glass tube, and capillary action pulls the water up the sides of the tube. Surface tension causes the meniscus
of water to be concave. Mercury does not wet the glass, so surface tension causes mercury to have a convex
meniscus.
When reading a barometer or manometer using a column of liquid in front of a calibrated scale,
read the height of the column at a point tangent to the meniscus rather than from the edge of the liquid on
the glass.
meniscus lens (optics). A simple lens having one concave and one convex side. If the convex side has a
longer focal length than the concave side, the lens is a diverging lens. But if the concave side has the longer
focal length, the lens is a converging lens.
mensuration. The act of measuring or computing lengths, areas, volumes, and angles of various geometric
shapes or quantities.
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Mercator projection (navigation). The projection used for map making in which the meridians of
longitude and parallels of latitude are straight, parallel lines. The distance between each meridian of
longitude is the same, but the parallels of latitude are close together near the equator and become
increasingly farther apart as they near the poles.
The shape and size of land masses near the poles are greatly distorted on a map drawn on a
Mercator projection.
mercerize. A treatment given to cotton thread to make it strong and lustrous. The thread is stretched while
it is soaked in a solution of caustic soda. Mercerized thread has a sheen similar to silk, it is stronger and
more pliable than untreated thread, and it accepts dye more readily.
mercury. A silvery-white, poisonous, metallic chemical element that is liquid at room temperature.
Mercury’s symbol is Hg, its atomic number is 80, and its atomic weight is 200.59.
Mercury is heavy (more than 13 times as heavy as water), is a good conductor of electricity, and
readily unites with other chemical elements. It is used in thermometers to measure temperature by the
amount it expands or contracts as temperature changes. It is also used in barometers to determine the
pressure of the atmosphere by measuring the height of the column of mercury the atmospheric pressure
supports.
mercury barometer. An instrument used to measure atmospheric pressure. A glass tube about one meter
long, with one end closed and the other end open, is filled with mercury, and the open end is submerged in
a bowl, or cistern, of mercury. The mercury in the tube will drop down, leaving a vacuum above the
mercury in the closed end.
Atmospheric pressure pressing down on the mercury in the bowl holds the mercury up inside the
tube. The height of the top of the mercury in the tube above the level of the mercury in the bowl is an
accurate measure of the amount of pressure produced by the weight of the atmosphere. Standard
atmospheric pressure at sea level holds the mercury up in the tube to a height of 760 millimeters, or 29.92
inches.
mercury cell (electrical battery). A type of primary electrical cell (a cell that cannot be recharged). A
mercury cell uses zinc for its anode (positive terminal), mercuric oxide for the cathode (negative terminal),
and potassium hydroxide for the electrolyte.
A mercury cell has a longer life than either an alkaline cell or a carbon-zinc cell, and its low
internal resistance allows it to hold a constant output voltage until it is almost completely discharged.
mercury switch. A form of electrical switch using mercury in a glass tube as a conductor. Two wires are
brought into the glass tube in such a way that they are near each other, but do not touch. When the tube is
tilted in such a way that mercury sealed in the tube covers the ends of the two wires, the switch is closed
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
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and current flows through the mercury. When the tube is tilted in the opposite direction, the mercury moves
away from the wires, the switch is open, and no current flows.
mercury thermometer. A form of liquid thermometer. A glass tube having an extremely small inside
　
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