These barometers do contain mercury, so certain precautions are necessary. Mercury (element Hg) is a silvery liquid that you have seen most often in thermometers. It is essential to move any barometer filled with mercury with caution, otherwise a rapid movement may cause the mercury to break the glass tube. Simply transporting the barometer on a 40 degree incline should protect most tubes, as this inclination prevents the mercury from moving inside. However, never mail, or commercially fly with, any barometer that contains mercury. It is against the law as mercury is considered a hazardous substance and your barometer may get confiscated. If necessary, it is a simple matter to obtain mercury at your location, and add it to your instrument, using what is known as a catheter filler. Mercury is used worldwide by most dentists for fillings in your teeth, so a good start is to ask a dentist for a small supply, if it is needed. It takes between 1/3 lb. to 2 lb. of mercury, depending on your tube size, to fill one barometer. Should mercury ever spill in your home, do not use a vacuum cleaner to clean it up as this will spread the mercury fumes. Most laboratory outlets have a "mercury spill kit", which is a powder you simply sprinkle on any escaped mercury, which renders it immediately harmless through a process called amalgamation. Elemental mercury by itself is not very harmful, but it is the vapors from heating it that are particularly dangerous if inhaled. Plenty of ventilation is necessary in the event of a spill. Though we have over 50 mercury barometers, and we have never spilled one drop in our home, it is wise to know what to do in the event of an accident. Please hang your barometer on a secure hook and in a strong location, away from any possible impact from man or beast. High school science labs and your local Town Health Department, will also supply lots of information and advice on any potential mercury spills.