Mercury columns in thermometers separate for a variety of reasons. Thermometers in such a condition may be prepared for use by one of the following methods, depending upon the type of separation found.

1. Separation in upper portion of column

For thermometers with maximum range of 260 °C (500 °F) having sufficiently large expansion chamber at top, place thermometer in liquid bath, using a liquid having a flash point well above thermometer’s range. Do not heat bulb with an open flame. With thermometer held in a vertical position, immerse as much of the stem as possible in the liquid. Heat bath slowly until the separated segments and a portion of the main (intact) column enter the expansion chamber at the top. (Be sure chamber is not filled more than half to two-thirds of volume or bulb may break.) The nitrogen pressure will force rejoining of the mercury; or thermometer may be gently tapped on gloved hand to reunite column. Keep thermometer in vertical position as it slowly cools.

2. Separation in lower portion of the column

Submerge bulb only in a solution of dry ice and alcohol (do not cool the stem or mercury column) to retract the mercury into the bulb. A slow and careful return to ambient will probably unite the column. Keep the thermometer vertical during this procedure. Special care must be taken in cases where the range includes the freezing point of mercury (approx. -39 °C or -38 °F) to allow a very slow return to ambient to avoid cracking the bulb.