INSTRUCTIONS FOR REUNITING (rejoining)
SEPARATIONS IN LIQUID IN GLASS THERMOMETERS
All of out precisions thermometer are closed under extremely high nitrogen pressure while drawing the mercury into the lower portion of the capillary. This Process, when coupled with acid washed tubing and triple distilled mercury, although costly, greatly reduces the frequency of separations in the capillary portion of the thermometer. Nevertheless, though misuse or rough treatment during shipment, separations do occur.
Many instructions for rejoining separations begin with "the mercury can be retracted into the bulb by immersing it in a suitable mixture of dry ice and alcohol"
This statement is not specific enough
. We recommend you determine the type of separation from the illustrations provided and proceed according to the instructions outlines below.
SEPARATION AT UPPER PORTION OF MERCURY COLUMN
Most well-constructed thermometers contain an expansion chamber or blister at the extreme top of the capillary. This chamber serves a twofold purpose. One, to accommodate an overflow of mercury when the thermometer is subject to temperatures in excess of its scale range, and two, as a means of rejoining this type of separation, While holding the instrument in a vertical position, slowly heat the bulb until the separated segments and a portion of the main (intact) column enter the chamber. (Great care must be taken to insure that the mercury does not fill more than ½ to ¾ of the chamber volume: otherwise, breakage of the bulb will result). The nitrogen pressure will force a rejoining of the mercury. Still holding the thermometer vertically, examine the column as it cools and retracts to be sure it is intact.
SEPARATION IN THE CONTRACTION CHAMBER
Separation of the mercury in the contraction chamber is an entirely different problem. Many thermometers contain scale ranges that begin well above ambient temperature. These Thermometers have a contraction chamber or enlargement that prevents the mercury from entering the bulb at ambient temperatures. Heavy jarring of the instrument or thermal shock can cause separation in the chamber. If the separated mercury is in the form of a speck or small amount, invert the thermometer and gently tap it against palm of the hand. This will cause a larger separation, adding additional volume and weight to the separation portion. The thermometer should then be righted and only the tip of the bulb should be dipped in ice water or salted ice water. Remove it from water and gently tap the bulb on a desk blotter and allow the separation portion to fall to the bottom of the chamber and re-join the mercury reservoir. Allow thermometer to warm to room temperature and check to be sure all separations have been removed.
SEPARATION IN THE LOWER PORTION OF THE COLUMN
Separations of this type are less frequent and more difficult to repair. There are many variables and no one explanation will cover all types of thermometer. The general procedure is to subject the bulb only to a temperature sufficient to retract all the mercury into the bulb. A slow return to ambient temperature will return an intact column. Our experience has shown that additional problems can be caused in these procedures and we point out the following cautions. Cautions must be taken where a range is such that at the freezing point of mercury -38.8°C (almost the same in °F) mercury still remains in the capillary. If the thermometer is returned to ambient temperatures rapidly after freezing, there is a chance the bulb will crack. This Breakage is caused by the mercury thawing in the capillary more slowly then the mercury in the bulb, thereby creating an impasse to the expanding mercury. To avoid the breakage, great care must be taken to allow the mercury in the bulb to liquefy at the same rate as the mercury in the capillary. While the thermometer is being allowed to return to ambient temperature, extreme care must be taken to insure that it is not jarred or at the slightest angle while the mercury returns to the capillary. Without these precautions, gas bubbles could develop in the bulb and cause inaccuracies. In this case, return the thermometer to the manufacturer.
ACCU-SAFE Instructions For Use