REPAIRING BROKEN MERCURY COLUMNS in THERMOMETERS J. R. ENDSLEY Freed-Hardeman College, Henderson, Tennessee
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REQUENTLY instructors find thermometers with mercury columns broken into short sections which are so widely separated that their accuracy is greatly diminished, if their usefulness is not entirely destroyed. These may be repaired in most cases, at least, by any one, if he will follow carefully the method described. These suggestions may not be new to many, but since the writer has never seen them in any publication he passes them on in the hope that they may prove helpful to some one. Adjust a medium-sized ring on a ring-stand so that it will be at the proper height for heating objects upon it with a low flame. Lay a wire gauze upon the ring and set a small beaker, 50 to 100 cc., upon it. Thrust the thermometer to be treated through a one-hole cork or rubber stopper, leaving the upper three or four inches projecting beyond the cork. By means of a buret clamp adjusted to the cork and ring-stand suspend the thermometer so that the mercury bulb is one-half inch or more above the bottom of the beaker and fasten securely. Add enough glycerin to cover the mercury bulb; some other liquid with a high boiling point may be used instead of glycerin. For thermometers with a range above such liquids a salt or compound
with a low melting point and a high boiling point may be substituted. Heat the beaker slowly-very slowly toward the last-until the mercury below the last gap in the column rises into the cavity at the top of the tube. Then remove the burner and gently tap the thermometer near the top as the temperature drops slowly. It is almost certain that the mercury will leave the cavity as a continuous column. This method has never failed to work for the writer upon first trial, but should it not be successful at first repeat the heating and tapping as directed. The writer has never had occasion to try the method on a thermometer which has no cavity at the top of the mercury tube but he believes that the procedure may be easily modified to handle such cases. After trying the above method, Mr. T. A. Frick, of Hiwassee College, reports that in case the mercury has been driven up, by careless students, into the cavity at the top of the tube and is stuck, it can be easily dislodged by inverting the thermometer and heating the upper end of it until most of the mercury has been driven out of the cavity and suddenly righting again. The tendency is for all the mercury to run down the tuhe and form an unbroken column.
