Patent GB-1087836-A (GB)
Title: Method of marking mercury glass thermometers
IPC: G01K5/02
Filed: 1965-03-04
Abstract: 1,087,836. Thermometers. S.N. BLACKMAN. rch 4, 1965 [Dec. 18, 1964], No. 9300/65. Heading G1D.  A method of stain marking a mercury glass thermometer comprises ascertaining the temperature rise characteristic of the mercury column, applying heat stainable markings to match the characteristic but without deliberate registration of the column and markings, heating and cooling the thermometer to form stain markings, registering the column to the applied markings by removing excess mercury into the calibrating chamber 18 and finally removing the calibrating chamber with its contained mercury. In the embodiment illustrated the thermometer is of the clinical type having a trap 20. The thermometer is initially raised to a 'key calibration temperature' which is below the lowest temperature to be measured but high enough to raise the mercury above the trap 20. The thermometer is then cooled so that the mercury column breaks at the trap and the mercury in the bore can be driven into the calibrating chamber. Low and high point markings are then made corresponding to the level of the mercury at precise low and high temperatures. From the position of these two marks the temperature rise characteristic can be found and an appropriate heat stainable scale applied to the thermometer. The scale is preferably positioned so that a certain temperature such as 102‹F. is always a fixed distance from the base of the bulb 16. The thermometer is then heated and cooled to anneal the full length of the thermometer and also to decompose the heat-stainable material and cause it to diffuse into the glass. The column is then registered with the applied scale by noting the difference between the low and high point markings and the corresponding scale points. The thermometer is de-aerated and all the mercury driven towards the reservoir. The thermometer is then raised to a temperature greater or less than the 'key calibration temperature' by the same number of degrees that the scale graduation is less than or greater than the corresponding marked point. The excess mercury is shaken into the calibrating chamber. Readjustment may be performed by placing the thermometer through a bore in a heated block Fig. 8 (not shown) maintained at a temperature high enough to vaporize mercury. A baffle 44 (not shown) is interposed between the heated block and the reservoir bulb. The lower surface of the heated block is registered with the 102‹F. graduation on the scale assuming that the thermometer was last heated to this temperature and any mercury above this level is vaporized. The upper end of the thermometer is finally flame-melted below the calibrating chamber, pinched off and discarded. In a modification of the invention, the de-aerated thermometer is heated sufficiently to connect the mercury into a single continuous mass and the thermometer warmed to a constant temperature corresponding to a low point mark such as 94‹F. The mercury column is then broken at a predetermined distance from the base by applying a high intensity zone of energy such as a laser beam. A high point marking is then made on the thermometer to enable the determination of the temperature rise characteristic. The scale is then applied as before and the thermometer heated and cooled to form a continuous mercury mass before heating to a fixed temperature i.e. 102‹F and breaking the thread at the level on the scale coinciding therewith by the laser beam.