and satisfactorily during scale correction tests 

 at atmospheric pressure, but when reversed 

 under a pressure of 100 kg/cm^ consistently 

 flooded. This may be presumed to have been 

 due to a deformation of the appendix by the 

 pressure, causing the mercury to stick in the 

 appendix, as no visible defect or bubble could 

 be detected, and in spite of repeated attempts to 

 correct the difficulty by manipulation, the in- 

 strument persisted in its behavior; normal 

 atmosphere, malfunctional at 100 kg/cm^. 

 Such a case is, of course, very unusual, and not 

 typical of a difficulty to be encountered at sea, 

 as the eccentricity would presumably have been 

 discovered in the testing laboratory and the 

 instrument disqualified from use. 



A-10 Mercury Stuck in Appendix. — Some-, 

 times, at reversal, the mercury column may 

 break behind the appendi.x in the throat of the 

 reservoir, so that the moving column breaks 

 away from tlie mercury in the appendix, leav- 

 ing some mercury stuck there (fig. A-lh). 

 This is most apt to be due to a physical defect 

 in the appendix, possibly the result of rough 

 handling or jarring, which causes the mercury 

 to become wedged in the appendix. Under 

 these conditions, the bond between the appendix 

 wall and the mercury is stronger than the 

 cohesive bond of the mercury itself at the 

 junction of the appendix with the main capillary 

 channel. At reversal, the weight of the mercury 

 column suspended from the reservoir may 

 either cause flooding or a separation of the 

 mercury column in the throat of the reservoir. 



In the case of thermometers in which the 

 mercury is stuck in the appendix, the mercury 

 column is very likely not to break at all at 

 reversal unless or until the instrument is jarred 

 or tapped, and then, of course, to break incor- 

 rectly or flood. Tapping or jarring with the 

 instrument in a reversed position is undesirable 

 as it tends to work gas up into (within) the 

 mercury column, thereby inducing other types 

 of malfunctions and complicating the situation. 



At least one manufacturer of reversing ther- 

 mometers claims that they can sometimes 

 correct a faulty appendix of this nature by 

 heating, the exact method not being specified, 

 but no examples of such repairs have been ob- 

 served to note the degree of success achieved 

 by this alleged cure, and no shipboard method 

 of corrective treatment has been discovered. 



A-11 Failure To Drain. — Failure to drain 

 spontaneously upon righting is not truly a 

 malfunction, in that it does not affect the 

 ability of the instrument to give accurate 

 temperature information. However, it is annoy- 

 ing and time-consuming at sea, as instruments 



H. O. 607 



350676 O — 56 12 



exhibiting this undesirable characteristic have 

 to be examined carefully at each station to 

 make sure they have drained before lowering, 

 and in severe cases, the instruments may even 

 have to be removed from the rack to cause 

 draining. 



Failure to drain spontaneously is more apt 

 to occur when a short column of mercury ex- 

 tends into the stem capillary from the bulb. 

 Contributing causes may be: not enough gas 

 in the outer end of the bulb (therefore gas in 

 the stem); a rough inner surface of the bulb; 

 the shape of the bulb cavity; or too small a 

 capillary diameter in the stem. 



Occasionally, a separation of the mercury 

 may take place in the throat of the bulb, leav- 

 ing the bulb full of mercury which refuses to 

 drain. This mercury cannot be rejoined to the 

 main body of mercury either by knocking off 

 globules of mercury (because there is no space 

 into which to knock them) or by the method 

 described herein above. The corrective treat- 

 ment for this condition as described by Richter 

 & Wiese may or may not be effective, and is 

 somewhat limited in its application. The 

 treatment described below has been used with 

 considerable success to rejoin the mercury in 

 some very stubborn cases of separations in the 

 throat of the bulb. It is essentially the same as 

 the standard manipulation procedure given by- 

 Richter & Wiese for eliminating bubbles near 

 the appendix, except that the cooling and heat- 

 ing cycles are in reverse sequence. 



When the bulb is full of separated mercury 

 which refuses to drain, hold the thermometer 

 horizontal (mercury still separated) and chill 

 the bulb end in ice water until the auxiliary 

 thermometer shows that main bulb is near zero 

 in tenjperature. Now quickly reverse the 

 thermometer, allowing the mercury in the stem 

 and pigtail to run down and join the mercury 

 in the bulb. Note: Since a large part of the 

 mercury normally present in the stem and pig- 

 tail is lodged in the bulb, it will be necessary 

 in the beginning to heat the reservoir to about 

 50° C. with the instrument upright, in order to 

 get enough mercury beyond the appendix to 

 break off; thereafter, this broken-off section of 

 mercury should be kept free in the stem and 

 pigtail, and not allowed to run back into the 

 reservoir. 



Now, with the thermometer reversed, heat 

 the bulb to about 50° C. or so, then quickly 

 right the thermometer, tap very lightly if 

 necessary to cause the mercury to separate at 

 the bubble in the throat of the bulb, and in- 

 stantly return the thermometer to a substan- 

 tiallj^ horizontal position so that the free portion 



163 



