of the mercury in the stem and pigtail will not 

 rejoin the merciiry in the reservoir. By this 

 sequence of treatment, the bubble will have 

 been moved outward a little toward the end of 

 the bulb. After repeating this cycle a number of 

 times, the bubble will have been moved far 

 enough into the bulb so that a small globule of 

 mercury can be knocked off of the mass remain- 

 ing in the bulb, and manipulation completed in 

 the usual manner. 



It should be noted that under the above con- 

 ditions, tapping the thermometer in the upright 

 position is not apt to do any damage, as there 

 is no mercury present in or near the appendix 

 which might injure the appendix. This is 

 because the cooling down of the reservoir after 

 heating to 50° C. will have withdrawn the 

 mercury in the throat of the reservoir back into 

 the reservoir, and all of the mercury outside of 

 the reservoir will be either stuck in the bulb or 

 free-running in the stem and pigtail at the 

 instant of tapping. From this, it may be con- 

 cluded that in some cases, draining may be 

 induced merely by tapping, without danger to 

 the thermometer, if the reservoir is heated to 

 about 50° C, with the instrument in the upright 

 position, the instrument then reversed and al- 

 lowed to cool so that the appendix area is void 

 of mercury, and then quickly righted and tapped 

 before any mercury has had time to flow back 

 into the appendix area. 



In the case of protected thermometers, the 

 chilling and heating sequence outlined above is 

 necessarily very slow, as the blanket of air 

 between the jacket and the bulb of the ther- 

 mometer must also be cooled and warmed. 

 When treating unprotected thermometers, it is 

 advantageous to remove the thermometer from 

 its jacket. 



A-12 Mercury Does Not Separate at Bubble 

 During Manipulation. — There may be encoun- 

 tered, from time to time, an instrument which 

 frequently or consistently malfunctions in the 

 manner described as No. 1 at the beginning of 

 this discussion, in which the cause of the mal- 

 function is obviously a bubble appearing near 

 the appendix, but which, after the first heating 

 and cooling cycle, refuses to separate again 

 at the point where the bubble is located. Such 

 an instrument, when violently reversed as 

 described by Ritcher & Wiese, will break cor- 

 rectly, instead of at the bubble, and the tail 

 end of the mercury broken off at reversal will 

 run down by the point at which the bubble was 

 trapped. When the instrument is again righted, 

 the leading end of the mercury column returning 

 to the reservoir will pick up the bubble and 

 carry it toward the reservoir. The bubble will 



then come to rest where the descending column 

 joins tlie mercury extending from the reservoir, 

 probably somewhere in the throat. At the next 

 reversal, the mercury will probably break again 

 at the bubble, producing another malfunction. 



The difficulty in such a case would appear to 

 be inherent in the construction of the thermom- 

 eter. The factors involved are apparently the 

 diameters of the capillary in the appendix area 

 and in the pigtail area in relation to a bubble 

 of a given size, and possibly also the location 

 of the bubble in the capillary. For example, 

 a bubble present in a part of the capillary where 

 the diameter is relatively small might reduce 

 the sectional area of the mercury thread at 

 that point sufficiently to induce separation at 

 the bubble rather than at the correct breaking 

 point when the thermometer is reversed. How- 

 ever, when the same size of bubble is trapped 

 against the capillary wall where the capillary 

 diameter is relatively large, as in parts of the 

 pigtail, the sectional area of the mercury thread 

 is only verj^ slightly reduced at the bubble. 

 The mercury is therefore sufficiently cohesive 

 at that point to resist separation, and separation 

 takes place instead at the correct breaking point 

 upon reversal. In all cases, the fundamental 

 force which causes separation is the gravita- 

 tional pull of the suspended column of mercury. 

 This will vary depending on the size of the mass 

 of mercury suspended below the bubble, in 

 other words on the location of the bubble. 

 Cases have been noted in which, during manip- 

 ulation, a bubble could be moved through at 

 least two heating and chilling cycles, more than 

 halfway through the pigtail, but on the next 

 attempted cycle, the amount of mercury beyond 

 (below) the appendix at reversal was great 

 enough in relation to the amount suspended 

 beyond the bubble to cause the cohesive bond 

 of the mercury to be broken at the correct 

 breaking point rather than at the bubble, with 

 the result that manipulation could not be com- 

 pleted. In cases where this difficulty arises, 

 patient and careful procedure may determine 

 just how far the bubole can be moved before 

 separation at reversal reverts to the correct 

 breaking point, and successful, complete manip- 

 ulation may eventually be achieved. 



When such difficulty in completing mani- 

 pulation occurs, it is particularly important 

 to observe the exact manner of holding the 

 thermometer for a snap reversal as described 

 by Richter & Wiese, that is, holding it firmly 

 in such a manner that, as nearly as possible, 

 the center around which the thermometer is 

 rotated when reversed is at the bubble. When 

 thus reversed with as sudden a motion as is 



166 



H. O. 607 



