the bulb, the more likely is the above-described 

 method to be usable. Certain internal shapes 

 of the bulb cavity do not usually lend them- 

 selves to this method, particularly that in 

 which the logitudinal section of the cavity is 

 substantially a double ogive, largest diameter 

 in the middle and coming to a point at the 

 closed end. 



A-8 Excessive Gas in Thermometer. — It 

 has been noted that thermometers may oc- 

 casionally contain too much gas, so that when 

 most of the gas is at the outer end of the 

 bulb (where it is supposed to be) and manipu- 

 lation is attempted, the gas tends to move the 

 outer portion of the mercury inward, joining 

 it prematurely to the portion extending into 

 the bulb from the stem. Under these condi- 

 tions, the mercury will not again separate at 

 the point of joining. In such case it is impos- 

 sible to complete the manipulation, but ex- 

 perience tends to indicate that with such an 

 instrument, a bubble trapped against the wall 

 of the bulb near the middle will probably not 

 cause any trouble, and in time may even work 

 its way out to the end of the bulb where it 

 belongs. 



A few cases have been noted in which there 

 was so much gas present in the thermometer 

 that at temperatures near zero, the weight of 

 the mercury broken off at reversal was in- 

 sufficient to overcome the pressure of the gas 

 in the end of the bulb. The result was that 

 the mercury did not completely fill the bulb, 

 consequently read high on the scale, and a 

 visible bubble existed in the end of the bulb. 

 Such behavior would not be classed as a 

 malfunction, even though a false indication of 

 the temperature resulted, since the mercury 

 column broke correctly at reversal. It should 

 rather be considered to be a defect in the 

 thermometer, which can only be corrected by 

 unsealing the capillary system and further 

 evacuating it. 



A-9 Flooding. — Flooding frequently ap- 

 pears to be due to gas being present in the 

 reservoir. The following technique has been 

 used with some degree of success to restore 

 normal functioning, provided that the mercury 

 is hot jammed or stuck in the appendix: 



First, reverse the thermometer at any tem- 

 perature, but bring it to a horizontal position 

 before the mercury has entirely filled the bulb, 

 leaving roughly one-fifth of the bulb's volume 

 void. Tiien, holding the thermometer very 

 firmly by the reservoir end, snap it sharply as 

 one might a clinical thermometer, returning 

 it instantly to a horizontal position. The 

 object of this is to forcibly cause the mercury 



to separate in the throat of the bulb, so that a 

 large mass of mercury is driven to the outer 

 end of the bulb, leaving a small void at the 

 inner end of the bulb near the throat (fig. 

 A-lf). Tliis mass of mercury will generally 

 hang or stick in the outer end of the bulb when 

 the instrument is carefully righted; if it will 

 not do so, but runs down into the stem to 

 rejoin the main body of mercury, the method 

 cannot be used. Now very carefully right 

 the thermometer and very gently place the 

 thermometer upright in an insulated container 

 with some broken pieces of dry ice. It will 

 be noted at this time, that the end of the column 

 of mercury contiguous to the reservoir is 

 probably somewhere in the lower part of the 

 pigtail. It is necessary to notice that the merc- 

 ury in this area is continuous from the reservior 

 outward, so that the contraction of the mercury 

 in the reservoir as it is chilled can draw the 

 mercury from the pigtail into the reservoir 

 (fig. A-lg). If the mercury is not continuous, 

 it may be necessary to tap the instrument 

 very gently to cause the mercury in the capil- 

 lary to run down by the appendix or constric- 

 tion and join with that in the reservoir. Too 

 severe tapping may permanently damage the 

 appendix, or cause the mass of mercury sus- 

 pended in the bulb to run down, so great care 

 should be used. Let the thermometer remain 

 in the dry ice for 10 minutes or so until the 

 mercury has contracted to its freezing point, 

 at which time it is hoped that all the mercury 

 (except the portion suspended in the bulb) 

 will be inside the reservoir, with any gas which 

 may have been trapped there above it. Now 

 remove the thermometer from the dry ice and 

 allow it to warm up, still holding it upright. 

 Heat should not be applied with anything 

 warmer than the hand until the instrument 

 has warmed to the point at which the condens- 

 ate on the outside does not freeze, then warm 

 water may be used. After heating to perhaps 

 50° C, the end of the column of mercury 

 contiguous to the reservoir will probably be 

 somewhere in the middle or upper part of the 

 pigtail, presumably with any gas that may 

 have been trapped in the reservoir above 

 (ahead of) it. Thereafter proceed with the 

 standard manipulation to move the bubble to 

 the outer end of the bulb. This procedure 

 may not be effective at once, and in the event 

 that the first attempt does not restore normal 

 functioning, several more attempts should be 

 made before abandoning the instrument as 

 hopeless. 



A single case has been noted in which an un- 

 protected thermometer functioned normally 



164 



H. O. 607 



