Total-immersion thermometer

Thermometers, total immersion, for indicating the required test temperature, with smallest graduations of l C (2 F) or less. No more than 25 mm (1 in.) of the mercury thread should extend above the surface of the bath at the test temperature. The ASTM 12C (12F) or IP 64C (64F) thermometer is suitable. 

When a thermometer which has been standardized for total immersion is used with a part of the liquid column at a temperature below that of the bulb, the reading is low and a correction must be applied. The stem correction, in degrees Celsius, is given by... 

Total immersion thermometers, 24 464 Total internal reflection principle,... 

A. Apparatus. Set up a melting point bath equipped with a mechanical stirrer and a source of heat that can be easily regulated. A beaker of 1 to 2 liters capacity about % full of clear peanut oil is recommended. Suspend an accurately standardized total immersion Centigrade thermometer in the bath so that the bulb is not less than 1.5 inches from die bottom of the bath. If the mercury column... 

Measure the temp of TNT with an ordinary thermometer and if it is betw 82—83°, insert a stopper fitted with a stirring loop and a BurStds thermometer, with. 02 divisions and calibrated to total immersion i)Arrange the thermometer so that the top part of the stopper is on the level with the 80.20° mark j)Stir constantly by moving the rod up and down k)Watch the thermometer and as soon as the temp, after falling steadily, starts to... 

The BurStds thermometer and other thermometers calibrated for total immersion should be used only for detn of sp of TNT by the Specification Method, while for routine tests the thermometers calibrated to partial immersion should be used. F or calibration of such thermometers proceed as follows a)Make a mark ca 5cm from the bottom of the bulb and at least lcm above the upper (small) mercury bulb on each special thermometer graduated in 0.1 or 0.05° b)Tie thermometers together in pairs (with a strip of rubber tubing) and be ready for calibration by custard cup method c)Wash and dry a Pyrex custard cup ca 2.5 in diam and ca 2.5 deep. In order to hold the cup and thermometers in place, use a wooden stand as shown in Fig... 

Total immersion type low temperature pentane thermometers (Kessler) were used to measure the temperature in the partial immersion mode. The readings are usually 7-8°C higher compared to the actual temperature under our reaction conditions. The temperatures reported here are all corrected by subtracting 7°C from the thermometer readings. The checkers used a Delta MC-20R digital thermometer (Sato Keiryoki Co., Japan). Temperature control is very important to obtain a satisfactory yield. 

Total-immersion thermometers. Thermometers that require the liquid in... 

There are tables that provide correction values for readings made when total-immersion thermometers are not sufficiently immersed. In the absence of such tables, use the formula for calculating stem correction given in the following equation. 

Partial-immersion thermometers have a greater tolerance (and therefore less precision) than total immersion thermometers. Interestingly enough, when a total immersion thermometer is only partially immersed and no stem correction is made, the accuracy is likely to be less than a partial-immersion thermometer. 

The thermometers are of the mercury in glass type, and the column above the liquid is filled with nitrogen. They may be standardized for total immersion or for partial immersion and should be used as near as practicable under the same condition of immersion. 

Total immersion means standardization with the thermometer immersed to the top of the mercury column, with the remainder of the stem and the upper expansion chamber exposed to the ambient temperature. Partial immersion means standardization with the thermometer immersed to the indicated immersion line etched on the front of the thermometer, with the remainder of the stem exposed to the ambient temperature. If used under any other condition of immersion, an emergent-stem correction is necessary to obtain correct temperature readings. 

When a total-immersion thermometer is used, correct for the temperature of the emergent stem by the formula... 

Thermometer Use a special total-immersion softening point thermometer,1 covering the range from 0° to 250° and graduated in 10 divisions. The bulb should be 15.9 0.8 mm in length and 6.35 0.4 mm in diameter. 

The melting points were taken with a short-stem total-immersion thermometer. 

Since the mercury in the thread, as well as that in the bulb, is susceptible to thermal expansion, it is important in precise work to take account of the temperature of the thermometer stem. Most thermometer calibrations, especially those for enclosed-stem types, are for total immersion—it is assumed that the thread is at the same temperature as the bulb. Other thermometers are meant to be used with partial inunersion, often to a ring engraved on the stem, and the remainder of the stem is assumed to be at room temperature (say, 25°C). For precise work, stem corrections should be made if the stem temperatures differ significantly from those assumed in the calibration. The correction that should be added to the thermometer reading is given by the equation... 

For most purposes a partial-immersion thermometer need not be stem corrected because of a few degrees variation in room temperature or a few degrees error in the immersion level. On the other hand, it is usually worthwhile to apply stem corrections to readings of a total-immersion thermometer when it is used in partial immersion, particularly when reading temperatmes well removed from room temperatures. 

Most laboratory thermometers have a mark around the stem that is three inches (76 mm) from the bottom of the bulb. This is the immersion line the thermometer will record accurate temperatures if immersed to this line. If the thermometer happens to be of the total immersion type then the readings will need to be corrected when taking melting and boiling points... 

Ordinary laboratory thermometers are designed for either total immersion or partial immersion. One can readily see that there would be a difference between these two conditions, since with total immersion the entire mercury column would be heated, and consequently the mercury would have a larger volume than obtained with partial immersion. The amount which must be added to a total-immersion thermometer when it is only partially immersed is given by... 

Thermometer correction. The temperature which is read on the thermometric scale must be corrected because there are several errors in such determinations. One source of error arises from the construction and calibration of the thermometer. The bore of the capillary may not have the same diameter throughout further, the scale graduation and the calibration of low-priced thermometers are not very accurate. A second source of error is the method used in the common melting point apparatus. The common thermometer has been calibrated while totally immersed in a bath. In the melting-point apparatus described, only a part of the stem is immersed. The column of mercury above the oil bath has a lower temperature than that at which the thermometer was calibrated. Therefore either a thermometer calibrated by partial immersion should be used or a correction must be made for the unequal heating of the mercury in the stem of the thermometer. Although thermometers calibrated by partial immersion are available, the latter practice is the more common. 

The above table was compiled for use at the Bureau of Standards, and is only applicable to thermometers of the laboratory type used under total-immersion conditions, i.e.y with bulb and stem containing the mercury column at the same temperature. 

Emergent Stem Correction for Mercuiy-in-glass Thermometers.—k large proportion of the thermometers now sold are graduated and standardized for the condition of total immersion, that is, for the condition that the bulb and all the portions of the stem which contain mercury, are heated to a uniform temperature. 

Partial Immersion Thermometers.—As a means of avoiding the necessity for applying the correction for the emergent stem, it has become customary to use partial immersion thermometers which are graduated to read correctly when immersed to a definite depth, say three inches, in a bath. Such thermometers should be, and usually are, marked to show the proper depth of immersion, and many of them have a line engraved around the stem to show this depth of immersion. While the accuracy attainable with a partial immersion thermometer is not so high as can he attained with a total immersion thermometer under favorable conditions, it is true that these favorable conditions are not often realized, and therefore in the great majority of cases, the partial immersion thermometer is to be preferred. It is probable that the partial immersion thermometer will be extensively used in this country. 

The apparatus employed for the test provides little in the way of fractionation and although the thermometer is accurately standardized at total immersion, it is used at partial immersion and no temperature corrections are made for emergent steam. However, provision is made in the test for correcting the thermometer readings for variations in atmospheric pressure whenever the barometric reading is sufficiently far from standard atmospheric pressure to make corrections desirable. Therefore, although the temperatures are highly reproducible they are not true vapor temperatures. 

The accuracy attainable with a liquid-in-glass thermometer is limited by the characteristics of the thermometer itself. Instability of the thermometric liquid, nonuniformity of capillary bore, and inaccuracies in scale graduation are the important factors. Uncertainties in corrections for the emergent stem may greatly limit the accuracy of partial-immersion thermometers. Generally, partial-immersion thermometers are assigned an uncertainty of 0.3°C in their calibration, whereas total immersion thermometers may have an uncertainty as small as 0.03°C. Observer errors add to the uncertainty but with care these can usually be made relatively small. 

Thermometers - make sure that you use a partial-immersion thermometer not a total-immersion thermometer- The type is written on the back of the thermometer. 

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