Thermometer special liquid

Special Liquid Thermometers. For low temperatures, one can use several kinds of liquid-in-glass thermometers. Toluene thermometers may be used down to — 95°C, and pentane thermometers will operate as low as — 130°C. However, it is usually more convenient, as well as more accurate, to use thermometric devices of other types, especially thermocouples or resistance thermometers. 

Soft, silver white metal that melts in the hand (29.8 °C) and remains liquid up to 2204 °C (difference 2174 °C, suitable for special thermometers). Gallium is quite widespread, but always in small amounts in admixtures. Its "career" took off with the advent of semiconductors. Ga arsenide and Ga phosphide, which are preferential to silicon in some applications, have extensive uses in microchips, diodes, lasers, and microwaves. The element is found in every mobile phone and computer. Ga nitride (GaN) is used in UV LEDs (ultraviolet light-emitting diodes). In this manner, a curiosity was transformed into a high-tech speciality. 

Most substances expand when heated and contract when cooled, but liquid mercury shows an especially large variation of volume with temperature. That is why it is so often used in thermometers and barometers. Mercury also mixes with a number of metals to form alloys called amalgams. Amalgam is a special name given to alloys of mercury. With silver it forms a silver amalgam, which quickly hardens. This is the silver filling used by dentists. 

Because of its high range of temperatures as a liquid (from 29.8°C to 2,403°C), it is used in special types of high-temperature thermometers. It is also alloyed with other metals to make alloys with low temperature melting points. 

Bimetal thermometers are made in ranges from + 1000°F (538°C) down to — 300°F (— 184°C) to and lower. However, at low temperatures, the rate of deflection drops off quite rapidly. Because of its long-term instability at high temperatures, the maximum temperature for continuous use is about 800°F (427°C). However, special bimetal thermometers can be obtained for continuous use up to 1200°F (649°C). Good bimetal thermometers retain their accuracy indefinitely. Usually industrial bimetal thermometers read with an accuracy of 1% at any point on the scale. The speed ot response of bimetal thermometers is generally about the same as that for liquid-in-glass thermometers in similar ranges. 

There arc several methods for measuring this depression In the Beckmann method the freezing point of pure solvent and that of solution is measured by a special type of thermometer, the "Beckmann thermometer. The solvent or solution is contained in a double-walled glass apparatus and placed in a freezing mixture not more than S°C below the freezing point of the solvent. By rapid stirring when the liquid has supercooled about i. crystallization is induced and the temperature rises to the freezing point. 

When it is necessary to control the temperature of the liquid, the tube is opened at one end immediately after the reading and a thermometer inserted. Better still, in cases where variations of temperature exert a marked influence on the result, special tubes may be used which are furnished with a T-branch containing a stopper traversed by a thermometer and are surrounded by a metallic jacket through which water at constant temperature is circulated. 

Some thermometers have standard taper joints or ridges on the body of the glass to fit specific equipment such as distillation or melting point apparatus. These thermometers provide two types of position control. They set the bulb at just the right height within specialized equipment and ensure that the liquid column is sufficiently immersed in the heated sample. However, most thermometers do not have built-in controls and the user must not only select the right thermometer, but also adjust the thermometer to its proper level within the equipment. 

NIST-calibrated thermometers are expensive, but very accurate tools. Unfortunately, they require special use and maintenance to maintain their integrity. Not only can abuse alter their calibration, but general use can as well. For example, if you are using an NIST-calibrated liquid-in-glass thermometer on a regular basis, an ice-point recalibration should be taken after each measurement. These variations should be added to the adjustments made to the corrected scale temperatures. 

The apparatus used in this experiment is shown in Fig. 1. The thermometer is either a special cryoscopic mercury thermometer of appropriate range, with graduations every 0.01 or 0.02°C, a resistance thermometer with a resolution of 0.01°C, or a calibrated thermistor. In this experiment an aqueous solution of a weak or strong acid is mixed with crushed ice until equilibrium is attained. The temperature is recorded, and two or more aliquots of the liquid phase are withdrawn for titration to determine the equilibrium nominal concentration iiiq. The ice to be used should preferably be distilled-water ice. 

In this section, the design and operation of familiar liquid thermometers, thermocouples, platinum resistance thermometers, thermistors, and optical pyrometers are discussed in detail. Briefer descriptions are also given of a variety of special thermometric devices such as quartz thermometers, germanium resistance thermometers, and sihcon-diode thermometers. 

A differential manometer of the Rayleigh type ( 14.VII A) was used in accurate measurements of the vapour pressure of water, and a simple apparatus for measuring the difference in vapour pressures of two liquids was described by Lord Kelvin. Stock s vapour pressure thermometer ( 19.V1 Q can be used to measure the vapour pressures of liquids, including those at low temperatures. Special techniques are necessary for very small vapour pressures,... 

Mercury is the only metal which is liquid at room temperature (cesium melts at 28.5" C, and gallium at 29.8°). It is iinreacrive, being below hydrogen in the electromotive-force series. Because of its unreactivity, fluidity, high density, and high electrical conductivity it finds extensive use in thermometers, barometers, and many special kinds of scientific Apparatus. 

Preparation of 1-hromobutane. You ve just finished the experiment and you re going to clean out your distillation apparatus. There is a residue of 1-bromobutane coating the three-way adapter, thermometer, inside of the condenser, and the adapter at the end. Do you wash the equipment in the sink and let this minuscule amount of a halogenated hydrocarbon go down the drain Or do you rinse everything with a little acetone into yet another beaker and pour that residue into the halogenated hydrocarbon bucket, fully aware that most of the liquid is acetone and doesn t need special halide treatment Check with your instructor. 

In principle, any device that has one or more physical properties uniquely related to temperature in a reproducible way can be used as a thermometer. Such a device is usually classified as either a primary or secondary thermometer. If the relation between the temperature and the measured physical quantity is described by an exact physical law, the thermometer is referred to as a primary thermometer otherwise, it is called a secondary thermometer. Examples of primary thermometers include special low-pressure gas thermometers that behave according to the ideal gas law and some radiation-sensitive thermometers that are based upon the Planck radiation law. Resistance thermometers, thermocouples, and liquid-in-glass thermometers all belong to the category of secondary thermometers. Ideally, a primary thermometer is capable of measuring the thermodynamic temperature directly, whereas a secondary thermometer requires a calibration prior to use. Furthermore, even with an exact calibration at fixed points, temperatures measured by a secondary thermometer still do not quite match the thermodynamic temperature these readings are calculated from interpolation formulae, so there are differences between these readings and the true thermodynamic temperatures. Of course, the better the thermometer and its calibration, the smaller the deviation would be. 

J. A. Wise, A Procedure for the Effective Recalibration of Liquid-in-Glass Thermometers, NIST Special Publication 819,1991. 

The sample holder system used contains six sample apertures. Five samples are maximally placed at the same time in this holder to keep one aperture free for the reference measurement, see Figure 4.9. This whole sample holder system is lifted into a special thermostat bath provided with a liquid nitrogen cooling coil. This cooling possibility extends the lower temperature limit of these measurements from 20°C to about -50°C. The bath is filled with a mixture of water/ethylene glycol (l/l) for measurements between -50°C and 80°C. Silicone oil (100 cS.) is used as medium for measurements between 0eC and 200°C. The sample temperature is measured by a platinum resistance thermometer, placed as close as possible to the sample in the ultrasonic beam. 

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