Thermometers general requirements

No corks or rubber stoppers are, in general, required. Contamination or discolouration due to these is therefore avoided. Occasionally, a small rubber stopper may be employed, e.g., for the insertion of a thermometer, but, should the very small surface of rubber thus exposed to the action of the organic vapours be undesirable, a thermometer with a ground glass cone can be used. 

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. 

General procedure for the preparation of ketones from A,/V-dimethylcarbox-amides and alkyllithiums.127c A suspension of lithium ribbon (1.6g-atom), cut into small pieces, in anhydrous ether (800 ml) is prepared in a flask fitted with a reflux condenser, nitrogen inlet tube, thermometer, a pressure-equalising addition funnel and a stirrer. The suspension is cooled to — 10 °C, and, while the system is being swept with nitrogen, a solution of the required alkyl bromide (0.83 mol) in ether (200 ml) is added over a period of 2 hours. The mixture is stirred for 1 hour longer at — 10 °C. Then the temperature is lowered to — 20 °C and a solution of the required iV,jV-dimethylcarboxamide in anhydrous ether (200 ml) is added dropwise over a period of 1.5 hours. The... 

Let us now consider step I, the adiabatic step, and the measurement of the temperature difference (Tj Tq), which is the fundamental measurement of calorimetry. If this step could be carried out in an ideal adiabatic calorimeter, the temperature variation would be like that shown in Fig. la. In this case there would be no difficulty in determining the temperature change AT = Tj - Tq, since (dT/dt) = 0 before the time of mixing the reactants and after the products achieve thermal equilibrium. The only cause of temperature change here is the chemical reaction. However, it is an unrealistic idealization to assume that step I is traly adiabatic as no thermal insulation is perfect, some heat will in general leak into or out of the system during the time required for the change in state to occur and for the thermometer to come into equilibrium with the product system. 

To meet the requirement of the plant there has been developed what is generally known as the industrial type of mercurial thermometer. As shown in Fig. 2, it is characterized by a heavy metal back and protecting tube for the bulb, large and distinct figures and graduation marks, and threaded connections for attaching the instrument firmly and quickly to some part of the apparatus. 

The dry-test meter and the wet-test gas meter are volume-measuring devices. A set of plastic bellows is alternately filled and emptied, thereby driving the dial points via a system of bell cranks very little pressure is required. A thermometer and manometer are provided with the meter, for temperature and pressure corrections. Dry-test gas meters are useful for large-volume measurements. The wet-test meter is generally more accurate that the dry-test meter for smaller volumes. The gas drives a rotor, which in turn drives the meter. The meter housing is partially filled with water through which the rotor turns. It is calibrated by the manufacturer at a given level of water. 

Resistive materials used in thermometry include platinum, copper, nickel, rhodium-iron, and certain semiconductors known as thermistors. Sensors made from platinum wires are called platinum resistance thermometers (PRTs) and, though expensive, are widely used. They have excellent stability and the potential for high-precision measurement. The temperature range of operation is from -260 to 1000°C. Other resistance thermometers are less expensive than PRTs and are useful in certain situations. Copper has a fairly linear resistance-temperature relationship, but its upper temperature limit is only about 150°C, and because of its low resistance, special measurements may be required. Nickel has an upper temperature limit of about 300°C, but it oxidizes easily at high temperature and is quite nonlinear. Rhodium-iron resistors are used in cryogenic temperature measurements below the range of platinum resistors [11]. Generally, these materials (except thermistors) have a positive temperature coefficient of resistance—the resistance increases with temperature. 

General directions for preparation of sulfenyl chlorides 664 The required thiophenol (0.1 mole) is added to anhydrous carbon tetrachloride (50 ml) in a three-necked flask fitted with a stirrer, dropping funnel, calcium chloride tube, and thermometer. Then a solution of chlorine (7.09 g, 0.01 mole) in anhydrous carbon tetrachloride (100 ml) is dropped in, with stirring, whilst the temperature is not allowed to rise above —1° (—12° for compounds having two methyl groups on an aromatic ring). Stirring is continued for a further 1 h, then the solvent is removed in a vacuum and the residue is distilled at reduced pressure. Yields are 80-90%. 

General method for preparation of diphenyl esters of Gong-chain alkyl)phosphonic acids Equivalent amounts of the alcohol and triphenyl phosphite, together with 10 moles-% of sodium iodide, are placed in a flaskfitted with a thermometer, gas-inlet tube, stirrer, and distillation head water at about 50° is circulated through the attached condenser to prevent crystallization of the phenol. Nitrogen is led into the flask while the mixture is heated at the required temperature by a radiant heater until no more phenol distils (about 20 h). The remaining material is distilled at < 0.05 mm and the distillate is taken up in ether. The ethereal solution is washed with 2N-sodium hydroxide solution, dried and evaporated, and the residue is redistilled. 

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