Temperature Beckmann thermometer

Beckmann thermometer A very sensitive mercury thermometer with a small temperature range which can be changed by transferring mercury between the capillary and a bulb reservoir. Used for accurate temperature measurements in the determination of molecular weights by freezing point depression or boiling point elevation. 

Read the temperature to 0,001° on a Beckmann thermometer provided with a catheto-meter... 

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. 

The Beckmann thermometer used with the bomb calorimeter should be calibrated for the normal depth of immersion with which it is used. To cover the normal range of laboratory temperatures, this calibration should be obtained for three settings of the zero on the scale, convenient values being 10, 15, and 20°C. Such a series of calibrations allows automatically for emergent stem corrections and variations in the value of the degree on the thermometer scale with different quantities of mercury in the bulb, in addition to those arising from inherent variations in the diameter of the capillary bore. 

Thermometer Scale Correction. An NBS thermometer was used for the adiabatic jacket and a Beckmann differential thermometer for the calorimeter water. The Beckmann thermometer was calibrated against the NBS thermometer. Corrections were made to the initial and final temperatures recorded on the Beckmann thermometer. 

The results are in very good agreement. For r/ohexane all four sets of investigators obtained a result within 0 2 kcal mole i of the mean, or within 0 02 per cent, which amply confirms the claimed accuracy of 0 02 per cent. It is noteworthy, too, that while investigators a, c, and d used approximately the same calorimetric technic ue, b used one which differed in important respects. The Amsterdam workers, b, used a Beckmann thermometer to measure the temperature rise and m.easured the amount of combustion by... 

Method. The calorimeter is generally kept well insulated so that loss or gain of heat from the environment is minimum. A sensitive thermometer estimates the temperature changes inside the calorimeter. A mercury Beckmann Thermometer was used extensively in the past but now many reliable and more accurate devices are available such as resistance thermometers and also semi-conducting devices like thermistors. 

Beckmann thermometer A type of mercury thermometer designed to measure small differences in temperature rather than scale degrees. Beckmann thermometers have a larger bulb than common thermometers and a stem with a small internal diameter, so that a range of 5°C covers about 30 centimeters in the stem. The mercury bulb is connected to the stem in such a way that the bulk of the mercury can be separated from the stem once a particular 5° range has been attained. The thermometer can thus be set for any particular range. It is named for the German chemist Ernst Beckmann (1853-1923). 

The isothermal method was used. Samples were withdrawn through a coarse filter paper into a weighed 10 ml pipet, weighed, diluted and analyzed acidimetrically (1). The cryohydric points of the system were found by adding the solid salts to ice and measuring the temperature with a Beckmann thermometer. When a constant minimum value was reached, samples were withdrawn and analyzed. 

This work anticipated that published by Faraday. Cavendish s paper on the Royal Society s instruments dealt not only with thermometers but also with the effect of capillarity on the height of mercury in a barometer tube and the correction for temperature, the rain-gauge, hygrometer, dipping needle, and variation compass. It contains careful observations on the construction and calibration of mercury thermometers. Lord Charles Cavendish had previously described what is essentially a Beckmann thermometer with a variable zero. Cavendish constructed an ingenious registering (maximum and minimum) thermometer, which is now in the Royal Institution. ... 

The test apparatus comprises a heat-of-solution calorimeter with accessories (Dewar flask, stirrer, funnel, etc.), an officially calibrated Beckmann thermometer and an appropriate acid mixture (nitric acid -l- hydrofluoric acid). The cement paste samples (their mix proportions, mixing procedure and temperature are specified) are stored in a water bath at 20° 0.5 C. The heats of solution of the unhydrated and of the hydrated cement are determined from the rise in temperature occurring when the samples dissolve (the test should be performed in constant-temperature surroundings) and from the determinations of the CaO content (or the losses on ignition, if applicable). Formulas for calculating the heat of solution from the test data are given in the Standard. It is an elaborate procedure. 

In the actual experiment, 20 g of the pure solvent (water) is taken in the inner freezing tube and stirred gently. The movement of the mercury thread in Beckmann thermometer is waiched carefully. The temperature first falls below the freezing point of the solvent. It is then stirred and as the solvent starts solidifying, the temperature rises rapidly and finally becomes stationary. This temperature is noted. Let it be T °. 

The Beckmann Thermometer.—In order that the determination of the molar weight shall be made with sufficient accuracy, it is necessary to be able to read the temperatures with an error not exceeding o ooi — o oo2° The thermometer should therefore be graduated to, at least, hundredths of a degree. Such a thermometer, however, if made in the ordinary way, would have only a very short range unless its length were made inconveniently great. It would be necessary, therefore, to have a number of these thermometers for use at different temperatures. To obviate this necessity, a thermometer was... 

Setting the Beckmann Thermometer.—Before using the Beckmann thermometer, it must be set, i.e. the amount of mercury in the bulb must be so regulated that at the particular temperature of the experiment, the end of the mercury thread is on the scale. This is done as follows —... 

Since the scale of the Beckmann thermometer does not extend upwards to the end of the capillary, the temperature of FlO. 43. this bath must be at least 2°—3° higher than the highest temperature to be met with in the experiment. 

Fit together the calorimeter and its protecting vessels (all well polished), as shown in Fig. 92, the outer vessel having been filled with water some hours previously in order that it may acquire, as nearly as possible, the temperature of the room. A Beckmann thermometer, previously set (p. 130) so that the mercury stands at the lower end of the scale at the temperature of the room, is passed through the holes in the covers of the calorimeter and supported so that the bulb passes about two-thirds down the calorimeter. The calorimeter is also furnished either with a simple ring stirrer to be worked by the hand, or, preferably, with a rotating screw stirrer to be worked by a small hot-air engine or electric motor. In the latter case the rotation should be as uniform as possible, and not too rapid. 

In the calorimeter are placed 250 c.a of the solution of caustic soda, while 250 c.c. of the hydrochloric acid are placed in a flask surrounded by several polished metal cylinders, to minimize changes of temperature by radiation (Fig. 92, B). A Beckmann thermometer is also supported in the acid solution. The readings on this thermometer must be compared with those on the thermometer placed in the alkali, in order that it may be known whether the temperature of the acid and alkali is the same at the time of mixing or, if not, what the difference of temperature is. 

The calorimeter may now be got ready. The water-mantle having been filled with water (preferably some hours previously), a thermometer is hung in the air-space inside. After it has taken the temperature of the enclosure, the temperature is read. A Beckmann thermometer is now set (p. 130) so that the lower end of the scale represents a temperature of about i 5-2 degrees below that found in the enclosure of the water-mantle. 

Beckmann, E. Modification of the thermometer for the determination of molecular weights and small temperature differences. Z. Phys. Chem. 51, 329-343 (1905)... 

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