Thermometer, Beckmann

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. 

Before describing the chief methods by which the molecular weight of an organic compound in solution may be determined, a description is given of the Beckmann thermometer, and of the Tabloid Press, both of which are frequently used in the above determinations. 

If a small Beckmann thermometer, similar to that used in the Sucharda-Bobranski method (p. 442) is available, the above method can be readily modified by replacing the tube T (Fig. 79) by an ordinary small boiling-tube without the side-arm A. The thermometer B and the stirrer S are fitted as in Fig. 79. The volume of solvent (usually ca 5 ml.) must of course cover the bulb of the thermometer. 

The cup F carries a third cup G which fits inside E, and which subsequently carries a small Beckmann thermometer having a rather narrow bulb. 

Freezing-point Determination. — I n the example to be described, pure benzene (see p. 136) is used as the solvent. Carefully dry the inner tube. Fit it wuth a cork and weigh it together w ith the coik suspended by a wire to the aim of the balance. Intioduce sufficient benzene to cov er the bulb of the Beckmann thermometer when it is pushed nearly to the bottom of the tube. About 10 c.c. will be found to be sufficient. Insert... 

The Bykman Depressimeter.—For rapid but less accurate determinations the apparatus of Eykman may be used, which is shown in Fig. 31. It consists of a small vessel, into the neck of which a thermometer is ground. The thermometer is of the Beckmann type but divided into twentieths of degrees. Phenol, m.p. 42-5°, is usually employed as the solvent. The vessel and thermometer are dried and weighed. Phenol melted on the water-bath is poured in to within about 5 c.c. of the neck,... 

Beckmann, E. Chem. Ber. 1886, 89, 988. Ernst Otto Beckmann (1853—1923) was bom in Solingen, Germany. He studied chemistry and pharmacy at Leipzig. In addition to the Beckmann rearrangement of oximes to amides, his name is associated with the Beckmann thermometer, used to measure freezing and hoihng point depressions. Mazur, R. H. J. Org. Chem. 1961,26, 1289. 

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

The freezing points of the solutions were determined in a Beckmann type apparatus with a Beckmann thermometer and a magnetically... 

BECKMANN, ERNST (1853-1923). Beckmann was a German chemist who discovered in 1886 the arrangement of oximes of ketones into acid amides or anilides, named the Beckmann molecular transformation. He was the inventor of two pieces of apparatus used in determining freezing and boiling points of solutions. The Beckmann thermometer is used for determining molecular weights in solutions. 

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... 

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