Immagini

DESCRIPTION

Exhibit 895 is a Beckmann crioscopic calorimeter for determining the freezing temperature of a liquid solution. It consists of a test tube BB (missing) having an entrance tube C on the side and a tap through which passes a thermometer T₁ and a stirrer S₁ (see design-1). This test tube is inserted in a larger test tube D; the space between these test tubes is filled with air in which occurs the heat exchange between the refrigerant in E and the liquid contained in test tube BB. Both tubes are immersed in the larger glass container E that is filled with the proper refrigerant and stired with the agitator S₂. The thermometer T₂ shows the temperature of the mixture in E.

Procedure:

The liquid for which the freezing temperature is desired is poured in test tube BB through entrance C that is then closed with a cork. The proper refrigerant (for example, salt and ice) is introduced in E and maintained uniform with the stirrer S₂. The apparatus is then watched until the temperature T₁ is one or two degrees below the probable freezing point of the liquid. Then the stirrer S₁ is suddenly raised and lowered rapidly until solidification occurs. The temperature T₁ increases and reaches quickly a constant value, which is the desired freezing point.

This apparatus is used to determine the molecular weight of a substance, utilyzing the lowering of the freezing point of a solution compared to the freezing point of the pure solvent and the experimental observation for which the lowering C of the freezing point of a solution is directly proportional to the molar fraction X of the solute. From this coefficient of proportionality κ = C / X, which for a given solvent is independent of the solute, one can calculate the molecular weight M of the solute with X = P / M, where P is the weight in grams of a substance disolved in 100 grams of solvent. In fact one has

Thus by the simple determination of the freezing point of a solution, we can determine the molecular weight of a substance. (see ref. 2)

For more details on the procedure, see ref. 1. Per maggiori dettagli sul funzionamento dell'apparecchio, vedi ref. 1.

See also exhibit 933

BIBLIOGRAPHY

• [1] BUSSETTI, Giovanni. “Esercitazioni pratiche di fisica". Libreria editrice universitaria Levrotto & Bella, 1965, pp. 341-344
• [2] Ganot's ,"Elementary Treatise on Physics", New York, 1902. Pagg. 330-332.
• [3] Edwin Edser," Heat for Advanced students", London, 1920. pagg. 167-169
• [4] N.Monroe Hopkins,"Experimental Electrochemistry", D. Van Nostrand Company, New York, 1905. Pagg. 32-36

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