Measurement of Elevation of Boiling Point by Cottrell’s Method
Cottrell’s method: Cottrell (1910) devised an ingenious method for measurement of boiling point in which superheating was completely eliminated the assembly is shown in Figure. A funnel with two or three pronged tubes fits into the boiling tube in such way that the ends of the ‘U’-shaped pronged tubes lie a little above the thermometer bulb, as shown in the figure.
Figure: Cottrell’s Apparatus
The solvent-layer remains well below the thermometer bulb. On boiling, the liquid is forced through the pronged tubes and is pumped on the thermometer bulb and form a continuous layer of the boiling liquid on the bulb. This pumping device followed by election of liquid on the tube eliminates superheating. The thermometer therefore, records the true boiling point. Other experimental procedures air identical with the Beckmann method. This method gives a more reliable measurement of the boiling point. In all boiling point measurements corrections due to change in the barometric reading, if any, should be incorporated.