Boiling point glass thermometers

Mix 400 mL of pure concentrated hydrochloric acid with 250-400 mL of distilled water so that the specific gravity of the resultant acid is 1.10 (test with a hydrometer). Insert a thermometer in the neck of a 1 L Pyrex distillation flask so that the bulb is just opposite the side tube, and attach a condenser to the side tube use an all-glass apparatus. Place 500 mL of the diluted acid in the flask, distil the liquid at a rate of about 3-4 mL min-1 and collect the distillate in a small Pyrex flask. From time to time pour the distillate into a 500 mL measuring cylinder. When 375 mL has been collected in the measuring cylinder, collect a further 50 mL in the small Pyrex flask watch the thermometer to see that the temperature remains constant. Remove the receiver and stopper it this contains the pure constant boiling point acid. Note the barometric pressure to the nearest millimetre at intervals during the distillation and take the mean value. Interpolate the concentration of the acid from Table 10.5. 

Mercury is the only metal that is in a liquid state at room temperatures and remains liquid at temperatures well below the freezing temperature of water. Mercury is a noncombustible, heavy, silvery-colored metal that evenly expands and contracts with temperature and does not wet or stick to glass, which makes it ideal as a liquid for thermometers. Mercury is slightly volatile and will give off toxic fumes, especially if heated. Its has a unique melting point of —38.83°C, a boiling point of 3,56.73°C, and a density of 13.5336 g/cm. ... 

The boiling point temperature was maintained within 0.02°C of the selected temperature, and measured by using a mercury-in-glass thermometer. The equilibrium pressure was measured by means of a mercury-in-glass manometer, and was readable within an accuracy of 0.1 mm. 

An electric vacuum pump is attached, through the usual traps, to the glass receiving flask. The substance distils when the boiling point is reached, as shown on. the thermometer, and may solidify on entering the flask, but by the application of heat it can be delivered to the bulb of the flask before it solidifies. 

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