Page:Outlines of Physical Chemistry - 1899.djvu/137

 with a Soxhlet bulb condenser, by means of a special form of adapter.

To carry out an experiment, a sufficiently thick layer of glass beads is put into the flask, then by means of a pipette a weighed quantity of the solvent is introduced. The neck through which the substance is introduced is then closed, and the apparatus heated over a Bunsen burner. Heat is communicated to the liquid through the asbestos plate and along the platinum wire. When the liquid boils, the flame is so regulated that the condenser returns a drop of liquid every five or ten seconds. After about a couple of hours a regular ebullition is established during which the temperature recorded by the thermometer varies only between very narrow limits (a few thousandths of a degree). The boiling point of the solvent is thus obtained.

A weighed quantity l of the substance under considera- tion is then introduced, and after a few minutes, when the thermometer has taken up a new constant position of equilibrium, the temperature is again read off.

Further small weighed quantities of the substance are added and the boiling point after each successive addition noted. In this way, a series of boiling points for more and more concentrated solutions is obtained.

As the whole experiment requires a considerable time, it is well to perform it only on a calm day during which no appreciable variation of the barometric pressure is taking place.

��and would require too long a description. — The latest form (1896) so far resembles the original one that it may be here shortly described. The flask is more cylindrical, and rests on a metal plate covered with asbestos sheet. A small glass cylinder is placed round the flask with the object of reducing radiation to a minimum. The thermo- meter passes through the central tubulus, and one of the lateral necks is occupied by a very simple form of condenser.

1 Solid substances are introduced in the form of small lumps or small compressed cylinders. They may also be introduced in the form of powder if enclosed in a piece of platinum gauze of very fine mesh. Liquids are best weighed and introduced by means of a special form of bent pipette.

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