. He should be informed, that this _chemical
operation_ (for technical terms should now be used) is called
_precipitation_: the substance that is separated from the mixture by
the introduction of another body, is cast down, or precipitated from
the mixture. In this instance, the spirit of wine attracted the
camphire, and therefore dissolved it. When the water was poured in,
the spirit of wine attracted the water more strongly than it did the
camphire; the camphire being let loose, fell to the bottom of the
vessel.

The pupil has now been shown two methods, by which a solid may be
separated from a fluid in which it has been dissolved.

A still should now be produced, and the pupil should be instructed in
the nature of distillation. By experiments he will learn the
difference between the _volatility_ of different bodies; or, in other
words, he will learn that some are made fluid, or are turned into
vapour, by a greater or less degree of heat than others. The degrees
of heat should be shown to him by the thermometer, and the use of the
thermometer, and its nature, should be explained. As the pupil already
knows that most bodies expand by heat, he will readily understand,
that an increase of heat extends the mercury in the bulb of the
thermometer, which, having no other space for its expansion, rises in
the small glass tube; and that the degree of heat to which it is
exposed, is marked by the figures on the scale of the instrument.

The business of distillation, is to separate the more volatile from
the less volatile of two bodies. The whole mixture is put into a
vessel, under which there is fire: the most volatile liquor begins
first to turn into vapour, and rises into a higher vessel, which,
being kept cold by water or snow, condenses the evaporated fluid;
after it has been condensed, it drops into another vessel. In the
experiment that the child has just tried, after having separated the
camphire from the spirit of wine by precipitation, he may separate the
spirit from the water by distillation. When the substance that rises,
or that is separated from other bodies by heat, is a solid, or when
what is collected after the operation, is solid, the process is not
called distillation, but sublimation.

Our pupil may next be made acquainted with the general qualities of
acids and alkalies. For instructing him in this part of chemistry,
definition should as much as possible be avoided; example, and occular
demonstration, s