Frugal Evaporation

Download frugevap.dmw

Fed up with too many data points in a recording? But don't want to miss the changes? You need a "Frugal Recording". In a frugal recording, a point is recorded only when a significant change occurs.

Evaporation experiments are ideal for studying using Datamass because they have a number of parameters (e.g. surface area, varying liquids) which can be studied easily. Doing repeated manual recordings is calculated only to lose pupils' interests, but using DataLogging each run can be left unattended until they are completed.

Method:

Choose a suitable recording range, 0-5g would be sensible. Place an empty watch glass on your balance and set the balance to zero with the 'Tare' button. Set up the frugal recording and pour the solvent onto the watch glass. Start the recording and go off and do something useful (like make the tea) and come back when it is finished.

Results:

The graph looks absolutely 'normal':

However, the two sections of the data table shown below carry the full story, every time the mass falls by 0.01g a reading is taken.

This is an extremely simple example of a frugal recording, a conventional experiment done in an unusual way. Of course, frugal recordings really come into their own when the changes are totally irregular and unpredictable, what I call the 'Cat Flap Experiment'.