Question: how can we find out what an unknown substance is?
Hypothesis: Different substances have different freezing and boiling points.
We can use this information to identify unknown substances.
Experiment design: we can determine or look up the freezing and boiling points of some known substances. We can then determine the freezing and boiling points of the unknown substances by heating and cooling them. If any of the boiling and freezing points of unknown substance match known substances, then we have identified the unknown substances.
Conclusion: We determined some unknown substance by measuring their freezing and boiling points and then comparing those figures to known freezing and boiling points of substances. We were able to identify the unknown substances.