All I can say about what was said about FREEZING pure glycerine into a solid mass that you can actually insert as a suppository is COMPLETELY WRONG.
While the freezing point is 17.8 degC, that is a definition most likely based on flow, not hardness. (I don't claim to be a chemist and maybe someone else who KNOWS, not someone who believes they know the answer can chime in. For example, your glass windows in your house and car are a FLUID by definition, so there is more here than meets the untrained eye.
I didn't think the earlier post was correct at all, so I put about an ounce of 99.5% pure, USP glycerine in a small stainless steel dish in the refrigerator (about 35degF or 2 degC) and it was NOT at all solid after two hours. It was slightly less flowable than out of the bottle at room temperature (68 degF or 20 degC), but nowhere near solid. Then I put it into the freezer (-6 degF or -21 degC) for two hours and it was still NOT solid by any account. It still had a viscosity and flow similar to honey at room temperature. Try it yourself and see.
Glycerine suppositories (like in the blue jars) are NOT pure glycerine. They contain a few other ingredients that make the suppository firm at room temperature, such as stearic acid or sodium stearate, sodium hydroxide to adjust pH, and some contain gelatin.
To answer the original poster, the liquid glycerine you mention can certainly be used as a laxative in the same manner as the Fleet Liquid Glycerine suppositories, except the so called Fleet "Liquid" glycerine suppositories, aren't really a suppository in the true sense of the word. They are little balls or tiny squeeze bulbs filled with 7.5 ml of glycerine that you squeeze the contents of, into your rectum.