Why the difference? Glycerine has a density of 1.26 gm/cm3, water has a density of 1.0 gm/cm3 and Ivory Soap has a density of 0.9 gm/cm3.
How to Make:
I mix the water and glycerine together and warm it briefly in a microwave so the soap that will be added dissolves more easily. I mostly measure by volume. With the liquids, I use a cheap plastic graduate. For the Ivory Soap, I get out my metric ruler and cut out a piece of the bar soap with my paring knife of the correct dimension to give me the volume that I want. I then cut up the soap into small pieces to make the soap easy dissolvable in the glycerine-water mixture.
Do NOT use any other kind of soap in place of IVORY SOAP, including other dish soaps, shampoos, liquid dishwasher soaps, liquid clothes washer soaps, detergents or the like. I could tell you a very long tail of woe about my experiences with these adulterated soaps which had me on the verge of quitting until I tried 99.99% pure Ivory Soap as a last resort. The problem with other soaps is that they are chock full of ingredients that are not disclosed on their labels. For example, the ingredients of a common dishwasher soap, Dawn, are shown in the second photo. It is contains many strange ingredients that react with glycerine as I found out the hard way.
My basic motivation for doing this was my fond memory of riding my BR with shampoo as the roller lubricant. Unfortunately, the shampoo gave out after a few miles and even eventually caused additional problems roller roughness problems.