Moisturizing Lotion

This exercise is not intellectually challenging, but it does illustrate the role of emulsifiers and most of the students enjoy taking their products home with them. For several years I have had to drop the whole cosmetics unit, and we haven't done this lab recently.

I got the idea for the recipe from The Formula Manual, published in 1975 by the Stark Research Corporation. We have lots of lanolin in our stock room and haven't been using it for much of anything else. The other ingredients are trivial. Students first prepare a water bath by dissolving 15 drops of glycerol in 50 mL of water in a 250-mL beaker. In a 100-mL beaker, they weigh 1 g of anhydrous lanolin (very sticky) and add 21 mL of mineral oil. They then put the 100-mL beaker in the 250-mL beaker and heat over a burner until the water temperature reaches 50 degrees. After turning off the burner, they mix the lanolin and mineral oil thoroughly using a wooden spatula. Then, and this is the tricky part, they pour a small amount (a few mL) of the glycerol/water from the larger beaker into the smaller one with thorough stirring. In a minute or so, it should thicken and get cloudy. They can then add more of the glycerol/water a little at a time with continued thorough stirring. Too rapid addition without adequate stirring causes a separation that is difficult or impossible to correct; at best, the products are only somewhat stable, and usually separate with time.

Fragrance or coloring can be added to the starting lanolin/mineral oil or glycerol/water mixtures or, probably, at any point during the preparation. Only small amounts are needed. Students can take the lotion home with them in plastic bottles which we get from local beauty parlors.

The exercise concludes with a question asking them to describe the purpose of each of the four ingredients (water, glycerol, lanolin, mineral oil).

Revised 9/1/06