Science Buddies: "Ask an Expert"

My daughter is doing the experiment (The Skinny on Moisturizers) where she is measuring the effectiveness of different types of moisturizers. She has to measure the height and weight of jello (after it has set in petri dishes for 4 hours in the fridge) with different types of moisturizers layered over it (with the exception of the control which will have to moisturizers) over a 2 week period. The experiment does not say whether the jello/moisturizer combo needs to be kept in the refrigerator. I would think no because 1) the coldness of the fridge would slow down evaporation and 2) if we keep it in the fridge, the lid on the petri dish would need to be kept on, further preventing evaporation (it would be difficult to have 20 petri dishes lined up single layer without lids for 2 weeks). My daughter says that if we keep the dishes out, the jello will melt, making it difficult to get the height measurements (you only measure the height of the jello, not the jello/moisturizer combo). Would a good compromise be to keep it in the basement where temperatures are cooler? It is now winter and with the heat on, the house is between 68-70 degrees. Thank you.

Hi!

That looks like a great project. And it's a great question you raise. I haven't done this experiment, but I would leave them out at RT if you can control that reasonably well - because you are looking for moisture loss to the air, which will be greater out in the room, not in the fridge. BUT if the products are getting too soft or the geletin isn't keeping firm (what temperature does jello melt at??), you may look for a cooler spot - like a basement, or or the fridge if you need to. The lids should be kept off, dishes in a single layer, away from drafts, fans, heat source, etc, that will speed drying.

I hope that helps. Let me know if you feel the experiment is going bad due to your location... but I don't expect that to happen!

Thanks,
Tonya