At about this time the high school had let out for the day, and Mary Lou’s whiz-kid brother Jason, and his raggamuffin friend Wilbie in too-large overalls showed up to see what was happening. Wilbie immediately suggested that there must be something other than NaCl they could use - one that would be even more soluble in water. So off the two high schoolers ran to find Prof. Bengston. Alas, he was in a faculty meeting, but the boys returned with the Chemistry and Physics Handbook - one of their old friends, which was the Bible of Chemistry.
They wondered if NaF might be more soluble than NaCl. No.
What about NaBr? YES! Fifty grams would dissolve in about 70 ml of water. Now that is salty! Soon they had made up about 10 ml of a saturated solution of NaBr in water, and lo and behold, the thread floated! Now to make various intermediate solutions: 0% (plain water), 10%, 20%, 30%, 40%, and 50% (the saturated one). Mary Lou hopped up and went over to get into the action and perhaps even be able to weasle her way to stand between Cheryl and Jimmy. But almost immediately Mary Lou got into trouble by knocking over one of the beakers they were making, and in trying to sponge up her mess, she only spread the highly salty solution all around the benchtop where it started to dry and leave a thick crust of salt.
Wishing her away, and knowing how gullible she was, the others began to talk about how nice it would be to have some donuts, and this made her hungry and so she quickly volunteered to run across the street to the deli to get some.
When she returned to tell them she had them and they could all go out and sit in the courtyard, she found the lab vacant. Just the six beakers of solutions sitting there unattended with the bit of red floating in one of them.
Since this was a chemistry lab, she decided to do some “chemistry.” She found the small set of food coloring bottles and put a few drops of red into the 0% beaker, some yellow in another, and so on until all six beakers were very colorful. Then she got the idea of trying to make a color sandwich of them - reasoning (!) that denser ones ought to stay beneath less dense ones. Into a larger beaker she set a funnel, and then poured the red solution into the funnel. Then she poured the yellow 10% solution in. Happily, the yellow made a layer right beneath the red lay. So she continued and poured the green 20% solution, and that was followed by the others - including the one in which the thread floated. She now saw the thread floating just where the orange and the purple layers met.Well, she was done for the day, stuck a stirring rod in and gave it a few swirls, watched the colors partially mix and form a rainbow spectrum, and saw the little bit of thread swirl around, and then left to eat the donuts alone.
As she was finishing the fourth one, she heard some happy shouts coming from the open lab window.
Putting the last donut back into the paper bag, she ran upstairs to see what the excitement was about. She got there just in time to see her brother push a long-snooted dropper into the beaker and draw up a little liquid at just the level where the thread was floating. With all the others following behind him, he carefully carried the dropper over to a clean test tube and squirted it in. Then, using a 2 ml pipet, he placed 2.00 ml into a pre-weighed dish, and weighed the liquid finding it to be 2.50 grams. He did the same with liquids drawn from both the very top and very bottom of the beaker and got values of 2.01 grams and 3.06 grams.
The lab gang was thrilled, and when Mary Lou finally admitted her involvment in beginning to clean up after them. She told them she had made the solutions colored and how she then dumped them all together in one beaker before leaving. When they returned they saw the thread neither at the bottom nor floating at the top, but floating at its bouyant point midway down the beaker.
“Oh, yes, I know. I did that. It was so obvious what needed to be done,” said Mary Lou trying to take all the credit even though she didn’t really understand what she had done. But she did notice that Jimmy was now standing close enough to her to feel his brushing against her as Jason again held up the beaker to take a closer look.
(The first two groups in each lab section to give Dr. V the right answer will get 5 extra points on the next quiz. List group members' names!):