Then, abruptly, our management and the spirit-of-the-times caught up with us and came down about contaminated blood products, and blood in general being a potential hazard. What if a student caught a horrible disease from handling a slide smeared with some other student's blood: what an expensive law-suit that would be. If we couldn't use blood what could we do to investigate this phenomenon - called osmosis, as you ask - what could we do? Borrow an experiment from another Course, of course!
[1M solution of sucrose has 342g of sugar dissolved in a litre [1000g], so it is a sticky disaster if anyone spills it, or slops it. I know, we've been there.]
Last year, it was a mess and not only the sticky one. The students' data was all over the shop: they couldn't work out how to record the data so that %weight-change was easy to calculate; and the actual measurements went up and down like random yoyos under anti-grav. I rewrote the protocol with two important changes.
- An exhortation to dab the potato discs dryish before weighing. A big drip of external water could overwhelm the subtle changes in internal water weight.
- Triplicate! If you measure everything in batches of three identical discs, then any random departures [dropped disc on floor where it acquired 1/10th gram of grit] can be smoothed out.