High School Biology-Chemistry SMILE Meeting
10 December
Notes Prepared by Porter Johnson

Ann Parham [Carver School]      Measuring Stress 
Ann described an activity that involved measuring stress as a function of level of activity, which involves using home-made stethoscopes, which are made from toilet paper tubes or the equivalent, with a diaphragm made by placing a rubber balloon over one end.  The balloon is held against the subject's chest, and the doctor's ear is placed at the other, open, end of the tube. Pulse rates for the subject were measured following two minutes of inactivity, as well as following periods of increasingly more intense activity --- walking, jogging, doing jumping jacks, and climbing stairs.  Several of us made the stethoscopes, but only a few could hear heartbeats because of background noise in the room.  The complete activity protocol was passed out on instruction sheets, as well as a table of typical student results.

Good work, Ann!

Chris Etapa [Gunsaulus Academy]      Measuring Density 
Chris followed up on the pencil gambit that she started at the last class, in which he seemed to demonstrate that the density of the pencil depends upon its orientation --- i.e., whether it is vertical or horizontal. She first floated a pencil on its side on the surface of water in a pan, and then she put the pencil down into a graduated cylinder containing water.  The pencil sank and touched the bottom of the cylinder, ALTHOUGH a good portion of the pencil was still above the water, because the cylinder was shorter than the pencil.  When we substituted a shorter pencil, it floated whether placed horizontally or vertically, so that we were spared the difficulty of having to conjure up some sort of explanation of the effect.  AHA!

Continuing with the density theme, Chris then demonstrated making density bottles by adding a few drops of blue food dye to a vessel containing approximately equal volumes of water and mineral spirits. Mineral spirits are sold at hardware stores as a paint thinner, and probably consist mostly of hydrocarbons (like gasoline) that are not soluble in water.  We saw two layers of fluid --- a clear layer (mineral spirits) on top, and a blue layer (water) on the bottom.  Several of us made our own density bottles.  When the bottles were shaken the layers seemed to mix, but they separated quickly into two separate layers when we stopped shaking the bottle.

Comment by Ken Schug:  Other household oils tend not to work as well, since they emulsify when shaken; that is, they break up into very small droplets that are very slow to come back together.  You can also prolong the separation time by adjusting the densities of the two immiscible liquids to be nearly equal.  He mentioned a system in which the upper layer assumed a hemispherical shape, rather than the usual flat interface surface, and said that when those systems are shaken, it may take many days for separation to re-appear.

Finally, in keeping with the spirit of the season, Chris demonstrated and gave out instructions for making an attractive holiday wreath from plastic sandwich bags [use the cheap ones, and not those with zip-lock tops, which would have to be removed in any case!].  Using a circular wire wreath frame that is readily available at craft stores, she tied the bags around the wire with a single overhand knot, and pushed the bags together tightly until the wreath frame was filled.  [Be sure to use the small wreath frame, since the medium sized frames would require several hundred bags.]  Then, she trimmed the outer ends of the bags with scissors and fluffed the bags.  The wreath can be even decorated with self-stick thingies, if desired.

Good work, Chris!

Barbara Pawela [retired]      Chemistry of Fire 
Barbara did a lecture experiment that involved the following interactive activities:

As expected, the candle in the larger jar burned slightly longer, but the jars were too close in size to show the effect dramatically.

Good work, Barbara!

Jyotiben Desai [Du Sable HS]      Dinosaurs for Sale 
Jyotiben concluded our semester's program by telling us how to put together dinosaurs that are available from WalgreensŪ, as well as Dollar StoresŪ.  thin slabs of wood contain different parts of the dinosaurs, that have been stamped out, which can easily be pushed out and reassembled to make small standing figures.

That's good to know,  Jyothiben!

Notes taken by Ken Schug.