HOW YOU CAN OBSERVE DIFFUSION
Gather these materials: Three small glasses filled with water; I crystal of
potassiumpermanganate(KMn0 4 ) ;I crystalofrock salt(NaCl);a glassrod.
blackIndiaink;an eyedropper.
Follow this procedure:Let the glassesofwaterstanduntil the waterappears
to be perfectly still and motionless. Dropthe crystal ofpotassiumperrnan-
ganateinto one, the crystal of salt in the next, and adropofIndiaink into the
third. Donotstir,touchor move the water in the glasses. Watch them for
several minutes and notice whathappens.Allow them tostandovernight,and
thencheck theappearanceofthe three solutions. Using a glass rod, taste a
dropofthesodiumchloridesolutionin the second glass.
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.\-c--.'Results: At first the potassiumpermanganatecrystal made athinline of
coloras it fellthroughthe water. Soon the wateraroundthe crystal became
colored. Afterstandingall night, the crystal dissolvedalmostcompletely and
the entire glassofwater became the same shadeofviolet.
As you watched the crystal of rock salt fallthroughthe water, there was no
visible change because the salt and waterbothare colorless. However, the rock
salt crystal did begin to dissolvealmostat once. After standingall night, the
entire glassofwatertastedsalty.
As it fellthroughthe water, thedropofIndiaink assumed a cloud-like shape,
butnevertheless fell to thebottom.Afterstandingall night, the inkcoloredthe
entire glassfulofwater evenly.
This mixingoccurredwithoutyourtouchingthesolutions.The moleculesof
water as well as the molecules of the crystals and the ink wereconstantlyin
motion,as all molecules are. In movingabout,theybumpedinto eachother~nd
rebounded,sothattheirmotionwascontinuous.Eventhoughthemotionw~sa
randomone, it resulted eventually in an evendistributionthroughoutthew~ter
ofthe substances youaddedto it. This is calleddiffusion.Diffusion occurs in all
fluids(liquids and gases)thatcombinein a purelymechanicalway (asopposed