The sunlightdidn'taffect thecolorofthe blueprintpapereither, butit did
producea chemical changethatyou could not see. Theequationfor thereaction
inducedby thesunlightis:
Fe2(C 204 ) 3 sunlight)2FeC 204 +2C0 2
You can tell from theequationthatthe big change was in theplacementof
theiron(Fe) atoms. In the ferric oxalate,therewere twoironatomsin each
molecule. However, in the newcompound,called ferrous oxalate,therewas only
oneironatomin each molecule.
When youputthe exposed blueprintpapersinto the developingsolution,
there was areactionbetween the ferrousoxalateand thepotassiumferricyanide.
Thisreactioncaused the bluecolortoappear.
Where theblueprintpaperremainedwhite, thisreactiondidnottakeplace,
because the drawing ink, theopaqueobjects and thedarkareasofthephoto-
graphicnegatives had prevented exposureofthose areas to sunlight.Ifyouhad
left the ferrousoxalateon theblueprint,it would haveeventuallyreacted with
sunlightand ruined theblueprint.Washing the ferrousoxalateaway,therefore,
made theblueprintpermanent.
HOWTO MAKE LIGHT-SENSITIVE PAPER FOR PHOTOGRAPHY
Gather thesematerials:Two pie pans filled withwater;2 teaspoons;sodium
chloride(NaCl);silvernitrate(AgN0 3 ) ; I packageofindexcards;a red light
bulb;andsome coins,buttons,keys, or leaves. You will need adarkcloset in
which to work or aroomwhere you can cover the windows and make itdark.
Follow this procedure: Dissolve 1teaspoonfulofsodiumchloridein one of
the pie pansofwaterand1 teaspoonfulofsilvernitratein theother.CAUTION:
Avoid getting any silvernitrateon your skin. Itstains skindarkbrown. The
stain is very difficult to remove and usually has to wear off. Soak the index
cards, several at a time, in thesodiumchloridesolution.Takethemoutand