let them drain off. They should be wet, but not dripping. Now darken the room.
The roomneedn'tbe pitch black; you may use a red electric light bulb to see by.
Put the cards in the silvernitratesolution, and allow them to remain in itfor
3 to 5 minutes. Then remove the cards and let them dry in adarkplace. At this
pointdo not allow the cards to be exposed to any light.When the cards are dry, place the coins,buttons,keys, or leaves on them.
Expose themtostrong sunlight or light from a bright fluorescent desk lamp
forabout5 minutes. Remove theopaqueobjects.
Results:The objects left white images onthecards. Those parts of the cards
thatwere uncovered weredarkgray or black. Since you did not"fix"the cards,
the images will eventually disappear.The white filmthatappearedon the cards when you took them outofthe
silvernitratesolution was the substance that made the cards sensitive to light.
The white film, which was so thin you may not have actually seenit,was silver
chloride, a compound thatresulted from the reaction between the sodium
chloride and the silver nitrate. Theequationfor the reaction is:
NaCI+AgNOs sunlight)NaNOs+AgCl
The light energy from the sun or the desk lampseparatedthe silver from the
film of silver chloride. This left adarkcoating of pure silver on those areasof
the cards thatwere exposed to the light. The other areas were unaffected
because the light could not passthroughtheopaqueobjects. The white filmof