putthe photog~aphicplates in t?epyrogallic acid (the developing solution),
the exposed gramsofsilverbromidewere changed to metallic silver, or a silver
saltthatwould not wash away. Thesodiumthiosulfate(the fixative) in pie plate
No.3stoppedthe actionof the developer on the silver bromide. Ofcourse
this is why it is called a fixative. The plate is now anegative.The term"negative':
indicates thatthe result is theoppositeofthe processthatcaused it. Inother
words, the plate becamedarkwhere it was exposed to light.Itis not necessary
tostorethe negatives in adarkplace or in a black envelope, but be careful not
toscratchthe surfaces. Save them to use in the nextexperiment.HOWTO PRINTAPICTURE FROM ft NEGATIVE,
OR MAKINGAPOSITIVE
Gather thesematerials:A red lightbulb;the light-sensitivepaperyou made
in theexperimenton page 77; anuprightstandandclamp;a flashlightattached
to the clamp as in the precedingexperiment;4 glass pie platescontainingthe
same liquids as in the preceding experiment,thatis,No.1,a pyrogallic acid or
hydroquinonesolution,No.2,plain water,No.3,a sodiumthiosulfatesolution,
andNo.4,plainwater;the negatives you made in the precedingexperiment;
papertowels; and a watch or clock.
Follow this procedure:Set up theapparatusin yourdarkroomexactly as in
the preceding experiment. Workunderthe red bulb. Take a pieceoflight-
sensitivepaperandputoneofthe negatives you made in the lastexperiment
over it.Arrangeotherpairs ofnegatives and. piecesoflight-sensitivepaper,
puttingthe negatives on top. Place oneofthe pairsoflight-sensitivepaperand
negativebeneaththe flashlight. Be sure to keep the gelatin side of the negative
upandmake no fingerprints on its surface.Turnon the flashlight and allow
thepairtostandundisturbedfor 3 minutes. Now turnoff the light. Put the
paperonly into each pie plate inturnand time it, as you did in the preceding
experiment.You may findthatyou will have tostrengthenyoursolutionsor
prolongyour timeintervalsto get the best results. Thisexperimentationwith
yourownequipmentto find the very bestarrangementis muchofthe funof
workingin alaboratory.
Results:The design on the negative wastransferred to the light-sensitive
paper,exceptthatthedarkareas on the negative came out as light areas on the
light-sensitivepaper.When youputthe negative over the light-sensitivepaper
andexposed the pairto light, the light reached the light-sensitivepaperonly
throughthe lightpartsofthe negative. The light-sensitive paper, as you recall
from page 80, was covered with a filmofsilver chloride. The exposure to light