,~f
Results:The gelatin became a thick paste in the cool water. When you added
it to the boiling water, it dissolved completely. When you dissolved the silver
bromide in the gelatin solution, the colorofthe solution may have changed,
but because you worked without light (except from the red bulb), it became no
darkerthan a pale amber. The reason for drying the gelatin-covered plates on
the aluminum foil isthataluminum does not absorb water. If you had used
papertowels, they would have absorbed someofthe water and silver bromide
from the gelatin solution and would have spoiled the plates. By folding the open
edges of the black paper, you prevented light from getting at the plates and spoil-
ing them.HOW TO MAKE ANEGATIVE
Gather these materials: Pyrogallic acid (C6Ha(OHh) or hydroquinone
(C6HiOHh); sodium thiosulfate (Na2S20a); black construction paper; a
flashlight with a bright white beam; an upright stand and clamp; the photo-
graphic plates you made in the preceding experiments; 4 shallow glass pie
plates; a watch or clock; 2 glass stirring rods; book ends; and paper towels.
You will have to do mostofthis experiment in yourdarkroom,so be surethat
the red light bulb is in place.
Follow this procedure:In daylight, arrange your work space as follows.
Attach the flashlight to the upright stand with the clamp. The flashlight should
be in a vertical position andabout12 inches above the surface you are working
on. The bulb should face downward. If the flashlight is too heavy for the clamp,
attachit to the stand with cellophane tape or masking tape. Then, starting from
the left, stack yourphotographicplates onedgenext to the upright stand. Use
book ends tosupportthem. Have your watch or clock where you can see it
easily because you will have to time some of the later procedures in this experi-
ment. Next, line up the 4 pie plates and number them. This may seem un-
necessary, but you will find it difficult at first to do things quickly and correctly
while working in the dark. Itis only sensible, therefore, to have everything
marked to lessen the possibilityofmaking mistakes. Now cover your working
area with paper towels. In the light, make several stencil designs in the black
paper and cut them out. You can easily do this by folding the paper into
quarters,then into eighths, and then cutting irregular pieces from each of the
folded edges. Now you are ready for the"dark"work. Put out the lights, cover
the windows withdarkcloth or paper, and proceed with only the red bulb lit.
Fill each pie platetfullofcold water. To plate No. I add 2 teaspoonfuls of
pyrogallic acid or hydroquinone. Don'tput anything into the water in pie
plateNo.2.In pie plateNo.3put 2 teaspoonfulsofsodium thiosulfate.Don't
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