ing all the time; finally, let him add the rest of the boiling
water, the operator still continuing the stirring. The paste is allowed
to cool, and will be thicker when cold than when hot. Remove the upper
portion entirely when quite cold, otherwise, if any left, it will give
rise to streaks. The author insists upon the necessity of all these
cares. Two sheets of paper are now placed side by side on a flat board,
then the surface of the first is covered with the paste by means of a
sponge, proceeding, before you leave it, all over the sheet in a
horizontal direction; the second sheet is covered in a like manner. By
the time the second sheet is pasted, the first one will be partially dry.
The sponge is now drawn over each sheet, in succession, in a perpendicular
direction in order to efface the streaks from the first sponging. If the
paste drags in a slimy manner, it is too strong, and a fresh arrowroot
must be prepared, because dilution only ends in failure. Why dry, the
paper is rolled under moderate pressure, and when it lies smoothly the
maximum pressure may be applied.

PLAIN COLLODION.
Alcohol 12 ounces
Ether 4 ounces
Pyroxyline 80 grains

SENSITIVE COLLODION.
Plain collodion 1 ounce
Nitrate of uranium, pure 30 grains
Nitrate or silver 5 grains

Add the uranium first, and as soon as it has dissolved all that it can,
add a grain or two of soda, and when settled pour off the supernatant
collodion and add the silver.(14) To coat the paper with collodion, use a
board with a handle beneath, such as is used by plasterers. On this place
a sheet of paper, the edges being turned up about the sixteenth of an
inch; this enables the whole of the sheet to be covered without spilling
the collodion or allowing it to run on the back of the paper.

There is a marked difference in the appearance of the prints when they
leave the pressure frame. Some samples of collodion cause the picture to
print of a beautiful green, others of a rich brown, and some of a yellow
or orange tint. The last take the longest of all to tone, and difficultly
assume the tint of well toned silver prints,(15) those printing to green
or brown tone very rapidly.

After printing the pictures are placed in diluted sulphuric acid, 1 to 30
of water, until the high lights are perfectly clear and white; this takes
from ten to fifteen minutes. After washing well under a stream of water,
they are placed in