tion
with iodine give birth to the blue tint. Consequently the action of
the iodine differs according to the extent of the erasure.

"When paper is partially erased and wet, as when letters are copied,
the same result although not so striking follows upon exposing it to
the iodine vapor after letting it dry thoroughly.

"Iodine affords in certain cases the means of detecting the nature of
the substance used for erasing. Bread crumbs or India rubber turn
yellow or brownish yellow tints and these are distinguished by more
intense coloration; erasure by means of bread crumbs causing the paper
to take a violet shade of great uniformity. These peculiarities are
due to the upheaval of the fibers caused by rubbing. In fact this
upheaval creates a larger absorbing surface and consequently a larger
proportion of iodine can cover the rubbed parts than it would if there
had been no friction.

"When paper upon which writing has been traced with a glass rod, the
tip of which is perfectly round and smooth, is exposed to iodine
vapor, the characters appear brown on yellow ground which wetting
turns to blue. This change also occurs when the paper written upon has
been run through a super-calender. If the paper is not wet the
characters can be made to appear or be blotted by the successive
action of sulphurous and iodine vapor.

"Writing done by means of glass tips instead of pens will show very
little, especially when traced between the lines written in ink. The
reaction, however, is of such sensitiveness that where characters have
been traced on a piece of paper under others they appear very plainly,
although physical examination would fail to reveal their existence,
but a somewhat lengthy exposure to iodine vapors will suffice to show
them.

"If the wrong side of the paper is exposed to the iodine vapor the
characters are visible; but of course in their inverted position.

"If the erasure has been so great as to take off a part of the
substance of the paper the reconstruction of the writing, so as to
make it legible, may be regarded as impossible. But in this case
subjecting the reverse side of the paper to the influence of the
iodine will bring out the reverse outlines of the blotted-out
characters so plainly that they can be read, especially if the paper
is placed before a mirror. In some instances, when pencil writing has
been strong enough, its traces can be reproduced in a letter press by
wetting a sheet of sized and cal