ntroduce from
twenty to thirty grams of iodine in crystals.

Place the portion of paper on which the vapor of iodine is to act at
the opening of the bottle, and cover it with the stopper of unpolished
glass, on which put a weight so as to exert a slight pressure, and in
order that the aperture may be hermetically closed. Then allow the
vapor of iodine to act on the dry paper for three or four minutes at
the temperature of 15 deg. to 16 deg. C. and examine it attentively. When the
surface has not been spotted by any liquid (water, alcohol, salt
water, vinegar, saliva, tears, urine acids, acid salts, or alkalis) a
uniform pale-yellow or yellowish-brown tinge will be noticed on all
parts of the paper exposed to the vapor of iodine.

Otherwise a different and easily distinguished tinge shows itself on
the surface that has been moistened and then dried in the open air.

Machine-made papers with starchy and resinous sizing give such decided
reactions that sometimes it is possible to distinguish by the color
the portion of the paper treated with alcohol from that moistened with
water. The spot produced by alcohol takes a kind of yellow tinge; that
formed by water becomes a violet blue, more or less deep, after having
dried at an ordinary temperature. As to the spots produced by other
aqueous liquids, they approach in appearance, though not in intensity,
those occasioned by pure water. Feeble acids, or those diluted by
water, act like water; but the concentrated mineral acids, in altering
more or less the substance of the sizing, produce spots that present
differences.

Spots which become apparent by using vapor of iodine are due to
chemical agents whose strength has altered either the fibers of the
surface, or the paste uniting them.

In a word, the test of a document or paper by vapor of iodine has the
double advantage of indicating the place of the supposed alteration
and operating afterwards with appropriate reagents to bring back the
traces of ink. It is only the reappearance of former letters or
figures written or effaced that demonstrates forgery. Much time may be
profitably spent in merely scanning each letter of a document, and the
writing by lines, paragraphs, and pages before a closer scrutiny.
Gradually, if the writing be genuine, its character will begin to
reveal itself, and unconsciously a hypothesis as to the physical
causes of the irregularities or characteristics will be formed.

When an entire document