按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
or petroleum spirit； whereby it is rendered semi…
transparent。 The use of alcohol or water is inadmissible。
〃Valuable information is often obtainable by
treating writing or other ink…marks with reagents。
Some inks are affected much more rapidly than
others； though the rate of change depends greatly
on the age of the writing。 Normal oxalic acid （63
grammes per litre）； or hydrochloric acid of
corresponding strength； should be applied to a part of
the ink marked with a feather or camel…hair brush
（or the writing may be traced over with a quill
pen）； and the action observed by means of a lens；
the reagent being allowed to dry on the paper。
Recent writing （one or two days old） in gallic inks
is changed by one application of oxalic acid to a
light gray； or by hydrochloric acid to yellow。
Older stains resist longer； in proportion to their
age； and a deeper color remains。 Log…wood ink
marks are mostly reddened by oxalic acid； and
alizarin marks become bluish； but aniline inks
are unaffected。 With hydrochloric acid； logwood
ink marks turn reddish or reddish…gray； alizarin
marks greenish； and aniline ink marks reddish or
brownish…gray。 The treatment with acid should
be followed by exposure to ammonia vapors； or
blotting paper wet with ammonia may be applied。
Thus treated； marks in logwood ink turn dark
violet or violet…black。 The age of ink marks very
greatly affects the rate of their fading when treated
with dilute ammonia； the old marks being more
refractory。 The behavior of ink marks when
treated with solution of bleaching powder is often
characteristic； the older writings resisting longer；
but unless the reagent be extremely dilute； writings
of all ages are removed almost simultaneously。
Hydrogen peroxide acts more slowly than bleaching
solution； but gives more definite results。 After
bleaching the mark by either reagent； the iron of
the ink remains mordanted on the paper； and the
mark may be restored by treatment with a dilute
solution of galls； tannic acid； or acidulated ferro…
cyanide。 The same reagents may be used for restoring
writing which has been faded from age
alone。
〃When ink marks have been erased or discharged
by chemical means； traces of the treatment
are often recognizable。 After effecting the erasure
the spot is often rubbed over with a powdered alum
or gum sandarac； or coated with gelatin or size。
The bleaching agents most likely to have been
used are oxalic； citric； or hydrochloric acid； bleaching
powder solution； or acid sulphite of sodium。
Moistened litmus paper will indicate the presence
of a free acid； and in some cases treatment with
ammonia fumes will restore the color。 The presence
of calcium； chlorides； or sulphates in the
water in which the paper is soaked will afford some
indication of bleaching powder or a sulphite having
been used。 Potassium ferro…cyanide will detect
any iron remaining in the paper。 Exposure to
iodine vapor often affords evidence of chemical
treatment； and other methods of examination
readily suggest themselves。〃
M。 Piesse； in the Scientific American； is authority
for a method of removing ink； found on 〃patent〃
check paper：
〃Alternately wash the paper with a camel's…
hair brush dipped in a solution of cyanide of
potassium and oxalic acid； then when the ink has
disappeared wash the paper with pure water。〃
Inks of the tanno…gallate of iron family； whether
containing 〃added〃 color or not； can be more or less
〃erased〃 by chlorinate of lime or soda； in the
presence of a weak acid。 These chemicals do not；
however； materially affect the prussian blue inks；
which require solutions of hydrate of potash or soda。
Real indigo can be removed by chloroform； morphine
or an aniline salt （indigo and aniline both owe their
names to the same Portuguese source）； which possess
the rare property of dissolving pure indigo。 Such
combination； if refractory in the presence of permanganate
of potash with sulphuric acid； must be followed
by an application of sulphurous acid。 In like
manner； inks composed of by…products of coal tar； can
be effectively treated； when irradicable with plain
water or soap and water。
The erasure and removal of most inks from paper
can be accomplished by the application of the chemicals
heretofore enumerated。 The requirements in
this direction of some inks； however； though of rare
occurrence； are to be met by the employment of other
and particular reagents。
Many of the tests specified in the Allen citation to
determine the character of ink constituents； if made
alone are practically valueless； because the same behavior
occurs with different materials employed in the
admixture of ink。 To avoid error in judgment the
operator should verify if possible by confirmatory
tests。 Thus； in the one for logwood； sulphurous acid
will cause a logwood ink mark to turn yellow； mercuric
chloride； orange； tartar…emetic； red； and if the
marks are faded ones； solutions of sulphate of iron
or bichromate of potash will restore them respectively
to a violet or blue…black color。
Prussian blue； aniline blue and indigo blue are to
be tested as follows： Solution of chloride of lime； no
change of color for prussian blue； decoloration or
faint yellow for aniline blue or indigo。 To discriminate
between the two latter； test with solution of
caustic soda； when decoloration or change of color
will indicate aniline blue and permanence will indicate
presence of indigo blue。
In the manufacture of the blue…black inks； a variety
of violets have been and are still employed。 Among
them are aniline violet； iodine violet； madder； alkanet；
orchil and logwood。
（a） Apply chloride of lime solution： 1。 No change
of color indicates alkanet。 2。 Any change； one of
the other five。
（b） Apply lemon juice： 1。 The violet becomes
brighter if it is one of the aniline violets； to be
distinguished from each other by applying one part of
hydrochloric acid to three parts of water； when it will
become violet…blue； changing to red if it is common
aniline…violet； but blue changing to a green hue and
upon adding plain water to a lilac or pearl gray if it
is iodine…violet （Hoffman's）。 It will also turn from
red to yellow in lemon juice。 To test for the other
three violets： （a） Apply chloride of lime； to be followed
by a solution of yellow prussiate of potash：
absence of a blue coloration leaves orchil and logwood
to be considered。 To distinguish between them apply
solution of hydrate of lime； whereby a change to
gray； followed by complete decoloration indicates logwood；
and a change to violet…blue； orchil。
The substances utilized with but few exceptions for
red ink are the 〃eosins；〃 possessing different names
like erythrosine； as well as different hues。 Antecedent
to about thirty…five years ago； cochineal （known
as 〃carmine〃）； madder； Brazil wood and saffron formed
the basis of most of the red in