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forty centuries of ink-第34章

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Ink marks made with a compound consisting of the

combination of iron and an infusion of galls or its

equivalent (a tanno…gallate of iron ink); as treated

with certain chemicals; change from a compound with

color to a chemical compound; with no color。 Nothing

has in fact been absolutely removed or eradicated;

but it is a mere change of form; a sort of re…arrangement

of the particles; the ingredients which formed

the original color being still present; but in such a

condition that they are invisible to the eye。 A restoration

of the invisible ink marks so that they can

be observed; becomes possible by the use of chemical

reagents and is the reverse of the one of erasure or

bleaching; and changes the constituents again into a

compound which has color from the one which had

none。 It does; not; however; reproduce the exact composition

originally existing。 Such a reagent simply

goes to the basis of the material as first used; takes

up what was left and reforms the particles sufficiently

to make them abundantly recognizable。 An apt

illustration of these chemical changes of color is found

in what is known as the phenolphtalein test solution;

which is colored deep purplish…red by alkali hydrates

or carbonates; and then by the addition of an acid

rendered colorless; to be again reddened by an over…

plus of the alkali and so on ad infinitum。



A popular material for the purpose of making

chemical erasures is chlorinated lime or soda; which

becomes more active by first touching the ink mark

to be removed with a one half strength solution of

acetic acid; this hastens the liberation of chlorine

gas; THE active agent which causes the 〃bleaching〃

to take place。 Hydrogen peroxide; also a bleaching

compound; is less rapid in its action than chlorinate

of soda; the same may be said of combinations of

oxalic and sulphurous acids。



The most effective re…agent for the restoration of a

chemically 〃bleached〃 iron ink mark is the sulphide

or sulphuret of ammonia (it has several names)。 This

penetrating chemical blackens metals or their salts;

whether visible or not; if brought together。 It must

not be used by direct contact; the best and safest

plan being to place a quantity in a small saucer; to be

set on the floor of a closed box; to fasten to the box

lid the specimen to be operated on; in this way the

restoration is due to the fumes of the chemical and a

possible danger of destruction of the specimen much

lessened; especially if the marks are very light or delicate

ones。 The restoration of color under particular

conditions may also be obtained by treatment with

tannic acid; potassium ferro…cyanide (acidulated) or a

weak solution of an infusion of galls。







CHAPTER XVIII。



INK CHEMISTRY。



SOME OBSERVATIONS AS TO CHEMICAL EXAMINATION OF

INK MARKS BY ALLENERASING OF INKS BY CHEMICAL

MEANSAPPROVED CHEMICAL TESTS IN THE

ASCERTAINMENT OF INK CONSTITUENTS。



A COMPILATION of the methods of Robertson;

W。 Thompson (Lord Kelvin); Irvine; Wislar; Hoffman

and others; relative to the chemical examination of ink

marks; is to be found in 〃Allen's Commercial Organic

Analysis。〃 Their experiments; however; date back

many years ago; a few of them before the time of the

use of the 〃anilines〃 for added color。 The so…called

〃alizarin〃 ink referred to has now become obsolete。

The following is the citation in part:



〃In chemico…legal cases it is sometimes of

importance to ascertain the nature of the ink used;

to compare it with specimens of writing of known

history; and to ascertain the relative ages of the

writings。 A minute inspection should first be

made with a magnifying power of about 10 diameters;

and any peculiarities of color; lustre; shade;

etc。; duly noted; and where lines cross each other

which lie uppermost。 The examination is often

facilitated by moistening the paper with benzine

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 b
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