forty centuries of ink-第34节

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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