forty centuries of ink-第36部分

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！



ink。



〃2d。　The　application　of　a　thin　layer　of　gum；　of

starch；　or　farina；　of　gelatine；　or　fish…glue；　with　a

view　of　sizing　certain　parts　of　the　paper；　or　of

causing　certain　bodies　to　adhere　to　it　momentarily；

is　detected　by　an　action　similar　to　that　which

shows　paper　to　have　lately　been　wetted　by　the　contact

of　liquids。



〃3d。　The　heterogeneousness　of　the　pulp　of　the

papers；　and　the　kind　of　size　with　which　they　are

impregnated；　lead　to　differences　in　the　results

which　are　observed　with　the　same　chemical　reagents。

We　shall　now　examine　each　of　these　propositions；

and　describe　the　means　which　we　have

employed　in　endeavoring　to　solve　questions　of　so

high　a　degree　of　interest。



〃1st。　The　homogeneousness　of　sized　paper　not

partially　altered　by　the　contact　of　liquids　（water；

alcohol；　salt…water；　vinegar；　saliva；　tears；　urine；

acid　salts；　and　alkaline　salts）　is　demonstrated　by

the　uniform　coloration　which　this　surface　takes　on

being　exposed；　if　not　wholly；　at　least　in　various

parts；　to　the　action　of　the　vapor　of　iodine　disengaged

at　the　ordinary　temperature　from　a　flask

containing　a　portion　of　the　metalloid。　When　the

surface　of　paper　not　stained　by　any　of　the　above

mentioned　liquids　is　exposed　to　the　action　of　this

vapor　for　three　or　four　minutes　in　a　room　the　temperature

of　which　is　about　60　degrees　F。；　a　uniform　yellowish；

or　light…brownish　yellow；　coloration　is　noticed

on　the　whole　extent　exposed　to　the　vapor　of

iodine；　in　the　contrary　case；　the　surface　which　has

been　moistened；　and　afterwards　dried　in　the　open

air；　is　perfectly　distinguished　by　a　different　and

well　circumscribed　tint。　On　the　papers　into　which

paste　starch　and　resin　have　been　introduced；　the

stains　present　such　delicate　reactions　that　we　may

sometimes　distinguish　by　their　color　the　portion　of

paper　which　has　been　moistened　with　alcohol　from

that　which　has　been　moistened　with　water。　The

stain　produced　by　alcohol　takes　a　bistre…yellow

tint；　that　formed　by　water　is　colored　of　a　more　or

less　deep　violet　blue；　the　desiccation　having　been

effected　at　the　ordinary　temperature。　For　the

stains　occasioned　on　these　same　papers　by　other

aqueous　liquids；　the　tint；　apart　from　its　intensity；

resembles　that　of　the　stains　of　pure　water。　The

feeble　or　dilute　acids　act　like　water　on　the　surface

of　the　same　paper　containing　starch　in　its　paste；

but　the　concentrated　mineral　acids；　by　altering

more　or　less　the　substances　which　enter　into　the

composition　of　the　latter；　give　test　to　the　stains

which　present　differences。　We　are　always　able

to　recognize　by　the　action　of　the　vapor　of　iodine

the　parts　of　the　paper　which　have　been　put　in

contact　with　chemical　agents；　the　energy　of　which

has　been　arrested　by　washing　in　cold　water。　We

are　able；　on　several　ancient　deeds；　written　on

stamped　paper；　and　a　few　words　of　which　had

been　removed　by　us　with　chemical　agents；　to

recognize　the　places　where　their　action　was　exerted；

to　see　and　to　measure　the　extent　which　they　occupied

on　the　surface　of　the　paper。



〃The　testing　of　a　paper　with　the　vapor　of

iodine　will　present　this　double　advantage　over　the

methods　hitherto　practiced　for　detecting　falsifications

in　writings；　that　it　points　out　at　once　the

place　in　the　paper　in　which　any　alteration　may　be

suspected；　and　that；　on　the　other　hand；　it　enables

us　to　act　afterwards　with　the　reagents　proper　for

causing　the　reappearance　of　the　traces　of　ink；　when

that　is　possible。　If　the　means　which　we　now　propose

cannot　always　make　the　former　writing

appear；　they　demonstrate　the　places　where　the

alterations　must　have　been　made；　when；　however；

the　want　of　uniformity　presented　by　the　surface

of　the　paper　is　not　explained　by　any　circumstance。

This　proof　becomes；　therefore；　a　weapon　which

the　guilty　person　cannot　avoid。　But　might　not

the　presence　of　a　stain；　or　several　stains；　developed

by　the　vapor　of　iodine；　in　different　parts　of　a　public

or　private　deed；　give　rise　to　a　suspicion；　where

these　stains　have；　perhaps；　been　occasioned　by　the

spilling　of　some　liquid　on　the　surface　of　the　paper？

and　would　it　not　be　rash　and　unjust　to　raise　an

accusation　from　such　a　fact？　There　would　indeed

be　great　temerity　in　drawing　such　a　conclusion

from　a　fortuitous　circumstance；　but　the　inference

which　may　be　drawn　from　the　place　occupied　by

these　stains　on　the　surface　of　the　paper；　from　the

more　or　less　significant　words　found　in　those　places；

would　not　permit　an　accusation　to　be　so　lightly

brought；　where　simple　reasoning　would　be　sufficient

to　destroy　its　basis。　Besides；　the　subsequent　reactions

which　would　be　made　would　certainly　never

revive　words　formerly　written　and　effaced；　whilst

the　latter　effects　may　be　often　produced；　more　or

less　visibly；　on　those　parts　of　the　paper　on　which

falsification　has　been　practiced；　figures　or　words

being　substituted　for　other　figures　or　words。



〃2d。　The　applications　made　to　the　surface　of

a　sheet　of　paper；　with　a　view　of　covering　it　again

at　certain　parts　with　a　fine　layer　of　gum；　gelatine；

starch　or　flour　paste；　or　in　other　places　to　cause

other　sheets　of　paper　to　adhere；　may　be　recognized

not　only　by　the　reflection　of　light　falling　upon　the

paper　inclined　at　a　certain　degree　of　obliquity；　and

by　the　transmission　of　light　through　the　paper；

but　also　by　the　varying　action　which　the　vapor　of

iodine　exerts　on　the　surface　which　is　not　homogeneous。

Papers　containing　starch　and　resin　are

more　powerfully　acted　upon　by　this　vapor　than

papers　of　a　less　complex　composition。　Both　in

the　parts　covered　with　starch；　or　paste　flour；　are

colored　in　a　few　minutes　of　a　violet　blue；　but

with　starched　papers　alone　a　more　intense　coloration

is　manifest　on　the　places　covered　again　with　a

thin　layer　of　gum　arabic；　size　or　gelatine。　By

looking；　then；　on　the　surface　of　the　paper；　held

somewhat　obliquely　to　incidental　light；　we　distinguish

clearly；　by　their　different　aspects；　the　parts

on　which　these　various　substances　have　been

applied。　The　vapor　of　iodine；　in　condensing　at

the　ordinary　temperature　on　the　surface　of　the

papers　to　which　any　kind　of　size　has　been　applied

in　various　places；　produces　differences　which　are

most　commonly　well　recognized　by　the　greater　or

less　transparence　of　the　paste　of　the　paper。



3d。　The　heterogeneousness　of　the　pulp　of　the

various　papers　of　commerce；　and　the　nature　of

the　size　with　which　they　are　penetrated；　cause

differences；　either　in　the　coloration　which　the　surface

of　these　papers　takes　when　exposed　to　the

vapor　of　iodine；　or　in　the　tint　which　is　manifested

in　the　portions　of　the　size　deposited　in　certain

portions　of　that　surface；　thus；　papers　with　starched

pulp　generally　turn　brown；　or　blue；　according　to

the　amount　of　water　that　remains　in　their　interstices；

other　papers　turn　yellow　only　under　the

influence　of　the　vapor　of　iodine；　and　the　parts

which　have　received　superficially　a　layer　of　another

agglutinative　body　resist　this　action　for　a　certain

time；　and　are　distinguished　from　the　parts　of　the

paper　which　are　not　covered　with　it。〃



My　own　investigations　confirm　to　a　great　extent

the　value　of　these　experiments　and　the　accuracy　of

the　deductions；　in　so　far　as　they　relate　to　〃linen〃

paper；　but　they　do　not　always　obtain　when　made　in

connection　with　paper　of　inferior　grades。



It　is　also　true　that　dry　paper　is　affected　differently

under　the　influence　of　the　vapor　of　iodine；　as　would

be　paper　which　had　been　moistened　and　then　dried；

but　the　part　which　had　been　moist　assumes　the　color

of　blue…violet；　while　unaltered　paper　assumes　a　yellow…

brown　color。　Even　when　the　paper　thus　treated　is

moistened　all　over　with　water；　there　will　be　a　difference；

for　those　parts　which　had　been　before　moistened；

will　appear　a　dark　violet…blue；　while　the　other　parts

will　show　a　plain　blue　coloration。



In　cases　where　pencil　writing　has　been　removed

with　a　soft　rubber　or　fresh　bread；　the　parts　thus

erased　will　assume；　when　subjected　to　iodine　fumes；　a

brown　color　trending　towards　violet　and　much　darker

than　the　undisturbed　portions　of　the　paper。　Lines

impressed　upon　paper　with　a　〃stylus；〃　a　glass　or

ordinary　dry　pen；　can　be　made　visible　by　the　fumes　of

iodine；　the　lines　showing　with　a　stronger　coloration

than　the　surrounding　paper。







CHAPTER　XX。




FUGITIVE　INK。



SOME　OBSERVATIONS　ABOUT　〃ADDED〃　COLOR　TO　INK

INVENTION　OF　COAL　TAR　COLORSCHRONOLOGICAL　HISTORY

OF　THE　〃ANILINES〃　EMPLOYED　AS　INKOTHER

SUBSTANCES　USED　FOR　THE　SAME　PURPOSE。



THE　term　〃added　color；〃　as　applied　to　ink；　is　the

popular　phraseology　for　a　multitude　of　materials

which　have　been　more　or　less　utilized　for　a　period　of

centuries；　in　adulterating　and　coloring　ink。　In　olden

times　they　were　introduced　into　ink　with　an　honest

belief　that　it　would　also　improve　and　ensure　its　lasting

qualities；　but　latterly　more　often　to　cheapen　the

cost　of