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