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