calculated　or　obtained。　This　is　more　particularly　to　be
  noted　in　the　case　of　black　writing　inks　otherwise
  known　as　the　tanno…gallate　of　iron　inks　＇gallic　and　gallotanic
  acid　obtained　from　nut…galls；　sulphate　of　iron；
  （green　copperas）　and　some　gummy　vehicle＇。
  The　variations　would　appear　to　be　largely　due　to　the
  difference　in　quality　of　the　gall…nuts；　treatment；　and
  temperature　of　the　atmosphere；　perhaps；　however；　not
  so　much　to…day　as　it　was　ten　or　twenty　years　ago；
  when　to　make　ink　of　this　character　boiling　processes
  were　employed。　Most　of　them　as　already　stated　are
  now　〃cold〃　made。
  Inks　of　this　class　consist　of　a　finely　divided　insoluble
  precipitate　suspended　in　water　by　the　use　of　gum　and
  possessing　a　slight　acidity。
  The　requisites　of　a　good　black　writing　ink　or
  black　writing　fluid　require　it　to　flow　readily　from
  the　pen；　to　indicate　in　a　short　time　a　black　color
  and　to　penetrate　the　paper　to　an　appreciable
  degree；　and　more　important　than　all　the　rest；　to　be　of
  great　durability。　When　kept　in　a　closed　vessel　no
  sediment　of　any　account　should　be　precipitated；　although
  such　will　be　the　case　in　open　ink…wells；　and
  this　the　quicker　the　more　the　air　is　permitted　to　get
  to　it。　If　it　is　to　be　used　for　record　or　documentary
  purposes　it　must　not　be　altogether　obliterated　if　brought
  into　contact　with　water　or　alcohol；　and　should　depend
  for　permanency　on　its　chemical　and　not　on　its　pigmentary
  qualities。
  The　second　class；　called　for　distinction　〃chemical
  writing　fluids；〃　possesses　the　same　essential　ingredients
  to　be　found　in　class　one；　but　much　less　in
  quantity　and　with　some　〃added〃　colored　substance
  which　I　shall　term　〃loading；〃　for　its　real　purpose　is　to
  cheapen　the　cost　of　production　and　not　altogether　as
  some　manufacturers　state　〃simply　to　give　them　an
  agreeable　color。〃
  Previous　to　the　discovery　of　the　soluble　anilines；
  logwood；　indigo；　madder；　orchil　and　other　dyeing
  materials　were　used　for　a　period　of　some　eighty　years
  and　vanadium　for　some　twenty　years　（very　costly
  at　that　time）；　for　this　purpose；　but　since　1874；　and
  with　frequent　changes　as　the　newer　aniline　compounds
  were　invented；　these　by…products　of　coal…tar；　as　well　as
  logwood；　etc。；　have　been　and　are　to…day　employed　for
  〃loading；〃　or　as　the　manufacturer　expresses；　it　〃added
  color。〃　The　chemical　writing　fluids　as　now　prepared；
  yield　when　first　written　a　blue　or　green　color　with　a
  tendency　to　change　to　black　afterwards。　They　are
  not　as　permanent　as　those　of　the　first　class。
  Another　black　ink　not　durable；　however；　is　〃logwood；〃
  its　extract　is　combined　with　a　little　chromate
  of　potassium　and　boiled　together　in　water。　It　possesses
  its　own　〃gum〃　and　contains　some　tannin。　In
  combination　with　alum　and　water；　it　forms　a　dark
  purple　ink。
  The　colored　writing　inks；　of　which　〃red〃　is　the
  more　important；　are　in　great　number　and　with　hardly
  an　exception　at　the　present　time；　manufactured　by
  adding　water　and　water…glass　to　a　soluble　aniline　red
  color。　Cochineal　which　was　used　for　red　ink　formerly
  is　now　almost　obsolete。　Nigrosine；　one　of　the　best
  known　of　them；　is　much　used　as　a　cheap　〃black〃　ink；
  but　as　it　is　blue　black　and　never　becomes　black；　it
  really　belongs　to　the　family　of　〃colored〃　writing
  inks。　They　possess　an　undeserved　popularity　for　they
  flow　freely　from　the　pen　which　they　do　not　corrode；
  nor　do　they　thicken　or　spoil　in　the　inkwell；　they　are
  however　very　〃fugitive〃　in　character　and　should　not
  be　employed　for　record；　legal；　monetary　or　other
  documentary　purposes。　The　indigo　and　prussian　blue
  inks　are　well　known；　the　former　under　certain　conditions
  a　very　permanent　ink；　the　latter　soon　disintegrating。
  Copying　inks　are　of　two　kinds；　one　dependent　on
  the　addition　of　glycerine；　sugar；　glucose　or　like　compounds
  to　the　black　writing　inks　or　chemical　writing
  fluids　heretofore　mentioned；　which　are　thereby　kept
  in　a　moist　offsetting　condition；　the　other　due　to　the
  solubility　of　the　pigmentary　color　with　water；　such　as
  the　aniline　inks　which　are　given　more　body　than
  those　for　ordinary　purposesand　the　logwoods　in
  which　the　pigment　is　developed　and　given　copying
  qualities　by　chemicals；　and　hence　becomes　responsive
  to　the　application　of　a　sheet　of　paper　dampened　with
  water。　Copying　ink　should　never　be　used　for
  〃record〃　purposes　as　it　is　affected　by　changes　of　the
  temperature。
  India　ink；　sometimes　called　China　ink；　or　as　formerly
  known　by　the　ancients　and　in　classical　and　later　times
  〃Indian　ink；〃　is　now　used　more　for　drawing　and　engrossing
  than　it　is　for　commercial　purposes。　It　belongs
  to　the　〃carbon〃　class　and　in　some　form　was
  the　first　one　used　in　the　very　earliest　times。　In
  China　it　is　applied　with　a　brush　or　pith　of　some　reed
  to　the　〃rice〃　paper　also　there　manufactured。　It　is
  easily　washed　away　unless　bichromate　of　ammonium
  or　potassium　in　minute　quantities　be　added　to　it；　and
  then　if　the　paper　on　which　it　appears　be　exposed　for　a
  short　time　to　the　action　of　the　actinic　rays　of　sunlight；
  this　gummy　compound　will　be　rendered　insoluble　and
  cannot　be　removed　with　any　fluid；　chemical　or　otherwise。
  It　possesses　also　great　advantages　in　drawing；
  since　it　acts　as　a　paint；　and　will　give　any　degree　of
  blackness　according　to　the　quantity　of　water　mixed　with　it。
  Secret　or　sympathetic　inks　are　invisible　until　the
  writing　is　subjected　to　a　subsequent　operation；　such
  as　warming　or　exposing　to　sunlight。　To　further　aid
  the　object　in　view；　the　paper　may　be　first　steeped　in
  a　liquid　and　the　writing　only　made　visible　by　using
  another　liquid　which　has　some　chemical　affinity　with
  the　previous　one。　The　number　of　this　kind　were　but
  few　but　have　multiplied　as　chemistry　progressed。
  The　ancients　were　acquainted　with　several　modes。
  Ovid　indiscreetly　advises　the　Roman　wives　and　maidens
  if　they　intend　to　make　their　correspondence　unreadable
  to　the　wrong　persons　to　write　with　new　milk；
  which　when　dried　may　be　rendered　visible　by　rubbing
  ashes　upon　it　or　a　hot　iron。　Pliny　suggests　milky
  juices　of　certain　plants　of　which　there　are　a　considerable
  variety。
  Indelible　ink　is　not　used　for　writing　purposes　on
  paper；　but　is　found　best　adapted　for　marking　linen
  and　cancellation　or　endorsing　purposes。　It　is　chiefly
  composed　of　nitrate　of　silver　preparations；　to　which
  heat　must　be　applied　after　it　has　been　dried；　or　a
  pigment　is　commingled　with　the　same　vehicles　used
  in　making　common　printing　ink　and　in　its　use　treated　as　such。
  Diamonds；　gold；　silver；　platinum　and　a　host　of　other
  materials　are　manufactured　into　ink　and　are　to　be
  placed　under　the　head　of　miscellaneous　inks。　They
  are　in　great　number　and　of　no　interest　in　respect　to
  ink　writing　except　for　engrossing　or　illuminating。
  Still　another　ink　once　held　in　much　esteem　and　now
  almost　obsolete　is　the　so…called　〃safety〃　ink。
  Manufacturers；　chemists　and　laymen　in　great　number
  for　many　years　wasted　money；　time　and　energy
  in　diligent　worship　at　a　secret　shrine　which　could　not
  give　the　information　they　sought。　A　summary　of　the
  meager　and　barren　results　they　secured　is　of　little
  value　and　unimportant。　Hence；　there　is　no　REAL　〃safety〃　ink。
  It　is　true　that　lampblack　（carbon）　as　made　into
  ink；　resists　any　chemical　or　chemicals；　but　simple
  water　applied　on　a　soft　sponge　will　soon　remove　such
  ink　marks。　The　reason　for　this　is　obvious；　the　ink
  does　not　penetrate　the　paper。
  〃Safety〃　ink　which　will　not　respond　to　acids　may
  be　affected　by　alkalis；　or　if　resisting　them　separately；
  will　yield　to　them　in　combination。
  CHAPTER　XV。
  OFFICIAL　AND　LEGAL　INK。
  FIRST　COMPLETE　OFFICIAL　INVESTIGATION　OF　INK　IN
  THIS　COUNTRYTHE　HONOR　DUE　TO　ROBERT　T。　SWAN
  OF　BOSTONRESUME　OF　HIS　REPORTS　TO　THE
  LEGISLATURE　OF　THE　STATE　OF　MASSACHUSETTSTHE
  SWAN　LAW　ADOPTED　IN　1894　BY　THE　STATE　OF
  MASSACHUSETTSUNITED　STATES　TREASURY　DEPARTMENT
  ADOPTS　AN　OFFICIAL　INK　IN　1901UNSUCCESSFUL
  ATTEMPT　TO　SECURE　INK　LEGISLATION　IN　THE　STATE
  OF　NEW　YORKCOMMENTS　OF　THE　PUBLIC　PRESS　OF
  THAT　PERIODDIFFERENT　WORKS　WHICH　MORE　OR
  LESS　DWELL　ON　THE　SUBJECT　OF　INK　FROM　1890　TO
  1900CITATIONS　FROM　ALLEN'S　COMMERCIAL　ORGANIC
  ANALYSISREFERENCE　TO　PAPER　ABOUT　INK
  READ　BEFORE　THE　NEW　YORK　STATE　BAR　ASSOCIATION。
  IT　was　not；　however；　until　1891　that　the　subject　of
  the　constitution　of　an　enduring　record　ink　received
  the　consideration　its　importance　deserved　and　in　this
  the　youngest　of　countries。　To　Robert　T。　Swan　of
  Boston　is　all　honor　due　for　the　very　unique　and
  comprehensive　methods　adopted　in　his　investigations。
  Appointed　〃commissioner　of　public　records〃　of　the
  state　of　Massachusetts；　he　has　set　an　example　which
  may　well　be　followed　by　other　states；　as　has　been
  done　in　a　lesser　degree　by　Connecticut　and　ten　years
  later　by　the　United　States　Treasury　Department；
  which　in　this　respect　is　so　ably　represented　in　part
  by　Dr。　Charles　A。　Crampton　of　Washington；　D。