vinegar　impregnated　with　saturn。
  〃Take　an　ounce　of　quick…lime；　and　half　an　ounce　of
  orpin；　powder　and　mix　them；　put　your　mixture　into
  a　matrass；　and　pour　upon　it　five　or　six　ounces　of　water；
  that　the　water　may　be　three　fingers　breadth　above
  the　powder；　stop　your　matrass　with　cork；　wax；　and　a
  bladder；　set　it　in　digestion　in　a　mild　sand　heat　ten　or
  twelve　hours；　shaking　the　matrass　from　time　to　time；
  then　let　it　settle；　the　liquid　becomes　clear　like　common
  water。
  〃Burn　cork；　and　quench　it　in　aqua　vitae；　then　dissolve
  it　in　a　sufficient　quantity　of　water；　wherein　you
  shall　have　melted　a　little　gumm　arabick；　in　order　to
  make　an　ink　as　black　as　common　ink。　You　must
  separate　the　cork　that　can't　dissolve；　and　if　the　ink　be
  not　black　enough；　add　more　cork　as　before。
  〃Get　the　impregnation　of　saturn　made　with　vinegar；
  distilled　as　I　have　shewn　before；　or　else　dissolve
  so　much　salt　of　saturn　as　a　quantity　of　water
  is　able　to　receive：　write　on　paper　with　a　new
  pen　dipt　in　this　liquor；　take　notice　of　the　place
  where　you　writ；　and　let　it　dry；　nothing　at　all　will
  appear。
  〃Write　upon　the　invisible　writing　with　the　ink
  made　of　burnt　cork；　and　let　it　dry；　that　which　you
  have　writ　will　appear　as　if　it　had　been　done　with　common
  ink。
  〃Dip　a　little　cotton　in　the　first　liquor　made　of　lime
  and　orpin；　but　the　liquor　must　be　first　settled　and
  clear；　rub　the　place　you　writ　upon　with　this　cotton
  and　that　which　appeared　will　presently　disappear；　and
  that　which　was　not　seen　will　appear。
  ANOTHER　EXPERIMENT。
  Take　a　book　four　fingers　breadth　in　bigness；　or
  bigger　if　you　will：　write　on　the　first　leaf　with　your
  impregnation　of　saturn；　or　else　put　a　paper　that　you
  have　writ　upon　between　the　leaves；　turn　to　t'　other
  side　of　the　Book；　and　having　observed　as　near　as　may
  be　the　opposite　place　to　your　writing；　rub　the　last　leaf
  of　the　book　with　cotton　dipt　in　liquor　made　of　quick…
  lime　and　orpin；　nay　and　leave　the　cotton　on　the　place
  clap　a　folded　paper　presently　upon　it；　and　shutting
  the　book　quickly；　strike　upon　it　with　your　hand　four
  or　five　good　strokes；　then　turn　the　book；　and　clap　it
  into　a　press　for　half　a　quarter　of　an　hour；　take　it　out
  and　open　it；　you'll　find　the　place　appear　black；　where
  you　had　writ　with　the　invisible　ink。　The　same　thing
  might　be　done　through　a　wall；　if　you　could　provide
  something　to　lay　on　both　sides；　that　might　hinder　the
  evaporation　of　the　spirits。
  REMARKS。
  〃These　operations　are　indeed　of　no　use；　but　because
  they　are　somewhat　surprizing；　I　hope　the　curious　will
  not　take　it　ill；　that　I　make　this　small　digression。
  〃It　is　a　hard　matter　to　explicate　well　the　effects　I
  have　now　related；　nevertheless　I　shall　endeavour　to
  illustrate　them　a　little；　without　having　recourse　to
  sympathy　and　antipathy；　which　are　general　terms；　and
  do　not　explicate　nothing　at　all；　but　before　I　begin；　we
  must　remark　several　things。
  〃The　first　is；　that　it　is　an　essential　point　to　quench
  the　coal　of　cork　in　aqua　vitae；　that　the　visible　ink　may
  become　black　with　it。
  〃Secondly；　that　the　blackness　of　this　ink　does
  proceed　from　the　fuliginosity　or　sooty　part　of　the　coal
  of　the　cork　which　is　exceeding　porous　and　light；　and
  that　this　fuliginosity　is　nothing　but　an　oil　very　much
  rarefied。
  〃Thirdly；　that　the　impregnation　of　saturn；　which
  makes　the　invisible　ink；　is　only　a　lead　dissolved；　and
  held　up　imperceptibly　in　an　acid　liquor；　as　I　have　said；
  when　I　spoke　of　this　metal。
  〃Fourthly；　that　the　first　of　these　liquors　in　a　mixture
  of　the　alkali　and　igneous　parts　of　quick…lime　with
  the　sulphureous　substance　of　arsenick；　for　the　orpin
  is　a　sort　of　arsenick；　as　I　said　before。
  〃All　this　being　granted；　as　no　body　can　reasonably
  think　otherwise；　I　now　affirm；　that　the　reason　why　the
  visible　ink　does　disappear；　when　the　defacing　liquor　is
  rubbed　upon　it；　is　that　this　liquor　consisting　of　an
  alkali　salt；　and　parts　that　are　oily　and　penetrating；
  this　mixture　does　make　a　kind　of　soap；　which　is　able
  to　dissolve　any　fuliginous　substance；　such　as　burnt
  cork；　especially　when　it　has　been　already　rarefied　and
  disposed　for　dissolution　by　aqua　vitae；　after　the　same
  manner　as　common　soap；　which　is　compounded　of　oil；
  and　an　alkali　salt；　is　able　to　take　away　any　spots　made
  by　grease。
  〃But　it　may　be　demanded；　why　after　the　dissolution
  the　blackness　does　disappear。
  〃I　answer；　that　the　fuliginous　parts　have　been　so
  divided；　and　locked　up　in　the　sulphureous　alkali　of
  the　liquor；　that　they　are　become　invisible；　and　we　see
  every　day　that　very　exact　solutions　do　render　the　thing
  dissolved　imperceptible；　and　without　colour。
  〃The　little　alkali　salt　which　is　in　the　burnt　cork
  may　also　the　better　serve　to　joyn　with　the　alkali　of
  the　quick…lime；　and　to　help　the　dissolution。
  〃As　for　the　invisible　ink；　it　is　easy　to　apprehend
  how　that　appears　black；　when　the　same　liquor；　which
  serves　to　deface　the　other；　is　used　upon　it。　For　whereas
  the　impregnation　of　saturn　is　only　a　lead　suspended　by
  the　edges；　of　the　acid　liquor；　this　lead　must　needs　revive；
  and　resume　its　black　colour；　when　that　which　held　it
  rarefied　is　entirely　destroyed；　so　the　alkali　of　quick…
  lime　being　filled　with　the　sulphurs　of　arsenick　becomes
  very　proper　to　break　and　destroy　the　acids；　and　to
  agglutinate　together　the　particles　of　lead。
  It　happens　that　the　visible　ink　does　disappear　by
  reason　that　the　parts　which　did　render　it　black　have
  been　dissolved；　and　the　invisible　ink　does　also　appear
  because　the　dissolved　parts　have　been　revived。
  〃Quick…lime　and；　orpiment　being　mixed　and　digested
  together　in　water；　do　yield　a　smell　much　like
  that　which　happens　when　common　sulphur　is　boiled　in
  a　lixivium；　of　tartar。　This　here　is　the　stronger；　because
  the　sulphur　of　arsenick　is　loaded　with　certain　salts
  that　make　a　stronger　impression　on　the　smell。　Quick…
  lime　is　an　alkali　that　operates　in　this　much　like　the
  salt　of　tartar　in　the　other　operation；　you　must　not
  leave　the　matrass　open；　because　the　force　of　this
  water　doth　consist　in　a　volatile。
  〃The　lime　retains　the　more　fixt　part　of　the　arsenick
  and　the　sulphurs　that　come　forth　are　so　much　the
  more　subtile；　as　they　are　separated　from　what　did　fix
  them　before；　and　this　appears　to　be　so；　because　the
  sulphurs　must　of　necessity　pass　through　all　the　book　to
  make　a　writing　of　a　clear　and　invisible　liquor　appear
  black　and　visible：　and　to　facilitate　this　penetration　the
  book　is　strook；　and　then　turned　about；　because　the　spirit
  or　volatile　sulphurs　do　always　tend　upwards；　you　must
  likewise　clap　it　into　a　press；　that　these　sulphurs　may
  not　be　dispersed　in　the　air。　I　have　found；　if　that　these
  circumstances　are　not　observed；　the　business　fails。
  Furthermore　that　which　persuades　me　that　the　sulphurs
  do　pass　through　the　book；　and　not　take　a　circuit
  to　slip　in　by　the　sides；　as　many　do　imagine；　is
  that　after　the　book　is　taken　out　of　the　press；　all　the
  inside　is　found　to　be　scented　with　the　smell　of　this
  liquor。
  〃There　is　one　thing　more　to　be　observed；　which　is；
  that　the　infusion　of　quick…lime　and　orpin　be　newly
  made；　because　otherwise　it　will　not　have　force　enough
  to　penetrate。　The　three　liquors　should　be　made　in
  different　places　too；　for　if　they　should　approach　near
  one　another；　they　would　be　spoiled。
  〃This　last　effect　does　likewise　proceed　from　the　defacing
  liquor；　for　because　upon　the　digestion　of　quick…
  lime　and　orpin；　it　is　a　thing　impossible　for　some　of　the
  particles　will　exalt；　stop　the　vessel　as　close　as　you
  will；　the　air　impregnated　with　these　little　bodies　does
  mix　with；　and　alter　the　inks；　insomuch　that　the　visible
  ink　does　thereby　become　the　less　black；　and　the　invisible
  ink　does　also　acquire　a　little　blackness。〃
  Priceless　MSS。　in　immense　number　written　in
  periods　between　the　third　and　thirteenth　centuries
  have　been　destroyed　by　modern　scholars　in　experimentations
  based　on　the　false　theory　that　the　faded
  inks　on　them；　whether　above　or　below　other　inks
  （palimpsests）；　contained　iron。
  Sulphocyanide　of　potassium　is　highly　esteemed　as　a
  reagent　for　the　restoration　of　writing；　if　iron　is　present。
  Theoretically；　it　is　one　of　the　best　for　such　a　purpose
  if　employed　with　acetic　acid。　It　causes；　however；　such
  a　decided　contraction　of　parchment　as　to　be　utterly
  useless；　but　for　paper　MSS。　is　excellent。　The　metallic
  sulphides　generally　pronounced　harmless；　causes
  the　writing　to　soften　and　become　illegible　in　a　short
  time。　On　the　other　hand；　yellow　prussiate　of　potash；
  with　acetic　acid　in　successive　operations　is　of　great
  service　in　treating　the　most　perplexing　palimpsests。
  Ink　which　badly　corrodes　a　steel　pen　need　not
  necessarily　be　condemned；　it　may　contain　just　the　qualities
  which　make　it　bind　to　the　paper　and　render　it
  more　durable。
  Some　inks　which　are　fairly　permanent　against　time
  if　not　tampered　with；　ca