414 
Our  Writing  Fluids. 
f  Am.  Jour.  Pharm. 
\     Sept.  1, 1872. 
ing-fluid,  viz. :  First,  the  cold  process  is  used.  Second,  the  want  of 
gum.  Third,  the  use  of  sulphate  of  indigo,  which  is  a  solvent  for  the 
black  precipitate,  the  tanno-gallate  of  iron  ;  hence  the  gum  arabic  is 
not  required,  as  it  is  only  used  to  suspend  this  precipitate.  Fourth, 
the  deficiency  of  iron,  which  may  be  accounted  for  by  the  pure  proto- 
sulphate  being  used,  which  cannot  contain,  or  should  not  contain  any 
oxide,  so  that  all  the  iron  is  free  to  combine  with  the  tannin.  Fifth, 
the  use  of  free  sulphuric  acid,  which  is  generally  looked  upon  as  det- 
rimental to  writing-fluids,  but  which  must  be  introduced  here  for  some 
purpose,  of  which  I  am  as  yet  ignorant. 
Thus  far  I  have  only  spoken  of  high-class  inks,  but  it  frequently 
occurs  that  an  article  is  required  which  is  to  be  sold  at  a  cheaper  rate 
than  that  wholly  made  from  galls ;  and  the  vegetable  world  gives  us 
an  ample  range  of  materials  to  select  from,  many  of  which  contain 
tannin  in  fair  quantity. 
In  this  case  other  ingredients  may  be  substituted  instead  of  part  of 
the  galls  ;  thus  we  often  see  logwood  substituted,  and  catechu,  su- 
mach, and  oak  bark  may  be  used  for  the  same  purpose.  Many  other 
substances,  such  as  elm-wood,  elder,  chestnut,  beech,  willow,  plum, 
cherry  and  poplar,  all  contain  a  certain  amount  of  astringent  proper- 
ties, but  none  of  them  are  to  be  compared  to  galls,  and  are  not  likely 
to  supersede  them  in  the  manufacture  of  ink,  so  long  as  galls  can  be 
had  for  anything  like  a  fair  price.  The  chemist  cannot  decide  in  fix- 
ing the  proportions  required  for  making  ink  as  he  would  do  almost  any 
other  chemical  problem,  as  the  substances  used  are  not  all  of  the 
same  relative  value,  nor,  indeed,  may  two  samples  of  the  same  sub- 
stance be  equally  rich  in  the  material  required,  viz.,  tannin  :  so  that 
he  must  make  an  analysis  every  time  he  prepares  his  ink,  to  estimate 
the  value  of  his  tannin  producer,  or,  what  is  more  convenient,  he 
must  fix  on  certain  proportions  which  are  known  to  produce  (by  expe- 
riment) good  results,  and  do  his  best  in  selecting  his  materials  up  to 
a  fair  average  standard. 
Thus  we  see  that,  although  galls  are  used  at  present  as  the  most 
suitable  substance  for  making  ink,  still  any  failure  or  stoppage  of  sup- 
ply in  the  production  of  galls  can  never  now  leave  us  entirely  depend- 
ent on  that  source  for  the  preparation  of  our  "writing-fluids." 
It  would  be  impossible,  and,  if  possible,  would  be  uninstructiveT  to 
mention  all  the  substances  which  have  found  their  way  into  formulae 
for  inks,  many  of  which  are  not  only  foolish,  but  incompatible,  show- 
ing a  want  of  chemical  knowledge. 
