Am.  Jour.  Pharm. 
Jan.,  1889. 
Photography. 
47 
In  1841  Fox  Talbot  patented  his  famous  calotype  process.  By  it  he  ob- 
tained invisible  images  on  paper,  made  sensitive  with  silver  iodide,  and  de- 
veloped them  by  means  of  a  solution  of  gallic  acid.  Paper  negatives,  which 
at  the  present  time,  by  reason  of  their  light  weight,  compactness,  etc.,  are 
promising  to  supersede  those  of  glass,  are  thus  by  no  means  "new,"  another 
proof  that  there  is  nothing  new  under  the  sun.  There  is  this  difference, 
however,  that  the  image  was  in  the  texture  of  the  paper  in  Talbot's  negatives, 
whilst  now  it  is  on  the  surface,  so  to  speak. 
Bat  if  photography  was  not  originally  given  out  to  the  world  as  the  inven- 
tion of  one  of  perfidious  Albion's  sons— although  at  the  same  time,  be  it  re- 
marked, historians  generally  concede  to  Wedgwood  the  honor  of  having  been 
the  first  photographer — we  can  console  ourselves  with  the  fact  that,  to  a 
worker  on  this  side  of  the  silver  streak,  Scott  Archer  to  wit,  belongs  the 
honor  of  having  introduced  the  collodion  process,  as  it  exists  to-day,  and  in 
importance  his  discovery  certainly  ranks  next  to  that  of  the  daguerreotype. 
As  he  had  not  taken  out  a  patent  for  his  process,  and  the  best  thanks  of  pho- 
tographers are  due  to  him  for  this,  our  Government  granted  at  his  prema- 
ture death  a  pension  to  his  bereaved  family,  because  he  had  been  11  the  dis- 
coverer of  a  scientific  process  of  great  value  to  the  nation,  and  from  which 
the  discoverer  had  reaped  little  or  no  benefit." 
His  collodion  process  then  came  extensively  into  use,  as  the  results  ob- 
tained by  it,  for  studio  work  in  general  and  portraiture  in  particular,  were 
vastly  superior  to  those  of  the  daguerreotype.  The  substitution  of  glass  for 
metal  &s  a  substratum  was  also  a  step  in  the  right  direction. 
But  even  here  photographers  did  not  by  any  manner  of  means  rest  con- 
tented, for  we  find  that  a  grand  improvement  was  soon  to  take  place  in  the 
introduction  of  gelatin  as  a  substitute  for  the  use  of  collodion,  first  proposed, 
after  satisfying  himself  with  experiment,  by  Dr.  Maddox,  and  made  practi- 
cally and  commercially  successful  by  Mr.  Kennet,  of,  strange  to  say,  Mad- 
dox street. 
Thus,  speaking  generally,  we  have  at  present  three  chief  photographic 
processes,  the  daguerreotype,  the  collodion,  and  the  one  just  mentioned,  or 
the  gelatin-bromide  process. 
The  daguerreotype  is  still  occasionally  preferred  for  some  special  kinds  of 
work,  and  the  collodion  process  has  its  advantages,  particularly  in  the  pro- 
duction of  "  positives,"  but  the  introduction  of  the  rapid  gelatin  dry  plate, 
devoid  of  all  the  "  messiness  "  of  the  old  wet  process,  may  fairly  be  said  to 
have  called  the  amateur  photographer  into  existence  and  made  him  a 
striking  feature  of  the  nineteenth  century. 
The  daguerreotype  consists  of  a  copper  plate,  which  is  first  coated  on  one 
side  with  a  very  thin  coat  of  metallic  silver  by  electro  deposition  and  then 
submitted  to  the  combined  action  of  bromine  and  iodine,  thus  forming  sil- 
ver bromo-iodide,  a  combination  which  has  been  proved  by  experiment  to 
be  much  more  sensitive  to  light  than  either  of  the  separate  single  salts. 
After  exposure  in  the  camera,  the  photographic  image  is  developed  by 
means  of  metallic  mercury  vapor,  usually  performed  by  heating  a  layer  of 
mercury  to  about  150°  Fahr.,  and  suspending  the  plate  over  it,  in  the  dark, 
