100 
Photography. 
Am.  Jour.  Pharm. 
Feb.,  1889. 
splendidly  as  a  most  energetic  sensitizer,  so  that  the  part  it  plays  may  not 
be  entirely  mechanical,  and  thus  the  slowest  gelatin  dry  plate  on  the  mar- 
ket is  twenty  times  more  rapid  than  the  old  wet-plate,  whilst  those  devoted 
to  instantaneous  work  are  about  sixty  times  more  sensitive. 
The  preparation  of  these  plates  requires  special  apparatus,  and  as  they 
can  now  be  bought  so  very  cheaply,  it  would  not  repay  an  amateur  to  make 
them,  so,  having  obtained  a  supply,  the  next  step  is  to  draw  on  them  a  pic- 
ture by  the  aid  of  light,  or  in  other  words,  to  take  a  photograph. 
Now  a  ray  of  ordinary  light  can  be  split  up  by  dispersion  into  a  series  of 
different  colors,  commencing  with  red  and  ending  in  violet,  the  latter  being 
the  most  refrangible,  the  former  least  so,  and  the  spectrum  so  obtained  also 
possesses  three  different  properties,  calorific,  illuminating  and  chemical. 
The  heating  effects  reside  chiefly  in  the  red  rays,  illuminating  in  the  yellow' 
whilst  the  violet  and  some  still  more  refrangible  or  ultra-violet  rays  consti- 
tute the  chemical  or  actinic  properties,  and  it  has  been  proved  that  the  de- 
composition of  silver  salts  by  light  is  almost  entirely  due  to  these  actinic 
rays.  Thus  we  are  enabled  to  do  all  our  work,  such  as  preparation  of  the 
plates,  development,  etc.,  with  impunity  in  a  deep  ruby  light,  which  has  no 
palpable  effect  on  the  most  rapid  gelatin.  But  it  will  now  also  be  appa- 
rent to  you  that  it  is  no  easy  matter  to  take  a  good  photograph  of,  say,  a 
fair  sitter,  possessing  lovely  blue  eyes  and  red  hair,  or  an  individual  fur- 
nished with  a  liberal  supply  of  yellow  freckles,  or  say,  a  painting  where  all 
the  varied  colors  of  the  spectrum  are  blended  together  in  one  harmonious 
whole;  but  for  work  of  this  sort  special  plates  are  prepared  called  "ortho- 
chromatic,"  in  which  the  sensitive  film  is  stained  with  some  aniline  dye;  an 
ammoniacal  solution  of  eosin  or  tetrabromfluorescein  has  been  found  to 
answer  extremely  well,  and  plates  prepared  with  it  are  the  subject  df  a 
patent. 
Any  object  which  reflects  yellow  or  red,  will  appear  almost  black  when 
reproduced  by  photography,  whilst  any  shade  of  blue  is  almost  equivalent 
to  white.  These  facts  must  be  borne  in  mind  when  calculating  the  time 
requisite  in  exposure. 
The  lenses  employed  must,  of  course,  be  rendered  achromatic.  This  is 
easily  effected  by  a  combination  of  flint  and  crown  glass,  but,  as  they  can 
not  be  entirely  freed  from  spherical  aberration,  we  are  obliged  to  use  dia- 
phragms to  cut  off  the  outer  rays,  in  order  to  obtain  pictures  sharp  and 
crisp  all  over. 
Cameras  are  made  in  a  variety  of  shapes  and  sizes.  With  regard  to  the 
latter  I  recommend  the  half-plate  size,  as  it  is  not  too  cumbersome  to  be- 
come a  nuisance  when  touring,  and  enlargements  can  be  easily  made  on  the 
"  bromide  "  paper  sold  for  the  purpose,  if  required.  The  shape  should  be 
square,  having  a  reversing  frame,  swing  back  and  rising  front.  The  first  is 
very  useful,  from  the  fact  that  we  can  take  a  photograph,  with  the  plate 
held  in  either  a  horizontal  or  vertical  position,  instead  of  having  to  alter  the 
position  of  the  camera  as  of  yore.  The  swing  back  is  brought  into  play, 
whenever  it  is  necessary  to  tilt  the  camera,  serving  to  keep  the  plate  as 
nearly  as  possible  in  a  perpendicular  plane,  whilst  the  rising  front  will  some- 
