236        Photographic  Development  by  Gas  Light.  {AmMa^Joi.arm' 
degree.  Any  professional  or  thoughtful  amateur  photographer 
will  see  the  application. 
In  the  experiments  which  were  carried  out  the  aperture  was  set 
at  eight,  the  lens  used  was  B.  and  L.'s  double  rapid  rectilinear  lens. 
All  exposures  made  were  in  bright  sunlight,  with  rapid  plates. 
After  exposure  the  plate  is  taken  into  a  room  free  from  day- 
light and  is  developed  about  8  inches  below  the  mantel  of  a  Wels- 
bach  light  or  between  two  other  strong  lights,  whether  electric,  oil 
or  acetylene.  The  developer  should  be  kept  ice  cold  to  obtain  the 
best  results.  In  transferring  the  plates  from  the  holder  to  the 
developing  tray  it  is  advisable  to  remove  them  in  the  shadow  or 
better  underneath  the  developing  table  and  quickly  transfer  them  to 
the  developer  in  the  tray. 
The  plate  before  entering  the  developer  is  of  a  yellowish  color, 
and  if  exposed  sufficiently  shows  very  faint  outlines  of  the  object 
photographed.  This  image  disappears  upon  entering  the  developer 
and  then  reappears  as  a  reddish-brown  image,  gradually  turning  to 
the  normal  grayish-black  color  of  the  ordinary  negative.  These 
positives  can  be  reduced  in  the  ordinary  way  with  potassium  ferri- 
cyanide  and  hyposulphite  of  soda. 
A  set  of  exposures  was  made  as  follows  : 
1  3^  second.    Normal  exposure  for  negative. 
2  1  minute. 
3  3  minutes. 
4  4  minutes. 
5  30  minutes. 
6  60  minutes,  180,000  times  normal  exposure  for  negative. 
The  above  were  developed  with  the  following  formula  : 
SOLUTION  NO.  I. 
Ounces.  Grammes. 
Water  25  1,000 
Hydrochinone  .  .  <  3  126 
Sodium  sulphite  cryst  x/2  21 
SOLUTION  no.  2. 
Water  *  *  25  1,000 
Sodium  carbonate  cryst  6  252 
Mix  the  two  solutions  in  equal  parts,  dilute  with  three  to  five 
times  its  bulk  of  water.  If  a  few  drops  of  a  10  per  cent,  solution 
of  potassium  bromide  be  added  it  will  give  brilliancy  to  the  plate 
but  will  not  assist  in  improving  detail. 
