292  Ferric  Salts  and  Thiocyanates.       {Am  j^ne.'S""1* 
points  where  the  eerie  salt  has  not  been  reduced  by  the  light.  It 
then  suffices  to  eliminate,  by  washing,  the  excess  of  the  reagent  as 
well  as  the  cerous  salt  to  obtain  a  proof  distinctly  fixed  It  is 
important  that  the  coloring  substance  produced  should  be  insoluble, 
so  that  it  may  not  be  carried  away  by  washing. 
We  found,  on  considering  their  photographic  utilization,  and  on 
comparing  the  action  of  the  ferric,  cobaltic,  manganic  and  eerie  salts 
upon  a  great  number  of  substances  of  the  aromatic  series,  that  the 
eerie  salts  are  capable  of  yielding  colored  reactions  much  more 
numerous  than  the  salts  of  the  other  metals. 
Among  the  most  characteristic  reactions  we  may  mention  the  fol- 
lowing : 
In  an  acid  solution  the  proofs  are  gray  with  phenol,  green  with 
aniline  salts,  blue  with  naphthylamine  a,  brown  with  amido-benzoic 
acid,  red  with  parasulphanilic  acid,  green  with  the  salts  of  ortho- 
toluidine,  etc.  On  treatment  with  ammonia  the  color  changes,  it 
becomes,  for  instance,  violet  with  aniline,  red  with  methylamine,  etc. 
Photographic  papers  prepared  with  cerium  salts  possess  a  much 
greater  sensitiveness  than  that  of  the  preparations  with  ferric  or 
manganic  salts. —  Comptes  rendus,  cxvi,  p.  574  ;  Chem.  News,  April 
21,  1893,  P-  l88. 
REACTIONS  OF  FERRIC  SALTS  WITH  THIOCYANATES.1 
By  H.  M.  Vernon. 
In  these  investigations,  colorimetric  observations  were  adopted 
for  comparison,  and  were  made  in  vertical,  flat-bottomed  tubes,  by 
comparing  the  solution  to  be  tested  with  an  adjustable  column, 
either  of  a  o-i  per  cent,  solution  of  picrocarmine,  or,  in  some  cases, 
of  a  dilute  solution  of  ferric  thiocyanate,  prepared  from  lithium 
thiocyanate  and  excess  of  ferric  chloride.  Solutions  were  examined 
containing  1,  2,  4,  7,  1 1,  18,  30  and  100  equivalents  of  ferric  chloride 
to  1  part  of  potassium  thiocyanate,  and  diluted  to  various  degrees, 
ranging  from  2-  to  120-fold.  In  equivalent  quantities,  these  two 
reagents  react  almost  completely  at  infinite  concentration,  to  form 
ferric  thiocyanate;  but  solutions  less  dilute  than  those  mentioned 
above  were  too  deep  in  color,  whilst  solutions  containing  one  or 
two  equivalents  of  ferric  chloride,  when  diluted  above  40  times, 
1  Chem.  News,  66,  177-179,  191-193,  202-203,  214-215  ;  Jour.  Chem.  Soc., 
Abstr.,  1893,  i,  p.  122. 
