176 
ACTION  OF  ALKALIES,  ETC. 
copoeia  (although  a  process  of  percolation  is  attempted  in  that 
case ;)  and,  I  may  add,  that  this  latter  quality,  if  not  actually 
adopted  at  Mr.  Squire's  .suggestion,  does  at  least  coincide  with 
his  practical  experience,  that  cinchona  baric  cannot  be  adequately 
exhausted  with  less  than  twelve  times  its  weight  of  water. — Lon- 
don Pharm.  Journ.,  October,  1866. 
ACTION  OF  ALKALIES  UPON  THE  FERRO-  AND  FERRI- 
CYANIDES  OF  IRON. 
.  By  William  Skey. 
Analyst  to  the  Geological  Survey,  New  Zealand. 
It  is  generally  set  forth  in  those  chemical  works  which  treat 
upon  these  substances  that  "  their  color  is  instantly  destroyed 
by  alkalies,"  but  from  the  results  of  a  few  experiments  made 
upon  them,  it  appears  this  statement  requires  some  qualifica- 
tion. 
Thus,  if  either  of  these  compounds  is  treated  with  a  very  weak 
solution  of  caustic  or  carbonated  alkali,  the  color  thereof  receives 
such  an  accession  in  its  intensity  as  to  rival  the  color  of  indigo 
blue. 
If  a  solution  of  "  Turnbull's  blue  "  is  employed,  the  change 
of  color  is  very  marked,  while  the  solution  keeps  as  clear  as  be- 
fore. If  used  for  writing  purposes,  it  gives  an  intense  blackish- 
blue  ink  on  drying,  and  which  is  of  some  permanency  ;  the  addi- 
tion of  a  certain  quantity  of  ferricyanide  of  potassium  affords  a 
bright  green  ink. 
Like  the  aqueous  solution  of  basic  Prussian  blue,  these  com- 
pounds are  precipitated  from  their  solution  by  the  addition  of 
alcohol  or  soluble  salts,  especially  if  these  have  strong  affinity 
for  water. 
It  appears  that  the  change  in  the  intensity  of  the  color  is 
caused  by  the  abstraction  of  a  portion  of  the  ferro-  or  ferri-cyanic 
acid,  for  if  these  compounds  are  repeatedly  washed  with  water 
until  nothing  more  is  dissolved  from  them,  the  addition  of  the 
alkali  in  quantity  only  sufficient  to  produce  these  changes,  im- 
mediately brings  either  of  these  acids  into  solution. 
A  great  excess  of  carbonate  of  ammonia,  by  virtue  of  the 
