196 
ON  FERRI  SUBCARBONAS. 
To  these  solutions  alcohol  was  added  in  the  requisite  propor- 
tion, filtered  and  washed,  and  the  resulting  precipitates  or  in- 
soluble portions  determined  as  follows : 
Kesidue  of  specimen  dried  at  60°  F.      1  gr. 
«  «  "         160°  to  175°  F.      3  grs. 
«  "  "        water  bath,  5-7  grs. 
To  facilitate  a  comparison  of  the  results  of  these  experiments, 
a  table  of  the  solubilities  of  the  several  precipitates  is  appended, 
the  insoluble  residues  being  deducted  from  the  weight  used,  and 
the  result  calculated  into  percentages. 
SOLUBILITIES  OF  PRECIPITATES. 
Exp.  1st.         Exp.  2d.      Exp.  3d.       Exp.  4th. 
Dried  at  60°  F.    93  per  ct.  96  per  ct.  98  per  ct.  98  per  ct. 
160°  to  175°  F.  81  "  86  "  85  ;'  93  " 
water  bath,  79     "     80     "     81     "     87  " 
Experiment  5th.  As  in  all  the  above  experiments,  the  most 
soluble  specimen  of  subcarbonate,  by  treatment  with  muriatic 
acid,  still  deposited  a  small  proportion  of  insoluble  matter,  an- 
other lot  of  the  powder  was  made.  In  this  the  Pharmacopoeia 
directions  as  to  quantity  were  taken  :  2  oz.  of  sulphate  of  iron, 
and  2j  oz.  of  carbonate  of  soda,  dissolved  each  in  a  pint  of  boil- 
ing water.  The  solutions  were  mixed  at  a  temperature  of  200°  F. 
The  resulting  protocarbonate  of  iron  was  washed  thoroughly 
in  a  precipitating  vessel,  with  warm  water,  the  supernatant  liquid 
at  each  washing  being  drawn  off  by  means  of  a  syphon,  until  the 
washings  gave  no  precipitate  with  a  solution  of  nitrate  of  baryta. 
Washing  by  decantation  was  found  to  be  much  preferable  to 
washing  on  a  filter. 
A  portion  of  this  precipitate  was  wrapped  in  bibulous  paper 
and  dried  on  a  sand  bath,  the  temperature  carefully  kept  at 
80°  F. ;  another  quantity  at  the  same  temperature,  but  thinly 
spread  on  paper  uncovered,  so  as  to  expose  a  large  surface  to 
the  action  of  the  air;  and  still  another  portion  subjected  to  a 
sand  bath  heat  of  180°  to  190°  F. 
When  these  specimens  were  thoroughly  dried  and  pulverized, 
they  were  found  to  differ  materially  in  color.  The  low  temper- 
ature gave  the  precipitated  carbonate  a  light  chocolate  brown 
shad  e,  and  the  high  heat  produced  a  reddish-brown  approaching 
that  of  Spanish  brown  of  commerce,  both  differed  materially  from 
the  article  usually  found  in  the  shops. 
