6o 
Arsenic  Antidote. 
f  Am.  Jour.  Phann. 
(  February,  1915. 
If  the  intent  of  the  U.  S.  Pharmacopoeia  (VIII)  was  to  indicate  the 
chemical  composition  of  the  preparation,  the  title  should  have  been 
made  "  Ferri  Hydroxidum  Cum  Magnesii  Oxido  et  Magnesii  Sul- 
phate." By  the  time  a  physician  finishes  writing  a  prescription  for  a 
preparation  with  a  title  like  this,  the  patient  may  be  dead ! 
Officially,  the  preparation  is  made  by  adding  a  mixture  of  mag- 
nesium oxide  (light  calcined  magnesia)  and  water  (which  becomes 
magnesium  hydroxide)  to  a  diluted  solution  o'f  ferric  sulphate,  and 
shaking  them  together  until  a  uniformly  smooth  mixture  results. 
In  making  the  preparation,  the  ferric  sulphate  and  magnesium 
hydroxide  are  decomposed  into  ferric  hydroxide  and  magnesium  sul- 
phate, an  excess  of  magnesium  hydroxide  being  employed,  which 
latter  is  partially  neutralized  by  the  free  acid  of  the  ferric  sulphate 
solution. 
The  reaction  is: 
Fe2(S04)3  +  3Mg(OH)2  =  2Fe(OH)8  +  3MgS04 
397-05  173.82  212.28  358.59 
The  chemical  reaction  that  takes  place  when  ferric  hydroxide 
comes  into  contact  with  arsenic  trioxide  or  arsenous  anhydride  is  a 
peculiar  one.  According  to  Attfield,  the  arsenous  compound  is 
oxidized,  while  the  ferric  compound  is  reduced — insoluble  ferrous 
arsenate  and  ferrous  hydrate  being  formed. 
The  reaction  is : 
4Fe(OH)3  +  As203  =  Fe3(AsOJ2  +  Fe(OH)2  +  5H20 
424.56        196.44        442.34  89.26  89.40 
In  the  official  process  for  making  "  Ferric  Hydroxide  with  Mag- 
nesium Oxide  "  there  is  used  solution  of  ferric  sulphate,  40  Cc. ;  mag- 
nesium oxide,  10  Gms. ;  water,  a  sufficient  quantity.  Mix  the  solu- 
tion of  ferric  sulphate  with  125  Cc.  of  water  and  keep  the  liquid 
in  a  well-stoppered  bottle.  Rub  the  magnesium  oxide  with  ccld 
water  to  a  smooth  and  thin  mixture,  transfer  this  to  a  bottle  capable 
of  holding  about  1000  Cc,  and  fill  it  with  water  to  about  three- 
fourths  of  its  capacity.  When  the  preparation  is  wanted  for  use, 
shake  the  magnesium  oxide  mixture  to  a  homogeneous,  thin  magma, 
add  it  gradually  to  the  diluted  ferric  sulphate  solution,  and  shake 
them  until  a  uniformly  smooth  mixture  results.  The  diluted  solution 
of  ferric  sulphate  and  the  mixture  of  magnesium  oxide  with  water 
are  directed  to  be  always  kept  on  hand  ready  for  immediate  use. 
