Am.  Jour.  Pharm. 
May,  1910. 
Anhydrous  Sodium  Sulphite. 
215 
the  amount  of  available  S02  which  is  available  in  an  equal  weight  of 
the  anhydrous  salt,  Na2S03 ;  or  perhaps  we  may  better  illustrate  this 
point  by  taking  the  actual  case  of  the  firm  referred  to  above,  from 
whom  samples  of  each  of  these  salts  were  obtained.  The  transpor- 
tation charges  for  equal  weights  of  these  salts  would  ordinarily  be 
equal  ;  although  the  amount  of  available  sulphite,  Na2S03,  in  the 
hydrated  salt  was  only  22.05  Per  cent,  of  its  weight  whereas  in  the 
anhydrous  salt  it  was  96.5  per  cent,  of  its  weight,  thus  making  the 
cost  of  transporting  the  sulphite  of  the  former  over  four  times 
its  corresponding  cost  in  the  latter  case.  Besides,  the  cost  of 
the  anhydrous  salt  was  less  than  twice  the  cost  of  an  equal  weight 
of  the  hydrated  salt,  although  on  the  basis  of  the  available  S02 
the  former  is  worth  double  the  price  of  the  latter,  even  if  both  were 
of  an  equal  degree  of  purity ;  thus  actually  making  the  anhydrous 
salt  a  cheaper  source  for  S02  than  the  corresponding  hydrated  salt, 
even  if  we  do  not  consider  the  difference  in  the  cost  of  transpor- 
tation ;  while  if  the  manufacture  of  the  anhydrous  salt  were  based  on 
the  principle  on  which  rests  the  method  of  Hartley  and  Barrett,^ 
namely,  that  crystallization  of  the  anhydrous  sulphite  is  obtainable 
by  boiling  its  aqueous  solution,  the  cost  of  the  anhydrous  salt 
could  probably  become  reduced  to  even  less  than  the  present  cost 
of  the  sodium  sulphite  of  the  U.S. P.  Finally,  the  anhydrous  sodium 
sulphite  has  also'  the  advantage  over  the  corresponding  hydrated  salt 
in  that  it  is  more  suitable  for  the  exact  weighing  of  prescribed 
amounts,  such  as  are  required  in  the  making  of  certain  preparations, 
or  for  yielding  previously  calculated  amounts  of  S02. 
Inasmuch,  however,  as  the  disadvantage  of  instability  applies  also 
to  the  acid  sodium  sulphite  or  bisulphite,  NaHS03,  which  is  included 
in  the  present  U.S. P. ;  and  perhaps  with  even  greater  force,  on 
account  of  its  apparently  higher  degree  of  instability,  as  was  indi- 
cated by  an  experiment  tried  in  this  laboratory,  and  as  is  also 
indicated  by  the  fact  that  the  U.S. P.  purity  requirement  for  this 
salt  is  only  90  per  cent,  against  94  per  cent,  in  the  case  of  the 
corresponding  normal  salt,  Na2S03.7H20 ;  it  appears  desirable, 
therefore,  to  avoid,  if  possible,  the  inclusion  of  the  acid  salt  in  the 
U.S. P.  as  a  substance  having  a  fixed  standard  of  purity.  In  fact, 
there  appears  no  sufficient  reason  why  the  acid  sodium  sulphite  might 
not  be  omitted  entirely  from  the  list  of  official  substances,  since  the 
8  Loc.  cit. 
