214  Anhydrous  Sodium  Sulphite.         { Am*M™ ri9ioarm' 
sulphite  in  a  condition  of  purity  representing  over  96  per  cent,  of 
the  theory,  it  would  seem  that  a  minimum  purity  requirement  of 
about  95  per  cent,  of  the  theory  would  certainly  not  be  unreasonable. 
In  this  connection  it  may  also  be  noted  that  while  the  primary 
reason  for  the  desirability  of  substituting  the  anhydrous  sodium 
sulphite  for  the  hydrated  variety  given  in  the  U.S. P.  is  the  great 
difference  in  their  stability  under  ordinary  conditions,  there  is  also 
TABLE  11 
Stability  < 
of  Anhydrous 
Sodium  Sulphite. 
(Kept  under  ordinary  conditions, 
in  glass-stoppered  bottles.) 
Length  of 
Amount  taken 
y  0"  Iodine 
mber  of 
time  kept 
for  analysis 
required 
Percentage 
imple 
(days) 
(gramme) 
(cc.) 
purity 
I 
I 
O.I260 
18.25 
9I-25 
I 
221 
0.I260 
18.OO 
90.00 
2 
I 
0.1260 
18.75 
93-75 
2 
221 
O.I26o 
18.60 
93.00 
3 
I 
0.I260 
19.20 
96.00 
3 
221 
0.1260 
18.85 
94-25 
4 
I 
O.I260 
I9.3O 
96.50 
4 
221 
O.I26o 
18.95 
94-75 
5 
I 
0.1260 
I9.3O 
96.50 
5 
221 
O.I260 
I9.O5 
95-25 
6 
I 
0.I260 
1945 
97-25 
6 
221 
O.I260 
I9.3O 
96.50 
7 
I 
O.I260 
I9.80 
99.00 
7 
221 
0.1260 
I9.60 
98.00 
an  economic  reason  favorable  to  such  change.  For,  inasmuch  as 
the  activity  or  value  of  the  sodium  sulphite  depends  entirely  on  the 
amount  of  available  S02  which  it  contains,  and  as  we  can  readily 
see  that  the  latter  would  constitute  a  proportionately  larger  amount 
in  the  anhydrous  salt  than  in  the  hydrated,  the  proposed  change 
would,  therefore,  result  in  considerable  saving  in  the  cost  of  trans- 
portation. Thus  a  pound  of  the  sodium  sulphite  of  the  U.S. P. 
(Na2S03.7H20) ,  even  when  absolutely  pure,  has  only  about  half 
