78 
Seidlitz  Powders. 
/Am.  Jour.  Pharm. 
X    February,  1902. 
exact  amount  required  by  the  Rochelle  salt.  This  may  be  cal- 
culated directly  from  the  C02  in  the  previous  determination,  but 
it  must  be  remembered  that  one-half  of  the  C02  from  the  bicar- 
bonate has  been  driven  off  during  its  conversion  into  bicarbonate  by 
ignition.  Therefore,  one-half  of  the  C02  yielded  by  the  bicarbonate 
must  be  used  for  determining  the  sulphuric  acid  required  for  the 
carbonate  yielded  from  it. 
This  is  shown  by  the  following  reactions : 
2NaHC03  +  heat  =  Na2C03  +  H20  +  C02 
2NaHC03  +  H2S04  =  Na2S04  +  H20  +  C02 
Na2C03  +  H2S04  =  Na2S04  +  H20  +  C02 
The  calculation  would  be  thus : 
(#•225)  -5-  -004184  =  26-8  c.c.  H2S04V.S. 
Then  74*75  c.c.  required  for  the  entire  carbonates  less  26-8  c.c. 
required  for  the  carbonate  from  the  bicarbonate,  leaves  47  95  c.c- 
required  for  the  Rochelle  salt. 
The  Rochelle  salt  is  then  ascertained  thus : 
47-95  X  '2684  =  1-28697  grammes  Rochelle  salt  found. 
Then, 
1*722  :  1-28697  :  :  100  :  74'73l  Per  cent.  Rochelle  salt. 
The  six  samples  were  all  examined  and  analyzed  by  the  methods 
just  described,  with  the  results  shown  in  the  following  table.  The 
U.S.P.  weights  and  theoretical  per  cent,  are  also  given  to  enable 
comparison : 
SEIDLITZ  MIXTURE. 
No. 
Weights  in 
Grammes. 
Results  of  Qualitative  Tests. 
Per  Cent. 
Sodium 
Bicarbonate. 
Per  Cent. 
Rochelle 
Salt. 
1 
10*676 
Trace  of  sulphates. 
24-962 
74731 
2 
10-323 
Traces  of  iron. 
30-73I 
68-818 
3 
10*948 
Traces  of  sulphates  and  chlorides. 
29-622 
66-792 
4 
10-043 
Traces  of  calcium  and  sulphates. 
23-963 
75-838 
5 
10-384 
Traces  of  chlorides. 
25*073 
71-702 
6 
10-279 
Traces  of  calcium  and  chlorides. 
25-296 
74-196 
U.S.P. 
io-333 
25-000 
75-000 
