Am.  Jour.  Pharm.  1 
October,  1900.  J 
Seidlitz  Powders. 
465 
ings.  As  the  weight  is  of  importance,  whether  the  ingredients  are 
pure  or  not,  the  weights  of  two  powders  of  each  druggist  are  given, 
followed  by  the  results  of  tests  of  identity  and  of  purity,  and, 
finally,  the  proportions  of  the  ingredients  found  by  quantitative 
examination. 
When  the  powders  obtained  came  to  be  examined  quantitatively, 
an  unexpected  difficulty  presented  itself.  When  the  percentages  of 
the  two  ingredients  obtained  by  titration  in  the  described  methods 
were  added  together,  instead  of  the  result  being  about  IOO 
they  all  were  considerably  above  that.  No.  I,  for  example,  gave 
31*44  per  cent,  of  sodium  bicarbonate  and  85-86  per  cent,  of 
rochelle  salt,  which,  added  together,  make  117-3  per  cent.  There 
is  only  one  way  in  which  it  can  reasonably  be  explained,  that  is,  by 
the  loss  of  moisture.  In  making  the  first  experiments  the  ingre- 
dients were  freshly  taken  from  tight  containers,  so  that  they  had  not 
the  chance  to  lose  moisture.  The  seidlitz  powders,  on  the  other 
hand,  contained  in  paper,  a  condition  highly  favorable  to  loss  of 
moisture,  and  probably  made  some  time  before  they  were  obtained, 
were  kept  for  some  time  in  a  rather  hot  room  before  they  were 
examined.  Rochelle  salt  is  described  by  the  Pharmacopoeia  as 
being  somewhat  efflorescent,  and  the  results  obtained  proved  that 
sodium  bicarbonate  also  loses  considerable  weight  under  the  de- 
scribed conditions.  It  is  obvious,  then,  that  some  change  in  the 
foregoing  calculation  would  have  to  be  made. 
Thus,  No.  1,  as  before  mentioned,  gave  31*44  per  cent,  of  sodium 
bicarbonate  and  85*86  per  cent,  of  rochelle  salt,  the  total  being 
117*3  per  cent.;  then  117-3  :  31'44  '•  100  :  26*805,  anc*  in  the  same 
way  for  the  rochelle  salt,  117*3  :  85-86  :  :  100  :  73*  I. 
All  that  is  necessary  with  regard  to  the  directions  for  quantita- 
tive analysis  would  be  to  make  the  above  calculations  in  case  the 
results  of  the  analysis,  give  over  100  per  cent. 
This,  however,  still  leaves  something  to  be  desired.  It  only 
shows  the  relative  proportions  of  pure  bicarbonate  of  soda  and 
pure  rochelle  salt  in  the  mixture.  It  does  not  show  the  absolute 
amount  of  pure  materials  in  100  parts  of  the  mixture;  in  other 
words,  the  two  percentages  will  be  always  100.  If  sodium  bicar- 
bonate which  contained  normal  carbonate  had  been  originally  used 
in  making  the  seidlitz  mixture,  it  would  not  enable  the  amount  of 
that  impurity  to  be  calculated.    It  would  be  calculated  into  bicar- 
