^'"seprisss'''"'""}        Sodio-Bismuth  Tartrate  and  Pepsin.  423 
now  gradually  neutralizing  the  excess  of  nitric  acid  by  means  of  sodium 
or  potassium  bicarbonate  a  seemingly  crystalline  normal  bismuth  tar- 
trate precipitates.  After  about  three-fourths  of  the  nitric  acid  present 
has  been  neutralize.!  all  the  bismuth  will  be  converted  into  tartrate 
and  thrown  out  of  solution. 
The  writer  deems  this  precipitate  a  normal  salt,  but  has  not  deter- 
mined its  composition,  and  hence  cannot  state  whether  it  is  a  hydrite 
or  not.  Its  provisional  formula  may  with  great  probability  be  indi- 
<;ated  as  Bi^T^.  x  Aq. 
Different  from  the  citrate,  the  tartrate  enters  into  permanent  and 
definite  chemical  union  with  normal  monad  tartrates,  but  in  addition 
also  forms  basic  or  hydro- tartrates.  The  writer  ascertained  that  the 
tartrate  formed  from  a  definite  amount  of  bismuthyl  nitrate,  dissolved 
in  a  definite  amount  of  normal  sodium  tartrate.  The  proportions 
were  such  that  the  salts  reacted,  molecule  for  molecule,  as  expressed  by 
the  following  equation : 
Bi=T 
I 
T    +  Na^T  =  2  (T^Bi— T— Na). 
Bi=T 
This  double  salt  has  a  decided  acid  reaction.  On  evaporating  its 
solution  it  is  obtained  in  colorless  transparent,  non-deliquescent  and 
readily  soluble  scales.  Its  composition  as  to  water  was  not  determined. 
A  small  proportion  of  tartaric  acid  has  no  effect  upon  this  double  salt, 
but  a  large  amount  appears  to  decompose  it.  When,  however,  an 
excess  of  normal  citrate  is  present,  tartaric  acid  may  be  added  to  any 
extent  without  effect.  A  new  acid  double  tartrate  evidently  forms 
under  these  conditions,  as  follows: 
BiT^ISTa+NaHT  =  Na— T— Bi— T— Na 
I 
T— H. 
If  a  solution  of  the  normal  double  tartrate  is  added  to  a  neutralized 
solution  of  pepsin,  a  voluminous  precipitate  appears  in  gelatinous 
flakes.  On  the  addition  of  sodium  bicarbonate,  this  precipitate 
promptly  redissolves,  leaving  a  solution  which  still  retains  a  decided 
acid  reaction.  It  is  also  a  remarkable  fact  that  the  addition  of  tar- 
taric acid  does  not  now  cause  a  reappearance  of  the  precipitate. 
These  results  and  the  subsequent  products  obtained  by  them  show 
