Am.  Jour.  Pharm.  \ 
January,  19 18. 
Current  Literature. 
49 
Solubility  of  Calcium  Carbonate  in  Boiling  Water. — Vari- 
ous statements  have  been  published  of  the  solubility  of  calcium  car- 
bonate in  water  at  ioo°  C,  as,  for  example,  o.iii  Gm.  (Fresenius), 
0.143  Gm.  (Pollacci),  0.034  Gm.  (Hofmann),  and  0.036  Gm. 
(Weltzien)  per  liter.  The  author's  experiments  show  that  this 
discrepancy  is  due  to  the  fact  that  calcium  carbonate  is  slowly  dis- 
sociated by  boiling  water,  with  the  loss  of  carbon  dioxide.  For  this 
reason  it  is  not  possible  to  obtain  a  solution  containing  only  calcium 
carbonate  in  boiling  water.  This  dissocation  does  not  continue 
indefinitely,  and  may  be  checked  by  adding  to  the  boiling  water  in 
which  the  calcium  carbonate  is  suspended  about  15  Cc.  of  a  solu- 
tion of  lime  (saturated  at  the  ordinary  temperature).  The  sub- 
stance found  in  the  solution  after  long-continued  boiling  of  calcium 
carbonate  with  water  consists  almost  entirely  of  free  lime.  Apart 
from  the  duration  of  boiling,  other  factors  which  have  an  influence 
upon  the  proportion  of  free  lime  which  dissolves  are  the  volume 
of  the  liquid  and  the  concentration  of  the  solution.  The  addition 
of  a  small  quantity  of  sodium  carbonate  prevents  the  dissociation 
and  the  solution  of  calcium  carbonate  in  boiling  water.  Advantage 
may  be  taken  of  this  in  estimating  calcium  in  the  form  of  carbonate. 
The  precipitate  is  washed  with  boiling  water  containing  0.05  Gm. 
of  anhydrous  sodium  carbonate  per  liter.  It  is  then  treated  with 
standard  hydrochloric  acid  until  completely  dissolved,  and  the  excess 
of  acid  titrated  with  standard  sodium  hydroxide  solution,  with 
methyl  orange  as  indicator.  The  error  due  to  the  sodium  carbonate 
solution  retained  by  the  precipitate  (about  2  Cc.)  is  negligible. 
Calcium  carbonate  produced  by  chemical  reactions  in  aqueous  solu- 
tions at  low  temperatures  forms  supersaturated  solutions,  the 
stability  of  which  depends  mainly  upon  the  concentration  and  the 
temperature.  (A.  Cavazzi,  Gazz.  Chim.  Ital.,  1917,  47,  49-63.  Re- 
printed from  The  Analyst.) 
Pure  Bismuth. — The  determination  of  minute  traces  of  impur- 
ity in  bismuth  is  difficult,  since  the  basic  salts  form  amorphous  precip- 
itates which  obstinately  retain  other  metals,  as  also  do  the  sulphide 
and  oxide.  The  electrolytic  method  of  separation  also  fails.  The 
best  means  of  obtaining  the  pure  metal  is  by  crystallizing  the  normal 
nitrate  from  strong  nitric  acid.  Fairly  pure  bismuth  nitrate  is  dis- 
solved in  half  its  weight  of  8  per  cent,  nitric  acid,  and  the  solution 
