Am'jJunUer'i8P8h4arm*}        Sod  io- Bismuth  Citro-Pyroborate .  319 
experiment  showed  that  the  two  salts  unite  in  the  proportion  of  one 
m.  of  each.    This  indicates  a  secondary  double  salt  constituted  thus  : 
Bi  —  B407 
II  I 
Ci  —  Na2 
That  is  a  sodio-bismuth  citropyroborate.  It  is  a  remarkable  point  in 
the  formation  of  this  salt  that  the  chemically  and  optically  neutral 
bismuth  citrate  in  combining  with  the  chemically  neutral  but  optically 
alkaline  sodium  pyroborate  produces  a  chemically  neutral  but  optically 
decidedly  acid  compound.  This  is  a  colorless  amorphous,  very  soluble 
non-deliquescent  salt.  It  is  insoluble  in  alcohol  but  miscible  with 
water  in  all  large  proportions  without  decomposition.  It  has  a  faint 
saline,  slightly  metallic  but  not  unpleasant  taste.  The  solution  of  this 
salt  is  not  disturbed  by  the  presence  of  neutral  chlorides.  Most  acids 
excepting  boric  acid  decompose  it  at  once  and  precipitate  a  bulky  and 
gelatinous  compound  of  bismuth  and  boric  acid.  This  precipitate  is 
insoluble  in  a  moderate  excess  of  acid  but  dissolves  readily  in  a  solu- 
tion of  borax.  In  the*  presence  of  excess  of  borax  no  precipitate  is 
formed  by  the  usual  acids  unless  these  predominate ;  citric  acid,  how- 
ever, causes  a  separation  of  crystalline  bismuth  citrate. 
When  the  solution  of  the  salt  is  evaporated  to  a  thin  syrupy  con- 
sistence it  becomes  slightly  turbid  on  cooling  and  deposits  a  large 
amount  of  colorless  crystals.  On  spontaneous  evaporation  the  remain- 
ing solution  yields  a  considerable  quantity  of  small  white  crystal.  By 
adding  water  to  the  whole  residue  the  colorless  crystals  rapidly  disin- 
tegrate and  an  augmentation  of  the  white  crystals  occurs.  The  appli- 
cation of  heat  in  the  presence  of  this  small  quantity  of  water  does  not 
reproduce  the  clear  solution.  But  the  addition  of  water  in  about  five 
times  the  weight  of  the  residue  and  subsequent  heating  promptly  eifects 
a  clear  solution  by  a  reconstitution  of  the  original  salt.  When,  how- 
ever, the  solution  of  the  salt  is  evaporated  at  a  uniform  temperature  to 
a  dense  syrupy  consistence  an  amorphous  beautiful  scaled  residue 
remains  which  resembles  in  appearance  the  official  ammonia-citrate  of 
bismuth.  A  small  quantity  of  water  again  decomposes  it  into  its 
primary  factors,  the  bismuth  citrate  and  sodium  pyroborate.  The 
former  appears  as  white,  insoluble  crystals,  whilst  the  latter  is  readily 
recognized  by  its  taste.  It  appears  therefore  that  the  new  salt  is  a 
scaled  amorphous  compound  which  is  permanent  in  the  absence  of 
water  and  equally  permanent  in  any  large  proportion  of  water,  but  is 
