GLEANINGS  FROM  THE  FRENCH  JOURNALS.  19 
M.  de  Letter  (see  this  Journal,  page  312,  1863),  which  has  in 
his  hands  produced  the  insoluble  modification  of  the  citrate  of 
magnesia.  The  author's  study  of  the  subject  has  satisfied  him 
that  citrate  of  magnesia  can  present  three  distinct  modifica- 
tions : 
1st.  Crystalline,  soluble  in  80  to  90  parts  of  water  (Ci.  3  MgO. 
+  14HO ; 
2d.  Amorphous,  soluble  in  two  parts  of  water  ; 
3d.  Metamorphous,  soluble  in  eight  or  ten  parts  of  water,  and 
having  a  very  great  tendency  to  assume  the  crystalline  con- 
dition. 
It  is  this  crystalline  modification  which  constitutes  the  in- 
soluble citrate,  and  which  presents  the  form  of  microscopic 
needles,  derived  from  a  right  rhomboidal  prism.  Its  production 
constitutes  an  embarrasment  which  ought  to  be  avoided,  since  it 
is  only  the  soluble  citrate  that  is  intended  to  be  used. 
M.  Hager  prepares  it  as  follows  : 
Forty  parts  of  citric  acid  of  commerce  is  reduced  to  powder, 
then  mixed  with  25  parts  of  carbonate  of  magnesia  of  the  shops, 
also  in  powder,  and  sufficient  alcohol  of  sp.  gr.  «833  is  added  to 
make  a  thick  mixture.  The  whole  is  allowed  to  stand  for  several 
hours  at  a  medium  temperature,  after  which  it  is  dried  in  a 
stove  or  in  a  water-bath  at  the  temperature  of  113°  F. 
The  dry  residue  is  the  product  sought.  It  is  soluble  in  two 
parts-and-a-half  of  water  at  60°  F.  by  standing  half  an  hour, 
but  at  a  temperature  of  86°  F.  it  dissolves  at  once. 
Whether  it  has  been  prepared  hot  or  cold,  with  little  or  much 
water,  the  solution  preserves  its  clearness  even  after  long  stand- 
ing. The  citrate  that  it  contains  is  neutral,  and  two  assays 
gave  12-7  and  13«1  eq.  of  water. 
To  obtain  the  soluble  citrate  without  doubt,  it  is  necessary 
that  the  carbonate  of  magnesia  employed  be  exempt  from  dust 
and  impurities  ;  and  further,  that  as  this  salt  [the  carbonate]  has 
not  always  the  same  composition,  it  is  safer  to  make  a  prelimi- 
nary assay  to  determine  the  proportions  of  acid  and  carbonate  to 
be  employed.  According  to  the  author,  25  of  carbonate  to  40 
of  acid  is  a  mean  proportion. 
The  metamorphous  salt  is  always  produced  by  the  process  of 
M.  Dorvault  [by  fusing  the  acid  with  a  little  water,  and  ad- 
