348 
PREPARATION  OF  MOLYBDATE  OP  AMMONIA. 
TO  PREVENT  CONCUSSIONS  ON  BOILING  IN  GLASS  VESSELS. 
By  Dr.  G.  C.  "Wittstein. 
On  heating  clear  liquids  in  glass  vessels,  it  frequently  occurs 
that  they  for  a  long  time  do  not  come  to  boiling,  and  sometimes, 
all  at  once,  boil  up,  foaming,  with  violent  concussions.  This 
occurs  more  frequently  with  alcoholic  and  ethereal  solutions,  and 
may  be  explained  by  an  over-heating  of  the  liquid,  caused  by  an 
even  distribution  and  consequent  accumulation  of  heat.  It  is  ne- 
cessary, therefore,  to  counteract  this  tendency  by  causing  a  more 
rapid  current  of  the  heat  towards  the  surface.  Such  a  current  is 
caused  by  the  presence  of  a  projecting  solid  body  on  the  bottom 
of  the  vessel,  such  as  a  grain  of  sand,  a  piece  of  glass,  quartz,  or 
platinum.  But  thus  the  purpose  is  only  partly  accomplished ;  the 
current  commencing  on  the  lowest  point  of  the  body,  is  lost  from 
the  upper  point  in  the  liquid  above,  particularly  if  its  height  be 
considerable,  and  the  same  phenomenon  of  concussions  may  oc- 
cur, though  generally  with  much  less  violence. 
All  inconveniences  will  be  entirely  obviated,  if  proper  care  is 
taken  to  conduct  the  heat  from  the  bottom  to  the  surface  ;  a 
glass  rod  will  answer  for  this  purpose  ;  but  for  liquids  of  a  high 
boiling  point,  such  as  sulphuric  acid,  a  better  conductor  is  to  be 
chosen,  and  a  platina  wire  of  the  thickness  of  a  knitting  needle 
is  the  most  proper  one.  Since  I  have  distilled  alcoholic,  ethereal, 
aqueous,  &c,  liquids,  with  a  glass  rod  of  the  proper  length  in- 
troduced, all  danger  of  foaming  and  concussions  have  been  obviat- 
ed; the  contents  of  the  retort  rapidly  come  to  the  boiling  point 
and  continue  to  boil  quietly  Wittstein  s  Viert.  Schr.  viii.  104 
J.  M.  M. 
PREPARATION  OF  MOLYBDATE  OF  AMMONIA. 
By  C.  Brunner. 
Since  the  employment  of  this  salt  for  the  detection  of  phos- 
phoric acid  has  become  indispensable  in  chemical  analyses,  seve- 
ral methods  have  been  recommended  for  its  preparation.  Most 
of  these  start  from  the  roasting  of  native  sulphuret  of  molybde- 
num in  contact  with  the  air,  until  all  the  sulphur  is  burnt  away 
