QUANTITATIVE  ESTIMATION  OF  TARTARIC  ACID.  33^ 
REDUCTION  OF  OXIDES  BY  HYDROGEN. 
M.  W.  Miiller  has  instituted  a  series  of  experiments  with  the 
view  to  determine  precisely  the  temperature  at  which  the  oxides 
of  metals  begin  to  be  reduced  by  hydrogen  gas.    He  has  ex- 
perimented with  oxides  of  various  metals  prepared  in  various 
ways,  and  also  determined  the  effect  of  other  gases,  nitrogen, 
and  aqueous  vapor,  upon  the  temperature  of  incipient  reduction™ 
Oxide  of  iron  prepared  by  cautiously  heating  metallic  iron  in 
contact  with  air  was  found  to  get  reduced  at  285°  C. ;  the  same 
oxide  prepared  from  nitrate  of  iron  was  reduced  at  286° ;  when 
rather  moist  hydrogen  was  applied  and  the  oxide  of  iron  pre- 
pared from  oxalate  of  the  protoxide,  the  temperature  of  reduc- 
tion was  found  to  be  278°.    Oxide  of  copper  prepared  from  the 
sulphate  of  that  metal  and  precipitated  by  caustic  soda,  and 
previously  heated  to  300°,  was  found  to  become  reduced  at 
135° ;  strongly  ignited  oxide  of  copper  became  reduced  at  142° 
on  an  average  of  five  experiments  ;  oxide  of  cobalt  becomes  re- 
duced at  about  332°  ;  oxide  of  zinc  could  not  be  reduced  at  a 
temperature  whereby  glass  became  fused ;  oxide  of  tin,  about 
174°  ;  oxide  of  lead,  at  from  310°  to  315°  ;  peroxide  of  mercury, 
230°  ;  oxide  of  silver,  at  between  73°  and  78°.    The  experi- 
ments have  been  extended  to  the  chlorides  and  sulphides  of 
some  metals.    Chloride  of  gold  does  not  appear  to  be  acted  upon 
below  200°,  but  at  a  higher  temperature  an  explosion  took  place. 
The  action  with  chloride  of  platinum  was  rather  strong  at  85°, 
and  rather  violent  at  165°  ;  reduction  of  the  metal  took  place. 
The  chlorides  of  silver  and  lead  are  not  reduced  below  the  boil- 
ing point  of  mercury,  but  requires  a  red  heat ;  sulphide  of  gold 
is  reduced  at  200°,  while  sulphide  of  platinum  is  reduced  at  the 
ordinary  temperature,  sulphuretted  hydrogen  gas  being  formed 
in  both  cases. — Lond.  Chem.  News,  April  9,  1869,  from  Poggen- 
dorff's  Annalen,  vol.  136,  part  i,  1869. 
QUANTITATIVE  ESTIMATION  OF  TARTARIC  ACID. 
Dr.  Martenson,  First  Assistant  in  the  Chemical  Laboratory 
of  the  Pharmaceutical  Institute  of  Dorpat,  Russia,  has  made 
a  series  of  experiments,  with  the  view  to  obtain  a  trustworthy 
