AmDecUrimarm'}    Some  Sodium  and  Manganese  Compounds.  619 
three  or  four  hours,  and  ultimately  run  into  lead-lined  wooden  tanks. 
Crystals  of  a  light  yellow  color  quickly  make  their  appearance,  which 
are  deprived  of  their  adherent  moisture  in  the  customary  manner.  The 
mother  liquor,  in  conjunction  with  other  liquors,  is  again  boiled  down 
to  crystallization.  In  this  way  crystals  are  obtained  of  the  following 
percentage  : — 
NaN02 
Per  cent. 
1st  crystallization  95*5  to  95*5 
2d  crystallization  94*8  to  95'5 
3d  crystallization  -..  94'2  to  94'5 
4th  crystallization  94'0  to  94'2 
By  drying  at  60°  C.  their  percentage  is  increased  to  96  per  cent. 
If  a  purer  product  be  required,  it  must  be  recrystallized.  Some  diffi- 
culty is  experienced  in  working  up  the  mother  liquors.  If  crystals  of 
only  94  per  cent,  of  NaNC>2,  or  below  that  strength,  be  obtained,  the 
mother  liquors  must  be  concentrated  by  themselves  in  pan  No.  2. 
Here  crystals  containing  86  to  92  per  cent,  of  NaN02  are  produced, 
which  are  employed  for  enriching  the  strength  of  fresh  liquors.  If 
the  crystals  from  pan  No.  2  sink  below  80  per  cent,  their  mother 
liquors  must  be  concentrated  separately  in  pan  No.  3,  whereby  crys- 
tals containing  50  to  75  per  cent,  of  NaN02  are  obtained.  These 
serve  for  enriching  the  liquors  in  pan  No.  2.  Weaker  crystals  are 
returned  to  the  melting  pot  and  treated  with  lead.  Nevertheless,  it  is 
sometimes  difficult  to  avoid  the  formation  of  salts,  which  require  a 
special  treatment  in  every  case. 
The  lead  oxide,  obtained  as  a  by-product,  is  washed,  and  afterwards 
converted  into  the  different  lead  preparations  of  commerce,  or  reduced 
to  metallic  lead,  when  it  returns  to  the  process. 
ACTION  OF  AIR  ON  MANGANESE  CARBONATE. 
At  the  ordinary  temperature  carbonate  of  manganese,  whether 
native,  precipitated,  or  crystallized  from  solution  in  carbonic  acid 
water,  is  oxidized  with  difficulty  whether  exposed  to  air  or  to  aerated 
water.  In  the  most  favorable  case — the  precipitated  carbonate  kept 
for  ten  years  in  aerated  water — the  proportion  of  oxygen  combined 
was  only  that  required  to  form  Mn02MnO.  The  same  compound, 
produced  by  directly  combining  an  equivalent  of  hydrated  manganese 
dioxide  with  one  of  hydrated  manganese  monoxide,  does  not  absorb 
any  additional  oxygen,  even  after  five  months'  exposure  to  air  or 
water.    Manganite,  MnQ2MnO,  is  then  the  limit  of  oxidation  at  the 
