552         NEW  PROPERTIES  AND  USES  OF  NAPHTHALIN. 
that  the  liquid,  in  quantities  of  one  to  two  pounds,  appears  to  be 
boiling.  The  absorbed  air  is  also  the  cause  of  the  open  spaces 
found  in  the  interior  of  the  sticks.  According  to  Yohl  the  air 
absorbed  by  naphthalin  is  considerably  richer  in  oxygen  than 
atmospheric  air  ;  i^erliai^B  it  is  pure  oxygen.  Melted  naphthalin 
readily  dissolves  substances  which  are  not  otherwise  easily  dis- 
solved. Yohl  discovered  that  indigo  is  dissolved  with  great  fa- 
cility, forming,  with  the  naphthalin,  a  dark  blue-violet  liquid, 
from  which  the  indigo,  in  cooling,  separates  and  forms  into  fine 
needles,  shining  like  copper.  The  amorphous  sulphides  of  ar- 
senic, tin  and  antimony  are  dissolved  readily,  and  separate  in 
cooling  into  crystalline  forms.  It  also  dissolves  phosphorus, 
sulphur,  iodine,  the  iodide  and  chloride  of  mercury,  arsenious, 
succinic,  benzoic,  and  oxalic  acids. 
The  sulphide  of  elayl,  of  Loewig  and  Weidman  (C*,  H^,  S^),  is 
taken  up  very  readily  by  melted  naphthalin,  which,  in  cooling, 
forms  small  grains,  proving,  under  the  microscope,  to  be  crystal- 
line masses. 
TRANSFORMATION  OF  NAPHTHALIN  INTO  BENZOIC  AND  BENZOL. 
The  first  step  in  the  preparation  of  benzoic  acid  from  naphtha- 
lin consists  in  the  conversion  of  the  latter  into  naphthalic  or 
phthalic  acid  by  the  method  of  Vohl ;  the  second  is  the  conver- 
sion of  phthalic  into  benzoic  acid. 
1.  Naphthalic  acid. — The  formula  of  naphthalin  being  C^^H^, 
that  of  naphthalic  acid  C^*^,  H^,  0*^ ;  the  operation  consists  in 
taking  C'^,  from  the  original  product  and  combining  0^  with 
it.  This  is  accomplished  by  dissolving  12  parts  of  pure  naptha- 
lin  ill  90  parts  of  concentrated  sulphuric  acid,  and  carefully  add- 
ing to  this  solution  80  parts  of  finel}^  pulverized  black  oxide  of 
mano-anese.  After  the  reaction  is  completed  the  product  is 
boiled  in  four  or  five  times  its  own  volume  of  water  until  the 
generation  of  carbonic  acid  has  almost  ceased  ;  then  the  liquid 
is  diluted  with  its  own  volume  of  water,  filtered,  and  evaporated 
by  steam  in  an  iron  boiler,  lined  on  the  inside  with  lead,  where- 
by sulphate  of  manganese  is  obtained  separately.  The  mother 
lye,  on  being  further  evaporated,  furnishes  the  naphthalic  acid. 
2.  Benzoic  Acid  from  Naphthalic  Acid, — This  process,  as 
