ON  A  PROCESS  FOR  OBTAINING  LITHOGRAPHS. 
1T3 
to  the  zinc.  With  large  quantities  the  acid  is  dissolved  in  as  little 
water  as  possible,  and  neutralized  with  carbonate  of  soda  ;  to 
this  solution  a  slight  excess  of  pure  sulphate  of  zinc  is  added, 
and  it  is  then  boiled  for  a  short  time  with  animal  charcoal,  and 
filtered  into  a  dilute  muriatic  acid,  by  which  the  hippuric  acid  is 
separated  in  colorless  crystals.  A  slight  excess  of  carbonate  of 
soda  is  not  injurious ;  on  the  contrary,  the  basic  carbonate  of 
zinc  holds  a  portion  of  the  coloring  matter,  and  consequently 
facilitates  the  decolorization. 
Hippurate  of  Zinc,  which  is  formed  on  the  addition  of  sulphate 
or  chloride  of  zinc  to  the  solution  of  a  hippurate,  or  by  the  boil- 
ing of  metallic  zinc  with  an  aqueous  solution  of  hippuric  acid, 
has  the  formula  C18  H8  NO5,  ZnO  +  5HO.  It  is  soluble  in 
53'1G  parts  of  water,  and  in  60-5  parts  of  alcohol  of  spec.  grav. 
0-82  at  the  temperature  of  63° -5  F.,  and  in  4  parts  of  boiling 
water.  In  boiling  alcohol  it  dissolves  still  more  readily.  Cold 
and  boiling  ether  scarcely  dissolve  it.  At  a  high  temperature  it 
melts,  and  like  free  hippuric  acid,  when  submitted  to  dry  dis- 
tillation, first  acquires  a  red,  and  afterwards  a  black  color ;  and 
lastly,  when  long  exposed  to  a  red  heat,  it  is  completely  decom- 
posed, giving  off  aromatic  vapors  of  nitrobenzole,  and  leaving 
ashes  of  oxide  of  zinc — Ohem.  Cfaz.,  Oct.  15,  1855,  from  Journ. 
fur  Prakt.  Chem.,  lxv.  p.  369. 
ON  A  PROCESS  FOR  OBTAINING  LITHOGRAPHS  BY  THE 
PHOTOGRAPH  PROCESS. 
By  Professor  Ramsey. 
Professor  Ramsey  described  a  process  by  which  Mr.  Robert 
MTherson,  of  Rome,  had  succeeded  in  obtaining  beautiful  photo- 
lithographs,  specimens  of  which  had  been  hungup  in  the  Photo- 
graph Exhibition  in  Buchanan  street.  The  steps  of  the  process 
are  as  follows  :  1.  Bitumen  is  dissolved  in  sulphuric  ether,  and 
the  solution  is  poured  on  an  ordinary  lithographic  stone.  The 
ether  quickly  evaporates,  and  leaves  a  thin  coating  of  bitumen 
spread  uniformly  over  the  stone.  This  coating  is  sensitive  to 
light,  a  discovery  made  originally  by  Mr.  Niepce,  of  Chalons. 
2.  A  negative  on  glass  or  waxed  paper,  is  applied  to  the  sensi- 
tive coating  of  bitumen,  and  exposed  to  the  full  rays  of  the  sun 
