3  9 6  Salicylic  Acid  and  Albuminoids.       { AmxJu°gu; \^m' 
to  make  a  more  accurate  investigation  of  salicylic  acid,  and  he  gives 
the  following  account  of  it.  It  crystallizes  from  concentrated  solu- 
tions in  slender,  almost  colorless  needles,  from  dilute  solutions  in 
larger  prismatic,  very  hard  crystals,  often  very  prettily  grouped.  If, 
however,  other  bodies  are  present  in  the  solution,  and  more  especially 
if  they  are  organic  bodies,  regular  crystals  are  not  formed,  but,  accord- 
ing to  the  nature  and  quantity  of  the  admixed  body,  either  crescent- 
shaped,  annular  or  tufted  forms  which  scarcely  resemble  crystals,  are 
obtained. 
When  the  foreign  body  is  removed  the  acid  gradually  regains  the 
capability  of  forming  acicular  crystals.  Freezing  the  solution  also 
brings  about  the  change.  The  acid  melts  at  157*5°,  and  sublimes  at 
200°,  but  even  at  8o°  a  considerable  quantity  volatilizes.  Perfectly 
pure  crystals  may  be  obtained  by  heating  a  solid  body  containing  the 
acid,  or  a  solution  of  the  acid  at  this  temperature  in  the  air-  or  water- 
bath.  The  acid,  as  is  well  known,  splits  up  on  boiling  into  carbon- 
dioxide  and  phenyl-alcohol ;  but.it  is  quite  sufficient  to  heat  the  solu- 
tion of  the  acid  or  certain  salts,  especially  in  presence  of  other  acids, 
for  a  long  time  on  the  water-bath,  to  bring  about  this  change.  Hydrated 
sulphuric  acid  decomposes  salicylic  acid  only  when  it  is  added  all  at 
once  to  the  solid  acid  or  its  solution. 
Permanganate  of  potassium,  especially  in  presence  of  sulphuric  acid, 
oxydizes  salicylic  acid,  and  among  other  products  of  the  decomposition 
are  found  formic  and  carbonic  acids  and  water.  A  similar  decompo- 
sition is  effected  by  boiling  the  acid  with  potassium  bichromate  and  sul- 
phuric acid.  If  the  solution  of  the  acid  is  heated  with  the  bichromate 
without  addition  of  sulphuric  acid,  a  body  passes  over  with  the  steam 
which  has  an  unpleasant  odor  ;  it  has  not  been  examined.  When 
salicylic  acid  is  brought  into  contact  with  ferric  acetate,  it  combines 
with  the  iron,  the  liquid  becomes  of  a  violet  color,  and  deposits  a  dirty 
violet  precipitate  of  Fe2H204. 
This  hydrate  dissolves  in  water  and  forms  a  golden-yellow  liquid, 
which  can  be  concentrated,  but  is  decomposed  by  contact  with  acids, 
bases,  salts,  alcohol,  erher,  and  even  filter  paper,  and  rendered  insoluble. 
If,  however,  the  solution  of  the  ferric  salt  is  tolerably  concentrated, 
and  especially  if  the  mixed  solution  is  not  too  acid,  a  brown  salicylate 
separates  out.    The  acid  behaves  in  a  similar  way  to  lead  acetate  ;  lead 
