450  Quinine,  Cinchonidine  and  Isomers.  {AmsiJtr,*Sarm' 
dride  is  formed  when  solutions  of  quinine  in  certain  indifferent 
solvents,  such  as  dilute  alcohol,  are  exposed  for  a  long  time  to  a 
temperature  of  300  C. ;  and  it  is  again  converted  into  ordinary 
quinine  when  subjected  to  the  continued  action  of  dilute  sulphuric 
acid.  When  the  anhydride  is  dissolved  with  moderately  warm 
dilute  sulphuric  acid  in  the  corresponding  molecular  proportions, 
only  ordinary  quinine  sulphate  crystallizes  on  concentrating  the 
solution,  so  that  there  is  in  that  case  a  rapid  conversion  of  the  one 
form  of  base  into  the  other. 
In  addition  to  the  former  statement  of  the  differences  between 
ordinary  quinine  and  the  crystalline  anhydride  Dr.  Hesse  adds  that, 
as  he  then  suggested,  they  are  to  be  regarded  as  isomeric  forms  of 
this  base,  and  in  order  to  distinguish  them  he  proposes  to  call  the 
higher  melting  base  homoquinine.  Although  this  name  has  already 
been  applied  by  Howard  and  Hodgkin  to  a  substance  that  after- 
wards proved  to  be  a  compound  of  quinine  with  another  base,  its 
appropriation  in  that  sense  has  now  been  done  away  with. 
The  relations  between  cinchonidine  and  homocinchonidine  are 
similar  to  those  obtaining  between  quinine  and  homoquinine.  The 
confusion  of  those  two  bases  that  is  still  met  with  in  chemical  litera- 
ture makes  a  brief  reference  to  the  history  of  both  substances  desir- 
able. In  1877,  Dr.  Hesse  showed  the  difference  between  these  bases 
by  the  behavior  of  their  neutral  sulphates,  but  assigned  to  homocin- 
chonidine the  formula  C19H22N20,  that  is  now  adopted,  and  to 
cinchonidine  the  old  formula  C20H24N2O,  expecting  that  his  further 
investigations  would  clear  up  this  point. 
Anticipating  that  result,  however,  Skraup  and  Vortmann  pub- 
lished a  paper  on  "  cinchonidine/'  in  which,  contrary  to  their  inten- 
tion, they  dealt  with  homocinchonidine  instead  of  cinchonidine,  and 
it  was  not  until  a  later  period  that  Skraup  recognized  the  identity  of 
homocinchonidine  with  the  base  to  which  Dr.  Hesse  had  given  that 
name.  The  fact  that  Skraup  and  Vortmann  were  working  with 
homocinchonidine,  and  not  as  they  thought  with  cinchonidine,  is 
shown  by  their  misinterpretation  of  a  statement  as  to  the  solubility 
of  homocinchonidine  in  ether  attributed  to  Koch  by  Skraup,  but 
which  was  never  made  by  Koch.  In  consequence  of  this  misunder- 
standing, Skraup  and  Vortmann  got  rid  of  the  cinchonidine,  and 
retained  the  homocinchonidine,  which  they  examined  and  described 
as  being  cinchonidine. 
