Am.  Jour.  Pharm. ) 
March,  1891.  / 
Paraldehyde. 
137 
the  '72  Adulteration  Act  for  selling  as  magnes.  cit.  an  article 
alleged  to  be  adulterated  with  sodse  carb.,  ac.  tart.,  sugar,  and  sodae 
sulph.  Again,  evidence  was  given  for  the  defence  to  the  effect  that 
the  substance  sold  was  what  is  known  and  sold  in  commerce  as 
magnes.  citrate.  Medical  evidence  was  also  given  to  the  effect  that 
when  a  medical  man  prescribed  magnes.  cit.  he  meant  the  article  as 
sold  by  defendant,  simply  an  effervescing  salt,  chiefly  for  the  tartrate 
of  soda  found  during  effervescence.  The  authorities  in  this 
case  also  dismissed  the  case.  Since  then  the  advance  made  in  the 
manufacture  of  effervescent  preparations  has  been  indeed  rapid,  and 
the  past  year  has  the  distinction  of  adding  to  the  official  list  four 
new  effervescent  salts,  three  of  them  granular.  (See  this  Journal, 
January,  pp.  14,  15.) 
THE  MELTING-POINT  OF  PARALDEHYDE. 
By  P.  W.  Squire. 
Paraldehyde,  like  oil  of  anise  and  many  other  liquids,  may  be 
cooled  without  agitation  to  a  temperature  far  below  its  real  freezing- 
point,  and  then  may  suddenly  set  into  a  solid  mass,  the  temperature 
at  the  same  time  rising  to  the  melting-point  of  the  crystals,  provid- 
ing that  the  reduction  of  temperature  has  not  been  carried  so  far 
that  the  heat  evolved  during  solidification  is  insufficient  to  raise  the 
mass  to  its  initial  melting-point.  If,  however,  the  liquid  be  stirred 
while  it  is  cooling,  or  a  paraldehyde  crystal  be  dropped  into  the 
liquid  while  just  at  its  crystallizing-point,  then  the  freezing-point  of 
the  liquid  and  the  melting-point  of  the  crystals  will  almost  coin- 
cide. 
The  melting-point  of  "  absolute  "  paraldehyde  does  not  seem  to 
have  been  determined  with  any  degree  of  certainty,  as  the  generally 
accepted  figure,  510  F.  (10-5°  C),  is  too  low.  The  melting-point 
of  the  crystals  obtainable  from  various  samples  appears  to  be  modi- 
fied by  the  presence  of  impurities  in  the  liquid  from  which  they  are 
crystallized.  Two  years  ago  the  best  commercial  sample  examined 
in  our  laboratory  began  to  crystallize  at  500  F.,  but  was  not  wholly 
solid  above  480,  this  latter  being  also  the  temperature  to  which  the 
thermometer  suddenly  rose  after  the  liquid  had  been  cooled  below 
its  freezing-point  and  then  stirred.  Several  other  samples  showed 
no  sign  of  solidification  above  440  F.,  and  obviously  contained  both 
aldehyde  and  acid.    We  find  now  that  paraldehyde  from  the  same 
