404  Assay  of  US.P.  Halogen  Compounds.  {%S^tSS' 
is  based  on  measuring  the  volume  of  chloroform  produced.  Accord- 
ing to  Holland,5  chloral  is  estimated  by  adding  a  measured  amount 
of  N  NaOH  to  render  the  solution  distinctly  alkaline  and  deter- 
mining the  excess  of  alkali  (Meyer's  method).  Schimpf 6  gives 
essentially  the  same  method,  but  also  includes  the  iodometric  method 
of  Rupp.7  However,  neither  the  alkalimetric  nor  the  iodometric 
method  is  applicable  to  the  estimation  of  chloral  in  the  embalming 
fluids  on  account  of  the  simultaneous  presence  of  formaldehyde. 
Fortunately,  the  fact  that  chloral  contains  chlorine,  which  can 
be  converted  into  a  chloride,  affords  a  simple  and  convenient  basis 
for  indirectly  estimating  the  amount  of  chloral.  Procedures  for 
decomposing  the  organic  molecule  so  as  to  obtain  its  chlorine  in 
the  form  of  chloride  are  given  by  many  authors  under  chloroform, 
but  under  chloral  preference  appears  to  be  given  to  some  form  of 
the  alkalimetric  method,  while  a  number  of  authors  even  omit 
any  reference  to  the  chloride  process  in  the  latter  case.  That  such 
preference  is  not  justifiable,  however,  may  be  seen  from  the  work 
of  Hinrichs,s  who  has  pointed  out  the  gross  errors  (varying  from 
1 80  to  200  per  cent.)  resulting  from  the  alkalimetric  procedure 
when  the  term  "  heating,"  as  used  by  the  British  Pharmacopoeia, 
is  taken  to  mean  warming  till  all  the  odor  of  chloroform  has 
disappeared.  Hinrichs,  therefore,  describes  a  modification  of  that 
method  which,  however,  still  does  not  make  it  suitable  in  the  case 
of  the  embalming  fluids ;  so  that  for  general  analytical  purposes  the 
chloride  method  is  probably  the  best  of  all. 
This  chloride  method  may  be  carried  out  according  to  either 
the  procedure  of  Wallis  9  or  that  of  Self.10  The  essential  feature 
of  Wallis'  procedure  is  the  decomposition  of  the  chloral  by  heating 
with  an  alcoholic  solution  of  alkali  under  pressure,  which  is  effected 
by  heating  the  mixture  in  a  closed  bottle  by  means  of  boiling  water 
for  three  hours.  This  is,  therefore,  practically  the  same  procedure 
as  that  previously  described  by  Puckner 11  for  the  estimation  of 
chloroform.  In  Self's  method  the  decomposition  of  the  chloral 
is  effected  by  boiling  the  solution  containing  the  chloral  with  zinc 
5  Holland :    Medical  Chemistry  and  Toxicology,  2d  ed.,  p.  412  (1908). 
6  Schimpf:   Manual  of  Volumetric  Analysis,  5th  ed.,  pp.  647-8  (1909). 
'Arch.  Pharm,,  241,  326-8  (1903),  and  Jour.  Chem.  Soc,  84,  (2),  699  (1903). 
8  Pharm.  Jour..  (4),  16,  530~532  (1903)- 
9  P harm.  Jour.,  (4),  22,  162-163  (1906). 
10 Pharm.  Jour.,  (4),  25,  4-7  (1907). 
11  Proc.  A.  Ph.  A.,  49,  294-297  (1901). 
