Am.  Jour.  Pharm. 
April,  19 1 7. 
Assay  Processes. 
167 
The  assay  of  crude  calcium  sulphide  introduces  a  new  method. 
To  the  salt,  water  is  added  and  ammonium  chloride  solution,  and 
allowed  to  stand  for  a  short  time.  Then  cadmium  chloride  is 
added,  and  after  agitating,  some  acetic  acid  is  added  and  the  whole 
heated  for  15  minutes.  The  supernatant  liquid  is  decanted  through 
a  filter,  and  the  precipitated  cadmium  sulphide  agitated  with  acetic 
acid,  and  the  precipitate  is  washed  with  acetic  acid.  The  precipi- 
tate is  returned  to  the  flask,  iodine  solution  added,  and  HQ.  The 
flask  is  stoppered,  and  the  excess  titrated  with  sodium  thiosulphate. 
Acetone.  In  this  assay  the  acetone  is  treated  with  KOH  and 
iodine  solution,  and  HC1,  and  titrated  with  sodium  thiosulphate. 
The  iodine  converts  the  acetone  into  tri-iodoacetone  and  hydriodic 
acid: 
CH3COCH3  + 16  =  CI3COCH3  +  3HL 
Acetone       Iodine     Tri-iodo-  Hydriodic 
acetone  Acid 
The  tri-iodoacetone  is  then  acted  upon  by  the  KOH,  being  converted 
into  iodoform  and  potassium  acetate,  and  the  hydriodic  acid  neu- 
tralized by  the  KOH : 
CI3COCH3     +     3HI     +  4KOH 
Tri-iodo-  Hydriodic  Potassium 
acetone  Acid  Hydroxide 
=  CHI,     +     3KI     +     H20     +  CH3COOK. 
Iodoform     Potassium  Potassium 
Iodide  acetate 
The  excess  of  iodine  forms  with  the  alkali  potassium  iodide  and 
iodate,  and  these  are  decomposed  by  the  HC1  into  iodine.  The  ex- 
cess of  iodine  used  is  determined  by  sodium  thiosulphate. 
Phenols  are  assayed  by  adding  to  them  n/10  to  bromine  solution 
and  HQ,  allowing  to  stand  15  minutes,  and  quickly  adding  potas- 
sium iodide,  care  being  taken  to  avoid  loss  of  bromine  or  iodine  by 
keeping  the  flask  tightly  stoppered.  After  standing  for  some  time, 
I  mil  chloroform  is  added,  shaken,  and  excess  of  iodine  titrated. 
This  assay  takes  place  in  three  stages.  In  the  first,  the  bromine 
combines  with  the  phenol,  forming  tribromphenol : 
C6H5OH     +     Br6     =     CeH2Br3OH     +  3HBr. 
Phenol  Bromine  Tribromphenol  Hydrobromic 
Acid 
