ON  WATER  IN  COMMERCIAL  IOIJ1NE. 
261 
slowly,  than  when  the  gall-nuts  are  made  into  a  paste  with  water, 
the  ferment  being  probably  insoluble. — Pharm.  Journ.,  March, 
1853,  from  Vierteljahresschrift  fur  praktische  Pharmacie,  Heft, 
i.  1853. 
ON  THE  DETERMINATION  OF  WATER  IN  COMMERCIAL  IODINE. 
By  M.  Bolley, 
Powdered  iodine  takes  up  a  tolerably  large  quantity  of  water, 
without  experiencing  any  remarkable  alteration  in  appearance. 
The  quantity  of  water  thus  mechanically  mixed  with  iodine  may, 
according  to  some  authorities,  amount  to  as  much  as  10  or  12  per 
cent.,  and  the  methods  for  determining  it  are  very  insufficient.  Al- 
though less  volatile  than  water,  this  substance,  like  many  others, 
is  very  readily  carried  off  by  the  vapor  of  water.  Che  vail  ier  re- 
commends that  the  quantity  of  water  should  be  determined  by 
pressing  a  known  weight  of  the  iodine  between  folds  of  bibulous 
paper,  and  then  weighing  it  again.  It  is  evident  that  this  method 
cannot  furnish  accurate  results.  Another  method  consists  in  rub- 
bing the  iodine  with  twice  its  weight  of  fused  chloride  of  calcium, 
and  heating  the  mixture  to  356°  F.  in  a  tubulated  retort,  by  which 
means  the  iodine  is  volatilized,  while  the  water  is  retained  by  the 
chloride  of  calcium.  In  this  case  care  must  be  taken  that  water 
is  not  evaporated  from  the  chloride,  and  there  is  considerable 
trouble  in  thoroughly  removing  the  iodine  from  the  neck  of  the 
retort. 
Bolley  proposes  the  following  method  as  being  both  simple  and 
accurate.  About  30  grs.  of  iodine  are  introduced  into  a  small 
porcelain  dish  previously  weighed,  about  240  grms.  of  mercury 
added,  and  the  whole  wTeighed  together  with  a  small  agate  pestle. 
The  dish  is  then  laid  upon  a  sheet  of  white  paper,  and  the  iodine 
and  mercury  rubbed  together  by  means  of  the  agate  pestle  until 
the  smell  of  iodine  has  disappeared  and  the  mass  has  assumed  a  red- 
dish-brown color.*    When  complete  combination  has  been  effected, 
*  It  suddenly  becomes  pasty,  and  closely  resembles  an  amalgam,  a  fact 
which  does  not  appear  to  have  been  noticed.  To  effect  this,  a  quantity  of 
mercury  six  or  eight  times  as  great  as  that  of  iodine  appears  necessary.  The 
uncombined  mercury  may  be  pressed  out  from  the  iodine,  which  does  not 
destroy  the  continuity  of  the  former. 
