ON  THE  ESTIMATION  OF  IODINE. 
263 
ON  THE  ESTIMATION  OF  IODINE. 
By  Dr.  Frederics  P^ny, 
Professor  of  Chemistry,  Anderidntan  University,  Glasgow. 
Among  the  many  applications  that  maybe  made  of  bichromate 
of  potash  to  the  purposes  of  centigrade  analysis,  there  is  none 
more  convenient  or  useful  than  its  employment  for  the  estima- 
tion of  •the  amount  of  iodine  in  samples  of  commercial  iodine 
and  of  iodide  of  potassium.  In  Glasgow  especially,  which  is 
the  principal  focus  of  the  manufacture  of  salts  of  potash,  and  of 
iodine  from  kelp,  and  where  the  problems  referred  to  are  fre- 
quently presented  for  solution,  an  expeditious  and  exact  method 
for  the  determination  of  iodine  becomes  truly  valuable. 
According  to  the  statements  of  a  party  well  qualified  to  judge, 
it  appears,  that  in  the  kelp  season  of  1851,  the  total  quantity  of 
kelp  brought  to  Glasgow  was  about  6000  tons  (22  J  cwt.  to  the 
ton,)  which  may  be  considered  a  fair  average  of  ordinary  sea- 
sons. On  account  of  the  greatly  increased  demand  for  potash- 
salts,  the  arrivals  in  1850  amounted  to  nearly  10,000  tons, 
which  is  considerably  higher  than  for  several  previous  years.* 
The  manufacture,  however,  is  not  confined  to  Glasgow ;  there 
are  iodine  works  at  Borrowstowness,  Greenock  and  Falkirk,  in 
Scotland,  at  Ramelton  in  Ireland,  and  at  Cherbourg  and  Brest 
in  France. 
The  centigrade  process,  here  to  be  described,  for  the  estima- 
tion of  iodine,  is  based  upon  the  fact,  that  chromic  acid  in  pre- 
sence of  hydrochloric  acid  causes  the  complete  decomposition  of 
soluble  metallic  iodides,  the  chloride  of  chromium  and  the 
chloride  of  the  other  metal  being  produced,  while  the  iodine  is 
thrown  down  in  the  solid  state.  Bichromate  of  potash  is  taken 
as  the  most  convenient  and  stable  form  of  chromic  acid.  The 
*  Kelp  Imports  in  Glasgoiv. 
1841-  42 
1842-  43 
1843-  44 
1844-  45 
1845-  46 
1846-  47 
July  to  July. 
2565  tons. 
1887  « 
1965  « 
3263  « 
6086  » 
3627  « 
Mr.  Glassford's  Kelp  Manufacture. 
