^^OcT'^iSs*^™  }         Commercial  Iodide  of  Potassium.  503 
(7.)  Test  for  Moisture. — Drying  to  a  constant  weight  at  100°C. 
(8.)  Test  for  Free  Iodine. — The  salt  will  be  colored.  A  solution 
shaken  in  a  test-tube  with  carbon  disulphide,  or  chloroform,  will 
impart  the  violet  color  to  the  subsiding  layer. 
(9.)  Test  for  Nitrate.  Precipitate  with  excess  of  silver  sulphate  solu- 
tion, and  test  the  filtrate  with  concentrated  sulphuric  acid  and  a  crystal 
of  ferrous  sulphate,  for  nitric  acid.  Adulteration  with  entire  crystals 
of  sodium  nitrate  has  been  noted  in  Europe. 
(10.)  Test  by  Insolubility  in  Alcohol.  One  gramme  of  the  dried  and 
iinely  pulverized  salt  is  digested  with  18  cc.  of  alcohol  (90  per  cent.), 
in  a  stoppered  test-tube,  at  ordinary  temperatures,  frequently  shaking, 
for  several  hours.  Sulphate,  carbonate,  iodate,  nitrate,  and  even  much 
bromide,  if  present,  will  remain  undissolved.  The  operation  serves 
•only  to  show  gross  adulterations,  and  any  residue  found  must  be  tested 
qualitatively.  If  absolute  alcohol  be  taken,  not  less  than  40  cc.  must 
be  used,  and  the  action  is  slow  and  unsatisfactory. 
The  summary  on  the  next  page  presents  the  results  of  the  tests  de- 
signated, according  to  details  already  given,  as  numbered.  The  obser- 
vations were  taken  across  a  test-tube  of  the  width  of  tico  centimeters — a 
little  more  than  |  inch — in  the  tests  (1),  (2)  with  lime-water,  (3),  (4), 
and  (5).  In  tests  (1)  "  without  starch,'^  the  same  results  were  obtained 
with  diluted  sulphuric  acid,  and  with  a  crystal  of  tartaric  acid.  In 
tests  (4),  the  U.  S.  Ph.  tests  were  supplemented  by  adding  hydrochloric 
acid,  because  of  the  alkalinity  found  in  some  of  the  samples,  and  to 
make  the  test  uniform  for  all. 
Numbers  1,  2,  and  3  were  the  American  samples;  numbers  4  and 
•5  were  the  European  samples. 
These  samples  of  home  manufacture  furnish  a  very  small  but  I 
believe  a  fair  representation  of  the  medicinal  iodide  of  potassium  of 
this  country.  Different  lots  of  the  salt,  as  put  out  by  any  one  of  our 
American  manufacturers  at  different  times,  will  certainly  differ  from 
each  other  materially,  and  perhaps  differ  as  much  as  do  the  several 
samples  in  this  examination.  By  taking  a  greater  number  of  samples, 
truer  averages  can  be  obtained,  and  no  comparison  between  the  goods 
of  different  manufacturing  houses  should  be  based  wholly  on  one  or 
two  samples  from  each,  or  on  samples  taken  at  one  time.  Of  the 
foreign  samples,  I  can  only  say  that  they  are  single  instances  of  the 
pharmacopoeial  salt  as  put  forth  by  foreign  makers  of  high  standing. 
It  will  be  seen  that  one  of  the  three  American  samples  stands  fully  as 
