VALUATION  OE  CYANIDE  OF  POTASSIUM. 
555 
This  difference  in  quantity  is  necessary  to  be  borne  in  mind 
by  the  medical  practitioner  when  prescribing  the  extract  and 
other  preparations  of  nux  vomica. — London  Pharm.  Journ., 
Sept.  1,  1856. 
ON  A  MEANS  OF  ESTIMATING   THE  MONEY  VALUE  AND 
STKENGTH  OF  COMMERCIAL  CYANIDE  OF  POTASSIUM. 
By  Thornton  J.  Herapath. 
There  is,  I  believe,  no  drug  which  is  so  frequently  met  with 
in  an  impure  state  as  cyanide  of  potassium.  This  is  owing  not 
so  much  to  the  propensity  which  certain  manufacturers  appear 
to  possess  of  adulterating  the  articles  sold  by  them  to  the  great- 
est possible  extent,  as  to  the  difficulty  which  is  experienced  in 
preparing  a  pure  article,  and  of  purifying  the  impure  cyanide 
after  it  has  been  manufactured.  In  a  paper  that  was  published 
in  Liebig's  Annalen  for  1851,  Professor  Liebig  has  stated  that 
commercial  cyanide  of  potassium,  prepared  by  his  method,  sel- 
dom contains  more  than  59  to  63.5  per  cent,  of  pure  cyanide. 
Having  recently  had  occasion  to  purchase  a  considerable  quan- 
tity of  this  chemical,  I  was  induced  to  undertake  a  series  of  ex- 
periments, with  a  view  of  ascertaining  the  most  expeditious 
method  of  testing  the  strength  or  money  value  of  the  various 
samples  that  were  offered  to  me.  The  process  I  ultimately 
adopted  was  a  modification  of  that  proposed  by  Mr.  Parkes  for 
the  determination  of  the  percentage  of  copper  in  copper  ores. 
It  is  based  on  the  property  which  alkaline  cyanides  possess  of 
decolorising  the  blue  solution  of  cuprate  of  ammonia,  or  am- 
monia c  a  1  salts  of  copper.  The  first  thing  to  be  done  in  testing 
cyanide  of  potassium  by  this  method,  is  to  prepare  a  standard 
solution  of  ammonio-sulphate  or  ammonio-nitrate  of  copper.  A 
certain  known  quantity  of  puretcrystallised  sulphate  of  copper,* 
made  by  crushing  the  pure  crystals  of  the  shops  into  a  mortar, 
and  pressing  the  powder  so  obtained  between  folds  of  bibulous 
paper,  is  taken,  and  dissolved  in  water,  or  an  equivalent  quan- 
tity of  pure  metallic  (electrotype)  copper  is  dissolved  in  dilute 
nitric  acid ;  and  the  solutions  so  prepared  are  then  diluted  with 
*Cu+0,  S03+Aq. 
