Am.  Jour.  Pharm.  ) 
December,  1920.  | 
Hydrocyanic  Acid. 
915 
Presence  of  any  free  HCl  would  raise  the  apparent  amount  of 
HCN  in  the  gravimetric  and  Volhard  processes.  The  acid  was 
diluted  to  contain  rather  less  than  2  p(^r  cent.  HCN. 
All  calculations  and  strengths  of  standard  solutions  were  based  on 
the  International  Atomic  Weights,  1 909 ;  for  silver,  nitrogen  and  car- 
bon the  atomic  weights  are  the  same  at  the  present  day. 
Se^ries  a. 
Process.  (Results  by  weight  in  weight.) 
Gravimetric  (as  AgCN)  (a)  i  .650%;  {b)  i  .643%  1  mean  of  4  =  1 .647% 
Gravimetric  (as  Silver)        1.648%;        1-645     J  (gravimetric). 
Volhard  (i  determination  only)  i  .  65 1  %  .  . 
Original  Liebig  (excess  of  NaOH  slight)  mean  of  6  =  i  .  650% 
Fordos  and  Gelis  mean  of  6  =  i .  645  % 
Using  NH3  +  KI  mean  of  6  =  I  .648% 
SeriKS  B. 
(Same  stock  of  acid,  but  two  months  later.) 
Acid  measured  off  by  pipette  (20  Cc.) 
Original  Liebig  process.  Mean  of  4  =  i  .216  w/v. 
Using  borax  Mean  of  4  =  i  215  w/v. 
Using  NH3  +  KI.  Mean  of  4  =  i. 213  w/v. 
(All  results  obtained  on  the  same  day.) 
The  iodide  method  adopted  was  to  use  about  equal  volumes  of 
10  per  cent,  ammonia  solution  and  dilute  hydrocyanic  acid,  adding 
from  0.1  to  0.2  Gm.  of  KI.  The  results  certainly  seem  to  show  that 
the  end-point  is  sharper  with  this  modification,  especially  when  over 
40  Cc.  (as  in  Series  B)  of  N / 10  AgNOa  was  required.  In  this  case 
using  the  same  amount  of  HCN  the  amount  of  N / 10  AgNOs  required 
was  0.03  to  0.05  Cc.  less  than  that  required  by  Liebig's  process. 
ACTION  OF  GIvYCERIN  AS  A  PRESERVATIVE. 
Williams  {Y.B.P.,  1874-1878)  recommended  the  addition  of 
glycerin  for  this  purpose — 20  per  cent,  was  found  to  preserve  the 
B.  P.  acid  almost  indefinitely.  Some  of  the  1.65  per  cent,  acid 
of  Series  A  was  mixed  with  sufficient  glycerin  to  make  the  mixture 
contain  25  per  cent,  glycerin.  This  was  found  to  contain  i  .23  per  cent. 
HCN  w/v.  when  made  up.  Nine  months  later  it  still  contained 
1. 1 9  per  cent. 
The  acid  remaining  after  Series  B  analyses  were  finished  was  al- 
lowed to  stand  for  the  same  period  in  diffused  light.  The  strength 
was  then  0.15%. 
