AmNov?r'i9i8arm; )  Decomposition  of  Hydrocyanic  Acid.  817 
(")                                        0>)  (*) 
Time  before  appearance 
AmoriEt  of  HCN  used.                          Made  up  with  5  Co.  05  of  yellow  color. 
(1)  5Cc.    8  per  cent.  acid.     Distilled  water   '  2  days. 
(2)  "                       "       Absolute  alcohol     2  days. 
(3)  "  "  "       Dilute  HoS04  (1  per  cent  on 
HCN)  "  23  days. 
(4)  "  "       Tartaric    acid    solution  (acid 
equivalent  half  that  of  the 
H9S04  in  Experiment  3)  12  days. 
(5)  "             "          "       Water  saturated  with  C09   13  days. 
(6)  "                       "       Tartaric  acid  solution  0.04  Gm.  Unaffected  after 
in  5  Cc.  4  months. 
(7)  5  Cc.    4  per  cent.  acid.     50  per  cent,  glycerin    2  weeks. 
(8)  "                       "       Distilled  water   2  weeks. 
(9)  "                       "       20  per  cent,  solution  of  man-  13  days. 
nitol 
In  each  case  0.5  Gm.  of  ground  glass  was  added,  and  the  sample 
shaken  from  day  to  day. 
It  appears  from  results  (5)  and  (2)  that  carbon  dioxide  has  con- 
siderable preservative  influence  on  the  acid,  while  absolute  alcohol 
has  none.  It  has  been  stated  by  Williamson  that  prussic  acid  con- 
taining 20  per  cent,  of  glycerin  keeps  indefinitely  ;  but  no  glycerin 
being  available  at  the  time,  it  was  thought  possible  that  such  a  com- 
pound as  tartaric  acid  might  prove  useful,  as  it  is  both  acidic  and  of 
similar  structure  to  glycerin.  It  is  evident,  however,  that  the  pre- 
servative influence  of  tartaric  acid  depends  entirely  on  its  acidity 
(3)  and  (4).  Later,  when  some  glycerin  was  obtained,  it  was  pos- 
sible to  test  the  statement  of  Williamson,  which,  if  true,  would  in- 
dicate the  possible  formation  of  a  compound,  just  as  boric  acid  forms 
compounds  with  glycerin  and  mannitol ;  but  whereas  the  addition 
of  glycerin  increases  the  acidity  of  boric  acid,  such  is  not  the  case 
with  hydrocyanic  acid;  and  experiments  (7),  (8),  (9)  above  show 
finally  that  neither  glycerin  nor  mannitol  has  any  influence  in  pre- 
serving the  acid. 
The  only  alternatives  to  the  use  of  some  such  acid  preservative 
as  is  suggested  above  would  appear  to  be  the  use  of  some  vessel  from 
which  water  does  not  dissolve  alkali,  or  the  use  of  a  glass  vessel 
coated  inside  with  some  suitable  neutral  material. 
