132 
ANALYSIS  OF  PRUSSIC  ACID,  &C. 
5th.  Where  great  accuracy  is  required,  as  in  analytic  investiga- 
tions, or  where  the  liquid  tested  has  a  density  differing  con- 
siderably from  that  of  water,  it  will  be  necessary  to  divide  the 
percentage  first  obtained  by  the  specific  gravity  of  the  liquid 
under  examination;  the  quotient  will  give  the  percentage 
strength  by  weight. 
6th.  In  determining  the  amount  of  prussic  acid  in  oil  of  bitter 
almonds,  or  oil  of  cherry  laurel,  dissolve  20  minims  of  the  oil 
in  enough  liquor  of  potassa  to  make  up  when  filtered  5  fl.  Z.  Test 
this  clear  solution  as  before  directed,  and  multiply  the  observed 
result  by  15,  and  divide  by  the  specific  gravity  of  the  oil. 
7th.  In  cases  of  liquids  having  a  greater  percentage  of  prussic 
acid  than  the  tube  will  indicate,  as  the  medicinal  prussic  acid,  &c. 
instead  of  filling  up  the  liquid  to  the  line  0  of  the  tube,  fill 
only  to  that  marked  \  or  J,  and  then  up  to  the  line  0  with  water. 
After  the  operation  is  finished,  multiply  the  result  by  4  or  2  ac- 
cording as  the  line  \  or  J  was  taken. 
In  repeating  any  of  the  processes  already  mentioned  a  second 
time  for  verification,  nearly  the  whole  amount  of  the  test  solu- 
tion as  indicated  by  the  first  trial,  can  be  poured  in  at  once,  and 
then  drop  by  drop,  till  the  proper  quantity  as  shown  by  the  tur- 
bidity is  added. 
In  conclusion  I  may  state,  that  in  trials  made  with  various 
lots  of  cherry  laurel  water,  I  have  met  with  some  that  contained 
scarcely  a  trace  of  prussic  acid,  and  therefore  as  a  remedial 
agent  was  entirely  worthless  ;  while  in  others,  the  proportion 
varied  from  the  minutest  quantity  up  to  the  full  average 
strength,  which  is  about  one-tenth  of  one  percent.  In  view  of 
this  great  uncertainty,  allow  me  again*  to  refer  to  the  following 
substitute  for  the  distilled  cherry  laurel  water,  which  will  be 
found  upon  analysis  to  contain  the  above  proportion  of  prussic 
acid. 
R.  Medicinal  Prussic  Acid,  fl.  3i. 
Oil  of  Bitter  Almonds,  n^ij. 
dissolved  in 
Alcohol       .        .         .  gij. 
Distilled  Water,  q.  s.        ft.  fl.  ^iij. 
*  The  original  of  this  formula  I  proposed  to  the  Philad.  College  of 
Pharmacy  several  years  ago. 
