490  Mayer's  Reagent  for  Alkaloids.  {'^°'-oct'!!;*if£.^''™* 
1  in  200  -0142 
1  in  300    -0140 
1  in  400  :  -0136 
1  in  500  •0128& 
1  in  600  -01163 
The  precipitates  from  0*100  of  alkaloid,  when  collected,  dried  and 
weighed,  ran  from  0'162  to  0*179,  with  an  average  of  0*173  correspond- 
ing to  55*9  per  cent,  to  61*7  per  cent.,  with  average  of  57.8  per  cent, 
alkaloid.  It  is  observed  that  aconite  root  and  fluid  extracts  of  the 
drug  contain  not  far  from  0*75  per  cent,  alkaloid  as  an  average  estimated 
as  aconitine.  Occasionally  the  amount  will  exceed  one  per  cent,  and 
rarely  fall  below  ^  per  cent.  It  will  also  be  noted  that  for  dilutions  of 
one  part  in  200  to  one  part  in  300  the  alkaloid  gives  the  best  results  in 
titration,  while  for  less  than  one  part  in  400  the  results  begin  to  vary 
considerably.  It  is  therefore  evident  that  a  dilution  should  be  adopted 
in  which  the  alkaloid  should  be  present  in  from  one  in  200  to  not  less 
than  one  in  400,  and  in  the  case  of  fluid  extracts  this  dilution  would 
be  20  cc.  representing  10  cc.  of  fluid  extract  and  therefore  this  dilu- 
tion was  adopted.^  The  figures  in  the  table  were  obtained  a^  follows  : 
A  fluid  measuring  20  cc.  may  be  said  to  weigh  20  grammes.  If  it 
contains  one  part  in  200  of  alkaloid  it  is  evident  that  there  is  0*100' 
grammes  (20  ~^  200  =  0*100)  of  alkaloid  present  in  it.  In  a  di- 
lution of  one  in  200  Mayer's  reagent  precipitates  0*0142  of  alkaloid 
and  7*04  cc.  (0*100  -f-  '0142  ■=  7*04)  of  reagent  are  required  to  pre- 
cipitate the  whole  of  the  alkaloid.  This  gives  the  figure  for  the  first  col- 
umn, the  equivalent  goes  into  the  third  column,  while  the  degree 
of  dilution  makes  up  the  second  column.  For  one  in  500  a  similar 
course  is  followed,  not  forgetting  that  in  dividing  the  weight  of  the 
alkaloid  by  the  equivalent  we  must  use  the  equivalent  for  one  in  500 
and  not  for  one  in  200  as  in  the  first  case  and  this  is  true  for  all  the  data 
in  the  first  column.  By  following  this  course  it  is  easy  to  see  how  the 
first  column  becomes  an  index  to  the  degree  of  dilution  and  enables 
the  analyst  to  select  the  proper  equivalent  for  his  calculations. 
On  this  basis  the  following  table  has  been  constructed  for  the  inter- 
pretation of  the  results  of  titration  : 
^  10  cc.  of  a  fl.  ex.  or  10  grammes  of  a  drug  containing  100  per  cent,  alkaloid 
would  yield  when  diluted  to  20  cc.  a  fluid  containing  one  part  in  200  of  alkaloid. 
If  it  only  contained  ^  per  cent,  alkaloid  this  would  correspond  on  diluting  to  20' 
cc.  to  a  fluid  containing  one  part  in  400,  and  it  will  thus  be  seen  that  the  range 
is  the  one  best  suited  to  determinations  of  the  alkaloid. 
