Am.  Jour.  Pharm. 
Bee.,  1886. 
}  A  Study  of  the  Use  of  Mayer's  Reagent 
579 
It  may  be  of  interest  to  state  that  of  the  45  parts  nitric  acid  used 
in  the  Pharmacopoeia,  only  33*66  are  required  to  form  mercuric  nitrate 
from  the  mercuric  oxide,  an  excess  of  11*34  parts,  or  25  per  cent  of 
the  quantity  used,  being  present  in  the  solution. 
In  the  formula  for  making  a  50  per  cent,  solution  of  mercuric 
nitrate,  there  is  needed  to  form  mercuric  nitrate  from  the  33.32  parts 
HgO,  28*04  parts  nitric  acid,  therefore  there  is  an  excess  of  16*96 
parts,  or  37*69  per  cent  of  the  quantity  used  in  the  solution. 
If  the  solution  of  nitrate  of  mercury  should  contain  an  excess  of 
25  per  cent  of  the  nitric  acid  used,  then  will  be  required  for  a  50  per 
cent,  solution  of  mercuric  nitrate : 
A  STUDY  OF  THE  USE  OF  MAYER'S  REAGENT  IN 
THE  ESTIMATION  OF  ALKALOIDS. 
By  A.  B.  Lyons,  M.  D.  * 
The  assumption  that  underlies  the  method  of  volumetric  estimation 
of  alkaloids  by  Mayer's  reagent  is,  that  the  precipitate  produced  by 
it  is  a  definite  chemical  compound  of  invariable  composition,  so  com- 
pletely insoluble  in  water  that  no  appreciable  quantity  of  the  alkaloid 
can  remain  in  solution  in  presence  of  an  excess  of  the  reagent.  Con- 
ditions such  as  these  obtain  in  the  case  of  many  reactions  between 
inorganic  salts,  and  under  such  conditions  alone  can  volumetric 
estimations  give  us  satisfactory  and  constant  results.  I  have  insti- 
tuted a  series  of  experiments  to  ascertain  to  what  extent  the  precipi- 
tation of  alkaloids  by  Mayer's  reagent  conforms  to  these  conditions. 
In  a  paper  published  some  twenty  years  ago  f  Thomas  B.  Groves 
pointed  out  the  circumstance  that  in  titrations  with  Mayer's  solution 
a  point  would  be  reached  before  precipitation  ceased  when  the.  filtered 
fluid  would  cause  a  precipitate  in  a  fresh  solution  of  the  alkaloid, 
showing  the  presence  already  of  an  excess  of  the  precipitant.  Mr. 
Groves  observed  that  in  some  instances  this  apparent  excess  after  a 
Red  oxide  of  mercury,  33  32  parts. 
Nitric  acid,  37*38  " 
Distilled  water,  29'30  " 
to  make  100  parts. 
*Read  before  the  Michigan  State  Pharmaceutical  Association,  October,  1886. 
f  Pharm.  Journal  II.,  6,  268. 
