ON  A  NEW  METHOD  OF  ALKALIMETRY. 
29 
ON  A  NEW  METHOD  OF  ALKALIMETRY. 
By  Astley  Paston  Price,  Ph.D.,  F.C.  S. 
Chemical  Assistant  in  the  Laboratory  of  the  Government  School  of  Mines. 
Having  had  occasion,  some  time  since,  to  test  the  comparative 
value  of  the  ordinary  alkalimetrical  processes,  I  was  somewhat 
surprised  at  the  discrepancies  in  the  results  I  obtained,  and  also 
at  the  somewhat  difficult  and  tedious  manipulation  necessary 
when  comparatively  accurate  determinations  were  required.  The 
most  serious  impediment  in  carrying  out  the  usual  alkalimetrical 
processes,  arises,  as  is  well  known,  from  the  liberation  of  car- 
bonic acid,  the  presence  of  which,  even  in  exceedingly  small 
quantity,  being  sufficient  to  mask  the  point  of  saturation,  and  to 
prevent  the  indication  of  the  presence  of  either  an  excess  of 
acid  or  of  alkali. 
After  having  experienced  the  difficulties  attendant  on  its  pres- 
ence, and  the  almost  impossibility  of  rapidly  and  entirely  expel- 
ling the  liberated  carbonic  acid  from  solution,  it  appeared  to  me 
most  desirable  to  seek  an  alkalimetrical  process,  in  which  the 
carbonic  acid  should  be  expelled  previous  to  determining  the 
saturating  power  of  the  alkali  under  examination.  It  further 
appeared  to  me,  that  in  the  alkalimetrical  processes  now  in  use, 
there  existed  another  very  serious  inconvenience,  in  that  the  per 
centage  of  alkali  was  determined  directly,  and  not  indirectly  ; 
that  is,  that  the  alkali  was  estimated,  and  not  the  impurities  which 
might  be  therein  contained.  This  may  perhaps  be  better  under- 
stood by  an  example.  Pure  carbonate  of  soda  contains  about 
58*5  per  cent,  of  alkali,  but  commercial  carbonate  contains  only 
about  50  per  cent.  Now  in  the  several  alkalimetrical  processes 
employed  in  the  arts,  the  50  per  cent,  of  alkali  is  estimated,  and 
not  the  8*5  per  cent,  of  impurities,  constituting,  as  these  impuri- 
ties invariably  do,  by  far  the  smaller  proportion  of  the  commer- 
cial alkalies  or  alkaline  carbonates. 
In  practice,  it  will,  I  believe,  be  found  advantageous  to  employ 
a  method  which,  by  indicating  the  amount  of  impurities  present, 
will  give  the  available  proportion  of  alkali. 
As  I  have  previously  remarked,  the  primary  difficulty  to  be 
overcome  is  the  entire  expulsion  of  carbonic  acid,  the  presence 
of  but  a  small  quantity  of  which  entirely  prevents  accurate 
determination,  not  only  owing  to  the  change  of  tint  produced 
