Am  Jour.  Pharm.  "j 
July. 1880.  j 
Volumetric  Analysis, 
341 
Quantitive  analysis  by  weight,  or  gravimetric,  ■analysis,  consists  in 
separating  and  accurately  weighing  the  constituents  of  a  compound. 
The  necessary  operations  are  frequently  very  complicated,  occupy- 
ing a  long  time,  and  in  many  cases  require  elaborate  apparatus,  as  also 
the  exercise  of  much  care  and  experimental  knowledge. 
Volumetric  analysis,  or  quantitive  analysis  by  measure,  on  the  other 
hand,  is  quickly  performed,  as  a  general  rule  is  susceptible  of  extreme 
accuracy,  and  needs  much  simpler  apparatus.  The  leading  principle 
of  the  method  consists  in  submitting  the  substances  to  be  estimated  to 
certain  characteristic  reactions,  employing  for  such  reactions  solutions 
•of  known  strength,  and  from  the  volume  of  solution  required  for  the 
production  of  such  reaction,  determining  the  weight  of  the  substance 
'to  be  e.timated,  by  aid  of  the  known  laws  of  chemical  equivalence. 
Suppose,  for  example,  that  it  is  desirable  to  know  the  quantity  of 
pure  silver  contained  in  a  "  Bland  dollar."  The  coin  is  first  dissolved 
in  pure  nitric  acid,  by  which  means  a  bluish  solution,  containing  silver, 
copper,  and  probably  other  metals,  is  obtained.  It  is  known  that 
chlorine  combines  with  silver,  forming  a  chloride  of  silver,  which  is 
insoluble  in  dilute  nitric  acid.  The  proportions  in  which  the  combina- 
tion takes  place  are  the  atomic  weights  of  the  two  substances,  or  35*5 
parts  of  chlorine  to  every  108  parts  of  silver  consequently,  if  a  solu- 
tion of  pure  chloride  of  sodium  be  prepared  by  dissolving  in  water  such 
a  weight  of  the  salt  as  will  be  equivalent  to  35*5  grains  of  chlorine  = 
58*5  grains  of  chloride  of  sodium  (its  molecular  weight),  and  the  solu- 
tion be  diluted  to  the  measure  of  1,000  grains  of  distilled  water,  every 
single  grain-measure  (or  one-thousandth  part)  of  this  solution,  upon 
being  carefully  added  to  the  silver  solution,  will  combine  with  o*io8 
grain  of  pure  silver  to  form  chloride  of  silver,  which,  being  insoluble, 
will  be  precipitated.  In  the  process  of  adding  the  salt  solution  to  the 
silver,  drop  by  drop,  a  point  is  at  least  reached  when  the  precipitate 
ceases  to  form,  thus  showing  that  all  the  silver  has  been  separated  from 
the  solution.  Upon  carefully  examining  the  graduated  vessel  from 
which  the  salt  solution  has  been  used,  it  at  once  becomes  apparent  how 
many  grain-measures  of  liquid  have  been  necessary  to  produce  complete 
decomposition  ;  and  to  obtain  the  answer  to  the  problem  is  a  simple 
matter  of  calculation. 
For  instance,  suppose  the  quantity  used  to  completely  decompose 
the  one-tenth  part  of  the  solution  of  silver  was  343  grain-measures  ; 
-this  number  multiplied  by  o*io8  (the  amount  of  silver  thrown  down  by 
