AraM°ay"moarm'}        Volumetric  Solutions  of  US. P.  209 
pared  with  such  an  element  as  iron  for  example  (which  is  quite 
often  used  in  standardizing  KMn04  solutions),  silver  offers  the 
additional  advantages  of  being  much  more  readily  prepared  in  per- 
fectly pure  state,  in  being  suitable  for  a  volumetric  process  in  which 
atmospheric  oxidation  can  have  no  influence,  and  in  being  suitable 
for  long  keeping  unaltered.  To  illustrate  the  last  mentioned  prop- 
erty of  silver  we  need  only  recall  that  when  at  the  request  of  Dumas, 
Stas  21  repeated  (1890)  his  work  on  silver,  he  found  that  the  silver 
which  he  used  in  his  atomic  weight  determinations  (probably  about 
i860)  contained  an  altogether  insignificant  amount  of  gases,  in 
no  case  greater  than  the  unavoidable  experimental  error.  In  other 
words,  although  many  years  had  elapsed  between  the  two  investiga- 
tions, yet  Stas  apparently  felt  confident,  and  his  results  prove,  that 
his  silver  had  remained  unaltered.  In  fact,  it  is  quite  within  the 
limits  of  probability  that  with  only  ordinary  precautions,  metallic 
silver  may  be  kept  unaltered  not  only  for  decades  but  even  for 
centuries.  Finally,  pure  metallic  silver  as  the  ultimate  standard 
in  volumetric  analysis  would  offer  the  additional  advantages  that 
when  used  in  the  form  of  bright  sheets,  its  undiminished  brightness 
could  always  be  taken  as  a  good  indication,  at  least,  of  its  having 
retained  its  original  purity ;  while  by  using  comparatively  large 
pieces  of  it,22  any  possible  loss  of  the  standard  substance  in  trans- 
ferring from  the  container  in  which  it  is  weighed  to  the  vessel  in 
which  the  analysis  is  carried  out,  would  be  entirely  avoided. 
Urged  by  such  reasoning  as  the  above,  the  writer  has  used  pure 
metallic  silver  as  the  standard  in  volumetric  analysis  for  some  time 
past  with  very  satisfactory  results.  The  plan  in  general  is  as  fol- 
lows :  About  0.5  Gm.  of  the  silver,  accurately  weighed,  is  placed  in 
an  Erlenmeyer  flask  of  about  200  ex.  capacity,  about  10  c.c.  of  mod- 
erately strong  (about  32  per  cent.)  nitric  acid  are  added,  and  a  small 
funnel  is  placed  in  the  mouth  of  the  flask  to  insure  against  loss  of 
liquid  by  spirting.  Gentle  heat  is  applied,  and  when  the  silver  has 
dissolved,  the  solution  is  diluted  with  about  25  c.c.  of  pure  distilled 
water  and  the  nitrous  acid  expelled  by  heating  the  solution  to  boiling. 
21  lour.  Chem.  Soc,  58,  561  (1890). 
23  If  metallic  silver  were  generally  adopted  as  the  ultimate  standard 
in  volumetric  analysis,  it  would  be  feasible  to  place  the  silver  on  the  market 
as  coin-like  disks  of  uniform,  accurate,  and  convenient  weight,  suitable  for 
direct  use  in  standardization ;  thus  saving  considerable  time  in  the  execution 
of  the  latter  and  further  eliminating  personal  error. 
