206 
Volumetric  Solutions  of  US. P. 
f  Am.  Jour.  Pkarm. 
(       May,  1910. 
in  a  desiccator,  since  in  an  atmosphere  devoid  of  moisture  it  loses 
water  of  crystallization.  Finally,  Iceland  spar,  which  has  recently 
been  advocated  by  Rose,1"  has  the  disadvantage  that  much  of  the 
material  now  sold  under  that  name  contains  magnesium  carbonate.1 ' 
On  the  other  hand,  of  all  the  volumetric  processes  at  present 
known,  there  is  probably  not  one  that  excels  in  elegance 12  or 
accuracy  the  well-known  Volhard  method  for  titrating  silver  by 
means  of  a  thiocyanate  solution.  In  fact,  its  advantages  are  so 
pronounced  that  Shutt  and  Charlton 13  have  even  recommended 
its  use  in  estimating  the  very  small  amounts  of  chlorine  in  potable 
waters,  in  preference  to  the  standard  chromate  method ;  while  the 
maximum  error  of  Rosanoff  and  Hill,14  when  applying  this  method 
to  the  estimation  of  chlorides  by  precipitating  with  a  known  excess 
of  silver  and  determining  the  remaining  silver  in  the  filtrate,  was 
only  0.17  per  cent.  Finally,  we  need  only  mention  the  fact  that 
Stas,1"'  in  his  classical  atomic  weight  work,  did  not  estimate  silver 
or  chlorine  gravimetrically  but  by  titration  by  the  method  of  Gay- 
Lussac.  Likewise.  Richards, 16  in  his  revision  of  Stas"  work,  esti- 
mated silver  and  chlorine  by  titration  with  the  aid  of  his  nephelom- 
eter.  It  is  thus  seen  that  the  experience  of  chemists  has  been 
that,  in  the  case  of  silver,  the  available  volumetric  methods  may 
even  exceed  in  accuracy  the  gravimetric  process ;  while  the  high 
value  of  the  latter,  as  a  means  for  standardizing  volumetric  solutions, 
has  been  expressed  by  more  than  one  author.17  If.  therefore,  we 
should  base  the  standardization  of  all.  or  at  least  most,  of  our 
10  C hem.  Eng.,  10,  204-206  (1909)- 
11  Morse :    Exercises  in' Quantitative  Chemistry  (1905),  p.  125. 
12  Vanino  and  Seitter  express  themselves  in  snch  connection  as  follows  : 
"  Hierher  zahlen  bekanntlich  die  elegantesten  und  genauesten  Methoden 
der  Maassanalyse.  wie  wir  solche  in  denjenigen  von  Gay-Lussac,  Mohr, 
Volhard,  und  Liebig  besitzen  und  welchen  sammtlich  eine — Silbernitratlosung 
— zu  Grunde  liegt." — Zcit.  anal.  Chem.,  41,  194,  (1902). 
13  Jour.  Chem.  Soc.  90,  ii,  894  (1906). 
"Jour.  Amer.  Chem.  Soc.,  29,  273  (1907). 
15  Richards:   Ibid,,  27,  461  (1905). 
10 Jour.  Amer.  Chem.  Soc.  27,  502-510  (1905). 
17  Parsons :  "  I  have  no  hesitancy,  when  convenience  is  also  taken  into 
consideration,  in  placing  the  determination  as  silver  chloride  at  the  head 
of  gravimetric  methods,"  for  standardization  purposes. — Jour.  Anal.  Chem.. 
6,  373S74  (1892).  Phelps  and  Hubbard:  "The  previously  most  valued 
standard — hydrochloric  acid  standardized  gravimetrically  as  silver  chloride." 
— Amer.  Jour.  Sci.,  23,  iv,  213  (1907). 
