ON  LEAD  CONTAINED  IN  SOME  SILVER  COINS. 
335 
ON  THE  AMOUNTS  OF  LEAD   CONTAINED  IN  SOME  SILVER 
COINS. 
By  Eliot  and  Storer. 
The  determination  of  the  amount  of  lead  in  American  silver 
coin  was  suggested  to  the  authors  hj  finding  half  of  one  per  cent 
of  lead  in  a  sample  of  zinc  such  as  is  used  at  the  United  States 
mint  for  reducing  chloride  of  silver.  (See  their  Memoir  on  the 
Impurities  of  Commercial  Zinc  in  Memoirs  Amer.  Acad.  [N.  s.], 
viii.  61 ;  also  this  Journal  [2],  xxxi.  142).  For  the  sake  of 
comparison  other  coins  were  subsequently  examined. 
Per  cent  of  Lead 
Kin  1  of  coin.  in  the  coin. 
1  American  half-dollar  of  1824,  .  .  .  0-310 
20  "  five-cent  pieces  of  1853,  .  .  0-209 
10  ten-cent  of  1854,         .       .  0-228 
2  "  twenty-five  cent  pieces  of  1858,  .  0-231 
Fine  Silver"  from  the  U.  S.  Assay  Office  in  N.  York,  1860,  0  161 
1  Spanish  dollar  of  1798,  Carolus  IV.      .       .  0-056 
1  Mexican  1829,        ....  0-043 
2  English  Shillings  of  1816,    ...       -  0-485 
1  French  five-frauo  piece  of  1852,  Napoleon  III.  0-428 
On  the  supposition  that  the  zinc  used  in  the  reduction  of  the 
silver  is  the  source  of  the  lead  in  the  American  coin,  the  au- 
thors calculate  the  amount  of  lead  which  would  thus  find  its  way 
into  the  coin.  Their  memoir,  already  cited,  gives  the  per  cents 
of  lead  found  in  two  specimens  of  Vieille  Montague  zinc  ;  if 
zinc  of  the  best  quality  (containing  0-292  per  cent  of  lead)  had 
been  used,  the  silver  coin  would  have  contained  0-158  per  cent 
of  lead;  if  the  second  quality  (containing  0-494  per  cent  of 
lead)  had  been  employed,  the  coin  would  have  contained  0-268 
per  cent  of  lead.  Between  these  two  limits  all  their  determina- 
tions of  lead  in  American  silver  coins  lie.  In  offering  this  ex- 
planation of  the  occurrence  of  lead  in  American  silver  coin,  the 
authors  would  by  no  means  affirm  that  the  zinc  is  the  exclusive 
source  of  this  impurity,  for  it  is  not  at  all  improbable  that  a  por. 
tion  of  the  lead  is  derived  from  the  leaden  vats  in  which  the  re- 
duction of  the  chloride  of  silver  is  effected,  or  from  the  sulphu- 
ric acid  which  is  used  to  excite  the  reaction.  The  process  of 
analysis  was  such  as  to  permit  the  separation  of  the  gold  con- 
tained in  each  kind  of  coin.  A  distinct  button  of  metallic  gold 
was  obtained  in  every  instance,  before  the  blowpipe,  but  the 
amount  of  gold  varied  to  a  considerable  extent;  it  was  abun- 
