IMPURITIES  OF  COMMERCIAL  ZINC. 
403 
A  qualitative  examination  of  the  residue  left  by  these  zincs, 
when  treated  with  dilute  acids,  showed  that  they  consisted 
chiefly  of  metallic  lead.  In  fact  the  authors  have  arrived  at  the 
conclusion,  that  lead  is  the  chief  impurity  in  commercial  zinc, 
and  that  carbon,  tin,  copper,  iron,  arsenic  and  other  impurities 
found  in  it  by  previous  observers,  occur  either  in  very  minute 
quantities,  or  rarely  and  doubtless  accidentally. 
Lead.  — The  authors  found  the  following  percentages  of 
metallic  lead,  estimated  as  sulphate,  using  diluted  S03  saturated 
with  sulphate  of  lead,  as  the  solvent  of  the  zinc,  and  treating  the 
insoluble  residue  with  diluted  N05  and  washing  it  well. 
Names  of  Zinc. 
Wt.  of  Zinc  taken. 
Wt.  of  Lead  obtained. 
Percent,  of  le? 
1.  Silesian, 
23.8066  grammes. 
0.3472 
1.460 
2.  Vieille  Montagne, 
25.2795  " 
0.0738 
0.292 
3.  New  Jersey, 
28.672  " 
0.0225 
0.079 
4.  Pennsylvania,* 
26.522  " 
0.0000 
0.000 
5.  U.  S.  Mint, 
6.  Rousseau  Freres, 
24.5308 
0.1212 
0.449 
24.3432 
0.0259 
0.106 
7.  Berlin, 
23.074  " 
0.2990 
1.297 
8.  Wrexham, 
9.  Mines  Royal, 
29.999 
0.3569 
1.192 
38.8276 
0.3197 
0.823 
10.  Dillwyn  &  Co., 
31.6425 
0.5256 
1.661 
11.  Messrs.  Vivian, 
27.724 
0.4203 
1.516 
The  authors  carefully  verified  their  processes  for  estimating 
the  lead  by  determining  the  S03  in  each  specimen  of  sulphate ; 
and  also  answered  the  question,  whether  the  use  of  diluted  S03 
saturated  with  sulphate  of  lead  would  introduce  lead  into  the 
result,  satisfactorily  in  the  negative. 
Cadmium  and  Tin. — The  filtrates  from  the  precipitates  of 
sulphate  of  lead  of  the  several  zincs  enumerated  above,  except 
that  from  Pennsylvania,  were  saturated  with  sulphuretted  hydro- 
gen for  twenty-four  hours  or  upwards,  and  the  small  precipitates 
which  separated  were  filtered  off,  washed  quickly  with  sulphur- 
etted hydrogen  water,  dried  and  ignited  ;  they  were  then  treated 
with  a  few  drops  of  nitric  acid,  again  evaporated  to  dryness, 
ignited  and  weighed.  The  color  of  these  precipitates  was  yellow- 
ish brown,  except  that  from  New  Jersey  zinc,  which  was  black- 
ish, owing  to  the  copper  it  contained  as  afterwards  ascertained. 
The  authors  determined  the  absence  of  arsenic  and  antimony, 
and  the  precipitates  were  therefore  the  oxides  of  tin  or  cadmium, 
or  both.  The  amounts  of  these  precipitates  from  the  same 
weights  of  zinc,  as  in  the  table  above,  and  in  the  same  order, 
*  This  Zinc  gave  no  residue. 
