404 
IMPURITIES  OF  COMMERCIAL  ZINC. 
omitting  the  Pennsylvania  zinc,  are  as  follows  :    The  numbers 
giving  the  amount  of  the  precipitates  per  cent,  of  the  zinc 
treated. 
No.    1.  0.0564  No.    7.  0.0178 
No.    2.  0.0281  No.    8.  0.0070 
No.    3.  0.4471  No.    9.  0.0041 
No.  5.  0.0098  No.  10.  0.0035 
No.   6.  0.0406  No.  11.  0.0285 
Of  these  samples,  numbers  1,  5,  6,  8,  9  and  10,  contained 
none  or  but  faint  traces  of  tin,  whilst  the  others  gave  distinct 
spangles  of  tin  by  the  blow-pipe  test. 
Copper. — None  of  the  specimens,  but  that  from  New  Jersey, 
gave  the  slightest  evidence  of  the  presence  of  copper,  and  that 
was  found  to  contain  0.1298  per  cent,  of  that  metal. 
Iron. — The  authors  examined  three  of  the  samples  for  this 
metal,  but  did  not  feel  it  needful  to  push  them  further,  as  pub- 
lished experiments  already  show  that  its  proportion  rarely 
exceeds  two-tenths  of  one  per  cent.  They  found  0.2088  per 
cent,  in  the  New  Jersey  zinc ;  0.0586  in  the  mint  zinc ;  and 
0.674  in  the  Berlin  (sheet)  zinc. 
Carbon. — The  authors  after  some  carefully  conducted  experi- 
ments, have  arrived  at  the  conclusion  that  carbon  is  much  more 
rarely  a  constituent  of  commercial  zinc  than  has  been  frequently 
believed,  as  their  very  accurate  experiments  gave  hardly  a  trace 
of  evidence  in  favor  of  its  presence. 
Sulphur. — The  authors  found  sulphur  present  in  each  of  the 
specimens  enumerated  by  adding  ten  or  fifteen  grammes  of  each 
zinc  to  a  mixture  of  chloride  of  calcium  and  pure  muriatic  con- 
tained in  a  small  flask,  the  neck  of  which  contained  paper  mois- 
tened with  alkaline  acetate  of  lead.  Every  precaution  was 
taken  to  avoid  sulphur  in  the  agents  used,  as  described  at  length, 
in  the  authors'  memoir. 
Arsenic. — The  authors  have  very  thoroughly  investigated  the 
subject  of  arsenic  as  an  ingredient  of  commercial  zinc,  and  to 
assure  themselves  of  the  accuracy  of  their  experiments  have 
investigated  the  American  acids  with  a  view  to  the  same  impur- 
ity. The  authors  believe  that  the  general  opinion  that  arsenic 
is  a  very  common  impurity  in  commercial  zinc  may  be  traced  to 
Proust,  who,  with  others,  long  before  the  discovery  of  cadmium 
