BLACK  SANDS  FROM  PLACER  MINES.  161 
Pinder  concentrator,  installed  by  the  Joshua  Hendy  Machine  Works,  of  San  Francisco,  and  operated 
by  the  inventor,  Capt.  J.  W.  Pinder. 
Woodbury.concentrating  table,  installed  and  operated  by  the  inventor,  Mr.  George  E.  Woodbury,  of 
San  Francisco,  Cal. 
Christensen  concentrator,  installed  and  operated  by  the  inventor,  Mr.  C.  Christensen,  of  Orctown, 
Dreg. 
Wetherill  magnetic  separator,  type  E,  full  size,  loaned  by  the  Wetherill  Magnetic  Separator  Company 
of  New  York.  This  machine  has  been  arranged  to  be  operated  with  a  current  varying  from  0.015 
ampere  to  3.5  amperes.  It  was  operated  by  Mr.  Harmon  V.  Morse,  of  Johns  Hopkins  University,  and 
by  Mr.  Hermann  Gray. 
Knowles  magnetic  separator,  furnished  by  the  American  Contractor  Company,  of  Joplin  Mo.,  and 
operated  by  Mr.  Thomas  W.  Johnson. 
Three  forms  of  hydraulic  classifiers,  devised  by  Prof.  Robert  H.  Richards. 
'   Amalgamating  table,  devised  by  Prof.  Robert  II.  Pichards. 
Glass  table  with  greased  surface  for  the  separation  of  special  minerals  after  the  South  African  dia- 
mond method. 
Hendy  Challenge  ore  feeder,  loaned  by  the  Joshua  Hendy  Machine  Works. 
Set  of  Imperial  ore  screens,  loaned  by  Mr.  John  Traylor,  of  Denver,  Colo.,  and  operated  by  Mr.  Clifford 
L.  Gardiner. 
Merrill  ore  muller,  invented  and  operated  by  Mr.  I.  J.  Merrill. 
Laboratory  rock  crusher  and  laboratory  ore  pulverizer. 
The  capacity  of  this  equipment  is  a  carload  of  sand  in  eight  hours.  The  plant  is  also 
provided  with  mechanical  agitating  apparatus  for  bottle  amalgamation  with  sodium 
amalgam. 
Assay  laboratory. — An  assay  laboratory,  20  by  20  feet,  has  been  established.  Here  the 
following  apparatus,  partly  lent  and  partly  purchased  of  the  F.  W.  Braun  Company,  of  San 
Francisco,  Cal.,  and  of  Messrs.  Eimer  &  Amend,  of  New  York  City,  has  been  installed: 
No.  40  Braun's  combination  crucible  and  cupelling  furnace,  with  complete  blowpipe  appa- 
ratus and  Cary  hydrocarbon  burner;  the  necessary  crucibles,  cupels,  scorifiers,  fluxes,  etc., 
and  weighing  devices,  supplied  by  Eimer  &  Amend,  including  very  fine  pulp  and  button 
balances.  The  last-named  firm  has  also  supplied  a  small  electric  furnace  and  electric  hot 
plate.  All  the  necessary  chemicals  and  apparatus  for  making  simple  mineralogic  deter- 
minations are  found  here. 
Method  of  treatment. — Obviously  the  course  of  treatment  used  has  varied  greatly  with  the 
kind  of  sand.  These  sands  are  grouped  in  two  classes:  (1)  Sea  sands,  river  sands,  and  sand- 
dune  material;  and  (2)  low-grade  gravels,  tailings  from  dredges  and  placer  workings,  and 
richer  heavy  tailings  from  the  clean-up  of  dredges,  etc. 
The  method  of  treatment  of  class  1  consists  of  sampling  and  feeding  to  a  Hendy  automatic 
feeder,  from  which  it  is  elevated  to  the  roof  of  the  building,  where  the  sand  passes  over  the 
Traylor  screen,  with  holes  1  mm.  in  diameter.  The  oversize  is  examined  and  the  undersize 
is  delivered  to  an  automatic  distributor  which  divides  it  evenly  to  the  four  tables  through 
four  iron  pipes.  Each  of  these  machines  separates  the  sands  into  three  portions — concen- 
trates, middlings,  and  tailings.  All  of  the  concentrates  and  middlings  are  collected,  and 
samples  of  the  tailings  are  taken  every  five  minutes.  Samples  of  these  concentrates,  mid- 
dlings, and  tailings  are  dried  and  then  treated  by  the  system  devised  by  Mr.  Henry  E.  Wood, 
of  Denver,  Colo.,  by  which  the  sands  are  first  separated  on  the  Wetherill  magnetic  separator 
into  six  portions  by  five  successively  increasing  strengths  of  current.  The  strengths  of 
current  used  in  this  machine  are  such  as  to  group  together  in  separate  portions  (1)  mag- 
netite, (2)  chromite  and  ilmenite,  (3)  garnet;  (4)  olivine,  hypersthene,  and  similar  heavy 
silicates;  (5)  monazite,  and  (6)  a  nonmagnetic  residue  containing  zircon,  quartz,  iridium, 
iridosmium,  gold,  and  some  of  the  platinum. a  These  separations  are  the  result  of  many 
experiments  in  regard  to  the  magnetic  permeability  of  these  minerals,  carried  out  on  speci- 
mens obtained  from  mineral  dealers  in  the  East. 
Each  portion  is  then  carefully  examined  by  mineralogists,  and  where  complete  separation 
is  not  already  effected  the  proportion  of  different  minerals  unseparated  is  ascertained  as 
carefully  as  possible  under  the  microscope. 
a  Much  of  the  crude  platinum  found,  occasionally  60  per  cent,  is  removable  by  a  magnet. 
