264    PRODUCTION  OF  NITRATE  OF  SODA  AT  IQUIQUE  (PERU). 
ning  parallel  with  it  through  the  province,  at  an  elevation  of 
3300  feet,  or  there  about,  is  the  Pain  pa  of  Taramugal.  This 
plain  or  pampa  was  a  sea  lake,  and  the  greater  part  is  covered 
with  salt  along  the  western  border ;  and  generally  not  extend- 
ing eastwards  more  than  500  yards  to  the  verge  of  the  old 
lake  is  found  the  "  caleche"  or  "  terra  salitrosa,"  rough  nitrate. 
Between  the  pampa  and  the  coast  exist  other  old  sea  lakes,  on 
the  borders  of  which  "  caleche  "  is  also  found  ;  but  these  deposits 
are  of  secondary  import.  The  "caleche  "  is  generally  found  in 
insulated  masses,  irregular  in  shape  and  thickness,  which  adds 
greatly  to  the  expense  of  working.  It  is  sometimes  found  with 
only  a  few  inches  of  sand  over  it,  but  more  frequently  covered 
with  a  hard  stone,  consisting  of  sand  indurated  with  salt  ;  this 
is  called  "  costra,"  the  thickness  of  which  varies  from  one  to  ten 
feet,  but  averages  three  feet.  The  «  caleche  "  varies  in  thick- 
ness from  one  to  nine  feet,  but  in  general  runs  from  three  to 
four  feet ;  below  this  exists  a  soft  sand,  containing  an  abundance 
of  crystals  of  glauberite  and  small  quantities  of  borates  of  lime 
and  soda.    The  strata  consists  of — 
1.  Loose  sand,  a  few  inches  thick. 
2.  Hard  sand,  indurated  with  salt,  from  one  to  ten  feet  thick, 
3.  "  Caleche,"  from  one  to  nine  feet  thick. 
4.  Soft  sand  or  cora. 
The  "  caleche  "  varies  in  quality  from  nearly  pure  salt  to  50 
and  60  per  cent,  of  nitrate,  generally  containing  the  following 
substances  :  Earthy  matter,  Nitrate  of  Soda,  Chloride  of  Sodium 
Sulphate  of  Soda,  Sulphate  of  Lime,  and  traces  of  Chloride  of 
Magnesium,  and  Iodides  and  Bromides. 
It  is  impossible  to  state  the  respective  proportions,  as  they 
vary  with  every  different  sample  The  method  of  extracting  and 
refining  nitrate  of  soda  is  as  follows  : — 
When  "caleche"  is  required,  the  barretero  (miner)  makes 
holes  in  the  ground  where  he  expects  to  find  it.  If  successful, 
he  fills  up  the  holes  with  coarse  gunpowder  made  on  the  spot 
(costing  three  and  a-half  dollars  per  quintal),  regulating  the 
charge  in  proportion  to  the  thickness  and  hardness  of  the 
14  costra  "  and  the  thickness  of  the  "  caleche;"  the  charge  varies 
from  one  to  eight  quintals,  and  occasionally  as  much  as  fourteen 
quintals  ;  when  blasted  the  whole  mass  is  turned  over  and  mixed. 
