146  Paints,  Colors  and  their  Analysis.     { %Jpcn^s?8arm' 
acid  with  plumbic  oxide,  and  precipitating  the  latter  by  carbonic  acid, 
prepared  from  lime-stone  or  marble  dust  and  muriatic  acid.  The  pro- 
duct of  the  Dutch  process  is  a  mixture  of  plumbic  oxyhydrate  and  car- 
bonate in  varying  proportions,  that  of  the  French  process  an  almost 
pure  carbonate.  The  gloss  and  brilliancy  of  the  pigment  is  chiefly 
due  to  the  plumbic  carbonate,  while  the  oxyhydrate  increases  its  body. 
Representatives  of  the  second  class  are  very  frequently  met  with  in  the 
trade,  containing  from  10  to  50  per  cent,  of  "  pure  white  lead,"  the 
remainder  being  substituted  by  oxide  of  zinc,  plumbic  sulphate,  chalk, 
whitening,  gypsum,  barytes  (BaS04),  clay,  etc. 
The  following  "  white  lead  "  may  fairly  represent  the  third  class  :  . 
Calcic  carbonate,            .          .           .  14  800  per  cent. 
Zinc  oxide,    ....  60*500 
Baric  sulphate,    ....  19*400 
Silicic  acid,    ....  i"35° 
Iron  and  alumina,           .           .           .  2*300 
Lime  (in  insoluble  residue),             .  0  560 
Sulphuric  acid  (in  HC1  sol.),       .           .  1*710 
Plumbic  oxide  (as  PbSOJ,  .    slight  trace. 
I00'620 
Insoluble  residue  in  hydrochloric  acid,  21*50  to  21*57  per  cent. 
It  is  evident  that  this  latter  "  white  lead  "  was  prepared  by  mixing 
and  grinding  together  whitening  15,  barytes  25  and  zinc  white  60 
parts.  Silicic  acid,  iron,  alumina  and  the  insoluble  portion  of  lime  are 
frequent  impurities  in  barytes.  Plumbic  oxide  is  very  often  found  in 
commercial  zincs,  in  quantities  varying  from  one-half  to  10  per  cent., 
as  we  will  see  later.  As  the  term  "  white  lead  "  has  become  almost 
synonymous  with  "  white  paint,"  it  will  suffice  to  state  that  numerous 
combinations  and  mixtures  of  all  the  white  pigments  mentioned,  are 
sold  partly  as  liquid,  or  ready  mixed  paints,  or  brought  in  the  market 
as  dry  colors  in  form  of  powder  or  ground  in  oil.  In  the  following  I 
add  a  few  analyses  of  "zincs,"  as  they  are  found  in  our  present 
market  : 
1.  Sample. 
Very  fine  white,  best  quality. 
Moisture,  0*4     per  cent.  Zinc  oxide,  99*1720  per  cent. 
Sulphuric  acid,      0*0122  Sulphate  zinc,  00243 
Zinc  oxide,         99*4  Sulphite  zinc,  0*3870 
Sulphurous  acid,   0*1711  Moisture,  0*4000 
99^833 
Contained 
traces 
of  iron. 
99'9833 
