A\l™\*£rm'}     Paints,  Colors  and  their  Analysis.  147 
2.  Sample.  3.  Sample. 
Zinc  oxide  (uncombined),  98-298  per  cent.        Moisture,  o  636  per  cent. 
Zinc  oxide  (combined),  0*270                     Sulphurous  acid,  o  627 
Sulphuric  acid,  0*375                     Sulphuric  acid,  4*656 
Sulphurous  acid,  0-122                     Plumbic  oxide,  5*453 
Lime  (as  sulphate),  0-123                     Zinc  oxide,  88  254 
Trace  of  iron,                                                 Lime  and  iron,  trace. 
9918"  99-676 
5 -453  per  cent.  PbO  is  equal  to  7*41  per  cent.  PbSC)4,  and  of  the 
sulphurous  acid  0*1125  per  cent,  was  combined,  and  0*5145  per  cent, 
mechanically  absorbed. 
Lime,  gypsum,  plumbic  sulphate  and  sulphurous  acid  are  accidental 
impurities  due  to  the  process  of  manufacture  and  depending  also  on 
the  quality  of  the  ore  from  which  the  zinc-white  is  directly  prepared. 
In  some  of  the  samples — particularly  in  moist  ones — the  larger  por- 
tion of  the  sulphurous  acid  is  merely  mechanically  absorbed  or  enclosed, 
and  can  be  expelled  with  the  moisture  by  heating  on  the  water  bath. 
In  the  course  of  time,  however,  zinc  sulphite,  ZnS03,  is  formed, 
which,  finally,  is  converted  into  zinc  sulphate  ZnS04.  If  such 
zincs  "  containing  sulphuric  acid  are  used  for  the  adulteration  of 
white  lead,  plumbic  sulphate  is  formed,  which  may  considerably  alter 
the  quality  of  the  paint.  A  patent  white  paint,  said  to  be  manfactured 
by  precipitating  zinc  sulphate  with  baric  sulphite,  analyzed  as  follows  : 
Baric  sulphate,  .  .  .  60*83  Per  cent. 
Zinc  sulphite,       .  .  .  .  32*28 
Zinc  oxide,     ....  6*88 
99*99 
That  "  pure  zincs,"  like  "  white  lead,"  are  sometimes  adulterated, 
may  be  illustrated  by  the  following  analysis : 
Baric  sulphate,  .  .  54*200  per  cent. 
Zinc  oxide,  .  .  .  44*300 
Sulphuric  acid,  .  .  .         0  788 
Lead,  lime  and  alumina,  .  .  traces. 
99-288 
It  is  evident  that  the  practical  working  formula  for  making  this  zinc- 
white  was  :  barytes,  55  and  zinc  (ZnO),  45  parts.  Besides  the  brands 
mentioned  there  are  numerous  white  paints  perfectly  free  from  lead  and 
zinc,  consisting  of  mixtures  of  China  clay,  barytes,  whitening,  etc. 
Blue  Colors  and  Paints. — The  most  prominent  pigments  of  this 
