150  Paints,  Colors  and  their  Analysis.  {AmxS'I?7h8a.rm' 
These  results,  like  the  preceding  analysis  of  coal  oil  blue,  lead  to 
the  following  working  formula  I,  while  a  sample  made  by  a  Pittsburg, 
firm  showed  the  composition  II. 
I.  II. 
Whitening,  .  .  .60  per  cent.  46  per  cent. 
Zinc  white,        ...  36  50 
Prussian  blue,  ...      4  4 
Yellow  Paints.  — Plumbic  chromate  is  the  most  prominent  color- 
ing constituent  of  these  paints.  Light  shades,  as  "canary,"  "  lemon," 
etc.,  are  obtained  either  by  admixture  of  white  substances  on  grinding, 
as  previously  mentioned,  or,  for  finer  brands,  by  precipitating  the  lead 
solution  (nitrate,  in  some  cases  acetate)  by  mixtures  of  potassic  bichro- 
mate and  alum  solutions,  thus  producing  mixed  precipitates  of  very 
finely  divided  plumbic  sulphate  and  chromate,  which  afterwards  can  be 
further  u  thinned  down  "  on  grinding.  The  more  dilute  the  solutions 
the  more  tender  and  finer  is  the  shade  of  the  product.  Acetic  solu- 
tions give  a  deeper  yellow  precipitate  than  those  of  plumbic  nitrate. 
Temperature,  dilution  and  the  mode  of  precipitation  also  exert  great 
influence  on  the  quality  of  the  product,  more  marked  in  this,  although 
generally  observed  in  the  manufacture  of  all  colors.  A  sample  of  com- 
mercial chrome-yellow  analyzed  as  follows  : 
Moisture,         .....      0-150  per  cent. 
Baric  sulphate,         ....  47*050 
Plumbic  sulphate,  ....  7*205 
Plumbic  chromate,   ....  45*849 
Gypsum,  ....  traces 
10C254 
Orange  shades  are  obtained  by  boiling  the  yellow  precipitate  with 
caustic  soda,  whereby  a  basic  chromate  is  formed.  Other  inorganic 
yellow  pigments,  as  baric  chromate,  cadmium  sulphide,  arsenic  sul- 
phide, etc.,  have  but  very  limited  application,  the  latter  on  account  of 
its  poisonous  qualities. 
Red  Paints. — Vermillion,  or  mercuric  sulphide,  and  chrome-red, 
or  so-called  American  vermillion,  a  very  basic  plumbic  chromate,  are 
extensively  used  in  painting,  the  latter  for  agricultural  implements,  the 
carriages  of  fire-engines,  etc. 
Vermillion  is  prepared  by  shaking  mercury  in  iron  flasks  with  solu- 
tions of  alkali-polysulphurets,  or  caustic  soda,  and  flowers  of  sulphur. 
The  shaking  is  done  by  machinery,  and  lasts  for  several  hours,  when 
