^'^oS.'T.mrl  White  Lead  Ground  in  Linseed  Oil.  469 
lead  is  mixed  with  oil,  it  becomes  more  difficult  to  ascertain  the  exact 
nature  of  the  adulterations,  since  the  methods  which  must  be  adopted 
in  order  to  destroy  the  oil,  (viz. :  incineration,  or  boiling  with  hydro- 
chloric acid,  and  gradually  adding  chlorate  of  potassa),  will  alter  to 
a  greater  extent  the  forms  of  combination  in  which  the  substances 
exist,  and  the  analyst  must  content  himself  with  merely  identifying 
the  different  acids  and  bases ;  the  quantities  of  these  will,  however, 
guide  him  in  his  conclusions  as  to  the  really  important  adulteration. 
Probably  by  powerful  pressure  in  blotting  paper,  between  hot  iron 
plates,  the  oil  might  be  so  far  extracted  as  to  allow  of  the  application 
of  the  ordinary  method  of  testing." 
But  such  a  process  would  be  altogether  too  tedious,  and  I  would 
suggest  the  following  plan  :  If  you  have  a  sample  of  white  lead  ground 
in  oil,  and  you  wish  to  test  it,  it  is  not  necessary  to  make  a  thorough- 
ly accurate  chemical  analysis  of  it,  all  you  want  is  the  detection  of 
one  or  more  probable  impurities,  and  these  generally  are  sulphate  of 
baryta,  sulphate  of  lead,  sulphate  of  lime,  (plaster  paris),  and  carbon- 
ate of  lime,  (chalk).  The  sulphate  of  baryta  is  almost  universally 
employed  in  adulterating  white  lead ;  in  fact  that  is  what  it  seems  to 
be  created  for,  and  the  manufacturer  of  white  lead  readily  takes  the 
advantage  of  the  whiteness,  the  fineness,  the  weight,  and,  above  all, 
the  cheapness  of  sulphate  of  baryta  ;  all  it  lacks  is  the  opacity,  com- 
monly termed  the  body,  for  it  does  not  cover  well. 
The  way  to  proceed  then,  is  as  follows :  Take  a  small  precipitating 
bottle,  weigh  it,  and  introduce  in  it  a  certain  quantity  of  the  white 
lead  ground  in  oil.  Then  add  about  four  times  the  quantity  of  ether, 
shake  frequently  till  all  oil  is  dissolved,  decant  and  add  another 
small  quantity  of  ether,  shake  again,  decant  and  repeat  the  operation 
till  a  few  drops  of  the  ether  used  will  not  stain  a  sheet  of  white  paper 
on  evaporating.  Collect  all  the  ether  used,  evaporate,  and  the  oil  is 
left  as  residue ;  weigh  it  and  calculate  the  percentage  of  oil  in  the 
white  lead.  Now  warm  the  bottle  with  the  dry  white  lead  in  it,  so  as 
to  eliminate  all  the  ether,  then  weigh  it,  and  the  difference  of  weight 
before  and  after  digestion  with  ether  must  be  equivalent  to  the  amount 
of  oil  extracted. 
To  the  powder  obtained,  add  a  little  nitric  acid  diluted  with  three 
times  its  volume  of  pure  water.  White  lead  being  a  basic  carbonate  of 
lead,  its  carbonic  acid  will  be  expelled  and  nitrate  of  lead  will  be  the 
compound  in  solution. 
