rochleder's  proximate  analysis. 
471 
small  quantity  of  washings,  is  mixed  with  pure  white  lead  into  a  paste,  and 
gently  hented  for  a  short  time.  The  white  color  of  the  milky  fluid  begins 
to  pass  into  a  reddish  grey  by  the  decomposition  of  the  phosphate  of  silver, 
which  is  soluble  in  a  small  quantity  in  water.  The  fluid  filtered  from  the 
insoluble  contents  is  freed  from  a  trace  of  lead  by  sulphuretted  hydrogen, 
separated  from  sulphuret  of  lead  by  filtration  and  evaporated  in  a  water- 
bath.  If  sugar  has  formed  by  the  treatment  with  hydrochloric  acid,  it  is 
obtained  as  a  syrupy  sweet  mass,  which  crystallizes  after  standing  some 
days,  but  requires  occasionally  some  weeks. 
When,  by  the  treatment  with  hydrochloric  acid  in  the  heat,  no  decomposi- 
tion products  insoluble  or  difficultly  solublehawe  separated,  and  in  the  re- 
ceiver furnished  with  a  refrigeratory  apparatus,  no  volatile  products  are  to 
be  found,  then  either  no  decomposition  has  ensued,  or  both  the  decompo- 
sition products  are  easily  soluble  in  the  water  containing  hydrochloric.  To 
discover  whether  soluble  decomposition  products  have  been  produced,  the 
acidulated  fluid  is  mixed  with  dry  carbonate  of  lead  as  long  as  eflFervescence 
results  by  the  addition  of  a  fresh  quantity  of  the  carbonate.  The  hydro- 
chloric acid  has  a  decomposing  action  on  the  carbonate  of  lead,  and  forms 
chlorideof  lead  under  the  development  of  carbonic  acid.  The  decompo- 
sition products  of  indifi'erent  copulated  compounds  do  not  attack,  in  the 
cold,  carbonate  of  lead  in  the  majority  of  cases,  because  a  strong  organic 
acid  seldom  results  from  the  decomposition  of  these  bodies.  Only  in  the 
heat  do  these  bodies  decompose  carbonate  of  lead.  On  the  contrary,  they 
decompose  more  readily  the  freshly  precipitated  moist  carbonate  of  lead, 
or  that  preserved  in  a  pasty  wet  state  after  precipitation.  The  chloride  of 
lead  is  filtered  from  the  liquid,  and  thus  much  hydrochloric  acid  is 
separated.  The  fluid  is  now  concentrated  in  a  water-bath,  whereby, 
especially  after  cooling,  the  greater  part  of  the  chloride  of  lead  contained 
in  the  fluid  separates.  I'he  separated  chloride  of  lead  is  filtered  ofi",  dried, 
after  it  has  been  well  pressed  between  bibulous  paper  frequently  renewed, 
and  now  heated  to  learn  whether  it  is  mixed  with  an  organic  substance, 
which  is  generally  not  the  case.  Should  anorganic  lead  compound  be  ad- 
mixed with  chloride  of  lead,  it  is  ascertained  whether  it  can  be  extracted 
with  alcohol  from  the  chloride  of  lead,  wherein  the  latter  is  insoluble.  When 
the  organic  lead  compound  is  not  soluble  in  alcohol,  the  chloride  of  lead 
mixed  with  the  organic  lead  compound  must  be  decomposed  under  water 
by  sulphuretted  hydrogen,  by  which  means  the  organic  substance  and 
hydrochloric  acid  are  obtained  in  the  fluid  filtered  from  the  sulphuret  of 
lead.  A  small  quantity  of  this  fluid  is  mixed  with  baryta  water,  to  ascer- 
tain whether,  besides  chloride  of  barium,  which  remains  in  solution,  a 
baryta  compound  of  the  organic  substance,  insoluble  in  water,  results. 
When  this  is  the  case,  the  solution  containing  chloride  of  barium  is  filtered 
from  the  baryta  compound,  which  is  washed  with  water,  and  the  organic 
body  which  was  combined  with  the  baryta,  that  is,  the  pure  decomposition 
product,  is  obtained  by  decomposing  the  baryta  compound  with  dilute  sul- 
