370 
rochleder's  proximate  analysis. 
part  does  not.  A  part  of  the  lead  compound  insoluble  in  water,  dissolves 
in  alcohol ;  on  the  contrary,  a  part  of  the  lead  compound,  insoluble  in 
spirit,  dissolves  in  water.  By  the  decomposition  of  lead  compounds  which 
are  precipitated  from  their  watery  solutions  by  alcohol,  and  by  the  de- 
compositions of  lead  compounds  which  are  precipitated  from  their  alco- 
holic solutions  by  water,  the  separation  of  substances  is  effected  which 
were  contained  in  the  lead  precipitates  together  at  the  same  time.  When 
the  decomposition  is  performed  with  sulphuretted  hydrogen,  the  sulphuret 
of  lead,  like  charcoal,  retains  often  one  or  more  of  the  constituents,  while 
other  constituents  pass  over  into  the  fluid  in  which  the  lead  compound 
was  diffused  before  treatment  with  sulphuretted  hydrogen. 
6.  Basic  acetate  of  lead. — In  general,  what  has  been  stated  of  the  neu- 
tral acetate  of  lead  is  applicable  to  this  reagent.  A  number  of  substances 
which  are  not  precipitated  by  the  neutral  salt,  give  insoluble  compounds 
by  the  addition  of  subacetate  of  lead  to  their  watery  or  spirituous  solution.. 
As  many  organic  substances  which  have  a  great  tendency  to  reduce  the 
oxides  of  the  noble  metals,  and  in  combination  with  alkalies  and  alkaline 
earths  absorb  oxygen  from  the  air,  form  with  lead  compounds  which  are 
less  subject  to  such  changes,  both  the  lead  salts  are  more  suitable,  in  many 
cases,  than  other  metallic  salts  to  effect  the  decomposition  and  separation 
of  substances.  Concerning  the  basic  acetate  of  lead,  it  is  particularly  to 
be  mentioned  that  it  precipitates  substances  from  acid  solutions  because 
it  saturates  the  free  acid,  and  is  converted  into  the  neutral  salt. 
These  substances  are  per  se  insoluble  in  the  fluid,  and  are  only  dissolved 
therein  by  the  agency  of  an  acid,  so  that  the  precipitate  may  contain  sub- 
stances which  do  not  form  compounds  with  oxide  of  lead. 
7.  Acetate  of  copper  can  be  used  in  many  cases  as  the  neutral  acetate  of 
lead,  but  seldom  offers  any  advantage  over  it. 
8.  Sulphate  of  copper  is  employed  in  the  same  cases  in  which  acetate  of 
copper  or  acetate  of  lead  is  used,  when  the  presence  of  acetic  acid  should 
be  prevented  in  the  fluid,  because  the  sulphuric  acid  which  is  here  intro- 
duced into  the  fluid  by  the  reagent  can  be  more  easily  and  quickly  re- 
moved than  acetic  acid.  The  application  of  sulphate  of  copper  for  dis- 
tinguishing grape  sugar  and  milk  sugar  from  gum-cane  sugar,  and  anal- 
ogous bodies,  is,  of  course,  well-known ;  but  I  may  mention  that  the  alka- 
line solution  of  copper  as  a  reagent  demands  great  care,  because  many  sub- 
stances effect  a  reduction  and  separation  of  the  suboxide  of  copper,  like 
grape  sugar  or  milk  sugar ;  on  the  contrary,  other  substances  have  not 
this  reaction. 
9.  Chloride  of  platinum,  and 
10.  Bichloride  of  mercury . — These  salts  serve  for  the  detection  and  sep- 
aration of  organic  bases.  (For  the  same  object,  under  certain  conditions, 
infusion  of  galls,  nitro-picric  acid,  and  sometimes  sulpho-cyanuret  of  pot- 
assium are  employed.) 
