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A  NEW  PRECIPITANT  FOR  THE  ALKALOIDS. 
times  taken  advantage  of  as  an  indication  of  the  age  of  the  port. 
The  difference  arises  partly  from  a  gradual  change  that  takes 
place  in  the  coloring  matter  of  the  wine,  partly  also  on  the  di- 
minished thickness  of  the  film  that  constitutes  the  bubble  of  the 
older  and  "thinner"  wine.  If  old  port  be  placed  in  a  hollow 
glass  wedge,  and  thus  interposed  between  the  eye  and  a  slit  in 
the  window-shutter,  in  such  a  way  that  the  line  of  light  is  seen 
traversing  the  different  thicknesses  of  the  liquid,  that  line  will 
appear  white  where  the  stratum  is  thinnest,  and  will  become  red 
very  suddenly  as  the  stratum  increases ;  almost  as  intensely  red, 
in  fact,  as  when  the  thickness  is  considerable ;  and  if  this  line 
of  light  be  analysed  by  a  prism,  it  will  be  seen  that  every  ray  of 
the  spectrum  traverses  the  thin  stratum,  but  that  suddenly  they 
are  cut  off,  all  at  very  nearly  the  same  distance,  with  the  ex- 
ception of  the  red  ray  and  a  portion  of  the  orange,  which  are 
transmitted  through  almost  any  amount  of  liquid. 
Some  bubbles,  as  is  well  known,  exhibit  that  beautiful  pheno- 
menon designated  "the  colors  of  thin  plates,"  or  "Newton's 
rings."  This  is  most  strikingly  displayed  by  the  froth  on  the 
surface  of  the  black  liquid  produced  by  adding  a  few  drops  of 
sulphuric  acid  to  oil  of  turpentine ;  the  play  of  colors  is  beau- 
tifully relieved  against  the  black  background  London  JPharm. 
Journ.,  from  London,  Edinburgh,  and  Lublin  Philosophical 
Magazine. 
A  NEW  PRECIPITANT  FOR  THE  ALKALOIDS. 
By  M.  Sonnenschein. 
Phospho-molybdic  acid  forms  with  ammonia,  in  acid  solutions, 
a  remarkably  insoluble  compound,  and  it  comports  itself  in  a 
singular  manner  with  those  compounds  which  are  analogous  to 
ammonia — the  nitrogenized  organic  bases — consequently  forming 
an  excellent  reagent  for  their  detection.  It  may  be  prepared  in 
the  following  manner: — 
Molybdate  of  ammonia  is  precipitated  by  phosphate  of  soda ; 
the  yellow  precipitate,  having  been  washed,  is  diffused  through 
water,  and  heated  with  sufficient  carbonate  of  soda  to  dissolve  it. 
The  solution  is  then  evaporated  to  dryness,  and  calcined  to  drive 
off  the  ammonia.    In  case  any  of  the  molybdic  acid  should  be 
