22 
Ammonio-nitrate  of  Silver. 
Am.  Jour.  Pharm 
Jan.,  1887. 
one  can  distinguish  the  coloration  due  to  santonin  from  that  which 
chrysophanic  acid  produces  by  adding  caustic  soda  to  the  urine  and 
then  shaking  up  with  amy  lie  alcohol.  When  the  coloration  proceeds 
from  santonin,  the  coloring  matter  passes  almost  entirely  into  the  alco- 
hol, and  the  urine  is  decolorized,  whilst,  if  the  color  is  due  to  chryso- 
phanic acid,  the  alcohol  takes  up  only  traces,  and  the  urine  remains 
red.  On  the  contrary,  if  the  urine  is  acidulated,  the  chrysophanic 
acid  can  be  taken  up  by  the  amylic  alcohol ;  if  one  then  shakes  this 
dissolvent  with  ammoniated  water,  the  aqueous  layer  becomes  red. 
Under  the  same  conditions  the  coloring  matter  proceeding  from  santo- 
nin is  not  taken  up.  The  spectrum  of  these  two  products  totally  dif- 
fers.— Berliner  klinische  Wochenschrift.    Med.  Chronicle,  Oct.  1886. 
AMMONIO-NITRATE  OF  SILVER. 
By  Harry  Napier  Draper,  F.C.S.,  M.R.I. A. 
It  is  not  a  little  remarkable  that  the  phenomena  attendant  upon  so 
familiar  a  process  as  the  preparation  of  a  solution  of  silver  ammonio- 
nitrate  should  remain  absolutely  unnoticed  by  the  text-books.  One 
of  the  most  recent  and  best  of  these  indeed  warns  the  student  against 
the  evaporation  of  the  liquid  "  as  there  is  a  risk  of  producing  an 
explosive  body/7  and  only  one  chemist,  as  far  as  I  can  find,  has  ven- 
tured upon  an  opinion  as  to  the  nature  of  the  precipitate  formed  on  the 
addition  of  ammonia  to  silver  nitrate.  Prescott1  looks  upon  it  as 
(NH3Ag)20  ;  admitting,  however,  that  this  formula  is  merely  hypo- 
thetical. 
I  cannot  think  that  it  will  be  uninteresting  if  I  shortly  state  the 
circumstances  under  which  some  years  ago  my  attention  was  directed 
to  this  subject.  There  is  a  very  excellent  and  frequently  used  method 
of  glass  silvering  particularly  applicable  to  the  production  of  telescopic 
specula,  which,  shortly  described,  consists  in  the  reduction  by  milk 
sugar  of  an  ammoniacal  solution  of  silver  nitrate  to  which  potassium 
hydrate  has  been  added. 
1  Journal  of  American  Chemical  Society,  and  Chemical  News,  vol.  xlii.,  p.  31. 
