Am-JJu7vr;1f92frm-}  Infusion  of  Digitalis.  363 
Since  that  time,  my  experiments  have  led  me  to  modify  the 
original  formula,  but  none  of  the  then  expressed  views.  These  modi- 
fications consist  simply  in  the  addition  of  a  small  quantity  of  ammo- 
nia water,  and  a  reduction  of  one-third  of  the  amount  of  alcohol 
ordered. 
Before  considering  the  new  formula  let  us  consider,  briefly,  a 
number  of  changes  which  the  official  infusion  undergoes  when  sub- 
jected to  certain  reagents.  The  freshly  made  infusion  is  weakly  acid 
in  reaction,  and  requires  the  immersion  of  the  litmus  paper  for  a 
moment  before  the  change  becomes  evident.  The  tincture,  however, 
shows  the  acid  reaction  more  promptly,  owing  probably  to  a 
greater  solubility  of  the  acid  or  acids  in  alcohol.  The  amber  color 
of  the  infusion  darkens  immediately  on  the  addition  of  ammonium 
hydrate,  and  deepens  in  color  until  it  becomes  a  dark  red  brown, 
almost  green  by  refracted  light.  The  ammoniated  infusion  does 
not  decompose  until  the  excess  of  ammonia  has  volatilized.  This, 
as  a  rule,  takes  some  time,  especially  if  the  container  be  well  corked. 
I  had,  until  recently,  a  sample  which  had  remained  permanent  for 
nearly  two  years  before  decomposition  commenced.  If  the  excess  of 
ammonium  hydrate  be  driven  off  by  heat,  the  infusion  becomes,  on 
the  addition  of  hydrochloric  acid,  a  light  reddish  orange. 
Tannin  added  to  the  plain  infusion  shows  no  change  (absence  of 
digitalin).  Fehling's  solution  gives  a  deep  green  color,  and  in  boil- 
ing yields  a  reddish  precipitate.  Silver  nitrate  solution,  on  boiling, 
is  reduced  to  oxide.  Lead  oxyacetate  solution  gives  a  greenish- 
yellow  precipitate,  and  the  reaction  of  the  infusion  ceases  to  be  acid, 
showing  that  the  acid  or  acids  present  form  insoluble  lead  salts. 
Ferric  chloride  solution  gives  a  deep  green  color  which,  on  heating, 
becomes  brown,  and  on  cooling  precipitates  a  dull  greenish  precipi- 
tate ;  a  dark  green  color  is  likewise  yielded  with  ferroso-ferric  salts. 
Lead  acetate  gives  a  greenish  yellow  precipitate  soluble  in  acetic 
acid,  which  does  not  turn  red  on  exposure  to  air  (absence  of  cate- 
chin1).  Aluminated  gelatin  has  no  precipitating  effect,  nor  have 
alkaloidal  solutions  (absence  of  tannin).  A  drop  of  tincture  of  ferric 
chloride  colors  the  infusion  a  deep  green,  and  on  the  further  addi- 
tion of  a  drop  or  two  of  diluted  ammonia  water,  the  green  color 
changes  to  a  deep  red  brown.    This  reaction  is  quite  characteristic. 
1  Dragendorff's  Plant  Analysis,  p.  138  and  p.  36. 
