152  Double  Nitrates  of  Silver  and  the  Alkalis.  {Axni^J^m' 
trated,  the  silver  salt,  being  less  soluble,  crystallizes  alone,  but  after 
a  time  the  double  nitrate  i\gN03,NH4N03,  separates  in  crystals 
similar  to  those  of  the  potassium  compound.  This  double  salt  is 
easily  obtained  whenever  the  mixed  solutions  contain  an  excess  of 
the  ammonium  salt. 
Rose  stated  that  a  solution  of  silver  and  sodium  nitrates  containing 
an  excess  of  the  former,  first  yields  crystals  of  silver  nitrate  only, 
and  afterwards  crystals  of  the  double  nitrates  AgN03,2XaN03 ;  and 
AgN03,4NaN03.  The  author  finds  that  when  the  silver  nitrate  is 
in  excess,  this  salt  crystallizes  alone  in  its  ordinary  form,  but  as  soon 
as  sodium  nitrate  begins  to  separate  also,  the  two  salts  crystallize 
together,  and  the  crystals  take  the  ordinary  form  of  sodium  nitrate. 
Whatever  the  original  composition  of  the  solution,  the  composition 
of  the  crystals  and  the  mother-liquor  varies  continuously,  however, 
and  no  definite  compounds  are  formed.  From  this  result  it  follows 
that  silver  nitrate  is  dimorphous,  and  that  one  of  its  forms  is  isomor- 
phous  with  sodium  nitrate,  but  the  author  has  not  been  able  to  obtain 
pure  silver  nitrate  in  rhombohedrons. 
Lithium  nitrate  crystallizes  below  10°  in  prismatic  needles  con- 
taining 5  H20,  and  if  a  mixture  of  silver  and  lithium  nitrates  is 
allowed  to  crystallize  at  this  temperature,  the  two  salts  crystallize 
separately.  Above  15°,  however,  lithium  nitrate  forms  anhydrous 
crystals  similar  to  those  of  sodium  nitrate,  and  if  a  solution  of  silver 
and  lithium  nitrates  is  concentrated  at  this  temperature,  the  two  salts 
crystallize  together  in  rhombohedrons,  but  the  composition  of  the 
crystals  and  the  mother-liquor  varies  continuously  as  in  the  case  of 
sodium  nitrate. — Jour.  Chem.  Soc,  1886,  p.  122;  Compt.  rend.,  ci, 
p.  878-881.   
Tlie  effects  of  alcohol,  of  beer,  of  black  coffee,  of  tobacco, 
of  salt,  and  of  alum,  on  digestion. — Dr.  Carl  Bikfalvi  (Pester  med. 
chir.  Presse),  thus  sums  up  the  conclusions  he  has  arrived  at  by  experimental 
research:  (1)  Alcohol  slows  the  natural  digestion  even  in  small  amounts.  It 
hinders  the  conversion  of  dextrin  into  grape  sugar  less  than  it  does  the  diges- 
tion of  albumins.  (2)  Beer,  even  in  small  amount,  does  not  assist  digestion. 
(3)  Wine  in  small  amount  does  not  injure  digestion,  and  may  even  help  it; 
large  quantities  delay  digestion.  (5)  Black  coffee  in  small  quantities  stimulates 
digestion,  in  large  quantities  hinders  it.  (6)  Tobacco  extract  has  no  apprecia- 
ble effect  on  artificial  digestion.  (7)  Small  quantities  of  common  salt  assist 
digestion,  larger  amounts  considerably  retard  it.  (8)  Alum  hinders  digestion, 
and,  even  in  very  small  amounts,  arrests  the  conversion  of  dextrin. — Med. 
Chronicle,  December,  1885,  p.  230. 
