PERCENTAGE  OF  ALCOHOL  IN  WINES. 
65 
brought  into  contact  with  charcoal,  paper,  wood,  alcohol,  &c, 
immediately  causes  explosive  combustion,  falling  not  short  in 
violence  of  that  of  chloride  of  nitrogen,  and  brought  on  the  skin 
fearful  wounds  are  produced,  which  do  not  heal  for  months. 
Like  nitric  acid,  it  cannot  be  distilled  without  decomposition, 
but  it  darkens,  and  heated  stronger,  decomposes  with  explosion. 
It  cannot  be  kept  for  any  length  of  time;  even  sealed  up  in 
glass  bulbs,  which  are  placed  in  the  dark,  it  decomposes  sud- 
denly after  some  time,  smashing  the  vessel  containing  it.  It 
mixes  with  water  with  a  hissing  noise  and  evolution  of  heat, 
uniting  and  forming  the  same  crystals  which  were  mentioned 
before,  and  was  used  for  preparing  the  pure  acid.  Those  crys- 
tals are  the  monohydrated  perchloric  acid.  They  melt  at  50° 
C,  and  heated  to  110°  C,  split  up  in  pure  perchloric  acid, 
which  distils  over,  and  an  oily  liquid  boiling  at  200°,  which  is 
also  obtained  by  boiling  aqueous  perchloric  acid  till  dense  white 
fumes  are  given  off.  That  oily  acid  has  a  constant  composition 
containing  72.3  per  cent,  pure  perchloric  acid  and  27.7  per 
cent,  of  water.  This  per-centage  corresponds,  however,  to  no 
definite  hydrate  of  simple  atomic  composition,  but  follows  the 
same  general  relations  respecting  composition  and  boiling  point, 
which,  as  I  have  shown  previously,  hold  good  for  so  many 
aqueous  acids,  namely,  that  the.  phenomena  of  constant  boiling 
point  and  constant  composition  depend  chiefly  upon  physical, 
and  not  on  chemical,  attractions. — Proceedings  of  the  British  As- 
sociation, from  the  Manchester  Guardian. 
EXPERIMENTS  ON  THE  BEST  MODE  OF  CORRECTLY  ESTIMA- 
TING THE  PER  CENTAGE  OF  ALCOHOL  EXISTING  IN 
WINES. 
By  John  Hoksley,  F.C.S.  London. 
Analyst  to  the  County  of  Gloucester. 
First,  note  the  specific  gravity  of  the  wine  to  be  tried,  say 
that  compared  with  distilled  water  at  1000,  it  is  -997,  or  3  short 
of  that  number  ;  then  take  5  fluid  ounces  of  the  wine  and  eva- 
porate it  by  rapid  boiling  in  a  sufficiently  capacious  flask  to  2 
ounces  ;  then  place  the  flask  in  a  pan  of  water  for  a  short  time 
5 
