304  Alcohol  Tables  of  the  New  Pharmacopoeia,  {'^'"june^sss'^'"* 
the  same,  consisting  of  50  parts  of  absolute  alcohol  and  53*71  parts  of 
water.  The  difference  of  the  sum  of  the  parts  of  alcohol  and  Avater 
and  the  resulting  100  parts  of  proof  spirit,  is  due  to  the  contraction 
which  takes  place  when  alcohol  and  water  combine.  This  settles  the 
true  meaning  of  the  term  proof  spirit  beyond  a  doubt,  and  it  must  be 
so  regarded  in  all  dealings. 
The  hydrometers  used  by  the  revenue  inspectors  and  furnished  to 
them  by  the  government,  are  based  upon  the  tables  as  prepared  by 
Tralles,  verified  and  calculated  for  different  degrees  of  temperature  by 
Profs.  Bache  and  McCulloh.  The  instruments  are  made  in  sets  of  five^ 
in  order  to  obtain  a  very  open  and  delicate  scale.  The  No.  1  ranges 
from  0  to  100 ;  No.  2  from  80  to  120 ;  No.  3  from  100  to  140  ;  No. 
4  from  130  to  170,  and  No.  5  from  160  to  200.  The  indications 
represent  the  percentage  of  proof  spirit  and  not  absolute  alcohol. 
The  English  law  defines  proof  spirit  by  act  58  of  George  III, 
where  it  is  stated  that  proof  spirit  is  that  liquor  which  at  the  tempera- 
ture of  51°  Fahr.  weighs  exactly  j-f  parts  of  an  equal  measure  of  dis- 
tilled water.  Distilled  water,  which  at  the  temperature  of  60^F.  as 
unity,  at  the  above  named  temperature  of  51  °F.  is  1*00063,  ^  of 
which  is  '9236.  At  a  temperature  of  60°F.  Proof  Spirit  has  a  specific 
gravity  of  '9198  and  contains  49*24  per  cent,  by  weight  of  alcohol." 
By  comparing  the  figures  here  quoted,  it  will  be  seen  that  the  United 
States  Pharmacopoeia  gives  the  standard  of  Great  Britain  for  proof 
spirit  in  preference  to  that  which  has  been  adopted  by  our  own  govern- 
ment. It  will  be  seen  also  that  the  percentage  in  England  is  taken  by 
weight,  while  here  it  is  taken  by  volume.  In  order  to  determine  the 
percentage  by  weight  when  that  by  volume  is  known,  multiply  the 
specific  gravity  of  absolute  alcohol,  which  is  *7939,  by  the  per  cent,  by 
volume,  and  divide  the  product  by  its  corresponding  specific  gravity. 
Thus  :  for  alcohol  of  94  per  cent,  by  volume,  first  multiply  *7939  by  94^ 
then  divide  the  product,  which  is  74*6266,  by  '8194,  the  specific  gravity 
of  94  per  cent,  alcohol,  this  will  give  91  for  the  equivalent  per  cent,  by 
weight.  It  is  a  fact  to  be  noticed,  that  the  percentage  of  water  by  vol- 
ume in  an  alcoholic  mixture,  cannot  be  estimated  merely  by  subtracting 
the  per  cent,  of  alcohol  from  100,  for  as  has  already  been  observed  in 
the  case  of  proof  spirit,  each  100  volumes  contain  50  volumes  of  alco- 
hol and  53*71  volumes  of  water,  and  not  equal  volumes  of  each.  But 
by  referring  to  the  headings  Alcohol  and  Alcohol  Dilutum,  in  the 
Pharmacopoeia,  we  find  alcohol  stated  to  be  a  liquid  composed  of  94 
