ON  THE  MANUFACTURE  OF  OLEUM  ^ETHEREUM. 
133 
layer  of  sand  under  it,  and  but  a  few  inches  up  its  sides,  which 
facilitates  its  rapid  cooling  when  desired. 
"The  fires  should  be  managed  without  the  damper;  all  that 
is  necessary  being  to  close  the  draft  door,  open  the  fire  door, 
and  cover  the  fire  with  coal  or  ashes,  according  to  circum- 
stances. 
"  The  presence  of  sulphate  of  lead  in  the  mixture,  or  of 
thiomelanic  acid  on  the  sides  of  the  retort,  has  a  tendency  to 
cause  frothing,  and  should  be  avoided. 
"The  temperature  should  be  raised  rapidly  to  300°  or  305° 
F.,  after  which  the  fire  is  immediately  to  be  dampened.  If  the 
fire  has  been  very  strong,  it  should  not  be  raised  above  300°  ; 
if  only  moderate,  it  may  be  raised  to  305°.  The  temperature 
will  then  generally  rise  spontaneously  to  from  310°  to  315°. 
"  The  temperature  should  be  kept  above  300°  as  long  as 
possible,  and  this  may  be  done  by  re-heating  as  often  as  it  falls 
to  near  300°.  As  soon  as  the  temperature  begins  to  rise  again, 
the  fire  must  be  dampened ;  for,  if  the  heating  be  continued 
until  the  temperature  reaches  310°,  it  is  very  apt  to  rise  above 
320°  and  cause  frothing.  It  should  always  be  avoided  to  raise 
the  temperature  above  320°,  as  the  yield  of  oil  of  wine  is  not 
increased  by  raising  it  above  that  point,  and  it  is  more  apt  to 
cause  frothing, 
"  If  the  liquid  froths,  the  first  step  must  be  to  pull  the  fire 
out  of  the  furnace  and  then  fan  the  retort  vigorously,  which 
frequently  prevents  frothing  over." 
In  conclusion,  it  may  not  be  uninteresting  to  give  an  account 
of  the  results  of  three  months'  distillation,  from  March  17th  to 
June  17th. 
The  total  amount  of  sulphuric  acid  used  was  5485  lbs. ;  of 
alcohol,  sp.  gr.  *809,  it  was  367f  galls.  This  yield  was  558 J- 
oz.  avoirdupois,  making  one  ounce  of  heavy  oil  of  wine  to  every 
70  ounces  by  weight  of  alcohol  and  157  ounces  of  sulphuric 
acid  used.  The  number  of  days  on  which  distillation  was  car- 
ried on  is  fifty-four,  during  which  time  one  hundred  and  two 
distillations  were  made.  Of  these,  fifteen  frothed  over,  out  of 
which  three  distillations  were  lost,  leaving  ninety-nine  distilla- 
