.  242  Calomel  in  Japan.  {AmMa^i8P9f rm' 
The  porosity  of  the  walls  of  the  apparatus,  particularly  of  the 
layer  of  mitsuchi  on  which  the  clay  cup  rests,  must  be  more  than 
sufficient  to  allow  enough  air  to  enter  during  the  working.  I  had 
supposed  that  the  hot  hydrochloric  acid  and  air  might,  in  contact 
with  the  earth,  have  yielded  a  little  chlorine,  but  the  temperature 
reached  in  the  process  normally  worked  seems  never  to  reach  that 
required  for  the  liberation  of  chlorine. 
The  Chinese  process,  if  correctly  described,  differs  from  that  used 
in  Japan  in  several  material  points,  one  of  which  is  that  the  mercury  is 
intimately  ground  up  with  the  other  materials,  and  one  fails  to  see 
what  reaction  can  take  place  between  it  and  the  two  others,  namely, 
salt  and  alum.  Heated,  the  mixture  must  give  off  mercury  and 
hydrochloric  acid,  and  then  these,  as  in  the  Japanese  process,  will, 
with  air,  give  the  calomel,  but  this  is  independent  of  the  previous 
intimate  mixture  of  the  mercury  with  the  salt  and  the  alum. 
Another  point  is  that  in  place  of  the  magnesium  chloride  of  sea 
water  as  the  source  of  hydrochloric  acid,  the  Chinese  are  said  to  use 
alum  or  copperas,  which,  with  the  salt,  will  react  to  give  hydro- 
chloric acid.  A  third  point  is  that  the  cover  is  said  to  be  closely 
luted  to  the  iron  pot,  which  must  nearly  exclude  the  air,  without 
which  it  is  impossible  to  explain  the  formation  of  the  calomel. 
Perhaps  this  is  the  reason  why  the  Chinese  process  is  said  to  take 
four  or  five  hours'  firing,  since  this  may  give  time  enough  for  the 
needed  oxygen  to  diffuse  through  the  cup  and  luting,  it  will  also 
account  for  the  fact,  if  it  is  one,  that  the  yield  of  calomel  is  markedly 
less  in  weight  than  the  mercury  used.  Again,  there  are  to  be 
noticed  the  statements  that  the  iron  pot  is  exposed  for  hours  to  the 
strong  heat  of  a  charcoal  fire,  and  that  the  hot  clay  cover  is  cooled 
by  throwing  cold  water  on  it,  statements  which  must  be  regarded  as 
greatly  exaggerated  if  not  erroneous.  Lastly,  the  calomel-giving 
vapors  are  allowed  to  remain  in  contact  with  the  hot  iron  of  the  pot, 
instead  of  being  kept  from  it  by  the  thick  lining  of  earth  provided 
in  the  Japanese  process,  a  contact  which  such  vapors  could  not 
stand  without  destruction.  I  think,  therefore,  that  we  may  be  fairly 
doubtful  whether  any  reliable  description  has  yet  been  given  con- 
cerning the  Chinese  process,  which  we  may  expect  to  find  to  differ 
little,  if  at  all,  from  the  Japanese  process,  except  in  salt  and  alum 
being  used  in  place  of  the  mother-liquor  of  sea-salt  or  "  water,"  as 
Gno  Ranzan  supposed  it  to  be. 
