228  Mr.  J.  Stevenson  on  the  Chemical  arid 
probably  had  an  important  regulating  effect  in  •  he  above 
respect,  by  removing  from  the  atmosphere  carbonic  acid 
evolved  from  volcanic  and  subterranean  sources.  Later  onr 
in  1880  or  so,  Schloesing  (also  as  quoted  by  Letts  and  Blake) 
maintained  that  the  oceans  were  gigantic  reservoirs  of  carbonic 
acid  and  functioned  as  automatic  regulators  of  the  amount 
in  the  atmosphere.  From  his  analyses  and  observations, 
he  calculated  that  the  oceans  held  in  reserve  a  disposable 
quantity  of  carbonic  anhydride  for  exchange  with  the  air, 
ten  times  greater  than  the  total  amount  contained  in  the 
atmosphere,  and  a  fortiori  very  much  larger  than  the  variations 
in  that  quantity. 
It  is  very  doubtful,  however,  if  Schloesing's  estimate  of 
the  disposable  quantity  of  carbonic  acid  in  the  sea  is  correct;; 
it  may  possibly  be  much  too  high.  Xo  doubt  the  total 
quantity  of  carbonic  acid  present  in  the  sea  in  various  forms 
is  very  great,  more  than  thirty  times  the  amount  present  in 
the  atmosphere  ;  but  as  by  far  the  greatest  proportion  of  it 
is  in  the  combined  condition  in  the  form  of  carbonate  and 
bicarbonate  of  lime  and  other  bases,  it  cannot  be  regarded  as 
being  disposable  or  readily  available  for  interchange  with 
the  atmosphere.  Prof.  Dittmar,  as  the  result  of  his  exami- 
nation of  analyses  of  sea-\\  ater,  especially  of  those  made  in 
the  course  of  the i  Challenger '  Expedition, concluded  that  there 
was  rarely  any  free  carbonic  acid  in  sea-water  at  all,  in  the 
ordinary  sense  of  the  term  ';  free."  for  there  is  usually  not 
enough  to  form  bicarbonate,  and  the  reaction  of  sea -water  is 
usually  alkaline.  There  was  usually,  however,  more  than 
enough  to  form  the  normal  carbonate,  and  anything  in  excess 
of  this  he  was  inclined  to  call  u  loose"  carbonic  acid. 
It  is  also  doubtful  if  we  could  as  yet  make  any  use  for  our 
purpose  of  the  analyses  made  in  connexion  with  the 
1  Challenger  '  Expedition  or  of  any  other  recorded  analyses  of 
sea-water,  for  the  reason  that  before  we  made  any  inference 
from  them  we  should  require  to  know  a  good  deal  about  the 
various  agencies  that  have  an  influence  on  the  amount  of 
carbonic  acid  in  sea-water.  "We  should  require  to  have  some 
information  regarding  the  amount  of  carbonic  acid  produced 
in  the  sea  by  animal  respiration,  the  amount  produced  by  the 
slow  oxidation  of  animal  and  vegetable  remains  in  contact 
with  oxide  of  iron  and  otherwise,  the  amount  evolved  into 
the  sea  from  volcanic  or  subterranean  sources,  the  amount 
decomposed  by  the  growth  of  vegetation  in  the  sea  and  the 
amount  removed,  or  changed  from  the  free  to  the  combined 
condition,  by  the  action  of  sea- water  on  rocks  containing 
silicates  of  lime  and  magnesia  and  other  strong  bases.     It  is. 
