84
ANALYTICAL  EXPERIMENTS
be  diffolved  in  water,  the  whole  of  it  must  be  capable  of  dissolution
in  that  fluid.
This  proposition  had,  at  that  time,  less  appearance  of  probability
than  any  of  the  former.  It  was  universally  believed  that  lime  was
only  partially  foluble  in  water  ;  and  different  opinions  were  entertained -
  of  the  proportion  of  it  that  could  be  diffolved.  Dr.  Alston  contended ¬
  that  a  fourth  part  of  it,  or  perhaps  a  little  more,  might  be  disfolved, ¬
  provided  a  very  large  quantity  of  water  was  employed;  such
as  500  times  the  weight  of  the  lime.  But  the  general  opinion  was
that  a  much  smaller  portion  of  it  only  was  soluble  and  active.  The
question  had  never  been  decided  by  an  accurate  experiment.
I  therefore  chofe  a  bit  of  chalk,  which,  when  heated  to  a  sufficient
degree  in  a  crucible,  afforded  a  little  mass  of  perfect  quicklime,  weighing ¬
  eight  grains.  This  little  maſs  was  thrown,  while  yet  warm,  into
a  small  quantity  of  warm  distilled  water  in  a  phial,  in  which  it  was
soon  flaked,  and  formed  a  white  mixture  like  milk.  This  mixture
was  immediately  poured  into  a  larger  glafs  vessel,  in  which  I  had
eighteen  ounces  of  distilled  water.
While  the  milky  mixture  was  diffused  through  the  water,  the  lime
was  ſeen  to  difsolve  almoft  entirely;  nothing  remained  undissolved
but  a  very  light  fæculency,  which  was  almoſt  transparent,  or  only
like  thin  clouds  in  the  liquor.  This  fæculency,  when  it  was  allowed
to  subside,  and  was  collected  with  the  greatest  care  on  a  small  filtre
and  dried,  weighed  only  the  third  part  of  a  grain.  In  some  repetitions ¬
  of  the  experiment  it  weighed  lefs,  and  in  others  a  little  more.
Being  examined  by  putting  it  on  a  plate  of  glass,  and  adding  a  drop
of  diluted  nitric  acid,  it  was  diffolved  in  part,  with  effervescence,  but  a
part  of  it  remained  undiffolved,  which  was  ochre  of  iron.  It  appeared, ¬
  therefore,  to  be  composed  of  a  minute  portion  of  the  lime,  which
had  fomehow  recovered  fixed  air,  and  of  ochre  of  iron,  and  perhaps  a
little  clay,  which  are  well  known  to  be  often  present,  in  smnall  quantity,
in  chalk.