on  Air , &:c.  197 
The  apparatus  ufed  in  making  the  following  experi- 
ments is  very  fimple;  and,  though  lefs  oftentatious,  may 
perhaps  be  more  accurate  than  more  complete  inftru- 
ments.  Firft,  a veflel  full  of  water,  of  a proper  fize  and 
figure.  Secondly,  a common  barometer  tube  of  a large 
bore,  fo  that  an  ounce  phial  full  of  air,  being  introduced 
into  it,  occupied  at  a medium  134  decimal  parts  of  an 
inch;  and  upon  a further  addition  of  an  half-ounce  phial 
ef  nitrous  air,  205 : this  tube  is  graduated  by  inches  and 
decimals.  Thirdly,  glafs  funnels,  with  necks  of  fuch  a 
fize  as  to  enter  the  tube. 
The  air,  the  fubjedi  of  the  experiment,  was  conveyed 
into  the  tube,  by  means  of  the  glafs  funnel,  under  water; 
the  nitrous  air  is  then  added  to  it  by  the  fame  method. 
The  fpace  occupied  by  them  both,  immediately  upon 
mixture,  is  noted  down,  as  alfo  the  time  by  a watch  : 
after  Handing  the  appointed  time  (half  an  hour,  except 
where  it  is  mentioned  otherwife)  the  fpace  then  occupied 
is  marked  down,  which  being  dedudted  from  the  firft 
gives  the  refult  of  diminution  fought  for : for  example, 
an  ounce  phial  of  air  from  a putrid  plumb,  with  the  ad- 
dition of  half  of  nitrous  air,  took  up  the  fpace  of  195 
(part  of  the  firft  being  abforbed  by  the  water  in  its  paf- 
fage  through  it) ; after  half  an  hour,  ftill  195;  fo  that  no 
diminution  following,  it  was  known  to  be  mephitic. 
C c 2 Auguft 
