When  no  more  air  escapes,  the  volume  is  determined  in  the
usual  way.  The  specific  gravity  of  the  substance  is  calculated
by  the  aid  of  the  following  formula:

(1  +  0.00366  .  t)  .  760
'    (B  -  iv)V  .  0.001293  '

in  which  0.001293  is  the  weight  of  1  cc.  air  in  grams  at  760
mm.  and  0°;  and,  further,

S=.  weight  of  substance  taken;

t  =  temperature  of  the  room,  or  of  the  water  in  the  measur-
ing apparatus;
B  =  height  of  barometer;
w  =  tension  of  aqueous  vapor;
V  =  observed  volume  of  air;

or,  the  formula  can  be  simplified  by  division,  when  it  takes
this  form:

n       g(l  +  0.00366  .  t)  587,780
(B-w)V

The  above  is  the  simplest  form  of  apparatus  used.  To  avoid
opening  and  shutting  the  vessel  in  order  to  introduce  the  sub-
stance, an  arrangement  has  been  devised  for  holding  the  sub-
stance below  the  stopper  until  the  proper  temperature  is
reached,  and  then  releasing  it  without  disturbing  the  stopper.
EXPERIMENTS  TO  ACCOMPANY  CHAPTER  VII.
•

OZONE.
Experiment  63. — Put  a  few  sticks  of  ordinary  phosphorus
on  the  bottom  of  a  good-sized  bottle  with  a  wide  mouth,  and


762    EXPERIMENTS  TO  ACCOMPANY  CHAPTJSB   VIII.
partly  cover  the  phosphorus  with  water.  In  a  short  time  the-
odor  of  ozone  will  be  perceptible,  and  the  gas  can  also  be  de-
tected by  means  of  strips  of  paper  which  have  been  moistened
with  a  dilute  solution  of  potassium  iodide  and  starch-paste.
See  whether  such  papers  are  changed  in  the  air  ?  What  is  the
cause  of  the  change  ?  If  convenient,  examine  the  air  in  the-
neighborhood  of  a  frictional  electrical  machine,  and  see-
whether  it  causes  the  papers  to  change  color.
HYDROGEN  DIOXIDE.
