ON  THE  IGNITING  POINT  OF  VAPOKS,  ETC.  253 
quite  so  low  a  temperature,  but  which  in  a  warm  room,  or  ex- 
posed to  the  suns'  rays,  do  give  off  vapors  sufficient  to  render 
them  dangerous ;  and  there  are  others,  again,  that  require  to  be 
considerably  raised  in  temperature  ere  vapor  is  evolved,  and,  in 
consequence,  may  be  considered  sufficiently  safe  where  ordinary 
care  is  employed. 
I  wish  it  to  be  distinctly  understood  that  it  is  the  vapor 
evolved  from  ordinary  commercial  substances,  and  not  the  point 
at  which  the  substance  itself  will  ignite  that  my  results  refer  to. 
To  illustrate  the  difference  in  the  igniting  point  of  the  vapors 
evolved  from  different  articles  of  commerce,  I  pour  into  one  glass 
a  small  quantity  of  sulphuric  ether,  and  into  another  glass  the 
same  volume  of  ordinary  paraffin  oil.  The  one  substance — ether 
— is  known  to  be  very  volatile,  and  on  bringiDg  a  light  to  within 
half  an  inch  of  its  surface  an  explosion  takes  places  ;  the  other 
— paraffin  oil — is  found  not  to  be  explosive  at  the  temperature 
of  this  room,  as  it  requires  a  higher  temperature  to  evolve  vapor 
before  an  explosion  will  take  place. 
In  the  subjoined  table,  showing  the  results  of  experiments 
made  by  me,  the  samples  having  been  purchased  in  the  usual 
way,  I  give  the  specific  gravity  of  the  different  commercial  pro- 
ducts, and  the  temperature  at  which  their  vapor  explodes  when 
a  lighted  taper  is  kept  at  IJ  inches  from  the  surface;  and  also 
the  temperature  at  which  the  vapor  explodes  when  the  lighted 
taper  is  kept  at  only  half  an  inch  from  the  surface  : — 
Igniting  Point  of  the  Yapors  of  some  Commercial  Products. 
Specific 
Gravity. 
Taper 
l^inches 
from 
Liquid. 
°F. 
Taper 
from 
Liquid. 
°F. 
Sulphuric  ether 
•747 
under 
53 
Bisulphide  of  carbon 
1-270 
53 
Petroleum  spirit 
•706 
53 
Paraffin  spirit 
•751 
70 
68 
Benzole,  90  per  cent. 
•861 
74 
71 
Crude  paraffin  oil 
•849 
74 
72 
Ditto  naphtha 
•884 
78 
74 
Brandy 
•940 
85 
Wood  naphtha 
•840 
88 
81 
Crude  paraffin  oil 
•891 
89 
84 
Ditto  naphtha 
-  -881 
90 
86 
