Sparking-Potentials  in  Carbon  dioxide  and  Nitrogen.       543 
Pressure  16  mms. 
d  
•J 
•3 
•5 
X=700 
s 
1-03 
1-075 
1-17 
a  =-32 
/3  small 
n  =  ead 
1-03 
1-1 
1-17 
In  order  to  test  whether  hydrogen  was  present  in  the  gas 
in  appreciable  quantities,  some  more  nitrogen  was  prepared 
by  the  same  method,  and  its  specific  gravity  carefully 
determined. 
The  mean  of  two  experiments  gave  "971  as  its  sp.  gr., 
which  was  probably  correct  to  '2  per  cent.,  as  an  error  of 
3  milligrams  in  weighing  would  only  have  produced  1  per 
cent,  error  in  the  result.     The  sp.  gr.  of  pure  nitrogen  is  '972. 
In  the  following  experiments  the  nitrogen  used  was 
prepared  by  a  similar  method  to  that  used  by  Lord  Rayleigh 
for  obtaining  nitrogen  from  air.  Air  was  passed  through 
strong  ammonia,  over  hot  copper,  through  dilute  sulphuric 
acid  to  remove  excess  of  ammonia,  then  over  hot  copper  oxide 
to  a  gas-holder,  where  it  stood  over  water  containing  sulphuric 
acid.  This  gas  was  afterwards  passed  through  a  solution  of 
caustic  potash,  and  again  over  heated  freshly  reduced  copper 
in  a  long  tube,  and  copper  oxide  in  another  long  tube.  The 
copper  oxide  was  kept  red-hot,  and  the  first  portions  of 
nitrogen  were  used  to  wash  the  receiver,  which  was  exhausted 
each  time.  After  an  hour  some  nitrogen  was  collected  and 
the  receiver  sealed.  From  the  receiver  the  gas  passed  into  the 
drying  apparatus  as  before.  Lord  Rayleigh  tested  the  efficacy 
of  this  method  of  removing  hydrogen,  by  allowing  a  constant 
stream  of  hydrogento  mix  with  his  gas  before  it  passed  over 
copper  oxide,  and  found  no  hydrogen  in  the  gas  at  the  finish. 
In  order  to  avoid  difficulties  arising  from  the  burning 
away  of  the  silver  on  the  positive  electrode,  a  zinc  plate 
perforated  with  fine  slits  was  used.  The  following  results 
w^ere  obtained. 
Pressure  4  mms. 
d  
•2 
•3 
•4 
•5 
•6 
123 
X-7U0             q  
4-2 
8-86 
19-2 
44-2 
a  =712 
42 
8-85 
18-0 
434 
123 
! 
|8  =-044            
Xa=502. 
V=507. 
