402 
MR.  FAIRBAIEN  ON  TKE  RESISTANCE  OF  TUBES  TO  COLLAPSE. 
This  constant  failure  at  the  joints  renders  the  experiments  on  internal  pressure  very 
unsatisfactory,  as  they  do  not  exhibit  the  rdtimate  strength  of  the  plate,  but  only  the 
strength  of  the  joint;  and  as  boilers  invariably  present  joints,  these  facts  are  probably 
of  some  significance  when  applied  to  them.  On  a careful  examination  of  the  fractures, 
that  of  the  tube  Yf  appeared  the  most  perfect.  Ye  was  not  so  well  soldered,  and  bm*st 
by  tearing  ofi"  the  rivet-heads,  and  T)d  was  torn  partly  thi’ough  the  plates  and  partly 
through  the  rivets ; the  plate  of  which  this  tube  was  composed  was,  however,  exceed- 
ingly brittle,  and  broke  like  cast-mon.  Tube  Gg  was  ruptured  in  the  same  way  and  in 
the  same  direction  as  the  others ; the  rivets  were  tom  through  the  plates,  and  the  solder- 
ing (not  very  sound)  was  ripped  up  for  10  inches  along  the  joint;  this  tube,  as  also  the 
others,  would  have  borne  a greater  pressure  had  the  joints  been  more  perfect  and  of 
sounder  workmanship. 
Comparing  the  tube  Cc,  1 foot  long,  with  the  tube  Yf,  4 feet  long,  and  assuming  the 
joints  to  be  equally  perfect  in  each,  it  would  appear  that  there  is  a slight  loss  of  strength 
when  the  length  is  increased ; and  this  again  suggests  the  question,  do  the  rigid  ends  in 
short  tubes  increase  the  strength  of  the  unsupported  portion  in  proportion  to  the  length 
of  the  tube  % For  example,  let  us  take  two  tubes  of  any  given  diameter,  the  one  10  feet 
and  the  other  20  feet  long ; it  would  appear,  primd  fade,  that  it  was  much  easier  to 
force  the  long  tube  into  the  form  of  a — — 
barrel,  as  at  a,  than  it  would  be  to  pro- 
duce the  same  form  in  the  shorter  tube, 
as  at  ^ ; in  an  elastic  material,  such  as  an 
indian-rubber  tube,  the  extension  would 
certainly  take  place  at  the  centre,  where 
the  particles  possess  diminished  resistance, 
arising  from  their  respective  distances  from  the  ends  or  points  of  support. 
To  ascertain  how  far  this  view  is  correct,  two  leaden  pipes  were  prepared  of  3 niches 
diameter,  and  of  the  lengths  of  1 foot  2^  inches,  and  2 feet  7 inches  respectively,  and 
these  were  submitted  to  the  following  experimental  tests : — 
a 
Table  XII.  Fesistance  of  Lead  Tubes  to  Internal  Pressure. 
Mark. 
o 
Diameter. 
inches. 
Length. 
inches. 
Thickness. 
inches. 
Pressure  of 
rupture, 
lbs.  per 
square  inch. 
Remarks. 
HA. 
41 
3 
14i 
•25 
374 
At  225  lbs.  pressure  for  Hh.  and  325  lbs.  for  Ji.  tlie 
F- 
42 
3 
31 
•25 
364 
After  having  been  taken  out  and  the  ends  replaced, 
they  burst,  as  in  the  Table.  j'a 
The  tube  H/i  ruptured  at  the  thin  part  of  the  metal,  the  water  bursting  through  a 
