592  Fire-Proofing  Treatment  of  Wood.  {AD^2eSm- 
by  Mr.  Jos.  L.  Ferrell,  of  Philadelphia,  in  the  invention  of  the 
apparatus  now  in  use  by  the  U.  S.  Fire-proof  Wood  Company  of 
Philadelphia,  and  which  was  described  and  figured  in  the  Scientific 
American  of  July  28,  1900.  By  the  replacement  of  the  hinged  gate 
by  a  heavy  gate,  sliding  between  vertical  guides  against  a  phosphor- 
bronze  bearing  and  placed  in  a  massive  gate  housing  near  the  end 
of  the  cylinder,  which  is  of  heavy  cast  tubing,  he  was  able  to  use 
pressures  ranging  from  400  to  1,500  pounds  in  extreme  cases.  By 
the  intervention  of  a  hydraulic  accumulator  he  was  able  to  perfectly 
cushion  the  shock  of  the  high-pressure  pumps  so  as  to  prevent  all 
bruising  of  the  wood  when  under  strong  pressure.  No  preliminary 
steaming  or  vacuum  is  necessary,  but  after  the  receiver  is  full  of 
liquid  and  the  pressure  is  applied,  the  liquid  penetrates  and,  in  what 
seems  an  incredibly  short  space  of  time,  has  followed  the  medullary 
rays  from  end  to  end  of  the  lumber  and  effected  what  is  bound  to 
be  a  thorough  core  saturation.  One  hundred  per  cent,  saturation 
(weighed  wet)  is  readily  effected  in  ten  minutes,  and  after  the  kiln 
drying  the  permanent  gain  in  the  weight  of  the  wood  will  be  found 
to  be  from  5  to  10  per  cent.,  distributed  throughout  its  whole  cellu- 
lar structure  and  not  on  the  surface  or  in  the  exterior  layers  only. 
Hard  woods  in  large  sizes  up  to  12  x  12  inches  have  been  so 
treated,  and  upon  being  sawed  through  have  been  found  to  have 
perfect  heart  saturation. 
With  the  mechanical  side  of  the  fire-proofing  treatment  thus  per- 
fected, let  us  turn  again  to  the  choice  of  a  chemical  which  shall 
prove  as  fire-resistant  as  possible  and  impart  this  quality  to  the  wood. 
Some  of  the  qualities  that  such  a  chemical  should  possess  may  be 
briefly  reviewed. 
(1)  It  must  not  be  of  a  hydroscopic  nature,  because  in  such  case 
it  would  destroy  paint  and  keep  the  surface  of  the  wood  in  an  unde- 
sirable moist  condition.  For  this  reason  the  chlorides  of  calcium, 
magnesium  and  zinc  are  excluded,  although  an  attempt  has  been 
recently  made  in  a  German  patent  to  produce  for  this  purpose  a 
basic  chloride  of  calcium  which  it  is  claimed  is  free  from  this  draw- 
back, and  is  recommended  for  fire-proofing  of  wood. 
(2)  It  must  not  be  a  volatile  substance,  because  in  such  case  it 
will  gradually  be  liberated  from  the  cells  of  the  wood  and  show 
as  an  efflorescence,  besides  leaving  the  wood  after  a  time  weaker  in 
its  fire-resistant  character.  The  ammonia  salts,  notably  the  sulphate 
