ADecSer%T-}    Fire-Proofing  Treatment  of  Wood.  593 
and  chloride,  will  not  stand  this  test  at  all  satisfactorily.  In  the 
dry  kiln,  the  liberation  of  ammoniacal  gas  begins  already  at  1 25 0  F., 
and  the  efflorescence  is  frequently  recognizable  even  when  the  sur- 
face has  been  varnished  if  the  wood  has  been  exposed  to  strong  sun. 
shine  for  any  length  of  time.  Of  course,  such  efflorescence  speedily 
ruins  the  appearance  of  a  varnished  wood. 
(3)  The  chemical  used  must  not  allow  of  fungous  growth,  for  in 
such  case  the  wood  will  decay  more  rapidly  than  untreated  wood. 
Here  again  the  ammonia  salts,  including  the  phosphate  as  well  as 
sulphate,  are  unsatisfactory,  as  when  the  conditions  of  warmth  and 
moisture  are  favorable  the  treated  wood  develops  a  fungus  rapidly 
and  deteriorates  in  strength. 
(4)  If  possible,  the  chemical  should  have  exactly  the  opposite 
character,  viz.,  a  distinct  preservative  effect,  so  that  the  life  of  the 
treated  wood  should  exceed  that  of  untreated  wood. 
(5)  There  should  be  no  noxious  gas  liberated  in  the  heating  or 
carbonizing  of  the  wood. 
(6)  The  chemical  used  must  not  be  poisonous  in  character,  so  that 
splinters  impregnated  with  it,  if  by  accident  run  into  the  flesh  or 
wounding  it,  shall  not  endanger  life  or  health. 
(7)  It  should  not  cause  the  corrosion  or  rusting  of  metals  which  in 
the  form  of  screws  or  bolts  are  passed  through  it. 
(8)  The  cost  must  be  moderate,  as  its  practical  utilization  will  be 
barred  if  the  materials  be  such  as  to  make  the  process  an  expensive 
one. 
After  a  most  exhaustive  series  of  experiments,  extending  over 
several  years,  with  a  wide  range  of  compounds,  Mr.  Ferrell,  the 
inventor  of  the  fire-proofing  method  just  referred  to,  has  found  in 
sulphate  of  alumina  a  compound  that  appears  to  answer  all  the 
requirements  as  stated.  It  has  the  additional  feature,  of  no  slight 
importance  in  its  bearing  upon  the  fire-proofing  effect,  that  when 
strongly  heated  it  leaves  an  infusible  and  non-conducting  residue  to 
cover  and  protect  the  cellular  structure  throughout  the  wood.  It 
absolutely  prevents  the  propagation  not  only  of  flame  throughout 
the  wood  but  even  of  a  glow  because  of  its  non-conducting  and 
unalterable  character. 
Sulphate  of  alumina  in  concentrated  solution  is  far  more  efficient 
than  an  alum  solution;  in  fact,  it  would  seem  as  if  the  alkaline 
sulphate  of  the  alum  simply  detracted  from  the  power  of  the  alumi- 
num sulphate  in  the  matter  of  making  wood  fire-resistant. 
