*Sg3££XF'}    Fire-Proofing  Treatment  of  Wood.  595 
from  the  liberation  of  a  gas  whose  action,  from  the  nature  of  things, 
could  be  evanescent  only. 
In  working  on  a  large  scale,  where  heavy  timbers  or  boards  in 
the  rough  are  treated,  the  saturation  with  the  sulphate  of  alumina 
solution  is  always  carried  out  until  complete  "  heart  saturation  "  is 
attained,  as  the  wood  has  to  be  sawed,  planed,  mortised  and  other- 
wise worked  and  cut  into,  and  all  surfaces  that  will  be  exposed  later 
must  be  fire-resistant  to  the  fullest  degree. 
As,  irrespective  of  the  large  number  of  both  soft  and  hard  woods 
that,  because  of  their  practical  value,  had  to  be  tested,  the  same 
kind  of  wood  will  differ  greatly  in  its  physical  characters,  according 
as  it  may  be  heart-wood  or  sap-wood,  and  according  as  it  may  be 
young  wood  or  thoroughly  matured,  a  vast  number  of  saturation 
tests  have  been  made  in  establishing  the  efficiency  of  the  different 
methods  of  working  and  the  value  of  different  solutions.  No  deduc- 
tion has  been  thought  to  be  of  value  that  was  not  based  upon  a 
large  number  of  tests  carried  out  under  similar  conditions  so  as  to 
obtain  an  average  that  could  be  relied  on.  The  immensity  of  the 
task  may  be  understood  when  it  is  stated  that  80,000  saturations 
and  fire  tests  with  complete  attending  records  have  been  made  of 
different  thicknesses  of  nineteen  different  varieties  of  wood  and  forty- 
six  chemical  formulas,  requiring  the  constant  application  of  the 
inventor  and  his  assistants  and  running  through  a  period  of  over  six 
years. 
One  remaining  question,  and  a  very  important  one,  is  what  effect 
has  the  fire-proofing  treatment  upon  the  structural  strength  of  the 
wood?  When  the  older  method  of  saturation,  whereby  the  wood 
was  steamed  and  then  subjected  to  pressure  for  long  periods,  was 
the  only  one  available,  it  was  recognized  that  a  compression  of  the 
cellular  structure  of  the  exterior  layers  of  the  wood  took  place  so 
that  the  wood  was  distinctly  weakened  and  the  results  for  tensile 
strength  and  bending  and  breaking  tests  were  accepted  as  neces- 
sarily lower  than  for  the  same  wood  untreated.  With  the  superior 
method  of  impregnation  now  adopted,  however,  no  such  allowance 
is  necessary,  and  the  treated  wood  is  in  no  way  inferior  in  strength 
to  the  untreated.  Professors  Mason  and  Bliss,  of  the  University  of 
New  Yorkj  have  made  a  large  number  of  physical  tests  upon  the 
wood  treated  by  the  Ferrell  process  and  have  established  this  im- 
portant fact  very  fully.    The  whole  matter,  however,  of  the  fire- 
