542 
ACTION  OF  SULPHATE  OP  COPPER. 
basic  sulphate  of  copper  remains  combined  in  the  pores  of  the 
wood  in  such  a  manner  that  it  cannot  be  washed  out  with  water. 
The  copper  salt  may  be  seen  by  its  green  color  in  the  spaces 
between  the  yearly  rings  in  the  less  compact  portions  of  the 
wood,  that  is  to  say,  in  those  portions  which  contain  the  sap. 
Those  varieties  of  wood  which  contain  the  most  resin  retain  the 
largest  amount  of  the  copper  salt, — oak,  for  example,  retaining 
but  little  of  it.  The  ligneous  fibre  itself  appears  to  have  little 
or  nothing  to  do  with  the  fixation  of  the  copper  salt,  and  indeed 
none  whatever  is  retained  in  chemical  combination,  so  that  it 
cannot  be  washed  out  with  water,  by  pure  cellulose.  When 
wood  from  which  all  resin  has  been  extracted  by  boiling  alcohol, 
is  impregnated  with  sulphate  of  copper,  it  does  not  become 
colored  like  the  original  resinous  wood,  and  the  copper  salt  con- 
tained in  it  may  readily  be  washed  out  with  water.  In  like 
manner,  from  impregnated  resinous  wood  all  the  copper  salt  may 
be  removed,  with  the  resin,  by  means  of  alcohol. 
The  constituents  of  the  blue  vitriol  are  consequently  fixed  in 
the  wood  by  means  of  the  resin  which  this  contains. 
Further,  it  is  found  that  the  impregnated  wood  contains  less 
nitrogen  than  that  which  is  unimpregnated,  and  that  it  is  even 
possible  to  remove  all  the  nitrogenous  components  of  the  wood 
by  long  continued  treatment  with  the  solution  of  sulphate  of 
copper.  The  nitrogenous  matters  being  soluble  in  an  excess  of 
this  solution,  just  as  the  precipitate  which  forms  when  aqueous 
solutions  of  albumen  and  sulphate  of  copper  are  mixed,  is  soluble 
in  excess  of  the  latter.  Since  the  nitrogenous  matters  are  well 
known  to  be  promoters  of  putrefaction,  their  removal  readily 
accounts  for  the  increased  durability  of  the  impregnated  wood. 
The  author  hopes  to  explain  in  a  similar  manner  the  action  of 
other  salts,  like  chloride  of  zinc,  &c.,  which  are  used  for  preser- 
ving timber,  and  is  now  engaged  in  investigating  the  question. 
The  utility  of  blue  vitriol  as  a  preservative  may  also  depend 
in  a  measure  upon  the  resinous  copper  salt  which  is  formed,  by 
which  the  pores  of  the  wood  are  more  or  less  filled  up,  and  the 
ligneous  fibre  covered  so  that  contact  with  the  air  is  prevented, 
and  the  attacks  of  insects  hindered.  It  is  suggested  that  those 
cases  in  which  the  anticipated  benefits  have  not  been  realized  in 
practice  by  impregnating  wood  with  a  solution  of  blue  vitriol, 
