On  the  Cost  of  Agricultural  Buildings.  571 
Scantings  of  Fir  Joists  for  single  Flooring. 
Length 
Width 
Depth 
Length 
Width 
Depth 
iu 
in 
in 
in 
in 
in 
feet. 
inches. 
inches. 
feet. 
inches. 
inches. 
6 
2 
6 
14 
2£ 
9 
8 
91 
7 
16 
** 
12 
10 
2* 
n 
18 
9i 
12 
12 
8 
20 
3 
12 
The  next  consideration  will  be  to  ascertain  the  qualities  and 
properties  of  the  several  descriptions  of  timber  most  commonly 
used.  That  of  oak  is  well  known,  and  requires  but  a passing 
notice.  Among  the  varieties  is  the  Esculus,  or  holm  oak,  which 
is  very  useful  for  building  purposes,  but  is  soon  destroyed  by 
damp.  The  Qucrcus  alba,  or  American  oak,  and  the  Quercus 
rubra  of  Canada,  are  of  quick  growth,  but  are  not  so  durable  as 
the  British  oak.  The  Riga  oak  is  very  clean,  and  free  from 
knots,  and  is  well  suited  for  forming  floors.  Oak,  when  properly 
seasoned,  loses  nearly  two-fifths  of  its  original  weight ; hence  the 
necessity  for  allowing  sufficient  time  for  the  juices  to  be  thoroughly 
drawn  off. 
Where  posts  or  piles  are  to  be  driven  into  the  earth,  they 
should  be  charred,  but  if  the  process  is  performed  upon  unsea- 
soned timber,  it  is  highly  injurious,  as  it  confines  rather  than 
expels  the  juices,  which  by  fermenting  causes  premature  decay. 
It  varies  in  its  specific  gravity,  according  to  the  soil  which  pro- 
duces it ; its  strength  is  in  proportion  to  its  density,  and  that 
timber  is  the  most  durable  which  has  this  quality  in  the  highest 
degree.  Density  is  mainly  owing  to  the  length  of  time  occupied 
in  the  production  of  the  wood ; that  which  grows  fast,  as  it  will 
do  on  light  soils,  is  not  so  heavy,  or  so  hard  and  compact,  as  that 
produced  on  cold  soils,  which  is  of  slower  growth. 
Trees  which  are  suffered  to  complete  their  growth  have  heart- 
wood  throughout  of  the  same  weight  and  strength ; while  those 
cut  down  prematurely  are  found  to  possess  these  requisites  only  in 
their  centre-wood,  which  is  considerably  harder  than  that  formed 
by  the  outer  concentric  rings.  It  may  be  said  to  decrease  in  hard- 
ness in  arithmetical  proportion  as  it  approaches  the  sap-wood. 
Fir  is  preferable  to  oak  for  girders  and  general  framing,  in 
consequence  of  its  lightness  and  inflexibility  : it  is  also  less  liable 
to  warp  than  any  other  timber,  especially  when  in  boards  or  small 
scantling ; is  less  expensive  to  convert  than  oak  ; is  not  quite  so 
durable,  but  much  cheaper.  The  red  or  yellow  fir  ( Pinus  sul- 
vestris ) is  the  best  and  most  durable  of  the  whole  varieties.  The 
best  quality  has  its  annular  rings  much  thinner  than  that  of 
inferior  timber,  and  in  sawing  does  not  cut  so  as  to  leave  a woolly 
surface,  neither  is  it  spongy. 
