92  North  American  Conifer  ce.  {^£^$1™* 
given  in  the  foot-note,  indicates  that  the  tree  and  its  products  were 
not  well  known  at  that  time.  The  paper  opens  by  stating  this  tree 
is  "  known  only  in  the  United  States  by  the  name  of  hemlock 
spruce,  and  in  Canada  by  the  French  is  called  perusse."  That 
the  resin  had  not  been  an  article  of  commerce  very  long  is  indicated 
by  the  following  :  "  The  resin  which  exudes  from  it  was  first  intro- 
duced into  this  City  (Philadelphia)  about  twelve  years  since,  and  was 
obtained  in  this  State  (Pennsylvania)  near  Silver  Lake, Susquehanna 
County.  But  its  history  even  here  has  been  but  little  known,  and 
still  less  elsewhere."  That  the  wood  of  the  hemlock  was  not  much 
esteemed  is  evidenced  by  the  statement  that  "of  all  the  great 
resinous  trees  of  America,  its  wood  is  of  least  value."  The  pro- 
cess of  collecting  the  resin  at  that  time  was  different  from  that  given 
by  more  recent  writers.  Then  it  was  prepared  by  boiling  the  bark 
with  water  and  skimming  off  the  melted  resin  as  it  rose  to  the 
surface.  The  quantity  yielded  by  a  single  tree  with  this  process 
was  said  to  be  from  4  to  6  pounds.  The  product  was  more  or  less 
contaminated  with  pieces  of  bark  and  was  submitted  to  a  process 
of  purification  by  melting  and  straining. 
A  more  recent  report,  by  Steanns,  in  1858,  already  referred  to, 
gives  the  process  of  preparation  as  wholly  from  the  wood,  two 
methods  for  this  purpose  being  employed,  one  by  making  cup-like 
incisions  in  the  body  of  the  living  tree  and  allowing  the  resin  to 
flow  out,  after  the  manner  of  collecting  turpentine ;  the  other,  by 
chopping  out  the  knots  in  the  wood,  which  are  rich  in  resin,  and 
boiling  them  with  water.  The  latter  method  is  not  considered  as 
good  as  the  former,  as  the  boiling  with  water  deprives  the  resin 
of  most  of  its  volatile  oil,  which  is  present  in  the  resin  obtained  by 
exudation. 
Canada  pitch  is  considered  to  be  equal,  if  not  superior,  to  Bur- 
gundy pitch  in  the  manufacture  of  plasters ;  but  both  have  given 
way,  in  the  modern  methods,  to  caoutchouc  and  asphalt,  chiefly 
the  latter. 
Very  little  is  known  of  the  chemistry  of  Canada  pitch ;  the  vola- 
tile oil  contained  in  it  is  probably  similar  to  that  obtained  from  the 
leaves,  and  just  described;  but  the  resin  or  resins,  which  constitute 
a  large  proportion  of  it,  have  not  been  studied.  - 
The  bark  of  the  trunk  is,  from  both  chemical  and  industrial 
standpoints,  of  great  importance ;  nevertheless,  there  does  not  ap- 
