554.  The  processes  of  the  glass-house  are  all  exceedingly
interesting  and  instructive — the  tools  few  and  simple — the
results  dependent  on  the  adroit  manipulations  of  the  work-
man. The  materials  are  fused  in  clay  pots,  of  which  seve-
ral are  heated  in  one  circular  reverberatory  furnace,  their


Wtiat  is  soluble  glass  ?  553.  What  is  glass  ?  What  determines  the
fusibility  of  glass  ?  What  sorts  are  named  ?  What  is  the  composition
of  window  and  plate  ?  What  of  crystal  ?  What  of  green  bottle-glass  ?
554.  How  ara  the  materials  fused?


ALUMINUM.
325


mouths  outward.  Fig.  363  shows  a  section
of  one  of  them.  After  two  days  and  nights,
the  metal,  or  fused  glass,  is  brought  to  a
homogeneous  condition  and  the  consistence  of
honey.  The  chief  instrument  of  the  glass-
blower  is  his  punta  rod,  which  is  simply  an
iron  tube  a  b,  fig  364,  open  at  both  ends  and
covered  by  a  wooden  collar  c  a  to  protect  the  ^.^^^  ggg_
hands  from  the  heat.  This  rod  is  thrust  into
the   pot  of  molten  glass  while  it  is  turned  in  the  hand,  a

portion   of   the    fluid  2^^  rf  ^

glass  adheres  to  it,  the  ®"     ^^S   ^  ^^^'  '  -^^

J  •        -xi^j  J  Fig;.  364.
rod  IS  withdrawn,  and  °

if  enough  has  not  adhered  to  meet  the  wants  of  the  work-
man, he  takes  up  a  second  portion.  This  he  first  fashions
into  a  cylindrical  form  upon  a
slab  of  iron,  rolling  the  rod  over
and  over  in  his  hand,  (fig.  365.)
Suppose  it  is  required  to  make
a  glass  tube,  such  as  is  so  much
used  in  the  laboratory.  He  ap-
plies his  mouth  to  the  end  of  the  punta-rod  and  blows.
