I20 
Glass  Manufacture 
lAm.  Jour.  Pharm. 
(    February,  1920. 
is  often  vaguely  referred  to  as  "a  super-cooled  liquid  rather  than  a 
solid,"  and  sometimes  as  a  "colloid."  Certain  opaline  and  colored 
glasses  certainly  contain  ultramicroscopic  particles ;  but  though  there 
is  reason  to  believe  that  the  complex  technical  glasses  are  not  sim- 
ple super-cooled  liquids,  positive  information  as  to  their  true  charac- 
ter is  lacking.  Vague  speculation  in  the  absence  of  facts  is  un- 
profitable. 
The  difficulty  of  investigating  the  properties  of  technical  glasses 
is  enhanced  by  the  fact  that,  unless  the  precautions  taken  in  the 
manufacture  of  optical  glass  are  observed,  different  samples  of  glass 
from  the  same  pot  may  vary  materially  in  composition.  Technical 
glasses  often,  if  not  usually,  actually  represent  unstable  systems. 
That  it  is  difficult  to  find  any  close  relationship  between  the  com- 
position and  properties  of  technical  glasses  is  not,  therefore,  to  be 
wondered  at.  At  the  outbreak  of  war  the  independent  workers 
who  undertook  the  investigation  of  glass  must  have  been  struck  with 
the  paucity  of  journal  and  textbook  literature  on  the  subject,  and 
with  the  fact  that  such  literature  as  existed  contained  no  practical 
details  and  a  few  analyses.  In  the  case  of  miners'  lamp  glasses 
official  tests  were  established,  and  the  requirements  of  the  makers 
of  lenses,  etc.,  were  definitely  known.  It  appeared,  however,  that 
few  chemists  ever  tested  the  glassware  they  used  in  their  labora- 
tories ;  the  results  of  a  few  tests  had  been  published,  but  as  to  which 
of  the  various  brands  were  really  the  best  was  rather  a  matter  of 
opinion,  or  even  of  prejudice,  than  of  scientific  proof. 
It  is  generally  recognized  that,  at  a  comparatively  early  stage 
in  the  war,  British  manufacturers  succeeded  in  producing  glasses 
for  many  essential  purposes  which  compared  very  favorably  with 
the  foreign  goods,  but  it  will  be  unfortunate  if  they  fail  to  realize 
that  there  is  yet  scope  for  improvement.  No  resistance  glass  for 
chemical  glassware  has  yet  been  discovered  which  is  sufficiently 
highly  resistant  to  all  ordinary  reagents  to  be  considered  to  be  an 
approach  to  perfection.  It  must  be  admitted  that  the  lamp  work- 
ers (workers  at  the  table  blowpipe)  have  reason  to  be  highly  dis- 
satisfied with  the  general  quality  of  the  tube  with  which  they  have 
had  to  work.  Difficulty  of  obtaining  materials  has  certainly  been 
a  handicap  to  the  manufacturer.  However,  it  is  a  fact  that,  while 
a  first-class  lamp-working  glass  must  be  soft,  and  must  have  a  low 
melting  point,  these  glasses  "plain"  (free  themselves  from  seeds 
or  bubbles)  only  when  very  strongly  heated  in  the  furnace.  The 
