124 
Class  Manufacture. 
(Am.  Jour.  Pharm. 
1    Fehraury,  1920. 
of  Glass  Technology,  The  Hilger  instrument  for  testing  goods  after 
annealing  has  found  wide  application. 
The  fact  is  that  both  ornamental  flint  glass  and  common  bottles 
anneal  without  difhculty,  the  one  on  account  of  the  nature  of  the 
glass,  the  other  on  account  of  the  fact  that  the  lehrs  contain  a  large 
mass  of  hot  material,  the  temperature  of  which  must  naturally 
change  slowly.  However,  in  dealing  with  light  articles,  particularly 
when,  as  in  the  case  of  chemical  or  illuminating  hollow  ware,  re- 
sistance glasses  are  used,  considerable  difficulties  are  experienced. 
The  glass  is  first  chilled  in  the  mould  so  as  to  set  up  the  condition 
arrived  at  in  the  so-called  toughened  glass.  An  unannealed  beaker 
will  stand  any  amount  of  rough  treatment,  and  liquid  may  be  boiled 
in  it.  However,  it  cannot  be  cut  off,  and  it  may  at  any  moment  flv 
to  pieces.  In  such  an  article  the  outer  surface  is  probably  fairly 
uniformly  in  compression  and  the  inner  surface  in  tension. 
The  first  stage  in  the  annealing  of  such  goods  is  to  heat  them 
to  a  temperature  not  far  below  the  softening  point  for  a  sufficient 
time  to  eliminate  the  stresses.  This  is  the  vital  part  of  the  process, 
for  it  seems  as  if  a  badly  annealed  article  were  practically  even  more 
unstable  than  such  an  article  before  annealing,  owing  to  the  inequality 
of  the  strains.  Very  even  and  regular  heating  is  necessary,  and  this 
is  only  attainable  in  specially  constructed  lehrs  heated  from  below 
as  well  as  from  above.  The  cooling  must  be  at  such  a  rate  as  to 
avoid  the  introduction  of  fresh  strains  in  the  glass.  The  annealing 
of  light  hollow  ware  is  of  vital  importance. 
In  branches  of  the  trade  in  which  the  goods  have  to  go  through 
a  number  of  processes,  success  or  failure  depends  very  largely  upon 
the  proper  layout  of  the  works,  and  the  arrangement  for  transport- 
ing the  goods  so  as  to  avoid  breakage  in  passing  from  department  to 
department ;  and  very  close  attention  will  have  to  be  paid  to  working 
conditions,  to  the  comfort  of  the  work  people,  and  to  their  conve- 
nience in  the  matter  of  hours  of  labor.  The  scientific  study  of  prob- 
lems relating  to  industrial  administration  has  made  great  progress 
in  America,  and  is  now  receiving  attention  in  this  country. 
The  foregoing  remarks  apply  to  the  glass  industry  in  general, 
but  the  varied  character  of  the  numerous  branches  makes  it  quite 
impossible  to  deal  with  matters  of  detail.  At  the  moment  special 
interest  attaches  to  certain  branches  of  the  industry  which  are  sched- 
uled for  protection  in  accordance  with  the  new  trade  policy.  These 
are:  "Optical  glass,  including  lenses,  prisms,  and  like  optical  de- 
