196  On  Breakage  of  Glass  Vessels.  {%i^i,\ln!^- 
ON  THE  PRESERVATION  OF  PHARMACEUTICAL  APPARATUS 
FROM  BREAKAGE  BY  CHANGE  OF  TEMPERATURE. 
By  Robert  Simpson. 
(From  the  Author's  Inaugural  Essay.) 
One  of  the  most  serious  losses  to  which  the  apothecary  is  subject,  is 
that  caused  by  the  constant  breakage  of  glassware.  Almost  every- 
thing we  handle  is  made  of  glass,  and  some  of  it  is  constantly  being 
broken.  The  causes  of  this  constant  breakage  are  mainly  two ; 
carelessness  and  disobedience  of  the  laws  of  nature.  In  regard  to  the 
first  cause,  little  need  here  be  said  ;  the  remedy  is  with  each  apothe- 
cary himself,  and  it  rests  with  him  whether  to  apply  it  or  not.  In 
regard  to  the  breakage  of  vessels  caused  by  disobedience  of  the 
laws  of  nature,  I  desire  to  present  a  few  thoughts,  confining  myself 
mainly  to  the  consideration  of  accidents  caused  by  disobedience  of 
the  law  so  often  disregarded  by  us.  I  refer  to  that  which  teaches  us 
that,  glass  being  a  very  bad  conductor  of  heat,  vessels  made  of  it 
will  generally  break,  if  suddenly  heated  on  the  inside,  by  pouring  in 
of  hot  liquids  while  the  glass  is  cold,  or  suddenly  cooled  by  the  pour- 
ing in  of  cold  liquids  while  the  glass  is  hot.  We  all  know  that  as  the 
hot  liquid  strikes  the  bottom  of  the  vessel,  the  layer  of  glass  in  con- 
tact with  the  hot  liquid  is  expanded,  and  owing  to  the  inferior  con- 
ducting power  of  the  glass,  the  lower  layers  do  not  become  heated  in 
time  to  expand  with  the  upper.  The  unequal  expansion  causes  such 
a  strain  upon  the  cooler  layers  of  the  glass  that  they  are  broken. 
When  cold  liquids  are  poured  into  hot  vessels,  the  inner  layers  are 
suddenly  contracted,  and  the  same  result  ensues  as  in  the  first  in- 
stance. This  law  is  known  to  all  apothecaries  and  yet  is  constantly 
disregarded.  In  many  of  our  operations  we  desire  to  know  the  exact 
measurement  of  hot  liquids ;  we  do  not  like  to  use  metallic  measures, 
and  have  not  the  same  confidence  in  their  accuracy  that  we  have  in 
the  accuracy  of  measures  of  glass.  Under  these  circumstances  we 
^  must  either  wait  for  the  liquid  to  cool  or  risk  the  breakage  of  the 
glass  measure. 
The  well  known  fact,  that  well  made  vessels  of  thin  glass  are  less 
liable  than  others  to  breakage  from  change  of  temperature,  is  fre- 
quently taken  advantage  of  for  some  operations,  but  for  general 
practice  is  impracticable.  It  is  between  two  and  three  years  since  a 
process  was  adopted  by  me,  by  means  of  which  I  have  been  enabled 
