276 
Varieties. 
Am.  Jour.  Pharn>. 
June,  1875. 
Cochineal  Insects  have  been  imported  into  Mysore  from  Teneriffe,  They 
have  taken  kindly  to  the  acclimatized  cactus  :  the  climate  is  suitable,  and  the  exper- 
iment promises  well. — Jour.  Applied  Science^  May  i,  1875. 
Assam  Rubber. — India  rubber  Irom  the  Ficus  elastica  of  Assam  is  a  product 
belonging  to  the  region  whose  commercial  centre  is  Calcutta  In  1872-73,  there 
was  a  large  increase  in  the  quantity  exported,  21,571  cwts.,  worth  £143,760,  against 
15,628  cwts.,  in  1871-72.  Some  India  rubber  also  comes  down  the  Irrawaddy  from 
the  same  region,  and  specimens  have  recently  been  submitted  to  the  Bengal  Cham- 
ber of  Commerce  from  the  Shan  States,  which  were  not  marketable  in  the  state  they 
were  sent,  but  which,  if  properly  prepared,  would  be  worth  fifty-nine  rupees  per 
maund  at  Calcutta. — Jour.  Applied  Science^  May  i,  1875. 
Hard  Glass. — The  subject  of  hard,  elastic  and  malleable  glass  is  beginning  to- 
attract  considerable  attention,  and  has  several  times  been  referred  to  in  our  columns. 
Some  experiments  made  by  Dr.  A.  Bauer;  in  Vienna,  have  recently  been  made- 
public,  and  will,  no  doubt,  prove  of  interest  to  our  readers.  He  remarks  at  the 
outset  that  the  plates  of  glass  prepared  by  him  do  not  differ  essentially  in  external 
appearance  from  ordinary  glass  ;  when  struck  they  have  a  peculiar  ring,  and  may 
frequently  be  thrown  on  the  ground  without  breaking ;  but  when  they  do  break, 
unlike  other  glass,  they  break  into  a  multitude  of  small  fragments  with  very  sharp 
corners,  which  is  a  great  disadvantage  of  this  glass.  They  stand  scratching  well,, 
but,  like  those  made  in  France,  they  break  when  struck  hard.  Dr.  Bauer  prepared 
his  plates  in  this  way  :  An  ordinary  sheet  of  glass  was  heated  until  it  began  to  bend^ 
and  was  then  dipped  into  a  bath  of  melted  paraffin  at  a  temperature  of  200*^  C. 
(392°  F.)  The  principal  object  was  not  to  cool  the  hot  and  soft  plate  steadily  and 
slowly,  as  is  usually  done,  but  to  cool  it  suddenly  to  a  certain  temperature  and  then 
to  allow  it  to  cool  slowly.  If  the  cooling  takes  place  in  this  manner  it  is  no  longer 
possible  to  cut  the  glass  with  a  diamond,  and  it  is  easy  to  prove  by  the  ordinary 
scale  of  hardness  that  its  hardness  is  greatly  increased.  The  thickness  of  the  glass 
has  also  increased  with  its  hardness  ;  the  ordinary  glass  used  by  Bauer  in  his  ex- 
periments was  2-429  to  2-438,  which,  after  hardening,  became  2-460  to  2"468.  It 
cannot  be  denied,  says  Bauer,  that  this  glass  will  be  useful  for  many  purposes,  and 
also  that  there  are  many  uses  to  which  it  cannot  be  applied  on  account  of  its  breaking 
into  such  small  pieces  when  it  does  break.  There  are  also  difficulties  met  with  in 
preparing  this  glass  on  a  large  scale,  especially  in  introducing  hollow  glass  and 
large  plates  quickly  and  uniformly  into  the  bath. 
It  is  not  as  yet  possible  to  explain  the  cause  of  the  glass  being  hardened  by  this 
method  of  cooling.  The  phenomenon  involuntarily  reminds  one  of  the  well-known 
Bologne  flasks  and  the  Prince  Rupert  drops,  but  the  breaking  of  the  latter  cannot 
be  sufficiently  explained,  since  we  know  that  this  does  not  happen  if  the  ends  are 
eaten  off  instead  of  being  broken.  We  are  also  reminded  that  when  cooled  slowly 
the  constituents  of  the  glass  separate  to  a  certain  extent,  which  ean  only  be  pre- 
vented by  a  rapid  cooling.  It  was  formerly  believed  that  glass  was  a  perfectly 
homogeneous  and  amorphous  substance.  In  1852,  however.  Prof.  Leydolt  proved 
by  etching  that  all  our  glass,  which  apparently  shows  no  signs  of  crystallization,, 
consists  of  a  mixture  which  is  in  part  crystalline.    When  glass  is  heated  to  fusion^ 
