238 
ON  FRUIT  ESSENCES. 
pendent  use,  is  in  the  elastic  valves,  in  two  varieties — the  one  for 
giving  vent  to.  the  products  of  fermentation,  when  desired  ;  such 
as  the  carbonic  acid  gas  generated  by  malt  liquors,  etc.,  the 
other  for  giving  admission  to  air,  so  as  to  enable  the  liquid  to 
flow  through  the  tap  or  other  orifice.  In 'the  one  case  a  cir- 
cular disk  of  vulcanized  india-rubber  is  made  to  cover  a  small 
opening  through  which  the  gas  is  free  to  escape,  but  meets  in  its 
passage  with  the  india-rubber,  which  being  forcibly  held  down 
round  its  edge  is  at  liberty  to  become  distended,  and  in  so  dis- 
tending opens  a  number  of  very  minute  holes,  which  have 
been  previously  pierced  through  its  surface.  When  the  pres- 
sure is  removed,  the  disk  again  becomes  flat  and  its  orifices  shut. 
The  degree  of  pressure  to  be  sustained  before  these  perforations 
open  is  perfectly  under  control,  and  may  be  adjusted  to  any  re- 
quired degree. 
In  the  other  form  a  small  cylinder  of  india-rubber,  closed  at 
its  lower  end,  is  drawn  over  a  corresponding  cylinder  of  wood 
with  a  hole  through  its  center,  and  then  tightly  bound  at  its 
upper  edge.  The  india-rubber  has  a  number  of  slits  made  in  its 
substance,  which  (when  any  orifice  through  which  the  liquor  may 
flow  is  opened)  receives  tbe  pressure  of  air,  and  yielding  to  this, 
open,  so  as  to  let  the  air  enter  the  vessel  in  exactly  the  same 
extent  as  the  liquor  is  withdrawn.  When  the  flow  of  liquor  is 
stopped,  the  edges  of  the  slits  become  drawn  together,  so  as  to 
prevent  any  escape  of  liquor  or  gas  in  a  wrong  direction. 
Should  there  be  any  pressure  from  within  upon  the  surface  of 
the  india-rubber,  this  will  only  tend  to  the  more  perfect  closing 
of  the  slits,  and  thus,  while  affording  sufficient  ingress,  altogether 
restrain  egress. — London  Pharm.  Journ.,  February,  1867,  from 
Journ.  Soc.  Arts. 
ON  FRUIT  ESSENCES. 
By  M.  Kletzinski. 
The  products  known  under  the  name  of  Fruit  Essences,  are 
alcoholic  solutions  of  different  ethers,  to  which  is  sometimes 
added  certain  acids,  or  certain  natural  essences.  Glycerine  is 
found  in  all;  it  appears  to  blend  the  different  odors,  and  to 
