286 
Emulsions. 
f  Am.  Jour.  Pharra 
I      June,  1881. 
K"0TE  BY  THE  Editor. — The  autlior  has  omitted  to  state  the 
method  by  which  the  sohibility  has  l3eeii  determined.  In  a  number 
of  the  above  cases  the  milkiness  is  probably  due  to  the  presence  of 
silica,  as  in  carbonate,  acetate  and  citrate  of  ])otassium,  or  to  calcium 
tartrate  in  potassium  tartrate. 
EMULSIONS. 
By  Emil  G.  H.  Graff,  Ph.G. 
From  an  Inaugural  Essay. 
An  emulsion  is  an  intimate  mixture  of  an  oily,  fatty  or  resinous 
substance  with  water  by  means  of  a  mucilaginous  or  albuminous  bind- 
ing medium.  In  entering  into  emulsions  these  substances  do  not  undergo 
a  chemical  change,  but  only  a  physical  one,  the  force  of  repulsion 
between  the  oils,  fats,  resins  and  water  being  overcome  by  the  binding 
medium  in  the  following  manner :  Each  globule  of  the  oily,  fatty  or 
resinous  matter  is  enveloped  in  a  thin  film  of  the  binding  medium 
and  in  this  way  becomes  miscible  with  water  in  any  proportion. 
Natural  Emulsions. 
The  milk  of  mammals  and  the  milky  plant  juices  are  prototypes  of 
emulsions.  In  the  former  casein  holds  the  fatty  substance,  butter,  in 
suspension  in  the  aqueous  part,  and  in  the  latter  vegetable  albumen 
2)erforms  the  office  of  binding  medium. 
Artificial  Emulsions. 
The  artificial  emulsions,  the  preparation  of  which  belongs  to  the 
duties  of  a  pharmacist,  may  be  divided  into  five  classes. 
Class  1.  Emulsions  of  oils,  liquid  balsams,  oleoresins,  resinous  fluid 
•extracts  and  tinctures. 
These  substances  are  generally  emulsified  by  means  of  gum  arabic, 
occasionally  use  is  also  made  of  yolk  of  egg,  gum  tragacanth  and 
tincture  of  soap  bark. 
A.  Gum  Arabic. — In  mulsifying  these  substances  with  gum  arabic 
two  different  methods  of  manipulation  are  in  use. 
First  Method. — One  part  of  gum  arabic  is  rubbed  up  in  a  mortar 
with  one  and  a  half  part  of  water,  until  a  perfectly  smooth  mucilage 
is  obtained ;  then  two  parts  of  oil  are  added  in  small  quantities  at  a 
time,  taking  care,  however,  to  emulsify  each  portion  thoroughly  before 
adding  another,  and  if  necessary,  i.  e.,  when  the  emulsion  becomes  too 
