382 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



In the same way an emulsion is obtained when oil or petroleum is 

 shaken up with egg-albumin. In both cases a layer of coagulated egg- 

 albumin is formed round each particle. 



To prove this : A little egg-albumin solution is shaken up in a test 

 tube ; a fine layer of mechanically coagulated egg-albumin will be seen 

 to be formed and it rises to the surface on standing. 



Protein solutions have free-surface coatings ; by mechanically 

 shaking, these are heaped up to form solid masses of protein. The 

 following simple experiment demonstrates the surface coating of a 

 protein solution : 



Two beakers are taken ; in the first is placed clean water, in the 

 second egg-white solution. On to the surface of each is floated a mag- 

 netised needle and a magnet is brought near. In the first beaker, 

 the needle spins round ; in the second, only a slight attraction or 

 repulsion is seen. If the beaker be suspended by a wire, in the 

 latter case the whole beaker would swing round, whereas in the former 

 only the needle would rotate (Ramsden). 



Milk and rubber latex are examples of naturally occurring per- 

 manent emulsions. Milk contains fat globules in a solution of the 

 protein caseinogen ; rubber latex contains drops in a solution of vege- 

 table protein. 



An extreme case is an emulsion of 99 per cent, of oil and I per 

 cent, of soap solution which is of such a consistency that it can be cut 

 into cubes. 



