COLLOIDS IN PROTOPLASM 



are the most important constituents of protoplasm. 

 The physical properties of Emulsion Colloids are 

 very characteristic in comparison with those 

 of the suspension colloids. The optical and 

 electrical methods which are so useful in study- 

 ing suspension colloids do not show remarkable 

 results in emulsion colloids. The suspended 

 particles are so small that their existence can only 

 indirectly be proved by the Tyndall phenomenon. 

 The particles in suspension colloids are charged 

 with a certain kind of electricity. The organic 

 colloids and the metals of the group of platinum 

 are charged with negative electricity, the hydroxide 

 sols of iron, aluminium, etc., with positive electri- 

 city. The kind of electricity never changes. In 

 consequence of this positive Colloids may be 

 precipitated by negatively electric colloids and 

 vice versa, but colloids of the same electric charge 

 are never precipitated by each other. The electric 

 conditions are quite different in emulsion colloids. 

 Cataphoresis can be shown, but working more 

 slowly. On the contrary, a very remarkable 

 characteristic of emulsion colloids is that the kind 

 of electricity with which they are charged can be 

 easily changed. Thus albumin particles can be 

 charged either with positive or with negative 

 electricity. It depends upon the chemical con- 

 dition of the medium of solution which electricity 

 is accepted by the albumin particles. If the 

 reaction of the medium is alkaline, the particles are 



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