PRACTICAL ORGANIC AND BIO-CHEMISTRY 



NATURE OF COLLOIDAL SOLUTIONS. 



Faraday, in 1857, who prepared a colloidal gold solution having a 

 red colour by treating gold chloride with an ethereal solution of 

 phosphorus, expressed the opinion that the gold was suspended in the 

 liquid in an extremely fine state of division. 



Colloidal solutions have been shown by various methods to consist 

 of suspensions of extremely fine particles. The colloidal condition is a 

 state, not a form of matter. 



Suspensions and Emulsions. Suspensoids and Emulsoids. 



According as the suspension of fine particles may consist either of 

 solid particles or of liquid particles, two classes are distinguished : 



(a) Suspensoid, in which the particles are solid, rigid and not 

 deformable. 



(b) Emulsoid, in which the particles are liquid and deformable. 

 Most of the natural colloidal solutions are emulsoids ; most of 



the artificial colloidal solutions are suspensoids. They are sometimes 

 referred to as reversible and irreversible respectively, this terminology 

 referring to their behaviour with electrolytes. 



Continuous and Disperse Phases. 



It is usual to refer to the particles in suspension as the disperse' 

 phase and the medium in which they are suspended as the continuous 

 phase. The continuous phase may be more concentrated in the form 

 of a jelly or even a solid ; the disperse phase will then consist of drops 

 of liquid or dilute solution in suspension. 



Filtration of the Particles Ultra-filtration. 



Though the minute particles in a sol cannot be filtered off through 

 filter paper yet they are retained if they be filtered through paper im- 

 pregnated with either gelatin hardened with formalin, or collodion 

 (Bechhold), or if they be filtered through a clay filter impregnated with 

 gelatin (Martin). The solution is forced through these filters by pres- 

 sure and a clear solution free from particles results. 



Size of the Particles. 



(a) Knowing the strength of the gelatin or collodion filter, from 

 which the size of the pores can be determined, the size of colloidal 

 particles can be estimated. The pores in a 2-5 and 5 per cent, collodion 

 filter are from 21 /*//, to 930 /zyu,. 1 Particles which are retained are 

 probably larger than the size of the pores. 



(b) In the Tyndall phenomenon the particles in the solution which 

 reflect the light must be smaller than the wave length of light, i.e. 

 from 450 to 760 fAfi for the visible spectrum. 



1 p. = 'ooi mm. fifj. = -ooi /t = -oooooi mm. 





