THE NEW YORK JOURNAL OF PHARMACY 



I Solid Ruby-glass, Sodium in Sodium Chloride, precious stones. 



Solid -< Liquid — Suspension — Colloids. (See below.) 



( Gas Cigar and other smoke, cosmic dust. 



( Solid— — Water in salts, occluded water in crystals. 

 Liquid — ■< Liquid — Emulsoids. (See below.) 

 ( Gas Vapors, Clouds — Foams. 



! Solid Gases in lava. 

 Liquid — Fog. 

 Gas Not a colloid system. 



Of the above, the two systems, Solid- 

 Liquid and Liquid-Liquid have been 

 studied most thorotighly and are of 

 special interest. 



The followinjT are the general charac- 

 tertistics of these two systems : 

 (a.) System: .Solid-liquid, also called 

 "Suspension colloid." 

 Type: A gold-sol. 

 (i) Viscosity is about that of 

 the dispersion medium. 



(2) They are .slightly turbid or 

 opalescent. Lender the ul- 

 tra-miscroscojje we see 

 bright and distinct spheres. 



(3) They exhibit Brownian 

 movement, the rapidity of 

 which increases with in- 

 crease of temperature and 

 decrease of viscosity of dis- 

 persion medium. 



(4) They have a distinct elec- 

 tric charge. After addition 

 of an electrolyte, they co- 

 agulate and separate. They 

 become irreversible, viz., 

 they cannot be brought in 

 suspension again bv simple 

 means. 



(5) Centrifugation may separ- 

 ate them as fine powder. 



(h) System: Liquid-Liquid, also termed 

 "Emulsion colloid." 

 Type is solution of albumen 

 in water. 



(i) High viscosity (inner frac- 

 tion). A tremendous in- 

 crease of viscosity follows 

 a slight concentration. 

 Higher temperature de- 

 creases viscosity. For ex- 

 ample, on heating a solu- 

 tion of gelatine from 21'' 

 C. to 31'^ C, the viscosity 

 decreases by about 1,000 

 per cent. 



(2) They foam upon shaking. 



(3) They exhibit pseudo-fluor- 

 escence (like suspensoids). 



(4) The U 1 1 r a-Miscroscope 

 shows a bright field, parti- 

 cles or spheres are, as a 

 rule, not seen. 



(5) They have no distinct elec- 

 tric charge. 



(6) They coagulate only upon 

 addition of large amounts 

 of electrolytes. 



(7) They may gelatinize or 

 swell. 



There are several difl'erent ways of 

 classifying colloids, none of which has 

 yet been definitely accepted. 



Preparations of Colloids : Inasmuch 

 as the colloids are in degree of disper- 

 sion, between coarse suspensions of mole- 

 cular and ionic solutions, we have two 

 general metlKxls of prei)aration. 



