20 GENERAL AND PHYSICO-CHEMICAL. 



According to the manner of preparation the colloids may have particles of different 

 sizes. (See page 00.) 



Submicrons have y also been detected in solutions of organic colloids. The 

 work of GATIN-GRUZEWSKA and BILTZ, * who used a specially pure glycogen, 

 must be especially mentioned. They found that the aqueous solution of glycogen 

 contained amicrons as well as easily recognizable submicrons, whose presence 

 was only evident by a homogeneous sphere of light, but on the addition of alcohol, 

 conglomerate into detectable submicrons. 



Molecular Movement. R. Bno\\N 2 first f6und that small particles 

 suspended in water showed a quivering motion, and this phenomenon 

 has been called, from its discoverer, Brownian molecular motion, although 

 the particles in no manner are to be considered' as molecules. This 

 phenomenon has been observed since then by many investigators in 

 fluids having suspended solid particles as well as in substances dissolved 

 in colloidal condition. 



The Brownian movement is considered by some as a manifestation of a general 

 molecular movement of matter. According to this view it is comparable with 

 the supposed motion of gas molecules according to the kinetic theory of gases. 

 PERRIN as well as SVEDBERG 3 claim that the law of gases also holds for very 

 dilute colloidal solutions. 



Electrical Transportation of Suspended Particles. A not too weak 

 electric current has the power of causing motion in small quantities 

 of fluid enclosed in a capillary tube or in a porous diaphragm. The 

 particles suspended in a fluid also wander under the influence of the 

 electric current, and indeed to the anode or cathode, according to the 

 nature of the fluid and the particles. This phenomenon is called cata- 

 phoresis. Such movements have also been found in colloidal solutions. 

 According to BiLTZ, 4 in dialyzed aqueous solution, the colloidal metallic 

 hydroxides wander to the cathode, and the other colloids (metals, 

 metallic sulphides, acids) wander to the anode. The colloidal particles 

 in water are therefore probably electrically charged, hence the nega- 

 tively charged wander to the anode and the positively charged to the 

 cathode. Dialyzed protein solutions show according to older investiga- 

 tions no cataphoresis. The addition of acid or alkali gives to the pro- 

 tein a positive or negative charge respectively, hence an alkaline solu- 

 tion wanders to the anode and an acid solution to the cathode (HARDY, 5 

 According to MiCHAELis 7 the proteins in perfectly neutral 



1 Pfliiger's Arch., 105, 115 (1904). 



2 Edinb. Phil. Journ., 5, 358 (1828); 8, 41 (1830). 



3 Perrin, Colloid-chem. Beihefte, 1, 221 (1910). Svedberg, Roll, Zeitschr., 7, 1 

 (1910). 



4 Ber d. d. chem. Gesellsch., 37, 1095 (1904). 

 * Journ. of Physiol., 24, 288 (1899). 



6 Hofmeister's Beitrage, 7, 531 (1906). 



7 Biochem. Zeitschr., 16, 81 (1909); 19, 181 (1909); 24, 79; 27, (38; 28, 193; 

 29, 439 (1910); 33, 456 (1911); 41, 373 (1912). 



