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20 GENERAL AND PHYSICO-CHEMICAL.
According to the manner of preparation the colloids may have particles of different
sizes. (See page 00.)
Submicrons have also been detected in solutions of organic colloids. The
work of Gatix-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. Brown 2
first found 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.
Perrix 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
Pal li
6
). According to Michaelis 7
the proteins in perfectly neutral
1
Pfliiger’s Arch., 105, 115 (1904).
»Edinb. Phil. Journ., 5, 358 (1828); 8, 41 (1830).
* Perrin, Colloid-chem. Beihefte, 1, 221 (1910). Svedberg, KoU. Zeitschr., 7, 1
(1910).
* Ber d. d. chem. Gesellsch., 37, 1095 (1904).
* Joum. of Physiol., 24, 288 (1899).
« Hofrneister’s Beitrage, 7, 531 (1906).
’Biochem. Zeitschr., 16, 81 (1909); 19, 181 (1909); 24, 79; 27, (38; 28, 193;
29, 439 (1010); 33, 456 (1911); 41, 373 (1912).
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