230 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
It is well known that various sulphides of the metals, as well as some of the 
metals themselves—particularly gold—can exist as colloid suspensions.Electric 
currents in acidulated water through gold electrodes easily produce red clouds of 
colloidal gold in the liquid. 6 Under certain conditions hydrogen sulphide may 
produce colloidal suspensions of sulphides instead of precipitates, and these again 
may be coagulated by the addition in sufficient amounts of an electrolyte, such as 
a chloride. On the other hand, the presence in fairly small quantity of a gelatin¬ 
izing colloid in a liquid may prevent this coagulation of colloidal suspensions by 
salts. How far crystals can be produced from such a colloidal solution or suspen¬ 
sion is not certain, but that quartz can and does crystallize from them seems fairly 
well established by observation on siliceous springs. Recent experiments also 
show that in a solution containing a colloid and an electrolyte, crystals can form 
which contain both substances. 0 
Colloid solutions diffuse with the utmost difficulty and are easily retained by 
porous walls or by other colloids, while crystallized substances (crystalloids) diffuse 
as easily through colloidal masses as through water.' 7 
It is possible to separate mixtures of colloids and crystalloids by diffusion 
through colloidal walls. Such a separation has undoubtedly taken place in the fis¬ 
sures. If we suppose a concentrated solution adjoining a weak one or adjoining 
pure water, diffusion will take place into the latter. Should the two solutions be 
separated by a semipermeable wall which wholly or partly prevents the transmis¬ 
sion of the solute, osmotic conditions will result and the surrounding water will wan¬ 
der into the concentrated solution and dilute the same. Such a condition of affairs 
might easily exist in certain veins. 
Diffusion in itself is a slow process, and yet in porous rocks may well play an 
important role, especially when chemical action accompanies it. In the latter case 
adsorption and metasomatism cause constantly changing conditions of saturation 
by which the process is made enormously complicated. As an evidence of this we 
refer to the chapter on metasomatic action (pp. 184-195), in which it is shown that 
pyritization, carbonatization, and the formation of sericite and adularia often vary 
quantitatively in the same rocks to a degree which renders it impossible to believe 
that the solutions could have preserved the same composition throughout. 
During the alteration of the country rock, sulphur, carbon dioxide, fluorine, 
and possibly also potassium, are the chief elements introduced, and in exchange 
sodium, with a little silica and lime, have been carried away. Quantitatively the 
most prominent newly fdrmed minerals are pyrite and dolomitic carbonates, and this 
suggests the question whether practically all of the pyritization and carbonatization 
in the country rock could not have been effected by means of H 2 S and C0 2 , dissolved 
in the waters. The diffusion of dissolved gases is governed by the same laws as is 
that of dissolved liquids or solids. In general the diffusion constant is smaller for 
bodies of higher molecular weights. Consequently we should expect, for instance, 
a Noyes, Arthur A., The preparation and properties of colloidal mixtures: Jour. Am. Chem. Soc., vol. 27, No. 2, February, 
1905, pp. 85-104. 
b Bredig, G., Anorganisehe Fermente: Darstellung kolloidaler Metalle auf electrische Wege und Untersuchung ihrer 
Katalytischen Eigenschaften, Leipzig, 1901. Cited by Noyes, loc. cit., p. 95. 
cVan Bemmelen, J. M., Zeitschr. f. anorgan. Chemie, vol. 36, 1903, p. 393. 
d Ostwald, W., Grundriss der allgemeinen Chemie, Leipzig, 1899, p. 197. 
