1909-10.] Composition and Character of Oceanic Red Clay. 199 
colloidal solid matter played no direct part ; they separated out of 
aqueous solution in the interstices between particles or lumps of Red 
Clay, and it may be surmised that in these regions diffusion of aqueous 
solutions from the deposit into the sea is, or once was, exceptionally 
slow. 
One of the oldest observations in the chemistry of colloids is that many 
inorganic colloidal solids may be brought into colloidal solution by minute 
quantities of acid or alkali (“ peptisation ”). This can also be accomplished, 
to a limited extent, with Red Clay. When shaken up with caustic soda 
solution of not more than t ^-q- n. strength, Red Clay yields a suspension 
which settles with great difficulty. After several months at rest the upper 
liquid is a clear yellow solution, transparent but slightly opalescent, of clay. 
This solution passes unchanged through ordinary filters, but is deprived of 
its dissolved matter when forced through a layer of clay; on making it 
faintly acid or adding salts or excess of caustic, the dissolved matter is pre- 
cipitated in flakes. The precipitate thus obtained from a colloidal solution 
of No. 4 was analysed and figures in Tables A and B as No. 14; this 
material was prepared from a second brew, and it is noteworthy that the 
product of the first extraction (not fully analysed) contained as much as 3J 
per cent, of Mn0 2 , which constituent apparently goes independently and 
preferentially into alkaline solution. There is a close resemblance in com- 
position between No. 14 and the hydrous portion of Red Clays generally, as 
shown by Table B ; that is to say, no ultimate constituent (barring man- 
ganese) of the clay is selectively dissolved or “ peptised.” We have here 
strong evidence that iron is not an admixture but an integral constituent of 
the clay-substance, seeing that ferric hydroxide by itself, wffiich is a positive 
colloid, would require a trace of acid to go into solution and would be pre- 
cipitated by a trace o£ alkali. 
When the colloidal nature of Red Clay is realised, the invariable presence 
of calcium, magnesium, and alkalies causes no surprise. Colloids of the clay 
type are able to adsorb much crystalloid matter from solutions with which 
they are in equilibrium. This retention of highly soluble matter may be 
ascribed to capillary effects at the enormous surfaces presented by the fine 
grains of clay and their internal framework, but the possibility that 
chemical affinities are also exerted is not to be disregarded. In Red Clay 
the four elements named are withdrawn, in approximately constant pro- 
portions, out of the surrounding sea- water. They are adsorbed not as salts 
but as hydroxides or perhaps as ions, since there is not nearly enough Cl 
or S0 4 present to balance them. 
In general, the amount of a given element adsorbed varies with the 
vol. xxx. 14 
