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COLLOIDS. 31
cally combined in definite proportions, hut the quantity continually
changes with the temperature and the vapor pressure. On the other
hand, the imbibition stands in close relation to the osmotic pressure
which is evident, if we define the osmotic pressure of a substance as
its ability to attract water. The relation between imbibition and
osmotic pressure is still closer in those cases when the Substance finally
is dissolved in water.
If a hydrogel is placed in a salt solution instead of in pure water,
the imbibition phenomena essentially change. This was first studied
by Hofmeister,1
using gelatin plates. The process is rather com-
plicated, as salt is taken up by one side of the gelatin plate and water
by the other, and the taking up of water is influenced by the quantity
of salt taken up. It has also been found that when gelatin plates are
treated with solutions of increasing concentration of the same salt,
the taking up of salt increases at first with the salt concentration, then
becomes slower, and attempts to reach a maximum and then remains
almost stationary. As long as the taking up of salt increases, the quan-
tity of water passing into the gelatin also increases; when the salt fails
to pass then the water also ceases to pass. It has also been found that
the maximum of salt absorption for sulphate, tartrate and citrate can
be attained with much lower molecular concentrations than with chloride,
nitrate and bromide. From this it follows that the sulphate, tartrate
and citrate have a retarding action upon imbibition within certain limits
of concentration, while the chloride, nitrate and bromide have an
accelerating action.
Pauli 2
has investigated the influence of salt solutions upon the solid-
ification and melting-point of gelatin. If the salts are arranged in the
order of their ability to lower the solidification point of gelatin we
come to the series sulphate, citrate, tartrate, acetate (water), chloride,
chlorate, nitrate, bromide, iodide. This series corresponds well with
that of Hofmeister.
Acids and alkalies exert a special influence upon gelatin, as they
both, in very dilute solutions, strongly accelerate imbibition (Spirq,3
Wo. Ostwald4
). From the previously mentioned investigations of
Lillie, on the osmotic tension of gelatin solutions, it was found that the
addition of acids and alkalies increased it (page 17).
Since Graham’s fundamental experiments it was believed that col-
loidal sols could not diffuse into gels while crystalloids could pass just
1
Arch. f. exp. Pathol, u. Pharm., 28, 210 (1891).
2
Pfluger’s Arch., 71, 333 (1898).
3
Hofmeister’s Beitriige, 5, 276 (1904).
4
Pfluger’s Arch., 108, 563 (1905).
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