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COLLOIDS. 17
Starling,1
Moore and Parker,2
Moore and Roaf 3
and Lillie,4 using
protein preparations which had not been exposed to any strong treat-
ment before use (serum proteins, ovalbumin), as well as Reid 5
(with
haemoglobin), have been able to detect a low osmotic pressure and
indeed by the aid of osmometric methods. According to Starling,
the proteins of the serum correspond to a pressure of 30-40 mm. Hg.
and Reid6 found a pressure of 3-4 mm. Hg. for a 1 per cent haemoglobin
solution.
Th© influence of added bodies upon the osmotic pressure has been tested by
Lillie by adding the substance to be tested in the same percentage concentration
to the inner and outer fluids. It was found that non-electrolytes were without
action while acid and alkalies increased the osmotic pressure of gelatin solutions,
while salts lowered the pressure of gelatin as well as ovalbumin solutions. Adam-
son and Roaf 7
arrived at similar results in regard to alkalies and acids. Besides
this, Lillie found that the osmotic pressure was dependent upon the past history
of the colloid. Warming as well as shaking the solutions seems to change the
aggregate condition, which returns very slowly or not at all. The changes
in the osmotic pressure produced by salts, Lillie explains by a change in the
aggregate condition of the colloid, by the addition of salts it is brought closer
to its precipitation point and is probably united in large aggregations. In this
way the number of particles is diminished and, as this number must be important
for the osmotic pressure, this pressure is lowered. In agreement with this
the above mentioned influence of acids and alkalies upon the osmotic pressure of
gelatin can be explained by an increase in the particles. 8
As we have seen above the determination of the elevation of the boil
ing-point or the depression of the freezing-point is the simplest way
for estimating the osmotic pressure of a crystalloid substance in solution.
If such determinations are made with a colloidal solution then unmeas-
urable results are found for the elevation of the boiling-point or the depres-
sion of the freezing-point. This indicates, as above stated, that the
molecules or the particles must be very large. F. Kraft9
found no
elevation of the boiling-point for soaps in watery solution but obtained
values which correspond to the calculated molecular weights when the
soaps were dissolved in alcohol. Therefore the soaps are colloidal in
watery solution and crystalloidal bodies in alcoholic solution.
Filterability. Large particles suspended in a liquid can be removed
from the fluid by filtering. The finer the suspended particles are the
1
Journ. of Physiol., 19, 322 (1896).
2
Amer. Journ. of Physiol., 7, 261 (1902).
3
Bioch. Journ., 2, 34 (1906).
* Amer. Journ. of Physiol., 20, 127 (1907).
6
Journ. of Physiol., 33, 12 (1905).
8
Bioch. Journ., 3, 422 (1908). /
’Ibid.
"Pauli, Koll. Zeitschr., 7, 241 (1900).
•Ber. d. d. chem. Gesellsch., 29, 1328 (1896); 32, 1584 (1899).
’
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