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PROPERTIES. 95
tionable whether there exists any proteid body which is soluble in water
without the aid of mineral substances. Nevertheless it has not been
thus far successfully proved that a native proteid body can be prepared
perfectly free from mineral substances without changing its constitution
or its properties. 1
As previously stated, the albuminous bodies are amphoteric elec-
trolytes, and are polyacidie liases as well as polybasic acids. The base-
and acid-combining powers of various proteids have been the subject of
numerous investigations which cannot be given in short. In regard to
various methods used in such investigations as well as to the dissociation
of protein salts we refer especially to the work of T. B. Robertson.2
The proteids can be salted out from their neutral solutions by neutral
salt? (NaCl, Na2S04 , MgS04 ,
[NH4] 2S04 ,
and many others) in sufficient
concentrations. By this salting out the properties remain unchanged
and the process is reversible, as on diminishing the concentration of the
salt the precipitate redissolves. The various proteids act in an entirely
different manner toward the same salt, and also for one and the same
proteid the behavior toward different neutral salts is different, as some
cause a precipitate, while others on the contrary do not precipitate.
The behavior of various proteids with one and the same salt, such
as MgSCU or (NEU^SO-i, is often made use of in the isolation of the
proteid, and special methods of separation are based’ upon fractional
precipitation. It has been shown that these methods may lead to great
errors, and give good results only under special conditions.3
The conditions are different from those of salting out, when the pro-
teid solution is precipitated by salts of the heavy metals. Here the
precipitates (often called metallic albuminates) are not true combina-
tions in constant proportions, but are rather to be considered as loose
adsorption compounds of the proteid with the salt.
4
These reactions
are irreversible in so far that dilution with water or removal of the salt
by means of dialysis does not restore the unchanged proteid. On the
other hand the precipitate, at least in certain cases may be redissolved
in an excess of the salt solution or of the proteid solution, and in this
sense the process is a reversible one.
1
See E. Harnack, Ber. d. d. chem. Gesellsch., 22, 23, 25, and 31; Werigo, Pfliiger’s
Archiv, 48; Biilow, ibid., 58; Schulz, Die Grosse des Eiweissmolekuls, Jena, 1903.
2
Ergeb. d. Physiol. 10; Journ. of physical Chem., 14, 15, and Journ. of biol. Chem.,
9.
3
See Cohnheim, Chemie der Eiweisskorper, 3. Aufl., 101 1 ; Pinkus, Journ. of Physiol.,
27; Pauli, Hofmeister’s Beitrage, 3, p. 225; Halsam, Journ. of Physiol., 32.
4
See Galeotti, Zeitschr. f. physiol. Chem., 40, 42, 44, and 48 and Bonamartini and
Lombardi, ibid., 58. See also the opposed views of Linpirh. ibid, 74.
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