PROPERTIES. 95 



tionable whether there exists any proteid body which is soluble in water 

 without the aid of mineral substances. Nevertheless it has not beer, 

 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 polyacidic bases 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 

 salts (NaCl, Na2S(>4, MgSCU, [NEUbSO^ 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 MgS04 or (NH^SCU, 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 Eiweissmolekiils, Jena, 1903. 



2 Ergeb. d. Physiol. 10; Journ. of physical Chem., 14, 15, and Journ. of biol. Chem., 

 9. 



3 SeeCohnheim, Chemie der Eiweisskorper, 3. Aufl., 1911; 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 Lippich, ibid, 74. 



