326 CHEMISTRY OF THE PROTEIDS CHAP. 



Schulz has drawn attention to the fact that this kind of crystal- 

 lisation differs essentially from other forms of crystallisations, inas- 

 much as it depends on the principle of salting-out, and Spiro 1 has 

 pointed out that the mixture of albumin, salt, and water, which at 

 first is fluid, becomes crystalline only secondarily. For these reasons 

 the crystals enclose always large amounts of the mother-liquor. To 

 obtain salt-free albumin, the crystals are first dissolved and the 

 albuminous solution is then dialysed, but colloidal impurities cannot 

 be got rid of by this means. 



Schulz and Zsigmondy 2 have shown that to remove colloidal 

 contaminations recrystallisation from three to six times is required 

 (see p. 333). Crystals prepared in this way must be carefully pro- 

 tected, as otherwise they may absorb again impurities, for Wichmann 

 has shown that crystals imbibe " like a sponge " all sorts of substances 

 from solutions. That this absorption is not a purely mechanical 

 process as held by Wichmann, 3 but a chemical process of the nature of 

 salt-formation, has been pointed out by the author, 4 who found that 

 albumin-crystals prepared by the method of Hopkins react promptly 

 with the Mylius-Ehrlich test for determining the presence of bases, 

 quite apart from the fact that the amino-nature of albumin allows the 

 latter, according to circumstances, to play the part of an acid or a 

 base. 



However important the crystallisation of albumins is for the con- 

 ception that albumins are uniform, chemical individuals, we must 

 never forget that albumins require a very thorough purification by 

 means of repeated crystallisation. The objection that recrystallisation 

 produces alterations is not valid, according to Schulz, and Schulz and 

 Zsigmondy. 



Krieger first suggested and Morner 5 has proved that albumin- 

 crystals are not free albumin, but either an acetate (Hopkins' method) 

 or a sulphate (Krieger's method). 



Albumin-crystals appear at first in very varying forms, such as 

 needles, platelets, tables, etc., and Giirber 6 was therefore of the 

 opinion that at least three distinct fractions were present in serum- 

 albumin. Krieger has shown, however, that the individual shapes of 

 serum-albumin-crystals show all stages of transition, and Wichmann 7 



1 K. Spiro, Hofmeister's Beitrage, 4. 300 (1903). 



2 F. N. Schulz and K. Zsigmondy, ibid. 3. 137 (1902). 



3 A. Wichmann, Zeitschr. f. physioL Chem. 27. 575 (1899). 



4 Mann, Physiological Histology, 1902, pp. 214, 289. 



5 K. A. H. Morner, Zeitschr. f. physioL Chem. 34. 207 (1901). 



6 A. Giirber, Sitzungsber. d. Wiirzburger Phys.-med. Ges. 1894, p. 143. 



7 A. Wichmann, Zeitschr. f. physioL Chem. 27. 575 (1899). 



