280 CHEMISTRY OF THE PROTEIDS CHAP. 



colloids taken into account the amphoteric character of amino-acids and 

 therefore of albumins. , 



Billitzer objects, however, to having the term of false colloids 

 restricted to those which possess a molecular weight of less than 

 30,000, as Sabanajew 1 proposes to do. Billitzer in 1905 has, however, 

 arrived at the same conclusion as the author did in 1902, namely, that 

 colloids are feeble electrolytes, see p. 279. 



4. The Salting-out of Albuminous Substances 



Albuminous substances may be precipitated from their solutions 

 without undergoing any alteration, by various inorganic salts. 



Virchow in 1854 first stated 2 that magnesium sulphate (which 

 Claud Bernhard had introduced), sodium chloride, and sodium sulphate, 

 by abstracting water from albuminous substances in solution, rendered 

 them insoluble. 



Hofmeister 3 in 1886 also suggested quite independently that such 

 neutral salts as sodium or potassium chloride and sodium nitrate 

 coagulate albuminous matter by withdrawing water from the albumin- 

 molecules, as these salts have a greater affinity for the water than 

 has the albumin. 



Nasse, in 1887, 4 was of opinion that coagulation did not depend 

 merely on the albumin molecules in their struggle for water becoming 

 vanquished by the salt molecules, because the quotients of the con- 

 centrations of certain given salts, necessary for producing coagulation, 

 are not the same for different albumins ; thus in the case of ammonium 

 and magnesium sulphates, the quotients were for : 



Gelatine Egg-white Serum-albumin Hemi-albumose Peptone 



0-84 1-03 0-94 0-85 1 



Although Nasse believes that in gelatine we are dealing practically 

 with dehydration, there is no doubt that other factors have to be 

 considered as well, in salting out with neutral salt-solutions. 



In 1888 Hofmeister 5 pointed out that whatever the nature of a 

 colloid, the salts always came in the same order, if the concentration 

 at which they commenced to precipitate was made the -standard. 

 But on studying his tables the agreement is not a complete one. 

 That the essential factor, when neutral salts are used, is one of salting 

 out the author firmly believes, and in his Physiological Histology he has 



1 Sabanajew, Journ. d. russ. chem. Ges. 1891, p 80. Abstracted in Chem. Centralbl. 

 1891, p. 10. 2 Virchow, Virchow's Arch. 6. 572 (1854). 



3 Franz Hofmeister, Arch. f. experiment. Pathol. u. Pliarmak. (1886). 



4 Nasse, Pfliiger's Arch. 41. 506 (1887). 



5 Hofmeister, Arch.f. experiment. Pathol. u. Pharmak. 24. 247 (1888). 



