290 CHEMISTRY OF THE PROTEIDS CHAP. 



showed x that two factors have to be considered in salting-out, namely, 

 not only the concentration but also the absolute quantity of the salt 

 used and the absolute quantity of the albumin to be salted out. This 

 fact the ignorance of which has repeatedly led to errors is readily 

 explained on the supposition that salting-out is equivalent to a distri- 

 bution of the solvent between the albumins and the salt. An exact 

 investigation of a large number of salts, as far as salting-out is con- 

 cerned, has been undertaken by Hofmeister 2 and his pupil Lewith 3 

 (see above, p. 281), and also by Posternak and Pauli. 4 (See below.) 



For the chemistry of proteids the question as to the extent to 

 which albumins in solution may be precipitated completely by different 

 salts is an especially important one. In this respect Cohnheim 

 distinguishes four groups of salts : 



1. Sodium : -chloride, -sulphate, -acetate, and -nitrate. They salt 



out certain albumins, such as fibrinogen and casein, even if 

 their solutions are not quite saturated. 



The author points out, however, that according to Pinkus 

 sodium sulphate in saturated solutions at 37 is in every 

 respect comparable to a saturated ammonium sulphate solution 

 at the ordinary temperature. 5 



2. Magnesium sulphate, which allows us to draw a sharp line 



between the more readily precipitable albumins, e.g. globulin, 

 and the less readily precipitable ones, e.g. albumins proper. 

 Magnesium + sodium sulphate, used in combination, precipi- 

 tate, according to Schafer, 6 also those albumins which are 

 not readily precipitable. 



3. Potassium acetate, calcium chloride, and calcium nitrate. They 



precipitate all native albumins from their solutions, but the lime 

 salts render the albumin-precipitates very quickly insoluble. 



4. Ammonium sulphate and zinc sulphate 7 are the most energetic 



precipitants. They precipitate also all the dissociation-pro- 

 ducts of albumin, except the peptones, and in this respect 

 they may be considered to be complete (Kuhne). 

 This order has been established empirically. 



1 W. Kiihne, 'Experiences with Albumoses and Peptones,' Zeitschr. f. Biol. 29. 1 

 (1892). 



2 F. Hofmeister, Arch. f. experiment. Pathol. u. Pharmakol. 24. 247 (1887) ; 25. 

 1 (1888). 3 J- Lewith, ibid. 24. 1 (1887). 



4 W. Pauli, Hofmeister' s Beitrage, 3. p. 225 (1902). 



5 Pinkus, Jowrn. of Physiol. 27. 57 (1901). See also Haslara, ibid. 32. 267 

 (1905). 6 E. A. Schafer, Journ. of Physiol. 3. 181 (1880). 



7 A. Bomer, Zeitschr. f. anal. Ohem. 34. 562 (1895) ; E. Zunz, Zeitschr. /. physiol. 

 Chem. 27. 219 (1899). 



