300 CHEMISTRY OF THE PROTEIDS CHAP. 



and less. How important a part an-ions play in the salts of the 

 alkalies has already been explained on p. 288. 



The diminishing influence of the an-ion, the author thinks, may be 

 accounted for by the plurivalent character of the kat-ion, which leads 

 to the formation of colloidal solutions. This tendency of salts to 

 form colloidal solutions, or, what means the same, to undergo hydro- 

 lysis, commencing amongst the alkaline earths, reaches its maximal 

 development amongst the heavy metals. While, to give an example, 

 the halogen salts of the alkalies are neutral and remain neutral on 

 being added to colloids, the halogen salts of the alkaline earths are 

 neutral in watery solutions, but become acid on being added to 

 colloidal solutions, as was first shown by Whitney and Ober ; 1 finally 

 (according to the author's investigations, see p. 308) the alkaline salts 

 of the heavy metals are acid in watery solutions, and remain acid in 

 colloidal solutions. Expressed in tabular form we find therefore : 



It is evident that in the case of the alkaline earths the colloid 

 assists the water in producing a hydrolysis of the calcium, barium, or 

 strontium salts, and this is a farther proof that colloids must be chemi- 

 cally active, that they are indeed electrolytes, as first pointed out by the 

 author (see p. 268), and it also follows, if it were not for the hydrolysis 

 which the salts undergo, and which renders them colloidal, that they 

 would not precipitate colloids. (See p. 270 for investigations of Spring.) 



The compounds which the kat-ions of the alkaline earths and the 

 kat-ions of the heavy metals form with colloids remain insoluble because 

 the (kat-ion + colloid) compound possesses less electro affinity than does 

 the H-ion, which becomes linked on to whatever an-ion (e.g. Cl') 

 originally accompanied the kat-ionic alkaline earth or heavy metal. 



Calcium chloride, according to Pauli, 2 has in the crystalline form 

 the precipitation limits of 8 '8 normal, while the anhydrous prepara- 

 tion has the limits 9 to 9 '2 normal. With 3 ccm. of CaCl 2 in these 

 concentrations, and with 2 ccm. of egg-white, there is produced at once 

 a bluish turbidity, which, after twenty-four hours, looks like ' thick 

 milk.' Barium chloride has somewhat lower precipitation limits. 



1 W. R. Whitney and J. E. Ober, Zeitschr. f. physik. Cliem. 39. 630 (1901-1902). 

 2 W. Pauli, Hqfmeisters Beitrdge, 5. 27 (1904). 



