256 CHEMISTRY OF THE PROTEIDS CHAP. 



hydrogen-ion of water; if the weaker ion of the solute is electro- 

 negative, then it is replaced by the alkaline hydroxyl-ion of water. 

 Thus corrosive sublimate and water, or sodium carbonate and water, 

 behave as follows : s j 



HgCl 2 + o;H 2 $. [HgOH] + H + Cl' + Cf+ H 2 

 Na 2 C0 8 + zH 2 $. [H 2 C0 3 ] + [Na + OH'] 2 + H 2 0. 



4. The substance, being composed of two feeble radicals, forms 

 with the solvent a hydrate which is only capable of undergoing com- 

 plete dissociation if along with this substance another salt is present, 

 by the dissociation of which either acid hydrogen- or alkaline hydroxyl- 

 ions are liberated. This view is fully discussed in Chapter VI. under 

 the heading of ' Theoretical Considerations. ' See also footnote on 

 p. 258. 



ELECTROLYTE. An electrolyte is defined by Arrhenius 1 as a 

 substance which imparts to water, which itself is a non-conductor, the 

 power of allowing an electric current to pass through it, in virtue of 

 the substance being in a state of electrical dissociation or ionisation, 

 there being formed, while no current is passing, two sets of ions, the 

 one having an electro-negative, the other an electro-positive charge. 



HYDROLYTE. If only one of the components of a salt becomes an 

 ion, while the other component transfers its positive charge to a 

 hydrogen atom of the water, and thereby converts the latter into the 

 acid hydrogen-ion, H, or its negative charge to the hydroxyl group, 

 OH, of water, and thereby changes the latter into the alkaline 

 hydroxyl-ion, OH', then the salt is said to undergo hydrolytic dis- 

 sociation, and substances behaving in this manner may be termed 

 hydrolytes. Examples of electrolytes and hydrolytes have been given 

 under Nos. 2 and 3 in the previous paragraph on ' solution.' 



COLLOID. This term was introduced by Thomas Graham 2 in 

 1861 for certain substances which differ from 'crystalloids' in 

 diffusing very slowly in water, in being unable to pass through animal 

 bladders and vegetable parchment, and in not crystallising readily. 

 Graham states : Crystalloids and colloids " are like different worlds of 

 matter." According to Graham, a colloid may occur in one or more 

 of these three states : 



1 . As a fluid mixture or ' sol ' ; a watery mixture, for example, 

 being called a 'hydrosol.' 



2. As a firm mixture or ' gel' ; thus ordinary gelatine- jelly is a 

 ' hydrogel ' of gelatine. 



1 S. Arrlienius, Zeit. f. physik. Chem. 1. 631 (1889). 

 2 Thomas Graham, Phil. Trans. 151. 183 and 373 (1861). 



