126 STUDIES IN I.MUr.MTY. 



iodide of starch). As a result of our experiments we conclude 

 that tlu- action of the citrate is directly on the flocculable sub- 

 stance itself and due to its adsorption by this substance. 



The complex, barium sulphate plus citrate, can he washed in 

 distilled water and resuspended in distilled water in the same way 

 as the complex of barium sulphate plus a colloid; it remains in sus- 

 pension. The stability of this com) ilex, however, is far from being 

 as great as complexes of barium sulphate with colloids, and we find 

 that it must be washed with rather small volumes of water, since 

 large amounts of water finally break it up and liberate the powder. 

 The stability of the complex is, however, sufficient to allow us to 

 study it by subjecting it to various influences. 



When we submit a complex of barium sulphate plus citrate that 

 has been washed and suspended in distilled water to the action of 

 an electric current we find that it is directed feebly though dis- 

 tinctly toward the anode. This fact, which is much more distinct 

 with a complex of barium sulphate and colloid, shows that the 

 adsorption of an electrolyte may endow a suspension with a dis- 

 tinct electric charge. In this connection we may recall that 

 Lottermoser* has shown that colloidal solutions of Agl may be 

 obtained from KI and AgN0 3 by means of an electric current 

 which moves it either toward the negative or positive pole, depend- 

 ing on whether the initial mixture contains an excess of KI or 

 an excess of AgNo 3 . The ions, Ag or I, in excess, bring about 

 a colloidal state under these conditions (Solbildner, de Jorclis), and 

 endow the particles of Agl with a positive or negative electric 

 charge. 



Arthus, in a brief note on the study of sodium citrate, shows not 

 only that it inhibits flocculation of clay by an amount of NaCl that 

 is sufficient ordinarily to produce agglutination, but he also shows 

 that this action of the citrate may be overcome by a larger amount 

 of NaCl. We have subjected the complex, barium sulphate plus 

 citrate, to the action of electrolytes in the same way that we treated 

 the complex of barium sulphate plus colloid. As in this latter in- 

 stance, the complex, barium sulphate and citrate, is flocculated 

 by a salt and sediments rapidly on the addition of a neutral salt, 

 a base or an acid. 



* Journ. fur prakt. Chem. 1906, LXXIII. 



