1544 
cipitate. In a solution of one part of methylene-blue in 500.000 parts 
of distilled water the phenomenon was not so clear as in a solution 
of the same strength made with ditch-water or Knopp’s fluid. A 
number of experiments in test tubes with methylene-blue, salts, gall- 
nut- and Spirogyra-tannin led to the conclusion that the appearance 
of a precipitate is not only affected by the presence of salts but 
that also atmospheric oxygen comes into play-and finally, that me- 
ihylene-blue itself has no precipitating action, but that in one way 
or another a tannin precipitate is formed which gradually takes up 
more and more of the dye. How the precipitate is produced I cannot 
definitely say, but its formation does certainly not depend on a 
simple precipitation of tannin by methylene-blue, as PFEFFER assumes. 
Chemistry. — “The influence of surface-active substances on the 
stability of suspensoids’. By Dr. H. R. Krurr. (Communicated 
by Prof. P. van ROMBURGH.) 
In the chemical literature of the colloids it is generally stated that 
electrolytes exert a great, and non-electrolytes no action on the 
stability of suspensoids, at least when those non-electrolytes are not 
colloids themselves. BopLANDER') found that the formation of sediment 
in a suspension of colloids was much accelerated by electrolytes, 
“dagegen sind die Nichtleiter wirkungslos’. And FRrvuNDLICH’) states 
of a series of organic substances that they “in grossen Ueberschuss 
selbst bei tagelanger Einwirkung, keinen Einfluss auf die Bestandig- 
keit des Arsensulphidsols ausiibten.” This, however, merely shows 
that these substances themselves do not cause a coagulation in a 
direct manner. 
If, however, we take the standpoint of the ingenious theory 
developed by Freunpiicn*), the complete absence of any influence 
on the stability is absurd. For when the stability is determined by 
the electrie charge of the particle (Harpy*), Burton®)) and when 
this charge is formed by the selective ion-adsorption (FREUNDLICH Le.) 
a cause which exerts an influence on the adsorption cannot be inert 
towards the stability. 
1) Nachr. Göttingen 1893, 267. 
2) Diss. Leipzig, 1903, p. 13, Zeitschr. f. physik. Chem. 44, 129 (1903). 
3) Consult his Kapiliarchemie, Leipzig 1909. 
4) Zeitschr. f. physik. Chem. 33, 385 (1900). 
5) Phil. Mag. [6] 12, 472 (1906). 
