Chemistry. — ‘Colloidal Sulphurcompounds of Ruthenium’. By 
Prof. F. M. Jancer and J. H. pr Boer. 
(Communicated in the meeting of May 29, 1920). 
§ 1. It was for the first time during the process of recovering 
ruthenium from residues, that we observed some phenomena 
indicating the existence of colloidal sulphur-compounds of that metal. 
The properties of the colloidal solutions thus obtained, appeared to 
be sufficiently interesting, to study the phenomena more in detail. 
The results of this investigation are accordingly summarized in the 
following paper. 
If a solution of freshly prepared ammoniwm-sulphide be added to 
a hot solution of some salt of tetravalent rutheniwm'), be it to the 
HO 
ro ED Bn: 
a brownish black precipitate of Rus, will be formed, which does 
not manifest any especially remarkable properties. Totally different, 
however, is the behaviour of these substances with respect to each 
other, if the experiment is carried out at lower temperatures, e. g. 
at O° C.: under these circumstances a dark, greenish black precipi- 
tate is formed, while a dark green colloidal solution appears at the 
same time. This solution is very unstable: it rapidly becomes turbid, 
depositing greenish black flakes of the same kind as the original 
precipitate. For the green solution is nothing but a colloidal 
solution of the original precipitate, produced by the addition of 
ammonium-sulphide; it shows the TrNparr-effect, and its dispersed 
particles appear to carry a negative electric charge, as follows from 
the electric cataphoresis of the solution. On being put into contact 
with the air for some hours, the solution is completely flocculated, 
and the supernatant liquid then shows only the yellow colour of 
the ammonium-polysulphides. The green solution is much more stable, 
if first strongly diluted with water; but even in these circum- 
stances it appears to be flocculated completely after twenty-four 
hours. Neither an addition of gum arabic, nor that of gelatine, can 
increase the stability of the colloidal solution. 
sulphate: Ru (SO,),, or to a complex salt *) like: | Ru 
1) U. Anrony and A. Lucuess1, Gazz. Chim. It. 28, (II), 139, (1898). 
2) A. Werner, Ber. d.d. chem. Ges., 40, 2621, (1907). 
