99 
the electrostatic charge of the anions, therefore, being decisive here, — 
a fact, which is in agreement with the stated positive charge of the 
dispersed particles. Such experiments were also carried out with a 
more concentrated solution, CaCl, being added to it. After one day 
already there appeared a precipitate, the colour of the solution being 
violet; after two days more precipitate was formed, while the colour 
became bluish violet; after five days the colour was dark bluish 
violet; after a fortnight it was similar and only a relatively small 
amount of precipitate was formed. In no case the colloidal solution 
was flocculated completely, it, therefore, appearing to be extremely 
stable. This follows also from the behaviour of the liquid, while being 
concentrated on the waterbath: even the last drops retain their bluish 
violet colour, and the amorphous reddish violet powder, which is conti- 
nually deposited at the surface-border of the liquid, may be redissolved 
immediately into a colloidal solution of the same kind as the original 
liquid. This reversibility of the colloid corresponds also here with a 
smaller sensitiveness to electrolytes. On complete evaporation a violet 
and a grey powder are obtained; only the violet one is reversible. If 
heated for some time, it turns grey, afterwards black, and then it 
can no longer be dissolved. After being dried at 110° C. until the 
weight has become constant, the powder is black and possesses a 
metallic lustre. 
Of this product the content of ruthenium was determined in the 
way formerly described, and by the aid of the micro-balance. 
Analysis: 17,23 mGr. of the powder contain 4,55 mGr. Ru. The 
amount of sulphur was determined by volumetric analysis: a solution, 
the rutheniwmeontent of which was accurately known, was oxydized 
by a solution of potassium-permanganate of known strength, and 
the amount of sulphate afterwards estimated as BaSO,. Such solu- 
tions were prepared from a known weight of the pure greenish 
black sulphide by oxydation of its solution by means of an air current. 
Analysis: A quantity of the solution containing 2,40 mGr. ruthe- 
nium, gave 21,4 mGr. BaSO,, corresponding with 2,93 mGr. sulphur, 
this being 32,18°/,. Therefore 41,42 °/, of owygen is present, cor- 
responding with the formula: RwS,O,,, which was afterwards con- 
firmed by other tests. 
Calculated for RuS,O,, : Observed : 
Ru: 26,16 °/, 96,40 */, 
S: 32,82 °/, 32,18 
O: 41,02%, 41,49 °/, 
The oxydation of the solution to ruthenium sulphate and free sulphuric 
acid can, therefore, be expressed by the equation: 
7% 
