101 
colloidal solution and that of the permanganate rapidly disappear, 
while in the liquid SO,-ion becomes demonstrable. 
ce. Addition of H,O, and some diluted acid soon makes the colour 
of the solution disappear, while sulphate is formed. 
d. The red-violet powder obtained by evaporation from the 
solution, prepared by oxydation of the original green solution by 
the air, no longer gives a reddish violet colloidal solution, after 
being exposed to the air for three weeks; it gives a slightly greenish 
solution of acid reaction, containing a perceptible amount of SO,-ion. 
These different reactions prove undoubtedly, that the violet RwS,O,, 
is an intermediate product, which by further absorption of oxygen 
is transformed into the sulphate: Ru(SO,),. The compound has the 
composition of a normal rudheniumsalt ofpyrosulphurous acid : H,S,O,, 
and more particularly, of a pyrosulphite of tetravalent ruthenium. 
In this way the pyrosulphite appears as an intermediate product 
in the oxydation-process of ruthentum-persulphide to rutheninm- 
sulphate; most remarkable in it is, moreover, the colloidal nature 
of this intermediary rutheniwm-pyrosulphite, the dispersed particles 
of which bear at the same time an electrostatic charge of opposite 
algebraic sign to those in the colloidal solution of the original 
persulphide. 
Some other reactions of the colloidal pyrosulphite may be of 
interest here: 
a. The colloidal solution of the salt is rapidly decolourized by 
strong sulphuric acid. 
b. Hydrochloric acid, especially in higher concentrations and at 
higher temperatures, has the same effect, while sulphuric acid is 
formed simultaneously. | 
e. Sodium hydroxide (1:3) slowly decolourized the solution, but at 
higher temperatures even a more dilute solution does this rapidly. 
d. On addition of mercurous nitrate, the violet colour disappears 
immediately; a brown turbidity appears, and, after some hours, a 
brownish black precipitate is formed, which is probably a sulphide 
of mercury. 
e. Ammonium sulphide does not give a precipitate, but makes 
the colour disappear; su/phurdioxide, however, has no appre- 
ciable effect. 
f. A solution of sever nitrate turns the colour slowly into a brown 
one, and a brownish black precipitate is gradually formed, which 
is soluble in ammonia. 
g- On boiling the colloidal solution with sodiwm carbonate, the 
colour is rapidly changed into a pale green one. 
