147 
of Edinburgh, Session 1884 - 85 . 
Thenard’s, it does not seem to have been generally believed that zinc 
did form any definite oxide higher than ZnO, if, in fact, it formed 
any other at all. The following quotation from Brandis seems to 
represent fairly the general idea on the subject held by chemists : — 
“ Thenard has described a peroxide of zinc obtained by agitating 
the hydrated oxide with oxygenated water ; at all events, this is 
no permanent compound, and certainly forms no distinct salts with 
the acids. We may therefore reject the suboxide and the peroxide 
of zinc as indefinite compounds, and consider this metal as sus- 
ceptible of one degree of oxidisement only, forming the protoxide.” 
Under these circumstances we thought the subject of sufficient 
interest to warrant us in bringing it before the Society, although 
we have not as yet obtained any of the peroxides mentioned in the 
title of this paper in a state of purity, nor are we as yet prepared 
to assign any formula to any one of them. Yet the results we have 
obtained prove the existence of peroxides of these metals, and tend 
to suggest the formula of the peroxides of zinc and cadmium. 
The preparation of these peroxides in a state of purity, or even 
an approximation to purity, demands attention to minute details, 
comparatively slight variations making a very decided difference in 
the products obtained or even preventing their formation. 
After a considerable number of experiments we obtained zinc 
and cadmium compounds containing a high percentage of oxygen ; 
but we have not been so successful in the case of magnesium or 
aluminium, partly perhaps, because we have not had time at our 
disposal to try a sufficient number of experiments under varying 
circumstances. 
The following are the results we have obtained : — 
To a solution of zinc sufficient ammonia is added to redissolve 
the precipitated hydrate, and to prevent its reprecipitation on dilu- 
tion with water to two or three times its former volume. If to this 
solution a dilute solution of peroxide of hydrogen be added, a 
copious white or slightly yellow precipitate is formed. This in 
itself points to some alteration having taken place, as if the precipi- 
tate were still hydrate of zinc, there is apparently no reason why it 
should not dissolve in the ammonia which is present. This preci- 
pitate, when filtered from the liquid and washed on the Bunsen 
pump six or seven times with cold water, possesses the properties of a 
