146 
Proceedings of the Royal Society 
sometimes repair in a single night the ravages of the day, there 
must be thousands of miles of disused workings annually left to 
their fate. When the earth-tubes crumble into dust in the summer 
season, the debris is scattered over the country by the wind, and in 
this way tends to increase and refresh the soil. During the rains, 
again, it is washed into the rivulets and borne away to fertilise with 
new alluvium the distant valleys, or carried downward to the ocean, 
where, along the coast-line, it “ sows the dust of continents to be.” 
4. On Peroxides of Zinc, Cadmium, Magnesium, and 
Aluminium. By J. Gibson, Ph.D., and R. M. Morri- 
son, D.Sc. # 
(Read July 5, 1880.) 
During the course of an investigation on the cerite metals we found 
that peroxide of hydrogen, added to the precipitated hydrates in 
presence of excess of alkali, is a very delicate test for cerium, even 
in presence of Lanthanum and Didymium, owing to the formation of 
a dark yellow or brown compound, probably a peroxide, which differs 
from that produced by chlorine under the similar circumstances. 
While examining a residue obtained by boiling a solution of La 
and Di with magnesite, to free it from cerium, we observed, on 
using this test, the following reaction, which led us to suspect the 
existence of a peroxide of magnesium, namely, that when H 2 0 2 was 
added to a solution containing chloride of magnesium and free 
ammonia, a copious white precipitate was formed. On repeating 
the experiment with solutions of a number of metals, we obtained 
precipitates which possessed the properties of peroxides. 
On referring to the literature of the subject, we found that the 
greater number had been already prepared in a similar manner by 
Thenard and others ; but we were unable to find any mention of 
peroxides of cadmium, magnesium, or aluminium. Thenard states 
that he was unable to obtain the peroxides of magnesium or 
aluminium ; and though he mentions having obtained a peroxide 
of zinc by means of peroxide of hydrogen, yet he regarded it 
apparently as too unstable to isolate. In spite of this assertion of 
* The printing of this paper was postponed for reasons stated in the follow- 
ing paper (see page 152 below). 
