( 154 ) 
felspar as well as the abundance of mica and olivine is sufficient!? 
expressed in the name micaleucite basalt. 
It is left to further explorations of this interesting territory, to make 
out to what extent the above mentioned suggestions are correct, and 
whether this rock belongs to a group of lamprophyric dyke rocks, 
of which the transitions to minettes and monchiquites are known 
in their leucite bearing varieties. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
EXPLANATION OF FIGURES. 
Above, a phenocryst of olivine; below a resorbed crystal of mica and to 
the left of this non-resorbed mica in the position of greatest absorption 
with well-defined cleavage lines. The matrix consists of leucite, augite 
microlites and ore. 
trom the top somewhat to the left to the bottom somewhat to the right 
the dark band consists of non-resorbed mica; the poikilitical character with 
regard to leucite and diopside microlites is clear. The olivine encloses a 
few ore granu'es and augite microlites. 
Resorbed mica, surrounded by a border of similarly orientated non resorbed 
mica (continued growth of the crystals after the resorption period). 
Leucite crystals with inclusions, poikilitically surrounded by non-resorbed 
Chemistry. — “On the radioactivity of Rubidium compounds .” 
By Dr. E. H. Buchner. (Communicated by Prof. A. F.Holleman). 
Although the experiments to be described are far from completed, 
I think it all the same desirable to make a provisional communi¬ 
cation as to the results already obtained, in view of the long time 
these kinds of experiments require. 
Campbell *) discovered about two years ago that potassium salts, 
although but very feebly so in comparison with uranium and the 
other radioactive salts, emit rays which ionise the air and so cause 
the discharge of an electroscope. This discovery was confirmed from 
various quarters and Levin and Ruer 3 ) succeeded in observing the 
action of potassium salts on the photographic plate. It seems, there¬ 
fore, to be pretty certain that potassium salts are either radioactive 
themselves, or are always contaminated with a radioactive substance; 
but as it has been proved that this impurity cannot be one of the 
known active substances it is natural to assume the existence of an 
active alkali metal, which should always exist in traces in potassium 
salts. In ord er to gradually solve this question, it seemed, in the 
x ) Le Radium IV, J99. 
2 ) Phys. Zeitschr. 9, 243. 
