JE$2ct7'kity hy Contact.- 
intense; but, in most cases, it was so weak, that repeated Con- 
tacts were wanted to render it sensible’ ■ The same result was 
obtained, when the lime was much hotter than the surrounding 
atmosphere. In one instance, the meta! became positively elec- 
trified, when the lime had been put in a perfectly dry bottle, 
which was well stopped by a cork and wax-paper, and left re- 
maining for twenty-four hours, and then its Contents poured up- 
on a glass plate. In another instance, the metal likewise be- 
came positively electrified, but not intensely ; in which case; the 
contents of the platina crucible, which had previously assumed 
the temperature of the atmosphere, were put in a dry porphyry 
mortar, so that the lower surface of the lime, which was touched 
by the zinc plate, became the upper one.' By means of friction, 
however, the metal appeared always to be intensely negatively 
electrified. 
I repeated now, the experiment with burned oyster shells j 
which, as it is well known, likewise give a pretty pure lime. The 
metal was in this case, as longas the crucible was still hot, always 
positively electrified; and shewed, even when the crucible had 
assumed the temperature of the atmosphere, a positive, though 
not intense electricity. This positive electricity appeared; when 
the surface of the lime in the platina crucible itself was touchec 
by an insulated zinc plate. The metal was likewise always po- 
sitively electrified, when it was rubbed with this kind of lime. 
Whilst, therefore, the lime from Carrara marble, by its con- 
tact with zinc, generally acquires a positive electricity, the 
lime from oyster shells acquires by its contact with zinc a nega- 
tive electricity. 
It seemed to be interesting to find out the cause of this diffe- 
rence. The first that occurred to me as the probable cause, was 
the different external condition of the two kinds of lime. The 
lime from Carrara marble was very rough, while the lime from 
oyster shells exhibited a very soft powder. 
By examining the Carrara marble, I found that it contains 
some magnesia. The lime extracted from oyster shells contains 
traces of sulphuret of lime, phosphate of lime, magnesia, and 
oxide of iron. I prepared, therefore, a perfectly pure lime, 
by dissolving Carrara marble in nitric acid, and digesting the 
solution with burned and slacked Carrara marble. Thus the 
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