462 Electro-magnetic Experiment. 
phuric acid, and abandon the silex, which immediately subsides. 
Others resist the action of this acid. 
If we mix in various proportions, very rich lime slacked in the 
usual way, with sand alone, or with puzzolana which resists the 
action of sulphuric acid, we obtain a mortar, which, placed under 
pure water, remains always soft, or acquires, after a long time, 
only a feeble consistence. The same mortar exposed to the air, 
soon hardens by drying, but is always easily broken or pulverized. 
But if the same experiment is made with a puzzolana readily 
affected and decomposed by sulphuric acid, a mortar is obtained, 
which soon ‘sets under water, and becomes gradually harder, but 
in air it does not acquire any great resistance in consequence of 
its drying too rapidly. 
Hydraulic lime presents phenomena nearly the reverse. That 
is to say, it furnishes good mortar when combined with sand 
alone, or with puzzolana unaffected by acids, whilst very unsa- 
tisfactory results are obtained by employing it with substances 
which unite well with rich or pure lime. 
Since the quality of natural hydraulic lime depends only on 
the presence of a certain quantity of clay or argill combined by 
heat with calcareous matter, it is natural to suppose that in 
mixing clay in suitable proportions with a rich slacked lime, and 
submitting the mixture to heat, the same result might: be ob- 
tained. Experiments made upon a large scale, and in various 
laces, have confirmed this opinion so fully, that it is now 
possible to fabricate almost every where, and at a very moderate 
price, artificial lime superior to the natural. 
ELECTRO-MAGNETIC EXPERIMENT. 
The discovery of M. Zamboni concerning the electricity pro- 
duced by the contact of a single solid canductor with a single fluid 
conductor has been confirmed by Professor Oersted of Copenha- 
gen, who thus expresses himself in a letter on the subject : 
< You know that such experiments are extremely delicate ; 
they seem to have been repeated only by Mr. Erman, and this 
celebrated and ingenious philosopher complains much of the ir- 
regularities which the experiments present. 1 have found in the 
electro-magnetic multiplier, invented by Schweigger, a mode of 
making these experiments with the greatest ease. I take two 
plates of zinc, of different breadths, one for example 3 lines 
broad, the other 143 I place them in a diluted acid, and I make 
= commnnication between each of them and one of the extre- 
iuities of the metallic wire of the multiplier. The action is thus 
rendered very sensible. The wider plate assumes in this galvanic 
are the place of the copper, the narrower that of the zinc. When 
we take two plates which are perfectly equal, and attach thetn 
to 
