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Tuesday Jan: 26
I have now before me Bergmans Commentated
Chemica e tertio novorum Societalis Reg.
Leicul. Ups. actirum tomo exerpla. Upsalise
Joh. Edman. Reg. Acad. Typograph 1777. 4to It consists
of two papers: one exhibiting a chemical
analysis of the contents and productions
of Volcanos: the other a chem. analysis of the
several sorts of pretious stones. In the first, p.
65 is an account of the Puzzolana, & which
is nearly the same thing, the Dutch Tras. It
gives the theory of the mortar and with those
substances most clearly & perfectly. I have therefore
extracted what relates to these subjects, which
is as follows.
16
In two specimens 100 parts of Puzzolana
I | II
Silicious (that is chrystalline) earth 55 | 60
Argillaceous 20 | 29
Calcarious 5 | 6
Calx of iron 20 | 15
100| 100
This substance as every body knows mixt up with quick lime
slacked in water presently grows into a stone:
which most useful property is much illustrated
by the account above given of its composition.
The firmness of mortar depends in a general
view upon the lime water, with which
the whole . This attracts the
aerial acid from the atmosphere:
which saturation, the particles
which were separated this is rather
obscure) [ haurto sparticula
soluta ] grow on as it were
to the others and glew them together, whereas
before they were connected only by a kind of
accompanied with a very weak
degree of cohesion. This combination is the sooner
effected, the quicker the water evaporates.
Common mortar is made with sand
a pure silicious earth: the particles of which
being like glass, neither take up water nor
contract
contract any adhesion with any other particles;
by which means the whole mass takes a long
time to dry and harden.
Now then if instead of sand, the puzzolana
be employ'd, the case is very different.
The particles of the clay not only greedily absorb
the water, but by their spongy texture serve
admirably well to connect and fasten with
the other ingredients. Ponder this, there
is the calx of iron, and which has still some
portion of phlogiston adhering to it. This, as
I have has been found by experience, contributes
greatly to the strength of the whole:
insomuch that if to your puzzolana you
add fresh quicklime (by which the water is not only
most greedily absorbed, but by means of the
heat produced by the mixture presently
drawn off in vapour) the whole mass, if
your workmen are lazy, will harden as
they are working it, and become unfit for
use.
The Dutch says (which signifies
mortar) is very nearly of the same
nature as the puzzolana except that it contains
rather more heterogeneous matters (
seems to mean silicious earth ) at least that
does which is brought from Ardernack
like somewhere in Germany near the
for besides particles of mica and iron ore
particles of schoerl and granate, & other substances
may also be distinguished by the eye
and in some measure separated by .
In general too it contains rather more calcarious
earth, as appears from its' effervescing
more violently in acid.
With respect to silicious earth, you are
to understand that the common clay,
which is brought from Cologne ( which I believe
is used for ) contains is commonly
half or even 3/4 of it and more, silicious earth
( See Bergmans Opuscula Vol. 1. p. 289. Holmise Upsalia & 1779.
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Identifier: | JB/539/002/001 "JB/" can not be assigned to a declared number type with value 539.
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1780-01-11 |
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539 |
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Correspondence |
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Jeremy Bentham |
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