TRAS 15

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.

17

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.

18

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.

19

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

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.

20

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.

21

With respect to silicious earth, you are to understand that

the

common clay,

which is brought from Cologne ( which I believe is used for

is commonly half or even 3/4 of it and more,

silicious earth ( See Bergmans

Opuscula Vol. 1. p. 289. Holmise Upsalia &

1779.