1806. | 
fragments of iron ore, of from eight to 
ten feet thicknefs, following exa&ly the 
parallelifm of the flightly inclined decli- 
vities. If the adjacent fields, there are 
many fubftances of the fame nature, of 
violet, brown, and black colours, which 
refemble lava, and which appear to have 
Deen brought to that ftate by ferving as 
hearths, or enclofures to the fres kindled 
in the fields by the peafants, either for 
agricultural purpofes, or perfonal conve- 
mience when they watch their flocks in 
winter. 
The fimilarity of thefe fubftances to 
Volcanic produéts led M. D. to form a ce- 
ment from them, by treating them in the 
fame manner as puzzolana earth. The 
quantity of iron which thefe oxides feemed 
to contain, the abundance of their fili- 
cecus particles, and the alumina which 
entered into their compofition; their great 
weight, and their non effervefcence with 
acids led him to prefume that the ceinent 
formed from them would bind under wa- 
ter. Numerous well-conduéted and {a- 
tisfactory experiments verified the folidity 
of his conjectures and proved that the 
fa&titious puzzolana had acquired under 
water a folidity at leaft equal to that of 
italy. In cafes where both were uied, 
and in which there could be no deception, 
the plaifter made with the Italian puzzo- 
lana was cracked and chapped, but that 
formed from the faétitious kind had 
entirely preferved the unity of its fur- 
face. 
ment which he met with from the govern- 
ment of his country, excited him to farther 
refearches into the principles of cement. 
He tried the calcination of various {chilts, 
of the bituminous, 
argillaceous forts; but thefe contained 
too {mall a portion of iron, for he avers 
that the puzzolanas owe their property 
‘ot hardening in water folely to the ferru- 
ginous particles which they contain, and 
that the puzzolana which forms a body in 
the water is not fit to be employed in the 
Openj air, where it cracks and chaps in 
all direStions. On the other hand, that 
which is proper for the air, and which 
acquires and preferves its tenacity in it, 
fets but imperfe&tly in water. Thele are 
diftinguithed by their colour as well as by 
the peculiarity of their properties. The 
puzzolana proper for works under water, 
is of a reddifh brown; that which is fit 
for works expofed tothe air, is a dark 
violet. The latter is ufed for terraces, 
the embankment of bafins, for the com- 
pofition of enclofures, or light roofs. It 
Montuiy Mac. Na 143. 
Proceedings of Learned Societies. 
M. Dodun’s fuccefs, and the encourage. 
ferruginous, and. 
441 
adheres fo ftrongly to glazed tiles, as not 
to be detached from them without break- 
ing the tiles. ‘The puzzolana ufed under 
water forms a moft folid body, 
months after immerfion it is an actual 
ftone, capable of receiving a polith. The 
lime in it is always converted into carbonate 
of lime in ten weeks. 
M. D.. next proceeds to defcribe the 
exterior characters of the quatziferous 
oxides of iron, which form the bafis of 
his fagtitious puzzolana. ‘Their colour is 
of a reddifh-brown before calcination, or 
flightly violet. A light torrification gives 
them a clearer red tint, or a deep violet; 
one more intenfe renders them of a deep 
brown inclining to black. Urged by a 
longer continued heat, the colour acquires 
a deep black, then the fubftance becomes 
porous entirely fimilar to certain lavas of 
modern and ancient volcanoes. ‘Their 
fracture is grained, and a little earthy, 
and {mall chryftals of quartz may be dif- 
tinguifhed in them by the naked eye, and 
almoft always angular fragments of grey 
or milky quartz :—their {mell is ftrongly 
argillaceouson breathing on them. There 
is no fire produced by the ufe of the 
feel, when it does not ftrike a quartzofe 
particle, They do not effervefce with 
‘acids either hot or cold. The magnet acts 
a little on thefe oxides before calcination, 
and ftrongly, or perceptibly after it. 
The weight is about 125, while that of 
the Italian puzzolana is but 91. 
Thefe oxides contain 
50 parts of filex. 
f iron. 
16 —-— of alumina, 
3 —-— of manganefe and lofs. 
gu wo umes) 
Ioo / 
The puzzolana of Italy containg 
50 parts of filex. 
25 of alumina. 
16 of iron, 
3 of lime. 
6 of lofs. 
100 
Their refpective properties may be appre- 
ciated according to the proportions of 
their integrant parts.. The excefs of alu- 
mina caufes the plaifter made from the 
Italian puzzolana to crack and chap inthe 
open air: this fault arifes from their greae 
oxidation, 
M. D. endeavoured to obtain a regulus 
from thefe oxides of iron by ufing violent 
heat. He followed the procefs of Kir- 
3L wan 
Three 
