406 
had lost one-thirtieth part of its weight. 
1 suspect this alabaster was one of the 
softest kind; but the experiment may 
serve to show, that this stone will not 
bear exposure to rain. There are ‘no 
other stones deserving the attention of 
the architect, but those of the silicious, 
argillaceous, and calcareous, genus, in 
the latter of which we may class mag- 
nesian lime-stone, the only building-stone 
into which magnesia enters 1n any con- 
siderable proportion. 
The decomposing and disintegrating 
agency of water, air, and change of tem- 
perature, on stones employed in archi- 
tecture, is the same by which Nature is 
constantly operating to convert solid 
rocks into soil. The fiat of Omnipotence 
“commands the hardest stones to be 
made bread,” or to become the means of 
supporting vegetable and animal life, but 
«the processes by which this effect is pro- 
duced, are slow and gradual. The earths 
of which all stones are cumposed, are 
either to a certain degree soluble in 
water, or are capable of being mecha- 
nically suspended in if when minutely 
‘divided, A drop of water, constantly run- 
ning across the hardest stone, soon marks 
tts path, by catting a furrow in the sur- 
‘face; hence, the well known adage * Non 
vised sepe cadendo.” This effect, how- 
ever, is slow, compared with that of other 
eauses, which are constantly operating, 
Water insinuates itself'nto the pores and 
“minute crevices of stones, and being ex- 
panded by increase of temperature, se- 
parates the parts from each other, but 
it produces this effect in a much greater 
degree when expanded by freezing. Frost 
as the most putent agent by which Nature 
‘operates fen masse,’ frequently splitting 
the hardest rocks, and levelling immense 
‘portions of mountains ina single night. 
dn building-stones which have a tens 
dency to a slaty structure, the destroying 
effects of trust are most likely to be soon 
perceptible, from the faciity with which 
water ca) insinuate itself between the 
Jamina. In stones of the argillaceous 
genus, the joint eects of water and air 
frequently produce a speedy decompo. 
sition, even of those of the hardest kind, 
Tf a stove have a strong earthy smell, 
when breathed upon, its durability may 
be suspected. Iron frequently enters in 
Jarge proportions into argillaceous stones, 
jn a state not perfectly oxydated, and 
acterwards combines with a further por- 
tion of oxygen, forming a brown incrus- 
tation to a certain depth, which becomes 
suft aud falls off, or is washed away, and 
On the Selection of Stones for public Buildings. 
’ 
[June 1, 
the process of decomposition goes on till 
the whole stone is changed. The argill,. 
or clay, in these stones, is also frequently 
capable of absorbing a greater portion of 
water; and the stone may be rendered 
soft by the combined operation of these 
two causes. Jt is in these stones that 
the different earths are combined, in the 
proportions best suited to the support of 
vegetable life. 
Lichens and mosses fix themselves on 
the surface of stones, and, by insinuating 
the minute fibres of their roots, tend to 
accelerate their decay and prepare a ve- 
getable mould for plants of a larger 
growth. The decomposition of many 
urgillaceous stones, which are most ne= 
cessary for the support of vegetable life, 
is most speedily effected by natural 
causes; hence, more caution and skill are 
necessary in their selection for architec- 
ture, No stones of this genus should 
ever be employed, which have not had 
the test of time, without a careful mine- 
ralogical and chemical examination of 
their nature and contents. This exami- 
nation would always precede the applicae 
tion of stones for public works or edifices, 
intended to endure for ages, were engi- 
neers and architects as attentive to their 
future fame, and the interests of pos- 
terity, as to present cmolument. Besides 
the chemical examination of stones, it is 
necessary to try the effect of various de- 
giees of heat, and of boiling water, upon 
them, apphed tor a considerable ume, 
and to note carefully their encrease or 
Joss of weight and other changes. In this 
Manner we may sometimes anticipate 
with certainty, in afew days, what will 
be the effects of less powerful, but long= 
continued natural operations in a serics 
of years. Vor purposes of durable archi- 
tecivre, no stones but those of the sili. 
cious genus should be employed in the 
exterior parts of buildings, la our moist 
and variable climate, afl-kinds of stone 
but the silicious wili perish sooner than 
in countries where the raius are less fre. 
quent. The present state of ourehurches 
and public buildings proves that the ses 
lection of building-stones has been left 
to ignorance or chance to determine, 
The antients, in their public works, ap- 
pear to have had a just regard to perpes 
tuate the glory of the era in which they 
lived, and to leave to posterity durable 
and useful monuments of their skill, 
which should secure their gratitude and 
veneration. The public architecture in 
this country. appears constructed on cal- 
culations of falee economy, and present 
convenience, 
