Year: 1860

In a paper recently read before the Royal
Society, Professor Anted sirected attention
the state of the stone in many of the prin-
cipal buildings in England and on the Con-
tinent, illustrating the extreme irregularity
with which various materials, and even sam.
Piles of the same materials, resist the action
Of the weather and fall into decay. He then
described the chief building materials, ex-
planning in each case the cause of decay
Commencing with general remark, that all
stones are rotten or weathered at the top of
a quarry or near an earthly surface, and this
the action the weather is in some measure
thus indicated, he first alluded to granite
He stated its properties Of hardness and
great durability in ordinary cases; but re-
marked that when soda replaced potash in
the felspar, the crystals of felspar were SUBJ
ject to the action of the weather; and that,
from some cause little known, the silica base
also occasionally failed. Still, the great prac-
tical objection to the use of granite is its
cost Passing next to the sandstones, he
defined them, mentioning the chief varieties


He stated that the nature of decay in sand
stones were generally the failure of the ce-
menting medium, which is sometimes si.ciou,
but more frequently calcareous or clayey, or
even oxide of iron. He pointed out the cause
of decay the want of sufficient cohesion in
cementing medum-the nature of the cement
ing medium itself, and the effect ofexpansion
and contraction of water absorbed by the
stone. The limestones were next considered,
and the principal varieties passed briefly
under review. They are all freestones-
some are crystalline, others semi. crystalline,
but most of them are earthly, or oolited and
absorbent. They consist of particles of car
Donate of lime, whether grains, as in the case
Of chalk, or accumulated Jumps, like oolite or
roe-stone, or fragments of shell ; and these
particles are cemented together by carbonate
of lime. The stones are generally laminated,
though the bedding is often extremely OBJ
scure. When exposed to the action Of the
air In towns, they absorb moisture and acid
gases very readily, and the result is a grad
ual destruction of the surface, and often a
rapid removal of the particles beneath the
surface, especially on the planes of bedding.
When stones are not placed in building as
they were in the quarry, the surface peels
off in natural films, and is more rapidly acted
on than it need be; but not unfrcquently,
even when well placed, the surface gets
hardened by exposure more rapidly than the
substance Of the stone, and scaling still
takes place. The more exposed parts, those
subject to drip and constant damp, and the
more delicately sculptured portions, are
among the first to decay and, owing prob
ably to differences in the mode or rate of
deposite of the mud of which the limestone
was formed, or some partial change that has
since taken place, there is great irregularity
in the rate of decay. Magnetism limestone,
or colomites, when quite crystalline, behave
like marble but when, as usual, only half
crystalline, they are very apt to become re-
duced to powder in parts, and the decay
thence proceeds with extreme rapidity. The
Professor next proceeded to consider the
remedies for decay. He alluded to paint as
at once unsightly and not permanently benefi-
cial, and included the large class of preser.
vatives that have been suggested, in which
any animal or vegetable oil or fatty matter
was contained, as equally valueless, either
peeling off or rotting in the stone, and leav-
ing soon exposed to ordinary decay. The
minera! bitumens, he stated, had not been
much tried, owing to their dark, unsightly
color. What is required is some mineral
preparation. He then alluded to the water
glass, soluble silicate Of potash, originally
described by DIR. Fuche, and applied to indu-
rate stone by NJ. Kuhlman. He explained
the principle of this process as depending on
slow decomposition by exposure to the air,
and stated that, as meanwhile the infuen-
ces Of the weather continued to act, the
method could not be adopted with advantage
in the op n air in damp climate, where
preservation is chiefly required. The only
plan that, as far as he was aware, met the
requirements of the case, he stated to be
that adopted by Mr.. Ransome, according te
which the absorbent surface, whether oil
stone or terra-cotta, was saturated with the
diluted solution Of soluble silicate of soda


and then treated with solution Of chloride
solutions, double decomposition is induced


The silicic acid parting with its soda to the


chlorine, producing chloride of sodium, Oh


common salt, and combining with the lime


to form siiicate oflime. The salt being wash


ed away, only the silcate of lime remains


The silicate oflime thus thrown down h,


next explained to be salt, which was no


only itself non-absorbent and singularl,


powerful in resisting the action of ordinary


atmospheric influences, but rs having tn


property of adhcring rapidly to the surfac
Of the minute particles ofwhich stone wa


formed. He illustrated this by the case 0
mortar and concrete, which owe their adhe
sive properties to this habit of silicate @


lime, which is the mineral formed by tn


mutual action of the cement On the substan


ces in contact with it. The stone havin,
its particles thus coated with silicate of lime


and all the absorbent surface being thus pro
teeted, the result is an immediate and grea


hardening of the stone, so far within its sub