402 
made, has been little understood or at- 
tended to. During a few months’ re- 
Sidence in the metropolis, I was induced, 
by the nature of my mineralogical pur- 
Suits, to pay some attention to the dif- 
ferent stones of which the pavements 
and public edifices are constructed. Ou 
walking into the court of Somerset- 
house, after some weeks of dry weather, 
I was particularly struck with the ap- 
pearance of the columns on the left 
hand, facing the west. “The stones, in 
three columns, were some of them en- 
tirely coated with soot, when the stanes 
above and below were perfectly white. 
In other ‘parts, a white stone was be- 
tween two black ones, and the division 
of colour as distinct as if the one had 
-been painted white and the other black. 
These stones were all equally exposed, 
and the variation of colour could not be 
explained by their situation. At first 
I conceived, that this difference of 
colour might be occasioned by some sub- 
stance entering into the composition of 
the black stone, that had a chemical 
affinity for ammonia, which is contained 
In soot; but, on examining some of the 
stones thatavere within my reach, I found 
that those which were covered with soot, 
had a hard, smooth, surface, and the 
white stones were evidently decaying. 
The particles on which the soot had 
fixed, were fallen off, and had laid bare 
the natural colour of the stone, as per- 
fectly as if they had been recently scraped 
with a chissel. In other parts of the 
building, I observed the visible decom- 
position of the stone, by moisture, par- 
-ticularly in the upper part of the alto 
relievo figures, 
This edifice, like most of the modern 
buildings in the metropolis, is constructed 
of Portland-stone; a peculiar kind of 
lime-stone, which I shall afterwards more 
particularly notice. It is evident, how- 
ever, that this stone which is considered 
of the same kind, and comes from the 
same place, varies much in its property 
of durability. 
- When the same stone is constantly 
exposed to the action of water, the dif- 
ference in its qualities of resisting decay 
is more apparent, as is evident from an 
inspection of London, Blackfriars, and 
Westminster, bridges, at low water.* 
Se a ee En aR NE! eS Gs OL 
* The stoves of Westminster bridge ap. 
pear to have been selected with more know- 
ledge, as they are much lees decayed than 
those of Blackfriars; the architect was a 
Freachman. 
‘ 
2 
Application of Mineralogical and Chemical Science 
[June 1 
The best kind of Portland stone is ill 
suited to resist the decomposing effects 
of water, the two former of these mag- 
nificent bridges, constructed at so much 
expence, are perishable monuments of 
the neglect of mineralogical science, 
In stones of the argillaceous genus, 
more striking instances of rapid decay 
occur. I have seen stones of this kind, 
in their native beds, or quarries, some 
hundred feet under the surface of the 
earth, so extemely hard, that they re- 
sisted the point of the pick-axe, and could 
only be removed by blasting with gun- 
powder; yet, when the saine stone was 
exposed to the air for a few mouths, it 
became soft and shivered into small 
pieces, The cause of this sudden de- 
cay, [ shall afterwards explain, It rarely 
happens that builders or architects have 
auy acquaintance with mineralogical'and 
chemical science, to enable thei to an- 
ticipate the changes which will be effected 
in the materials they select, by the action 
of the agents to which they are to be ex- 
posed, The loss and disappointment 
which this ignorance has occasioued in 
the construction of many publie works, is 
well known.—A remarkable instance of 
this kind lately took place at Paris. A 
gentleman was walking with an eminent 
mineralogist in one of the newly-erected 
public edifices; they were pleased with 
the appearance of some large columns in 
the interior; when the latter had exa- 
mined them tore closely, he predicted, 
from the nature of the stones, that they 
would perish in less than three years, 
About ten months after, the gentleman 
happened to pass the same place, and 
observed the stones of these columns were 
shivering so rapidly, that workmen were 
then enzaged in replacing them; which 
had become necessary to seeure the 
roof. In forming the tunnel of the Hud- 
derstield canal, which is three miles in 
length, the workmen in one part had tu 
cut through a bed of stone of consider- 
able extent, so hard that they were 
obliged to remove it by blasting. It ap- 
peared so compact and firm, that ft was 
thought unnecessary to wall and arch the 
passage; but, in a few months after the 
access of air to it, it shivered and fell in; 
and the removal and repair occasioned 
much delay and expense. It was a dark 
campne argillaceous stone, containing 
oxyd of iron, and resembling son-e kinds 
of basalt; but its. shistose or slaty 
structure was soon apparent, and it 
became as soft as the bituminous shale 
which accompanies coal, Some kinds of 
stone. 
