102 N A 'T U R A Ifo I I I S T O R Y
Reel, weighs to water-a»*2'4 % * i- The fpecimen weighed in
air'fifteen penhy-weightsten grains i and’after being bnmetfod three
minutes, and cmefoUy‘4 ripfed, it weighed fiftéeB-penny-weights^ten
grams and half, by which it Sppearshthat this marble admitted no
water at all into its pores. It burrfifto a whitef e ê^a f , but make*
no figh 'ö f férthènting afterwards, when fpxinkled with common
water: Much better is the marble about a mile north of Piadftow,
at a place-called Porrrüflën, where th’ere are in the cliff gTfcaf quantities
of marble, the ftrata one foot and half thick-at- a medium,
intermixed with Ihelfy flat; the marble is fometimes cut into chimney-
pieces and tables, makes flabs for hearths, and fmall fquares for infert-
ing between the angles o f free-foone; pavements 5 r:the ground of it
fomewhat blacker than the foregoing, a n d '^ v ^ T ^ ^ . | | V f o A e
ground* grit, texture, finer and clofer; the formeiitations “#iöi acids
the fame’ : it takes a very high polifh, but’ fo hard withal, that
perhaps Italian marble is foil as cheap *. Among theXSorhifo marbles,
according to Linnaeus’s Syftem, (fee page i $ê) wrhfoft reckon
avfine gypfom or plaifter of Pam, difeoVered'ld:tefy; in the pfoi& o f
St: Glare, near Lifkerd, equal to arty thing of that kind found abroad.
sect.ix. It may not b e ; here unfeafonable t6 add a : remark or two
Of theweight upon the weight and dampnels of ftones in general, and o f the
S f i T 6 feitgwng in particular. As by - -weighing Tfoemwe
difcovered their .foecific ■ gravity nearly, with -regard to-oilb
another and lo the common ftandard-water f i p b y weighing them
carefoily wiped after their immerfion* We may pemC%e%hst4 uafi^-
rity o f water has entered their pores, and in what time, which may
lead us to fane ufefol obfervaricMis ; and^ amOtg the eftimate
the dampnefc o f each fort o f ftone in Walk and pS^ments;
foraccording to the quantity of water imbibed ip<anyj(we& time,
and its fiownels or readinefs to remit and evaporate that moifture,
fo wffl be the dampnels df any wall built of that ftone with like
and equal cement. I f it retains as well as imbibes, then it muft
be latorated with water before it can occafion any damp; -and therefore
the free-ftone a f Garantok, and any other Of like nature", imr-
bihrng freely, and retaining greedily, will fook entirely into its body
all the common moifture of the air and cement, and keep it there
without imparting any perceivable quantity to the infide of the wall
or room. I f it imbibes water foddenly and as readily parts with it, as
fome of our granites do, it will infallibly occafion damps within and
without; it will difperfe it’s dampnels inwards, yielding it to the
h Dr. Woodward takes notice of mafBle'hbddlês
variegated1 with 'brown, red, and white, from the
fhores of the Land’s End. - Cat. A x , b 7.
* There is a blue-black {tone of a marble texture
’found on Gunhilly downs ; I have noted it
'alftrin the.iparifh-of Kîlkhampïdn : it cutï- into neat
moldings, and brars,carving : it will not ferment
with acids.
* 'Portland, iBafh, and. Oxford,
attraction
•0 <F.T;a O O R M *WAA.4T 4 L. xg% i ,
attmtftion'of the greater-heat within,a moqrmv wall, than there is
on the oUtfid# o f the wall. If it be fo haid that it will not admit
of any water into it’s pores, which is the cafe of fome marbles ,
however ooeafion great damps, r by, condenfing the mgifture
of the air (which would otherwife gently difperfe and vanilh) into
water, to fuch a degree, that pavements, ornaments and pannels,
of fuch marble, fhall fweat «(as the ufuaj phrafe is) and even run
with water. It being the ufiial and juft method to line walls with ^
brick,- to make the walls whollbme arid dry, in order, to. difcqver
by what means bricks obviate damps, I made the following experiments
in July, 1755. I took two bits from off the fame brick, of
the clofeft and moft uniform texture N°. i . weighed in air, 314."^
grains; after it had been immerfed five minutes mywater, j t , weighed',
|(afier being carefully wiped with afJiain/lloth) 3 68 «grains, fo ,th$t *
it imbibed,| by an, immerfion of five, minutes-, ^4 grpifis which^
to it-s* whole is as one-fifth - -
2, .'weighea in air ^26"grains,'but after ah immerfion 'of'five„.
minutes,,,39 2 »grains, .having imbibed 66 grains; 'the fame brick having^,
sofie’fif it’s angles placed contiguous tQ.forne drops sofiiviief j IfuckeS
up ftill foo®e.;. a third dpseknenfdof like vwnljflsmie, (which had
not feeen immerfed at alfi I on touching
them out of fight immediately. #y thsfo experiments it isi-plafii,
that fafok does notkibbviate 'damps'ksif it?s ayferfiola1' fo, or repulfion.-
o f water, bcoaufe it imbibes water more mpacioufiy than&nyiftone.
I placed therefore both t id e pieces of brick fo . charged with
water, in a South dry window, Jnly i 5,^1.755, at nfoe undock,
a. m.;. hybaselv© at naonlNi',a had evaporated five grains, ,hy half
paft three, ip. m. it had loft fixe grains more ; atrfive it had rather
gained than/loft (the weather proving rainy); bysthfoe- quarters after
fisc, p. na. it had ioft only half a grain in three hours and & quarter,
ithe weather eratiouipg .ekrndy, iwith fome rsan ; at half hour aftier
five tiae next asnqmiog, July it had ioftsmore,; fonrigrains and
a half, and by nine,; a. m. which acompleatsedithe 24 hours,-»ife; had
: loft more, four graiasj;rifb that; In 24 hetefes thh ©fee©®* hrick hod
^evaporated -by natural heat, nineteen grainSj i wiiach, to l^y-fopty
the quantity imbibed is fomewhat anore than one .third'.1
N°. 2 had been purpofely for a. moment or two, put contiguous
to water again, ta-try if it would, imbibe more moifture than it’s*
immerfion had fopplied it with, and yet in 24 hours, this fpecamen
evaporated only fiaXeen grMns;-diz. one quart« and ®w6i-lpcteehiths
of what h had imbibed.
So retentive is brick o f that mbifture which it admits-^fty. which
i t appears that brick obviates damps, iiot foy rcfiftingkor dfefending
See Carantoc marble abqve.
the