Encyclopaedia Britannica > Volume 7, ETM-GOA

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¥?tz-{le* Ciuf/s ; ‘The New Natura Brevium ; Of the Surveying the acidity of the folvent, but may arife from the phlo- Fixed
°f huands; .and The Book of Hufhandry. He died in gifton contained in it. —~v
Fixed Air. 1 S38- . “ F‘xed air is.a1/0 luppofa* to be an acid, by dimi-
y—»< FITZ-STEPHEN (William), a learned monk of niihing the caufticity and promoting the cryftallization
Canterbury, of Norman extraction, but born of icfpec- of fixed alkalies: but this hypothefis does not agree
table parents in the city of London. He lived in the with the effeCts which are produced by the combina-
12th century; and being attached to the fervice of arch- tion of acids with alkalies. By thefe combinations
biihop Becket, was prefent at the time of his murder, neutral falls are produced; but alkalies do not become
In the year 1174, he wrote in Latin, The Life of St neutral by combination with fixed air, being only
Thomas, archh'fhop and martyr; in which, as Becket changed by fuch an union from cauftic and deliquef-
was a native of the metropolis, he introduces a defcrip- cent to mild and cryftallizable alkalies : whence it is
tion of the city of London, with a mifcellaneous de¬
tail of the manners and ufages of the citizens : this is
defervedly confidered as a great curiofity, being the
earlieft profeffed account of London extant. Fitz-Ste-
phen died in 1191.
FIVES, or Vives. See Farrierv, Se£l. xiv. 2.
FIXATION, in chemilhy, the rendering any vo¬
latile fubftance fixed, fo as not to fly off upon being ex-
pofed to a great heat: hence, «
FIXED bodies, are thofe which bear a confiderable
degree of heat without evaporating, or lofitlg any of
their weight. Among the moft fixed bodies are dia¬
monds, gold, &c. See Diamond, Gold, &c.
Fixed, or Fixalle Air, an invifible and permanently
elaftic fluid, fuperior in gravity to the common atmofphe-
ric air and moll other aerial fluids, exceedingly deftruc-
tive to animal life ; produced in great quantities, natu¬
rally from combullible bodies, and artificially by many
chemical procefles. From its apparently acid properties
it has obtained the name of aerial acid, cretaceous acid, and
carbonic acid; from its noxious qualities, it has been
called mephitic air, or mephitic gas; and, from the cir-
cumitance of being produced in vaft quantities during
the combuftion of charcoal, it firft obtained from Van
evident, that the alteration in them produced by fixed
air is not to be attributed to the introdudtion of an
acid.
“ We mult therefore (continues our author) turn our
eyes to the coniideration of fome other principle by
which thefe effe&s may be produced; and this prin-
ple appears to be phlogifton. The phlogifticated al¬
kaline lixivium is perfeftly mild when faturated ; and
by a flight evaporation is reduced to a concrete
cryltalline mafs, which does not deliquefee or imbibe
the leaft moilture from the air, and no longer retains
any alkaline charadter or property. M. Beaume, by an
elegant and ingenious experiment, has proved the pre¬
fence of phlogifton in mild alkalies; and has fliown,
that their power of eryftallizing depends upon their
union with that principle. He heated in a filver veffel
a lixivium of mild alkali, which imparted to the filver a
covering or coating of inflammable matter, by which
its furface was tarnilhed and became black. The lixi¬
vium was feveral times poured out of the filver velfel j
and after the furface of the metal had been freed from
the tarnilh, the lixivium was replaced in it, and again
heated, by which the tarnifh was renewed. This was
repeated till the lixivium no longer communicated any
Helmont the name of gas fylwfire. The term fixed ftain to the filver. The caufticity of the lixivium in-
air has been given from its property of readily lofing creafed in proportion as it imparted its phlogifton to
its elafticity, and fixing itfelf in many bodies, particu- the filver; and at the end of the procefs the alkali be-
lavly thofe of the calcareous kind ; and though fome came perfe&ly cauftic and incapable of cryftallizing.
objected to the propriety of the term, the fluid in “ Thofe inftances, and many others which might be
queftion is fo well known by the name of fixed air, adduced, feem to prove that the change which fixed
that we choofe ftill to retain it. air produces in cauftic alkalies is not effe&ed by acid
The nature and properties of fixed air are explained but phlogiftic matter. It is certain, that the matter
under the article Aerology. It is there confidered communicated to lime by fixed air is the very fame
as an acid, and the reafons for fuppofing it to be which it imparts to alkalies: for it may be transferred,
compofed of phlogifton and dephlogifticated air are fet unchanged, from one of thefe fubftances to another;
forth. In a paper of the Manchefter Tranfa&ions by and when united to either of them, ftill retains the
Mr Delaval on the permanent colours of opaque bodies, fame qualities. Therefore, if phlogifton renders al-
j he confiders the nature of fixed air, and gives an ac- kalies mild, and effedfs their cryftallization, the fame
Mr Dela- count fomewhat different. He denies its acid property, principle alfo precipitates lime, and in like manoer
fixeefri/ ^as keen generally looked upon as fo well afeer- reftores it to its ftate of mild calcareous earth.
© xe ‘*ir-t3;ne(ji “The change of colour produced in vege- “ The experiments and obfervations on which Dr
table juices by the eleftric fpark (fays he), is adduced Black has eftablilhed his comprehenfive and conliftent
as a proof of the acidity of fixed air ; but it has been theory, clearly prove, that lime is precipitated from
already fliown, that this does not arife from acid, but lime-water by fixed air; but his views were not ex-
* See Wro-phlogiftic matter *. The acid quality of fixed air is
matics, alf0 generally inferred from its power of diffolving
® 31, iron. But phlogifton is alfo a folvent of iron. Thus
a confiderable portion of that metal is always diffolved
and held in fblution by the phlogifticated alkaline
lixivium, which confifts of inflammable matter calci¬
ned with fixed alkali. M. Margraaf has ftiown, that
feveral other metals are foluble in this lixivium. Hence
it is evident, that the folubility of iron does not prove
5
tended to an inveftigation of the particular matter or
quality whereby fixed air operates that effe&.
“Lime, which has been precipitated from lime-water,
and reftored to the ftate of a mild calcareous earth, is
again foluble by the addition of a larger proportion of
fixed air ; which has been confidered as an additional
proof of the acidity of the latter. It has alfo been confi¬
dered as an extraordinary circumftance, that two fuch
oppolite effects Ihould be produced by the fame fubftance.
The