90 
OF THE INFLAMMATION . 
. OF PYROPHORI. . 
To the Editor of the Monthly Magazine. 
UST RS 
SEE, with great pleefure, that you 
are extremely fuccefsful in your at- 
tempts to cook up the wi/e with the duice, 
The public relith the dith, Nay, 1 be- 
lieve, there never was a Scotfman fonder 
of his Aaggice, nor a Englifhman -of his 
beef-fieak, nor a Spaniard- of his olla 
podrida, nor an Italian of his macaront, 
than are all thofe among my neighbours, 
who are thought connoiffeurs in the food 
of the mind, of the Monihly Magazine. 
You cannot be ill-pleafed to know, that 
your Mifcellany has found its way as 
far north as did Cromwell's foldiers, and 
Englith caébages, in the middle of the 
Jaft century; and is read with cagernefs 
on the claffic grounds of Macbeth, and of 
Offian. 
It is 
THEORY 
not, however, a clafizc matter, but 
a fimall chemical trifle, with which I] now 
with totrouble you. There is-a particu- 
_lar compofition, known to chemifs by 
the name cf pyropdorus, becaufe it pof- 
fefles the property of being liable tofpon- 
tancous inflammation tn the open air. 
Tc was compofed by Homberg, apothecary 
and chemift to the famous regent duke 
of Orleans, by the diftiliation of alum 
with the refidue of human excrement. 
“There are very many vegetables and 
animel ‘matters which, if treated with: 
alum, afford this pyrophorus. It may be 
. . , : eZ, \ 
obtained from. the greater number of 
thofe falts which contain fulphuric acid: 
in union with whatever cafe. M. Prouft 
has even proved, that any fubftance con- 
taining’ carbonaceous matter, In wuion- 
with an earth or oxyde, is fulceptible of 
this fpontaneous combuftion m the air. 
Tt is now commonly prepared by meling 
three parts of alum with one part of 
fugar, honey, or meal, expofing the 
melted, cooled, and hardened mixture, a 
fecond:time, to heat, till ir be kindled to 
burn -for 2 few moments, with a bluetfh 
flame; then cooling the matter thus 
burned and preferving: it in a dry flatk, 
clofely fiopped, to be ufed as pyrophorus, 
Expofure to the atmofphere brings it in- 
flantly co burn with a flame fuffciently 
vivid. The more humid the air, fo 
much the more readily does this inflam- 
mation take place. 4... eS 
To -account.for.a phenomenon fo re- 
markable, as the fpontaneous infamma- 
tion of this pyvophor7s, chemifls have 
éfered feveral different theories; which 
are almoft all alike unfatisfactory. Hom- 
Inflammation of Pyrophori. 
[Jane 
berg and Lemery fuppofed, that the pre- 
fence of calcareous earth in the mixture 
was the caufe of the inflammation. Le Jay 
de Savigny imagined the mixture to ton- 
tain a glacial oil of vitriol, which, attracting 
moifture from the atmofphere, gradually 
heated the mafs to inflammation by this 
means. Mr. Bewly, ina letter to Dr-Priett- 
ley, afcribesthe fame effc& tothe prefence 
of 2 principle in the pyrophorus, by which 
there 1s nitrous acid attraéted from the 
atmofphere, Others have conjeétured, 
that the combuttion of pyrophorus by {pon-. 
taneous inflammation, might be owing to 
its always containing in it a quantity of 
phofphorus. But none of all thefe 
theorics has been received in ‘he world 
as completely jut and tatisfaétory. 
Now, fir, I think ] can exhibit a new 
and pccusiar theory of the relaiions of this 
curious chemical phenomenon, of which 
the ftriking truth and fimplicicy thall not 
fail to command the immediate affent af 
all intelliven: chemifts. 
In combutftion in general, the principal 
thing that always takes place is the new 
combination of oxygen on the one hand, 
with carbon, cr fume difference matter, on 
the other hand. The oxygen for this 
new combination is ufually detached out 
of its union with light and caloric in vital 
air. -The light and calorie which it 
deferts, are, in confequence of this defer- 
tion, commonly evolved into a momenta- 
‘rily, free ftare, in which they prefent 
themfelyes to, our fenfes, as heat and 
flame, . But carbon and cther combuftible 
matters cannot, in every temperature, nor 
in, every ftate of aggregation, detach 
oxygen out of viral air, and by its abftrac- 
tion produce an evolution of heat and 
flame. It is neceflacy, in order to this 
event, that the carbon or other combufti- 
ble matter be, where it is prefented ta 
the contact of the vital air, confiderably 
comminuted; and that the vital air ex- 
hibited to it be, at the fame time, fuper- 
calorated, in fuch a manner, as that the 
ordinary mutual attraétions of its ingre- 
dicnts may be greatly weakened by the 
fuper-caloration. In this ftate alone of 
the refpective fubftances, does the phe- 
nomenon of combuftion ufually take place. 
But there are oxygencus compounds in 
which the oxygen is much more flightly 
combined than it is in yital air: and it is 
pofble to exhibit carbon ‘to ‘oxygen in 
fome ftates which fhall be more favour. 
able to combuftion than others. In cer 
tain flates of moft of the acids and the 
metallic oxydes, oxygen undeniably exifts 
in them, in a very loofe combination. 
Deftroy, 
