1798: | 
Deftroy, as muchas poffible, the aggrega- 
tion of thefe acids and oxydes; and lect 
the aggregation of the carbon, which Is 
to be brought into contaét with them, be, 
ina like manner, deftroyed. Mix thefe 
two comminuted fubftances together, and | 
the mixture will be always a pyropborus, 
if the feeblenefs of the combination of 
the oxygen in the oxyde and the acid, 
together with the comminution and the 
commixture of the carbon and the oxy- 
genous compound, be particularly Ee 
vourable to combuftion, in the fame pre- 
cifé degree with the comminution and 
the funer-caloration of ordinary cafes : 
but the prefence of air is neceffary to the 
{pontaneous inflammation of this pyropbo- 
rus; becaufe only air can begin combul- 
tion, and make it not tacit, but. per- 
ceptible, by means of light and flame. If 
not before the air be prefented, yet at 
leaft almof as foon as it prefenred, the 
temperature, necefiary to the decompofi- 
tion of vital air, is already excited. Moif- 
ture in the atmolphere is favourable to 
the inflammation of pyropborus, for the 
fame reafon for which water poured in 
fmall quant'ties upon a ftrong fire, rather 
feeds than tends to extinguith the flame. 
The water or vapour is decompofed into 
its conftituent parts; and thefe aid the 
combuftion. 
1. Pyropborus, therefore, burns {pon- 
taneoufly with accefs of air, becasfe it 
contains oxygea in fo loofe a combina- 
tion, and in fuch mixture with carbon, 
that thefe advantages towards infamma- 
tion are fully equivalent to that fuper- 
cealoration which is produced i ordinary 
combuftions by the application of free, 
external heat. 
“2. All mixtures are fufceptible’ of 
{pontancous inflammation, in which oxy- 
gen and combuftible matters are mingled 
together, with the above advantages.” 
Such is my humble zbeory of the {fpon- © 
taneous inflammation of fyropdort. 
I am, fir, , 
An admirer of your Mifcellany, 
And your yery humble fervant, 
J. M‘o. 
Invernels Academy, Dec. 12, 1797- 

To the Editor af the Monthly Magazine. 
STR, 
| your Magazine for laft month, I was 
a little furprifed at the communication 
of your correfpondent, “ Thomas How- 
ley,” on the fubjeét of the eleétric “ pro- 
perly belonging to India rubber.” 
. That two people thould accidentally 
fumble upon the fame difcoyery, at the 
Eleftric Property of India Rubber. 
2t- 
fame time, is a little fingular; but it may 
in a degree account for the apparent pla- 
giarifms in the writings of people whofe 
purfuits are fimilar. About the time that 
your corre{pondent obferved the eleétric 
fluid occafioned by the friétion of India 
rubber upon paper, I, alfo, accidentally 
noticed fimilar effeéts, which I .commu- 
nicated in November laft, to a fociety for 
experiments in natural philofophy, of 
which I am a member, in this place. 
Previous to this, I had written a letter, 
with an intention of fending it to you; 
but being defirous of making farther ex- 
periments, I deferred fending it. 
From the different experiments I have 
made, it appears to me, that your corre- 
fpondent is miftaken, if, by faying ‘ the 
property belonging to the elattic refin,’’ 
he fuppofes that the eleétric fluid 1s pro- 
duced from the India rubber. I appre- 
hend it will be found to proceed from the 
fubftance on which ghe paper is laid to be 
rubbed upon, for if it be laid upon a quire 
of paper, a deal table, a piece of leather, 
or parchment, which are very weak non- 
electrics, no effeét, or very tittle, will be 
produced, not more than if laid ona plate 
of glafs, which is an electric; on a linen 
cloth laid on a table, more will be obferv- 
ed; and, if laid on the following fub- 
ftances, the eleétric power will be very 
perceptible, and, I believe, more and more 
in the order of enumeration ufed, viz. a 
-{mooth ftone, a mahogany board, a board 
painted yellow, a board painted chocolate, 
a board painted white, a plate of iron, &c. 
It is to be underftood, that 10 every 
experiment the paper muft be warmed.a 
little, and if the fubftance on which it is 
Jaid to be rubbed be a good conduétor, a 
fpark of a confiderable length may be 
drawn from it (hence an eafy criterion te 
judge of the beft non-eleétrics.) 
The paper may be held by one corner, 
and railed from the tabie, or whatever it 
may lie upon, while under the ftrokes of 
the rubber (of which a few will be fuff- 
cient) when the fpark may be drawn. 
If the India rubber, or any other elec- 
tric, be applied to the excited paper, it 
will difcharge itfelf immediately ; but the 
cracking noife made when difcharged by a 
non-eleétric, will not be heard. 1th 
The property of exciting paper does 
not belong exclufively to India rubber; 
almoft any fubftance, either electric or 
non-eleétric, will produce the eleétric 
fluid, if applied to paper as a rubber, 
though net quite fo much as India rubber : 
amongft many other fubftances which T 
have tried, with the fame effect, I men- 
tion 
