ON THE IGNITING-POINT OF PETROLEUM. 
321 
terial to be ignited. Neither the petroleum nor the gunpowder, however, is 
any the less dangerous on that account; for, should the ignition of the mix¬ 
ture of petroleum-vapour and air cause an explosion so slight as only to force 
up a little of the petroleum into fine splash or spray, ignition of the petroleum 
will inevitably ensue, as in that condition petroleum is inflammable even at very 
cold temperatures. 
But to proceed to show why a given specimen of petroleum may be observed 
to ignite at various temperatures. 
TJie time employed in the operation of taking the igniting-point of petroleum 
as usually performed, is the first cause of variation to which I shall allude. 
About two ounces of a specimen of petroleum marked “ Ladoga” was placed in 
a small dish or capsule about five inches wide and one inch deep, and very slowly 
warmed by a gas-lamp, a small flame being passed near the surface of the liquid 
every quarter or half minute. The liquid was stirred with the bulbed end of a 
thermometer, the temperature rising at the rate of about a degree per minute. 
In this way the experiment was carried on until at 124°, as marked on the 
stem of the thermometer, the petroleum-vapour ignited, and the liquid also 
ignited at the same instant. A similar experiment was performed on a fresh 
specimen of the same oil, except that the temperature was quickly raised ; igni¬ 
tion of the vapour took place at 95° and the oil itself took fire at 111°. It 
would seem that the highly volatile portion of the petroleum, the portion which 
forms inflammable vapour, soon escapes when the oil is heated in an open vessel, 
leaving a liquid less inflammable than before. We know, from the researches 
of Ronalds, Schorlemmer, Pelouze, Cahours, and others, that petroleum, utterly 
unlike sperm, colza, olive, and the other old burning oils, is a mixture of a large 
number of liquids of different degrees of volatility, and, indeed, containing 
bodies which when isolated are permanent gases, hence the above result might 
have been expected. 
T]\q rate of escape of vapour horn. i\\^ oil and from the operating vessel is 
another cause of variation in the igniting-point. Some of the same “ Ladoga ” 
oil was treated as already described, except that it was heated somewhat quickly, 
and was only stirred just before taking a reading of temperature. This time 
ignition occurred at 98°. Stirring, as is well known, promotes the escape of 
vapour from a liquid, and in this case also by causing eddies and currents of air 
promotes its escape from the surface of the liquid. 
The form of the vessel in which the petroleum is heated, by accelerating or 
retarding the escape of vapour, also causes variation in the igniting-point. Some 
“ Ladoga ” oil was heated gradually but quickly in a wide-mouthed bottle ; the 
mixture of petroleum-vapour and air thus formed in the upper part of the 
bottle gave indications of ignition at 92°, and fairly burnt at 94°, several de¬ 
grees below the igniting-point in an open vessel. 
The arrangement of the vessel over the source of heat of course influences the 
result. If a dish, etc., be so placed that its upper walls, not covered by the liquid, 
become much hotter than the lower portions, then the petroleum stirred up on 
to the hot part is quickly converted into vapour and ignites, while perhaps the 
liquid itself is comparatively cool. This is simply bad manipulation, and any 
one making an error of this kind should not be trusted with the performance of 
such experiments. Making the experiment in a deep glass beaker, or wide¬ 
mouthed glass bottle, and so frequently introducing a large test-flame, that the 
upper part of the vessel becomes full of the products of combustion to the ex¬ 
clusion of much of the air would, of course, be equally bad manipulation. It is, 
perhaps, unnecessary to allude to these causes of variation, but that inany of 
those to whom these remarks are addressed deal much in petroleum, but have 
no knowledge of practical chemistry. The usefulness, therefore, of the obser¬ 
vations must be the excuse if they are trite and commonplace. 
