On the Igniting Point of Petroleum. KY, 
a small quantity of air, burns very well at a jet (so long as 
the petroleum which supplies the vapour is kept boiling), 
but the vapour itself is not explosive. In short, petroleum 
itself, or petroleum-vapour itself, is no more inflammable 
than common air; it is the #zxrture of petroleum-vapour 
and air that is dangerous. It is almost as easy to show 
that a jet of air will burn in an atmosphere of petroleum- 
vapour as it is to show that a jet of petroleum-vapour will 
burn in an atmosphere of air. 
Now crude petroleum generally gives off, at common 
temperatures, quite enough vapour to form an explosive 
mixture with air, if the air be in a confined space, as in a 
partially empty lamp, bottle, or cask. For this, among 
other reasons, crude petroleum is always refined before it is 
sold to the general public; it is distilled, and the portion 
which first rises into vapour is collected apart, and, under 
the name of petroleum-spirit, used as a substitute for tur- 
pentine, The next, and larger portion which distils is the 
refined petroleum, so extensively sold under various names 
as a cheap illuminating oil. The residue is heavy oil used 
for lubricating purposes. 
Refined petroleum still has the characteristic odour of 
petroleum. Even at the coldest temperature it emits suf- 
ficient vapour to be most obviously perceptible to the nose, 
but not sufficient to form with the air in the vicinity of the 
oil an explosive mixture. But as we rise to the warmth of 
summer, or of a hot room, or the still higher temperature in 
the neighbourhood of a lighted lamp, a point may bereached 
at which the oil emits vapour at such a rate that before it 
can diffuse away into the air of the apartment, explosive 
proportions are arrived at, and on a flame being brought 
into contact with the mixture, explosion results. Now this 
point, the point to which the petroleum must be raised in 
temperature before this vapour isemitted sufficiently rapidly 
to form an explosive mixture with the air in the vicinity, 
will of course vary according to the quality of the petro- 
leum, will vary with the proportion of “ spirit” removed by 
the refiner. If enough has been boiled off, the oil is per- 
fectly safe; but, unfortunately, it is not to the interest of 
all parties to remove the spirit, hence much of the petro- 
leum sold in retail shops is dangerous to use. Should a 
- lamp fed with it become a little warmer than usual, an ex- 
plosive mixture forms in the chamber of the lamp, and any 
flame brought accidentally or thoughtlessly into contact 
_ with the mixture gives rise to explosion. Hence the Legis- 
