ON THE IGNITING-rOINT OF PETROLEUM. 
319 
proportions, forms an explosive mixture. The combustible properties of this 
vapour closely resemble those of common coal-gas. As with coal-gas so with 
petroleum vapour,—a small quantity in a large quantity of air gives odour to 
the air but does not form an explosive mixture. Again, coal-gas, as supplied to 
the consumer, always contains a small percentage of air, and yet the mixture is 
not explosive, so petroleum vapour, even though containing 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 mixture 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 conhned 
space, as in a partially empt}’- lamp, bottle, or cask. For this, among other 
reasons, crude petroleum is always refined before it is sold to the general pub¬ 
lic ; 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 resi¬ 
due is heavy oil used for lubricating purposes. 
Refined petroleum still has the characteristic odour of petroleum. Even at 
the coldest temperatures it emits sufficient vapour to be most obviously per¬ 
ceptible 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 be reached at which the oil emits vapour at such a rate that 
before it can dififuse 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 its vapour is emitted sufficiently rapidly to form 
an explosive mixture with the air in the vicinity, will of course vary according 
to the quality of the petroleum, will vary with the proportion of “ spirit ” re¬ 
moved by the refiner. If enough has been boiled off, the oil is perfectly safe; 
but, unfortunately, it is not to the interest of all parties to remove the spirit, 
hence much of the petroleum sold in retail shops is dangerous to use. Should a 
lamp fed with it become a little warmer than usual, an explosive 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 Legislature 
of this country has wisely ordered (25 & 26 Viet. cap. 66) that large quantities 
of crude petroleum shall not be stored within fifty yards of a dwelling-house 
or warehouse except under license ; and the Act states that “ Petroleum shall 
include any product thereof that gives off an inflammable vapour at a tem¬ 
perature of less than one hundred degrees of Fahrenheit’s thermometer.” That 
is to say, refined petroleum, such as is commonly vended in retail shops as 
“Crystal Oil,” “Photogen,” “American Paraffin Oil,” etc. etc., for illumina¬ 
ting purposes, must not be kept in or near a house in larger quantities than 
forty gallons, unless proof is forthcoming that it does not give off inflammable 
vapour below 100° F. If it will stand this test, then the liquid is not petroleum 
within the meaning of the Act, and the owner of it runs no risk. I have 
purposely characterized this Act as wisely framed, because some have questioned 
the wisdom of placing restrictions on the sale of petroleum and its products 
(refined petroleum and petroleum-spirit), while naphtha, spirituous liquors, 
knives, razors, and still more dangerous things, are freely bought and sold 
