586 
LIVERPOOL chemists’ ASSOCIATION. 
sessing, amongst other properties, different specific gravity, igniting point, and boiling 
point. The same remarks apply to the refined commercial products ; they have not one 
definite composition, but are made up of hydrocarbons, varying in speciGc gravity and 
igniting and boiling points. To separate these commercial products one from the other, 
advaiitage is taken of the difference in boiling point, which runs through a range of 
several hundred degrees, and the process of fractional distillation is resorted to. The 
actual point of separation of these products one from another is, however, probably not 
the same in any two works, yet it is of great importance that products sold under the 
same name, and for the same purpose, by different makers, should approximate as 
closely as possible in quality. The spirit consists of those portions of the crude oil pos¬ 
sessing the lightest specific gravity and lowest igniting point, and, boiling at compara¬ 
tively low temperature, passes over from the still first, and is collected separately. Those 
portions forming the burning oil, having a higher boiling point, distil over at a higher 
temperature, they have a heavier specific gravity and a higher igniting point; whilst 
the lubricating oil, again, is composed of those portions possessing still heavier specific 
gravity, and higher igniting and boiling point. During the process of distillation the 
rise in specific gravity, etc., is so gradual, and the different products merge so one into 
the other, that it depends much upon the whim of the manufacturer as to the exact 
point of separation ; but, unless this is fixed at the proper point, the products cannot be 
satisfactory. Now, bearing these matters in mind, it will be easy to follow a few fur¬ 
ther remarks upon the igniting point of the lamp oil. If the collection of burning oil 
commences at too early a stage, it follows that portions of the spirit are mixed with it, 
and an oil of low igniting-point produced. On the other hand, if the collection of the 
burning oil is carried too far, portions of the lubricating oil are mixed with it; a higher 
igniting point will be the result, but the specific gravity will be so increased that the oil 
will not rise properly in the wick. Now, there is seldom much chance of the latter 
taking place, for, if the collection of burning oil is continued beyond the proper limit, 
the resulting product is of a deeper colour, and this is objectionable to the buyer; and 
as it is a fault readily detected by the eye, it is at once noticed. But in the former case 
the fault, although far greater, is not so readily detected, and the appearance of the oil 
is probably improved instead of being deteriorated; but here “appearances are deceit¬ 
ful.” The point of ignition being low, the oil is not so safe to use in a lamp. I do not 
consider that any oil should be sold as a lamp oil unless it has an igniting point not under 
110° F., for the simple reason that a temperature closely approaching 110° F. is obtained 
in an ordinary mineral oil lamp. Experiments made by Dr. Attfield, of London, and 
which I have carefully repeated with similar results, show conclusively that this is the 
case. Although the oil in the reservoir of the lamp may not, under ordinary circum¬ 
stances, become warmer than 80° F., yet, in its passage up the wick, it has to pass 
through the heated brass-work, the temperature of which, at that part presented to the 
interior of the reservoir, ranges, according to careful experiments, from 100° to 110° 
F. ; and during the passage of the oil through the brass-work, if it has a lower ignit¬ 
ing point than the temperatures just mentioned, it will evolve vapour into the upper 
part of the reservoir, and, if any air is also present, an explosive mixture will be pro¬ 
duced. It is by no means the case that an accident must necessarily occur under such 
circumstances, but it is possible, and such a possibility ought not to exist. As long as 
the inflammable mixture does not come in contact with the flame, no accident will 
occur ; but so long as vapour is produced, and exists in the lamp, so long is it possible 
that it may come into contact with the flame and an accident occur, especially as lamps 
are now constructed. The air-hole which allows of air entering the lamp to take the 
place of oil which rises through the wick, is usually placed close to the flame. Theie is 
no reason why this should be so, and it is very desirable that such an aperture should he 
placed at some other part of the lamp, or it should, as Dr. Attfield suggests, be packed 
with wires after the principle of the oxy-hydrogen jet. The portion of this brass-work 
facing the interior of the lamp should also be covered with bone, glass, or some other 
material possessing bad conducting powder of heat, so that the passage through which all 
the oil has to pass to get to the flame shall be kept as cool as possible. As a rule, there 
is ahvays a strong current of air passing upw'ards from the lamp, preventing the passage 
of the flame down into the reservoir; but if this current is reversed, an explosion may 
occur, or, if not an actual explosion sufficient to shatter the lamp to pieces, the vapour 
may take fire, and dangerous consequences ensue. For this reason,—and it cannotj 
