On the Igniting Pot of Petroleum. 2456 
Now the ignition method is sufficiently simple in principle ; 
but from the foregoing, and many other experiments, I 
would advise the rejection of its application in an open 
dish, saucer, basin, or bowl. Even if this experiment could 
be always similarly performed under constant conditions, 
which is impossible, the rapidity with which vapour escapes 
from the surface of the liquid renders a thermometer read- 
ing, taken under the experiment, an unfair indication of the 
temperature at which inflammable vapour would be 
given off from the petroleum in a lamp or other closed or 
partially closed vessel. Of course experiments, made with- 
out a thermometer, are not sufficiently delicate for the 
purposes of the analyst. Again, the petroleum must not 
be heated in a common bottle, on account of the great 
liability of the latter to fracture; nor is it necessary to use 
a vessel contrived for violently agitating the oil and air to- 
gether. But if the bottle be substituted by a short, wide 
tube of glass, thin, so that it can be heated with safety,— 
by, in short, a rather wide variety of the common test-tube 
of our analytical laboratories; then, if equal quantities of 
petroleum be operated on, the liquid be fairly well stirred 
and shaken, and the test-flame be always introduced to the 
same distance from the surface of the liquid, constant re- 
sults may be expected. The same tube may be used in 
which to insert a hydrometer to take the specific gravity of 
the oil, and thus, with a naked thermometer somewhat 
longer than the test-tube to act also as a stirring rod, we 
have a compact and inexpensive apparatus. These articles 
have been made for me by Mr. Casella, the well-known 
physical instrument maker of Hatton garden; he has in- 
cluded them all in a neat pocket case, introducing a small 
spirit-lamp also; but I need not say that the petroleum 
test-tube may be heated over a gas-flame, by partial 
immersion in a vessel of hot water, or by any other con- 
venient plan. Half way up the test-tube is a mark indicat- 
ing the amount of petroleum to be operated on. ‘The test- 
flame should be introduced to within half an inch of the 
surface of the oil. 
I will conclude by giving detailed directions by which to 
take both the igniting-point and specific gravity of a speci- 
men of petroleum or paraffin oil. Into a test-tube of thin 
glass 6 or 64 inches long, and 14 in diameter, pour the 
gravity as to readily ascend a wick, and so high in igniting-point 
as not to be dangerous under ordinary circumstances. 
FoF P2 
