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PHARMACEUTICAL MEETING. 
ciple, easy of execution, occupying little time in performance, and inexpensive; 
and when this is found, to take steps for accomplishing a far more difficult task, 
namely, securing its universal adoption. Xow 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 thermometric reading, taken under the ex¬ 
periment, 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 without a thermometer, are not suffi¬ 
ciently 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 together. 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 results 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 included them all in a neat pocket case, intro¬ 
ducing 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 convenient plan. Half-way up the test-tube is a mark indicating 
the amount of petroleum to be operated on. The test-flame should be intro¬ 
duced 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 specimen of petroleum or paraffin oil. 
Into a test-tube of thin glass 6 or inches long, and inch in diameter, 
pour the liquid until the tube is half-full. Stir the liquid well with a naked 
thermometer, having the usual degrees marked on the stem, shaking also so as 
to keep the upper part of the tube well v/etted with the liquid, and note the 
temperature. How introduce a flame (of a thin splint of wood, or, far better, a 
small gas flame a quarter or an eighth of an inch long) into the mouth of the 
tubs to within half an inch of the surface of the liquid, cjuickly withdrawing 
it, and noticing whether a thin blue flame runs between the test-flame and the 
surface of the oil. If not, warm the tube by passing the bottom of it gently 
through a spirit-lamp, or other flame, or by dipping the lower portion of the 
tube into hot water, constantly stirring the liquid with the thermometer, fre¬ 
quently noting the temperature, and introducing the test-flame every minute 
or so. The temperature at which the thin blue flame appears will be the igni- 
ting-point of the petroleum, the point at which it gives off inflammable va¬ 
pour. To correct this result* let the tube gradually cool, introducing the test- 
flame as before. The lowest temperature at which the vapour takes fire is the 
true igniting-point. To ascertain the specific gravity, pour the petroleum or 
paraffin oil into the test-tube until the latter is about three-fourths full; in¬ 
sert a thermometer, and warm or cool until the temperature is about 60 de¬ 
grees now immerse the hydrometer, and take care that it fairly floats in the 
^ Five degrees of temperature make about one degree difference of specific gravity. At 
70° Fahr. an oil wfill be about two degi’ees lighter in specific gravity than at 60° Fahr., and a.t 
50 Fahr. two dcgi*ees heavier. 
