CHEMISTRY. 191 







under the experiment, an unfair indication of the temperature at 

 which inflammable vapor 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 sufficiently deli- 

 cate 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 con- 

 trived 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, H 

 equal quantities of petroleum be operated on, the liquid be 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 ap- 

 paratus. 



I will conclude by giving detailed directions by which to take 

 both the iguiting-point and specific gravity of a specimen of petro- 

 leum or paraffine oil. Into a test-tube of thin glass 6 or 6 inches 

 long, and 1| inches 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 wetted with the liquid, and note 

 the temperature. Now 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 tube to within half an inch of 

 the surface of the liquid, quickly 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, frequently noting the tempera- 

 ture, and introducing the test-flame every minute or so. The 

 temperature at which the thin blue flame appears will be the ignit- 

 ing-point of the petroleum, the point at which it gives off inflam- 

 mable vapor. To correct this result, let the tube gradualty cool, 

 introducing the test-flame as before. The lowest temperature at 

 which the vapor takes fire is the true igniting-point. To ascertain 

 the specific gravity, pour the petroleum or paraffine oil into the 

 test-tube until the latter is about three-fourths full ; insert a ther- 

 mometer, and warm or cool until the temperature is about 60 ; * 

 now immerse the hydrometer, and take care that it fairly floats in 

 the liquid ; the point on the stem of the hydrometer cut by the 

 under surface of the liquid will be the specific gravity. 



This particular hydrometer might be termed a petroleometer. 



* Five degrees of temperature make about one degree difference of specific 

 gravity. At 70 P. an oil will be about two degrees lighter in specific gravity 

 thau at (J0 F., and at 50 F. two degrees heavier. 





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