INVESTIGATIONS RELATIVE TO ILLUMINATING MATERIALS. 505 



vacuum through the whole length of the column, and thus to gather np 

 any particles of air that might adhere to the side of the tube; this left 

 a space, when the inverted tube was held vertically, of about three 

 inches of the open end of the tube unfilled with mercury; this being 

 refilled, the finger applied to the open end and the tube again replaced 

 with the open end downward in the basin, the v^acuum produced by this 

 process was nearly as perfect as if the mercury had been boiled in the 

 tube, or the latter filled with the metal in a vacuum. Al'ter this, a small 

 quantity of oil to be tested was drawn into a small glass syringe, the 

 curved point of which being introduced beneath the open mouth of the 

 tube under the surface of the mercury, a small quantity of the liquid was 

 injected into the column; this rapidly rose by its levity to the top, and 

 there a portion of it flashed into vapor, as was evident by the depres- 

 sion of the mercurial column. 



From this experiment it is evident that kerosene, even of a high flash- 

 ing temperature, does give off vapor at ordinary temperature. It is 

 however of so feeble tension that it does not appear capable of produc- 

 ing explosion unless considerable time be allowed for its accumulation. 

 It might not be apparent that although vapor was given off in a vac- 

 uum, as in this case, it would be given ofl' under the full, pressure of 

 the atmosphere ; but it has been shown by the experiments of Mr. Dal- 

 ton and others, that vapors diffuse themselves in a space filled with 

 atmospheric air with the same elasticity and quantity as in a vacuum, 

 time only being required to produce the effect in the atmosphere. 



The oils were also examined as to the remains of any free acid which 

 they might contain, by simply immersing in each sample a slip of litmus 

 paper, which was suffered to remain in the liquid for 24 hours; under 

 this test several of the samples exhibited a redness, denoting the pres- 

 ence of an acid which might corrode the metal of the lamps, also indi- 

 cating the want of a thorough washing of the oil by an alkaline water. 



Another experiment, which was exhibited to us by one of the proprie- 

 tors of the oil which has a flashing test of about 140° F., consisted in 

 lighting a lamp-wick charged with the oil and plunging it into a vessel 

 filled with the same. The oil did not take fire, although the combustion 

 of the wick was vigorous, and, indeed, the flame was put out when the 

 wick was plunged beneath the surface of the oil. This experiment, 

 which is frequently exhibited to the public, tends to give a sense of 

 safety in the use of mineral oil which is at least in some degree falla- 

 cious. To illustrate this, the following experiments were made: First a 

 slip of cotton cloth, about 6 inches wide and 2 feet long, was saturated 

 witli oil having a flashing test of 140°, and suspended vertically from a 

 ring-stand; a lighted match was then applied to the middle of the length 

 of the slip, when it instantly took fire, and burned with a fierceness 

 which was truly appalling. 



After this two iiieces of cloth, one of cotton and the other of woolen, 

 were saturated with petroleum and placed flat on two pieces of tinned 



