506 WRITINGS OF JOSEPH HENRY. [1875 



higher flashing test gave ofif a vapor at the ordinary temper- 

 ature of the atmosphere ; for example, at about 70°. For this 

 purpose a barometer tube of about 33 inches in length, and 

 an interior diameter of one-half of an inch, was filled with 

 warm mercury, and inverted in a basin of the same metal- 

 The finger was then placed under the open mouth of the tube 

 in the basin and the tube slowly inverted so as gradually to 

 pass the vacuum through the whole length of the column, and 

 thus to gather up 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 re-filled, the fin- 

 ger applied to the open end, and the tube again replaced 

 with the open end downward in the basin, the vacuum pro- 

 duced 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. After 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 depression of the mercurial 

 column. 



From this experiment it is evident that kerosene — even 

 of a high flashing temperature, does give off vapor at or- 

 dinary temperature. It is however of so feeble tension that 

 it does not appear capable of producing explosion unless 

 considerable time be allowed for its accumulation. It might 

 not be apparent that although vapor was given ofi" in a 

 vacuum, it would be given off under the full pressure 

 of the atmosphere ; but it has been shown by the experi- 

 ments of Dalton and others that vapors difi'use themselves 

 in a space filled with atmospheric air with the same elas- 

 ticity 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 



