PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 383 



gradually heating the oil, and when the vapor explodes observing the tem- 

 perature of the oil by a thermometer. In order to heat the Oil uniformly, 

 we set the cup which contains it in a water bath, and we must take care 

 not to heat it from other sources. If the flame by which the vapor is to be 

 exploded communicates by means of metal with the oil, the oil will be 

 heated by this flame. I therefore interpose two pieces of clay, to prevent 

 the heat from being conducted from the flame to the oil. In order to heat 

 the oil evenly in all parts, I keep tlie surface of the oil exactly at the same; 

 level as the surface of the water in the bath. Then I keep the flame always 

 at the same height above the surface. of the oil, for I find that a variation of 

 the sixteenth of an inch in this height will make a difference of several 

 degrees in the result. I insert a thermometer in the oil; and my instru- 

 ment is nearly the same as this, excepting that I dispense with the cover 

 and closed chamber above, and my lighting flame is stationary, while in 

 this a taper is applied from time to time as the temperature rises. I should 

 like the gentleman to point out why my instrument will not give as relia- 

 ble tests as this. 



Mr. Churchill. — I have examined all of these instruments with great labor 

 and care, and I am satisfied that it is necessary to cover the oil cup, and 

 catch the vapors in a close chamber. If the cup is not covered, the least 

 current of air blows the vapors away. It is surprising how little move- 

 ment of air will entirely destroy the operation of the instrument; and unless 

 the vapor is confined in actual contact with the flame, it frequently will not 

 ignite. In the burner, which has a number of radiating jets, I have tried 

 the experiment of extinguishing one jet, and I have seen the gas continue 

 to issue between- the two adjacent flames for forty seconds before it took 

 fire. I have also repeatedly seen the gas burst out from the side of a flame, 

 and blow off without burning for some time. It seems to be the property 

 of these vapors to mingle with the air with great reluctance. I have no 

 doubt that the difficulty of burning petroleum without a chimney is princi- 

 pally owing to the fact that some portion of the vapor escapes unconsumed, 

 and thus carries iis disagreeable odor into the room. From this property 

 of the vapors, I think the close chamber indispensable. I believe there are 

 also fatal objections to the fixed taper. It aids in heating the oil in some 

 portions of the cup, and may thus raise explosive vapors at temperatures 

 which will not be indicated by the thermometer. 



Mr. Stetson. — Through what range of temperature have you found the 

 rock oils in the market to form the explosive vapors ? 



Mr. Churchill— From ^0'' to 134° Fah. 



Mr. Guiseppe Tagliabue. — I have no disposition to find fault with my 

 nephew's instrument, but I think the cover and close chamber are neces- 

 sary. There are 500 barrels of petroleum now in the market, which cannot 

 be. sold in consequence of the oil forming explosive vapors at too low a 

 temperature. 



Mr. G. Tagliabue, in answer to a question, stated that the results with his 

 instrument are reliable within 11 to 2° Fah. He thought 1|° to be the 

 range of the errors of the instrument. 



