188 ANNUAL OF SCIENTIFIC DISCOVERY. 



nets of the reaction of hydrogen upon it. For example, hydro- 

 gen, reacting upon acetylene, forms ethylene and hydride of 

 ethylene ; a new reaction of hydrogen will form hydrocarbons of 

 the marsh gas series, the same which constitute American petro- 

 leum. An almost unlimited diversity in these reactions is possible ; 

 and it would seem that all that is necessary for the formation of 

 the natural carbides of hydrogen is the intervention of heat, 

 water, alkaline metals, and carbonic acid. Ann. de Chimie et 

 Physique. 



ON THE IGNITING-POINT OF PETROLEUM. BY DR. JOHN 



ATTFIELD. 



It is now well known that petroleum, as it issues from the earth, 

 and as met with in commerce in the crude state, emits a vapor of 

 powerful odor, which is inflammable, and which, consequently, 

 when mingled with air in certain proportions, forms an explosive 

 mixture. The combustible properties of this vapor closely re- 

 semble those of common coal-gas. As with coal-gas, so with 

 petroleum vapor, a small quantity in a large quantity of air 

 gives odor to the air, but does not form an explosive mixture. 

 Again, coal-gas, as supplied to the consumer, always contains a 

 small percentage of air, and yet the mixture is not explosive ; so 

 petroleum vapor, even though containing a small quantity of air, 

 burns very well as a jet (so long as the petroleum which supplies 

 the vapor is kept boiling), but the vapor itself is not explosive. In 

 short, petroleum itself, or petroleum vapor itself, is no more in- 

 flammable than common air ; it is the mixture of petroleum vapor 

 and air that is dangerous. It is almost as easy to show that a jet 

 of air will burn in an atmosphere of petroleum vapor as it is to 

 show that a jet of petroleum vapor will burn in an atmosphere of 

 air. 



Now, crude petroleum generally gives off, at common tempera- 

 tures, quite enough vapor to form an explosive mixture with air, 

 if the air be in a confined space, as in a partially empty lamp, bot- 

 tle, or cask. For this, among other reasons, ijrucle petroleum is 

 always refined before it is sold to the general public ; it is dis- 

 tilled, and the portion which first rises into vapor is collected 

 apart, and, under the name of peti oleum spirit, used as a substi- 

 tute for turpentine. The next and larger portion which distils is 

 the refined petroleum, so extensively sold under various names as 

 a cheap illuminating oil. The residue is heavy oil used for lubri- 

 cating purposes. 



Refined petroleum still has the characteristic odor of petroleum. 

 Even at the coldest temperatures it emits sufficient vapor to be 

 most obviously perceptible to the nose, but not sufficient to form 

 with the air in the vicinity of the oil an explosive mixture. But 

 as we rise to the warmth of summer, or of a hot room, or to the 

 still higher temperature in the neighborhood of a lighted lamp, a 

 point may be reached at which the oil emits vapor at such a rate 

 that before it can diffuse away into the air of the apartment, ex- 

 plosive proportions are arrived at, and, on aflame being brought 



