190 



ANNUAL OF SCIENTIFIC DISCOVERY. 



tic, and the whole well shaken for three or four seconds. 'It will 

 be noticed that differences of igniting-point in any one specimen 

 are obtained, varying from 10 to 30. The table shows that, as 

 much of it " gives off an inflammable vapor at a temperature of 

 less than 100 of Fahrenheit's thermometer," the law has not yet 

 had the effect anticipated, namely, the exclusion from retail trade 

 of that quality of petroleum which is so badly refined as to have 

 dangerous, because unsuspected, properties. 



TABLE OF GRAVITIES AND IGNITING-POINTS OF COMMERCIAL PETROLEUM. 



And now with regard to a method of taking the igniting-point 

 of petroleum vapor, which shall be reliable and constant in the 

 results of its application. 



As petroleum is not a definite chemical compound, but a vary- 

 ing mixture of several hydrocarbons ; as, in short, it has no con- 

 stant chemical or physical property of which advantage might be 

 taken in devising a ready method of taking igniting-points, it fol- 

 lows that the method selected must be more or less arbitrary, 

 empirical, conventional. 



The only feasible plan would seem to be, to select a direct 

 method, simple in principle, easy of execution, occupying little 

 time in performance, and inexpensive ; and, when this is found, to 

 take steps for accomplishing a far more difficult task, namely, se- 

 curing its universal adoption. Now the ignition method is suffi- 

 ciently simple in principle ; but from the foregoing, and many 

 other experiments, I would advise the rejection of its application 

 in an open dish, saucer, basin, or bowl. Even if this experiment 

 could be always similarly performed under constant conditions, 

 which is impossible, the rapidity with which vapor escapes from 

 the surface of the liquid renders a thermonietric reading, taken 



