DANGEROUS KEROSENE AND ITS DETECTION. 465 



ity of this method depends upon the assumption that a definite re- 

 lation exists between vapor-tension and flashing - point in all kero- 

 senes. It has, however, been shown in the most conclusive manner, 

 that this is not the case.* Four different oils, which all had a flash- 

 ing-point of 285° to 29*5° C, as determined by one of the most 

 trustworthy of the testers before described, were found to give, at 

 28° C, vapor-tensions of 75, 104, 118, and 168 millimetres (of water) ; 

 and, at 40° C, tensions of 126, 149, 165, and 201 millimetres. Fur- 

 ther, seven different kerosenes gave, when tested by the two meth- 

 ods, the following results : 



It thus appears that the results obtained by the measurement of the 

 vapor-tension are quite worthless as indications of the dangerous char- 

 acter of kerosene, and the method must be regarded as far less reliable 

 than even the imperfect ways of testing which have been already dis- 

 cussed. 



The uncertainties of the foregoing methods are entirely avoided 

 by a distillatio7i test, which also enables one to decide the quality of 

 the oil as an illuminating material, and thus gives the fullest informa- 

 tion in regard to its nature.f The oil is separated by the distillation 

 into three fractions : a light oil distilling below 150° C. ; illuminating 

 oil coming over between 150° and 270° C. ; and a heavy oil which 

 boils above 270° C. The first fractional distillate represents the dan- 

 gerous constituents, and should not exceed, according to Bielstein, five 

 per cent of the whole. The heavy oil affects the freedom with which 

 the kerosene burns in a lamp, and, in American kerosene, should not 

 form more than fifteen per cent of the oil. The operation must be 

 conducted with care, in a flask provided with a dephlegmator, and the 

 fractions, as well as the original sample, must be weighed. These cir- 

 cumstances are likely to prevent the general adoption of a method 

 which is otherwise so simple and satisfactory, and kerosene will prob- 

 ably be tested in the future, as now, by the determination of its flash- 

 ing-point. 



In 1879 Victor Meyer J suggested a principle by which the mini- 

 mum, or, as he called it, " true or absolute " flashing-point, could be de- 

 termined. It is to saturate air with oil-vapor at the test-temperature. 

 His method is simply this : A glass cylinder of about 200 c. c. capacity 

 is partly filled with oil, stoppered with a cork through which a ther- 



* Englcr and Haass, loc. cii. f " Zeitschrift fQr anal. Cbcm.," xxii, 813. 



X Wagner's " Jahresbericht," 1879, 1176. 

 VOL. XXI v. — 30 



