DANGEROUS KEROSENE AND ITS DETECTION. 467 



run through the oil for at least one minute before the flash occurs. It 

 may perhaps seem, at first thought, that a continuous current of air 

 would dilute the vapor to such an extent that the flashing-point must 

 be materially raised, and that this effect must be more marked as the 

 velocity of the current is increased. This is, however, not the case. 

 On the contrary, while a slow, continuous current raises the flashing- 

 point appreciably, a sufficiently rapid one gives nearly the same results 

 as the intermittent method ; nor does any further increase in the ve- 

 locity alter the flashing-point to a sensible extent. It has indeed been 

 found that a large dilution of kerosene-vapor with air is necessary to 

 furnish the conditions for the most violent explosion ; and these con- 

 ditions are also those for the readiest flash by this method of testing. 

 The most explosive mixture, according to Chandler, is formed by nine 

 parts of air to one of vapor. The passage of a large quantity of air 

 through the oil tends, of course, to make the flashing-point higher, by 

 carrying away with it the more volatile portions which determine the 

 flash, and this effect is greater when the quantity of oil is small and the 

 air-current long continued. It is, consequently, necessary in the em- 

 ployment of this method to know the minimum quantity of oil and the 

 maximum duration of air-current which will permit concordant results. 

 These limits have been ascertained in a recent investigation,* the 

 results or which are given a little further on. 



A tester of still simpler construction than that of Liebermann has also 

 been proposed. f It consists, as shown in the cut, of a glass cylinder, 

 closed at one end by a cork, through which 

 a small bent tube, d, c, 5, passes. Just with- 

 in the cork the end of this tube contracts to 

 a small orifice. The other end of the tube 

 connects with a small bellows, or other source 

 of slightly compressed air, the flow of which 

 can be regulated by the pinch-cock e. 



Experiments made with cylinders of dif- 

 ferent dimensions have shown that the best 

 results are obtained when the diameter is 

 between 2*5 and 4 c. m. The length (if only 

 great enough to allow at least the minimum 

 quantity of oil to be used) makes no differ- 

 ence. Cylinders of the same diameter but 

 of different lengths, when filled with oil to 

 within the same distance from the top, all give the same flashing-point. 

 Change in length in such cases is simply equivalent to change in the 

 quantity of oil employed in the test, and it has been proved that the 

 quantity of oil does not affect the determination when it is above a cer- 

 tain minimum. 



* " American Chemical Journal," vi, No 1. 

 f Ibid , iv, No. 4, 286, and " Bcr, d. Deutachen chem. Qesell.," xv, 2856. 



no. 8. 



