DANGEROUS KEROSENE AND ITS DETECTION. 463 



find Engler and Haass,* at the close of a careful investigation into the 

 reliability of petroleum-testers, in which all the more promising meth- 

 ods were laboriously examined and compared, laying down these gen- 

 eral principles, which are to be observed in the construction and use 

 of this class of testers : 



1. The quantity of oil must be the same in all experiments. — In 

 the Saybolt tester, for instance, which was adopted in 1879 by the 

 New York Produce Exchange (chiefly, however, for the purpose of 

 determining the burning-point), variations of one millimetre, or about 

 one twenty-fifth of an inch, in the height of the oil, cause differences 

 of some degrees in the flashing-point. 



2. The oil must be heated slowly and uniformly. 



3. The temperature of the oil at the beginning of the test must be 

 at least 18° Fahr. (10° C) below its flashing-point (which is approxi- 

 mately determined by a preliminary test). Hence, a low-grade oil, 

 which flashes not far from the air temperature, must be cooled down 

 before an accurate determination can be made. 



4. The size and intensity of the flame or spark used to produce the 

 flash must remain unchanged in all tests. Increase in size or intensity 

 lowers the flashing-point. 



5. The distance of the flash-flame or spark from the surface of the 

 oil must be the same in all tests. The flashing-point is lowered by 

 decreasing this distance. Care must be taken that this distance is not 

 so small that a local evolution of vapor from the surface occurs. 



6. The time during which the flame or spark acts must be reduced 

 to a minimum, increase in the time causing a sensible lowering of the 

 flashing-point. 



7. On account of the practical purpose for which the tests are 

 made, the conditions under which the vapor is formed in the tester 

 should correspond as closely as possible to those which determine its 

 formation and explosion in lamps, etc. 



Comment upon methods which depend for trustworthy results 

 upon such a formidable array of conditions is hardly necessary ; the 

 best apparatus must be electrical and costly, and even then unreliable 

 except in the hands of an expert. We are not surprised to find Mr. 

 A. H. Elliott, in his report of a similar investigation ordered by the 

 New York State Board of Health, giving as his general conclusion : 

 " Of all the apparatus examined, not one can be called perfectly 

 satisfactory. ... Of the electric testers it may be stated, that any 

 advantage obtained from the use of electricity is more than over- 

 come by the trouble necessary to maintain the galvanic battery and 

 induction-coil." But, even if the performance of some of these in- 

 struments is such as to yield concordant results, when all the precau- 

 tions are carefully heeded, these results can have only a relative sig- 

 nificance, and agreement of different testers can only be secured by 

 * "Zeitschrift fur anal. Chcm.," xx, 1. 



