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THE POPULAR SCIENCE MONTHLY. 



mometer passes, and heated by plunging into warm water ; when the 

 temperature is reached at which the test is to be made, the cylinder is 

 briskly shaken, the stopper removed, and a small flame introduced. 

 Flashing-points obtained by this plan are considerably lower than 

 those given by the methods which have been discussed, and are found, 

 moreover, to be largely independent of the conditions so essential to 

 success in the latter. 



Haass * has described an elaborate and clever apparatus based on 

 the same principle, and differing essentially from Meyer's only in the 

 substitution of an electric spark, at a fixed distance from the surface 

 of the oil, for the flame which the latter employed. In both of these 

 methods the flashing-point depends upon the time allowed between the 

 shaking and testing, Haass recommending an interval of one minute 

 after the bubbles have disappeared from the surface of the oil, in 

 order to permit the suspended oil-particles to settle. The shaking, 

 which must be repeated from degree to degree, is a troublesome feat- 

 ure of these methods, and, though Meyer's apparatus is certainly sim- 

 ple and inexpensive enough, that of Haass is difficult of construction, 

 electrical, and costly. The general principle of these methods is, how- 

 ever, without question the correct one for obtaining a minimum (and 

 approximately " absolute ") flashing-point, and it is to L. Liebermann f 

 that we owe the suggestion of an ingenious and successful plan for 



Fig. 2. Liebermann's Tester. 



avoiding the difficulties mentioned above. In Liebermann's method 

 the saturation of air with vapor is accomplished by forcing an air- 

 current through the oil as it is warmed from degree to degree ; and 

 the test made by bringing a small flame to the mouth of the oil-holder 

 at the same instant. 



It has, however, been shown that the intermittent current of air 

 which is recommended gives somewhat irregular results, and that more 

 concordant flashing-points are obtained by letting a continuous current 



* "Chem. Industrie," 1880, 123, and " Zeitschrift fur anal. Chem.," xx, 29. 

 f " Zeitschrift fur anal. Chem.," xxi, 321. 



