10 The Bulletin. 



perfect purification or the presence of heavy oils. Kerosene which 

 has been exposed to light often acquires a yellow color and does not 

 burn as well as the same oil would burn if protected from light. 



The gravity test is usually made with a hydrometer, but when 

 greater accuracy is required a weighing tube or a picnomtter is used. 

 Oils of high gravity do not ascend the wick as well as lighter oils, 

 do not give as much light, and char the wick. 



A test of kerosene oils by burning them in similar lamps and 

 noting the rates of consumption and the comparative intensities of 

 light yielded gives a good idea of the nature of the oil. Kerosenes 

 containing a large proportion of light oils give a better light, but 

 burn faster than others, while the presence of heavy oils retards the 

 consumption and diminishes the light. An oil containing an excess 

 of both light and heavy oils may give a good light at first, but after 

 a while the flame will diminish in size and luminosity, and the 

 wick will begin to char. The absence of an objectionable portion of 

 heavy oil as indicated by a distillation test, and the light-giving 

 power, are important characteristics in judging the quality of a 

 sample of kerosene. 



FLASH TEST. 



The flash test determines whether an oil is safe for household use. 

 The danger involved in the use of kerosene is traceable to the presence 

 in the oil *of some of the volatile products whose vapor forms an 

 explosive mixture with air. For the purpose of ascertaining whether 

 a sample of kerosene contains these more volatile substances its 

 -flash-point is determined by heating it slowly in a specially con- 

 structed apparatus and observing the temperature at which the mix- 

 ture of vapor and air over the surface of the oil can just be ex- 

 ploded. By the flash-point, then, we mean the temperature at which 

 the oil will give off a vapor that will explode when mixed with air 

 in proper proportions. Any kerosene oil, therefore, is dangerous 

 at its flashing temperature, but experience has shown that there is 

 very little danger with a flashing temperature of 100° F. The 

 flash-point should be higher than any temperature to which the oil 

 is exposed. Since the temperature in the climate of North Carolina 

 often goes above 90° F., to say nothing of the temperature in the 

 bowl of the lamp, which is several degrees higher than the outside 

 air, the Board of Agriculture requires that all illuminating oils sold 

 in the State shall stand a flash test of 100° F. in the Elliott Closed 

 Cup. 



There are several instruments in common use for making the flash 

 test, but the Elliott Cup is regarded as the most accurate for ordinary 

 use, for the reason that it indicates more exactly the temperature 

 at which the oil begins to give off an explosive vapor. 



